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=============================
User Guide for AMDGPU Backend
=============================
.. contents::
:local:
Introduction
============
The AMDGPU backend provides ISA code generation for AMD GPUs, starting with the
R600 family up until the current GCN families. It lives in the
``llvm/lib/Target/AMDGPU`` directory.
LLVM
====
.. _amdgpu-target-triples:
Target Triples
--------------
Use the ``clang -target <Architecture>-<Vendor>-<OS>-<Environment>`` option to
specify the target triple:
.. table:: AMDGPU Architectures
:name: amdgpu-architecture-table
============ ==============================================================
Architecture Description
============ ==============================================================
``r600`` AMD GPUs HD2XXX-HD6XXX for graphics and compute shaders.
``amdgcn`` AMD GPUs GCN GFX6 onwards for graphics and compute shaders.
============ ==============================================================
.. table:: AMDGPU Vendors
:name: amdgpu-vendor-table
============ ==============================================================
Vendor Description
============ ==============================================================
``amd`` Can be used for all AMD GPU usage.
``mesa3d`` Can be used if the OS is ``mesa3d``.
============ ==============================================================
.. table:: AMDGPU Operating Systems
:name: amdgpu-os-table
============== ============================================================
OS Description
============== ============================================================
*<empty>* Defaults to the *unknown* OS.
``amdhsa`` Compute kernels executed on HSA [HSA]_ compatible runtimes
such as AMD's ROCm [AMD-ROCm]_.
``amdpal`` Graphic shaders and compute kernels executed on AMD PAL
runtime.
``mesa3d`` Graphic shaders and compute kernels executed on Mesa 3D
runtime.
============== ============================================================
.. table:: AMDGPU Environments
:name: amdgpu-environment-table
============ ==============================================================
Environment Description
============ ==============================================================
*<empty>* Default.
============ ==============================================================
.. _amdgpu-processors:
Processors
----------
Use the ``clang -mcpu <Processor>`` option to specify the AMDGPU processor. The
names from both the *Processor* and *Alternative Processor* can be used.
.. table:: AMDGPU Processors
:name: amdgpu-processor-table
=========== =============== ============ ===== ================= ======= ======================
Processor Alternative Target dGPU/ Target ROCm Example
Processor Triple APU Features Support Products
Architecture Supported
[Default]
=========== =============== ============ ===== ================= ======= ======================
**Radeon HD 2000/3000 Series (R600)** [AMD-RADEON-HD-2000-3000]_
-----------------------------------------------------------------------------------------------
``r600`` ``r600`` dGPU
``r630`` ``r600`` dGPU
``rs880`` ``r600`` dGPU
``rv670`` ``r600`` dGPU
**Radeon HD 4000 Series (R700)** [AMD-RADEON-HD-4000]_
-----------------------------------------------------------------------------------------------
``rv710`` ``r600`` dGPU
``rv730`` ``r600`` dGPU
``rv770`` ``r600`` dGPU
**Radeon HD 5000 Series (Evergreen)** [AMD-RADEON-HD-5000]_
-----------------------------------------------------------------------------------------------
``cedar`` ``r600`` dGPU
``cypress`` ``r600`` dGPU
``juniper`` ``r600`` dGPU
``redwood`` ``r600`` dGPU
``sumo`` ``r600`` dGPU
**Radeon HD 6000 Series (Northern Islands)** [AMD-RADEON-HD-6000]_
-----------------------------------------------------------------------------------------------
``barts`` ``r600`` dGPU
``caicos`` ``r600`` dGPU
``cayman`` ``r600`` dGPU
``turks`` ``r600`` dGPU
**GCN GFX6 (Southern Islands (SI))** [AMD-GCN-GFX6]_
-----------------------------------------------------------------------------------------------
``gfx600`` - ``tahiti`` ``amdgcn`` dGPU
``gfx601`` - ``hainan`` ``amdgcn`` dGPU
- ``oland``
- ``pitcairn``
- ``verde``
**GCN GFX7 (Sea Islands (CI))** [AMD-GCN-GFX7]_
-----------------------------------------------------------------------------------------------
``gfx700`` - ``kaveri`` ``amdgcn`` APU - A6-7000
- A6 Pro-7050B
- A8-7100
- A8 Pro-7150B
- A10-7300
- A10 Pro-7350B
- FX-7500
- A8-7200P
- A10-7400P
- FX-7600P
``gfx701`` - ``hawaii`` ``amdgcn`` dGPU ROCm - FirePro W8100
- FirePro W9100
- FirePro S9150
- FirePro S9170
``gfx702`` ``amdgcn`` dGPU ROCm - Radeon R9 290
- Radeon R9 290x
- Radeon R390
- Radeon R390x
``gfx703`` - ``kabini`` ``amdgcn`` APU - E1-2100
- ``mullins`` - E1-2200
- E1-2500
- E2-3000
- E2-3800
- A4-5000
- A4-5100
- A6-5200
- A4 Pro-3340B
``gfx704`` - ``bonaire`` ``amdgcn`` dGPU - Radeon HD 7790
- Radeon HD 8770
- R7 260
- R7 260X
**GCN GFX8 (Volcanic Islands (VI))** [AMD-GCN-GFX8]_
-----------------------------------------------------------------------------------------------
``gfx801`` - ``carrizo`` ``amdgcn`` APU - xnack - A6-8500P
[on] - Pro A6-8500B
- A8-8600P
- Pro A8-8600B
- FX-8800P
- Pro A12-8800B
\ ``amdgcn`` APU - xnack ROCm - A10-8700P
[on] - Pro A10-8700B
- A10-8780P
\ ``amdgcn`` APU - xnack - A10-9600P
[on] - A10-9630P
- A12-9700P
- A12-9730P
- FX-9800P
- FX-9830P
\ ``amdgcn`` APU - xnack - E2-9010
[on] - A6-9210
- A9-9410
``gfx802`` - ``iceland`` ``amdgcn`` dGPU - xnack ROCm - FirePro S7150
- ``tonga`` [off] - FirePro S7100
- FirePro W7100
- Radeon R285
- Radeon R9 380
- Radeon R9 385
- Mobile FirePro
M7170
``gfx803`` - ``fiji`` ``amdgcn`` dGPU - xnack ROCm - Radeon R9 Nano
[off] - Radeon R9 Fury
- Radeon R9 FuryX
- Radeon Pro Duo
- FirePro S9300x2
- Radeon Instinct MI8
\ - ``polaris10`` ``amdgcn`` dGPU - xnack ROCm - Radeon RX 470
[off] - Radeon RX 480
- Radeon Instinct MI6
\ - ``polaris11`` ``amdgcn`` dGPU - xnack ROCm - Radeon RX 460
[off]
``gfx810`` - ``stoney`` ``amdgcn`` APU - xnack
[on]
**GCN GFX9** [AMD-GCN-GFX9]_
-----------------------------------------------------------------------------------------------
``gfx900`` ``amdgcn`` dGPU - xnack ROCm - Radeon Vega
[off] Frontier Edition
- Radeon RX Vega 56
- Radeon RX Vega 64
- Radeon RX Vega 64
Liquid
- Radeon Instinct MI25
``gfx902`` ``amdgcn`` APU - xnack - Ryzen 3 2200G
[on] - Ryzen 5 2400G
``gfx904`` ``amdgcn`` dGPU - xnack *TBA*
[off]
.. TODO::
Add product
names.
``gfx906`` ``amdgcn`` dGPU - xnack - Radeon Instinct MI50
[off] - Radeon Instinct MI60
``gfx908`` ``amdgcn`` dGPU - xnack *TBA*
[off]
sram-ecc
[on]
``gfx909`` ``amdgcn`` APU - xnack *TBA* (Raven Ridge 2)
[on]
.. TODO::
Add product
names.
**GCN GFX10** [AMD-GCN-GFX10]_
-----------------------------------------------------------------------------------------------
``gfx1010`` ``amdgcn`` dGPU - xnack *TBA*
[off]
- wavefrontsize64
[off]
- cumode
[off]
.. TODO::
Add product
names.
``gfx1011`` ``amdgcn`` dGPU - xnack *TBA*
[off]
- wavefrontsize64
[off]
- cumode
[off]
.. TODO::
Add product
names.
``gfx1012`` ``amdgcn`` dGPU - xnack *TBA*
[off]
- wavefrontsize64
[off]
- cumode
[off]
.. TODO::
Add product
names.
=========== =============== ============ ===== ================= ======= ======================
.. _amdgpu-target-features:
Target Features
---------------
Target features control how code is generated to support certain
processor specific features. Not all target features are supported by
all processors. The runtime must ensure that the features supported by
the device used to execute the code match the features enabled when
generating the code. A mismatch of features may result in incorrect
execution, or a reduction in performance.
The target features supported by each processor, and the default value
used if not specified explicitly, is listed in
:ref:`amdgpu-processor-table`.
Use the ``clang -m[no-]<TargetFeature>`` option to specify the AMDGPU
target features.
For example:
``-mxnack``
Enable the ``xnack`` feature.
``-mno-xnack``
Disable the ``xnack`` feature.
.. table:: AMDGPU Target Features
:name: amdgpu-target-feature-table
====================== ==================================================
Target Feature Description
====================== ==================================================
-m[no-]xnack Enable/disable generating code that has
memory clauses that are compatible with
having XNACK replay enabled.
This is used for demand paging and page
migration. If XNACK replay is enabled in
the device, then if a page fault occurs
the code may execute incorrectly if the
``xnack`` feature is not enabled. Executing
code that has the feature enabled on a
device that does not have XNACK replay
enabled will execute correctly, but may
be less performant than code with the
feature disabled.
-m[no-]sram-ecc Enable/disable generating code that assumes SRAM
ECC is enabled/disabled.
-m[no-]wavefrontsize64 Control the default wavefront size used when
generating code for kernels. When disabled
native wavefront size 32 is used, when enabled
wavefront size 64 is used.
-m[no-]cumode Control the default wavefront execution mode used
when generating code for kernels. When disabled
native WGP wavefront execution mode is used,
when enabled CU wavefront execution mode is used
(see :ref:`amdgpu-amdhsa-memory-model`).
====================== ==================================================
.. _amdgpu-address-spaces:
Address Spaces
--------------
The AMDGPU architecture supports a number of memory address spaces. The address
space names use the OpenCL standard names, with some additions.
The AMDGPU address spaces correspond to architecture-specific LLVM address
space numbers used in LLVM IR.
The AMDGPU address spaces are described in
:ref:`amdgpu-address-spaces-table`. Only 64-bit process address spaces are
supported for the ``amdgcn`` target.
.. table:: AMDGPU Address Spaces
:name: amdgpu-address-spaces-table
================================= =============== =========== ================ ======= ============================
.. 64-Bit Process Address Space
--------------------------------- --------------- ----------- ---------------- ------------------------------------
Address Space Name LLVM IR Address HSA Segment Hardware Address NULL Value
Space Number Name Name Size
================================= =============== =========== ================ ======= ============================
Generic 0 flat flat 64 0x0000000000000000
Global 1 global global 64 0x0000000000000000
Region 2 N/A GDS 32 *not implemented for AMDHSA*
Local 3 group LDS 32 0xFFFFFFFF
Constant 4 constant *same as global* 64 0x0000000000000000
Private 5 private scratch 32 0x00000000
Constant 32-bit 6 *TODO*
Buffer Fat Pointer (experimental) 7 *TODO*
================================= =============== =========== ================ ======= ============================
**Generic**
The generic address space uses the hardware flat address support available in
GFX7-GFX10. This uses two fixed ranges of virtual addresses (the private and
local apertures), that are outside the range of addressable global memory, to
map from a flat address to a private or local address.
FLAT instructions can take a flat address and access global, private
(scratch), and group (LDS) memory depending on if the address is within one
of the aperture ranges. Flat access to scratch requires hardware aperture
setup and setup in the kernel prologue (see
:ref:`amdgpu-amdhsa-kernel-prolog-flat-scratch`). Flat access to LDS requires
hardware aperture setup and M0 (GFX7-GFX8) register setup (see
:ref:`amdgpu-amdhsa-kernel-prolog-m0`).
To convert between a private or group address space address (termed a segment
address) and a flat address the base address of the corresponding aperture
can be used. For GFX7-GFX8 these are available in the
:ref:`amdgpu-amdhsa-hsa-aql-queue` the address of which can be obtained with
Queue Ptr SGPR (see :ref:`amdgpu-amdhsa-initial-kernel-execution-state`). For
GFX9-GFX10 the aperture base addresses are directly available as inline
constant registers ``SRC_SHARED_BASE/LIMIT`` and ``SRC_PRIVATE_BASE/LIMIT``.
In 64-bit address mode the aperture sizes are 2^32 bytes and the base is
aligned to 2^32 which makes it easier to convert from flat to segment or
segment to flat.
A global address space address has the same value when used as a flat address
so no conversion is needed.
**Global and Constant**
The global and constant address spaces both use global virtual addresses,
which are the same virtual address space used by the CPU. However, some
virtual addresses may only be accessible to the CPU, some only accessible
by the GPU, and some by both.
Using the constant address space indicates that the data will not change
during the execution of the kernel. This allows scalar read instructions to
be used. The vector and scalar L1 caches are invalidated of volatile data
before each kernel dispatch execution to allow constant memory to change
values between kernel dispatches.
**Region**
The region address space uses the hardware Global Data Store (GDS). All
wavefronts executing on the same device will access the same memory for any
given region address. However, the same region address accessed by wavefronts
executing on different devices will access different memory. It is higher
performance than global memory. It is allocated by the runtime. The data
store (DS) instructions can be used to access it.
**Local**
The local address space uses the hardware Local Data Store (LDS) which is
automatically allocated when the hardware creates the wavefronts of a
work-group, and freed when all the wavefronts of a work-group have
terminated. All wavefronts belonging to the same work-group will access the
same memory for any given local address. However, the same local address
accessed by wavefronts belonging to different work-groups will access
different memory. It is higher performance than global memory. The data store
(DS) instructions can be used to access it.
**Private**
The private address space uses the hardware scratch memory support which
automatically allocates memory when it creates a wavefront, and frees it when
a wavefronts terminates. The memory accessed by a lane of a wavefront for any
given private address will be different to the memory accessed by another lane
of the same or different wavefront for the same private address.
If a kernel dispatch uses scratch, then the hardware allocates memory from a
pool of backing memory allocated by the runtime for each wavefront. The lanes
of the wavefront access this using dword (4 byte) interleaving. The mapping
used from private address to backing memory address is:
``wavefront-scratch-base +
((private-address / 4) * wavefront-size * 4) +
(wavefront-lane-id * 4) + (private-address % 4)``
If each lane of a wavefront accesses the same private address, the
interleaving results in adjacent dwords being accessed and hence requires
fewer cache lines to be fetched.
There are different ways that the wavefront scratch base address is
determined by a wavefront (see
:ref:`amdgpu-amdhsa-initial-kernel-execution-state`).
Scratch memory can be accessed in an interleaved manner using buffer
instructions with the scratch buffer descriptor and per wavefront scratch
offset, by the scratch instructions, or by flat instructions. Multi-dword
access is not supported except by flat and scratch instructions in
GFX9-GFX10.
**Constant 32-bit**
*TODO*
**Buffer Fat Pointer**
The buffer fat pointer is an experimental address space that is currently
unsupported in the backend. It exposes a non-integral pointer that is in
the future intended to support the modelling of 128-bit buffer descriptors
plus a 32-bit offset into the buffer (in total encapsulating a 160-bit
*pointer*), allowing normal LLVM load/store/atomic operations to be used to
model the buffer descriptors used heavily in graphics workloads targeting
the backend.
.. _amdgpu-memory-scopes:
Memory Scopes
-------------
This section provides LLVM memory synchronization scopes supported by the AMDGPU
backend memory model when the target triple OS is ``amdhsa`` (see
:ref:`amdgpu-amdhsa-memory-model` and :ref:`amdgpu-target-triples`).
The memory model supported is based on the HSA memory model [HSA]_ which is
based in turn on HRF-indirect with scope inclusion [HRF]_. The happens-before
relation is transitive over the synchronizes-with relation independent of scope,
and synchronizes-with allows the memory scope instances to be inclusive (see
table :ref:`amdgpu-amdhsa-llvm-sync-scopes-table`).
This is different to the OpenCL [OpenCL]_ memory model which does not have scope
inclusion and requires the memory scopes to exactly match. However, this
is conservatively correct for OpenCL.
.. table:: AMDHSA LLVM Sync Scopes
:name: amdgpu-amdhsa-llvm-sync-scopes-table
======================= ===================================================
LLVM Sync Scope Description
======================= ===================================================
*none* The default: ``system``.
Synchronizes with, and participates in modification
and seq_cst total orderings with, other operations
(except image operations) for all address spaces
(except private, or generic that accesses private)
provided the other operation's sync scope is:
- ``system``.
- ``agent`` and executed by a thread on the same
agent.
- ``workgroup`` and executed by a thread in the
same work-group.
- ``wavefront`` and executed by a thread in the
same wavefront.
``agent`` Synchronizes with, and participates in modification
and seq_cst total orderings with, other operations
(except image operations) for all address spaces
(except private, or generic that accesses private)
provided the other operation's sync scope is:
- ``system`` or ``agent`` and executed by a thread
on the same agent.
- ``workgroup`` and executed by a thread in the
same work-group.
- ``wavefront`` and executed by a thread in the
same wavefront.
``workgroup`` Synchronizes with, and participates in modification
and seq_cst total orderings with, other operations
(except image operations) for all address spaces
(except private, or generic that accesses private)
provided the other operation's sync scope is:
- ``system``, ``agent`` or ``workgroup`` and
executed by a thread in the same work-group.
- ``wavefront`` and executed by a thread in the
same wavefront.
``wavefront`` Synchronizes with, and participates in modification
and seq_cst total orderings with, other operations
(except image operations) for all address spaces
(except private, or generic that accesses private)
provided the other operation's sync scope is:
- ``system``, ``agent``, ``workgroup`` or
``wavefront`` and executed by a thread in the
same wavefront.
``singlethread`` Only synchronizes with, and participates in
modification and seq_cst total orderings with,
other operations (except image operations) running
in the same thread for all address spaces (for
example, in signal handlers).
``one-as`` Same as ``system`` but only synchronizes with other
operations within the same address space.
``agent-one-as`` Same as ``agent`` but only synchronizes with other
operations within the same address space.
``workgroup-one-as`` Same as ``workgroup`` but only synchronizes with
other operations within the same address space.
``wavefront-one-as`` Same as ``wavefront`` but only synchronizes with
other operations within the same address space.
``singlethread-one-as`` Same as ``singlethread`` but only synchronizes with
other operations within the same address space.
======================= ===================================================
AMDGPU Intrinsics
-----------------
The AMDGPU backend implements the following LLVM IR intrinsics.
*This section is WIP.*
.. TODO::
List AMDGPU intrinsics.
AMDGPU Attributes
-----------------
The AMDGPU backend supports the following LLVM IR attributes.
.. table:: AMDGPU LLVM IR Attributes
:name: amdgpu-llvm-ir-attributes-table
======================================= ==========================================================
LLVM Attribute Description
======================================= ==========================================================
"amdgpu-flat-work-group-size"="min,max" Specify the minimum and maximum flat work group sizes that
will be specified when the kernel is dispatched. Generated
by the ``amdgpu_flat_work_group_size`` CLANG attribute [CLANG-ATTR]_.
"amdgpu-implicitarg-num-bytes"="n" Number of kernel argument bytes to add to the kernel
argument block size for the implicit arguments. This
varies by OS and language (for OpenCL see
:ref:`opencl-kernel-implicit-arguments-appended-for-amdhsa-os-table`).
"amdgpu-num-sgpr"="n" Specifies the number of SGPRs to use. Generated by
the ``amdgpu_num_sgpr`` CLANG attribute [CLANG-ATTR]_.
"amdgpu-num-vgpr"="n" Specifies the number of VGPRs to use. Generated by the
``amdgpu_num_vgpr`` CLANG attribute [CLANG-ATTR]_.
"amdgpu-waves-per-eu"="m,n" Specify the minimum and maximum number of waves per
execution unit. Generated by the ``amdgpu_waves_per_eu``
CLANG attribute [CLANG-ATTR]_.
"amdgpu-ieee" true/false. Specify whether the function expects the IEEE field of the
mode register to be set on entry. Overrides the default for
the calling convention.
"amdgpu-dx10-clamp" true/false. Specify whether the function expects the DX10_CLAMP field of
the mode register to be set on entry. Overrides the default
for the calling convention.
======================================= ==========================================================
Code Object
===========
The AMDGPU backend generates a standard ELF [ELF]_ relocatable code object that
can be linked by ``lld`` to produce a standard ELF shared code object which can
be loaded and executed on an AMDGPU target.
Header
------
The AMDGPU backend uses the following ELF header:
.. table:: AMDGPU ELF Header
:name: amdgpu-elf-header-table
========================== ===============================
Field Value
========================== ===============================
``e_ident[EI_CLASS]`` ``ELFCLASS64``
``e_ident[EI_DATA]`` ``ELFDATA2LSB``
``e_ident[EI_OSABI]`` - ``ELFOSABI_NONE``
- ``ELFOSABI_AMDGPU_HSA``
- ``ELFOSABI_AMDGPU_PAL``
- ``ELFOSABI_AMDGPU_MESA3D``
``e_ident[EI_ABIVERSION]`` - ``ELFABIVERSION_AMDGPU_HSA``
- ``ELFABIVERSION_AMDGPU_PAL``
- ``ELFABIVERSION_AMDGPU_MESA3D``
``e_type`` - ``ET_REL``
- ``ET_DYN``
``e_machine`` ``EM_AMDGPU``
``e_entry`` 0
``e_flags`` See :ref:`amdgpu-elf-header-e_flags-table`
========================== ===============================
..
.. table:: AMDGPU ELF Header Enumeration Values
:name: amdgpu-elf-header-enumeration-values-table
=============================== =====
Name Value
=============================== =====
``EM_AMDGPU`` 224
``ELFOSABI_NONE`` 0
``ELFOSABI_AMDGPU_HSA`` 64
``ELFOSABI_AMDGPU_PAL`` 65
``ELFOSABI_AMDGPU_MESA3D`` 66
``ELFABIVERSION_AMDGPU_HSA`` 1
``ELFABIVERSION_AMDGPU_PAL`` 0
``ELFABIVERSION_AMDGPU_MESA3D`` 0
=============================== =====
``e_ident[EI_CLASS]``
The ELF class is:
* ``ELFCLASS32`` for ``r600`` architecture.
* ``ELFCLASS64`` for ``amdgcn`` architecture which only supports 64-bit
process address space applications.
``e_ident[EI_DATA]``
All AMDGPU targets use ``ELFDATA2LSB`` for little-endian byte ordering.
``e_ident[EI_OSABI]``
One of the following AMDGPU architecture specific OS ABIs
(see :ref:`amdgpu-os-table`):
* ``ELFOSABI_NONE`` for *unknown* OS.
* ``ELFOSABI_AMDGPU_HSA`` for ``amdhsa`` OS.
* ``ELFOSABI_AMDGPU_PAL`` for ``amdpal`` OS.
* ``ELFOSABI_AMDGPU_MESA3D`` for ``mesa3D`` OS.
``e_ident[EI_ABIVERSION]``
The ABI version of the AMDGPU architecture specific OS ABI to which the code
object conforms:
* ``ELFABIVERSION_AMDGPU_HSA`` is used to specify the version of AMD HSA
runtime ABI.
* ``ELFABIVERSION_AMDGPU_PAL`` is used to specify the version of AMD PAL
runtime ABI.
* ``ELFABIVERSION_AMDGPU_MESA3D`` is used to specify the version of AMD MESA
3D runtime ABI.
``e_type``
Can be one of the following values:
``ET_REL``
The type produced by the AMDGPU backend compiler as it is relocatable code
object.
``ET_DYN``
The type produced by the linker as it is a shared code object.
The AMD HSA runtime loader requires a ``ET_DYN`` code object.
``e_machine``
The value ``EM_AMDGPU`` is used for the machine for all processors supported
by the ``r600`` and ``amdgcn`` architectures (see
:ref:`amdgpu-processor-table`). The specific processor is specified in the
``EF_AMDGPU_MACH`` bit field of the ``e_flags`` (see
:ref:`amdgpu-elf-header-e_flags-table`).
``e_entry``
The entry point is 0 as the entry points for individual kernels must be
selected in order to invoke them through AQL packets.
``e_flags``
The AMDGPU backend uses the following ELF header flags:
.. table:: AMDGPU ELF Header ``e_flags``
:name: amdgpu-elf-header-e_flags-table
================================= ========== =============================
Name Value Description
================================= ========== =============================
**AMDGPU Processor Flag** See :ref:`amdgpu-processor-table`.
-------------------------------------------- -----------------------------
``EF_AMDGPU_MACH`` 0x000000ff AMDGPU processor selection
mask for
``EF_AMDGPU_MACH_xxx`` values
defined in
:ref:`amdgpu-ef-amdgpu-mach-table`.
``EF_AMDGPU_XNACK`` 0x00000100 Indicates if the ``xnack``
target feature is
enabled for all code
contained in the code object.
If the processor
does not support the
``xnack`` target
feature then must
be 0.
See
:ref:`amdgpu-target-features`.
``EF_AMDGPU_SRAM_ECC`` 0x00000200 Indicates if the ``sram-ecc``
target feature is
enabled for all code
contained in the code object.
If the processor
does not support the
``sram-ecc`` target
feature then must
be 0.
See
:ref:`amdgpu-target-features`.
================================= ========== =============================
.. table:: AMDGPU ``EF_AMDGPU_MACH`` Values
:name: amdgpu-ef-amdgpu-mach-table
================================= ========== =============================
Name Value Description (see
:ref:`amdgpu-processor-table`)
================================= ========== =============================
``EF_AMDGPU_MACH_NONE`` 0x000 *not specified*
``EF_AMDGPU_MACH_R600_R600`` 0x001 ``r600``
``EF_AMDGPU_MACH_R600_R630`` 0x002 ``r630``
``EF_AMDGPU_MACH_R600_RS880`` 0x003 ``rs880``
``EF_AMDGPU_MACH_R600_RV670`` 0x004 ``rv670``
``EF_AMDGPU_MACH_R600_RV710`` 0x005 ``rv710``
``EF_AMDGPU_MACH_R600_RV730`` 0x006 ``rv730``
``EF_AMDGPU_MACH_R600_RV770`` 0x007 ``rv770``
``EF_AMDGPU_MACH_R600_CEDAR`` 0x008 ``cedar``
``EF_AMDGPU_MACH_R600_CYPRESS`` 0x009 ``cypress``
``EF_AMDGPU_MACH_R600_JUNIPER`` 0x00a ``juniper``
``EF_AMDGPU_MACH_R600_REDWOOD`` 0x00b ``redwood``
``EF_AMDGPU_MACH_R600_SUMO`` 0x00c ``sumo``
``EF_AMDGPU_MACH_R600_BARTS`` 0x00d ``barts``
``EF_AMDGPU_MACH_R600_CAICOS`` 0x00e ``caicos``
``EF_AMDGPU_MACH_R600_CAYMAN`` 0x00f ``cayman``
``EF_AMDGPU_MACH_R600_TURKS`` 0x010 ``turks``
*reserved* 0x011 - Reserved for ``r600``
0x01f architecture processors.
``EF_AMDGPU_MACH_AMDGCN_GFX600`` 0x020 ``gfx600``
``EF_AMDGPU_MACH_AMDGCN_GFX601`` 0x021 ``gfx601``
``EF_AMDGPU_MACH_AMDGCN_GFX700`` 0x022 ``gfx700``
``EF_AMDGPU_MACH_AMDGCN_GFX701`` 0x023 ``gfx701``
``EF_AMDGPU_MACH_AMDGCN_GFX702`` 0x024 ``gfx702``
``EF_AMDGPU_MACH_AMDGCN_GFX703`` 0x025 ``gfx703``
``EF_AMDGPU_MACH_AMDGCN_GFX704`` 0x026 ``gfx704``
*reserved* 0x027 Reserved.
``EF_AMDGPU_MACH_AMDGCN_GFX801`` 0x028 ``gfx801``
``EF_AMDGPU_MACH_AMDGCN_GFX802`` 0x029 ``gfx802``
``EF_AMDGPU_MACH_AMDGCN_GFX803`` 0x02a ``gfx803``
``EF_AMDGPU_MACH_AMDGCN_GFX810`` 0x02b ``gfx810``
``EF_AMDGPU_MACH_AMDGCN_GFX900`` 0x02c ``gfx900``
``EF_AMDGPU_MACH_AMDGCN_GFX902`` 0x02d ``gfx902``
``EF_AMDGPU_MACH_AMDGCN_GFX904`` 0x02e ``gfx904``
``EF_AMDGPU_MACH_AMDGCN_GFX906`` 0x02f ``gfx906``
``EF_AMDGPU_MACH_AMDGCN_GFX908`` 0x030 ``gfx908``
``EF_AMDGPU_MACH_AMDGCN_GFX909`` 0x031 ``gfx909``
*reserved* 0x032 Reserved.
``EF_AMDGPU_MACH_AMDGCN_GFX1010`` 0x033 ``gfx1010``
``EF_AMDGPU_MACH_AMDGCN_GFX1011`` 0x034 ``gfx1011``
``EF_AMDGPU_MACH_AMDGCN_GFX1012`` 0x035 ``gfx1012``
================================= ========== =============================
Sections
--------
An AMDGPU target ELF code object has the standard ELF sections which include:
.. table:: AMDGPU ELF Sections
:name: amdgpu-elf-sections-table
================== ================ =================================
Name Type Attributes
================== ================ =================================
``.bss`` ``SHT_NOBITS`` ``SHF_ALLOC`` + ``SHF_WRITE``
``.data`` ``SHT_PROGBITS`` ``SHF_ALLOC`` + ``SHF_WRITE``
``.debug_``\ *\** ``SHT_PROGBITS`` *none*
``.dynamic`` ``SHT_DYNAMIC`` ``SHF_ALLOC``
``.dynstr`` ``SHT_PROGBITS`` ``SHF_ALLOC``
``.dynsym`` ``SHT_PROGBITS`` ``SHF_ALLOC``
``.got`` ``SHT_PROGBITS`` ``SHF_ALLOC`` + ``SHF_WRITE``
``.hash`` ``SHT_HASH`` ``SHF_ALLOC``
``.note`` ``SHT_NOTE`` *none*
``.rela``\ *name* ``SHT_RELA`` *none*
``.rela.dyn`` ``SHT_RELA`` *none*
``.rodata`` ``SHT_PROGBITS`` ``SHF_ALLOC``
``.shstrtab`` ``SHT_STRTAB`` *none*
``.strtab`` ``SHT_STRTAB`` *none*
``.symtab`` ``SHT_SYMTAB`` *none*
``.text`` ``SHT_PROGBITS`` ``SHF_ALLOC`` + ``SHF_EXECINSTR``
================== ================ =================================
These sections have their standard meanings (see [ELF]_) and are only generated
if needed.
``.debug``\ *\**
The standard DWARF sections. See :ref:`amdgpu-dwarf` for information on the
DWARF produced by the AMDGPU backend.
``.dynamic``, ``.dynstr``, ``.dynsym``, ``.hash``
The standard sections used by a dynamic loader.
``.note``
See :ref:`amdgpu-note-records` for the note records supported by the AMDGPU
backend.
``.rela``\ *name*, ``.rela.dyn``
For relocatable code objects, *name* is the name of the section that the
relocation records apply. For example, ``.rela.text`` is the section name for
relocation records associated with the ``.text`` section.
For linked shared code objects, ``.rela.dyn`` contains all the relocation
records from each of the relocatable code object's ``.rela``\ *name* sections.
See :ref:`amdgpu-relocation-records` for the relocation records supported by
the AMDGPU backend.
``.text``
The executable machine code for the kernels and functions they call. Generated
as position independent code. See :ref:`amdgpu-code-conventions` for
information on conventions used in the isa generation.
.. _amdgpu-note-records:
Note Records
------------
The AMDGPU backend code object contains ELF note records in the ``.note``
section. The set of generated notes and their semantics depend on the code
object version; see :ref:`amdgpu-note-records-v2` and
:ref:`amdgpu-note-records-v3`.
As required by ``ELFCLASS32`` and ``ELFCLASS64``, minimal zero byte padding
must be generated after the ``name`` field to ensure the ``desc`` field is 4
byte aligned. In addition, minimal zero byte padding must be generated to
ensure the ``desc`` field size is a multiple of 4 bytes. The ``sh_addralign``
field of the ``.note`` section must be at least 4 to indicate at least 8 byte
alignment.
.. _amdgpu-note-records-v2:
Code Object V2 Note Records (-mattr=-code-object-v3)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.. warning:: Code Object V2 is not the default code object version emitted by
this version of LLVM. For a description of the notes generated with the
default configuration (Code Object V3) see :ref:`amdgpu-note-records-v3`.
The AMDGPU backend code object uses the following ELF note record in the
``.note`` section when compiling for Code Object V2 (-mattr=-code-object-v3).
Additional note records may be present, but any which are not documented here
are deprecated and should not be used.
.. table:: AMDGPU Code Object V2 ELF Note Records
:name: amdgpu-elf-note-records-table-v2
===== ============================== ======================================
Name Type Description
===== ============================== ======================================
"AMD" ``NT_AMD_AMDGPU_HSA_METADATA`` <metadata null terminated string>
===== ============================== ======================================
..
.. table:: AMDGPU Code Object V2 ELF Note Record Enumeration Values
:name: amdgpu-elf-note-record-enumeration-values-table-v2
============================== =====
Name Value
============================== =====
*reserved* 0-9
``NT_AMD_AMDGPU_HSA_METADATA`` 10
*reserved* 11
============================== =====
``NT_AMD_AMDGPU_HSA_METADATA``
Specifies extensible metadata associated with the code objects executed on HSA
[HSA]_ compatible runtimes such as AMD's ROCm [AMD-ROCm]_. It is required when
the target triple OS is ``amdhsa`` (see :ref:`amdgpu-target-triples`). See
:ref:`amdgpu-amdhsa-code-object-metadata-v2` for the syntax of the code
object metadata string.
.. _amdgpu-note-records-v3:
Code Object V3 Note Records (-mattr=+code-object-v3)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The AMDGPU backend code object uses the following ELF note record in the
``.note`` section when compiling for Code Object V3 (-mattr=+code-object-v3).
Additional note records may be present, but any which are not documented here
are deprecated and should not be used.
.. table:: AMDGPU Code Object V3 ELF Note Records
:name: amdgpu-elf-note-records-table-v3
======== ============================== ======================================
Name Type Description
======== ============================== ======================================
"AMDGPU" ``NT_AMDGPU_METADATA`` Metadata in Message Pack [MsgPack]_
binary format.
======== ============================== ======================================
..
.. table:: AMDGPU Code Object V3 ELF Note Record Enumeration Values
:name: amdgpu-elf-note-record-enumeration-values-table-v3
============================== =====
Name Value
============================== =====
*reserved* 0-31
``NT_AMDGPU_METADATA`` 32
============================== =====
``NT_AMDGPU_METADATA``
Specifies extensible metadata associated with an AMDGPU code
object. It is encoded as a map in the Message Pack [MsgPack]_ binary
data format. See :ref:`amdgpu-amdhsa-code-object-metadata-v3` for the
map keys defined for the ``amdhsa`` OS.
.. _amdgpu-symbols:
Symbols
-------
Symbols include the following:
.. table:: AMDGPU ELF Symbols
:name: amdgpu-elf-symbols-table
===================== ================== ================ ==================
Name Type Section Description
===================== ================== ================ ==================
*link-name* ``STT_OBJECT`` - ``.data`` Global variable
- ``.rodata``
- ``.bss``
*link-name*\ ``.kd`` ``STT_OBJECT`` - ``.rodata`` Kernel descriptor
*link-name* ``STT_FUNC`` - ``.text`` Kernel entry point
*link-name* ``STT_OBJECT`` - SHN_AMDGPU_LDS Global variable in LDS
===================== ================== ================ ==================
Global variable
Global variables both used and defined by the compilation unit.
If the symbol is defined in the compilation unit then it is allocated in the
appropriate section according to if it has initialized data or is readonly.
If the symbol is external then its section is ``STN_UNDEF`` and the loader
will resolve relocations using the definition provided by another code object
or explicitly defined by the runtime.
If the symbol resides in local/group memory (LDS) then its section is the
special processor-specific section name ``SHN_AMDGPU_LDS``, and the
``st_value`` field describes alignment requirements as it does for common
symbols.
.. TODO::
Add description of linked shared object symbols. Seems undefined symbols
are marked as STT_NOTYPE.
Kernel descriptor
Every HSA kernel has an associated kernel descriptor. It is the address of the
kernel descriptor that is used in the AQL dispatch packet used to invoke the
kernel, not the kernel entry point. The layout of the HSA kernel descriptor is
defined in :ref:`amdgpu-amdhsa-kernel-descriptor`.
Kernel entry point
Every HSA kernel also has a symbol for its machine code entry point.
.. _amdgpu-relocation-records:
Relocation Records
------------------
AMDGPU backend generates ``Elf64_Rela`` relocation records. Supported
relocatable fields are:
``word32``
This specifies a 32-bit field occupying 4 bytes with arbitrary byte
alignment. These values use the same byte order as other word values in the
AMDGPU architecture.
``word64``
This specifies a 64-bit field occupying 8 bytes with arbitrary byte
alignment. These values use the same byte order as other word values in the
AMDGPU architecture.
Following notations are used for specifying relocation calculations:
**A**
Represents the addend used to compute the value of the relocatable field.
**G**
Represents the offset into the global offset table at which the relocation
entry's symbol will reside during execution.
**GOT**
Represents the address of the global offset table.
**P**
Represents the place (section offset for ``et_rel`` or address for ``et_dyn``)
of the storage unit being relocated (computed using ``r_offset``).
**S**
Represents the value of the symbol whose index resides in the relocation
entry. Relocations not using this must specify a symbol index of
``STN_UNDEF``.
**B**
Represents the base address of a loaded executable or shared object which is
the difference between the ELF address and the actual load address.
Relocations using this are only valid in executable or shared objects.
The following relocation types are supported:
.. table:: AMDGPU ELF Relocation Records
:name: amdgpu-elf-relocation-records-table
========================== ======= ===== ========== ==============================
Relocation Type Kind Value Field Calculation
========================== ======= ===== ========== ==============================
``R_AMDGPU_NONE`` 0 *none* *none*
``R_AMDGPU_ABS32_LO`` Static, 1 ``word32`` (S + A) & 0xFFFFFFFF
Dynamic
``R_AMDGPU_ABS32_HI`` Static, 2 ``word32`` (S + A) >> 32
Dynamic
``R_AMDGPU_ABS64`` Static, 3 ``word64`` S + A
Dynamic
``R_AMDGPU_REL32`` Static 4 ``word32`` S + A - P
``R_AMDGPU_REL64`` Static 5 ``word64`` S + A - P
``R_AMDGPU_ABS32`` Static, 6 ``word32`` S + A
Dynamic
``R_AMDGPU_GOTPCREL`` Static 7 ``word32`` G + GOT + A - P
``R_AMDGPU_GOTPCREL32_LO`` Static 8 ``word32`` (G + GOT + A - P) & 0xFFFFFFFF
``R_AMDGPU_GOTPCREL32_HI`` Static 9 ``word32`` (G + GOT + A - P) >> 32
``R_AMDGPU_REL32_LO`` Static 10 ``word32`` (S + A - P) & 0xFFFFFFFF
``R_AMDGPU_REL32_HI`` Static 11 ``word32`` (S + A - P) >> 32
*reserved* 12
``R_AMDGPU_RELATIVE64`` Dynamic 13 ``word64`` B + A
========================== ======= ===== ========== ==============================
``R_AMDGPU_ABS32_LO`` and ``R_AMDGPU_ABS32_HI`` are only supported by
the ``mesa3d`` OS, which does not support ``R_AMDGPU_ABS64``.
There is no current OS loader support for 32-bit programs and so
``R_AMDGPU_ABS32`` is not used.
.. _amdgpu-dwarf:
DWARF
-----
.. warning::
This section describes a **provisional proposal** that is not currently
fully implemented and is subject to change.
Standard DWARF [DWARF]_ sections can be generated. These contain information
that maps the code object executable code and data to the source language
constructs. It can be used by tools such as debuggers and profilers.
This section defines the AMDGPU target specific DWARF. It applies to DWARF
Version 4 and 5.
.. _amdgpu-dwarf-overview:
Overview
~~~~~~~~
The AMDGPU has several features that require additional DWARF functionality in
order to support optimized code.
A single code object can contain code for kernels that have different wave
sizes. The vector registers and some scalar registers are based on the wave
size. AMDGPU defines distinct DWARF registers for each wave size. This
simplifies the consumer of the DWARF so that each register has a fixed size,
rather than being dynamic according to the wave mode. Similarly, distinct DWARF
registers are defined for those registers that vary in size according to the
process address size. This allows a consumer to treat a specific AMDGPU target
as a single architecture regardless of how it is configured. The compiler
explicitly specifies the registers that match the mode of the code it is
generating.
AMDGPU optimized code may spill vector registers to non-global address space
memory, and this spilling may be done only for lanes that are active on entry to
the subprogram. To support this, a location description that can be created as a
masked select is required.
Since the active lane mask may be held in a register, a way to get the value of
a register on entry to a subprogram is required. To support this an operation
that returns the caller value of a register as specified by the Call Frame
Information (see :ref:`amdgpu-call-frame-information`) is required.
Current DWARF uses an empty expression to indicate an undefined location
description. Since the masked select composite location description operation
takes more than one location description, it is necessary to have an explicit
way to specify an undefined location description. Otherwise it is not possible
to specify that a particular one of the input location descriptions is
undefined.
CFI describes restoring callee saved registers that are spilled. Currently CFI
only allows a location description that is a register, memory address, or
implicit location description. AMDGPU optimized code may spill scalar registers
into portions of vector registers. This requires extending CFI to allow any
location description.
The vector registers of the AMDGPU are represented as their full wave size,
meaning the wave size times the dword size. This reflects the actual hardware,
and allows the compiler to generate DWARF for languages that map a thread to the
complete wave. It also allows more efficient DWARF to be generated to describe
the CFI as only a single expression is required for the whole vector register,
rather than a separate expression for each lane's dword of the vector register.
It also allows the compiler to produce DWARF that indexes the vector register if
it spills scalar registers into portions of a vector registers.
Since DWARF stack value entries have a base type and AMDGPU registers are a
vector of dwords, the ability to specify that a base type is a vector is
required.
If the source language is mapped onto the AMDGPU wavefronts in a SIMT manner,
then the variable DWARF location expressions must compute the location for a
single lane of the wavefront. Therefore, a DWARF operator is required to denote
the current lane, much like ``DW_OP_push_object_address`` denotes the current
object. The ``DW_OP_*piece`` operators only allow literal indices. Therefore, a
composite location description is required that can take a computed index of a
location description (such as a vector register).
If the source language is mapped onto the AMDGPU wavefronts in a SIMT manner the
compiler can use the AMDGPU execution mask register to control which lanes are
active. To describe the conceptual location of non-active lanes a DWARF
expression is needed that can compute a per lane PC. For efficiency, this is
done for the wave as a whole. This expression benefits by having a masked select
composite location description operation. This requires an attribute for source
location of each lane. The AMDGPU may update the execution mask for whole wave
operations and so needs an attribute that computes the current active lane mask.
AMDGPU needs to be able to describe addresses that are in different kinds of
memory. Optimized code may need to describe a variable that resides in pieces
that are in different kinds of storage which may include parts of registers,
memory that is in a mixture of memory kinds, implicit values, or be undefined.
DWARF has the concept of segment addresses. However, the segment cannot be
specified within a DWARF expression, which is only able to specify the offset
portion of a segment address. The segment index is only provided by the entity
that species the DWARF expression. Therefore, the segment index is a property
that can only be put on complete objects, such as a variable. That makes it only
suitable for describing an entity (such as variable or subprogram code) that is
in a single kind of memory. Therefore, AMDGPU uses the DWARF concept of address
spaces. For example, a variable may be allocated in a register that is partially
spilled to the call stack which is in the private address space, and partially
spilled to the local address space.
DWARF uses the concept of an address in many expression operators but does not
define how it relates to address spaces. For example,
``DW_OP_push_object_address`` pushes the address of an object. Other contexts
implicitly push an address on the stack before evaluating an expression. For
example, the ``DW_AT_use_location`` attribute of the
``DW_TAG_ptr_to_member_type``. The expression that uses the address needs to do
so in a general way and not need to be dependent on the address space of the
address. For example, a pointer to member value may want to be applied to an
object that may reside in any address space.
The number of registers and the cost of memory operations is much higher for
AMDGPU than a typical CPU. The compiler attempts to optimize whole variables and
arrays into registers. Currently DWARF only allows ``DW_OP_push_object_address``
and related operations to work with a global memory location. To support AMDGPU
optimized code it is required to generalize DWARF to allow any location
description to be used. This allows registers, or composite location
descriptions that may be a mixture of memory, registers, or even implicit
values.
Allowing a location description to be an entry on the DWARF stack allows them to
compose naturally. It allows objects to be located in any kind of memory address
space, in registers, be implicit values, be undefined, or a composite of any of
these.
By extending DWARF carefully, all existing DWARF expressions can retain their
current semantic meaning. DWARF has implicit conversions that convert from a
value that is treated as an address in the default address space to a memory
location description. This can be extended to allow a default address space
memory location description to be implicitly converted back to its address
value. To allow composition of composite location descriptions, an explicit
operator that indicates the end is required. This can be implied if the end of a
DWARF expression is reached, allowing current DWARF expressions to remain legal.
The ``DW_OP_plus`` and ``DW_OP_minus`` can be defined to operate on a memory
location description in the default target architecture address space and a
generic type, and produce a memory location description. This allows them to
continue to be used to offset an address. To generalize offsetting to any
location description, including location descriptions that describe when bytes
are in registers, are implicit, or a composite of these, the
``DW_OP_LLVM_offset`` and ``DW_OP_LLVM_bit_offset`` operations are added. These
do not perform wrapping which would be hard to define for location descriptions
of non-memory kinds. This allows ``DW_OP_push_object_address`` to push a
location description that may be in a register, or be an implicit value, and the
DWARF expression of ``DW_TAG_ptr_to_member_type`` can contain
``DW_OP_LLVM_offset`` to offset within it. ``DW_OP_LLVM_bit_offset`` generalizes
DWARF to work with bit fields.
The DWARF ``DW_OP_xderef*`` operation allows a value to be converted into an
address of a specified address space which is then read. But provides no way to
create a memory location description for an address in the non-default address
space. For example, AMDGPU variables can be allocated in the local address space
at a fixed address. It is required to have an operation to create an address in
a specific address space that can be used to define the location description of
the variable. Defining this operation to produce a location description allows
the size of addresses in an address space to be larger than the generic type.
If an operation had to produce a value that can be implicitly converted to a
memory location description, then it would be limited to the size of the generic
type which matches the size of the default address space. Its value would be
unspecified and likely not match any value in the actual program. By making the
result a location description, it allows a consumer great freedom in how it
implements it. The implicit conversion back to a value can be limited only to
the default address space to maintain compatibility.
Similarly ``DW_OP_breg*`` treats the register as containing an address in the
default address space. It is required to be able to specify the address space of
the register value.
Almost all uses of addresses in DWARF are limited to defining location
descriptions, or to be dereferenced to read memory. The exception is
``DW_CFA_val_offset`` which uses the address to set the value of a register. By
defining the CFA DWARF expression as being a memory location description, it can
maintain what address space it is, and that can be used to convert the offset
address back to an address in that address space. (An alternative is to defined
``DW_CFA_val_offset`` to implicitly use the default address space, and add
another operation that specifies the address space.)
This approach allows all existing DWARF to have the identical semantics. It
allows the compiler to explicitly specify the address space it is using. For
example, a compiler could choose to access private memory in a swizzled manner
when mapping a source language to a wave in a SIMT manner, or to access it in an
unswizzled manner if mapping the same language with the wave being the thread.
It also allows the compiler to mix the address space it uses to access private
memory. For example, for SIMT it can still spill entire vector registers in an
unswizzled manner, while using swizzled for SIMT variable access. This approach
allows memory location descriptions for different address spaces to be combined
using the regular ``DW_OP_*piece`` operators.
Location descriptions are an abstraction of storage, they give freedom to the
consumer on how to implement them. They allow the address space to encode lane
information so they can be used to read memory with only the memory description
and no extra arguments. The same set of operations can operate on locations
independent of their kind of storage. The ``DW_OP_deref*`` therefore can be used
on any storage kind. ``DW_OP_xderef*`` is unnecessary except to become a more
compact way to convert a segment address followed by dereferencing it.
Several approaches were considered, and the one proposed appears to be the
cleanest and offers the greatest improvement of DWARF's ability to support
optimized code. Examining the gdb debugger and LLVM compiler, it appears only to
require modest changes as they both already have to support general use of
location descriptions. It is anticipated that will be the case for other
debuggers and compilers.
The following provides the definitions for the additional operators, as well as
clarifying how existing expression operators, CFI operators, and attributes
behave with respect to generalized location descriptions that support address
spaces. It has been defined such that it is backwards compatible with DWARF 5.
The definitions are intended to fully define well-formed DWARF in a consistent
style. Some sections are organized to mirror the DWARF 5 specification
structure, with non-normative text shown in *italics*.
.. _amdgpu-dwarf-language-names:
Language Names
~~~~~~~~~~~~~~
Language codes defined for use with the ``DW_AT_language`` attribute are
defined in :ref:`amdgpu-dwarf-language-names-table`.
.. table:: AMDGPU DWARF Language Names
:name: amdgpu-dwarf-language-names-table
==================== ====== =================== =============================
Language Name Code Default Lower Bound Description
==================== ====== =================== =============================
``DW_LANG_LLVM_HIP`` 0x8100 0 AMD HIP Language. See [HIP]_.
==================== ====== =================== =============================
The ``DW_LANG_LLVM_HIP`` language can be supported by extending the C++
language.
.. _amdgpu-dwarf-register-mapping:
Register Mapping
~~~~~~~~~~~~~~~~
DWARF registers are encoded as numbers, which are mapped to architecture
registers. The mapping for AMDGPU is defined in
:ref:`amdgpu-dwarf-register-mapping-table`.
.. table:: AMDGPU DWARF Register Mapping
:name: amdgpu-dwarf-register-mapping-table
============== ================= ======== ==================================
DWARF Register AMDGPU Register Bit Size Description
============== ================= ======== ==================================
0 PC_32 32 Program Counter (PC) when
executing in a 32-bit process
address space. Used in the CFI to
describe the PC of the calling
frame.
1 EXEC_MASK_32 32 Execution Mask Register when
executing in wave 32 mode.
2-15 *Reserved*
16 PC_64 64 Program Counter (PC) when
executing in a 64-bit process
address space. Used in the CFI to
describe the PC of the calling
frame.
17 EXEC_MASK_64 64 Execution Mask Register when
executing in wave 64 mode.
18-31 *Reserved*
32-95 SGPR0-SGPR63 32 Scalar General Purpose
Registers.
96-127 *Reserved*
128-511 *Reserved*
512-1023 *Reserved*
1024-1087 *Reserved*
1088-1129 SGPR64-SGPR105 32 Scalar General Purpose Registers
1130-1535 *Reserved*
1536-1791 VGPR0-VGPR255 32*32 Vector General Purpose Registers
when executing in wave 32 mode.
1792-2047 *Reserved*
2048-2303 AGPR0-AGPR255 32*32 Vector Accumulation Registers
when executing in wave 32 mode.
2304-2559 *Reserved*
2560-2815 VGPR0-VGPR255 64*32 Vector General Purpose Registers
when executing in wave 64 mode.
2816-3071 *Reserved*
3072-3327 AGPR0-AGPR255 64*32 Vector Accumulation Registers
when executing in wave 64 mode.
3328-3583 *Reserved*
============== ================= ======== ==================================
The vector registers are represented as the full size for the wavefront. They
are organized as consecutive dwords (32-bits), one per lane, with the dword at
the least significant bit position corresponding to lane 0 and so forth. DWARF
location expressions involving the ``DW_OP_LLVM_offset`` and
``DW_OP_LLVM_push_lane`` operations are used to select the part of the vector
register corresponding to the lane that is executing the current thread of
execution in languages that are implemented using a SIMD or SIMT execution
model.
If the wavefront size is 32 lanes then the wave 32 mode register definitions
are used. If the wavefront size is 64 lanes then the wave 64 mode register
definitions are used. Some AMDGPU targets support executing in both wave 32
and wave 64 mode. The register definitions corresponding to the wave mode
of the generated code will be used.
If code is generated to execute in a 32-bit process address space then the
32-bit process address space register definitions are used. If code is
generated to execute in a 64-bit process address space then the 64-bit process
address space register definitions are used. The ``amdgcn`` target only
supports the 64-bit process address space.
Address Class Mapping
~~~~~~~~~~~~~~~~~~~~~
DWARF address classes are used for languages with the concept of memory address
spaces. They are used in the ``DW_AT_address_class`` attribute for pointer type,
reference type, subroutine, and subroutine type debugger information entries
(DIEs).
The address class mapping for AMDGPU is defined in
:ref:`amdgpu-dwarf-address-class-mapping-table`.
.. table:: AMDGPU DWARF Address Class Mapping
:name: amdgpu-dwarf-address-class-mapping-table
=========================== ===== =================
DWARF AMDGPU
--------------------------------- -----------------
Address Class Name Value Address Space
=========================== ===== =================
``DW_ADDR_none`` 0x00 Generic (Flat)
``DW_ADDR_AMDGPU_global`` 0x01 Global
``DW_ADDR_AMDGPU_region`` 0x02 Region (GDS)
``DW_ADDR_AMDGPU_local`` 0x03 Local (group/LDS)
``DW_ADDR_AMDGPU_constant`` 0x04 Global
``DW_ADDR_AMDGPU_private`` 0x05 Private (Scratch)
=========================== ===== =================
See :ref:`amdgpu-address-spaces` for information on the AMDGPU address spaces
including address size and NULL value.
For AMDGPU the address class encodes the address class as declared in the
source language type.
For AMDGPU if no ``DW_AT_address_class`` attribute is present, then the
``DW_ADDR_none`` address class is used.
.. note::
The ``DW_ADDR_none`` default was defined as ``Generic`` and not ``Global``
to match the LLVM address space ordering. This ordering was chosen to better
support CUDA-like languages such as HIP that do not have address spaces in
the language type system, but do allow variables to be allocated in
different address spaces. So effectively all CUDA and HIP source language
addresses are generic.
.. note::
Currently DWARF defines address class values as architecture specific. It
is unclear how language specific address spaces are intended to be
represented in DWARF.
For example, OpenCL defines address spaces for ``global``, ``local``,
``constant``, and ``private``. These are part of the type system and are
modifies to pointer types. In addition, OpenCL defines ``generic`` pointers
that can reference either the ``global``, ``local``, or ``private`` address
spaces. To support the OpenCL language the debugger would want to support
casting pointers between the ``generic`` and other address spaces, and
possibly using pointer casting to form an address for a specific address
space out of an integral value.
The method to use to dereference a pointer type or reference type value is
defined in DWARF expressions using ``DW_OP_xderef*`` which uses an
architecture specific address space.
DWARF defines the ``DW_AT_address_class`` attribute on pointer types and
reference types. It specifies the method to use to dereference them. Why
is the value of this not the same as the address space value used in
``DW_OP_xderef*`` since in both cases it is architecture specific and the
architecture presumably will use the same set of methods to dereference
pointers in both cases?
Since ``DW_AT_address_class`` uses an architecture specific value it cannot
in general capture the source language address space type modifier concept.
On some architectures all source language address space modifies may
actually use the same method for dereferencing pointers.
One possibility is for DWARF to add an ``DW_TAG_LLVM_address_class_type``
type modifier that can be applied to a pointer type and reference type. The
``DW_AT_address_class`` attribute could be re-defined to not be architecture
specific and instead define generalized language values that will support
OpenCL and other languages using address spaces. The ``DW_AT_address_class``
could be defined to not be applied to pointer or reference types, but
instead only to the ``DW_TAG_LLVM_address_class_type`` type modifier entry.
If a pointer type or reference type is not modified by
``DW_TAG_LLVM_address_class_type`` or if ``DW_TAG_LLVM_address_class_type``
has no ``DW_AT_address_class`` attribute, then the pointer type or reference
type would be defined to use the ``DW_ADDR_none`` address class as
currently. Since modifiers can be chained, it would need to be defined if
multiple ``DW_TAG_LLVM_address_class_type`` modifies was legal, and if so if
the outermost one is the one that takes precedence.
A target implementation that supports multiple address spaces would need to
map ``DW_ADDR_none`` appropriately to support CUDA-like languages
that have no address classes in the type system, but do support variable
allocation in address spaces. See the above note that describes why AMDGPU
choose to make ``DW_ADDR_none`` map to the ``Generic`` AMDGPU address space
and not the ``Global`` address space.
An alternative would be to define ``DW_ADDR_none`` as being the global
address class and then change ``DW_ADDR_global`` to ``DW_ADDR_generic``.
Compilers generating DWARF for CUDA-like languages would then have to define
every CUDA-like language pointer type or reference type using
``DW_TAG_LLVM_address_class_type`` with a ``DW_AT_address_class`` attribute
of ``DW_ADDR_generic`` to match the language semantics. The AMDGPU
alternative avoids needing to do this and seems to fit better into how CLANG
and LLVM have added support for the CUDA-like languages on top of existing
C++ language support.
A new ``DW_AT_address_space`` attribute could be defined that can be applied
to pointer type, reference type, subroutine, and subroutine type to describe
how objects having the given type are dereferenced or called (the role that
``DW_AT_address_class`` currently provides). The values of
``DW_AT_address_space`` would be architecture specific and the same as used
in ``DW_OP_xderef*``.
.. _amdgpu-dwarf-address-space-mapping:
Address Space Mapping
~~~~~~~~~~~~~~~~~~~~~
DWARF address spaces are used in location expressions to describe the memory
space where data resides. Address spaces correspond to a target specific memory
space and are not tied to any source language concept.
The AMDGPU address space mapping is defined in
:ref:`amdgpu-dwarf-address-space-mapping-table`.
.. table:: AMDGPU DWARF Address Space Mapping
:name: amdgpu-dwarf-address-space-mapping-table
======================================= ===== ======= ======== ================= =======================
DWARF AMDGPU Notes
--------------------------------------- ----- ---------------- ----------------- -----------------------
Address Space Name Value Address Bit Size Address Space
--------------------------------------- ----- ------- -------- ----------------- -----------------------
.. 64-bit 32-bit
process process
address address
space space
======================================= ===== ======= ======== ================= =======================
``DW_ASPACE_none`` 0x00 8 4 Global *default address space*
``DW_ASPACE_AMDGPU_generic`` 0x01 8 4 Generic (Flat)
``DW_ASPACE_AMDGPU_region`` 0x02 4 4 Region (GDS)
``DW_ASPACE_AMDGPU_local`` 0x03 4 4 Local (group/LDS)
*Reserved* 0x04
``DW_ASPACE_AMDGPU_private_lane`` 0x05 4 4 Private (Scratch) *focused lane*
``DW_ASPACE_AMDGPU_private_wave`` 0x06 4 4 Private (Scratch) *unswizzled wave*
*Reserved* 0x07-
0x1F
``DW_ASPACE_AMDGPU_private_lane<0-63>`` 0x20- 4 4 Private (Scratch) *specific lane*
0x5F
======================================= ===== ======= ======== ================= =======================
See :ref:`amdgpu-address-spaces` for information on the AMDGPU address spaces
including address size and NULL value.
The ``DW_ASPACE_none`` address space is the default address space used in DWARF
operations that do not specify an address space. It therefore has to map to the
global address space so that the ``DW_OP_addr*`` and related operations can
refer to addresses in the program code.
The ``DW_ASPACE_AMDGPU_generic`` address space allows location expressions to
specify the flat address space. If the address corresponds to an address in the
local address space then it corresponds to the wave that is executing the
focused thread of execution. If the address corresponds to an address in the
private address space then it corresponds to the lane that is executing the
focused thread of execution for languages that are implemented using a SIMD or
SIMT execution model.
.. note::
CUDA-like languages such as HIP that do not have address spaces in the
language type system, but do allow variables to be allocated in different
address spaces, will need to explicitly specify the
``DW_ASPACE_AMDGPU_generic`` address space in the DWARF operations as the
default address space is the global address space.
The ``DW_ASPACE_AMDGPU_local`` address space allows location expressions to
specify the local address space corresponding to the wave that is executing the
focused thread of execution.
The ``DW_ASPACE_AMDGPU_private_lane`` address space allows location expressions
to specify the private address space corresponding to the lane that is
executing the focused thread of execution for languages that are implemented
using a SIMD or SIMT execution model.
The ``DW_ASPACE_AMDGPU_private_wave`` address space allows location expressions
to specify the unswizzled private address space corresponding to the wave that
is executing the focused thread of execution. The wave view of private memory
is the per wave unswizzled backing memory layout defined in
:ref:`amdgpu-address-spaces`, such that address 0 corresponds to the first
location for the backing memory of the wave (namely the address is not offset
by ``wavefront-scratch-base``). So to convert from a
``DW_ASPACE_AMDGPU_private_lane`` to a ``DW_ASPACE_AMDGPU_private_wave``
segment address perform the following:
::
private-address-wave =
((private-address-lane / 4) * wavefront-size * 4) +
(wavefront-lane-id * 4) + (private-address-lane % 4)
If the ``DW_ASPACE_AMDGPU_private_lane`` segment address is dword aligned and
the start of the dwords for each lane starting with lane 0 is required, then
this simplifies to:
::
private-address-wave =
private-address-lane * wavefront-size
A compiler can use this address space to read a complete spilled vector
register back into a complete vector register in the CFI. The frame pointer can
be a private lane segment address which is dword aligned, which can be shifted
to multiply by the wave size, and then used to form a private wave segment
address that gives a location for a contiguous set of dwords, one per lane,
where the vector register dwords are spilled. The compiler knows the wave size
since it generates the code. Note that the type of the address may have to be
converted as the size of a private lane segment address may be smaller than the
size of a private wave segment address.
The ``DW_ASPACE_AMDGPU_private_lane<n>`` address space allows location
expressions to specify the private address space corresponding to a specific
lane. For example, this can be used when the compiler spills scalar registers
to scratch memory, with each scalar register being saved to a different lane's
scratch memory.
.. _amdgpu-dwarf-expressions:
Expressions
~~~~~~~~~~~
The following sections define the new DWARF expression operator used by AMDGPU,
as well as clarifying the extensions to already existing DWARF 5 operations.
DWARF expressions describe how to compute a value or specify a location
description. An expression is encoded as a stream of operations, each consisting
of an opcode followed by zero or more literal operands. The number of operands
is implied by the opcode.
Operations represent a postfix operation on a simple stack machine. They can act
on entries on the stack, including adding entries and removing entries. If the
kind of a stack entry does not match the kind required by the operation, and is
not implicitly convertible to the required kind, then the DWARF expression is
ill-formed.
Each stack entry can be one of two kinds: a value or a location description.
Value stack entries are described in :ref:`amdgpu-value-operations` and
location description stack entries are described in
:ref:`amdgpu-location-description-operations`.
*The evaluation of a DWARF expression can provide the location description of an
object, the value of an array bound, the length of a dynamic string, the desired
value itself, and so on.*
The result of the evaluation of a DWARF expression is defined as:
* If evaluation of the DWARF expression is on behalf of a ``DW_OP_call*``
operation for a ``DW_AT_location`` attribute that belongs to a
``DW_TAG_dwarf_procedure`` debugging information entry, then all the entries
on the stack are left, and execution of the DWARF expression containing the
``DW_OP_call*`` operation continues.
* If evaluation of the DWARF expression requires a location description, then:
* If the stack is empty, an undefined location description is returned.
* If the top stack entry is a location description, or can be converted to
one, then the, possibly converted, location description is returned. Any
other entries on the stack are discarded.
* Otherwise the DWARF expression is ill-formed.
.. note::
Could define this case as returning an implicit location description as
if the ``DW_OP_implicit`` operation is performed.
* If evaluation of the DWARF expression requires a value, then:
* If the top stack entry is a value, or can be converted to one, then the,
possibly converted, value is returned. Any other entries on the stack are
discarded.
* Otherwise the DWARF expression is ill-formed.
.. _amdgpu-stack-operations:
Stack Operations
++++++++++++++++
The following operations manipulate the DWARF stack. Operations that index
the stack assume that the top of the stack (most recently added entry) has index
0. They allow the stack entries to be either a value or location description.
If any stack entry accessed by a stack operation is an incomplete composite
location description, then the DWARF expression is ill-formed.
.. note::
These operations now support stack entries that are values and location
descriptions.
.. note::
If it is desired to also make them work with incomplete composite location
descriptions then would need to define that the composite location storage
specified by the incomplete composite location description is also replicated
when a copy is pushed. This ensures that each copy of the incomplete composite
location description can updated the composite location storage they specify
independently.
1. ``DW_OP_dup``
``DW_OP_dup`` duplicates the stack entry at the top of the stack.
2. ``DW_OP_drop``
``DW_OP_drop`` pops the stack entry at the top of the stack and discards it.
3. ``DW_OP_pick``
``DW_OP_pick`` has a single unsigned 1-byte operand that is treated as an
index I. A copy of the stack entry with index I is pushed onto the stack.
4. ``DW_OP_over``
``DW_OP_over`` pushes a copy of the entry entry with index 1.
*This is equivalent to a ``DW_OP_pick 1`` operation.*
5. ``DW_OP_swap``
``DW_OP_swap`` swaps the top two stack entries. The entry at the top of the
stack becomes the second stack entry, and the second stack entry becomes the
top of the stack.
6. ``DW_OP_rot``
``DW_OP_rot`` rotates the first three stack entries. The entry at the top of
the stack becomes the third stack entry, the second entry becomes the top of
the stack, and the third entry becomes the second entry.
.. _amdgpu-value-operations:
Value Operations
++++++++++++++++
Each value stack entry has a type and a value, and can represent a value of
any supported base type of the target machine. The base type specifies the size
and encoding of the value.
.. note::
It may be better to add an implicit pointer value kind that is produced when
``DW_OP_deref*`` retrieves the full contents of an implicit pointer location
storage created by the ``DW_OP_implicit_pointer`` or
``DW_OP_LLVM_aspace_implicit_pointer`` operations.
Instead of a base type, value stack entries can have a distinguished generic
type, which is an integral type that has the size of an address in the target
architecture default address space on the target machine and unspecified
signedness.
*The generic type is the same as the unspecified type used for stack operations
defined in DWARF Version 4 and before.*
An integral type is a base type that has an encoding of ``DW_ATE_signed``,
``DW_ATE_signed_char``, ``DW_ATE_unsigned``, ``DW_ATE_unsigned_char``,
``DW_ATE_boolean``, or any target architecture defined integral encoding in the
inclusive range ``DW_ATE_lo_user`` to ``DW_ATE_hi_user``.
.. note::
Unclear if ``DW_ATE_address`` is an integral type. gdb does not seem to
consider as integral.
1. ``DW_OP_LLVM_push_lane`` *New*
``DW_OP_LLVM_push_lane`` pushes a value with the generic type that is the
target architecture lane identifier of the thread of execution for which a
user presented expression is currently being evaluated. For languages that
are implemented using a SIMD or SIMT execution model this is the lane number
that corresponds to the source language thread of execution upon which the
user is focused. Otherwise this is the value 0.
For AMDGPU, the lane identifier returned by ``DW_OP_LLVM_push_lane``
corresponds to the the hardware lane number which is numbered from 0 to the
wavefront size minus 1.
2. ``DW_OP_entry_value``
``DW_OP_entry_value`` pushes the value that the described location held upon
entering the current subprogram.
It has two operands. The first is an unsigned LEB128 integer. The second is
a block of bytes, with a length equal to the first operand, treated as a
DWARF expression E.
E is evaluated as if it had been evaluated upon entering the current
subprogram. E assumes no values are present on the DWARF stack initially and
results in exactly one value being pushed on the DWARF stack when completed.
``DW_OP_push_object_address`` is not meaningful inside of this DWARF
operation.
If the result of E is a register location description (see
:ref:`amdgpu-register-location-descriptions`), ``DW_OP_entry_value`` pushes
the value that register had upon entering the current subprogram. The value
entry type is the target machine register base type. If the register value
is undefined or the register location description bit offset is not 0, then
the DWARF expression is ill-formed.
*The register location description provides a more compact form for the case
where the value was in a register on entry to the subprogram.*
Otherwise, the expression result is required to be a value, and
``DW_OP_entry_value`` pushes that value.
*The values needed to evaluate* ``DW_OP_entry_value`` *could be obtained in
several ways. The consumer could suspend execution on entry to the
subprogram, record values needed by* ``DW_OP_entry_value`` *expressions
within the subprogram, and then continue; when evaluating*
``DW_OP_entry_value``\ *, the consumer would use these recorded values
rather than the current values. Or, when evaluating* ``DW_OP_entry_value``\
*, the consumer could virtually unwind using the Call Frame Information
(see* :ref:`amdgpu-call-frame-information`\ *) to recover register values
that might have been clobbered since the subprogram entry point.*
.. note::
Unclear why this operation is defined this way. If the expression is
simply using existing variables then it is just a regular expression. It
is unclear how the compiler instructs the consumer how to create the saved
copies of the variables on entry. Seems only the compiler knows how to do
this. If the main purpose is only to read the entry value of a register
using CFI then would be better to have an operation that explicitly does
just that such as ``DW_OP_LLVM_call_frame_entry_reg``.
.. _amdgpu-location-description-operations:
Location Description Operations
+++++++++++++++++++++++++++++++
Information about the location of program objects is provided by location
descriptions. Location descriptions specify the storage that holds the program
objects, and a position within the storage.
A location storage is a linear stream of bits that can hold values. Each
location storage has a size in bits and can be accessed using a zero-based bit
offset. The ordering of bits within location storage uses the bit numbering and
direction conventions that are appropriate to the current language on the target
architecture.
.. note::
For AMDGPU bytes are ordered with least significant bytes first, and bits are
ordered within bytes with least significant bits first.
There are five kinds of location storage: undefined, memory, register, implicit,
and composite. Memory and register location storage corresponds to the target
architecture memory address spaces and registers. Implicit location storage
corresponds to fixed values that can only be read. Undefined location storage
indicates no value is available and therefore cannot be read or written.
Composite location storage allows a mixture of these where some bits come from
one kind of location storage and some from another kind of location storage.
.. note::
It may be better to add an implicit pointer location storage kind for
``DW_OP_implicit_pointer`` or ``DW_OP_LLVM_aspace_implicit_pointer``.
Location description stack entries specify a location storage to which they
refer, and a bit offset relative to the start of the location storage.
General Operations
##################
1. ``DW_OP_LLVM_offset`` *New*
``DW_OP_LLVM_offset`` pops two stack entries. The first must be an integral
type value that is treated as a byte displacement D. The second must be a
location description L.
It adds the value of D scaled by 8 (the byte size) to the bit offset of L,
and pushes the updated L.
If the updated bit offset of L is less than 0 or greater than or equal to
the size of the location storage specified by L, then the DWARF expression
is ill-formed.
2. ``DW_OP_LLVM_offset_uconst`` *New*
``DW_OP_LLVM_offset_uconst`` has a single unsigned LEB128 integer operand
that is treated as a displacement D.
It pops one stack entry that must be a location description L. It adds the
value of D scaled by 8 (the byte size) to the bit offset of L, and pushes
the updated L.
If the updated bit offset of L is less than 0 or greater than or equal to
the size of the location storage specified by L, then the DWARF expression
is ill-formed.
*This operation is supplied specifically to be able to encode more field
displacements in two bytes than can be done with* ``DW_OP_lit<n>
DW_OP_LLVM_offset``\ *.*
3. ``DW_OP_LLVM_bit_offset`` *New*
``DW_OP_LLVM_bit_offset`` pops two stack entries. The first must be an
integral type value that is treated as a bit displacement D. The second must
be a location description L.
It adds the value of D to the bit offset of L, and pushes the updated L.
If the updated bit offset of L is less than 0 or greater than or equal to
the size of the location storage specified by L, then the DWARF expression
is ill-formed.
4. ``DW_OP_deref``
The ``DW_OP_deref`` operation pops one stack entry that must be a location
description L.
A value of the bit size of the generic type is retrieved from the location
storage specified by L starting at the bit offset specified by L. The
retrieved generic type value V is pushed on the stack.
If any bit of the value is retrieved from the undefined location storage, or
the offset of any bit exceeds the size of the location storage specified by
L, then the DWARF expression is ill-formed.
See :ref:`amdgpu-implicit-location-descriptions` for special rules
concerning implicit location descriptions created by the
``DW_OP_implicit_pointer`` and ``DW_OP_LLVM_implicit_aspace_pointer``
operations.
5. ``DW_OP_deref_size``
``DW_OP_deref_size`` has a single 1-byte unsigned integral constant treated
as a byte result size S.
It pops one stack entry that must be a location description L.
A value of S scaled by 8 (the byte size) bits is retrieved from the location
storage specified by L starting at the bit offset specified by L. The value
V retrieved is zero-extended to the bit size of the generic type before
being pushed onto the stack with the generic type.
If S is larger than the byte size of the generic type, if any bit of the
value is retrieved from the undefined location storage, or if the offset of
any bit exceeds the size of the location storage specified by L, then the
DWARF expression is ill-formed.
See :ref:`amdgpu-implicit-location-descriptions` for special rules
concerning implicit location descriptions created by the
``DW_OP_implicit_pointer`` and ``DW_OP_LLVM_implicit_aspace_pointer``
operations.
6. ``DW_OP_deref_type``
``DW_OP_deref_type`` has two operands. The first is a 1-byte unsigned
integral constant whose value S is the same as the size of the base type
referenced by the second operand. The second operand is an unsigned LEB128
integer that represents the offset of a debugging information entry E in the
current compilation unit, which must be a ``DW_TAG_base_type`` entry that
provides the type of the result value.
It pops one stack entry that must be a location description L. A value of
the bit size S is retrieved from the location storage specified by L
starting at the bit offset specified by the L. The retrieved result type
value V is pushed on the stack.
If any bit of the value is retrieved from the undefined location storage, or
if the offset of any bit exceeds the size of the specified location storage,
then the DWARF expression is ill-formed.
See :ref:`amdgpu-implicit-location-descriptions` for special rules
concerning implicit location descriptions created by the
``DW_OP_implicit_pointer`` and ``DW_OP_LLVM_implicit_aspace_pointer``
operations.
*While the size of the pushed value could be inferred from the base type
definition, it is encoded explicitly into the operation so that the
operation can be parsed easily without reference to the* ``.debug_info``
*section.*
7. ``DW_OP_xderef`` *Deprecated*
``DW_OP_xderef`` pops two stack entries. The first must be an integral type
value that is treated as an address A. The second must be an integral type
value that is treated as an address space identifier AS for those
architectures that support multiple address spaces.
The operation is equivalent to performing ``DW_OP_swap;
DW_OP_LLVM_form_aspace_address; DW_OP_deref``. The retrieved generic type
value V is left on the stack.
8. ``DW_OP_xderef_size`` *Deprecated*
``DW_OP_xderef_size`` has a single 1-byte unsigned integral constant treated
as a byte result size S.
It pops two stack entries. The first must be an integral type value that is
treated as an address A. The second must be an integral type value that is
treated as an address space identifier AS for those architectures that
support multiple address spaces.
The operation is equivalent to performing ``DW_OP_swap;
DW_OP_LLVM_form_aspace_address; DW_OP_deref_size S``. The zero-extended
retrieved generic type value V is left on the stack.
9. ``DW_OP_xderef_type`` *Deprecated*
``DW_OP_xderef_type`` has two operands. The first is a 1-byte unsigned
integral constant S whose value is the same as the size of the base type
referenced by the second operand. The second operand is an unsigned LEB128
integer R that represents the offset of a debugging information entry E in
the current compilation unit, which must be a ``DW_TAG_base_type`` entry
that provides the type of the result value.
It pops two stack entries. The first must be an integral type value that is
treated as an address A. The second must be an integral type value that is
treated as an address space identifier AS for those architectures that
support multiple address spaces.
The operation is equivalent to performing ``DW_OP_swap;
DW_OP_LLVM_form_aspace_address; DW_OP_deref_type S R``. The retrieved result
type value V is left on the stack.
10. ``DW_OP_push_object_address``
``DW_OP_push_object_address`` pushes the location description L of the
object currently being evaluated as part of evaluation of a user presented
expression.
This object may correspond to an independent variable described by its own
debugging information entry or it may be a component of an array, structure,
or class whose address has been dynamically determined by an earlier step
during user expression evaluation.
*This operator provides explicit functionality (especially for arrays
involving descriptions) that is analogous to the implicit push of the base
address of a structure prior to evaluation of a
``DW_AT_data_member_location`` to access a data member of a structure.*
11. ``DW_OP_call2, DW_OP_call4, DW_OP_call_ref``
``DW_OP_call2``, ``DW_OP_call4``, and ``DW_OP_call_ref`` perform DWARF
procedure calls during evaluation of a DWARF expression or location
description.
``DW_OP_call2`` and ``DW_OP_call4``, have one operand that is a 2- or 4-byte
unsigned offset, respectively, of a debugging information entry D in the
current compilation unit.
``DW_OP_LLVM_call_ref`` has one operand that is a 4-byte unsigned value in
the 32-bit DWARF format, or an 8-byte unsigned value in the 64-bit DWARF
format, that is treated as an offset of a debugging information entry D in a
``.debug_info`` section, which may be contained in an executable or shared
object file other than that containing the operator. For references from one
executable or shared object file to another, the relocation must be
performed by the consumer.
*Operand interpretation of* ``DW_OP_call2``\ *,* ``DW_OP_call4``\ *, and*
``DW_OP_call_ref`` *is exactly like that for* ``DW_FORM_ref2``\ *,
``DW_FORM_ref4``\ *, and* ``DW_FORM_ref_addr``\ *, respectively.*
If D has a ``DW_AT_location`` attribute, then the DWARF expression E
corresponding to the current program location is selected.
.. note::
To allow ``DW_OP_call*`` to compute the location description for any
variable or formal parameter regardless of whether the producer has
optimized it to a constant, the following rule could be added:
.. note::
If D has a ``DW_AT_const_value`` attribute, then a DWARF expression E
consisting a ``DW_OP_implicit_value`` operation with the value of the
``DW_AT_const_value`` attribute is selected.
This would be consistent with ``DW_OP_implicit_pointer``.
Alternatively, could deprecate using ``DW_AT_const_value`` for
``DW_TAG_variable`` and ``DW_TAG_formal_parameter`` debugger information
entries that are constants and instead use ``DW_AT_location`` with an
implicit location description instead, then this rule would not be
required.
Otherwise, an empty expression E is selected.
If D is a ``DW_TAG_dwarf_procedure`` debugging information entry, then E is
evaluated using the same DWARF expression stack. Any existing stack entries
may be accessed and/or removed in the evaluation of E, and the evaluation of
E may add any new stack entries.
*Values on the stack at the time of the call may be used as parameters by
the called expression and values left on the stack by the called expression
may be used as return values by prior agreement between the calling and
called expressions.*
Otherwise, E is evaluated on a separate DWARF stack and the resulting
location description L is pushed on the ``DW_OP_call*`` operation's stack.
.. note:
In DWARF 5, if D does not have a ``DW_AT_location`` then ``DW_OP_call*``
is defined to have no effect. It is unclear that this is the right
definition as a producer should be able to rely on using ``DW_OP_call*``
to get a location description for any non-\ ``DW_TAG_dwarf_procedure``
debugging information entries, and should not be creating DWARF with
``DW_OP_call*`` to a ``DW_TAG_dwarf_procedure`` that does not have a
``DW_AT_location`` attribute.
12. ``DW_OP_LLVM_call_frame_entry_reg`` *New*
``DW_OP_LLVM_call_frame_entry_reg`` has a single unsigned LEB128 integer
operand that is treated as a target architecture register number R.
It pushes a location description L that holds the value of register R on
entry to the current subprogram as defined by the Call Frame Information
(see :ref:`amdgpu-call-frame-information`).
*If there is no Call Frame Information defined, then the default rules for
the target architecture are used. If the register rule is* undefined\ *,
then the undefined location description is pushed. If the register rule is*
same value\ *, then a register location description for R is pushed.*
Undefined Location Descriptions
###############################
The undefined location storage represents a piece or all of an object that is
present in the source but not in the object code (perhaps due to optimization).
Neither reading or writing to the undefined location storage is meaningful.
An undefined location description specifies the undefined location storage.
There is no concept of the size of the undefined location storage, nor of a bit
offset for an undefined location description. The ``DW_OP_LLVM_*offset``
operations leave an undefined location description unchanged. The
``DW_OP_*piece`` operations can explicitly or implicitly specify an undefined
location description, allowing any size and offset to be specified, and results
in a part with all undefined bits.
1. ``DW_OP_LLVM_undefined`` *New*
``DW_OP_LLVM_undefined`` pushes an undefined location description L.
Memory Location Descriptions
############################
There is a memory location storage that corresponds to each of the target
architecture linear memory address spaces. The size of each memory location
storage corresponds to the range of the addresses in the address space.
*It is target architecture defined how address space location storage maps to
target architecture physical memory. For example, they may be independent memory
or more than one location storage may alias the same physical memory possibly at
different offsets and with different interleaving. The mapping may also be
dictated by the source language address classes.*
A memory location description specifies a memory location storage. The bit
offset corresponds to an address in the address space scaled by 8 (the byte
size). Bits accessed using a memory location description, access the
corresponding target architecture memory starting at the bit offset.
``DW_ASPACE_none`` is defined as the target architecture default address space.
*The target architecture default address space for AMDGPU is the global address
space.*
If a stack entry is required to be a location description, but it is a value
with the generic type, then it is implicitly convert to a memory location
description that specifies memory in the target architecture default address
space with a bit offset equal to the value scaled by 8 (the byte size).
.. note::
If want to allow any integral type value to be implicitly converted to a
memory location description in the target architecture default address
space:
.. note::
If a stack entry is required to be a location description, but it is a
value with an integral type, then it is implicitly convert to a memory
location description. The stack entry value is zero extended to the size
of the generic type and the least significant generic type size bits are
treated as a twos-complement unsigned value to be used as an address. The
converted memory location description specifies memory location storage
corresponding to the target architecture default address space with a bit
offset equal to the address scaled by 8 (the byte size).
The implicit conversion could also be defined as target specific. For
example, gdb checks if the value is an integral type. If it is not it gives
an error. Otherwise, gdb zero-extends the value to 64 bits. If the gdb
target defines a hook function then it is called and it can modify the 64
bit value, possibly sign extending the original value. Finally, gdb treats
the 64 bit value as a memory location address.
If a stack entry is required to be a location description, but it is an implicit
pointer value IPV with the target architecture default address space, then it is
implicitly convert to the location description specified by IPV. See
:ref:`amdgpu-implicit-location-descriptions`.
If a stack entry is required to be a value with a generic type, but it is a
memory location description in the target architecture default address space
with a bit offset that is a multiple of 8, then it is implicitly converted to a
value with a generic type that is equal to the bit offset divided by 8 (the byte
size).
1. ``DW_OP_addr``
``DW_OP_addr`` has a single byte constant value operand, which has the size
of the generic type, treated as an address A.
It pushes a memory location description L on the stack that specifies the
memory location storage for the target architecture default address space
with a bit offset equal to A scaled by 8 (the byte size).
*If the DWARF is part of a code object, then A may need to be relocated. For
example, in the ELF code object format, A must be adjusted by the difference
between the ELF segment virtual address and the virtual address at which the
segment is loaded.*
2. ``DW_OP_addrx``
``DW_OP_addrx`` has a single unsigned LEB128 integer operand that is treated
as a zero-based index into the ``.debug_addr`` section relative to the value
of the ``DW_AT_addr_base`` attribute of the associated compilation unit. The
address value A in the ``.debug_addr`` section has the size of generic type.
It pushes a memory location description L on the stack that specifies the
memory location storage for the target architecture default address space
with a bit offset equal to A scaled by 8 (the byte size).
*If the DWARF is part of a code object, then A may need to be relocated. For
example, in the ELF code object format, A must be adjusted by the difference
between the ELF segment virtual address and the virtual address at which the
segment is loaded.*
3. ``DW_OP_LLVM_form_aspace_address`` *New*
``DW_OP_LLVM_form_aspace_address`` pops top two stack entries. The first
must be an integral type value that is treated as an address space
identifier AS for those architectures that support multiple address spaces.
The second must be an integral type value that is treated as an address A.
The address size S is defined as the address bit size of the target
architecture's address space that corresponds to AS.
A is adjusted by zero extending it to S bits and the least significant S
bits are treated as a twos-complement unsigned value.
``DW_OP_LLVM_form_aspace_address`` pushes a memory location description L
that specifies the memory location storage that corresponds to AS, with a
bit offset equal to the adjusted A scaled by 8 (the byte size).
If AS is not one of the values defined by the target architecture's
``DW_ASPACE_*`` values, then the DWARF expression is ill-formed.
See :ref:`amdgpu-implicit-location-descriptions` for special rules
concerning implicit pointer values produced by dereferencing implicit
location descriptions created by the ``DW_OP_implicit_pointer`` and
``DW_OP_LLVM_implicit_aspace_pointer`` operations.
The AMDGPU address spaces are defined in
:ref:`amdgpu-dwarf-address-space-mapping-table`.
4. ``DW_OP_form_tls_address``
``DW_OP_form_tls_address`` pops one stack entry that must be an integral
type value, and treats it as a thread-local storage address.
``DW_OP_form_tls_address`` pushes a memory location description L for the
target architecture default address space that corresponds to the
thread-local storage address.
The meaning of the thread-local storage address is defined by the run-time
environment. If the run-time environment supports multiple thread-local
storage blocks for a single thread, then the block corresponding to the
executable or shared library containing this DWARF expression is used.
*Some implementations of C, C++, Fortran, and other languages, support a
thread-local storage class. Variables with this storage class have distinct
values and addresses in distinct threads, much as automatic variables have
distinct values and addresses in each function invocation. Typically, there
is a single block of storage containing all thread-local variables declared
in the main executable, and a separate block for the variables declared in
each shared library. Each thread-local variable can then be accessed in its
block using an identifier. This identifier is typically an offset into the
block and pushed onto the DWARF stack by one of the* ``DW_OP_const<n><x>``
*operations prior to the* ``DW_OP_form_tls_address`` *operation. Computing
the address of the appropriate block can be complex (in some cases, the
compiler emits a function call to do it), and difficult to describe using
ordinary DWARF location descriptions. Instead of forcing complex
thread-local storage calculations into the DWARF expressions, the*
``DW_OP_form_tls_address`` *allows the consumer to perform the computation
based on the run-time environment.*
5. ``DW_OP_call_frame_cfa``
``DW_OP_call_frame_cfa`` pushes the memory location description L of the
Canonical Frame Address (CFA) of the current function, obtained from the
Call Frame Information (see :ref:`amdgpu-call-frame-information`).
*Although the value of* ``DW_AT_frame_base`` *can be computed using other
DWARF expression operators, in some cases this would require an extensive
location list because the values of the registers used in computing the CFA
change during a subroutine. If the Call Frame Information is present, then
it already encodes such changes, and it is space efficient to reference
that.*
6. ``DW_OP_fbreg``
``DW_OP_fbreg`` has a single signed LEB128 integer operand that is treated
as a byte displacement D.
The DWARF expression E corresponding to the current program location is
selected from the ``DW_AT_frame_base`` attribute of the current function and
evaluated. The resulting memory location description L's bit offset is
updated as if the ``DW_OP_LLVM_offset D`` operation were applied. The
updated L is pushed.
*This is typically a stack pointer register plus or minus some offset.*
7. ``DW_OP_breg0, DW_OP_breg1, ..., DW_OP_breg31``
The ``DW_OP_breg<n>`` operations encode the numbers of up to 32 registers,
numbered from 0 through 31, inclusive. The register number R corresponds to
the ``n`` in the operation name.
They have a single signed LEB128 integer operand that is treated as a byte
displacement D.
The address space identifier AS is defined as the one corresponding to the
target architecture's default address space.
The address size S is defined as the address bit size of the target
architecture's address space corresponding to AS.
The contents of the register specified by R is retrieved as a
twos-complement unsigned value and zero extended to S bits. D is added and
the least significant S bits are treated as a twos-complement unsigned value
to be used as an address A.
They push a memory location description L that specifies the memory location
storage that corresponds to AS, with a bit offset equal to A scaled by 8
(the byte size).
8. ``DW_OP_bregx``
``DW_OP_bregx`` has two operands. The first is an unsigned LEB128 integer
that is treated as a register number R. The second is a signed LEB128
integer that is treated as a byte displacement D.
The action is the same as for ``DW_OP_breg<n>`` except that R is used as the
register number and D is used as the byte displacement.
9. ``DW_OP_LLVM_aspace_bregx`` *New*
``DW_OP_LLVM_aspace_bregx`` has two operands. The first is an unsigned
LEB128 integer that is treated as a register number R. The second is a
signed LEB128 integer that is treated as a byte displacement D. It pops one
stack entry that is required to be an integral type value that is treated as
an address space identifier AS for those architectures that support multiple
address spaces.
The action is the same as for ``DW_OP_breg<n>`` except that R is used as the
register number, D is used as the byte displacement, and AS is used as the
address space identifier.
If AS is not one of the values defined by the target architecture's
``DW_ASPACE_*`` values, then the DWARF expression is ill-formed.
.. note::
Could also consider adding ``DW_OP_aspace_breg0, DW_OP_aspace_breg1, ...,
DW_OP_aspace_bref31`` which would save encoding size.
.. _amdgpu-register-location-descriptions:
Register Location Descriptions
##############################
There is a register location storage that corresponds to each of the target
architecture registers. The size of each register location storage corresponds
to the size of the corresponding target architecture register.
A register location description specifies a register location storage. The bit
offset corresponds to a bit position within the register. Bits accessed using a
register location description, access the corresponding target architecture
register starting at the bit offset.
1. ``DW_OP_reg0, DW_OP_reg1, ..., DW_OP_reg31``
``DW_OP_reg<n>`` operations encode the numbers of up to 32 registers,
numbered from 0 through 31, inclusive. The target architecture register
number R corresponds to the ``n`` in the operation name.
``DW_OP_reg<n>`` pushes a register location description L that specifies the
register location storage that corresponds to R, with a bit offset of 0.
2. ``DW_OP_regx``
``DW_OP_regx`` has a single unsigned LEB128 integer operand that is treated
as a target architecture register number R.
``DW_OP_regx`` pushes a register location description L that specifies the
register location storage that corresponds to R, with a bit offset of 0.
*These operations name a register location. To fetch the contents of a register,
it is necessary to use* ``DW_OP_regval_type``\ *, or one of the register based
addressing operations such as* ``DW_OP_bregx``\ *, or using* ``DW_OP_deref*``
*on a register location description.*
.. _amdgpu-implicit-location-descriptions:
Implicit Location Descriptions
##############################
Implicit location storage represents a piece or all of an object which has no
actual location in the program but whose contents are nonetheless known, either
as a constant or can be computed from other locations and values in the program.
An implicit location description specifies an implicit location storage. The bit
offset corresponds to a bit position within the implicit location storage. Bits
accessed using an implicit location description, access the corresponding
implicit storage value starting at the bit offset.
1. ``DW_OP_implicit_value``
``DW_OP_implicit_value`` has two operands. The first is an unsigned LEB128
integer treated as a byte size S. The second is a block of bytes with a
length equal to S treated as a literal value V.
An implicit location storage LS is created with the literal value V and a
size of S. An implicit location description L is pushed that specifies LS
with a bit offset of 0.
2. ``DW_OP_stack_value``
``DW_OP_stack_value`` pops one stack entry that must be a value treated as a
literal value V.
An implicit location storage LS is created with the literal value V and a
size equal to V's base type size. An implicit location description L is
pushed that specifies LS with a bit offset of 0.
The ``DW_OP_stack_value`` operation specifies that the object does not exist
in memory but its value is nonetheless known and is at the top of the DWARF
expression stack. In this form of location description, the DWARF expression
represents the actual value of the object, rather than its location.
See :ref:`amdgpu-implicit-location-descriptions` for special rules
concerning implicit pointer values produced by dereferencing implicit
location descriptions created by the ``DW_OP_implicit_pointer`` and
``DW_OP_LLVM_implicit_aspace_pointer`` operations.
.. note::
Since location descriptions are allowed on the stack, the
``DW_OP_stack_value`` operation no longer terminates the DWARF expression.
3. ``DW_OP_implicit_pointer``
*An optimizing compiler may eliminate a pointer, while still retaining the
value that the pointer addressed.* ``DW_OP_implicit_pointer`` *allows a
producer to describe this value.*
``DW_OP_implicit_pointer`` specifies that the object is a pointer to the
target architecture default address space that cannot be represented as a
real pointer, even though the value it would point to can be described. In
this form of location description, the DWARF expression refers to a
debugging information entry that represents the actual location description
of the object to which the pointer would point. Thus, a consumer of the
debug information would be able to access the the dereferenced pointer, even
when it cannot access of the pointer itself.
``DW_OP_implicit_pointer`` has two operands. The first is a 4-byte unsigned
value in the 32-bit DWARF format, or an 8-byte unsigned value in the 64-bit
DWARF format, that is treated as a debugging information entry reference R.
The second is a signed LEB128 integer that is treated as a byte
displacement D.
R is used as the offset of a debugging information entry E in a
``.debug_info`` section, which may be contained in an executable or shared
object file other than that containing the operator. For references from one
executable or shared object file to another, the relocation must be
performed by the consumer.
*The first operand interpretation is exactly like that for*
``DW_FORM_ref_addr``\ *.*
The address space identifier AS is defined as the one corresponding to the
target architecture's default address space.
The address size S is defined as the address bit size of the target
architecture's address space corresponding to AS.
An implicit location storage LS is created that has the bit size of S. An
implicit location description L is pushed that specifies LS and has a bit
offset of 0.
If a ``DW_OP_deref*`` operation pops a location description L' and retrieves
S' bits where some retrieved bits come from LS such that either:
1. L' is an implicit location description that specifies LS with bit offset
0, and S' equals S.
2. L' is a complete composite location description that specifies a
canonical form composite location storage LS'. The bits retrieved all
come from a single part P' of LS'. P' has a bit size of S and has
an implicit location description PL'. PL' specifies LS with a bit offset
of 0.
Then the value V pushed by the ``DW_OP_deref*`` operation is an implicit
pointer value IPV with an address space of AS, a debugging information entry
of E, and a base type of T. If AS is the target architecture default address
space, then T is the generic type. Otherwise, T is an architecture specific
integral type with a bit size equal to S.
Otherwise, if a ``DW_OP_deref*`` operation is applied to a location
description such that some retrieved bits come from LS, then the DWARF
expression is ill-formed.
If IPV is either implicitly converted to a location description (only done
if AS is the target architecture default address space) or used by
``DW_OP_LLVM_form_aspace_address`` (only done if the address space specified
is AS), then the resulting location description is:
* If E has a ``DW_AT_location`` attribute, the DWARF expression
corresponding to the current program location is selected and evaluated
from the ``DW_AT_location`` attribute. The expression result is the
resulting location description RL.
* If E has a ``DW_AT_const_value`` attribute, then an implicit location
storage RLS is created from the ``DW_AT_const_value`` attribute's value,
with a size matching the size of the ``DW_AT_const_value`` attribute's
value. The resulting implicit location description RL specifies RLS with a
bit offset of 0.
.. note::
If deprecate using ``DW_AT_const_value`` for variables and formal
parameters and instead use ``DW_AT_location`` with an implicit location
description instead, then this rule would not be required.
* Otherwise the DWARF expression is ill-formed.
The bit offset of RL is updated as if the ``DW_OP_LLVM_offset D`` operation
were applied.
If a ``DW_OP_stack_value`` operation pops a value that is the same as IPV,
then it pushes a location description that is the same as L.
The DWARF expression is ill-formed if it accesses LS or IPV in any other
manner.
*The restrictions on how an implicit pointer location description created by
``DW_OP_implicit_pointer`` and ``DW_OP_LLVM_aspace_implicit_pointer``, or an
implicit pointer value created by ``DW_OP_deref*``, can be used are to
simplify the DWARF consumer.*
4. ``DW_OP_LLVM_aspace_implicit_pointer`` *New*
``DW_OP_LLVM_aspace_implicit_pointer`` has two operands that are the same as
for ``DW_OP_implicit_pointer``.
It pops one stack entry that must be an integral type value that is treated
as an address space identifier AS for those architectures that support
multiple address spaces.
The implicit location description L that is pushed is the same as for
``DW_OP_implicit_pointer`` except that the address space identifier used is
AS.
If AS is not one of the values defined by the target architecture's
``DW_ASPACE_*`` values, then the DWARF expression is ill-formed.
*The debugging information entry referenced by a* ``DW_OP_implicit_pointer`` or
``DW_OP_LLVM_aspace_implicit_pointer`` *operation is typically a*
``DW_TAG_variable`` *or* ``DW_TAG_formal_parameter`` *entry whose*
``DW_AT_location`` *attribute gives a second DWARF expression or a location list
that describes the value of the object, but the referenced entry may be any
entry that contains a* ``DW_AT_location`` *or* ``DW_AT_const_value`` *attribute
(for example,* ``DW_TAG_dwarf_procedure``\ *). By using the second DWARF
expression, a consumer can reconstruct the value of the object when asked to
dereference the pointer described by the original DWARF expression containing
the* ``DW_OP_implicit_pointer`` or ``DW_OP_LLVM_aspace_implicit_pointer``
*operation.*
Composite Location Descriptions
###############################
A composite location storage represents an object or value which may be
contained in part of another location storage, or contained in parts of more
than one location storage.
Each part has a part location description L and a part bit size S. The bits of
the part comprise S contiguous bits from the location storage specified by L,
starting at the bit offset specified by L. All the bits must be within the size
of the location storage specified by L or the DWARF expression is ill-formed.
A composite location storage can have zero or more parts. The parts are
contiguous such that the zero-based location storage bit index will range over
each part with no gaps between them. Therefore, the size of a composite location
storage is the size of its parts. The DWARF expression is ill-formed if the size
of the contiguous location storage is larger than the size of the memory
location storage corresponding to the target architecture's largest address
space.
The canonical form of a composite location storage is computed by applying the
following steps to a composite location storage:
1. If any part P has a composite location description L, it is replaced by a
copy of the parts of the composite location storage specified by L that are
selected by the bit size of P starting at the bit offset of L. The location
description of the first copied part has its bit offset updated as
necessary, and the last copied part has its bit size updated as necessary,
to reflect the bits selected by P. This rule is applied repeatedly until no
part has a composite location description.
2. If the size on any part is zero, it is removed.
3. If any adjacent parts P\ :sup:`1` to P\ :sup:`n` have location descriptions
that specify the same location storage LS such that the bits selected form a
contiguous portion of LS, then they are replaced by a single new part P'. P'
has a location description L that specifies LS with the same bit offset as
P\ :sup:`1`\ 's location description, and a bit size equal to the sum of the
bit sizes of P\ :sup:`1` to P\ :sup:`n` inclusive.
A composite location description specifies the canonical form of a composite
location storage and a bit offset.
There are operations that push a composite location description that specifies a
composite location storage that is created by the operation.
There are other operations that allow a composite location storage and a
composite location description that specifies it to be created incrementally.
Each part is described by a separate operation. There may be one or more
operations to create the final composite location storage and associated
description. A series of such operations describes the parts of the composite
location storage that are in the order that the associated part operations are
executed.
To support incremental creation, a composite location description can be in an
incomplete state. When an incremental operation operates on an incomplete
composite location description, it adds a new part, otherwise it creates a new
composite location description. The ``DW_OP_LLVM_piece_end`` operation
explicitly makes an incomplete composite location description complete.
If the top stack entry is an incomplete composite location description after the
execution of a DWARF expression has completed, it is converted to a complete
composite location description.
If a stack entry is required to be a location description, but it is an
incomplete composite location description, then the DWARF expression is
ill-formed.
*Note that a DWARF expression may arbitrarily compose composite location
descriptions from any other location description, including other composite
location descriptions.*
*The incremental composite location description operations are defined to be
compatible with the definitions in DWARF 5 and earlier.*
1. ``DW_OP_piece``
``DW_OP_piece`` has a single unsigned LEB128 integer that is treated as a
byte size S.
The action is based on the context:
* If the stack is empty, then an incomplete composite location description
L is pushed that specifies a new composite location storage LS and has a
bit offset of 0. LS has a single part P that specifies the undefined
location description, and has a bit size of S scaled by 8 (the byte size).
* If the top stack entry is an incomplete composite location description L,
then the composite location storage LS that it specifies is updated to
append a part that specifies an undefined location description, and has a
bit size S scaled by 8 (the byte size).
* If the top stack entry is a location description or can be converted to
one, then it is popped and treated as a part location description PL.
Then:
* If the stack is empty or the top stack entry is not an incomplete
composite location description, then an incomplete composite location
description L is pushed that specifies a new composite location storage
LS. LS has a single part that specifies PL, and has a bit size of S
scaled by 8 (the byte size).
* Otherwise, the composite location storage LS specified by the top stack
incomplete composite location description L is updated to append a part
that specifies PL, and has a bit size S scaled by 8 (the byte size).
* Otherwise, the DWARF expression is ill-formed
If LS is not in canonical form it is updated to be in canonical form.
*Many compilers store a single variable in sets of registers, or store a
variable partially in memory and partially in registers.* ``DW_OP_piece``
*provides a way of describing how large a part of a variable a particular
DWARF location description refers to.*
*If a computed byte displacement is required, the* ``DW_OP_LLVM_offset``
*can be used to update the part location description.*
2. ``DW_OP_bit_piece``
``DW_OP_bit_piece`` has two operands. The first is an unsigned LEB128
integer that is treated as the part bit size S. The second is an unsigned
LEB128 integer that is treated as a bit displacement D.
The action is the same as for ``DW_OP_piece`` except that any part created
has the bit size S, and the location description of any created part has its
bit offset updated as if the ``DW_OP_LLVM_bit_offset D`` operation were
applied.
*If a computed bit displacement is required, the* ``DW_OP_LLVM_bit_offset``
*can be used to update the part location description.*
.. note::
The bit offset operand is not needed as ``DW_OP_LLVM_bit_offset`` can be
used on the part's location description.
3. ``DW_OP_LLVM_piece_end`` *New*
If the top stack entry is an incomplete composite location description L,
then it is updated to be a complete composite location description with the
same parts. Otherwise, the DWARF expression is ill-formed.
4. ``DW_OP_LLVM_extend`` *New*
``DW_OP_LLVM_extend`` has two operands. The first is an unsigned LEB128
integer that is treated as the element bit size S. The second is an unsigned
LEB128 integer that is treated as a count C.
It pops one stack entry that must be a location description and is treated
as the part location description PL.
A complete composite location description L is pushed that comprises C parts
that each specify PL and have a bit size of S.
The DWARF expression is ill-formed if the element bit size or count are 0.
5. ``DW_OP_LLVM_select_bit_piece`` *New*
``DW_OP_LLVM_select_bit_piece`` has two operands. The first is an unsigned
LEB128 integer that is treated as the element bit size S. The second is an
unsigned LEB128 integer that is treated as a count C.
It pops three stack entries. The first must be an integral type value that
is treated as a bit mask value M. The second must be a location description
that is treated as the one-location description L1. The third must be a
location description that is treated as the zero-location description L0.
A complete composite location description L is pushed that specifies a new
composite location storage LS. LS comprises C parts that each specify a part
location description PL and have a bit size of S. The PL for part N is
defined as:
1. If the Nth least significant bit of M is a zero then the PL for part N
is the same as L0, otherwise it is the same as L1.
2. The PL for part N is updated as if the ``DW_OP_LLVM_bit_offset N*S``
operation was applied.
If LS is not in canonical form it is updated to be in canonical form.
The DWARF expression is ill-formed if S or C are 0, or if the bit size of M
is less than C.
``DW_OP_bit_piece`` *is used instead of* ``DW_OP_piece`` *when the piece to be
assembled into a value or assigned to is not byte-sized or is not at the start
of the part location description.*
.. note::
For AMDGPU:
* In CFI expressions ``DW_OP_LLVM_select_bit_piece`` is used to describe
unwinding vector registers that are spilled under the execution mask to
memory: the zero location description is the vector register, and the one
location description is the spilled memory location. The
``DW_OP_LLVM_form_aspace_address`` is used to specify the address space of
the memory location description.
* ``DW_OP_LLVM_select_bit_piece`` is used by the ``lane_pc`` attribute
expression where divergent control flow is controlled by the execution mask.
An undefined location description together with ``DW_OP_LLVM_extend`` is
used to indicate the lane was not active on entry to the subprogram.
Expression Operation Encodings
++++++++++++++++++++++++++++++
The following table gives the encoding of the DWARF expression operations added
for AMDGPU.
.. table:: AMDGPU DWARF Expression Operation Encodings
:name: amdgpu-dwarf-expression-operation-encodings-table
================================== ===== ======== ===============================
Operation Code Number Notes
of
Operands
================================== ===== ======== ===============================
DW_OP_LLVM_form_aspace_address 0xe7 0
DW_OP_LLVM_push_lane 0xea 0
DW_OP_LLVM_offset 0xe9 0
DW_OP_LLVM_offset_uconst *TBD* 1 ULEB128 byte displacement
DW_OP_LLVM_bit_offset *TBD* 0
DW_OP_LLVM_call_frame_entry_reg *TBD* 1 ULEB128 register number
DW_OP_LLVM_undefined *TBD* 0
DW_OP_LLVM_aspace_bregx *TBD* 2 ULEB128 register number,
ULEB128 byte displacement
DW_OP_LLVM_aspace_implicit_pointer *TBD* 2 4- or 8-byte offset of DIE,
SLEB128 byte displacement
DW_OP_LLVM_piece_end *TBD* 0
DW_OP_LLVM_extend *TBD* 2 ULEB128 bit size,
ULEB128 count
DW_OP_LLVM_select_bit_piece *TBD* 2 ULEB128 bit size,
ULEB128 count
================================== ===== ======== ===============================
.. _amdgpu-dwarf-debugging-information-entry-attributes:
Debugging Information Entry Attributes
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This section provides changes to existing debugger information attributes and
defines attributes added by the AMDGPU target.
1. ``DW_AT_location``
If the result of the ``DW_AT_location`` DWARF expression is required to be a
location description, then it may have any kind of location description (see
:ref:`amdgpu-location-description-operations`).
2. ``DW_AT_const_value``
.. note::
Could deprecate using the ``DW_AT_const_value`` attribute for
``DW_TAG_variable`` or ``DW_TAG_formal_parameter`` debugger information
entries that are constants. Instead, ``DW_AT_location`` could be used with
a DWARF expression that produces an implicit location description now that
any location description can be used within a DWARF expression. This
allows the ``DW_OP_call*`` operations to be used to push the location
description of any variable regardless of how it is optimized.
3. ``DW_AT_frame_base``
A ``DW_TAG_subprogram`` or ``DW_TAG_entry_point`` debugger information entry
may have a ``DW_AT_frame_base`` attribute, whose value is a DWARF expression
or location list that describes the *frame base* for the subroutine or entry
point.
If the result of the DWARF expression is a register location description,
then the ``DW_OP_deref`` operation is applied to compute the frame base
memory location description in the target architecture default address
space.
.. note::
This rule could be removed and require the producer to create the
required location descriptor directly using ``DW_OP_call_frame_cfa``,
``DW_OP_fbreg``, ``DW_OP_breg*``, or ``DW_OP_LLVM-aspace_bregx``. This
would also then allow a target to implement the call frames withing a
large register.
Otherwise, the result of the DWARF expression is required to be a memory
location description in any of the target architecture address spaces which
is the frame base.
4. ``DW_AT_data_member_location``
For a ``DW_AT_data_member_location`` attribute there are two cases:
1. If the value is an integer constant, it is the offset in bytes from the
beginning of the containing entity. If the beginning of the containing
entity has a non-zero bit offset then the beginning of the member entry
has that same bit offset as well.
2. Otherwise, the value must be a DWARF expression or location list. The
DWARF expression E corresponding to the current program location is
selected. The location description of the beginning of the containing
entity is pushed on the DWARF stack before E is evaluated. The result of
the evaluation is the location description of the base of the member
entry.
.. note::
The beginning of the containing entity can now be any location
description and can be bit aligned.
5. ``DW_AT_use_location``
The ``DW_TAG_ptr_to_member_type`` debugging information entry has a
``DW_AT_use_location`` attribute whose value is a DWARF expression or
location list. The DWARF expression E corresponding to the current program
location is selected. It is used to computes the location description of the
member of the class to which the pointer to member entry points
*The method used to find the location description of a given member of a
class or structure is common to any instance of that class or structure and
to any instance of the pointer or member type. The method is thus associated
with the type entry, rather than with each instance of the type.*
The ``DW_AT_use_location`` description is used in conjunction with the
location descriptions for a particular object of the given pointer to member
type and for a particular structure or class instance.
Two values are pushed onto the DWARF expression stack before E is evaluated.
The first value pushed is the value of the pointer to member object itself.
The second value pushed is the location description of the base of the
entire structure or union instance containing the member whose address is
being calculated.
6. ``DW_AT_data_location``
The ``DW_AT_data_location`` attribute may be used with any type that
provides one or more levels of hidden indirection and/or run-time parameters
in its representation. Its value is a DWARF expression E which computes the
location description of the data for an object. When this attribute is
omitted, the location description of the data is the same as the location
description of the object.
*E will typically begin with ``DW_OP_push_object_address`` which loads the
location description of the object which can then serve as a descriptor in
subsequent calculation.*
7. ``DW_AT_vtable_elem_location``
An entry for a virtual function also has a ``DW_AT_vtable_elem_location``
attribute whose value is a DWARF expression or location list. The DWARF
expression E corresponding to the current program location is selected. The
location description of the object of the enclosing type is pushed onto the
expression stack before E is evaluated. The resulting location description
is the slot for the function within the virtual function table for the
enclosing class.
8. ``DW_AT_static_link``
If a ``DW_TAG_subprogram`` or ``DW_TAG_entry_point`` debugger information
entry is nested, it may have a ``DW_AT_static_link`` attribute, whose value
is a DWARF expression or location list. The DWARF expression E corresponding
to the current program location is selected. The result of evaluating E is
the frame base memory location description of the relevant instance of the
subroutine that immediately encloses the subroutine or entry point.
9. ``DW_AT_return_addr``
A ``DW_TAG_subprogram``, ``DW_TAG_inlined_subroutine``, or
``DW_TAG_entry_point`` debugger information entry may have a
``DW_AT_return_addr`` attribute, whose value is a DWARF expression or
location list. The DWARF expression E corresponding to the current program
location is selected. The result of evaluating E is the location description
for the place where the return address for the subroutine or entry point is
stored.
.. note::
It is unclear why ``DW_TAG_inlined_subroutine`` has a
``DW_AT_return_addr`` attribute but not a ``DW_AT_frame_base`` or
``DW_AT_static_link`` attribute. Seems it would either have all of them or
none. Since inlined subprograms do not have a frame it seems they would
have none of these attributes.
10. ``DW_AT_LLVM_lanes`` *New*
For languages that are implemented using a SIMD or SIMT execution model, a
``DW_TAG_subprogram``, ``DW_TAG_inlined_subroutine``, or
``DW_TAG_entry_point`` debugger information entry may have a
``DW_AT_LLVM_lanes`` attribute whose value is an integer constant that is
the number of lanes per thread.
If not present, the default value of 1 is used.
The DWARF is ill-formed if the value is 0.
11. ``DW_AT_LLVM_lane_pc`` *New*
For languages that are implemented using a SIMD or SIMT execution model, a
``DW_TAG_subprogram``, ``DW_TAG_inlined_subroutine``, or
``DW_TAG_entry_point`` debugging information entry may have a
``DW_AT_LLVM_lane_pc`` attribute whose value is a DWARF expression or
location list. The DWARF expression E corresponding to the current program
location is selected. The result of evaluating E is a location description
that references a wave size vector of generic type elements. Each element
holds the conceptual program location of the corresponding lane, where the
least significant element corresponds to the first target architecture lane
identifier and so forth. If the lane was not active when the subprogram was
called, its element is an undefined location description.
*``DW_AT_LLVM_lane_pc`` allows the compiler to indicate conceptually where
each lane of a SIMT thread is positioned even when it is in divergent
control flow that is not active.*
If not present, the thread is not being used in a SIMT manner, and the
thread's program location is used.
*See* :ref:`amdgpu-dwarf-amdgpu-dw-at-llvm-lane-pc` *for AMDGPU
information.*
12. ``DW_AT_LLVM_active_lane`` *New*
For languages that are implemented using a SIMD or SIMT execution model, a
``DW_TAG_subprogram``, ``DW_TAG_inlined_subroutine``, or
``DW_TAG_entry_point`` debugger information entry may have a
``DW_AT_LLVM_active_lane`` attribute whose value is a DWARF expression or
location list. The DWARF expression E corresponding to the current program
location is selected. The result of evaluating E is a integral value that is
the mask of active lanes for the current program location. The Nth least
significant bit of the mask corresponds to the Nth lane. If the bit is 1 the
lane is active, otherwise it is inactive.
*Some targets may update the target architecture execution mask for regions
of code that must execute with different sets of lanes than the current
active lanes. For example, some code must execute in whole wave mode.
``DW_AT_LLVM_active_lane` allows the compiler can provide the means to
determine the actual active lanes.*
If not present and ``DW_AT_LLVM_lanes`` is greater than 1, then the target
architecture execution mask is used.
*See* :ref:`amdgpu-dwarf-amdgpu-dw-at-llvm-active-lane` *for AMDGPU
information.*
13. ``DW_AT_LLVM_vector_size`` *New*
A base type V may have the ``DW_AT_LLVM_vector_size`` attribute whose value
is an integer constant that is the vector size S.
The representation of a vector base type is as S contiguous elements, each
one having the representation of a base type E that is the same as V without
the ``DW_AT_LLVM_vector_size`` attribute.
If not present, the base type is not a vector.
The DWARF is ill-formed if S not greater than 0.
.. note::
LLVM has mention of non-upstreamed debugger information entry that is
intended to support vector types. However, that was not for a base type
so would not be suitable as the type of a stack value entry. But perhaps
that could be replaced by using this attribute.
14. ``DW_AT_LLVM_augmentation`` *New*
A compilation unit may have a ``DW_AT_LLVM_augmentation`` attribute, whose
value is an augmentation string.
*The augmentation string allows users to indicate that there is additional
target-specific information in the debugging information entries. For
example, this might be information about the version of target-specific
extensions that are being used.*
If not present, or if the string is empty, then the compilation unit has no
augmentation string.
.. note::
For AMDGPU, the augmentation string contains:
::
[amd:v0.0]
The "vX.Y" specifies the major X and minor Y version number of the AMDGPU
extensions used in the DWARF of the compilation unit. The version number
conforms to [SEMVER]_.
Attribute Encodings
+++++++++++++++++++
The following table gives the encoding of the debugging information entry
attributes added for AMDGPU.
.. table:: AMDGPU DWARF Attribute Encodings
:name: amdgpu-dwarf-attribute-encodings-table
================================== ===== ====================================
Attribute Name Value Classes
================================== ===== ====================================
DW_AT_LLVM_lanes constant
DW_AT_LLVM_lane_pc exprloc, loclist
DW_AT_LLVM_active_lane exprloc, loclist
DW_AT_LLVM_vector_size constant
DW_AT_LLVM_augmentation string
================================== ===== ====================================
.. _amdgpu-call-frame-information:
Call Frame Information
~~~~~~~~~~~~~~~~~~~~~~
DWARF Call Frame Information describes how an agent can virtually *unwind*
call frames in a running process or core dump.
.. note::
AMDGPU conforms to the DWARF standard with additional support added for
address spaces. Register unwind DWARF expressions are generalized to allow any
location description, including composite and implicit location descriptions.
Structure of Call Frame Information
+++++++++++++++++++++++++++++++++++
The register rules are:
*undefined*
A register that has this rule has no recoverable value in the previous frame.
(By convention, it is not preserved by a callee.)
*same value*
This register has not been modified from the previous frame. (By convention,
it is preserved by the callee, but the callee has not modified it.)
*offset(N)*
The previous value of this register is saved at the location description
computed as if the ``DW_OP_LLVM_offset N`` operation is applied to the current
CFA memory location description where N is a signed byte offset.
*val_offset(N)*
The previous value of this register is the address in the address space of the
memory location description computed as if the ``DW_OP_LLVM_offset N``
operation is applied to the current CFA memory location description where N is
a signed byte displacement.
If the register size does not match the size of an address in the address
space of the current CFA memory location description, then the DWARF is
ill-formed .
*register(R)*
The previous value of this register is stored in another register numbered R.
If the register sizes do not match, then the DWARF is ill-formed.
*expression(E)*
The previous value of this register is located at the location description
produced by executing the DWARF expression E (see
:ref:`amdgpu-dwarf-expressions`).
*val_expression(E)*
The previous value of this register is the value produced by executing the
DWARF expression E (see :ref:`amdgpu-dwarf-expressions`).
If value type size does not match the register size, then the DWARF is
ill-formed.
*architectural*
The rule is defined externally to this specification by the augmenter.
A Common Information Entry holds information that is shared among many Frame
Description Entries. There is at least one CIE in every non-empty
``.debug_frame`` section. A CIE contains the following fields, in order:
1. ``length`` (initial length)
A constant that gives the number of bytes of the CIE structure, not
including the length field itself. The size of the length field plus the
value of length must be an integral multiple of the address size specified
in the ``address_size`` field.
2. ``CIE_id`` (4 or 8 bytes, see
:ref:`amdgpu-dwarf-32-bit-and-64-bit-dwarf-formats`)
A constant that is used to distinguish CIEs from FDEs.
In the 32-bit DWARF format, the value of the CIE id in the CIE header is
0xffffffff; in the 64-bit DWARF format, the value is 0xffffffffffffffff.
3. ``version`` (ubyte)
A version number. This number is specific to the call frame information and
is independent of the DWARF version number.
The value of the CIE version number is 4.
4. ``augmentation`` (sequence of UTF-8 characters)
A null-terminated UTF-8 string that identifies the augmentation to this CIE
or to the FDEs that use it. If a reader encounters an augmentation string
that is unexpected, then only the following fields can be read:
* CIE: length, CIE_id, version, augmentation
* FDE: length, CIE_pointer, initial_location, address_range
If there is no augmentation, this value is a zero byte.
*The augmentation string allows users to indicate that there is additional
target-specific information in the CIE or FDE which is needed to virtually
unwind a stack frame. For example, this might be information about
dynamically allocated data which needs to be freed on exit from the
routine.*
*Because the .debug_frame section is useful independently of any
``.debug_info`` section, the augmentation string always uses UTF-8
encoding.*
.. note::
For AMDGPU, the augmentation string contains:
::
[amd:v0.0]
The "vX.Y" specifies the major X and minor Y version number of the AMDGPU
extensions used in the DWARF of the compilation unit. The version number
conforms to [SEMVER]_.
5. ``address_size`` (ubyte)
The size of a target address in this CIE and any FDEs that use it, in bytes.
If a compilation unit exists for this frame, its address size must match the
address size here.
.. note::
For AMDGPU:
* The address size for the ``Global`` address space defined in
:ref:`amdgpu-dwarf-address-space-mapping-table`.
6. ``segment_selector_size`` (ubyte)
The size of a segment selector in this CIE and any FDEs that use it, in
bytes.
.. note::
For AMDGPU:
* Does not use a segment selector so this is 0.
7. ``code_alignment_factor`` (unsigned LEB128)
A constant that is factored out of all advance location instructions (see
:ref:`amdgpu-dwarf-row-creation-instructions`). The resulting value is
``(operand * code_alignment_factor)``.
.. note::
For AMDGPU:
* 4 bytes.
.. TODO::
Add to :ref:`amdgpu-processor-table` table.
8. ``data_alignment_factor`` (signed LEB128)
A constant that is factored out of certain offset instructions (see
:ref:`amdgpu-dwarf-cfa-definition-instructions` and
:ref:`amdgpu-dwarf-register-rule-instructions`). The resulting value is
``(operand * data_alignment_factor)``.
.. note::
For AMDGPU:
* 4 bytes.
.. TODO::
Add to :ref:`amdgpu-processor-table` table.
9. ``return_address_register`` (unsigned LEB128)
An unsigned LEB128 constant that indicates which column in the rule table
represents the return address of the function. Note that this column might
not correspond to an actual machine register.
.. note::
For AMDGPU:
* ``PC_32`` for 32-bit processes and ``PC_64`` for
64-bit processes defined in :ref:`amdgpu-dwarf-register-mapping`.
10. ``initial_instructions`` (array of ubyte)
A sequence of rules that are interpreted to create the initial setting of
each column in the table.
The default rule for all columns before interpretation of the initial
instructions is the undefined rule. However, an ABI authoring body or a
compilation system authoring body may specify an alternate default value for
any or all columns.
.. note::
For AMDGPU:
* Since a subprogram A with fewer registers can be called from subprogram
B that has more allocated, A will not change any of the extra registers
as it cannot access them. Therefore, The default rule for all columns is
``same value``.
11. ``padding`` (array of ubyte)
Enough ``DW_CFA_nop`` instructions to make the size of this entry match the
length value above.
An FDE contains the following fields, in order:
1. ``length`` (initial length)
A constant that gives the number of bytes of the header and instruction
stream for this function, not including the length field itself. The size of
the length field plus the value of length must be an integral multiple of
the address size.
2. ``CIE_pointer`` (4 or 8 bytes, see
:ref:`amdgpu-dwarf-32-bit-and-64-bit-dwarf-formats`)
A constant offset into the ``.debug_frame`` section that denotes the CIE
that is associated with this FDE.
3. ``initial_location`` (segment selector and target address)
The address of the first location associated with this table entry. If the
segment_selector_size field of this FDE’s CIE is non-zero, the initial
location is preceded by a segment selector of the given length.
4. ``address_range`` (target address)
The number of bytes of program instructions described by this entry.
5. ``instructions`` (array of ubyte)
A sequence of table defining instructions that are described in
:ref:`amdgpu-dwarf-call-frame-instructions`.
6. ``padding`` (array of ubyte)
Enough ``DW_CFA_nop`` instructions to make the size of this entry match the
length value above.
.. _amdgpu-dwarf-call-frame-instructions:
Call Frame Instructions
+++++++++++++++++++++++
Some call frame instructions have operands that are encoded as DWARF expressions
E (see :ref:`amdgpu-dwarf-expressions`). The DWARF operators that can be used in
E have the following restrictions:
* ``DW_OP_addrx``, ``DW_OP_call2``, ``DW_OP_call4``, ``DW_OP_call_ref``,
``DW_OP_const_type``, ``DW_OP_constx``, ``DW_OP_convert``,
``DW_OP_deref_type``, ``DW_OP_regval_type``, and ``DW_OP_reinterpret``
operators are not allowed because the call frame information must not depend
on other debug sections.
* ``DW_OP_push_object_address`` is not allowed because there is no object
context to provide a value to push.
* ``DW_OP_call_frame_cfa`` and ``DW_OP_entry_value`` are not allowed because
their use would be circular.
* ``DW_OP_LLVM_call_frame_entry_reg`` is not allowed if evaluating E causes a
circular dependency between ``DW_OP_LLVM_call_frame_entry_reg`` operators.
*For example, if a register R1 has a* ``DW_CFA_def_cfa_expression``
*instruction that evaluates a* ``DW_OP_LLVM_call_frame_entry_reg`` *operator
that specifies register R2, and register R2 has a*
``DW_CFA_def_cfa_expression`` *instruction that that evaluates a*
``DW_OP_LLVM_call_frame_entry_reg`` *operator that specifies register R1.*
*Call frame instructions to which these restrictions apply include*
``DW_CFA_def_cfa_expression``\ *,* ``DW_CFA_expression``\ *, and*
``DW_CFA_val_expression``\ *.*
.. _amdgpu-dwarf-row-creation-instructions:
Row Creation Instructions
#########################
These instructions are the same as in DWARF 5.
.. _amdgpu-dwarf-cfa-definition-instructions:
CFA Definition Instructions
###########################
1. ``DW_CFA_def_cfa``
The ``DW_CFA_def_cfa`` instruction takes two unsigned LEB128 operands
representing a register number R and a (non-factored) byte displacement D.
The required action is to define the current CFA rule to be the memory
location description that is the result of evaluating the DWARF expression
``DW_OP_bregx R, D``.
.. note::
Could also consider adding ``DW_CFA_def_aspace_cfa`` and
``DW_CFA_def_aspace_cfa_sf`` which allow a register R, offset D, and
address space AS to be specified. For example, that would save a byte of
encoding over using ``DW_CFA_def_cfa R, D; DW_CFA_LLVM_def_cfa_aspace
AS;``.
2. ``DW_CFA_def_cfa_sf``
The ``DW_CFA_def_cfa_sf`` instruction takes two operands: an unsigned LEB128
value representing a register number R and a signed LEB128 factored byte
displacement D. The required action is to define the current CFA rule to be
the memory location description that is the result of evaluating the DWARF
expression ``DW_OP_bregx R, D*data_alignment_factor``.
*The action is the same as ``DW_CFA_def_cfa`` except that the second operand
is signed and factored.*
3. ``DW_CFA_def_cfa_register``
The ``DW_CFA_def_cfa_register`` instruction takes a single unsigned LEB128
operand representing a register number R. The required action is to define
the current CFA rule to be the memory location description that is the
result of evaluating the DWARF expression ``DW_OP_constu AS;
DW_OP_aspace_bregx R, D`` where D and AS are the old CFA byte displacement
and address space respectively.
If the subprogram has no current CFA rule, or the rule was defined by a
``DW_CFA_def_cfa_expression`` instruction, then the DWARF is ill-formed.
4. ``DW_CFA_def_cfa_offset``
The ``DW_CFA_def_cfa_offset`` instruction takes a single unsigned LEB128
operand representing a (non-factored) byte displacement D. The required
action is to define the current CFA rule to be the memory location
description that is the result of evaluating the DWARF expression
``DW_OP_constu AS; DW_OP_aspace_bregx R, D`` where R and AS are the old CFA
register number and address space respectively.
If the subprogram has no current CFA rule, or the rule was defined by a
``DW_CFA_def_cfa_expression`` instruction, then the DWARF is ill-formed.
5. ``DW_CFA_def_cfa_offset_sf``
The ``DW_CFA_def_cfa_offset_sf`` instruction takes a signed LEB128 operand
representing a factored byte displacement D. The required action is to
define the current CFA rule to be the memory location description that is
the result of evaluating the DWARF expression ``DW_OP_constu AS;
DW_OP_aspace_bregx R, D*data_alignment_factor`` where R and AS are the old
CFA register number and address space respectively.
If the subprogram has no current CFA rule, or the rule was defined by a
``DW_CFA_def_cfa_expression`` instruction, then the DWARF is ill-formed.
*The action is the same as ``DW_CFA_def_cfa_offset`` except that the operand
is signed and factored.*
6. ``DW_CFA_LLVM_def_cfa_aspace`` *New*
The ``DW_CFA_LLVM_def_cfa_aspace`` instruction takes a single unsigned
LEB128 operand representing an address space identifier AS for those
architectures that support multiple address spaces. The required action is
to define the current CFA rule to be the memory location description L that
is the result of evaluating the DWARF expression ``DW_OP_constu AS;
DW_OP_aspace_bregx R, D`` where R and D are the old CFA register number and
byte displacement respectively.
If AS is not one of the values defined by the target architecture's
``DW_ASPACE_*`` values then the DWARF expression is ill-formed.
7. ``DW_CFA_def_cfa_expression``
The ``DW_CFA_def_cfa_expression`` instruction takes a single operand encoded
as a ``DW_FORM_exprloc`` value representing a DWARF expression E. The
required action is to define the current CFA rule to be the memory location
description computed by evaluating E.
*See :ref:`amdgpu-dwarf-call-frame-instructions` regarding restrictions on
the DWARF expression operators that can be used in E.*
If the result of evaluating E is not a memory location description with bit
offset that is a multiple of 8 (the byte size), then the DWARF is
ill-formed.
.. _amdgpu-dwarf-register-rule-instructions:
Register Rule Instructions
##########################
.. note::
For AMDGPU:
* The register number follows the numbering defined in
:ref:`amdgpu-dwarf-register-mapping`.
1. ``DW_CFA_undefined``
The ``DW_CFA_undefined`` instruction takes a single unsigned LEB128 operand
that represents a register number R. The required action is to set the rule
for the register specified by R to ``undefined``.
2. ``DW_CFA_same_value``
The ``DW_CFA_same_value`` instruction takes a single unsigned LEB128 operand
that represents a register number R. The required action is to set the rule
for the register specified by R to ``same value``.
3. ``DW_CFA_offset``
The ``DW_CFA_offset`` instruction takes two operands: a register number R
(encoded with the opcode) and an unsigned LEB128 constant representing a
factored displacement D. The required action is to change the rule for the
register specified by R to be an *offset(D*data_alignment_factor)* rule.
.. note::
Seems this should be named ``DW_CFA_offset_uf`` since the offset is
unsigned factored.
4. ``DW_CFA_offset_extended``
The ``DW_CFA_offset_extended`` instruction takes two unsigned LEB128
operands representing a register number R and a factored displacement D.
This instruction is identical to ``DW_CFA_offset`` except for the encoding
and size of the register operand.
.. note::
Seems this should be named ``DW_CFA_offset_extended_uf`` since the
displacement is unsigned factored.
5. ``DW_CFA_offset_extended_sf``
The ``DW_CFA_offset_extended_sf`` instruction takes two operands: an
unsigned LEB128 value representing a register number R and a signed LEB128
factored displacement D. This instruction is identical to
``DW_CFA_offset_extended`` except that D is signed.
6. ``DW_CFA_val_offset``
The ``DW_CFA_val_offset`` instruction takes two unsigned LEB128 operands
representing a register number R and a factored displacement D. The required
action is to change the rule for the register indicated by R to be a
*val_offset(D*data_alignment_factor)* rule.
.. note::
Seems this should be named ``DW_CFA_val_offset_uf`` since the displacement
is unsigned factored.
7. ``DW_CFA_val_offset_sf``
The ``DW_CFA_val_offset_sf`` instruction takes two operands: an unsigned
LEB128 value representing a register number R and a signed LEB128 factored
displacement D. This instruction is identical to ``DW_CFA_val_offset``
except that D is signed.
8. ``DW_CFA_register``
The ``DW_CFA_register`` instruction takes two unsigned LEB128 operands
representing register numbers R1 and R2 respectively. The required action is
to set the rule for the register specified by R1 to be *register(R)* where R
is R2.
9. ``DW_CFA_expression``
The ``DW_CFA_expression`` instruction takes two operands: an unsigned LEB128
value representing a register number R, and a ``DW_FORM_block`` value
representing a DWARF expression E. The required action is to change the rule
for the register specified by R to be an *expression(E)* rule. The memory
location description of the current CFA is pushed on the DWARF stack prior
to execution of E.
*That is, the DWARF expression computes the location description where the
register value can be retrieved.*
*See :ref:`amdgpu-dwarf-call-frame-instructions` regarding restrictions on
the DWARF expression operators that can be used in E.*
10. ``DW_CFA_val_expression``
The ``DW_CFA_val_expression`` instruction takes two operands: an unsigned
LEB128 value representing a register number R, and a ``DW_FORM_block`` value
representing a DWARF expression E. The required action is to change the rule
for the register specified by R to be a *val_expression(E)* rule. The memory
location description of the current CFA is pushed on the DWARF evaluation
stack prior to execution of E.
*That is, E computes the value of register R.*
*See :ref:`amdgpu-dwarf-call-frame-instructions` regarding restrictions on
the DWARF expression operators that can be used in E.*
If the result of evaluating E is not a value with a base type size that
matches the register size, then the DWARF is ill-formed.
11. ``DW_CFA_restore``
The ``DW_CFA_restore`` instruction takes a single operand (encoded with the
opcode) that represents a register number R. The required action is to
change the rule for the register specified by R to the rule assigned it by
the initial_instructions in the CIE.
12. ``DW_CFA_restore_extended``
The ``DW_CFA_restore_extended`` instruction takes a single unsigned LEB128
operand that represents a register number R. This instruction is identical
to ``DW_CFA_restore`` except for the encoding and size of the register
operand.
Row State Instructions
######################
These instructions are the same as in DWARF 5.
Call Frame Calling Address
++++++++++++++++++++++++++
*When virtually unwinding frames, consumers frequently wish to obtain the
address of the instruction which called a subroutine. This information is not
always provided. Typically, however, one of the registers in the virtual unwind
table is the Return Address.*
If a Return Address register is defined in the virtual unwind table, and its
rule is undefined (for example, by ``DW_CFA_undefined``), then there is no
return address and no call address, and the virtual unwind of stack activations
is complete.
*In most cases the return address is in the same context as the calling address,
but that need not be the case, especially if the producer knows in some way the
call never will return. The context of the ’return address’ might be on a
different line, in a different lexical block, or past the end of the calling
subroutine. If a consumer were to assume that it was in the same context as the
calling address, the virtual unwind might fail.*
*For architectures with constant-length instructions where the return address
immediately follows the call instruction, a simple solution is to subtract the
length of an instruction from the return address to obtain the calling
instruction. For architectures with variable-length instructions (for example,
x86), this is not possible. However, subtracting 1 from the return address,
although not guaranteed to provide the exact calling address, generally will
produce an address within the same context as the calling address, and that
usually is sufficient.*
.. note::
For AMDGPU the instructions are variable size and a consumer can subtract 1
from the return address to get the address of a byte within the call site
instructions.
Call Frame Information Instruction Encodings
++++++++++++++++++++++++++++++++++++++++++++
The following table gives the encoding of the DWARF call frame information
instructions added for AMDGPU.
.. table:: AMDGPU DWARF Call Frame Information Instruction Encodings
:name: amdgpu-dwarf-call-frame-information-instruction-encodings-table
=================================== ==== ==== ============== ================
Instruction High Low Operand 1 Operand 1
2 6
Bits Bits
=================================== ==== ==== ============== ================
DW_CFA_LLVM_def_cfa_aspace 0 0Xxx ULEB128
=================================== ==== ==== ============== ================
Line Table
~~~~~~~~~~
.. note::
AMDGPU does not use the ``isa`` state machine registers and always sets it to
0.
.. TODO::
Should the ``isa`` state machine register be used to indicate if the code is
in wave32 or wave64 mode? Or used to specify the architecture ISA?
Accelerated Access
~~~~~~~~~~~~~~~~~~
Lookup By Name
++++++++++++++
.. note::
For AMDGPU:
* The rule for debugger information entries included in the name
index in the optional ``.debug_names`` section is extended to also include
named ``DW_TAG_variable`` debugging information entries with a
``DW_AT_location`` attribute that includes a
``DW_OP_LLVM_form_aspace_address`` operation.
* The lookup by name section header ``augmentation_string`` string field contains:
::
[amd:v0.0]
The "vX.Y" specifies the major X and minor Y version number of the AMDGPU
extensions used in the DWARF of the compilation unit. The version number
conforms to [SEMVER]_.
Lookup By Address
+++++++++++++++++
.. note::
For AMDGPU:
* The lookup by address section header table:
``address_size`` (ubyte)
Match the address size for the ``Global`` address space defined in
:ref:`amdgpu-dwarf-address-space-mapping-table`.
``segment_selector_size`` (ubyte)
AMDGPU does not use a segment selector so this is 0. The entries in the
``.debug_aranges`` do not have a segment selector.
Data Representation
~~~~~~~~~~~~~~~~~~~
.. _amdgpu-dwarf-32-bit-and-64-bit-dwarf-formats:
32-Bit and 64-Bit DWARF Formats
+++++++++++++++++++++++++++++++
.. note::
For AMDGPU:
* For the ``amdgcn`` target only 64-bit process address space is supported
* The producer can generate either 32-bit or 64-bit DWARF format.
1. Within the body of the ``.debug_info`` section, certain forms of attribute
value depend on the choice of DWARF format as follows. For the 32-bit DWARF
format, the value is a 4-byte unsigned integer; for the 64-bit DWARF format,
the value is an 8-byte unsigned integer.
.. table:: AMDGPU DWARF ``.debug_info`` section attribute sizes
:name: amdgpu-dwarf-debug-info-section-attribute-sizes
=================================== =====================================
Form Role
=================================== =====================================
DW_FORM_line_strp offset in ``.debug_line_str``
DW_FORM_ref_addr offset in ``.debug_info``
DW_FORM_sec_offset offset in a section other than
``.debug_info`` or ``.debug_str``
DW_FORM_strp offset in ``.debug_str``
DW_FORM_strp_sup offset in ``.debug_str`` section of
supplementary object file
DW_OP_call_ref offset in ``.debug_info``
DW_OP_implicit_pointer offset in ``.debug_info``
DW_OP_LLVM_aspace_implicit_pointer offset in ``.debug_info``
=================================== =====================================
Unit Headers
++++++++++++
.. note::
For AMDGPU:
* For AMDGPU the ``address_size`` field of the DWARF unit headers matches the
address size for the ``Global`` address space defined in
:ref:`amdgpu-dwarf-address-space-mapping-table`.
.. _amdgpu-dwarf-amdgpu-dw-at-llvm-lane-pc:
AMDGPU DW_AT_LLVM_lane_pc
~~~~~~~~~~~~~~~~~~~~~~~~~
The ``DW_AT_LLVM_lane_pc`` attribute can be used to specify the program location
of the separate lanes of a SIMT thread. See
:ref:`amdgpu-dwarf-debugging-information-entry-attributes`.
If the lane is an active lane then this will be the same as the current program
location.
If the lane is inactive, but was active on entry to the subprogram, then this is
the program location in the subprogram at which execution of the lane is
conceptual positioned.
If the lane was not active on entry to the subprogram, then this will be the
undefined location. A client debugger can check if the lane is part of a valid
work-group by checking that the lane is in the range of the associated
work-group within the grid, accounting for partial work-groups. If it is not
then the debugger can omit any information for the lane. Otherwise, the debugger
may repeatedly unwind the stack and inspect the ``DW_AT_LLVM_lane_pc`` of the
calling subprogram until it finds a non-undefined location. Conceptually the
lane only has the call frames that it has a non-undefined
``DW_AT_LLVM_lane_pc``.
The following example illustrates how the AMDGPU backend can generate a location
list for the nested ``IF/THEN/ELSE`` structures of the following subprogram
pseudo code for a target with 64 lanes per wave.
.. code::
:number-lines:
SUBPROGRAM X
BEGIN
a;
IF (c1) THEN
b;
IF (c2) THEN
c;
ELSE
d;
ENDIF
e;
ELSE
f;
ENDIF
g;
END
The AMDGPU backend may generate the following pseudo LLVM MIR to manipulate the
execution mask (``EXEC``) to linearized the control flow. The condition is
evaluated to make a mask of the lanes for which the condition evaluates to true.
First the ``THEN`` region is executed by setting the ``EXEC`` mask to the
logical ``AND`` of the current ``EXEC`` mask with the condition mask. Then the
``ELSE`` region is executed by negating the ``EXEC`` mask and logical ``AND`` of
the saved ``EXEC`` mask at the start of the region. After the ``IF/THEN/ELSE``
region the ``EXEC`` mask is restored to the value it had at the beginning of the
region. This is shown below. Other approaches are possible, but the basic
concept is the same.
.. code::
:number-lines:
$lex_start:
a;
%1 = EXEC
%2 = c1
$lex_1_start:
EXEC = %1 & %2
$if_1_then:
b;
%3 = EXEC
%4 = c2
$lex_1_1_start:
EXEC = %3 & %4
$lex_1_1_then:
c;
EXEC = ~EXEC & %3
$lex_1_1_else:
d;
EXEC = %3
$lex_1_1_end:
e;
EXEC = ~EXEC & %1
$lex_1_else:
f;
EXEC = %1
$lex_1_end:
g;
$lex_end:
To create the location list that defines the location description of a vector of
lane program locations, the LLVM MIR ``DBG_VALUE`` pseudo instruction can be
used to annotate the linearized control flow. This can be done by defining an
artificial variable for the lane PC. The location list created for it is used to
define the value of the ``DW_AT_LLVM_lane_pc`` attribute.
A DWARF procedure is defined for each well nested structured control flow region
which provides the conceptual lane program location for a lane if it is not
active (namely it is divergent). The expression for each region inherits the
value of the immediately enclosing region and modifies it according to the
semantics of the region.
For an ``IF/THEN/ELSE`` region the divergent program location is at the start of
the region for the ``THEN`` region since it is executed first. For the ``ELSE``
region the divergent program location is at the end of the ``IF/THEN/ELSE``
region since the ``THEN`` region has completed.
The lane PC artificial variable is assigned at each region transition. It uses
the immediately enclosing region's DWARF procedure to compute the program
location for each lane assuming they are divergent, and then modifies the result
by inserting the current program location for each lane that the ``EXEC`` mask
indicates is active.
By having separate DWARF procedures for each region, they can be reused to
define the value for any nested region. This reduces the amount of DWARF
required.
The following provides an example using pseudo LLVM MIR.
.. code::
:number-lines:
$lex_start:
DEFINE_DWARF %__uint_64 = DW_TAG_base_type[
DW_AT_name = "__uint64";
DW_AT_byte_size = 8;
DW_AT_encoding = DW_ATE_unsigned;
];
DEFINE_DWARF %__active_lane_pc = DW_TAG_dwarf_procedure[
DW_AT_name = "__active_lane_pc";
DW_AT_location = [
DW_OP_regx PC;
DW_OP_LLVM_extend 64, 64;
DW_OP_regval_type EXEC, %uint_64;
DW_OP_LLVM_select_bit_piece 64, 64;
];
];
DEFINE_DWARF %__divergent_lane_pc = DW_TAG_dwarf_procedure[
DW_AT_name = "__divergent_lane_pc";
DW_AT_location = [
DW_OP_LLVM_undefined;
DW_OP_LLVM_extend 64, 64;
];
];
DBG_VALUE $noreg, $noreg, %DW_AT_LLVM_lane_pc, DIExpression[
DW_OP_call_ref %__divergent_lane_pc;
DW_OP_call_ref %__active_lane_pc;
];
a;
%1 = EXEC;
DBG_VALUE %1, $noreg, %__lex_1_save_exec;
%2 = c1;
$lex_1_start:
EXEC = %1 & %2;
$lex_1_then:
DEFINE_DWARF %__divergent_lane_pc_1_then = DW_TAG_dwarf_procedure[
DW_AT_name = "__divergent_lane_pc_1_then";
DW_AT_location = DIExpression[
DW_OP_call_ref %__divergent_lane_pc;
DW_OP_xaddr &lex_1_start;
DW_OP_stack_value;
DW_OP_LLVM_extend 64, 64;
DW_OP_call_ref %__lex_1_save_exec;
DW_OP_deref_type 64, %__uint_64;
DW_OP_LLVM_select_bit_piece 64, 64;
];
];
DBG_VALUE $noreg, $noreg, %DW_AT_LLVM_lane_pc, DIExpression[
DW_OP_call_ref %__divergent_lane_pc_1_then;
DW_OP_call_ref %__active_lane_pc;
];
b;
%3 = EXEC;
DBG_VALUE %3, %__lex_1_1_save_exec;
%4 = c2;
$lex_1_1_start:
EXEC = %3 & %4;
$lex_1_1_then:
DEFINE_DWARF %__divergent_lane_pc_1_1_then = DW_TAG_dwarf_procedure[
DW_AT_name = "__divergent_lane_pc_1_1_then";
DW_AT_location = DIExpression[
DW_OP_call_ref %__divergent_lane_pc_1_then;
DW_OP_xaddr &lex_1_1_start;
DW_OP_stack_value;
DW_OP_LLVM_extend 64, 64;
DW_OP_call_ref %__lex_1_1_save_exec;
DW_OP_deref_type 64, %__uint_64;
DW_OP_LLVM_select_bit_piece 64, 64;
];
];
DBG_VALUE $noreg, $noreg, %DW_AT_LLVM_lane_pc, DIExpression[
DW_OP_call_ref %__divergent_lane_pc_1_1_then;
DW_OP_call_ref %__active_lane_pc;
];
c;
EXEC = ~EXEC & %3;
$lex_1_1_else:
DEFINE_DWARF %__divergent_lane_pc_1_1_else = DW_TAG_dwarf_procedure[
DW_AT_name = "__divergent_lane_pc_1_1_else";
DW_AT_location = DIExpression[
DW_OP_call_ref %__divergent_lane_pc_1_then;
DW_OP_xaddr &lex_1_1_end;
DW_OP_stack_value;
DW_OP_LLVM_extend 64, 64;
DW_OP_call_ref %__lex_1_1_save_exec;
DW_OP_deref_type 64, %__uint_64;
DW_OP_LLVM_select_bit_piece 64, 64;
];
];
DBG_VALUE $noreg, $noreg, %DW_AT_LLVM_lane_pc, DIExpression[
DW_OP_call_ref %__divergent_lane_pc_1_1_else;
DW_OP_call_ref %__active_lane_pc;
];
d;
EXEC = %3;
$lex_1_1_end:
DBG_VALUE $noreg, $noreg, %DW_AT_LLVM_lane_pc, DIExpression[
DW_OP_call_ref %__divergent_lane_pc;
DW_OP_call_ref %__active_lane_pc;
];
e;
EXEC = ~EXEC & %1;
$lex_1_else:
DEFINE_DWARF %__divergent_lane_pc_1_else = DW_TAG_dwarf_procedure[
DW_AT_name = "__divergent_lane_pc_1_else";
DW_AT_location = DIExpression[
DW_OP_call_ref %__divergent_lane_pc;
DW_OP_xaddr &lex_1_end;
DW_OP_stack_value;
DW_OP_LLVM_extend 64, 64;
DW_OP_call_ref %__lex_1_save_exec;
DW_OP_deref_type 64, %__uint_64;
DW_OP_LLVM_select_bit_piece 64, 64;
];
];
DBG_VALUE $noreg, $noreg, %DW_AT_LLVM_lane_pc, DIExpression[
DW_OP_call_ref %__divergent_lane_pc_1_else;
DW_OP_call_ref %__active_lane_pc;
];
f;
EXEC = %1;
$lex_1_end:
DBG_VALUE $noreg, $noreg, %DW_AT_LLVM_lane_pc DIExpression[
DW_OP_call_ref %__divergent_lane_pc;
DW_OP_call_ref %__active_lane_pc;
];
g;
$lex_end:
The DWARF procedure ``%__active_lane_pc`` is used to update the lane pc elements
that are active with the current program location.
Artificial variables %__lex_1_save_exec and %__lex_1_1_save_exec are created for
the execution masks saved on entry to a region. Using the ``DBG_VALUE`` pseudo
instruction, location lists that describes where they are allocated at any given
program location will be created. The compiler may allocate them to registers,
or spill them to memory.
The DWARF procedures for each region use saved execution mask value to only
update the lanes that are active on entry to the region. All other lanes retain
the value of the enclosing region where they were last active. If they were not
active on entry to the subprogram, then will have the undefined location
description.
Other structured control flow regions can be handled similarly. For example,
loops would set the divergent program location for the region at the end of the
loop. Any lanes active will be in the loop, and any lanes not active must have
exited the loop.
An ``IF/THEN/ELSEIF/ELSEIF/...`` region can be treated as a nest of
``IF/THEN/ELSE`` regions.
The DWARF procedures can use the active lane artificial variable described in
:ref:`amdgpu-dwarf-amdgpu-dw-at-llvm-active-lane` rather than the actual
``EXEC`` mask in order to support whole or quad wave mode.
.. _amdgpu-dwarf-amdgpu-dw-at-llvm-active-lane:
AMDGPU DW_AT_LLVM_active_lane
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The ``DW_AT_LLVM_active_lane`` attribute can be used to specify the lanes that
are conceptually active for a SIMT thread. See
:ref:`amdgpu-dwarf-debugging-information-entry-attributes`.
The execution mask may be modified to implement whole or quad wave mode
operations. For example, all lanes may need to temporarily be made active to
execute a whole wave operation. Such regions would save the ``EXEC`` mask,
update it to enable the necessary lanes, perform the operations, and then
restore the ``EXEC`` mask from the saved value. While executing the whole wave
region, the conceptual execution mask is the saved value, not the ``EXEC``
value.
This is handled by defining an artificial variable for the active lane mask. The
active lane mask artificial variable would be the actual ``EXEC`` mask for
normal regions, and the saved execution mask for regions where the mask is
temporarily updated. The location list created for this artificial variable is
used to define the value of the ``DW_AT_LLVM_active_lane`` attribute.
Source Text
~~~~~~~~~~~
Source text for online-compiled programs (e.g. those compiled by the OpenCL
runtime) may be embedded into the DWARF v5 line table using the ``clang
-gembed-source`` option, described in table :ref:`amdgpu-debug-options`.
For example:
``-gembed-source``
Enable the embedded source DWARF v5 extension.
``-gno-embed-source``
Disable the embedded source DWARF v5 extension.
.. table:: AMDGPU Debug Options
:name: amdgpu-debug-options
==================== ==================================================
Debug Flag Description
==================== ==================================================
-g[no-]embed-source Enable/disable embedding source text in DWARF
debug sections. Useful for environments where
source cannot be written to disk, such as
when performing online compilation.
==================== ==================================================
This option enables one extended content types in the DWARF v5 Line Number
Program Header, which is used to encode embedded source.
.. table:: AMDGPU DWARF Line Number Program Header Extended Content Types
:name: amdgpu-dwarf-extended-content-types
============================ ======================
Content Type Form
============================ ======================
``DW_LNCT_LLVM_source`` ``DW_FORM_line_strp``
============================ ======================
The source field will contain the UTF-8 encoded, null-terminated source text
with ``'\n'`` line endings. When the source field is present, consumers can use
the embedded source instead of attempting to discover the source on disk. When
the source field is absent, consumers can access the file to get the source
text.
The above content type appears in the ``file_name_entry_format`` field of the
line table prologue, and its corresponding value appear in the ``file_names``
field. The current encoding of the content type is documented in table
:ref:`amdgpu-dwarf-extended-content-types-encoding`
.. table:: AMDGPU DWARF Line Number Program Header Extended Content Types Encoding
:name: amdgpu-dwarf-extended-content-types-encoding
============================ ====================
Content Type Value
============================ ====================
``DW_LNCT_LLVM_source`` 0x2001
============================ ====================
.. _amdgpu-code-conventions:
Code Conventions
================
This section provides code conventions used for each supported target triple OS
(see :ref:`amdgpu-target-triples`).
AMDHSA
------
This section provides code conventions used when the target triple OS is
``amdhsa`` (see :ref:`amdgpu-target-triples`).
.. _amdgpu-amdhsa-code-object-target-identification:
Code Object Target Identification
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The AMDHSA OS uses the following syntax to specify the code object
target as a single string:
``<Architecture>-<Vendor>-<OS>-<Environment>-<Processor><Target Features>``
Where:
- ``<Architecture>``, ``<Vendor>``, ``<OS>`` and ``<Environment>``
are the same as the *Target Triple* (see
:ref:`amdgpu-target-triples`).
- ``<Processor>`` is the same as the *Processor* (see
:ref:`amdgpu-processors`).
- ``<Target Features>`` is a list of the enabled *Target Features*
(see :ref:`amdgpu-target-features`), each prefixed by a plus, that
apply to *Processor*. The list must be in the same order as listed
in the table :ref:`amdgpu-target-feature-table`. Note that *Target
Features* must be included in the list if they are enabled even if
that is the default for *Processor*.
For example:
``"amdgcn-amd-amdhsa--gfx902+xnack"``
.. _amdgpu-amdhsa-code-object-metadata:
Code Object Metadata
~~~~~~~~~~~~~~~~~~~~
The code object metadata specifies extensible metadata associated with the code
objects executed on HSA [HSA]_ compatible runtimes such as AMD's ROCm
[AMD-ROCm]_. The encoding and semantics of this metadata depends on the code
object version; see :ref:`amdgpu-amdhsa-code-object-metadata-v2` and
:ref:`amdgpu-amdhsa-code-object-metadata-v3`.
Code object metadata is specified in a note record (see
:ref:`amdgpu-note-records`) and is required when the target triple OS is
``amdhsa`` (see :ref:`amdgpu-target-triples`). It must contain the minimum
information necessary to support the ROCM kernel queries. For example, the
segment sizes needed in a dispatch packet. In addition, a high level language
runtime may require other information to be included. For example, the AMD
OpenCL runtime records kernel argument information.
.. _amdgpu-amdhsa-code-object-metadata-v2:
Code Object V2 Metadata (-mattr=-code-object-v3)
++++++++++++++++++++++++++++++++++++++++++++++++
.. warning:: Code Object V2 is not the default code object version emitted by
this version of LLVM. For a description of the metadata generated with the
default configuration (Code Object V3) see
:ref:`amdgpu-amdhsa-code-object-metadata-v3`.
Code object V2 metadata is specified by the ``NT_AMD_AMDGPU_METADATA`` note
record (see :ref:`amdgpu-note-records-v2`).
The metadata is specified as a YAML formatted string (see [YAML]_ and
:doc:`YamlIO`).
.. TODO::
Is the string null terminated? It probably should not if YAML allows it to
contain null characters, otherwise it should be.
The metadata is represented as a single YAML document comprised of the mapping
defined in table :ref:`amdgpu-amdhsa-code-object-metadata-map-table-v2` and
referenced tables.
For boolean values, the string values of ``false`` and ``true`` are used for
false and true respectively.
Additional information can be added to the mappings. To avoid conflicts, any
non-AMD key names should be prefixed by "*vendor-name*.".
.. table:: AMDHSA Code Object V2 Metadata Map
:name: amdgpu-amdhsa-code-object-metadata-map-table-v2
========== ============== ========= =======================================
String Key Value Type Required? Description
========== ============== ========= =======================================
"Version" sequence of Required - The first integer is the major
2 integers version. Currently 1.
- The second integer is the minor
version. Currently 0.
"Printf" sequence of Each string is encoded information
strings about a printf function call. The
encoded information is organized as
fields separated by colon (':'):
``ID:N:S[0]:S[1]:...:S[N-1]:FormatString``
where:
``ID``
A 32-bit integer as a unique id for
each printf function call
``N``
A 32-bit integer equal to the number
of arguments of printf function call
minus 1
``S[i]`` (where i = 0, 1, ... , N-1)
32-bit integers for the size in bytes
of the i-th FormatString argument of
the printf function call
FormatString
The format string passed to the
printf function call.
"Kernels" sequence of Required Sequence of the mappings for each
mapping kernel in the code object. See
:ref:`amdgpu-amdhsa-code-object-kernel-metadata-map-table-v2`
for the definition of the mapping.
========== ============== ========= =======================================
..
.. table:: AMDHSA Code Object V2 Kernel Metadata Map
:name: amdgpu-amdhsa-code-object-kernel-metadata-map-table-v2
================= ============== ========= ================================
String Key Value Type Required? Description
================= ============== ========= ================================
"Name" string Required Source name of the kernel.
"SymbolName" string Required Name of the kernel
descriptor ELF symbol.
"Language" string Source language of the kernel.
Values include:
- "OpenCL C"
- "OpenCL C++"
- "HCC"
- "OpenMP"
"LanguageVersion" sequence of - The first integer is the major
2 integers version.
- The second integer is the
minor version.
"Attrs" mapping Mapping of kernel attributes.
See
:ref:`amdgpu-amdhsa-code-object-kernel-attribute-metadata-map-table-v2`
for the mapping definition.
"Args" sequence of Sequence of mappings of the
mapping kernel arguments. See
:ref:`amdgpu-amdhsa-code-object-kernel-argument-metadata-map-table-v2`
for the definition of the mapping.
"CodeProps" mapping Mapping of properties related to
the kernel code. See
:ref:`amdgpu-amdhsa-code-object-kernel-code-properties-metadata-map-table-v2`
for the mapping definition.
================= ============== ========= ================================
..
.. table:: AMDHSA Code Object V2 Kernel Attribute Metadata Map
:name: amdgpu-amdhsa-code-object-kernel-attribute-metadata-map-table-v2
=================== ============== ========= ==============================
String Key Value Type Required? Description
=================== ============== ========= ==============================
"ReqdWorkGroupSize" sequence of If not 0, 0, 0 then all values
3 integers must be >=1 and the dispatch
work-group size X, Y, Z must
correspond to the specified
values. Defaults to 0, 0, 0.
Corresponds to the OpenCL
``reqd_work_group_size``
attribute.
"WorkGroupSizeHint" sequence of The dispatch work-group size
3 integers X, Y, Z is likely to be the
specified values.
Corresponds to the OpenCL
``work_group_size_hint``
attribute.
"VecTypeHint" string The name of a scalar or vector
type.
Corresponds to the OpenCL
``vec_type_hint`` attribute.
"RuntimeHandle" string The external symbol name
associated with a kernel.
OpenCL runtime allocates a
global buffer for the symbol
and saves the kernel's address
to it, which is used for
device side enqueueing. Only
available for device side
enqueued kernels.
=================== ============== ========= ==============================
..
.. table:: AMDHSA Code Object V2 Kernel Argument Metadata Map
:name: amdgpu-amdhsa-code-object-kernel-argument-metadata-map-table-v2
================= ============== ========= ================================
String Key Value Type Required? Description
================= ============== ========= ================================
"Name" string Kernel argument name.
"TypeName" string Kernel argument type name.
"Size" integer Required Kernel argument size in bytes.
"Align" integer Required Kernel argument alignment in
bytes. Must be a power of two.
"ValueKind" string Required Kernel argument kind that
specifies how to set up the
corresponding argument.
Values include:
"ByValue"
The argument is copied
directly into the kernarg.
"GlobalBuffer"
A global address space pointer
to the buffer data is passed
in the kernarg.
"DynamicSharedPointer"
A group address space pointer
to dynamically allocated LDS
is passed in the kernarg.
"Sampler"
A global address space
pointer to a S# is passed in
the kernarg.
"Image"
A global address space
pointer to a T# is passed in
the kernarg.
"Pipe"
A global address space pointer
to an OpenCL pipe is passed in
the kernarg.
"Queue"
A global address space pointer
to an OpenCL device enqueue
queue is passed in the
kernarg.
"HiddenGlobalOffsetX"
The OpenCL grid dispatch
global offset for the X
dimension is passed in the
kernarg.
"HiddenGlobalOffsetY"
The OpenCL grid dispatch
global offset for the Y
dimension is passed in the
kernarg.
"HiddenGlobalOffsetZ"
The OpenCL grid dispatch
global offset for the Z
dimension is passed in the
kernarg.
"HiddenNone"
An argument that is not used
by the kernel. Space needs to
be left for it, but it does
not need to be set up.
"HiddenPrintfBuffer"
A global address space pointer
to the runtime printf buffer
is passed in kernarg.
"HiddenHostcallBuffer"
A global address space pointer
to the runtime hostcall buffer
is passed in kernarg.
"HiddenDefaultQueue"
A global address space pointer
to the OpenCL device enqueue
queue that should be used by
the kernel by default is
passed in the kernarg.
"HiddenCompletionAction"
A global address space pointer
to help link enqueued kernels into
the ancestor tree for determining
when the parent kernel has finished.
"HiddenMultiGridSyncArg"
A global address space pointer for
multi-grid synchronization is
passed in the kernarg.
"ValueType" string Required Kernel argument value type. Only
present if "ValueKind" is
"ByValue". For vector data
types, the value is for the
element type. Values include:
- "Struct"
- "I8"
- "U8"
- "I16"
- "U16"
- "F16"
- "I32"
- "U32"
- "F32"
- "I64"
- "U64"
- "F64"
.. TODO::
How can it be determined if a
vector type, and what size
vector?
"PointeeAlign" integer Alignment in bytes of pointee
type for pointer type kernel
argument. Must be a power
of 2. Only present if
"ValueKind" is
"DynamicSharedPointer".
"AddrSpaceQual" string Kernel argument address space
qualifier. Only present if
"ValueKind" is "GlobalBuffer" or
"DynamicSharedPointer". Values
are:
- "Private"
- "Global"
- "Constant"
- "Local"
- "Generic"
- "Region"
.. TODO::
Is GlobalBuffer only Global
or Constant? Is
DynamicSharedPointer always
Local? Can HCC allow Generic?
How can Private or Region
ever happen?
"AccQual" string Kernel argument access
qualifier. Only present if
"ValueKind" is "Image" or
"Pipe". Values
are:
- "ReadOnly"
- "WriteOnly"
- "ReadWrite"
.. TODO::
Does this apply to
GlobalBuffer?
"ActualAccQual" string The actual memory accesses
performed by the kernel on the
kernel argument. Only present if
"ValueKind" is "GlobalBuffer",
"Image", or "Pipe". This may be
more restrictive than indicated
by "AccQual" to reflect what the
kernel actual does. If not
present then the runtime must
assume what is implied by
"AccQual" and "IsConst". Values
are:
- "ReadOnly"
- "WriteOnly"
- "ReadWrite"
"IsConst" boolean Indicates if the kernel argument
is const qualified. Only present
if "ValueKind" is
"GlobalBuffer".
"IsRestrict" boolean Indicates if the kernel argument
is restrict qualified. Only
present if "ValueKind" is
"GlobalBuffer".
"IsVolatile" boolean Indicates if the kernel argument
is volatile qualified. Only
present if "ValueKind" is
"GlobalBuffer".
"IsPipe" boolean Indicates if the kernel argument
is pipe qualified. Only present
if "ValueKind" is "Pipe".
.. TODO::
Can GlobalBuffer be pipe
qualified?
================= ============== ========= ================================
..
.. table:: AMDHSA Code Object V2 Kernel Code Properties Metadata Map
:name: amdgpu-amdhsa-code-object-kernel-code-properties-metadata-map-table-v2
============================ ============== ========= =====================
String Key Value Type Required? Description
============================ ============== ========= =====================
"KernargSegmentSize" integer Required The size in bytes of
the kernarg segment
that holds the values
of the arguments to
the kernel.
"GroupSegmentFixedSize" integer Required The amount of group
segment memory
required by a
work-group in
bytes. This does not
include any
dynamically allocated
group segment memory
that may be added
when the kernel is
dispatched.
"PrivateSegmentFixedSize" integer Required The amount of fixed
private address space
memory required for a
work-item in
bytes. If the kernel
uses a dynamic call
stack then additional
space must be added
to this value for the
call stack.
"KernargSegmentAlign" integer Required The maximum byte
alignment of
arguments in the
kernarg segment. Must
be a power of 2.
"WavefrontSize" integer Required Wavefront size. Must
be a power of 2.
"NumSGPRs" integer Required Number of scalar
registers used by a
wavefront for
GFX6-GFX10. This
includes the special
SGPRs for VCC, Flat
Scratch (GFX7-GFX10)
and XNACK (for
GFX8-GFX10). It does
not include the 16
SGPR added if a trap
handler is
enabled. It is not
rounded up to the
allocation
granularity.
"NumVGPRs" integer Required Number of vector
registers used by
each work-item for
GFX6-GFX10
"MaxFlatWorkGroupSize" integer Required Maximum flat
work-group size
supported by the
kernel in work-items.
Must be >=1 and
consistent with
ReqdWorkGroupSize if
not 0, 0, 0.
"NumSpilledSGPRs" integer Number of stores from
a scalar register to
a register allocator
created spill
location.
"NumSpilledVGPRs" integer Number of stores from
a vector register to
a register allocator
created spill
location.
============================ ============== ========= =====================
.. _amdgpu-amdhsa-code-object-metadata-v3:
Code Object V3 Metadata (-mattr=+code-object-v3)
++++++++++++++++++++++++++++++++++++++++++++++++
Code object V3 metadata is specified by the ``NT_AMDGPU_METADATA`` note record
(see :ref:`amdgpu-note-records-v3`).
The metadata is represented as Message Pack formatted binary data (see
[MsgPack]_). The top level is a Message Pack map that includes the
keys defined in table
:ref:`amdgpu-amdhsa-code-object-metadata-map-table-v3` and referenced
tables.
Additional information can be added to the maps. To avoid conflicts,
any key names should be prefixed by "*vendor-name*." where
``vendor-name`` can be the name of the vendor and specific vendor
tool that generates the information. The prefix is abbreviated to
simply "." when it appears within a map that has been added by the
same *vendor-name*.
.. table:: AMDHSA Code Object V3 Metadata Map
:name: amdgpu-amdhsa-code-object-metadata-map-table-v3
================= ============== ========= =======================================
String Key Value Type Required? Description
================= ============== ========= =======================================
"amdhsa.version" sequence of Required - The first integer is the major
2 integers version. Currently 1.
- The second integer is the minor
version. Currently 0.
"amdhsa.printf" sequence of Each string is encoded information
strings about a printf function call. The
encoded information is organized as
fields separated by colon (':'):
``ID:N:S[0]:S[1]:...:S[N-1]:FormatString``
where:
``ID``
A 32-bit integer as a unique id for
each printf function call
``N``
A 32-bit integer equal to the number
of arguments of printf function call
minus 1
``S[i]`` (where i = 0, 1, ... , N-1)
32-bit integers for the size in bytes
of the i-th FormatString argument of
the printf function call
FormatString
The format string passed to the
printf function call.
"amdhsa.kernels" sequence of Required Sequence of the maps for each
map kernel in the code object. See
:ref:`amdgpu-amdhsa-code-object-kernel-metadata-map-table-v3`
for the definition of the keys included
in that map.
================= ============== ========= =======================================
..
.. table:: AMDHSA Code Object V3 Kernel Metadata Map
:name: amdgpu-amdhsa-code-object-kernel-metadata-map-table-v3
=================================== ============== ========= ================================
String Key Value Type Required? Description
=================================== ============== ========= ================================
".name" string Required Source name of the kernel.
".symbol" string Required Name of the kernel
descriptor ELF symbol.
".language" string Source language of the kernel.
Values include:
- "OpenCL C"
- "OpenCL C++"
- "HCC"
- "HIP"
- "OpenMP"
- "Assembler"
".language_version" sequence of - The first integer is the major
2 integers version.
- The second integer is the
minor version.
".args" sequence of Sequence of maps of the
map kernel arguments. See
:ref:`amdgpu-amdhsa-code-object-kernel-argument-metadata-map-table-v3`
for the definition of the keys
included in that map.
".reqd_workgroup_size" sequence of If not 0, 0, 0 then all values
3 integers must be >=1 and the dispatch
work-group size X, Y, Z must
correspond to the specified
values. Defaults to 0, 0, 0.
Corresponds to the OpenCL
``reqd_work_group_size``
attribute.
".workgroup_size_hint" sequence of The dispatch work-group size
3 integers X, Y, Z is likely to be the
specified values.
Corresponds to the OpenCL
``work_group_size_hint``
attribute.
".vec_type_hint" string The name of a scalar or vector
type.
Corresponds to the OpenCL
``vec_type_hint`` attribute.
".device_enqueue_symbol" string The external symbol name
associated with a kernel.
OpenCL runtime allocates a
global buffer for the symbol
and saves the kernel's address
to it, which is used for
device side enqueueing. Only
available for device side
enqueued kernels.
".kernarg_segment_size" integer Required The size in bytes of
the kernarg segment
that holds the values
of the arguments to
the kernel.
".group_segment_fixed_size" integer Required The amount of group
segment memory
required by a
work-group in
bytes. This does not
include any
dynamically allocated
group segment memory
that may be added
when the kernel is
dispatched.
".private_segment_fixed_size" integer Required The amount of fixed
private address space
memory required for a
work-item in
bytes. If the kernel
uses a dynamic call
stack then additional
space must be added
to this value for the
call stack.
".kernarg_segment_align" integer Required The maximum byte
alignment of
arguments in the
kernarg segment. Must
be a power of 2.
".wavefront_size" integer Required Wavefront size. Must
be a power of 2.
".sgpr_count" integer Required Number of scalar
registers required by a
wavefront for
GFX6-GFX9. A register
is required if it is
used explicitly, or
if a higher numbered
register is used
explicitly. This
includes the special
SGPRs for VCC, Flat
Scratch (GFX7-GFX9)
and XNACK (for
GFX8-GFX9). It does
not include the 16
SGPR added if a trap
handler is
enabled. It is not
rounded up to the
allocation
granularity.
".vgpr_count" integer Required Number of vector
registers required by
each work-item for
GFX6-GFX9. A register
is required if it is
used explicitly, or
if a higher numbered
register is used
explicitly.
".max_flat_workgroup_size" integer Required Maximum flat
work-group size
supported by the
kernel in work-items.
Must be >=1 and
consistent with
ReqdWorkGroupSize if
not 0, 0, 0.
".sgpr_spill_count" integer Number of stores from
a scalar register to
a register allocator
created spill
location.
".vgpr_spill_count" integer Number of stores from
a vector register to
a register allocator
created spill
location.
=================================== ============== ========= ================================
..
.. table:: AMDHSA Code Object V3 Kernel Argument Metadata Map
:name: amdgpu-amdhsa-code-object-kernel-argument-metadata-map-table-v3
====================== ============== ========= ================================
String Key Value Type Required? Description
====================== ============== ========= ================================
".name" string Kernel argument name.
".type_name" string Kernel argument type name.
".size" integer Required Kernel argument size in bytes.
".offset" integer Required Kernel argument offset in
bytes. The offset must be a
multiple of the alignment
required by the argument.
".value_kind" string Required Kernel argument kind that
specifies how to set up the
corresponding argument.
Values include:
"by_value"
The argument is copied
directly into the kernarg.
"global_buffer"
A global address space pointer
to the buffer data is passed
in the kernarg.
"dynamic_shared_pointer"
A group address space pointer
to dynamically allocated LDS
is passed in the kernarg.
"sampler"
A global address space
pointer to a S# is passed in
the kernarg.
"image"
A global address space
pointer to a T# is passed in
the kernarg.
"pipe"
A global address space pointer
to an OpenCL pipe is passed in
the kernarg.
"queue"
A global address space pointer
to an OpenCL device enqueue
queue is passed in the
kernarg.
"hidden_global_offset_x"
The OpenCL grid dispatch
global offset for the X
dimension is passed in the
kernarg.
"hidden_global_offset_y"
The OpenCL grid dispatch
global offset for the Y
dimension is passed in the
kernarg.
"hidden_global_offset_z"
The OpenCL grid dispatch
global offset for the Z
dimension is passed in the
kernarg.
"hidden_none"
An argument that is not used
by the kernel. Space needs to
be left for it, but it does
not need to be set up.
"hidden_printf_buffer"
A global address space pointer
to the runtime printf buffer
is passed in kernarg.
"hidden_hostcall_buffer"
A global address space pointer
to the runtime hostcall buffer
is passed in kernarg.
"hidden_default_queue"
A global address space pointer
to the OpenCL device enqueue
queue that should be used by
the kernel by default is
passed in the kernarg.
"hidden_completion_action"
A global address space pointer
to help link enqueued kernels into
the ancestor tree for determining
when the parent kernel has finished.
"hidden_multigrid_sync_arg"
A global address space pointer for
multi-grid synchronization is
passed in the kernarg.
".value_type" string Required Kernel argument value type. Only
present if ".value_kind" is
"by_value". For vector data
types, the value is for the
element type. Values include:
- "struct"
- "i8"
- "u8"
- "i16"
- "u16"
- "f16"
- "i32"
- "u32"
- "f32"
- "i64"
- "u64"
- "f64"
.. TODO::
How can it be determined if a
vector type, and what size
vector?
".pointee_align" integer Alignment in bytes of pointee
type for pointer type kernel
argument. Must be a power
of 2. Only present if
".value_kind" is
"dynamic_shared_pointer".
".address_space" string Kernel argument address space
qualifier. Only present if
".value_kind" is "global_buffer" or
"dynamic_shared_pointer". Values
are:
- "private"
- "global"
- "constant"
- "local"
- "generic"
- "region"
.. TODO::
Is "global_buffer" only "global"
or "constant"? Is
"dynamic_shared_pointer" always
"local"? Can HCC allow "generic"?
How can "private" or "region"
ever happen?
".access" string Kernel argument access
qualifier. Only present if
".value_kind" is "image" or
"pipe". Values
are:
- "read_only"
- "write_only"
- "read_write"
.. TODO::
Does this apply to
"global_buffer"?
".actual_access" string The actual memory accesses
performed by the kernel on the
kernel argument. Only present if
".value_kind" is "global_buffer",
"image", or "pipe". This may be
more restrictive than indicated
by ".access" to reflect what the
kernel actual does. If not
present then the runtime must
assume what is implied by
".access" and ".is_const" . Values
are:
- "read_only"
- "write_only"
- "read_write"
".is_const" boolean Indicates if the kernel argument
is const qualified. Only present
if ".value_kind" is
"global_buffer".
".is_restrict" boolean Indicates if the kernel argument
is restrict qualified. Only
present if ".value_kind" is
"global_buffer".
".is_volatile" boolean Indicates if the kernel argument
is volatile qualified. Only
present if ".value_kind" is
"global_buffer".
".is_pipe" boolean Indicates if the kernel argument
is pipe qualified. Only present
if ".value_kind" is "pipe".
.. TODO::
Can "global_buffer" be pipe
qualified?
====================== ============== ========= ================================
..
Kernel Dispatch
~~~~~~~~~~~~~~~
The HSA architected queuing language (AQL) defines a user space memory
interface that can be used to control the dispatch of kernels, in an agent
independent way. An agent can have zero or more AQL queues created for it using
the ROCm runtime, in which AQL packets (all of which are 64 bytes) can be
placed. See the *HSA Platform System Architecture Specification* [HSA]_ for the
AQL queue mechanics and packet layouts.
The packet processor of a kernel agent is responsible for detecting and
dispatching HSA kernels from the AQL queues associated with it. For AMD GPUs the
packet processor is implemented by the hardware command processor (CP),
asynchronous dispatch controller (ADC) and shader processor input controller
(SPI).
The ROCm runtime can be used to allocate an AQL queue object. It uses the kernel
mode driver to initialize and register the AQL queue with CP.
To dispatch a kernel the following actions are performed. This can occur in the
CPU host program, or from an HSA kernel executing on a GPU.
1. A pointer to an AQL queue for the kernel agent on which the kernel is to be
executed is obtained.
2. A pointer to the kernel descriptor (see
:ref:`amdgpu-amdhsa-kernel-descriptor`) of the kernel to execute is obtained.
It must be for a kernel that is contained in a code object that that was
loaded by the ROCm runtime on the kernel agent with which the AQL queue is
associated.
3. Space is allocated for the kernel arguments using the ROCm runtime allocator
for a memory region with the kernarg property for the kernel agent that will
execute the kernel. It must be at least 16 byte aligned.
4. Kernel argument values are assigned to the kernel argument memory
allocation. The layout is defined in the *HSA Programmer's Language
Reference* [HSA]_. For AMDGPU the kernel execution directly accesses the
kernel argument memory in the same way constant memory is accessed. (Note
that the HSA specification allows an implementation to copy the kernel
argument contents to another location that is accessed by the kernel.)
5. An AQL kernel dispatch packet is created on the AQL queue. The ROCm runtime
api uses 64-bit atomic operations to reserve space in the AQL queue for the
packet. The packet must be set up, and the final write must use an atomic
store release to set the packet kind to ensure the packet contents are
visible to the kernel agent. AQL defines a doorbell signal mechanism to
notify the kernel agent that the AQL queue has been updated. These rules, and
the layout of the AQL queue and kernel dispatch packet is defined in the *HSA
System Architecture Specification* [HSA]_.
6. A kernel dispatch packet includes information about the actual dispatch,
such as grid and work-group size, together with information from the code
object about the kernel, such as segment sizes. The ROCm runtime queries on
the kernel symbol can be used to obtain the code object values which are
recorded in the :ref:`amdgpu-amdhsa-code-object-metadata`.
7. CP executes micro-code and is responsible for detecting and setting up the
GPU to execute the wavefronts of a kernel dispatch.
8. CP ensures that when the a wavefront starts executing the kernel machine
code, the scalar general purpose registers (SGPR) and vector general purpose
registers (VGPR) are set up as required by the machine code. The required
setup is defined in the :ref:`amdgpu-amdhsa-kernel-descriptor`. The initial
register state is defined in
:ref:`amdgpu-amdhsa-initial-kernel-execution-state`.
9. The prolog of the kernel machine code (see
:ref:`amdgpu-amdhsa-kernel-prolog`) sets up the machine state as necessary
before continuing executing the machine code that corresponds to the kernel.
10. When the kernel dispatch has completed execution, CP signals the completion
signal specified in the kernel dispatch packet if not 0.
Image and Samplers
~~~~~~~~~~~~~~~~~~
Image and sample handles created by the ROCm runtime are 64-bit addresses of a
hardware 32 byte V# and 48 byte S# object respectively. In order to support the
HSA ``query_sampler`` operations two extra dwords are used to store the HSA BRIG
enumeration values for the queries that are not trivially deducible from the S#
representation.
HSA Signals
~~~~~~~~~~~
HSA signal handles created by the ROCm runtime are 64-bit addresses of a
structure allocated in memory accessible from both the CPU and GPU. The
structure is defined by the ROCm runtime and subject to change between releases
(see [AMD-ROCm-github]_).
.. _amdgpu-amdhsa-hsa-aql-queue:
HSA AQL Queue
~~~~~~~~~~~~~
The HSA AQL queue structure is defined by the ROCm runtime and subject to change
between releases (see [AMD-ROCm-github]_). For some processors it contains
fields needed to implement certain language features such as the flat address
aperture bases. It also contains fields used by CP such as managing the
allocation of scratch memory.
.. _amdgpu-amdhsa-kernel-descriptor:
Kernel Descriptor
~~~~~~~~~~~~~~~~~
A kernel descriptor consists of the information needed by CP to initiate the
execution of a kernel, including the entry point address of the machine code
that implements the kernel.
Kernel Descriptor for GFX6-GFX10
++++++++++++++++++++++++++++++++
CP microcode requires the Kernel descriptor to be allocated on 64 byte
alignment.
.. table:: Kernel Descriptor for GFX6-GFX10
:name: amdgpu-amdhsa-kernel-descriptor-gfx6-gfx10-table
======= ======= =============================== ============================
Bits Size Field Name Description
======= ======= =============================== ============================
31:0 4 bytes GROUP_SEGMENT_FIXED_SIZE The amount of fixed local
address space memory
required for a work-group
in bytes. This does not
include any dynamically
allocated local address
space memory that may be
added when the kernel is
dispatched.
63:32 4 bytes PRIVATE_SEGMENT_FIXED_SIZE The amount of fixed
private address space
memory required for a
work-item in bytes. If
is_dynamic_callstack is 1
then additional space must
be added to this value for
the call stack.
127:64 8 bytes Reserved, must be 0.
191:128 8 bytes KERNEL_CODE_ENTRY_BYTE_OFFSET Byte offset (possibly
negative) from base
address of kernel
descriptor to kernel's
entry point instruction
which must be 256 byte
aligned.
351:272 20 Reserved, must be 0.
bytes
383:352 4 bytes COMPUTE_PGM_RSRC3 GFX6-9
Reserved, must be 0.
GFX10
Compute Shader (CS)
program settings used by
CP to set up
``COMPUTE_PGM_RSRC3``
configuration
register. See
:ref:`amdgpu-amdhsa-compute_pgm_rsrc3-gfx10-table`.
415:384 4 bytes COMPUTE_PGM_RSRC1 Compute Shader (CS)
program settings used by
CP to set up
``COMPUTE_PGM_RSRC1``
configuration
register. See
:ref:`amdgpu-amdhsa-compute_pgm_rsrc1-gfx6-gfx10-table`.
447:416 4 bytes COMPUTE_PGM_RSRC2 Compute Shader (CS)
program settings used by
CP to set up
``COMPUTE_PGM_RSRC2``
configuration
register. See
:ref:`amdgpu-amdhsa-compute_pgm_rsrc2-gfx6-gfx10-table`.
448 1 bit ENABLE_SGPR_PRIVATE_SEGMENT Enable the setup of the
_BUFFER SGPR user data registers
(see
:ref:`amdgpu-amdhsa-initial-kernel-execution-state`).
The total number of SGPR
user data registers
requested must not exceed
16 and match value in
``compute_pgm_rsrc2.user_sgpr.user_sgpr_count``.
Any requests beyond 16
will be ignored.
449 1 bit ENABLE_SGPR_DISPATCH_PTR *see above*
450 1 bit ENABLE_SGPR_QUEUE_PTR *see above*
451 1 bit ENABLE_SGPR_KERNARG_SEGMENT_PTR *see above*
452 1 bit ENABLE_SGPR_DISPATCH_ID *see above*
453 1 bit ENABLE_SGPR_FLAT_SCRATCH_INIT *see above*
454 1 bit ENABLE_SGPR_PRIVATE_SEGMENT *see above*
_SIZE
457:455 3 bits Reserved, must be 0.
458 1 bit ENABLE_WAVEFRONT_SIZE32 GFX6-9
Reserved, must be 0.
GFX10
- If 0 execute in
wavefront size 64 mode.
- If 1 execute in
native wavefront size
32 mode.
463:459 5 bits Reserved, must be 0.
511:464 6 bytes Reserved, must be 0.
512 **Total size 64 bytes.**
======= ====================================================================
..
.. table:: compute_pgm_rsrc1 for GFX6-GFX10
:name: amdgpu-amdhsa-compute_pgm_rsrc1-gfx6-gfx10-table
======= ======= =============================== ===========================================================================
Bits Size Field Name Description
======= ======= =============================== ===========================================================================
5:0 6 bits GRANULATED_WORKITEM_VGPR_COUNT Number of vector register
blocks used by each work-item;
granularity is device
specific:
GFX6-GFX9
- vgprs_used 0..256
- max(0, ceil(vgprs_used / 4) - 1)
GFX10 (wavefront size 64)
- max_vgpr 1..256
- max(0, ceil(vgprs_used / 4) - 1)
GFX10 (wavefront size 32)
- max_vgpr 1..256
- max(0, ceil(vgprs_used / 8) - 1)
Where vgprs_used is defined
as the highest VGPR number
explicitly referenced plus
one.
Used by CP to set up
``COMPUTE_PGM_RSRC1.VGPRS``.
The
:ref:`amdgpu-assembler`
calculates this
automatically for the
selected processor from
values provided to the
`.amdhsa_kernel` directive
by the
`.amdhsa_next_free_vgpr`
nested directive (see
:ref:`amdhsa-kernel-directives-table`).
9:6 4 bits GRANULATED_WAVEFRONT_SGPR_COUNT Number of scalar register
blocks used by a wavefront;
granularity is device
specific:
GFX6-GFX8
- sgprs_used 0..112
- max(0, ceil(sgprs_used / 8) - 1)
GFX9
- sgprs_used 0..112
- 2 * max(0, ceil(sgprs_used / 16) - 1)
GFX10
Reserved, must be 0.
(128 SGPRs always
allocated.)
Where sgprs_used is
defined as the highest
SGPR number explicitly
referenced plus one, plus
a target-specific number
of additional special
SGPRs for VCC,
FLAT_SCRATCH (GFX7+) and
XNACK_MASK (GFX8+), and
any additional
target-specific
limitations. It does not
include the 16 SGPRs added
if a trap handler is
enabled.
The target-specific
limitations and special
SGPR layout are defined in
the hardware
documentation, which can
be found in the
:ref:`amdgpu-processors`
table.
Used by CP to set up
``COMPUTE_PGM_RSRC1.SGPRS``.
The
:ref:`amdgpu-assembler`
calculates this
automatically for the
selected processor from
values provided to the
`.amdhsa_kernel` directive
by the
`.amdhsa_next_free_sgpr`
and `.amdhsa_reserve_*`
nested directives (see
:ref:`amdhsa-kernel-directives-table`).
11:10 2 bits PRIORITY Must be 0.
Start executing wavefront
at the specified priority.
CP is responsible for
filling in
``COMPUTE_PGM_RSRC1.PRIORITY``.
13:12 2 bits FLOAT_ROUND_MODE_32 Wavefront starts execution
with specified rounding
mode for single (32
bit) floating point
precision floating point
operations.
Floating point rounding
mode values are defined in
:ref:`amdgpu-amdhsa-floating-point-rounding-mode-enumeration-values-table`.
Used by CP to set up
``COMPUTE_PGM_RSRC1.FLOAT_MODE``.
15:14 2 bits FLOAT_ROUND_MODE_16_64 Wavefront starts execution
with specified rounding
denorm mode for half/double (16
and 64-bit) floating point
precision floating point
operations.
Floating point rounding
mode values are defined in
:ref:`amdgpu-amdhsa-floating-point-rounding-mode-enumeration-values-table`.
Used by CP to set up
``COMPUTE_PGM_RSRC1.FLOAT_MODE``.
17:16 2 bits FLOAT_DENORM_MODE_32 Wavefront starts execution
with specified denorm mode
for single (32
bit) floating point
precision floating point
operations.
Floating point denorm mode
values are defined in
:ref:`amdgpu-amdhsa-floating-point-denorm-mode-enumeration-values-table`.
Used by CP to set up
``COMPUTE_PGM_RSRC1.FLOAT_MODE``.
19:18 2 bits FLOAT_DENORM_MODE_16_64 Wavefront starts execution
with specified denorm mode
for half/double (16
and 64-bit) floating point
precision floating point
operations.
Floating point denorm mode
values are defined in
:ref:`amdgpu-amdhsa-floating-point-denorm-mode-enumeration-values-table`.
Used by CP to set up
``COMPUTE_PGM_RSRC1.FLOAT_MODE``.
20 1 bit PRIV Must be 0.
Start executing wavefront
in privilege trap handler
mode.
CP is responsible for
filling in
``COMPUTE_PGM_RSRC1.PRIV``.
21 1 bit ENABLE_DX10_CLAMP Wavefront starts execution
with DX10 clamp mode
enabled. Used by the vector
ALU to force DX10 style
treatment of NaN's (when
set, clamp NaN to zero,
otherwise pass NaN
through).
Used by CP to set up
``COMPUTE_PGM_RSRC1.DX10_CLAMP``.
22 1 bit DEBUG_MODE Must be 0.
Start executing wavefront
in single step mode.
CP is responsible for
filling in
``COMPUTE_PGM_RSRC1.DEBUG_MODE``.
23 1 bit ENABLE_IEEE_MODE Wavefront starts execution
with IEEE mode
enabled. Floating point
opcodes that support
exception flag gathering
will quiet and propagate
signaling-NaN inputs per
IEEE 754-2008. Min_dx10 and
max_dx10 become IEEE
754-2008 compliant due to
signaling-NaN propagation
and quieting.
Used by CP to set up
``COMPUTE_PGM_RSRC1.IEEE_MODE``.
24 1 bit BULKY Must be 0.
Only one work-group allowed
to execute on a compute
unit.
CP is responsible for
filling in
``COMPUTE_PGM_RSRC1.BULKY``.
25 1 bit CDBG_USER Must be 0.
Flag that can be used to
control debugging code.
CP is responsible for
filling in
``COMPUTE_PGM_RSRC1.CDBG_USER``.
26 1 bit FP16_OVFL GFX6-GFX8
Reserved, must be 0.
GFX9-GFX10
Wavefront starts execution
with specified fp16 overflow
mode.
- If 0, fp16 overflow generates
+/-INF values.
- If 1, fp16 overflow that is the
result of an +/-INF input value
or divide by 0 produces a +/-INF,
otherwise clamps computed
overflow to +/-MAX_FP16 as
appropriate.
Used by CP to set up
``COMPUTE_PGM_RSRC1.FP16_OVFL``.
28:27 2 bits Reserved, must be 0.
29 1 bit WGP_MODE GFX6-GFX9
Reserved, must be 0.
GFX10
- If 0 execute work-groups in
CU wavefront execution mode.
- If 1 execute work-groups on
in WGP wavefront execution mode.
See :ref:`amdgpu-amdhsa-memory-model`.
Used by CP to set up
``COMPUTE_PGM_RSRC1.WGP_MODE``.
30 1 bit MEM_ORDERED GFX6-9
Reserved, must be 0.
GFX10
Controls the behavior of the
waitcnt's vmcnt and vscnt
counters.
- If 0 vmcnt reports completion
of load and atomic with return
out of order with sample
instructions, and the vscnt
reports the completion of
store and atomic without
return in order.
- If 1 vmcnt reports completion
of load, atomic with return
and sample instructions in
order, and the vscnt reports
the completion of store and
atomic without return in order.
Used by CP to set up
``COMPUTE_PGM_RSRC1.MEM_ORDERED``.
31 1 bit FWD_PROGRESS GFX6-9
Reserved, must be 0.
GFX10
- If 0 execute SIMD wavefronts
using oldest first policy.
- If 1 execute SIMD wavefronts to
ensure wavefronts will make some
forward progress.
Used by CP to set up
``COMPUTE_PGM_RSRC1.FWD_PROGRESS``.
32 **Total size 4 bytes**
======= ===================================================================================================================
..
.. table:: compute_pgm_rsrc2 for GFX6-GFX10
:name: amdgpu-amdhsa-compute_pgm_rsrc2-gfx6-gfx10-table
======= ======= =============================== ===========================================================================
Bits Size Field Name Description
======= ======= =============================== ===========================================================================
0 1 bit ENABLE_SGPR_PRIVATE_SEGMENT Enable the setup of the
_WAVEFRONT_OFFSET SGPR wavefront scratch offset
system register (see
:ref:`amdgpu-amdhsa-initial-kernel-execution-state`).
Used by CP to set up
``COMPUTE_PGM_RSRC2.SCRATCH_EN``.
5:1 5 bits USER_SGPR_COUNT The total number of SGPR
user data registers
requested. This number must
match the number of user
data registers enabled.
Used by CP to set up
``COMPUTE_PGM_RSRC2.USER_SGPR``.
6 1 bit ENABLE_TRAP_HANDLER Must be 0.
This bit represents
``COMPUTE_PGM_RSRC2.TRAP_PRESENT``,
which is set by the CP if
the runtime has installed a
trap handler.
7 1 bit ENABLE_SGPR_WORKGROUP_ID_X Enable the setup of the
system SGPR register for
the work-group id in the X
dimension (see
:ref:`amdgpu-amdhsa-initial-kernel-execution-state`).
Used by CP to set up
``COMPUTE_PGM_RSRC2.TGID_X_EN``.
8 1 bit ENABLE_SGPR_WORKGROUP_ID_Y Enable the setup of the
system SGPR register for
the work-group id in the Y
dimension (see
:ref:`amdgpu-amdhsa-initial-kernel-execution-state`).
Used by CP to set up
``COMPUTE_PGM_RSRC2.TGID_Y_EN``.
9 1 bit ENABLE_SGPR_WORKGROUP_ID_Z Enable the setup of the
system SGPR register for
the work-group id in the Z
dimension (see
:ref:`amdgpu-amdhsa-initial-kernel-execution-state`).
Used by CP to set up
``COMPUTE_PGM_RSRC2.TGID_Z_EN``.
10 1 bit ENABLE_SGPR_WORKGROUP_INFO Enable the setup of the
system SGPR register for
work-group information (see
:ref:`amdgpu-amdhsa-initial-kernel-execution-state`).
Used by CP to set up
``COMPUTE_PGM_RSRC2.TGID_SIZE_EN``.
12:11 2 bits ENABLE_VGPR_WORKITEM_ID Enable the setup of the
VGPR system registers used
for the work-item ID.
:ref:`amdgpu-amdhsa-system-vgpr-work-item-id-enumeration-values-table`
defines the values.
Used by CP to set up
``COMPUTE_PGM_RSRC2.TIDIG_CMP_CNT``.
13 1 bit ENABLE_EXCEPTION_ADDRESS_WATCH Must be 0.
Wavefront starts execution
with address watch
exceptions enabled which
are generated when L1 has
witnessed a thread access
an *address of
interest*.
CP is responsible for
filling in the address
watch bit in
``COMPUTE_PGM_RSRC2.EXCP_EN_MSB``
according to what the
runtime requests.
14 1 bit ENABLE_EXCEPTION_MEMORY Must be 0.
Wavefront starts execution
with memory violation
exceptions exceptions
enabled which are generated
when a memory violation has
occurred for this wavefront from
L1 or LDS
(write-to-read-only-memory,
mis-aligned atomic, LDS
address out of range,
illegal address, etc.).
CP sets the memory
violation bit in
``COMPUTE_PGM_RSRC2.EXCP_EN_MSB``
according to what the
runtime requests.
23:15 9 bits GRANULATED_LDS_SIZE Must be 0.
CP uses the rounded value
from the dispatch packet,
not this value, as the
dispatch may contain
dynamically allocated group
segment memory. CP writes
directly to
``COMPUTE_PGM_RSRC2.LDS_SIZE``.
Amount of group segment
(LDS) to allocate for each
work-group. Granularity is
device specific:
GFX6:
roundup(lds-size / (64 * 4))
GFX7-GFX10:
roundup(lds-size / (128 * 4))
24 1 bit ENABLE_EXCEPTION_IEEE_754_FP Wavefront starts execution
_INVALID_OPERATION with specified exceptions
enabled.
Used by CP to set up
``COMPUTE_PGM_RSRC2.EXCP_EN``
(set from bits 0..6).
IEEE 754 FP Invalid
Operation
25 1 bit ENABLE_EXCEPTION_FP_DENORMAL FP Denormal one or more
_SOURCE input operands is a
denormal number
26 1 bit ENABLE_EXCEPTION_IEEE_754_FP IEEE 754 FP Division by
_DIVISION_BY_ZERO Zero
27 1 bit ENABLE_EXCEPTION_IEEE_754_FP IEEE 754 FP FP Overflow
_OVERFLOW
28 1 bit ENABLE_EXCEPTION_IEEE_754_FP IEEE 754 FP Underflow
_UNDERFLOW
29 1 bit ENABLE_EXCEPTION_IEEE_754_FP IEEE 754 FP Inexact
_INEXACT
30 1 bit ENABLE_EXCEPTION_INT_DIVIDE_BY Integer Division by Zero
_ZERO (rcp_iflag_f32 instruction
only)
31 1 bit Reserved, must be 0.
32 **Total size 4 bytes.**
======= ===================================================================================================================
..
.. table:: compute_pgm_rsrc3 for GFX10
:name: amdgpu-amdhsa-compute_pgm_rsrc3-gfx10-table
======= ======= =============================== ===========================================================================
Bits Size Field Name Description
======= ======= =============================== ===========================================================================
3:0 4 bits SHARED_VGPR_COUNT Number of shared VGPRs for wavefront size 64. Granularity 8. Value 0-120.
compute_pgm_rsrc1.vgprs + shared_vgpr_cnt cannot exceed 64.
31:4 28 Reserved, must be 0.
bits
32 **Total size 4 bytes.**
======= ===================================================================================================================
..
.. table:: Floating Point Rounding Mode Enumeration Values
:name: amdgpu-amdhsa-floating-point-rounding-mode-enumeration-values-table
====================================== ===== ==============================
Enumeration Name Value Description
====================================== ===== ==============================
FLOAT_ROUND_MODE_NEAR_EVEN 0 Round Ties To Even
FLOAT_ROUND_MODE_PLUS_INFINITY 1 Round Toward +infinity
FLOAT_ROUND_MODE_MINUS_INFINITY 2 Round Toward -infinity
FLOAT_ROUND_MODE_ZERO 3 Round Toward 0
====================================== ===== ==============================
..
.. table:: Floating Point Denorm Mode Enumeration Values
:name: amdgpu-amdhsa-floating-point-denorm-mode-enumeration-values-table
====================================== ===== ==============================
Enumeration Name Value Description
====================================== ===== ==============================
FLOAT_DENORM_MODE_FLUSH_SRC_DST 0 Flush Source and Destination
Denorms
FLOAT_DENORM_MODE_FLUSH_DST 1 Flush Output Denorms
FLOAT_DENORM_MODE_FLUSH_SRC 2 Flush Source Denorms
FLOAT_DENORM_MODE_FLUSH_NONE 3 No Flush
====================================== ===== ==============================
..
.. table:: System VGPR Work-Item ID Enumeration Values
:name: amdgpu-amdhsa-system-vgpr-work-item-id-enumeration-values-table
======================================== ===== ============================
Enumeration Name Value Description
======================================== ===== ============================
SYSTEM_VGPR_WORKITEM_ID_X 0 Set work-item X dimension
ID.
SYSTEM_VGPR_WORKITEM_ID_X_Y 1 Set work-item X and Y
dimensions ID.
SYSTEM_VGPR_WORKITEM_ID_X_Y_Z 2 Set work-item X, Y and Z
dimensions ID.
SYSTEM_VGPR_WORKITEM_ID_UNDEFINED 3 Undefined.
======================================== ===== ============================
.. _amdgpu-amdhsa-initial-kernel-execution-state:
Initial Kernel Execution State
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This section defines the register state that will be set up by the packet
processor prior to the start of execution of every wavefront. This is limited by
the constraints of the hardware controllers of CP/ADC/SPI.
The order of the SGPR registers is defined, but the compiler can specify which
ones are actually setup in the kernel descriptor using the ``enable_sgpr_*`` bit
fields (see :ref:`amdgpu-amdhsa-kernel-descriptor`). The register numbers used
for enabled registers are dense starting at SGPR0: the first enabled register is
SGPR0, the next enabled register is SGPR1 etc.; disabled registers do not have
an SGPR number.
The initial SGPRs comprise up to 16 User SRGPs that are set by CP and apply to
all wavefronts of the grid. It is possible to specify more than 16 User SGPRs
using the ``enable_sgpr_*`` bit fields, in which case only the first 16 are
actually initialized. These are then immediately followed by the System SGPRs
that are set up by ADC/SPI and can have different values for each wavefront of
the grid dispatch.
SGPR register initial state is defined in
:ref:`amdgpu-amdhsa-sgpr-register-set-up-order-table`.
.. table:: SGPR Register Set Up Order
:name: amdgpu-amdhsa-sgpr-register-set-up-order-table
========== ========================== ====== ==============================
SGPR Order Name Number Description
(kernel descriptor enable of
field) SGPRs
========== ========================== ====== ==============================
First Private Segment Buffer 4 V# that can be used, together
(enable_sgpr_private with Scratch Wavefront Offset
_segment_buffer) as an offset, to access the
private address space using a
segment address.
CP uses the value provided by
the runtime.
then Dispatch Ptr 2 64-bit address of AQL dispatch
(enable_sgpr_dispatch_ptr) packet for kernel dispatch
actually executing.
then Queue Ptr 2 64-bit address of amd_queue_t
(enable_sgpr_queue_ptr) object for AQL queue on which
the dispatch packet was
queued.
then Kernarg Segment Ptr 2 64-bit address of Kernarg
(enable_sgpr_kernarg segment. This is directly
_segment_ptr) copied from the
kernarg_address in the kernel
dispatch packet.
Having CP load it once avoids
loading it at the beginning of
every wavefront.
then Dispatch Id 2 64-bit Dispatch ID of the
(enable_sgpr_dispatch_id) dispatch packet being
executed.
then Flat Scratch Init 2 This is 2 SGPRs:
(enable_sgpr_flat_scratch
_init) GFX6
Not supported.
GFX7-GFX8
The first SGPR is a 32-bit
byte offset from
``SH_HIDDEN_PRIVATE_BASE_VIMID``
to per SPI base of memory
for scratch for the queue
executing the kernel
dispatch. CP obtains this
from the runtime. (The
Scratch Segment Buffer base
address is
``SH_HIDDEN_PRIVATE_BASE_VIMID``
plus this offset.) The value
of Scratch Wavefront Offset must
be added to this offset by
the kernel machine code,
right shifted by 8, and
moved to the FLAT_SCRATCH_HI
SGPR register.
FLAT_SCRATCH_HI corresponds
to SGPRn-4 on GFX7, and
SGPRn-6 on GFX8 (where SGPRn
is the highest numbered SGPR
allocated to the wavefront).
FLAT_SCRATCH_HI is
multiplied by 256 (as it is
in units of 256 bytes) and
added to
``SH_HIDDEN_PRIVATE_BASE_VIMID``
to calculate the per wavefront
FLAT SCRATCH BASE in flat
memory instructions that
access the scratch
aperture.
The second SGPR is 32-bit
byte size of a single
work-item's scratch memory
usage. CP obtains this from
the runtime, and it is
always a multiple of DWORD.
CP checks that the value in
the kernel dispatch packet
Private Segment Byte Size is
not larger, and requests the
runtime to increase the
queue's scratch size if
necessary. The kernel code
must move it to
FLAT_SCRATCH_LO which is
SGPRn-3 on GFX7 and SGPRn-5
on GFX8. FLAT_SCRATCH_LO is
used as the FLAT SCRATCH
SIZE in flat memory
instructions. Having CP load
it once avoids loading it at
the beginning of every
wavefront.
GFX9-GFX10
This is the
64-bit base address of the
per SPI scratch backing
memory managed by SPI for
the queue executing the
kernel dispatch. CP obtains
this from the runtime (and
divides it if there are
multiple Shader Arrays each
with its own SPI). The value
of Scratch Wavefront Offset must
be added by the kernel
machine code and the result
moved to the FLAT_SCRATCH
SGPR which is SGPRn-6 and
SGPRn-5. It is used as the
FLAT SCRATCH BASE in flat
memory instructions.
then Private Segment Size 1 The 32-bit byte size of a
(enable_sgpr_private single
work-item's
scratch_segment_size) memory
allocation. This is the
value from the kernel
dispatch packet Private
Segment Byte Size rounded up
by CP to a multiple of
DWORD.
Having CP load it once avoids
loading it at the beginning of
every wavefront.
This is not used for
GFX7-GFX8 since it is the same
value as the second SGPR of
Flat Scratch Init. However, it
may be needed for GFX9-GFX10 which
changes the meaning of the
Flat Scratch Init value.
then Grid Work-Group Count X 1 32-bit count of the number of
(enable_sgpr_grid work-groups in the X dimension
_workgroup_count_X) for the grid being
executed. Computed from the
fields in the kernel dispatch
packet as ((grid_size.x +
workgroup_size.x - 1) /
workgroup_size.x).
then Grid Work-Group Count Y 1 32-bit count of the number of
(enable_sgpr_grid work-groups in the Y dimension
_workgroup_count_Y && for the grid being
less than 16 previous executed. Computed from the
SGPRs) fields in the kernel dispatch
packet as ((grid_size.y +
workgroup_size.y - 1) /
workgroupSize.y).
Only initialized if <16
previous SGPRs initialized.
then Grid Work-Group Count Z 1 32-bit count of the number of
(enable_sgpr_grid work-groups in the Z dimension
_workgroup_count_Z && for the grid being
less than 16 previous executed. Computed from the
SGPRs) fields in the kernel dispatch
packet as ((grid_size.z +
workgroup_size.z - 1) /
workgroupSize.z).
Only initialized if <16
previous SGPRs initialized.
then Work-Group Id X 1 32-bit work-group id in X
(enable_sgpr_workgroup_id dimension of grid for
_X) wavefront.
then Work-Group Id Y 1 32-bit work-group id in Y
(enable_sgpr_workgroup_id dimension of grid for
_Y) wavefront.
then Work-Group Id Z 1 32-bit work-group id in Z
(enable_sgpr_workgroup_id dimension of grid for
_Z) wavefront.
then Work-Group Info 1 {first_wavefront, 14'b0000,
(enable_sgpr_workgroup ordered_append_term[10:0],
_info) threadgroup_size_in_wavefronts[5:0]}
then Scratch Wavefront Offset 1 32-bit byte offset from base
(enable_sgpr_private of scratch base of queue
_segment_wavefront_offset) executing the kernel
dispatch. Must be used as an
offset with Private
segment address when using
Scratch Segment Buffer. It
must be used to set up FLAT
SCRATCH for flat addressing
(see
:ref:`amdgpu-amdhsa-kernel-prolog-flat-scratch`).
========== ========================== ====== ==============================
The order of the VGPR registers is defined, but the compiler can specify which
ones are actually setup in the kernel descriptor using the ``enable_vgpr*`` bit
fields (see :ref:`amdgpu-amdhsa-kernel-descriptor`). The register numbers used
for enabled registers are dense starting at VGPR0: the first enabled register is
VGPR0, the next enabled register is VGPR1 etc.; disabled registers do not have a
VGPR number.
VGPR register initial state is defined in
:ref:`amdgpu-amdhsa-vgpr-register-set-up-order-table`.
.. table:: VGPR Register Set Up Order
:name: amdgpu-amdhsa-vgpr-register-set-up-order-table
========== ========================== ====== ==============================
VGPR Order Name Number Description
(kernel descriptor enable of
field) VGPRs
========== ========================== ====== ==============================
First Work-Item Id X 1 32-bit work item id in X
(Always initialized) dimension of work-group for
wavefront lane.
then Work-Item Id Y 1 32-bit work item id in Y
(enable_vgpr_workitem_id dimension of work-group for
> 0) wavefront lane.
then Work-Item Id Z 1 32-bit work item id in Z
(enable_vgpr_workitem_id dimension of work-group for
> 1) wavefront lane.
========== ========================== ====== ==============================
The setting of registers is done by GPU CP/ADC/SPI hardware as follows:
1. SGPRs before the Work-Group Ids are set by CP using the 16 User Data
registers.
2. Work-group Id registers X, Y, Z are set by ADC which supports any
combination including none.
3. Scratch Wavefront Offset is set by SPI in a per wavefront basis which is why
its value cannot included with the flat scratch init value which is per
queue.
4. The VGPRs are set by SPI which only supports specifying either (X), (X, Y)
or (X, Y, Z).
Flat Scratch register pair are adjacent SGRRs so they can be moved as a 64-bit
value to the hardware required SGPRn-3 and SGPRn-4 respectively.
The global segment can be accessed either using buffer instructions (GFX6 which
has V# 64-bit address support), flat instructions (GFX7-GFX10), or global
instructions (GFX9-GFX10).
If buffer operations are used then the compiler can generate a V# with the
following properties:
* base address of 0
* no swizzle
* ATC: 1 if IOMMU present (such as APU)
* ptr64: 1
* MTYPE set to support memory coherence that matches the runtime (such as CC for
APU and NC for dGPU).
.. _amdgpu-amdhsa-kernel-prolog:
Kernel Prolog
~~~~~~~~~~~~~
The compiler performs initialization in the kernel prologue depending on the
target and information about things like stack usage in the kernel and called
functions. Some of this initialization requires the compiler to request certain
User and System SGPRs be present in the
:ref:`amdgpu-amdhsa-initial-kernel-execution-state` via the
:ref:`amdgpu-amdhsa-kernel-descriptor`.
.. _amdgpu-amdhsa-kernel-prolog-cfi:
CFI
+++
1. The CFI return address is undefined.
2. The CFI CFA is defined using an expression which evaluates to a memory
location description for the private segment address ``0``.
.. _amdgpu-amdhsa-kernel-prolog-m0:
M0
++
GFX6-GFX8
The M0 register must be initialized with a value at least the total LDS size
if the kernel may access LDS via DS or flat operations. Total LDS size is
available in dispatch packet. For M0, it is also possible to use maximum
possible value of LDS for given target (0x7FFF for GFX6 and 0xFFFF for
GFX7-GFX8).
GFX9-GFX10
The M0 register is not used for range checking LDS accesses and so does not
need to be initialized in the prolog.
.. _amdgpu-amdhsa-kernel-prolog-stack-pointer:
Stack Pointer
+++++++++++++
If the kernel has function calls it must set up the ABI stack pointer described
in :ref:`amdgpu-amdhsa-function-call-convention-non-kernel-functions` by
setting SGPR32 to the the unswizzled scratch offset of the address past the
last local allocation.
.. _amdgpu-amdhsa-kernel-prolog-frame-pointer:
Frame Pointer
+++++++++++++
If the kernel needs a frame pointer for the reasons defined in
``SIFrameLowering`` then SGPR33 is used and is always set to ``0`` in the
kernel prolog. If a frame pointer is not required then all uses of the frame
pointer are replaced with immediate ``0`` offsets.
.. _amdgpu-amdhsa-kernel-prolog-flat-scratch:
Flat Scratch
++++++++++++
If the kernel or any function it calls may use flat operations to access
scratch memory, the prolog code must set up the FLAT_SCRATCH register pair
(FLAT_SCRATCH_LO/FLAT_SCRATCH_HI which are in SGPRn-4/SGPRn-3). Initialization
uses Flat Scratch Init and Scratch Wavefront Offset SGPR registers (see
:ref:`amdgpu-amdhsa-initial-kernel-execution-state`):
GFX6
Flat scratch is not supported.
GFX7-GFX8
1. The low word of Flat Scratch Init is 32-bit byte offset from
``SH_HIDDEN_PRIVATE_BASE_VIMID`` to the base of scratch backing memory
being managed by SPI for the queue executing the kernel dispatch. This is
the same value used in the Scratch Segment Buffer V# base address. The
prolog must add the value of Scratch Wavefront Offset to get the
wavefront's byte scratch backing memory offset from
``SH_HIDDEN_PRIVATE_BASE_VIMID``. Since FLAT_SCRATCH_LO is in units of 256
bytes, the offset must be right shifted by 8 before moving into
FLAT_SCRATCH_LO.
2. The second word of Flat Scratch Init is 32-bit byte size of a single
work-items scratch memory usage. This is directly loaded from the kernel
dispatch packet Private Segment Byte Size and rounded up to a multiple of
DWORD. Having CP load it once avoids loading it at the beginning of every
wavefront. The prolog must move it to FLAT_SCRATCH_LO for use as FLAT
SCRATCH SIZE.
GFX9-GFX10
The Flat Scratch Init is the 64-bit address of the base of scratch backing
memory being managed by SPI for the queue executing the kernel dispatch. The
prolog must add the value of Scratch Wavefront Offset and moved to the
FLAT_SCRATCH pair for use as the flat scratch base in flat memory
instructions.
.. _amdgpu-amdhsa-kernel-prolog-private-segment-buffer:
Private Segment Buffer
++++++++++++++++++++++
A set of four SGPRs beginning at a four-aligned SGPR index are always selected
to serve as the scratch V# for the kernel as follows:
- If it is know during instruction selection that there is stack usage,
SGPR0-3 is reserved for use as the scratch V#. Stack usage is assumed if
optimisations are disabled (``-O0``), if stack objects already exist (for
locals, etc.), or if there are any function calls.
- Otherwise, four high numbered SGPRs beginning at a four-aligned SGPR index
are reserved for the tentative scratch V#. These will be used if it is
determined that spilling is needed.
- If no use is made of the tentative scratch V#, then it is unreserved
and the register count is determined ignoring it.
- If use is made of the tenatative scratch V#, then its register numbers
are shifted to the first four-aligned SGPR index after the highest one
allocated by the register allocator, and all uses are updated. The
register count includes them in the shifted location.
- In either case, if the processor has the SGPR allocation bug, the
tentative allocation is not shifted or unreserved in order to ensure
the register count is higher to workaround the bug.
.. note::
This approach of using a tentative scratch V# and shifting the register
numbers if used avoids having to perform register allocation a second
time if the tentative V# is eliminated. This is more efficient and
avoids the problem that the second register allocation may perform
spilling which will fail as there is no longer a scratch V#.
When the kernel prolog code is being emitted it is known whether the scratch V#
described above is actually used. If it is, the prolog code must set it up by
copying the Private Segment Buffer to the scratch V# registers and then adding
the Private Segment Wavefront Offset to the queue base address in the V#. The
result is a V# with a base address pointing to the beginning of the wavefront
scratch backing memory.
The Private Segment Buffer is always requested, but the Private Segment
Wavefront Offset is only requested if it is used (see
:ref:`amdgpu-amdhsa-initial-kernel-execution-state`).
.. _amdgpu-amdhsa-memory-model:
Memory Model
~~~~~~~~~~~~
This section describes the mapping of LLVM memory model onto AMDGPU machine code
(see :ref:`memmodel`).
The AMDGPU backend supports the memory synchronization scopes specified in
:ref:`amdgpu-memory-scopes`.
The code sequences used to implement the memory model are defined in table
:ref:`amdgpu-amdhsa-memory-model-code-sequences-gfx6-gfx10-table`.
The sequences specify the order of instructions that a single thread must
execute. The ``s_waitcnt`` and ``buffer_wbinvl1_vol`` are defined with respect
to other memory instructions executed by the same thread. This allows them to be
moved earlier or later which can allow them to be combined with other instances
of the same instruction, or hoisted/sunk out of loops to improve
performance. Only the instructions related to the memory model are given;
additional ``s_waitcnt`` instructions are required to ensure registers are
defined before being used. These may be able to be combined with the memory
model ``s_waitcnt`` instructions as described above.
The AMDGPU backend supports the following memory models:
HSA Memory Model [HSA]_
The HSA memory model uses a single happens-before relation for all address
spaces (see :ref:`amdgpu-address-spaces`).
OpenCL Memory Model [OpenCL]_
The OpenCL memory model which has separate happens-before relations for the
global and local address spaces. Only a fence specifying both global and
local address space, and seq_cst instructions join the relationships. Since
the LLVM ``memfence`` instruction does not allow an address space to be
specified the OpenCL fence has to conservatively assume both local and
global address space was specified. However, optimizations can often be
done to eliminate the additional ``s_waitcnt`` instructions when there are
no intervening memory instructions which access the corresponding address
space. The code sequences in the table indicate what can be omitted for the
OpenCL memory. The target triple environment is used to determine if the
source language is OpenCL (see :ref:`amdgpu-opencl`).
``ds/flat_load/store/atomic`` instructions to local memory are termed LDS
operations.
``buffer/global/flat_load/store/atomic`` instructions to global memory are
termed vector memory operations.
For GFX6-GFX9:
* Each agent has multiple shader arrays (SA).
* Each SA has multiple compute units (CU).
* Each CU has multiple SIMDs that execute wavefronts.
* The wavefronts for a single work-group are executed in the same CU but may be
executed by different SIMDs.
* Each CU has a single LDS memory shared by the wavefronts of the work-groups
executing on it.
* All LDS operations of a CU are performed as wavefront wide operations in a
global order and involve no caching. Completion is reported to a wavefront in
execution order.
* The LDS memory has multiple request queues shared by the SIMDs of a
CU. Therefore, the LDS operations performed by different wavefronts of a
work-group can be reordered relative to each other, which can result in
reordering the visibility of vector memory operations with respect to LDS
operations of other wavefronts in the same work-group. A ``s_waitcnt
lgkmcnt(0)`` is required to ensure synchronization between LDS operations and
vector memory operations between wavefronts of a work-group, but not between
operations performed by the same wavefront.
* The vector memory operations are performed as wavefront wide operations and
completion is reported to a wavefront in execution order. The exception is
that for GFX7-GFX9 ``flat_load/store/atomic`` instructions can report out of
vector memory order if they access LDS memory, and out of LDS operation order
if they access global memory.
* The vector memory operations access a single vector L1 cache shared by all
SIMDs a CU. Therefore, no special action is required for coherence between the
lanes of a single wavefront, or for coherence between wavefronts in the same
work-group. A ``buffer_wbinvl1_vol`` is required for coherence between
wavefronts executing in different work-groups as they may be executing on
different CUs.
* The scalar memory operations access a scalar L1 cache shared by all wavefronts
on a group of CUs. The scalar and vector L1 caches are not coherent. However,
scalar operations are used in a restricted way so do not impact the memory
model. See :ref:`amdgpu-address-spaces`.
* The vector and scalar memory operations use an L2 cache shared by all CUs on
the same agent.
* The L2 cache has independent channels to service disjoint ranges of virtual
addresses.
* Each CU has a separate request queue per channel. Therefore, the vector and
scalar memory operations performed by wavefronts executing in different
work-groups (which may be executing on different CUs) of an agent can be
reordered relative to each other. A ``s_waitcnt vmcnt(0)`` is required to
ensure synchronization between vector memory operations of different CUs. It
ensures a previous vector memory operation has completed before executing a
subsequent vector memory or LDS operation and so can be used to meet the
requirements of acquire and release.
* The L2 cache can be kept coherent with other agents on some targets, or ranges
of virtual addresses can be set up to bypass it to ensure system coherence.
For GFX10:
* Each agent has multiple shader arrays (SA).
* Each SA has multiple work-group processors (WGP).
* Each WGP has multiple compute units (CU).
* Each CU has multiple SIMDs that execute wavefronts.
* The wavefronts for a single work-group are executed in the same
WGP. In CU wavefront execution mode the wavefronts may be executed by
different SIMDs in the same CU. In WGP wavefront execution mode the
wavefronts may be executed by different SIMDs in different CUs in the same
WGP.
* Each WGP has a single LDS memory shared by the wavefronts of the work-groups
executing on it.
* All LDS operations of a WGP are performed as wavefront wide operations in a
global order and involve no caching. Completion is reported to a wavefront in
execution order.
* The LDS memory has multiple request queues shared by the SIMDs of a
WGP. Therefore, the LDS operations performed by different wavefronts of a
work-group can be reordered relative to each other, which can result in
reordering the visibility of vector memory operations with respect to LDS
operations of other wavefronts in the same work-group. A ``s_waitcnt
lgkmcnt(0)`` is required to ensure synchronization between LDS operations and
vector memory operations between wavefronts of a work-group, but not between
operations performed by the same wavefront.
* The vector memory operations are performed as wavefront wide operations.
Completion of load/store/sample operations are reported to a wavefront in
execution order of other load/store/sample operations performed by that
wavefront.
* The vector memory operations access a vector L0 cache. There is a single L0
cache per CU. Each SIMD of a CU accesses the same L0 cache. Therefore, no
special action is required for coherence between the lanes of a single
wavefront. However, a ``BUFFER_GL0_INV`` is required for coherence between
wavefronts executing in the same work-group as they may be executing on SIMDs
of different CUs that access different L0s. A ``BUFFER_GL0_INV`` is also
required for coherence between wavefronts executing in different work-groups
as they may be executing on different WGPs.
* The scalar memory operations access a scalar L0 cache shared by all wavefronts
on a WGP. The scalar and vector L0 caches are not coherent. However, scalar
operations are used in a restricted way so do not impact the memory model. See
:ref:`amdgpu-address-spaces`.
* The vector and scalar memory L0 caches use an L1 cache shared by all WGPs on
the same SA. Therefore, no special action is required for coherence between
the wavefronts of a single work-group. However, a ``BUFFER_GL1_INV`` is
required for coherence between wavefronts executing in different work-groups
as they may be executing on different SAs that access different L1s.
* The L1 caches have independent quadrants to service disjoint ranges of virtual
addresses.
* Each L0 cache has a separate request queue per L1 quadrant. Therefore, the
vector and scalar memory operations performed by different wavefronts, whether
executing in the same or different work-groups (which may be executing on
different CUs accessing different L0s), can be reordered relative to each
other. A ``s_waitcnt vmcnt(0) & vscnt(0)`` is required to ensure
synchronization between vector memory operations of different wavefronts. It
ensures a previous vector memory operation has completed before executing a
subsequent vector memory or LDS operation and so can be used to meet the
requirements of acquire, release and sequential consistency.
* The L1 caches use an L2 cache shared by all SAs on the same agent.
* The L2 cache has independent channels to service disjoint ranges of virtual
addresses.
* Each L1 quadrant of a single SA accesses a different L2 channel. Each L1
quadrant has a separate request queue per L2 channel. Therefore, the vector
and scalar memory operations performed by wavefronts executing in different
work-groups (which may be executing on different SAs) of an agent can be
reordered relative to each other. A ``s_waitcnt vmcnt(0) & vscnt(0)`` is
required to ensure synchronization between vector memory operations of
different SAs. It ensures a previous vector memory operation has completed
before executing a subsequent vector memory and so can be used to meet the
requirements of acquire, release and sequential consistency.
* The L2 cache can be kept coherent with other agents on some targets, or ranges
of virtual addresses can be set up to bypass it to ensure system coherence.
Private address space uses ``buffer_load/store`` using the scratch V#
(GFX6-GFX8), or ``scratch_load/store`` (GFX9-GFX10). Since only a single thread
is accessing the memory, atomic memory orderings are not meaningful and all
accesses are treated as non-atomic.
Constant address space uses ``buffer/global_load`` instructions (or equivalent
scalar memory instructions). Since the constant address space contents do not
change during the execution of a kernel dispatch it is not legal to perform
stores, and atomic memory orderings are not meaningful and all access are
treated as non-atomic.
A memory synchronization scope wider than work-group is not meaningful for the
group (LDS) address space and is treated as work-group.
The memory model does not support the region address space which is treated as
non-atomic.
Acquire memory ordering is not meaningful on store atomic instructions and is
treated as non-atomic.
Release memory ordering is not meaningful on load atomic instructions and is
treated a non-atomic.
Acquire-release memory ordering is not meaningful on load or store atomic
instructions and is treated as acquire and release respectively.
AMDGPU backend only uses scalar memory operations to access memory that is
proven to not change during the execution of the kernel dispatch. This includes
constant address space and global address space for program scope const
variables. Therefore the kernel machine code does not have to maintain the
scalar L1 cache to ensure it is coherent with the vector L1 cache. The scalar
and vector L1 caches are invalidated between kernel dispatches by CP since
constant address space data may change between kernel dispatch executions. See
:ref:`amdgpu-address-spaces`.
The one exception is if scalar writes are used to spill SGPR registers. In this
case the AMDGPU backend ensures the memory location used to spill is never
accessed by vector memory operations at the same time. If scalar writes are used
then a ``s_dcache_wb`` is inserted before the ``s_endpgm`` and before a function
return since the locations may be used for vector memory instructions by a
future wavefront that uses the same scratch area, or a function call that
creates a frame at the same address, respectively. There is no need for a
``s_dcache_inv`` as all scalar writes are write-before-read in the same thread.
For GFX6-GFX9, scratch backing memory (which is used for the private address
space) is accessed with MTYPE NC_NV (non-coherent non-volatile). Since the
private address space is only accessed by a single thread, and is always
write-before-read, there is never a need to invalidate these entries from the L1
cache. Hence all cache invalidates are done as ``*_vol`` to only invalidate the
volatile cache lines.
For GFX10, scratch backing memory (which is used for the private address space)
is accessed with MTYPE NC (non-coherent). Since the private address space is
only accessed by a single thread, and is always write-before-read, there is
never a need to invalidate these entries from the L0 or L1 caches.
For GFX10, wavefronts are executed in native mode with in-order reporting of
loads and sample instructions. In this mode vmcnt reports completion of load,
atomic with return and sample instructions in order, and the vscnt reports the
completion of store and atomic without return in order. See ``MEM_ORDERED``
field in :ref:`amdgpu-amdhsa-compute_pgm_rsrc1-gfx6-gfx10-table`.
In GFX10, wavefronts can be executed in WGP or CU wavefront execution mode:
* In WGP wavefront execution mode the wavefronts of a work-group are executed
on the SIMDs of both CUs of the WGP. Therefore, explicit management of the per
CU L0 caches is required for work-group synchronization. Also accesses to L1
at work-group scope need to be explicitly ordered as the accesses from
different CUs are not ordered.
* In CU wavefront execution mode the wavefronts of a work-group are executed on
the SIMDs of a single CU of the WGP. Therefore, all global memory access by
the work-group access the same L0 which in turn ensures L1 accesses are
ordered and so do not require explicit management of the caches for
work-group synchronization.
See ``WGP_MODE`` field in
:ref:`amdgpu-amdhsa-compute_pgm_rsrc1-gfx6-gfx10-table` and
:ref:`amdgpu-target-features`.
On dGPU the kernarg backing memory is accessed as UC (uncached) to avoid needing
to invalidate the L2 cache. For GFX6-GFX9, this also causes it to be treated as
non-volatile and so is not invalidated by ``*_vol``. On APU it is accessed as CC
(cache coherent) and so the L2 cache will be coherent with the CPU and other
agents.
.. table:: AMDHSA Memory Model Code Sequences GFX6-GFX10
:name: amdgpu-amdhsa-memory-model-code-sequences-gfx6-gfx10-table
============ ============ ============== ========== =============================== ==================================
LLVM Instr LLVM Memory LLVM Memory AMDGPU AMDGPU Machine Code AMDGPU Machine Code
Ordering Sync Scope Address GFX6-9 GFX10
Space
============ ============ ============== ========== =============================== ==================================
**Non-Atomic**
----------------------------------------------------------------------------------------------------------------------
load *none* *none* - global - !volatile & !nontemporal - !volatile & !nontemporal
- generic
- private 1. buffer/global/flat_load 1. buffer/global/flat_load
- constant
- volatile & !nontemporal - volatile & !nontemporal
1. buffer/global/flat_load 1. buffer/global/flat_load
glc=1 glc=1 dlc=1
- nontemporal - nontemporal
1. buffer/global/flat_load 1. buffer/global/flat_load
glc=1 slc=1 slc=1
load *none* *none* - local 1. ds_load 1. ds_load
store *none* *none* - global - !nontemporal - !nontemporal
- generic
- private 1. buffer/global/flat_store 1. buffer/global/flat_store
- constant
- nontemporal - nontemporal
1. buffer/global/flat_store 1. buffer/global/flat_store
glc=1 slc=1 slc=1
store *none* *none* - local 1. ds_store 1. ds_store
**Unordered Atomic**
----------------------------------------------------------------------------------------------------------------------
load atomic unordered *any* *any* *Same as non-atomic*. *Same as non-atomic*.
store atomic unordered *any* *any* *Same as non-atomic*. *Same as non-atomic*.
atomicrmw unordered *any* *any* *Same as monotonic *Same as monotonic
atomic*. atomic*.
**Monotonic Atomic**
----------------------------------------------------------------------------------------------------------------------
load atomic monotonic - singlethread - global 1. buffer/global/flat_load 1. buffer/global/flat_load
- wavefront - generic
load atomic monotonic - workgroup - global 1. buffer/global/flat_load 1. buffer/global/flat_load
- generic glc=1
- If CU wavefront execution mode, omit glc=1.
load atomic monotonic - singlethread - local 1. ds_load 1. ds_load
- wavefront
- workgroup
load atomic monotonic - agent - global 1. buffer/global/flat_load 1. buffer/global/flat_load
- system - generic glc=1 glc=1 dlc=1
store atomic monotonic - singlethread - global 1. buffer/global/flat_store 1. buffer/global/flat_store
- wavefront - generic
- workgroup
- agent
- system
store atomic monotonic - singlethread - local 1. ds_store 1. ds_store
- wavefront
- workgroup
atomicrmw monotonic - singlethread - global 1. buffer/global/flat_atomic 1. buffer/global/flat_atomic
- wavefront - generic
- workgroup
- agent
- system
atomicrmw monotonic - singlethread - local 1. ds_atomic 1. ds_atomic
- wavefront
- workgroup
**Acquire Atomic**
----------------------------------------------------------------------------------------------------------------------
load atomic acquire - singlethread - global 1. buffer/global/ds/flat_load 1. buffer/global/ds/flat_load
- wavefront - local
- generic
load atomic acquire - workgroup - global 1. buffer/global/flat_load 1. buffer/global_load glc=1
- If CU wavefront execution mode, omit glc=1.
2. s_waitcnt vmcnt(0)
- If CU wavefront execution mode, omit.
- Must happen before
the following buffer_gl0_inv
and before any following
global/generic
load/load
atomic/store/store
atomic/atomicrmw.
3. buffer_gl0_inv
- If CU wavefront execution mode, omit.
- Ensures that
following
loads will not see
stale data.
load atomic acquire - workgroup - local 1. ds_load 1. ds_load
2. s_waitcnt lgkmcnt(0) 2. s_waitcnt lgkmcnt(0)
- If OpenCL, omit. - If OpenCL, omit.
- Must happen before - Must happen before
any following the following buffer_gl0_inv
global/generic and before any following
load/load global/generic load/load
atomic/store/store atomic/store/store
atomic/atomicrmw. atomic/atomicrmw.
- Ensures any - Ensures any
following global following global
data read is no data read is no
older than the load older than the load
atomic value being atomic value being
acquired. acquired.
3. buffer_gl0_inv
- If CU wavefront execution mode, omit.
- If OpenCL, omit.
- Ensures that
following
loads will not see
stale data.
load atomic acquire - workgroup - generic 1. flat_load 1. flat_load glc=1
- If CU wavefront execution mode, omit glc=1.
2. s_waitcnt lgkmcnt(0) 2. s_waitcnt lgkmcnt(0) &
vmcnt(0)
- If CU wavefront execution mode, omit vmcnt.
- If OpenCL, omit. - If OpenCL, omit
lgkmcnt(0).
- Must happen before - Must happen before
any following the following
global/generic buffer_gl0_inv and any
load/load following global/generic
atomic/store/store load/load
atomic/atomicrmw. atomic/store/store
atomic/atomicrmw.
- Ensures any - Ensures any
following global following global
data read is no data read is no
older than the load older than the load
atomic value being atomic value being
acquired. acquired.
3. buffer_gl0_inv
- If CU wavefront execution mode, omit.
- Ensures that
following
loads will not see
stale data.
load atomic acquire - agent - global 1. buffer/global/flat_load 1. buffer/global_load
- system glc=1 glc=1 dlc=1
2. s_waitcnt vmcnt(0) 2. s_waitcnt vmcnt(0)
- Must happen before - Must happen before
following following
buffer_wbinvl1_vol. buffer_gl*_inv.
- Ensures the load - Ensures the load
has completed has completed
before invalidating before invalidating
the cache. the caches.
3. buffer_wbinvl1_vol 3. buffer_gl0_inv;
buffer_gl1_inv
- Must happen before - Must happen before
any following any following
global/generic global/generic
load/load load/load
atomic/atomicrmw. atomic/atomicrmw.
- Ensures that - Ensures that
following following
loads will not see loads will not see
stale global data. stale global data.
load atomic acquire - agent - generic 1. flat_load glc=1 1. flat_load glc=1 dlc=1
- system 2. s_waitcnt vmcnt(0) & 2. s_waitcnt vmcnt(0) &
lgkmcnt(0) lgkmcnt(0)
- If OpenCL omit - If OpenCL omit
lgkmcnt(0). lgkmcnt(0).
- Must happen before - Must happen before
following following
buffer_wbinvl1_vol. buffer_gl*_invl.
- Ensures the flat_load - Ensures the flat_load
has completed has completed
before invalidating before invalidating
the cache. the caches.
3. buffer_wbinvl1_vol 3. buffer_gl0_inv;
buffer_gl1_inv
- Must happen before - Must happen before
any following any following
global/generic global/generic
load/load load/load
atomic/atomicrmw. atomic/atomicrmw.
- Ensures that - Ensures that
following loads following loads
will not see stale will not see stale
global data. global data.
atomicrmw acquire - singlethread - global 1. buffer/global/ds/flat_atomic 1. buffer/global/ds/flat_atomic
- wavefront - local
- generic
atomicrmw acquire - workgroup - global 1. buffer/global/flat_atomic 1. buffer/global_atomic
2. s_waitcnt vm/vscnt(0)
- If CU wavefront execution mode, omit.
- Use vmcnt if atomic with
return and vscnt if atomic
with no-return.
- Must happen before
the following buffer_gl0_inv
and before any following
global/generic
load/load
atomic/store/store
atomic/atomicrmw.
3. buffer_gl0_inv
- If CU wavefront execution mode, omit.
- Ensures that
following
loads will not see
stale data.
atomicrmw acquire - workgroup - local 1. ds_atomic 1. ds_atomic
2. waitcnt lgkmcnt(0) 2. waitcnt lgkmcnt(0)
- If OpenCL, omit. - If OpenCL, omit.
- Must happen before - Must happen before
any following the following
global/generic buffer_gl0_inv.
load/load
atomic/store/store
atomic/atomicrmw.
- Ensures any - Ensures any
following global following global
data read is no data read is no
older than the older than the
atomicrmw value atomicrmw value
being acquired. being acquired.
3. buffer_gl0_inv
- If OpenCL omit.
- Ensures that
following
loads will not see
stale data.
atomicrmw acquire - workgroup - generic 1. flat_atomic 1. flat_atomic
2. waitcnt lgkmcnt(0) 2. waitcnt lgkmcnt(0) &
vm/vscnt(0)
- If CU wavefront execution mode, omit vm/vscnt.
- If OpenCL, omit. - If OpenCL, omit
waitcnt lgkmcnt(0)..
- Use vmcnt if atomic with
return and vscnt if atomic
with no-return.
waitcnt lgkmcnt(0).
- Must happen before - Must happen before
any following the following
global/generic buffer_gl0_inv.
load/load
atomic/store/store
atomic/atomicrmw.
- Ensures any - Ensures any
following global following global
data read is no data read is no
older than the older than the
atomicrmw value atomicrmw value
being acquired. being acquired.
3. buffer_gl0_inv
- If CU wavefront execution mode, omit.
- Ensures that
following
loads will not see
stale data.
atomicrmw acquire - agent - global 1. buffer/global/flat_atomic 1. buffer/global_atomic
- system 2. s_waitcnt vmcnt(0) 2. s_waitcnt vm/vscnt(0)
- Use vmcnt if atomic with
return and vscnt if atomic
with no-return.
waitcnt lgkmcnt(0).
- Must happen before - Must happen before
following following
buffer_wbinvl1_vol. buffer_gl*_inv.
- Ensures the - Ensures the
atomicrmw has atomicrmw has
completed before completed before
invalidating the invalidating the
cache. caches.
3. buffer_wbinvl1_vol 3. buffer_gl0_inv;
buffer_gl1_inv
- Must happen before - Must happen before
any following any following
global/generic global/generic
load/load load/load
atomic/atomicrmw. atomic/atomicrmw.
- Ensures that - Ensures that
following loads following loads
will not see stale will not see stale
global data. global data.
atomicrmw acquire - agent - generic 1. flat_atomic 1. flat_atomic
- system 2. s_waitcnt vmcnt(0) & 2. s_waitcnt vm/vscnt(0) &
lgkmcnt(0) lgkmcnt(0)
- If OpenCL, omit - If OpenCL, omit
lgkmcnt(0). lgkmcnt(0).
- Use vmcnt if atomic with
return and vscnt if atomic
with no-return.
- Must happen before - Must happen before
following following
buffer_wbinvl1_vol. buffer_gl*_inv.
- Ensures the - Ensures the
atomicrmw has atomicrmw has
completed before completed before
invalidating the invalidating the
cache. caches.
3. buffer_wbinvl1_vol 3. buffer_gl0_inv;
buffer_gl1_inv
- Must happen before - Must happen before
any following any following
global/generic global/generic
load/load load/load
atomic/atomicrmw. atomic/atomicrmw.
- Ensures that - Ensures that
following loads following loads
will not see stale will not see stale
global data. global data.
fence acquire - singlethread *none* *none* *none*
- wavefront
fence acquire - workgroup *none* 1. s_waitcnt lgkmcnt(0) 1. s_waitcnt lgkmcnt(0) &
vmcnt(0) & vscnt(0)
- If CU wavefront execution mode, omit vmcnt and
vscnt.
- If OpenCL and - If OpenCL and
address space is address space is
not generic, omit. not generic, omit
lgkmcnt(0).
- If OpenCL and
address space is
local, omit
vmcnt(0) and vscnt(0).
- However, since LLVM - However, since LLVM
currently has no currently has no
address space on address space on
the fence need to the fence need to
conservatively conservatively
always generate. If always generate. If
fence had an fence had an
address space then address space then
set to address set to address
space of OpenCL space of OpenCL
fence flag, or to fence flag, or to
generic if both generic if both
local and global local and global
flags are flags are
specified. specified.
- Must happen after
any preceding
local/generic load
atomic/atomicrmw
with an equal or
wider sync scope
and memory ordering
stronger than
unordered (this is
termed the
fence-paired-atomic).
- Must happen before
any following
global/generic
load/load
atomic/store/store
atomic/atomicrmw.
- Ensures any
following global
data read is no
older than the
value read by the
fence-paired-atomic.
- Could be split into
separate s_waitcnt
vmcnt(0), s_waitcnt
vscnt(0) and s_waitcnt
lgkmcnt(0) to allow
them to be
independently moved
according to the
following rules.
- s_waitcnt vmcnt(0)
must happen after
any preceding
global/generic load
atomic/
atomicrmw-with-return-value
with an equal or
wider sync scope
and memory ordering
stronger than
unordered (this is
termed the
fence-paired-atomic).
- s_waitcnt vscnt(0)
must happen after
any preceding
global/generic
atomicrmw-no-return-value
with an equal or
wider sync scope
and memory ordering
stronger than
unordered (this is
termed the
fence-paired-atomic).
- s_waitcnt lgkmcnt(0)
must happen after
any preceding
local/generic load
atomic/atomicrmw
with an equal or
wider sync scope
and memory ordering
stronger than
unordered (this is
termed the
fence-paired-atomic).
- Must happen before
the following
buffer_gl0_inv.
- Ensures that the
fence-paired atomic
has completed
before invalidating
the
cache. Therefore
any following
locations read must
be no older than
the value read by
the
fence-paired-atomic.
3. buffer_gl0_inv
- If CU wavefront execution mode, omit.
- Ensures that
following
loads will not see
stale data.
fence acquire - agent *none* 1. s_waitcnt lgkmcnt(0) & 1. s_waitcnt lgkmcnt(0) &
- system vmcnt(0) vmcnt(0) & vscnt(0)
- If OpenCL and - If OpenCL and
address space is address space is
not generic, omit not generic, omit
lgkmcnt(0). lgkmcnt(0).
- If OpenCL and
address space is
local, omit
vmcnt(0) and vscnt(0).
- However, since LLVM - However, since LLVM
currently has no currently has no
address space on address space on
the fence need to the fence need to
conservatively conservatively
always generate always generate
(see comment for (see comment for
previous fence). previous fence).
- Could be split into
separate s_waitcnt
vmcnt(0) and
s_waitcnt
lgkmcnt(0) to allow
them to be
independently moved
according to the
following rules.
- s_waitcnt vmcnt(0)
must happen after
any preceding
global/generic load
atomic/atomicrmw
with an equal or
wider sync scope
and memory ordering
stronger than
unordered (this is
termed the
fence-paired-atomic).
- s_waitcnt lgkmcnt(0)
must happen after
any preceding
local/generic load
atomic/atomicrmw
with an equal or
wider sync scope
and memory ordering
stronger than
unordered (this is
termed the
fence-paired-atomic).
- Must happen before
the following
buffer_wbinvl1_vol.
- Ensures that the
fence-paired atomic
has completed
before invalidating
the
cache. Therefore
any following
locations read must
be no older than
the value read by
the
fence-paired-atomic.
- Could be split into
separate s_waitcnt
vmcnt(0), s_waitcnt
vscnt(0) and s_waitcnt
lgkmcnt(0) to allow
them to be
independently moved
according to the
following rules.
- s_waitcnt vmcnt(0)
must happen after
any preceding
global/generic load
atomic/
atomicrmw-with-return-value
with an equal or
wider sync scope
and memory ordering
stronger than
unordered (this is
termed the
fence-paired-atomic).
- s_waitcnt vscnt(0)
must happen after
any preceding
global/generic
atomicrmw-no-return-value
with an equal or
wider sync scope
and memory ordering
stronger than
unordered (this is
termed the
fence-paired-atomic).
- s_waitcnt lgkmcnt(0)
must happen after
any preceding
local/generic load
atomic/atomicrmw
with an equal or
wider sync scope
and memory ordering
stronger than
unordered (this is
termed the
fence-paired-atomic).
- Must happen before
the following
buffer_gl*_inv.
- Ensures that the
fence-paired atomic
has completed
before invalidating
the
caches. Therefore
any following
locations read must
be no older than
the value read by
the
fence-paired-atomic.
2. buffer_wbinvl1_vol 2. buffer_gl0_inv;
buffer_gl1_inv
- Must happen before any - Must happen before any
following global/generic following global/generic
load/load load/load
atomic/store/store atomic/store/store
atomic/atomicrmw. atomic/atomicrmw.
- Ensures that - Ensures that
following loads following loads
will not see stale will not see stale
global data. global data.
**Release Atomic**
----------------------------------------------------------------------------------------------------------------------
store atomic release - singlethread - global 1. buffer/global/ds/flat_store 1. buffer/global/ds/flat_store
- wavefront - local
- generic
store atomic release - workgroup - global 1. s_waitcnt lgkmcnt(0) 1. s_waitcnt lgkmcnt(0) &
vmcnt(0) & vscnt(0)
- If CU wavefront execution mode, omit vmcnt and
vscnt.
- If OpenCL, omit. - If OpenCL, omit
lgkmcnt(0).
- Must happen after
any preceding
local/generic
load/store/load
atomic/store
atomic/atomicrmw.
- Could be split into
separate s_waitcnt
vmcnt(0), s_waitcnt
vscnt(0) and s_waitcnt
lgkmcnt(0) to allow
them to be
independently moved
according to the
following rules.
- s_waitcnt vmcnt(0)
must happen after
any preceding
global/generic load/load
atomic/
atomicrmw-with-return-value.
- s_waitcnt vscnt(0)
must happen after
any preceding
global/generic
store/store
atomic/
atomicrmw-no-return-value.
- s_waitcnt lgkmcnt(0)
must happen after
any preceding
local/generic
load/store/load
atomic/store
atomic/atomicrmw.
- Must happen before - Must happen before
the following the following
store. store.
- Ensures that all - Ensures that all
memory operations memory operations
to local have have
completed before completed before
performing the performing the
store that is being store that is being
released. released.
2. buffer/global/flat_store 2. buffer/global_store
store atomic release - workgroup - local 1. waitcnt vmcnt(0) & vscnt(0)
- If CU wavefront execution mode, omit.
- If OpenCL, omit.
- Could be split into
separate s_waitcnt
vmcnt(0) and s_waitcnt
vscnt(0) to allow
them to be
independently moved
according to the
following rules.
- s_waitcnt vmcnt(0)
must happen after
any preceding
global/generic load/load
atomic/
atomicrmw-with-return-value.
- s_waitcnt vscnt(0)
must happen after
any preceding
global/generic
store/store atomic/
atomicrmw-no-return-value.
- Must happen before
the following
store.
- Ensures that all
global memory
operations have
completed before
performing the
store that is being
released.
1. ds_store 2. ds_store
store atomic release - workgroup - generic 1. s_waitcnt lgkmcnt(0) 1. s_waitcnt lgkmcnt(0) &
vmcnt(0) & vscnt(0)
- If CU wavefront execution mode, omit vmcnt and
vscnt.
- If OpenCL, omit. - If OpenCL, omit
lgkmcnt(0).
- Must happen after
any preceding
local/generic
load/store/load
atomic/store
atomic/atomicrmw.
- Could be split into
separate s_waitcnt
vmcnt(0), s_waitcnt
vscnt(0) and s_waitcnt
lgkmcnt(0) to allow
them to be
independently moved
according to the
following rules.
- s_waitcnt vmcnt(0)
must happen after
any preceding
global/generic load/load
atomic/
atomicrmw-with-return-value.
- s_waitcnt vscnt(0)
must happen after
any preceding
global/generic
store/store
atomic/
atomicrmw-no-return-value.
- s_waitcnt lgkmcnt(0)
must happen after
any preceding
local/generic load/store/load
atomic/store atomic/atomicrmw.
- Must happen before - Must happen before
the following the following
store. store.
- Ensures that all - Ensures that all
memory operations memory operations
to local have have
completed before completed before
performing the performing the
store that is being store that is being
released. released.
2. flat_store 2. flat_store
store atomic release - agent - global 1. s_waitcnt lgkmcnt(0) & 1. s_waitcnt lgkmcnt(0) &
- system - generic vmcnt(0) vmcnt(0) & vscnt(0)
- If OpenCL, omit - If OpenCL, omit
lgkmcnt(0). lgkmcnt(0).
- Could be split into - Could be split into
separate s_waitcnt separate s_waitcnt
vmcnt(0) and vmcnt(0), s_waitcnt vscnt(0)
s_waitcnt and s_waitcnt
lgkmcnt(0) to allow lgkmcnt(0) to allow
them to be them to be
independently moved independently moved
according to the according to the
following rules. following rules.
- s_waitcnt vmcnt(0) - s_waitcnt vmcnt(0)
must happen after must happen after
any preceding any preceding
global/generic global/generic
load/store/load load/load
atomic/store atomic/
atomic/atomicrmw. atomicrmw-with-return-value.
- s_waitcnt vscnt(0)
must happen after
any preceding
global/generic
store/store atomic/
atomicrmw-no-return-value.
- s_waitcnt lgkmcnt(0) - s_waitcnt lgkmcnt(0)
must happen after must happen after
any preceding any preceding
local/generic local/generic
load/store/load load/store/load
atomic/store atomic/store
atomic/atomicrmw. atomic/atomicrmw.
- Must happen before - Must happen before
the following the following
store. store.
- Ensures that all - Ensures that all
memory operations memory operations
to memory have to memory have
completed before completed before
performing the performing the
store that is being store that is being
released. released.
2. buffer/global/ds/flat_store 2. buffer/global/ds/flat_store
atomicrmw release - singlethread - global 1. buffer/global/ds/flat_atomic 1. buffer/global/ds/flat_atomic
- wavefront - local
- generic
atomicrmw release - workgroup - global 1. s_waitcnt lgkmcnt(0) 1. s_waitcnt lgkmcnt(0) &
vmcnt(0) & vscnt(0)
- If CU wavefront execution mode, omit vmcnt and
vscnt.
- If OpenCL, omit.
- Must happen after
any preceding
local/generic
load/store/load
atomic/store
atomic/atomicrmw.
- Could be split into
separate s_waitcnt
vmcnt(0), s_waitcnt
vscnt(0) and s_waitcnt
lgkmcnt(0) to allow
them to be
independently moved
according to the
following rules.
- s_waitcnt vmcnt(0)
must happen after
any preceding
global/generic load/load
atomic/
atomicrmw-with-return-value.
- s_waitcnt vscnt(0)
must happen after
any preceding
global/generic
store/store
atomic/
atomicrmw-no-return-value.
- s_waitcnt lgkmcnt(0)
must happen after
any preceding
local/generic
load/store/load
atomic/store
atomic/atomicrmw.
- Must happen before - Must happen before
the following the following
atomicrmw. atomicrmw.
- Ensures that all - Ensures that all
memory operations memory operations
to local have have
completed before completed before
performing the performing the
atomicrmw that is atomicrmw that is
being released. being released.
2. buffer/global/flat_atomic 2. buffer/global_atomic
atomicrmw release - workgroup - local 1. waitcnt vmcnt(0) & vscnt(0)
- If CU wavefront execution mode, omit.
- If OpenCL, omit.
- Could be split into
separate s_waitcnt
vmcnt(0) and s_waitcnt
vscnt(0) to allow
them to be
independently moved
according to the
following rules.
- s_waitcnt vmcnt(0)
must happen after
any preceding
global/generic load/load
atomic/
atomicrmw-with-return-value.
- s_waitcnt vscnt(0)
must happen after
any preceding
global/generic
store/store atomic/
atomicrmw-no-return-value.
- Must happen before
the following
store.
- Ensures that all
global memory
operations have
completed before
performing the
store that is being
released.
1. ds_atomic 2. ds_atomic
atomicrmw release - workgroup - generic 1. s_waitcnt lgkmcnt(0) 1. s_waitcnt lgkmcnt(0) &
vmcnt(0) & vscnt(0)
- If CU wavefront execution mode, omit vmcnt and
vscnt.
- If OpenCL, omit. - If OpenCL, omit
waitcnt lgkmcnt(0).
- Must happen after
any preceding
local/generic
load/store/load
atomic/store
atomic/atomicrmw.
- Could be split into
separate s_waitcnt
vmcnt(0), s_waitcnt
vscnt(0) and s_waitcnt
lgkmcnt(0) to allow
them to be
independently moved
according to the
following rules.
- s_waitcnt vmcnt(0)
must happen after
any preceding
global/generic load/load
atomic/
atomicrmw-with-return-value.
- s_waitcnt vscnt(0)
must happen after
any preceding
global/generic
store/store
atomic/
atomicrmw-no-return-value.
- s_waitcnt lgkmcnt(0)
must happen after
any preceding
local/generic load/store/load
atomic/store atomic/atomicrmw.
- Must happen before - Must happen before
the following the following
atomicrmw. atomicrmw.
- Ensures that all - Ensures that all
memory operations memory operations
to local have have
completed before completed before
performing the performing the
atomicrmw that is atomicrmw that is
being released. being released.
2. flat_atomic 2. flat_atomic
atomicrmw release - agent - global 1. s_waitcnt lgkmcnt(0) & 1. s_waitcnt lkkmcnt(0) &
- system - generic vmcnt(0) vmcnt(0) & vscnt(0)
- If OpenCL, omit - If OpenCL, omit
lgkmcnt(0). lgkmcnt(0).
- Could be split into - Could be split into
separate s_waitcnt separate s_waitcnt
vmcnt(0) and vmcnt(0), s_waitcnt
s_waitcnt vscnt(0) and s_waitcnt
lgkmcnt(0) to allow lgkmcnt(0) to allow
them to be them to be
independently moved independently moved
according to the according to the
following rules. following rules.
- s_waitcnt vmcnt(0) - s_waitcnt vmcnt(0)
must happen after must happen after
any preceding any preceding
global/generic global/generic
load/store/load load/load atomic/
atomic/store atomicrmw-with-return-value.
atomic/atomicrmw.
- s_waitcnt vscnt(0)
must happen after
any preceding
global/generic
store/store atomic/
atomicrmw-no-return-value.
- s_waitcnt lgkmcnt(0) - s_waitcnt lgkmcnt(0)
must happen after must happen after
any preceding any preceding
local/generic local/generic
load/store/load load/store/load
atomic/store atomic/store
atomic/atomicrmw. atomic/atomicrmw.
- Must happen before - Must happen before
the following the following
atomicrmw. atomicrmw.
- Ensures that all - Ensures that all
memory operations memory operations
to global and local to global and local
have completed have completed
before performing before performing
the atomicrmw that the atomicrmw that
is being released. is being released.
2. buffer/global/ds/flat_atomic 2. buffer/global/ds/flat_atomic
fence release - singlethread *none* *none* *none*
- wavefront
fence release - workgroup *none* 1. s_waitcnt lgkmcnt(0) 1. s_waitcnt lgkmcnt(0) &
vmcnt(0) & vscnt(0)
- If CU wavefront execution mode, omit vmcnt and
vscnt.
- If OpenCL and - If OpenCL and
address space is address space is
not generic, omit. not generic, omit
lgkmcnt(0).
- If OpenCL and
address space is
local, omit
vmcnt(0) and vscnt(0).
- However, since LLVM - However, since LLVM
currently has no currently has no
address space on address space on
the fence need to the fence need to
conservatively conservatively
always generate. If always generate. If
fence had an fence had an
address space then address space then
set to address set to address
space of OpenCL space of OpenCL
fence flag, or to fence flag, or to
generic if both generic if both
local and global local and global
flags are flags are
specified. specified.
- Must happen after
any preceding
local/generic
load/load
atomic/store/store
atomic/atomicrmw.
- Could be split into
separate s_waitcnt
vmcnt(0), s_waitcnt
vscnt(0) and s_waitcnt
lgkmcnt(0) to allow
them to be
independently moved
according to the
following rules.
- s_waitcnt vmcnt(0)
must happen after
any preceding
global/generic
load/load
atomic/
atomicrmw-with-return-value.
- s_waitcnt vscnt(0)
must happen after
any preceding
global/generic
store/store atomic/
atomicrmw-no-return-value.
- s_waitcnt lgkmcnt(0)
must happen after
any preceding
local/generic
load/store/load
atomic/store atomic/
atomicrmw.
- Must happen before - Must happen before
any following store any following store
atomic/atomicrmw atomic/atomicrmw
with an equal or with an equal or
wider sync scope wider sync scope
and memory ordering and memory ordering
stronger than stronger than
unordered (this is unordered (this is
termed the termed the
fence-paired-atomic). fence-paired-atomic).
- Ensures that all - Ensures that all
memory operations memory operations
to local have have
completed before completed before
performing the performing the
following following
fence-paired-atomic. fence-paired-atomic.
fence release - agent *none* 1. s_waitcnt lgkmcnt(0) & 1. s_waitcnt lgkmcnt(0) &
- system vmcnt(0) vmcnt(0) & vscnt(0)
- If OpenCL and - If OpenCL and
address space is address space is
not generic, omit not generic, omit
lgkmcnt(0). lgkmcnt(0).
- If OpenCL and - If OpenCL and
address space is address space is
local, omit local, omit
vmcnt(0). vmcnt(0) and vscnt(0).
- However, since LLVM - However, since LLVM
currently has no currently has no
address space on address space on
the fence need to the fence need to
conservatively conservatively
always generate. If always generate. If
fence had an fence had an
address space then address space then
set to address set to address
space of OpenCL space of OpenCL
fence flag, or to fence flag, or to
generic if both generic if both
local and global local and global
flags are flags are
specified. specified.
- Could be split into - Could be split into
separate s_waitcnt separate s_waitcnt
vmcnt(0) and vmcnt(0), s_waitcnt
s_waitcnt vscnt(0) and s_waitcnt
lgkmcnt(0) to allow lgkmcnt(0) to allow
them to be them to be
independently moved independently moved
according to the according to the
following rules. following rules.
- s_waitcnt vmcnt(0) - s_waitcnt vmcnt(0)
must happen after must happen after
any preceding any preceding
global/generic global/generic
load/store/load load/load atomic/
atomic/store atomicrmw-with-return-value.
atomic/atomicrmw.
- s_waitcnt vscnt(0)
must happen after
any preceding
global/generic
store/store atomic/
atomicrmw-no-return-value.
- s_waitcnt lgkmcnt(0) - s_waitcnt lgkmcnt(0)
must happen after must happen after
any preceding any preceding
local/generic local/generic
load/store/load load/store/load
atomic/store atomic/store
atomic/atomicrmw. atomic/atomicrmw.
- Must happen before - Must happen before
any following store any following store
atomic/atomicrmw atomic/atomicrmw
with an equal or with an equal or
wider sync scope wider sync scope
and memory ordering and memory ordering
stronger than stronger than
unordered (this is unordered (this is
termed the termed the
fence-paired-atomic). fence-paired-atomic).
- Ensures that all - Ensures that all
memory operations memory operations
have have
completed before completed before
performing the performing the
following following
fence-paired-atomic. fence-paired-atomic.
**Acquire-Release Atomic**
----------------------------------------------------------------------------------------------------------------------
atomicrmw acq_rel - singlethread - global 1. buffer/global/ds/flat_atomic 1. buffer/global/ds/flat_atomic
- wavefront - local
- generic
atomicrmw acq_rel - workgroup - global 1. s_waitcnt lgkmcnt(0) 1. s_waitcnt lgkmcnt(0) &
vmcnt(0) & vscnt(0)
- If CU wavefront execution mode, omit vmcnt and
vscnt.
- If OpenCL, omit. - If OpenCL, omit
s_waitcnt lgkmcnt(0).
- Must happen after - Must happen after
any preceding any preceding
local/generic local/generic
load/store/load load/store/load
atomic/store atomic/store
atomic/atomicrmw. atomic/atomicrmw.
- Could be split into
separate s_waitcnt
vmcnt(0), s_waitcnt
vscnt(0) and s_waitcnt
lgkmcnt(0) to allow
them to be
independently moved
according to the
following rules.
- s_waitcnt vmcnt(0)
must happen after
any preceding
global/generic load/load
atomic/
atomicrmw-with-return-value.
- s_waitcnt vscnt(0)
must happen after
any preceding
global/generic
store/store
atomic/
atomicrmw-no-return-value.
- s_waitcnt lgkmcnt(0)
must happen after
any preceding
local/generic load/store/load
atomic/store atomic/atomicrmw.
- Must happen before - Must happen before
the following the following
atomicrmw. atomicrmw.
- Ensures that all - Ensures that all
memory operations memory operations
to local have have
completed before completed before
performing the performing the
atomicrmw that is atomicrmw that is
being released. being released.
2. buffer/global/flat_atomic 2. buffer/global_atomic
3. s_waitcnt vm/vscnt(0)
- If CU wavefront execution mode, omit vm/vscnt.
- Use vmcnt if atomic with
return and vscnt if atomic
with no-return.
waitcnt lgkmcnt(0).
- Must happen before
the following
buffer_gl0_inv.
- Ensures any
following global
data read is no
older than the
atomicrmw value
being acquired.
4. buffer_gl0_inv
- If CU wavefront execution mode, omit.
- Ensures that
following
loads will not see
stale data.
atomicrmw acq_rel - workgroup - local 1. waitcnt vmcnt(0) & vscnt(0)
- If CU wavefront execution mode, omit.
- If OpenCL, omit.
- Could be split into
separate s_waitcnt
vmcnt(0) and s_waitcnt
vscnt(0) to allow
them to be
independently moved
according to the
following rules.
- s_waitcnt vmcnt(0)
must happen after
any preceding
global/generic load/load
atomic/
atomicrmw-with-return-value.
- s_waitcnt vscnt(0)
must happen after
any preceding
global/generic
store/store atomic/
atomicrmw-no-return-value.
- Must happen before
the following
store.
- Ensures that all
global memory
operations have
completed before
performing the
store that is being
released.
1. ds_atomic 2. ds_atomic
2. s_waitcnt lgkmcnt(0) 3. s_waitcnt lgkmcnt(0)
- If OpenCL, omit. - If OpenCL, omit.
- Must happen before - Must happen before
any following the following
global/generic buffer_gl0_inv.
load/load
atomic/store/store
atomic/atomicrmw.
- Ensures any - Ensures any
following global following global
data read is no data read is no
older than the load older than the load
atomic value being atomic value being
acquired. acquired.
4. buffer_gl0_inv
- If CU wavefront execution mode, omit.
- If OpenCL omit.
- Ensures that
following
loads will not see
stale data.
atomicrmw acq_rel - workgroup - generic 1. s_waitcnt lgkmcnt(0) 1. s_waitcnt lgkmcnt(0) &
vmcnt(0) & vscnt(0)
- If CU wavefront execution mode, omit vmcnt and
vscnt.
- If OpenCL, omit. - If OpenCL, omit
waitcnt lgkmcnt(0).
- Must happen after
any preceding
local/generic
load/store/load
atomic/store
atomic/atomicrmw.
- Could be split into
separate s_waitcnt
vmcnt(0), s_waitcnt
vscnt(0) and s_waitcnt
lgkmcnt(0) to allow
them to be
independently moved
according to the
following rules.
- s_waitcnt vmcnt(0)
must happen after
any preceding
global/generic load/load
atomic/
atomicrmw-with-return-value.
- s_waitcnt vscnt(0)
must happen after
any preceding
global/generic
store/store
atomic/
atomicrmw-no-return-value.
- s_waitcnt lgkmcnt(0)
must happen after
any preceding
local/generic load/store/load
atomic/store atomic/atomicrmw.
- Must happen before - Must happen before
the following the following
atomicrmw. atomicrmw.
- Ensures that all - Ensures that all
memory operations memory operations
to local have have
completed before completed before
performing the performing the
atomicrmw that is atomicrmw that is
being released. being released.
2. flat_atomic 2. flat_atomic
3. s_waitcnt lgkmcnt(0) 3. s_waitcnt lgkmcnt(0) &
vm/vscnt(0)
- If CU wavefront execution mode, omit vm/vscnt.
- If OpenCL, omit. - If OpenCL, omit
waitcnt lgkmcnt(0).
- Must happen before - Must happen before
any following the following
global/generic buffer_gl0_inv.
load/load
atomic/store/store
atomic/atomicrmw.
- Ensures any - Ensures any
following global following global
data read is no data read is no
older than the load older than the load
atomic value being atomic value being
acquired. acquired.
3. buffer_gl0_inv
- If CU wavefront execution mode, omit.
- Ensures that
following
loads will not see
stale data.
atomicrmw acq_rel - agent - global 1. s_waitcnt lgkmcnt(0) & 1. s_waitcnt lgkmcnt(0) &
- system vmcnt(0) vmcnt(0) & vscnt(0)
- If OpenCL, omit - If OpenCL, omit
lgkmcnt(0). lgkmcnt(0).
- Could be split into - Could be split into
separate s_waitcnt separate s_waitcnt
vmcnt(0) and vmcnt(0), s_waitcnt
s_waitcnt vscnt(0) and s_waitcnt
lgkmcnt(0) to allow lgkmcnt(0) to allow
them to be them to be
independently moved independently moved
according to the according to the
following rules. following rules.
- s_waitcnt vmcnt(0) - s_waitcnt vmcnt(0)
must happen after must happen after
any preceding any preceding
global/generic global/generic
load/store/load load/load atomic/
atomic/store atomicrmw-with-return-value.
atomic/atomicrmw.
- s_waitcnt vscnt(0)
must happen after
any preceding
global/generic
store/store atomic/
atomicrmw-no-return-value.
- s_waitcnt lgkmcnt(0) - s_waitcnt lgkmcnt(0)
must happen after must happen after
any preceding any preceding
local/generic local/generic
load/store/load load/store/load
atomic/store atomic/store
atomic/atomicrmw. atomic/atomicrmw.
- Must happen before - Must happen before
the following the following
atomicrmw. atomicrmw.
- Ensures that all - Ensures that all
memory operations memory operations
to global have to global have
completed before completed before
performing the performing the
atomicrmw that is atomicrmw that is
being released. being released.
2. buffer/global/flat_atomic 2. buffer/global_atomic
3. s_waitcnt vmcnt(0) 3. s_waitcnt vm/vscnt(0)
- Use vmcnt if atomic with
return and vscnt if atomic
with no-return.
waitcnt lgkmcnt(0).
- Must happen before - Must happen before
following following
buffer_wbinvl1_vol. buffer_gl*_inv.
- Ensures the - Ensures the
atomicrmw has atomicrmw has
completed before completed before
invalidating the invalidating the
cache. caches.
4. buffer_wbinvl1_vol 4. buffer_gl0_inv;
buffer_gl1_inv
- Must happen before - Must happen before
any following any following
global/generic global/generic
load/load load/load
atomic/atomicrmw. atomic/atomicrmw.
- Ensures that - Ensures that
following loads following loads
will not see stale will not see stale
global data. global data.
atomicrmw acq_rel - agent - generic 1. s_waitcnt lgkmcnt(0) & 1. s_waitcnt lgkmcnt(0) &
- system vmcnt(0) vmcnt(0) & vscnt(0)
- If OpenCL, omit - If OpenCL, omit
lgkmcnt(0). lgkmcnt(0).
- Could be split into - Could be split into
separate s_waitcnt separate s_waitcnt
vmcnt(0) and vmcnt(0), s_waitcnt
s_waitcnt vscnt(0) and s_waitcnt
lgkmcnt(0) to allow lgkmcnt(0) to allow
them to be them to be
independently moved independently moved
according to the according to the
following rules. following rules.
- s_waitcnt vmcnt(0) - s_waitcnt vmcnt(0)
must happen after must happen after
any preceding any preceding
global/generic global/generic
load/store/load load/load atomic
atomic/store atomicrmw-with-return-value.
atomic/atomicrmw.
- s_waitcnt vscnt(0)
must happen after
any preceding
global/generic
store/store atomic/
atomicrmw-no-return-value.
- s_waitcnt lgkmcnt(0) - s_waitcnt lgkmcnt(0)
must happen after must happen after
any preceding any preceding
local/generic local/generic
load/store/load load/store/load
atomic/store atomic/store
atomic/atomicrmw. atomic/atomicrmw.
- Must happen before - Must happen before
the following the following
atomicrmw. atomicrmw.
- Ensures that all - Ensures that all
memory operations memory operations
to global have have
completed before completed before
performing the performing the
atomicrmw that is atomicrmw that is
being released. being released.
2. flat_atomic 2. flat_atomic
3. s_waitcnt vmcnt(0) & 3. s_waitcnt vm/vscnt(0) &
lgkmcnt(0) lgkmcnt(0)
- If OpenCL, omit - If OpenCL, omit
lgkmcnt(0). lgkmcnt(0).
- Use vmcnt if atomic with
return and vscnt if atomic
with no-return.
- Must happen before - Must happen before
following following
buffer_wbinvl1_vol. buffer_gl*_inv.
- Ensures the - Ensures the
atomicrmw has atomicrmw has
completed before completed before
invalidating the invalidating the
cache. caches.
4. buffer_wbinvl1_vol 4. buffer_gl0_inv;
buffer_gl1_inv
- Must happen before - Must happen before
any following any following
global/generic global/generic
load/load load/load
atomic/atomicrmw. atomic/atomicrmw.
- Ensures that - Ensures that
following loads following loads
will not see stale will not see stale
global data. global data.
fence acq_rel - singlethread *none* *none* *none*
- wavefront
fence acq_rel - workgroup *none* 1. s_waitcnt lgkmcnt(0) 1. s_waitcnt lgkmcnt(0) &
vmcnt(0) & vscnt(0)
- If CU wavefront execution mode, omit vmcnt and
vscnt.
- If OpenCL and - If OpenCL and
address space is address space is
not generic, omit. not generic, omit
lgkmcnt(0).
- If OpenCL and
address space is
local, omit
vmcnt(0) and vscnt(0).
- However, - However,
since LLVM since LLVM
currently has no currently has no
address space on address space on
the fence need to the fence need to
conservatively conservatively
always generate always generate
(see comment for (see comment for
previous fence). previous fence).
- Must happen after
any preceding
local/generic
load/load
atomic/store/store
atomic/atomicrmw.
- Could be split into
separate s_waitcnt
vmcnt(0), s_waitcnt
vscnt(0) and s_waitcnt
lgkmcnt(0) to allow
them to be
independently moved
according to the
following rules.
- s_waitcnt vmcnt(0)
must happen after
any preceding
global/generic
load/load
atomic/
atomicrmw-with-return-value.
- s_waitcnt vscnt(0)
must happen after
any preceding
global/generic
store/store atomic/
atomicrmw-no-return-value.
- s_waitcnt lgkmcnt(0)
must happen after
any preceding
local/generic
load/store/load
atomic/store atomic/
atomicrmw.
- Must happen before - Must happen before
any following any following
global/generic global/generic
load/load load/load
atomic/store/store atomic/store/store
atomic/atomicrmw. atomic/atomicrmw.
- Ensures that all - Ensures that all
memory operations memory operations
to local have have
completed before completed before
performing any performing any
following global following global
memory operations. memory operations.
- Ensures that the - Ensures that the
preceding preceding
local/generic load local/generic load
atomic/atomicrmw atomic/atomicrmw
with an equal or with an equal or
wider sync scope wider sync scope
and memory ordering and memory ordering
stronger than stronger than
unordered (this is unordered (this is
termed the termed the
acquire-fence-paired-atomic acquire-fence-paired-atomic
) has completed ) has completed
before following before following
global memory global memory
operations. This operations. This
satisfies the satisfies the
requirements of requirements of
acquire. acquire.
- Ensures that all - Ensures that all
previous memory previous memory
operations have operations have
completed before a completed before a
following following
local/generic store local/generic store
atomic/atomicrmw atomic/atomicrmw
with an equal or with an equal or
wider sync scope wider sync scope
and memory ordering and memory ordering
stronger than stronger than
unordered (this is unordered (this is
termed the termed the
release-fence-paired-atomic release-fence-paired-atomic
). This satisfies the ). This satisfies the
requirements of requirements of
release. release.
- Must happen before
the following
buffer_gl0_inv.
- Ensures that the
acquire-fence-paired
atomic has completed
before invalidating
the
cache. Therefore
any following
locations read must
be no older than
the value read by
the
acquire-fence-paired-atomic.
3. buffer_gl0_inv
- If CU wavefront execution mode, omit.
- Ensures that
following
loads will not see
stale data.
fence acq_rel - agent *none* 1. s_waitcnt lgkmcnt(0) & 1. s_waitcnt lgkmcnt(0) &
- system vmcnt(0) vmcnt(0) & vscnt(0)
- If OpenCL and - If OpenCL and
address space is address space is
not generic, omit not generic, omit
lgkmcnt(0). lgkmcnt(0).
- If OpenCL and
address space is
local, omit
vmcnt(0) and vscnt(0).
- However, since LLVM - However, since LLVM
currently has no currently has no
address space on address space on
the fence need to the fence need to
conservatively conservatively
always generate always generate
(see comment for (see comment for
previous fence). previous fence).
- Could be split into - Could be split into
separate s_waitcnt separate s_waitcnt
vmcnt(0) and vmcnt(0), s_waitcnt
s_waitcnt vscnt(0) and s_waitcnt
lgkmcnt(0) to allow lgkmcnt(0) to allow
them to be them to be
independently moved independently moved
according to the according to the
following rules. following rules.
- s_waitcnt vmcnt(0) - s_waitcnt vmcnt(0)
must happen after must happen after
any preceding any preceding
global/generic global/generic
load/store/load load/load
atomic/store atomic/
atomic/atomicrmw. atomicrmw-with-return-value.
- s_waitcnt vscnt(0)
must happen after
any preceding
global/generic
store/store atomic/
atomicrmw-no-return-value.
- s_waitcnt lgkmcnt(0) - s_waitcnt lgkmcnt(0)
must happen after must happen after
any preceding any preceding
local/generic local/generic
load/store/load load/store/load
atomic/store atomic/store
atomic/atomicrmw. atomic/atomicrmw.
- Must happen before - Must happen before
the following the following
buffer_wbinvl1_vol. buffer_gl*_inv.
- Ensures that the - Ensures that the
preceding preceding
global/local/generic global/local/generic
load load
atomic/atomicrmw atomic/atomicrmw
with an equal or with an equal or
wider sync scope wider sync scope
and memory ordering and memory ordering
stronger than stronger than
unordered (this is unordered (this is
termed the termed the
acquire-fence-paired-atomic acquire-fence-paired-atomic
) has completed ) has completed
before invalidating before invalidating
the cache. This the caches. This
satisfies the satisfies the
requirements of requirements of
acquire. acquire.
- Ensures that all - Ensures that all
previous memory previous memory
operations have operations have
completed before a completed before a
following following
global/local/generic global/local/generic
store store
atomic/atomicrmw atomic/atomicrmw
with an equal or with an equal or
wider sync scope wider sync scope
and memory ordering and memory ordering
stronger than stronger than
unordered (this is unordered (this is
termed the termed the
release-fence-paired-atomic release-fence-paired-atomic
). This satisfies the ). This satisfies the
requirements of requirements of
release. release.
2. buffer_wbinvl1_vol 2. buffer_gl0_inv;
buffer_gl1_inv
- Must happen before - Must happen before
any following any following
global/generic global/generic
load/load load/load
atomic/store/store atomic/store/store
atomic/atomicrmw. atomic/atomicrmw.
- Ensures that - Ensures that
following loads following loads
will not see stale will not see stale
global data. This global data. This
satisfies the satisfies the
requirements of requirements of
acquire. acquire.
**Sequential Consistent Atomic**
----------------------------------------------------------------------------------------------------------------------
load atomic seq_cst - singlethread - global *Same as corresponding *Same as corresponding
- wavefront - local load atomic acquire, load atomic acquire,
- generic except must generated except must generated
all instructions even all instructions even
for OpenCL.* for OpenCL.*
load atomic seq_cst - workgroup - global 1. s_waitcnt lgkmcnt(0) 1. s_waitcnt lgkmcnt(0) &
- generic vmcnt(0) & vscnt(0)
- If CU wavefront execution mode, omit vmcnt and
vscnt.
- Could be split into
separate s_waitcnt
vmcnt(0), s_waitcnt
vscnt(0) and s_waitcnt
lgkmcnt(0) to allow
them to be
independently moved
according to the
following rules.
- Must - waitcnt lgkmcnt(0) must
happen after happen after
preceding preceding
global/generic load local load
atomic/store atomic/store
atomic/atomicrmw atomic/atomicrmw
with memory with memory
ordering of seq_cst ordering of seq_cst
and with equal or and with equal or
wider sync scope. wider sync scope.
(Note that seq_cst (Note that seq_cst
fences have their fences have their
own s_waitcnt own s_waitcnt
lgkmcnt(0) and so do lgkmcnt(0) and so do
not need to be not need to be
considered.) considered.)
- waitcnt vmcnt(0)
Must happen after
preceding
global/generic load
atomic/
atomicrmw-with-return-value
with memory
ordering of seq_cst
and with equal or
wider sync scope.
(Note that seq_cst
fences have their
own s_waitcnt
vmcnt(0) and so do
not need to be
considered.)
- waitcnt vscnt(0)
Must happen after
preceding
global/generic store
atomic/
atomicrmw-no-return-value
with memory
ordering of seq_cst
and with equal or
wider sync scope.
(Note that seq_cst
fences have their
own s_waitcnt
vscnt(0) and so do
not need to be
considered.)
- Ensures any - Ensures any
preceding preceding
sequential sequential
consistent local consistent global/local
memory instructions memory instructions
have completed have completed
before executing before executing
this sequentially this sequentially
consistent consistent
instruction. This instruction. This
prevents reordering prevents reordering
a seq_cst store a seq_cst store
followed by a followed by a
seq_cst load. (Note seq_cst load. (Note
that seq_cst is that seq_cst is
stronger than stronger than
acquire/release as acquire/release as
the reordering of the reordering of
load acquire load acquire
followed by a store followed by a store
release is release is
prevented by the prevented by the
waitcnt of waitcnt of
the release, but the release, but
there is nothing there is nothing
preventing a store preventing a store
release followed by release followed by
load acquire from load acquire from
competing out of competing out of
order.) order.)
2. *Following 2. *Following
instructions same as instructions same as
corresponding load corresponding load
atomic acquire, atomic acquire,
except must generated except must generated
all instructions even all instructions even
for OpenCL.* for OpenCL.*
load atomic seq_cst - workgroup - local *Same as corresponding
load atomic acquire,
except must generated
all instructions even
for OpenCL.*
1. s_waitcnt vmcnt(0) & vscnt(0)
- If CU wavefront execution mode, omit.
- Could be split into
separate s_waitcnt
vmcnt(0) and s_waitcnt
vscnt(0) to allow
them to be
independently moved
according to the
following rules.
- waitcnt vmcnt(0)
Must happen after
preceding
global/generic load
atomic/
atomicrmw-with-return-value
with memory
ordering of seq_cst
and with equal or
wider sync scope.
(Note that seq_cst
fences have their
own s_waitcnt
vmcnt(0) and so do
not need to be
considered.)
- waitcnt vscnt(0)
Must happen after
preceding
global/generic store
atomic/
atomicrmw-no-return-value
with memory
ordering of seq_cst
and with equal or
wider sync scope.
(Note that seq_cst
fences have their
own s_waitcnt
vscnt(0) and so do
not need to be
considered.)
- Ensures any
preceding
sequential
consistent global
memory instructions
have completed
before executing
this sequentially
consistent
instruction. This
prevents reordering
a seq_cst store
followed by a
seq_cst load. (Note
that seq_cst is
stronger than
acquire/release as
the reordering of
load acquire
followed by a store
release is
prevented by the
waitcnt of
the release, but
there is nothing
preventing a store
release followed by
load acquire from
competing out of
order.)
2. *Following
instructions same as
corresponding load
atomic acquire,
except must generated
all instructions even
for OpenCL.*
load atomic seq_cst - agent - global 1. s_waitcnt lgkmcnt(0) & 1. s_waitcnt lgkmcnt(0) &
- system - generic vmcnt(0) vmcnt(0) & vscnt(0)
- Could be split into - Could be split into
separate s_waitcnt separate s_waitcnt
vmcnt(0) vmcnt(0), s_waitcnt
and s_waitcnt vscnt(0) and s_waitcnt
lgkmcnt(0) to allow lgkmcnt(0) to allow
them to be them to be
independently moved independently moved
according to the according to the
following rules. following rules.
- waitcnt lgkmcnt(0) - waitcnt lgkmcnt(0)
must happen after must happen after
preceding preceding
global/generic load local load
atomic/store atomic/store
atomic/atomicrmw atomic/atomicrmw
with memory with memory
ordering of seq_cst ordering of seq_cst
and with equal or and with equal or
wider sync scope. wider sync scope.
(Note that seq_cst (Note that seq_cst
fences have their fences have their
own s_waitcnt own s_waitcnt
lgkmcnt(0) and so do lgkmcnt(0) and so do
not need to be not need to be
considered.) considered.)
- waitcnt vmcnt(0) - waitcnt vmcnt(0)
must happen after must happen after
preceding preceding
global/generic load global/generic load
atomic/store atomic/
atomic/atomicrmw atomicrmw-with-return-value
with memory with memory
ordering of seq_cst ordering of seq_cst
and with equal or and with equal or
wider sync scope. wider sync scope.
(Note that seq_cst (Note that seq_cst
fences have their fences have their
own s_waitcnt own s_waitcnt
vmcnt(0) and so do vmcnt(0) and so do
not need to be not need to be
considered.) considered.)
- waitcnt vscnt(0)
Must happen after
preceding
global/generic store
atomic/
atomicrmw-no-return-value
with memory
ordering of seq_cst
and with equal or
wider sync scope.
(Note that seq_cst
fences have their
own s_waitcnt
vscnt(0) and so do
not need to be
considered.)
- Ensures any - Ensures any
preceding preceding
sequential sequential
consistent global consistent global
memory instructions memory instructions
have completed have completed
before executing before executing
this sequentially this sequentially
consistent consistent
instruction. This instruction. This
prevents reordering prevents reordering
a seq_cst store a seq_cst store
followed by a followed by a
seq_cst load. (Note seq_cst load. (Note
that seq_cst is that seq_cst is
stronger than stronger than
acquire/release as acquire/release as
the reordering of the reordering of
load acquire load acquire
followed by a store followed by a store
release is release is
prevented by the prevented by the
waitcnt of waitcnt of
the release, but the release, but
there is nothing there is nothing
preventing a store preventing a store
release followed by release followed by
load acquire from load acquire from
competing out of competing out of
order.) order.)
2. *Following 2. *Following
instructions same as instructions same as
corresponding load corresponding load
atomic acquire, atomic acquire,
except must generated except must generated
all instructions even all instructions even
for OpenCL.* for OpenCL.*
store atomic seq_cst - singlethread - global *Same as corresponding *Same as corresponding
- wavefront - local store atomic release, store atomic release,
- workgroup - generic except must generated except must generated
all instructions even all instructions even
for OpenCL.* for OpenCL.*
store atomic seq_cst - agent - global *Same as corresponding *Same as corresponding
- system - generic store atomic release, store atomic release,
except must generated except must generated
all instructions even all instructions even
for OpenCL.* for OpenCL.*
atomicrmw seq_cst - singlethread - global *Same as corresponding *Same as corresponding
- wavefront - local atomicrmw acq_rel, atomicrmw acq_rel,
- workgroup - generic except must generated except must generated
all instructions even all instructions even
for OpenCL.* for OpenCL.*
atomicrmw seq_cst - agent - global *Same as corresponding *Same as corresponding
- system - generic atomicrmw acq_rel, atomicrmw acq_rel,
except must generated except must generated
all instructions even all instructions even
for OpenCL.* for OpenCL.*
fence seq_cst - singlethread *none* *Same as corresponding *Same as corresponding
- wavefront fence acq_rel, fence acq_rel,
- workgroup except must generated except must generated
- agent all instructions even all instructions even
- system for OpenCL.* for OpenCL.*
============ ============ ============== ========== =============================== ==================================
The memory order also adds the single thread optimization constrains defined in
table
:ref:`amdgpu-amdhsa-memory-model-single-thread-optimization-constraints-gfx6-gfx10-table`.
.. table:: AMDHSA Memory Model Single Thread Optimization Constraints GFX6-GFX10
:name: amdgpu-amdhsa-memory-model-single-thread-optimization-constraints-gfx6-gfx10-table
============ ==============================================================
LLVM Memory Optimization Constraints
Ordering
============ ==============================================================
unordered *none*
monotonic *none*
acquire - If a load atomic/atomicrmw then no following load/load
atomic/store/ store atomic/atomicrmw/fence instruction can
be moved before the acquire.
- If a fence then same as load atomic, plus no preceding
associated fence-paired-atomic can be moved after the fence.
release - If a store atomic/atomicrmw then no preceding load/load
atomic/store/ store atomic/atomicrmw/fence instruction can
be moved after the release.
- If a fence then same as store atomic, plus no following
associated fence-paired-atomic can be moved before the
fence.
acq_rel Same constraints as both acquire and release.
seq_cst - If a load atomic then same constraints as acquire, plus no
preceding sequentially consistent load atomic/store
atomic/atomicrmw/fence instruction can be moved after the
seq_cst.
- If a store atomic then the same constraints as release, plus
no following sequentially consistent load atomic/store
atomic/atomicrmw/fence instruction can be moved before the
seq_cst.
- If an atomicrmw/fence then same constraints as acq_rel.
============ ==============================================================
Trap Handler ABI
~~~~~~~~~~~~~~~~
For code objects generated by AMDGPU backend for HSA [HSA]_ compatible runtimes
(such as ROCm [AMD-ROCm]_), the runtime installs a trap handler that supports
the ``s_trap`` instruction with the following usage:
.. table:: AMDGPU Trap Handler for AMDHSA OS
:name: amdgpu-trap-handler-for-amdhsa-os-table
=================== =============== =============== =======================
Usage Code Sequence Trap Handler Description
Inputs
=================== =============== =============== =======================
reserved ``s_trap 0x00`` Reserved by hardware.
``debugtrap(arg)`` ``s_trap 0x01`` ``SGPR0-1``: Reserved for HSA
``queue_ptr`` ``debugtrap``
``VGPR0``: intrinsic (not
``arg`` implemented).
``llvm.trap`` ``s_trap 0x02`` ``SGPR0-1``: Causes dispatch to be
``queue_ptr`` terminated and its
associated queue put
into the error state.
``llvm.debugtrap`` ``s_trap 0x03`` - If debugger not
installed then
behaves as a
no-operation. The
trap handler is
entered and
immediately returns
to continue
execution of the
wavefront.
- If the debugger is
installed, causes
the debug trap to be
reported by the
debugger and the
wavefront is put in
the halt state until
resumed by the
debugger.
reserved ``s_trap 0x04`` Reserved.
reserved ``s_trap 0x05`` Reserved.
reserved ``s_trap 0x06`` Reserved.
debugger breakpoint ``s_trap 0x07`` Reserved for debugger
breakpoints.
reserved ``s_trap 0x08`` Reserved.
reserved ``s_trap 0xfe`` Reserved.
reserved ``s_trap 0xff`` Reserved.
=================== =============== =============== =======================
.. _amdgpu-amdhsa-function-call-convention:
Call Convention
~~~~~~~~~~~~~~~
.. note::
This section is currently incomplete and has inakkuracies. It is WIP that will
be updated as information is determined.
See :ref:`amdgpu-dwarf-address-space-mapping` for information on swizzled
addresses. Unswizzled addresses are normal linear addresses.
.. _amdgpu-amdhsa-function-call-convention-kernel-functions:
Kernel Functions
++++++++++++++++
This section describes the call convention ABI for the outer kernel function.
See :ref:`amdgpu-amdhsa-initial-kernel-execution-state` for the kernel call
convention.
The following is not part of the AMDGPU kernel calling convention but describes
how the AMDGPU implements function calls:
1. Clang decides the kernarg layout to match the *HSA Programmer's Language
Reference* [HSA]_.
- All structs are passed directly.
- Lambda values are passed *TBA*.
.. TODO::
- Does this really follow HSA rules? Or are structs >16 bytes passed
by-value struct?
- What is ABI for lambda values?
4. The kernel performs certain setup in its prolog, as described in
:ref:`amdgpu-amdhsa-kernel-prolog`.
.. _amdgpu-amdhsa-function-call-convention-non-kernel-functions:
Non-Kernel Functions
++++++++++++++++++++
This section describes the call convention ABI for functions other than the
outer kernel function.
If a kernel has function calls then scratch is always allocated and used for
the call stack which grows from low address to high address using the swizzled
scratch address space.
On entry to a function:
1. SGPR0-3 contain a V# with the following properties (see
:ref:`amdgpu-amdhsa-kernel-prolog-private-segment-buffer`):
* Base address pointing to the beginning of the wavefront scratch backing
memory.
* Swizzled with dword element size and stride of wavefront size elements.
2. The FLAT_SCRATCH register pair is setup. See
:ref:`amdgpu-amdhsa-kernel-prolog-flat-scratch`.
3. GFX6-8: M0 register set to the size of LDS in bytes. See
:ref:`amdgpu-amdhsa-kernel-prolog-m0`.
4. The EXEC register is set to the lanes active on entry to the function.
5. MODE register: *TBD*
6. VGPR0-31 and SGPR4-29 are used to pass function input arguments as described
below.
7. SGPR30-31 return address (RA). The code address that the function must
return to when it completes. The value is undefined if the function is *no
return*.
8. SGPR32 is used for the stack pointer (SP). It is an unswizzled scratch
offset relative to the beginning of the wavefront scratch backing memory.
The unswizzled SP can be used with buffer instructions as an unswizzled SGPR
offset with the scratch V# in SGPR0-3 to access the stack in a swizzled
manner.
The unswizzled SP value can be converted into the swizzled SP value by:
| swizzled SP = unswizzled SP / wavefront size
This may be used to obtain the private address space address of stack
objects and to convert this address to a flat address by adding the flat
scratch aperture base address.
The swizzled SP value is always 4 bytes aligned for the ``r600``
architecture and 16 byte aligned for the ``amdgcn`` architecture.
.. note::
The ``amdgcn`` value is selected to avoid dynamic stack alignment for the
OpenCL language which has the largest base type defined as 16 bytes.
On entry, the swizzled SP value is the address of the first function
argument passed on the stack. Other stack passed arguments are positive
offsets from the entry swizzled SP value.
The function may use positive offsets beyond the last stack passed argument
for stack allocated local variables and register spill slots. If necessary
the function may align these to greater alignment than 16 bytes. After these
the function may dynamically allocate space for such things as runtime sized
``alloca`` local allocations.
If the function calls another function, it will place any stack allocated
arguments after the last local allocation and adjust SGPR32 to the address
after the last local allocation.
9. All other registers are unspecified.
10. Any necessary ``waitcnt`` has been performed to ensure memory is available
to the function.
On exit from a function:
1. VGPR0-31 and SGPR4-29 are used to pass function result arguments as
described below. Any registers used are considered clobbered registers.
2. The following registers are preserved and have the same value as on entry:
* FLAT_SCRATCH
* EXEC
* GFX6-8: M0
* All SGPR and VGPR registers except the clobbered registers of SGPR4-31 and
VGPR0-31.
For the AMDGPU backend, an inter-procedural register allocation (IPRA)
optimization may mark some of clobbered SGPR4-31 and VGPR0-31 registers as
preserved if it can be determined that the called function does not change
their value.
2. The PC is set to the RA provided on entry.
3. MODE register: *TBD*.
4. All other registers are clobbered.
5. Any necessary ``waitcnt`` has been performed to ensure memory accessed by
function is available to the caller.
.. TODO::
- On gfx908 are all ACC registers clobbered?
- How are function results returned? The address of structured types is passed
by reference, but what about other types?
The function input arguments are made up of the formal arguments explicitly
declared by the source language function plus the implicit input arguments used
by the implementation.
The source language input arguments are:
1. Any source language implicit ``this`` or ``self`` argument comes first as a
pointer type.
2. Followed by the function formal arguments in left to right source order.
The source language result arguments are:
1. The function result argument.
The source language input or result struct type arguments that are less than or
equal to 16 bytes, are decomposed recursively into their base type fields, and
each field is passed as if a separate argument. For input arguments, if the
called function requires the struct to be in memory, for example because its
address is taken, then the function body is responsible for allocating a stack
location and copying the field arguments into it. Clang terms this *direct
struct*.
The source language input struct type arguments that are greater than 16 bytes,
are passed by reference. The caller is responsible for allocating a stack
location to make a copy of the struct value and pass the address as the input
argument. The called function is responsible to perform the dereference when
accessing the input argument. Clang terms this *by-value struct*.
A source language result struct type argument that is greater than 16 bytes, is
returned by reference. The caller is responsible for allocating a stack location
to hold the result value and passes the address as the last input argument
(before the implicit input arguments). In this case there are no result
arguments. The called function is responsible to perform the dereference when
storing the result value. Clang terms this *structured return (sret)*.
*TODO: correct the sret definition.*
.. TODO::
Is this definition correct? Or is sret only used if passing in registers, and
pass as non-decomposed struct as stack argument? Or something else? Is the
memory location in the caller stack frame, or a stack memory argument and so
no address is passed as the caller can directly write to the argument stack
location. But then the stack location is still live after return. If an
argument stack location is it the first stack argument or the last one?
Lambda argument types are treated as struct types with an implementation defined
set of fields.
.. TODO::
Need to specify the ABI for lambda types for AMDGPU.
For AMDGPU backend all source language arguments (including the decomposed
struct type arguments) are passed in VGPRs unless marked ``inreg`` in which case
they are passed in SGPRs.
The AMDGPU backend walks the function call graph from the leaves to determine
which implicit input arguments are used, propagating to each caller of the
function. The used implicit arguments are appended to the function arguments
after the source language arguments in the following order:
.. TODO::
Is recursion or external functions supported?
1. Work-Item ID (1 VGPR)
The X, Y and Z work-item ID are packed into a single VGRP with the following
layout. Only fields actually used by the function are set. The other bits
are undefined.
The values come from the initial kernel execution state. See
:ref:`amdgpu-amdhsa-vgpr-register-set-up-order-table`.
.. table:: Work-item implict argument layout
:name: amdgpu-amdhsa-workitem-implict-argument-layout-table
======= ======= ==============
Bits Size Field Name
======= ======= ==============
9:0 10 bits X Work-Item ID
19:10 10 bits Y Work-Item ID
29:20 10 bits Z Work-Item ID
31:30 2 bits Unused
======= ======= ==============
2. Dispatch Ptr (2 SGPRs)
The value comes from the initial kernel execution state. See
:ref:`amdgpu-amdhsa-sgpr-register-set-up-order-table`.
3. Queue Ptr (2 SGPRs)
The value comes from the initial kernel execution state. See
:ref:`amdgpu-amdhsa-sgpr-register-set-up-order-table`.
4. Kernarg Segment Ptr (2 SGPRs)
The value comes from the initial kernel execution state. See
:ref:`amdgpu-amdhsa-sgpr-register-set-up-order-table`.
5. Dispatch id (2 SGPRs)
The value comes from the initial kernel execution state. See
:ref:`amdgpu-amdhsa-sgpr-register-set-up-order-table`.
6. Work-Group ID X (1 SGPR)
The value comes from the initial kernel execution state. See
:ref:`amdgpu-amdhsa-sgpr-register-set-up-order-table`.
7. Work-Group ID Y (1 SGPR)
The value comes from the initial kernel execution state. See
:ref:`amdgpu-amdhsa-sgpr-register-set-up-order-table`.
8. Work-Group ID Z (1 SGPR)
The value comes from the initial kernel execution state. See
:ref:`amdgpu-amdhsa-sgpr-register-set-up-order-table`.
9. Implicit Argument Ptr (2 SGPRs)
The value is computed by adding an offset to Kernarg Segment Ptr to get the
global address space pointer to the first kernarg implicit argument.
The input and result arguments are assigned in order in the following manner:
..note::
There are likely some errors and ommissions in the following description that
need correction.
..TODO::
Check the clang source code to decipher how funtion arguments and return
results are handled. Also see the AMDGPU specific values used.
* VGPR arguments are assigned to consecutive VGPRs starting at VGPR0 up to
VGPR31.
If there are more arguments than will fit in these registers, the remaining
arguments are allocated on the stack in order on naturally aligned
addresses.
.. TODO::
How are overly aligned structures allocated on the stack?
* SGPR arguments are assigned to consecutive SGPRs starting at SGPR0 up to
SGPR29.
If there are more arguments than will fit in these registers, the remaining
arguments are allocated on the stack in order on naturally aligned
addresses.
Note that decomposed struct type arguments may have some fields passed in
registers and some in memory.
..TODO::
So a struct which can pass some fields as decomposed register arguments, will
pass the rest as decomposed stack elements? But an arguent that will not start
in registers will not be decomposed and will be passed as a non-decomposed
stack value?
The following is not part of the AMDGPU function calling convention but
describes how the AMDGPU implements function calls:
1. SGPR33 is used as a frame pointer (FP) if necessary. Like the SP it is an
unswizzled scratch address. It is only needed if runtime sized ``alloca``
are used, or for the reasons defined in ``SIFrameLowering``.
2. Runtime stack alignment is not currently supported.
.. TODO::
- If runtime stack alignment is supported then will an extra argument
pointer register be used?
2. Allocating SGPR arguments on the stack are not supported.
3. No CFI is currently generated. See :ref:`amdgpu-call-frame-information`.
..note::
CFI will be generated that defines the CFA as the unswizzled address
relative to the wave scratch base in the unswizzled private address space
of the lowest address stack allocated local variable.
``DW_AT_frame_base`` will be defined as the swizzled address in the
swizzled private address space by dividing the CFA by the wavefront size
(since CFA is always at least dword aligned which matches the scratch
swizzle element size).
If no dynamic stack alignment was performed, the stack allocated arguments
are accessed as negative offsets relative to ``DW_AT_frame_base``, and the
local variables and register spill slots are accessed as positive offsets
relative to ``DW_AT_frame_base``.
4. Function argument passing is implemented by copying the input physical
registers to virtual registers on entry. The register allocator can spill if
necessary. These are copied back to physical registers at call sites. The
net effect is that each function call can have these values in entirely
distinct locations. The IPRA can help avoid shuffling argument registers.
5. Call sites are implemented by setting up the arguments at positive offsets
from SP. Then SP is incremented to account for the known frame size before
the call and decremented after the call.
..note::
The CFI will reflect the changed calculation needed to compute the CFA
from SP.
6. 4 byte spill slots are used in the stack frame. One slot is allocated for an
emergency spill slot. Buffer instructions are used for stack accesses and
not the ``flat_scratch`` instruction.
..TODO::
Explain when the emergency spill slot is used.
.. TODO::
Possible broken issues:
- Stack arguments must be aligned to required alignment.
- Stack is aligned to max(16, max formal argument alignment)
- Direct argument < 64 bits should check register budget.
- Register budget calculation should respect ``inreg`` for SGPR.
- SGPR overflow is not handled.
- struct with 1 member unpeeling is not checking size of member.
- ``sret`` is after ``this`` pointer.
- Caller is not implementing stack realignment: need an extra pointer.
- Should say AMDGPU passes FP rather than SP.
- Should CFI define CFA as address of locals or arguments. Difference is
apparent when have implemented dynamic alignment.
- If ``SCRATCH`` instruction could allow negative offsets then can make FP be
highest address of stack frame and use negative offset for locals. Would
allow SP to be the same as FP and could support signal-handler-like as now
have a real SP for the top of the stack.
- How is ``sret`` passed on the stack? In argument stack area? Can it overlay
arguments?
AMDPAL
------
This section provides code conventions used when the target triple OS is
``amdpal`` (see :ref:`amdgpu-target-triples`) for passing runtime parameters
from the application/runtime to each invocation of a hardware shader. These
parameters include both generic, application-controlled parameters called
*user data* as well as system-generated parameters that are a product of the
draw or dispatch execution.
User Data
~~~~~~~~~
Each hardware stage has a set of 32-bit *user data registers* which can be
written from a command buffer and then loaded into SGPRs when waves are launched
via a subsequent dispatch or draw operation. This is the way most arguments are
passed from the application/runtime to a hardware shader.
Compute User Data
~~~~~~~~~~~~~~~~~
Compute shader user data mappings are simpler than graphics shaders, and have a
fixed mapping.
Note that there are always 10 available *user data entries* in registers -
entries beyond that limit must be fetched from memory (via the spill table
pointer) by the shader.
.. table:: PAL Compute Shader User Data Registers
:name: pal-compute-user-data-registers
============= ================================
User Register Description
============= ================================
0 Global Internal Table (32-bit pointer)
1 Per-Shader Internal Table (32-bit pointer)
2 - 11 Application-Controlled User Data (10 32-bit values)
12 Spill Table (32-bit pointer)
13 - 14 Thread Group Count (64-bit pointer)
15 GDS Range
============= ================================
Graphics User Data
~~~~~~~~~~~~~~~~~~
Graphics pipelines support a much more flexible user data mapping:
.. table:: PAL Graphics Shader User Data Registers
:name: pal-graphics-user-data-registers
============= ================================
User Register Description
============= ================================
0 Global Internal Table (32-bit pointer)
+ Per-Shader Internal Table (32-bit pointer)
+ 1-15 Application Controlled User Data
(1-15 Contiguous 32-bit Values in Registers)
+ Spill Table (32-bit pointer)
+ Draw Index (First Stage Only)
+ Vertex Offset (First Stage Only)
+ Instance Offset (First Stage Only)
============= ================================
The placement of the global internal table remains fixed in the first *user
data SGPR register*. Otherwise all parameters are optional, and can be mapped
to any desired *user data SGPR register*, with the following restrictions:
* Draw Index, Vertex Offset, and Instance Offset can only be used by the first
active hardware stage in a graphics pipeline (i.e. where the API vertex
shader runs).
* Application-controlled user data must be mapped into a contiguous range of
user data registers.
* The application-controlled user data range supports compaction remapping, so
only *entries* that are actually consumed by the shader must be assigned to
corresponding *registers*. Note that in order to support an efficient runtime
implementation, the remapping must pack *registers* in the same order as
*entries*, with unused *entries* removed.
.. _pal_global_internal_table:
Global Internal Table
~~~~~~~~~~~~~~~~~~~~~
The global internal table is a table of *shader resource descriptors* (SRDs)
that define how certain engine-wide, runtime-managed resources should be
accessed from a shader. The majority of these resources have HW-defined formats,
and it is up to the compiler to write/read data as required by the target
hardware.
The following table illustrates the required format:
.. table:: PAL Global Internal Table
:name: pal-git-table
============= ================================
Offset Description
============= ================================
0-3 Graphics Scratch SRD
4-7 Compute Scratch SRD
8-11 ES/GS Ring Output SRD
12-15 ES/GS Ring Input SRD
16-19 GS/VS Ring Output #0
20-23 GS/VS Ring Output #1
24-27 GS/VS Ring Output #2
28-31 GS/VS Ring Output #3
32-35 GS/VS Ring Input SRD
36-39 Tessellation Factor Buffer SRD
40-43 Off-Chip LDS Buffer SRD
44-47 Off-Chip Param Cache Buffer SRD
48-51 Sample Position Buffer SRD
52 vaRange::ShadowDescriptorTable High Bits
============= ================================
The pointer to the global internal table passed to the shader as user data
is a 32-bit pointer. The top 32 bits should be assumed to be the same as
the top 32 bits of the pipeline, so the shader may use the program
counter's top 32 bits.
Unspecified OS
--------------
This section provides code conventions used when the target triple OS is
empty (see :ref:`amdgpu-target-triples`).
Trap Handler ABI
~~~~~~~~~~~~~~~~
For code objects generated by AMDGPU backend for non-amdhsa OS, the runtime does
not install a trap handler. The ``llvm.trap`` and ``llvm.debugtrap``
instructions are handled as follows:
.. table:: AMDGPU Trap Handler for Non-AMDHSA OS
:name: amdgpu-trap-handler-for-non-amdhsa-os-table
=============== =============== ===========================================
Usage Code Sequence Description
=============== =============== ===========================================
llvm.trap s_endpgm Causes wavefront to be terminated.
llvm.debugtrap *none* Compiler warning given that there is no
trap handler installed.
=============== =============== ===========================================
Source Languages
================
.. _amdgpu-opencl:
OpenCL
------
When the language is OpenCL the following differences occur:
1. The OpenCL memory model is used (see :ref:`amdgpu-amdhsa-memory-model`).
2. The AMDGPU backend appends additional arguments to the kernel's explicit
arguments for the AMDHSA OS (see
:ref:`opencl-kernel-implicit-arguments-appended-for-amdhsa-os-table`).
3. Additional metadata is generated
(see :ref:`amdgpu-amdhsa-code-object-metadata`).
.. table:: OpenCL kernel implicit arguments appended for AMDHSA OS
:name: opencl-kernel-implicit-arguments-appended-for-amdhsa-os-table
======== ==== ========= ===========================================
Position Byte Byte Description
Size Alignment
======== ==== ========= ===========================================
1 8 8 OpenCL Global Offset X
2 8 8 OpenCL Global Offset Y
3 8 8 OpenCL Global Offset Z
4 8 8 OpenCL address of printf buffer
5 8 8 OpenCL address of virtual queue used by
enqueue_kernel.
6 8 8 OpenCL address of AqlWrap struct used by
enqueue_kernel.
7 8 8 Pointer argument used for Multi-gird
synchronization.
======== ==== ========= ===========================================
.. _amdgpu-hcc:
HCC
---
When the language is HCC the following differences occur:
1. The HSA memory model is used (see :ref:`amdgpu-amdhsa-memory-model`).
.. _amdgpu-assembler:
Assembler
---------
AMDGPU backend has LLVM-MC based assembler which is currently in development.
It supports AMDGCN GFX6-GFX10.
This section describes general syntax for instructions and operands.
Instructions
~~~~~~~~~~~~
.. toctree::
:hidden:
AMDGPU/AMDGPUAsmGFX7
AMDGPU/AMDGPUAsmGFX8
AMDGPU/AMDGPUAsmGFX9
AMDGPU/AMDGPUAsmGFX900
AMDGPU/AMDGPUAsmGFX904
AMDGPU/AMDGPUAsmGFX906
AMDGPU/AMDGPUAsmGFX908
AMDGPU/AMDGPUAsmGFX10
AMDGPU/AMDGPUAsmGFX1011
AMDGPUModifierSyntax
AMDGPUOperandSyntax
AMDGPUInstructionSyntax
AMDGPUInstructionNotation
An instruction has the following :doc:`syntax<AMDGPUInstructionSyntax>`:
| ``<``\ *opcode*\ ``> <``\ *operand0*\ ``>, <``\ *operand1*\ ``>,...
<``\ *modifier0*\ ``> <``\ *modifier1*\ ``>...``
:doc:`Operands<AMDGPUOperandSyntax>` are comma-separated while
:doc:`modifiers<AMDGPUModifierSyntax>` are space-separated.
The order of operands and modifiers is fixed.
Most modifiers are optional and may be omitted.
Links to detailed instruction syntax description may be found in the following
table. Note that features under development are not included
in this description.
=================================== =======================================
Core ISA ISA Extensions
=================================== =======================================
:doc:`GFX7<AMDGPU/AMDGPUAsmGFX7>` \-
:doc:`GFX8<AMDGPU/AMDGPUAsmGFX8>` \-
:doc:`GFX9<AMDGPU/AMDGPUAsmGFX9>` :doc:`gfx900<AMDGPU/AMDGPUAsmGFX900>`
:doc:`gfx902<AMDGPU/AMDGPUAsmGFX900>`
:doc:`gfx904<AMDGPU/AMDGPUAsmGFX904>`
:doc:`gfx906<AMDGPU/AMDGPUAsmGFX906>`
:doc:`gfx908<AMDGPU/AMDGPUAsmGFX908>`
:doc:`gfx909<AMDGPU/AMDGPUAsmGFX900>`
:doc:`GFX10<AMDGPU/AMDGPUAsmGFX10>` :doc:`gfx1011<AMDGPU/AMDGPUAsmGFX1011>`
:doc:`gfx1012<AMDGPU/AMDGPUAsmGFX1011>`
=================================== =======================================
For more information about instructions, their semantics and supported
combinations of operands, refer to one of instruction set architecture manuals
[AMD-GCN-GFX6]_, [AMD-GCN-GFX7]_, [AMD-GCN-GFX8]_, [AMD-GCN-GFX9]_ and
[AMD-GCN-GFX10]_.
Operands
~~~~~~~~
Detailed description of operands may be found :doc:`here<AMDGPUOperandSyntax>`.
Modifiers
~~~~~~~~~
Detailed description of modifiers may be found
:doc:`here<AMDGPUModifierSyntax>`.
Instruction Examples
~~~~~~~~~~~~~~~~~~~~
DS
++
.. code-block:: nasm
ds_add_u32 v2, v4 offset:16
ds_write_src2_b64 v2 offset0:4 offset1:8
ds_cmpst_f32 v2, v4, v6
ds_min_rtn_f64 v[8:9], v2, v[4:5]
For full list of supported instructions, refer to "LDS/GDS instructions" in ISA
Manual.
FLAT
++++
.. code-block:: nasm
flat_load_dword v1, v[3:4]
flat_store_dwordx3 v[3:4], v[5:7]
flat_atomic_swap v1, v[3:4], v5 glc
flat_atomic_cmpswap v1, v[3:4], v[5:6] glc slc
flat_atomic_fmax_x2 v[1:2], v[3:4], v[5:6] glc
For full list of supported instructions, refer to "FLAT instructions" in ISA
Manual.
MUBUF
+++++
.. code-block:: nasm
buffer_load_dword v1, off, s[4:7], s1
buffer_store_dwordx4 v[1:4], v2, ttmp[4:7], s1 offen offset:4 glc tfe
buffer_store_format_xy v[1:2], off, s[4:7], s1
buffer_wbinvl1
buffer_atomic_inc v1, v2, s[8:11], s4 idxen offset:4 slc
For full list of supported instructions, refer to "MUBUF Instructions" in ISA
Manual.
SMRD/SMEM
+++++++++
.. code-block:: nasm
s_load_dword s1, s[2:3], 0xfc
s_load_dwordx8 s[8:15], s[2:3], s4
s_load_dwordx16 s[88:103], s[2:3], s4
s_dcache_inv_vol
s_memtime s[4:5]
For full list of supported instructions, refer to "Scalar Memory Operations" in
ISA Manual.
SOP1
++++
.. code-block:: nasm
s_mov_b32 s1, s2
s_mov_b64 s[0:1], 0x80000000
s_cmov_b32 s1, 200
s_wqm_b64 s[2:3], s[4:5]
s_bcnt0_i32_b64 s1, s[2:3]
s_swappc_b64 s[2:3], s[4:5]
s_cbranch_join s[4:5]
For full list of supported instructions, refer to "SOP1 Instructions" in ISA
Manual.
SOP2
++++
.. code-block:: nasm
s_add_u32 s1, s2, s3
s_and_b64 s[2:3], s[4:5], s[6:7]
s_cselect_b32 s1, s2, s3
s_andn2_b32 s2, s4, s6
s_lshr_b64 s[2:3], s[4:5], s6
s_ashr_i32 s2, s4, s6
s_bfm_b64 s[2:3], s4, s6
s_bfe_i64 s[2:3], s[4:5], s6
s_cbranch_g_fork s[4:5], s[6:7]
For full list of supported instructions, refer to "SOP2 Instructions" in ISA
Manual.
SOPC
++++
.. code-block:: nasm
s_cmp_eq_i32 s1, s2
s_bitcmp1_b32 s1, s2
s_bitcmp0_b64 s[2:3], s4
s_setvskip s3, s5
For full list of supported instructions, refer to "SOPC Instructions" in ISA
Manual.
SOPP
++++
.. code-block:: nasm
s_barrier
s_nop 2
s_endpgm
s_waitcnt 0 ; Wait for all counters to be 0
s_waitcnt vmcnt(0) & expcnt(0) & lgkmcnt(0) ; Equivalent to above
s_waitcnt vmcnt(1) ; Wait for vmcnt counter to be 1.
s_sethalt 9
s_sleep 10
s_sendmsg 0x1
s_sendmsg sendmsg(MSG_INTERRUPT)
s_trap 1
For full list of supported instructions, refer to "SOPP Instructions" in ISA
Manual.
Unless otherwise mentioned, little verification is performed on the operands
of SOPP Instructions, so it is up to the programmer to be familiar with the
range or acceptable values.
VALU
++++
For vector ALU instruction opcodes (VOP1, VOP2, VOP3, VOPC, VOP_DPP, VOP_SDWA),
the assembler will automatically use optimal encoding based on its operands. To
force specific encoding, one can add a suffix to the opcode of the instruction:
* _e32 for 32-bit VOP1/VOP2/VOPC
* _e64 for 64-bit VOP3
* _dpp for VOP_DPP
* _sdwa for VOP_SDWA
VOP1/VOP2/VOP3/VOPC examples:
.. code-block:: nasm
v_mov_b32 v1, v2
v_mov_b32_e32 v1, v2
v_nop
v_cvt_f64_i32_e32 v[1:2], v2
v_floor_f32_e32 v1, v2
v_bfrev_b32_e32 v1, v2
v_add_f32_e32 v1, v2, v3
v_mul_i32_i24_e64 v1, v2, 3
v_mul_i32_i24_e32 v1, -3, v3
v_mul_i32_i24_e32 v1, -100, v3
v_addc_u32 v1, s[0:1], v2, v3, s[2:3]
v_max_f16_e32 v1, v2, v3
VOP_DPP examples:
.. code-block:: nasm
v_mov_b32 v0, v0 quad_perm:[0,2,1,1]
v_sin_f32 v0, v0 row_shl:1 row_mask:0xa bank_mask:0x1 bound_ctrl:0
v_mov_b32 v0, v0 wave_shl:1
v_mov_b32 v0, v0 row_mirror
v_mov_b32 v0, v0 row_bcast:31
v_mov_b32 v0, v0 quad_perm:[1,3,0,1] row_mask:0xa bank_mask:0x1 bound_ctrl:0
v_add_f32 v0, v0, |v0| row_shl:1 row_mask:0xa bank_mask:0x1 bound_ctrl:0
v_max_f16 v1, v2, v3 row_shl:1 row_mask:0xa bank_mask:0x1 bound_ctrl:0
VOP_SDWA examples:
.. code-block:: nasm
v_mov_b32 v1, v2 dst_sel:BYTE_0 dst_unused:UNUSED_PRESERVE src0_sel:DWORD
v_min_u32 v200, v200, v1 dst_sel:WORD_1 dst_unused:UNUSED_PAD src0_sel:BYTE_1 src1_sel:DWORD
v_sin_f32 v0, v0 dst_unused:UNUSED_PAD src0_sel:WORD_1
v_fract_f32 v0, |v0| dst_sel:DWORD dst_unused:UNUSED_PAD src0_sel:WORD_1
v_cmpx_le_u32 vcc, v1, v2 src0_sel:BYTE_2 src1_sel:WORD_0
For full list of supported instructions, refer to "Vector ALU instructions".
.. TODO::
Remove once we switch to code object v3 by default.
.. _amdgpu-amdhsa-assembler-predefined-symbols-v2:
Code Object V2 Predefined Symbols (-mattr=-code-object-v3)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.. warning:: Code Object V2 is not the default code object version emitted by
this version of LLVM. For a description of the predefined symbols available
with the default configuration (Code Object V3) see
:ref:`amdgpu-amdhsa-assembler-predefined-symbols-v3`.
The AMDGPU assembler defines and updates some symbols automatically. These
symbols do not affect code generation.
.option.machine_version_major
+++++++++++++++++++++++++++++
Set to the GFX major generation number of the target being assembled for. For
example, when assembling for a "GFX9" target this will be set to the integer
value "9". The possible GFX major generation numbers are presented in
:ref:`amdgpu-processors`.
.option.machine_version_minor
+++++++++++++++++++++++++++++
Set to the GFX minor generation number of the target being assembled for. For
example, when assembling for a "GFX810" target this will be set to the integer
value "1". The possible GFX minor generation numbers are presented in
:ref:`amdgpu-processors`.
.option.machine_version_stepping
++++++++++++++++++++++++++++++++
Set to the GFX stepping generation number of the target being assembled for.
For example, when assembling for a "GFX704" target this will be set to the
integer value "4". The possible GFX stepping generation numbers are presented
in :ref:`amdgpu-processors`.
.kernel.vgpr_count
++++++++++++++++++
Set to zero each time a
:ref:`amdgpu-amdhsa-assembler-directive-amdgpu_hsa_kernel` directive is
encountered. At each instruction, if the current value of this symbol is less
than or equal to the maximum VPGR number explicitly referenced within that
instruction then the symbol value is updated to equal that VGPR number plus
one.
.kernel.sgpr_count
++++++++++++++++++
Set to zero each time a
:ref:`amdgpu-amdhsa-assembler-directive-amdgpu_hsa_kernel` directive is
encountered. At each instruction, if the current value of this symbol is less
than or equal to the maximum VPGR number explicitly referenced within that
instruction then the symbol value is updated to equal that SGPR number plus
one.
.. _amdgpu-amdhsa-assembler-directives-v2:
Code Object V2 Directives (-mattr=-code-object-v3)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.. warning:: Code Object V2 is not the default code object version emitted by
this version of LLVM. For a description of the directives supported with
the default configuration (Code Object V3) see
:ref:`amdgpu-amdhsa-assembler-directives-v3`.
AMDGPU ABI defines auxiliary data in output code object. In assembly source,
one can specify them with assembler directives.
.hsa_code_object_version major, minor
+++++++++++++++++++++++++++++++++++++
*major* and *minor* are integers that specify the version of the HSA code
object that will be generated by the assembler.
.hsa_code_object_isa [major, minor, stepping, vendor, arch]
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
*major*, *minor*, and *stepping* are all integers that describe the instruction
set architecture (ISA) version of the assembly program.
*vendor* and *arch* are quoted strings. *vendor* should always be equal to
"AMD" and *arch* should always be equal to "AMDGPU".
By default, the assembler will derive the ISA version, *vendor*, and *arch*
from the value of the -mcpu option that is passed to the assembler.
.. _amdgpu-amdhsa-assembler-directive-amdgpu_hsa_kernel:
.amdgpu_hsa_kernel (name)
+++++++++++++++++++++++++
This directives specifies that the symbol with given name is a kernel entry
point (label) and the object should contain corresponding symbol of type
STT_AMDGPU_HSA_KERNEL.
.amd_kernel_code_t
++++++++++++++++++
This directive marks the beginning of a list of key / value pairs that are used
to specify the amd_kernel_code_t object that will be emitted by the assembler.
The list must be terminated by the *.end_amd_kernel_code_t* directive. For any
amd_kernel_code_t values that are unspecified a default value will be used. The
default value for all keys is 0, with the following exceptions:
- *amd_code_version_major* defaults to 1.
- *amd_kernel_code_version_minor* defaults to 2.
- *amd_machine_kind* defaults to 1.
- *amd_machine_version_major*, *machine_version_minor*, and
*amd_machine_version_stepping* are derived from the value of the -mcpu option
that is passed to the assembler.
- *kernel_code_entry_byte_offset* defaults to 256.
- *wavefront_size* defaults 6 for all targets before GFX10. For GFX10 onwards
defaults to 6 if target feature ``wavefrontsize64`` is enabled, otherwise 5.
Note that wavefront size is specified as a power of two, so a value of **n**
means a size of 2^ **n**.
- *call_convention* defaults to -1.
- *kernarg_segment_alignment*, *group_segment_alignment*, and
*private_segment_alignment* default to 4. Note that alignments are specified
as a power of 2, so a value of **n** means an alignment of 2^ **n**.
- *enable_wgp_mode* defaults to 1 if target feature ``cumode`` is disabled for
GFX10 onwards.
- *enable_mem_ordered* defaults to 1 for GFX10 onwards.
The *.amd_kernel_code_t* directive must be placed immediately after the
function label and before any instructions.
For a full list of amd_kernel_code_t keys, refer to AMDGPU ABI document,
comments in lib/Target/AMDGPU/AmdKernelCodeT.h and test/CodeGen/AMDGPU/hsa.s.
.. _amdgpu-amdhsa-assembler-example-v2:
Code Object V2 Example Source Code (-mattr=-code-object-v3)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.. warning:: Code Object V2 is not the default code object version emitted by
this version of LLVM. For a description of the directives supported with
the default configuration (Code Object V3) see
:ref:`amdgpu-amdhsa-assembler-example-v3`.
Here is an example of a minimal assembly source file, defining one HSA kernel:
.. code::
:number-lines:
.hsa_code_object_version 1,0
.hsa_code_object_isa
.hsatext
.globl hello_world
.p2align 8
.amdgpu_hsa_kernel hello_world
hello_world:
.amd_kernel_code_t
enable_sgpr_kernarg_segment_ptr = 1
is_ptr64 = 1
compute_pgm_rsrc1_vgprs = 0
compute_pgm_rsrc1_sgprs = 0
compute_pgm_rsrc2_user_sgpr = 2
compute_pgm_rsrc1_wgp_mode = 0
compute_pgm_rsrc1_mem_ordered = 0
compute_pgm_rsrc1_fwd_progress = 1
.end_amd_kernel_code_t
s_load_dwordx2 s[0:1], s[0:1] 0x0
v_mov_b32 v0, 3.14159
s_waitcnt lgkmcnt(0)
v_mov_b32 v1, s0
v_mov_b32 v2, s1
flat_store_dword v[1:2], v0
s_endpgm
.Lfunc_end0:
.size hello_world, .Lfunc_end0-hello_world
.. _amdgpu-amdhsa-assembler-predefined-symbols-v3:
Code Object V3 Predefined Symbols (-mattr=+code-object-v3)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The AMDGPU assembler defines and updates some symbols automatically. These
symbols do not affect code generation.
.amdgcn.gfx_generation_number
+++++++++++++++++++++++++++++
Set to the GFX major generation number of the target being assembled for. For
example, when assembling for a "GFX9" target this will be set to the integer
value "9". The possible GFX major generation numbers are presented in
:ref:`amdgpu-processors`.
.amdgcn.gfx_generation_minor
++++++++++++++++++++++++++++
Set to the GFX minor generation number of the target being assembled for. For
example, when assembling for a "GFX810" target this will be set to the integer
value "1". The possible GFX minor generation numbers are presented in
:ref:`amdgpu-processors`.
.amdgcn.gfx_generation_stepping
+++++++++++++++++++++++++++++++
Set to the GFX stepping generation number of the target being assembled for.
For example, when assembling for a "GFX704" target this will be set to the
integer value "4". The possible GFX stepping generation numbers are presented
in :ref:`amdgpu-processors`.
.. _amdgpu-amdhsa-assembler-symbol-next_free_vgpr:
.amdgcn.next_free_vgpr
++++++++++++++++++++++
Set to zero before assembly begins. At each instruction, if the current value
of this symbol is less than or equal to the maximum VGPR number explicitly
referenced within that instruction then the symbol value is updated to equal
that VGPR number plus one.
May be used to set the `.amdhsa_next_free_vpgr` directive in
:ref:`amdhsa-kernel-directives-table`.
May be set at any time, e.g. manually set to zero at the start of each kernel.
.. _amdgpu-amdhsa-assembler-symbol-next_free_sgpr:
.amdgcn.next_free_sgpr
++++++++++++++++++++++
Set to zero before assembly begins. At each instruction, if the current value
of this symbol is less than or equal the maximum SGPR number explicitly
referenced within that instruction then the symbol value is updated to equal
that SGPR number plus one.
May be used to set the `.amdhsa_next_free_spgr` directive in
:ref:`amdhsa-kernel-directives-table`.
May be set at any time, e.g. manually set to zero at the start of each kernel.
.. _amdgpu-amdhsa-assembler-directives-v3:
Code Object V3 Directives (-mattr=+code-object-v3)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Directives which begin with ``.amdgcn`` are valid for all ``amdgcn``
architecture processors, and are not OS-specific. Directives which begin with
``.amdhsa`` are specific to ``amdgcn`` architecture processors when the
``amdhsa`` OS is specified. See :ref:`amdgpu-target-triples` and
:ref:`amdgpu-processors`.
.amdgcn_target <target>
+++++++++++++++++++++++
Optional directive which declares the target supported by the containing
assembler source file. Valid values are described in
:ref:`amdgpu-amdhsa-code-object-target-identification`. Used by the assembler
to validate command-line options such as ``-triple``, ``-mcpu``, and those
which specify target features.
.amdhsa_kernel <name>
+++++++++++++++++++++
Creates a correctly aligned AMDHSA kernel descriptor and a symbol,
``<name>.kd``, in the current location of the current section. Only valid when
the OS is ``amdhsa``. ``<name>`` must be a symbol that labels the first
instruction to execute, and does not need to be previously defined.
Marks the beginning of a list of directives used to generate the bytes of a
kernel descriptor, as described in :ref:`amdgpu-amdhsa-kernel-descriptor`.
Directives which may appear in this list are described in
:ref:`amdhsa-kernel-directives-table`. Directives may appear in any order, must
be valid for the target being assembled for, and cannot be repeated. Directives
support the range of values specified by the field they reference in
:ref:`amdgpu-amdhsa-kernel-descriptor`. If a directive is not specified, it is
assumed to have its default value, unless it is marked as "Required", in which
case it is an error to omit the directive. This list of directives is
terminated by an ``.end_amdhsa_kernel`` directive.
.. table:: AMDHSA Kernel Assembler Directives
:name: amdhsa-kernel-directives-table
======================================================== =================== ============ ===================
Directive Default Supported On Description
======================================================== =================== ============ ===================
``.amdhsa_group_segment_fixed_size`` 0 GFX6-GFX10 Controls GROUP_SEGMENT_FIXED_SIZE in
:ref:`amdgpu-amdhsa-kernel-descriptor-gfx6-gfx10-table`.
``.amdhsa_private_segment_fixed_size`` 0 GFX6-GFX10 Controls PRIVATE_SEGMENT_FIXED_SIZE in
:ref:`amdgpu-amdhsa-kernel-descriptor-gfx6-gfx10-table`.
``.amdhsa_user_sgpr_private_segment_buffer`` 0 GFX6-GFX10 Controls ENABLE_SGPR_PRIVATE_SEGMENT_BUFFER in
:ref:`amdgpu-amdhsa-kernel-descriptor-gfx6-gfx10-table`.
``.amdhsa_user_sgpr_dispatch_ptr`` 0 GFX6-GFX10 Controls ENABLE_SGPR_DISPATCH_PTR in
:ref:`amdgpu-amdhsa-kernel-descriptor-gfx6-gfx10-table`.
``.amdhsa_user_sgpr_queue_ptr`` 0 GFX6-GFX10 Controls ENABLE_SGPR_QUEUE_PTR in
:ref:`amdgpu-amdhsa-kernel-descriptor-gfx6-gfx10-table`.
``.amdhsa_user_sgpr_kernarg_segment_ptr`` 0 GFX6-GFX10 Controls ENABLE_SGPR_KERNARG_SEGMENT_PTR in
:ref:`amdgpu-amdhsa-kernel-descriptor-gfx6-gfx10-table`.
``.amdhsa_user_sgpr_dispatch_id`` 0 GFX6-GFX10 Controls ENABLE_SGPR_DISPATCH_ID in
:ref:`amdgpu-amdhsa-kernel-descriptor-gfx6-gfx10-table`.
``.amdhsa_user_sgpr_flat_scratch_init`` 0 GFX6-GFX10 Controls ENABLE_SGPR_FLAT_SCRATCH_INIT in
:ref:`amdgpu-amdhsa-kernel-descriptor-gfx6-gfx10-table`.
``.amdhsa_user_sgpr_private_segment_size`` 0 GFX6-GFX10 Controls ENABLE_SGPR_PRIVATE_SEGMENT_SIZE in
:ref:`amdgpu-amdhsa-kernel-descriptor-gfx6-gfx10-table`.
``.amdhsa_wavefront_size32`` Target GFX10 Controls ENABLE_WAVEFRONT_SIZE32 in
Feature :ref:`amdgpu-amdhsa-kernel-descriptor-gfx6-gfx10-table`.
Specific
(-wavefrontsize64)
``.amdhsa_system_sgpr_private_segment_wavefront_offset`` 0 GFX6-GFX10 Controls ENABLE_SGPR_PRIVATE_SEGMENT_WAVEFRONT_OFFSET in
:ref:`amdgpu-amdhsa-compute_pgm_rsrc2-gfx6-gfx10-table`.
``.amdhsa_system_sgpr_workgroup_id_x`` 1 GFX6-GFX10 Controls ENABLE_SGPR_WORKGROUP_ID_X in
:ref:`amdgpu-amdhsa-compute_pgm_rsrc2-gfx6-gfx10-table`.
``.amdhsa_system_sgpr_workgroup_id_y`` 0 GFX6-GFX10 Controls ENABLE_SGPR_WORKGROUP_ID_Y in
:ref:`amdgpu-amdhsa-compute_pgm_rsrc2-gfx6-gfx10-table`.
``.amdhsa_system_sgpr_workgroup_id_z`` 0 GFX6-GFX10 Controls ENABLE_SGPR_WORKGROUP_ID_Z in
:ref:`amdgpu-amdhsa-compute_pgm_rsrc2-gfx6-gfx10-table`.
``.amdhsa_system_sgpr_workgroup_info`` 0 GFX6-GFX10 Controls ENABLE_SGPR_WORKGROUP_INFO in
:ref:`amdgpu-amdhsa-compute_pgm_rsrc2-gfx6-gfx10-table`.
``.amdhsa_system_vgpr_workitem_id`` 0 GFX6-GFX10 Controls ENABLE_VGPR_WORKITEM_ID in
:ref:`amdgpu-amdhsa-compute_pgm_rsrc2-gfx6-gfx10-table`.
Possible values are defined in
:ref:`amdgpu-amdhsa-system-vgpr-work-item-id-enumeration-values-table`.
``.amdhsa_next_free_vgpr`` Required GFX6-GFX10 Maximum VGPR number explicitly referenced, plus one.
Used to calculate GRANULATED_WORKITEM_VGPR_COUNT in
:ref:`amdgpu-amdhsa-compute_pgm_rsrc1-gfx6-gfx10-table`.
``.amdhsa_next_free_sgpr`` Required GFX6-GFX10 Maximum SGPR number explicitly referenced, plus one.
Used to calculate GRANULATED_WAVEFRONT_SGPR_COUNT in
:ref:`amdgpu-amdhsa-compute_pgm_rsrc1-gfx6-gfx10-table`.
``.amdhsa_reserve_vcc`` 1 GFX6-GFX10 Whether the kernel may use the special VCC SGPR.
Used to calculate GRANULATED_WAVEFRONT_SGPR_COUNT in
:ref:`amdgpu-amdhsa-compute_pgm_rsrc1-gfx6-gfx10-table`.
``.amdhsa_reserve_flat_scratch`` 1 GFX7-GFX10 Whether the kernel may use flat instructions to access
scratch memory. Used to calculate
GRANULATED_WAVEFRONT_SGPR_COUNT in
:ref:`amdgpu-amdhsa-compute_pgm_rsrc1-gfx6-gfx10-table`.
``.amdhsa_reserve_xnack_mask`` Target GFX8-GFX10 Whether the kernel may trigger XNACK replay.
Feature Used to calculate GRANULATED_WAVEFRONT_SGPR_COUNT in
Specific :ref:`amdgpu-amdhsa-compute_pgm_rsrc1-gfx6-gfx10-table`.
(+xnack)
``.amdhsa_float_round_mode_32`` 0 GFX6-GFX10 Controls FLOAT_ROUND_MODE_32 in
:ref:`amdgpu-amdhsa-compute_pgm_rsrc1-gfx6-gfx10-table`.
Possible values are defined in
:ref:`amdgpu-amdhsa-floating-point-rounding-mode-enumeration-values-table`.
``.amdhsa_float_round_mode_16_64`` 0 GFX6-GFX10 Controls FLOAT_ROUND_MODE_16_64 in
:ref:`amdgpu-amdhsa-compute_pgm_rsrc1-gfx6-gfx10-table`.
Possible values are defined in
:ref:`amdgpu-amdhsa-floating-point-rounding-mode-enumeration-values-table`.
``.amdhsa_float_denorm_mode_32`` 0 GFX6-GFX10 Controls FLOAT_DENORM_MODE_32 in
:ref:`amdgpu-amdhsa-compute_pgm_rsrc1-gfx6-gfx10-table`.
Possible values are defined in
:ref:`amdgpu-amdhsa-floating-point-denorm-mode-enumeration-values-table`.
``.amdhsa_float_denorm_mode_16_64`` 3 GFX6-GFX10 Controls FLOAT_DENORM_MODE_16_64 in
:ref:`amdgpu-amdhsa-compute_pgm_rsrc1-gfx6-gfx10-table`.
Possible values are defined in
:ref:`amdgpu-amdhsa-floating-point-denorm-mode-enumeration-values-table`.
``.amdhsa_dx10_clamp`` 1 GFX6-GFX10 Controls ENABLE_DX10_CLAMP in
:ref:`amdgpu-amdhsa-compute_pgm_rsrc1-gfx6-gfx10-table`.
``.amdhsa_ieee_mode`` 1 GFX6-GFX10 Controls ENABLE_IEEE_MODE in
:ref:`amdgpu-amdhsa-compute_pgm_rsrc1-gfx6-gfx10-table`.
``.amdhsa_fp16_overflow`` 0 GFX9-GFX10 Controls FP16_OVFL in
:ref:`amdgpu-amdhsa-compute_pgm_rsrc1-gfx6-gfx10-table`.
``.amdhsa_workgroup_processor_mode`` Target GFX10 Controls ENABLE_WGP_MODE in
Feature :ref:`amdgpu-amdhsa-kernel-descriptor-gfx6-gfx10-table`.
Specific
(-cumode)
``.amdhsa_memory_ordered`` 1 GFX10 Controls MEM_ORDERED in
:ref:`amdgpu-amdhsa-compute_pgm_rsrc1-gfx6-gfx10-table`.
``.amdhsa_forward_progress`` 0 GFX10 Controls FWD_PROGRESS in
:ref:`amdgpu-amdhsa-compute_pgm_rsrc1-gfx6-gfx10-table`.
``.amdhsa_exception_fp_ieee_invalid_op`` 0 GFX6-GFX10 Controls ENABLE_EXCEPTION_IEEE_754_FP_INVALID_OPERATION in
:ref:`amdgpu-amdhsa-compute_pgm_rsrc2-gfx6-gfx10-table`.
``.amdhsa_exception_fp_denorm_src`` 0 GFX6-GFX10 Controls ENABLE_EXCEPTION_FP_DENORMAL_SOURCE in
:ref:`amdgpu-amdhsa-compute_pgm_rsrc2-gfx6-gfx10-table`.
``.amdhsa_exception_fp_ieee_div_zero`` 0 GFX6-GFX10 Controls ENABLE_EXCEPTION_IEEE_754_FP_DIVISION_BY_ZERO in
:ref:`amdgpu-amdhsa-compute_pgm_rsrc2-gfx6-gfx10-table`.
``.amdhsa_exception_fp_ieee_overflow`` 0 GFX6-GFX10 Controls ENABLE_EXCEPTION_IEEE_754_FP_OVERFLOW in
:ref:`amdgpu-amdhsa-compute_pgm_rsrc2-gfx6-gfx10-table`.
``.amdhsa_exception_fp_ieee_underflow`` 0 GFX6-GFX10 Controls ENABLE_EXCEPTION_IEEE_754_FP_UNDERFLOW in
:ref:`amdgpu-amdhsa-compute_pgm_rsrc2-gfx6-gfx10-table`.
``.amdhsa_exception_fp_ieee_inexact`` 0 GFX6-GFX10 Controls ENABLE_EXCEPTION_IEEE_754_FP_INEXACT in
:ref:`amdgpu-amdhsa-compute_pgm_rsrc2-gfx6-gfx10-table`.
``.amdhsa_exception_int_div_zero`` 0 GFX6-GFX10 Controls ENABLE_EXCEPTION_INT_DIVIDE_BY_ZERO in
:ref:`amdgpu-amdhsa-compute_pgm_rsrc2-gfx6-gfx10-table`.
======================================================== =================== ============ ===================
.amdgpu_metadata
++++++++++++++++
Optional directive which declares the contents of the ``NT_AMDGPU_METADATA``
note record (see :ref:`amdgpu-elf-note-records-table-v3`).
The contents must be in the [YAML]_ markup format, with the same structure and
semantics described in :ref:`amdgpu-amdhsa-code-object-metadata-v3`.
This directive is terminated by an ``.end_amdgpu_metadata`` directive.
.. _amdgpu-amdhsa-assembler-example-v3:
Code Object V3 Example Source Code (-mattr=+code-object-v3)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Here is an example of a minimal assembly source file, defining one HSA kernel:
.. code::
:number-lines:
.amdgcn_target "amdgcn-amd-amdhsa--gfx900+xnack" // optional
.text
.globl hello_world
.p2align 8
.type hello_world,@function
hello_world:
s_load_dwordx2 s[0:1], s[0:1] 0x0
v_mov_b32 v0, 3.14159
s_waitcnt lgkmcnt(0)
v_mov_b32 v1, s0
v_mov_b32 v2, s1
flat_store_dword v[1:2], v0
s_endpgm
.Lfunc_end0:
.size hello_world, .Lfunc_end0-hello_world
.rodata
.p2align 6
.amdhsa_kernel hello_world
.amdhsa_user_sgpr_kernarg_segment_ptr 1
.amdhsa_next_free_vgpr .amdgcn.next_free_vgpr
.amdhsa_next_free_sgpr .amdgcn.next_free_sgpr
.end_amdhsa_kernel
.amdgpu_metadata
---
amdhsa.version:
- 1
- 0
amdhsa.kernels:
- .name: hello_world
.symbol: hello_world.kd
.kernarg_segment_size: 48
.group_segment_fixed_size: 0
.private_segment_fixed_size: 0
.kernarg_segment_align: 4
.wavefront_size: 64
.sgpr_count: 2
.vgpr_count: 3
.max_flat_workgroup_size: 256
...
.end_amdgpu_metadata
If an assembly source file contains multiple kernels and/or functions, the
:ref:`amdgpu-amdhsa-assembler-symbol-next_free_vgpr` and
:ref:`amdgpu-amdhsa-assembler-symbol-next_free_sgpr` symbols may be reset using
the ``.set <symbol>, <expression>`` directive. For example, in the case of two
kernels, where ``function1`` is only called from ``kernel1`` it is sufficient
to group the function with the kernel that calls it and reset the symbols
between the two connected components:
.. code::
:number-lines:
.amdgcn_target "amdgcn-amd-amdhsa--gfx900+xnack" // optional
// gpr tracking symbols are implicitly set to zero
.text
.globl kern0
.p2align 8
.type kern0,@function
kern0:
// ...
s_endpgm
.Lkern0_end:
.size kern0, .Lkern0_end-kern0
.rodata
.p2align 6
.amdhsa_kernel kern0
// ...
.amdhsa_next_free_vgpr .amdgcn.next_free_vgpr
.amdhsa_next_free_sgpr .amdgcn.next_free_sgpr
.end_amdhsa_kernel
// reset symbols to begin tracking usage in func1 and kern1
.set .amdgcn.next_free_vgpr, 0
.set .amdgcn.next_free_sgpr, 0
.text
.hidden func1
.global func1
.p2align 2
.type func1,@function
func1:
// ...
s_setpc_b64 s[30:31]
.Lfunc1_end:
.size func1, .Lfunc1_end-func1
.globl kern1
.p2align 8
.type kern1,@function
kern1:
// ...
s_getpc_b64 s[4:5]
s_add_u32 s4, s4, func1@rel32@lo+4
s_addc_u32 s5, s5, func1@rel32@lo+4
s_swappc_b64 s[30:31], s[4:5]
// ...
s_endpgm
.Lkern1_end:
.size kern1, .Lkern1_end-kern1
.rodata
.p2align 6
.amdhsa_kernel kern1
// ...
.amdhsa_next_free_vgpr .amdgcn.next_free_vgpr
.amdhsa_next_free_sgpr .amdgcn.next_free_sgpr
.end_amdhsa_kernel
These symbols cannot identify connected components in order to automatically
track the usage for each kernel. However, in some cases careful organization of
the kernels and functions in the source file means there is minimal additional
effort required to accurately calculate GPR usage.
Additional Documentation
========================
.. [AMD-RADEON-HD-2000-3000] `AMD R6xx shader ISA <http://developer.amd.com/wordpress/media/2012/10/R600_Instruction_Set_Architecture.pdf>`__
.. [AMD-RADEON-HD-4000] `AMD R7xx shader ISA <http://developer.amd.com/wordpress/media/2012/10/R700-Family_Instruction_Set_Architecture.pdf>`__
.. [AMD-RADEON-HD-5000] `AMD Evergreen shader ISA <http://developer.amd.com/wordpress/media/2012/10/AMD_Evergreen-Family_Instruction_Set_Architecture.pdf>`__
.. [AMD-RADEON-HD-6000] `AMD Cayman/Trinity shader ISA <http://developer.amd.com/wordpress/media/2012/10/AMD_HD_6900_Series_Instruction_Set_Architecture.pdf>`__
.. [AMD-GCN-GFX6] `AMD Southern Islands Series ISA <http://developer.amd.com/wordpress/media/2012/12/AMD_Southern_Islands_Instruction_Set_Architecture.pdf>`__
.. [AMD-GCN-GFX7] `AMD Sea Islands Series ISA <http://developer.amd.com/wordpress/media/2013/07/AMD_Sea_Islands_Instruction_Set_Architecture.pdf>`_
.. [AMD-GCN-GFX8] `AMD GCN3 Instruction Set Architecture <http://amd-dev.wpengine.netdna-cdn.com/wordpress/media/2013/12/AMD_GCN3_Instruction_Set_Architecture_rev1.1.pdf>`__
.. [AMD-GCN-GFX9] `AMD "Vega" Instruction Set Architecture <http://developer.amd.com/wordpress/media/2013/12/Vega_Shader_ISA_28July2017.pdf>`__
.. [AMD-GCN-GFX10] `AMD "RDNA 1.0" Instruction Set Architecture <https://gpuopen.com/wp-content/uploads/2019/08/RDNA_Shader_ISA_5August2019.pdf>`__
.. [AMD-ROCm] `ROCm: Open Platform for Development, Discovery and Education Around GPU Computing <http://gpuopen.com/compute-product/rocm/>`__
.. [AMD-ROCm-github] `ROCm github <http://github.com/RadeonOpenCompute>`__
.. [HSA] `Heterogeneous System Architecture (HSA) Foundation <http://www.hsafoundation.com/>`__
.. [HIP] `HIP Programming Guide <https://rocm-documentation.readthedocs.io/en/latest/Programming_Guides/Programming-Guides.html#hip-programing-guide>`__
.. [ELF] `Executable and Linkable Format (ELF) <http://www.sco.com/developers/gabi/>`__
.. [DWARF] `DWARF Debugging Information Format <http://dwarfstd.org/>`__
.. [YAML] `YAML Ain't Markup Language (YAML™) Version 1.2 <http://www.yaml.org/spec/1.2/spec.html>`__
.. [MsgPack] `Message Pack <http://www.msgpack.org/>`__
.. [SEMVER] `Semantic Versioning <https://semver.org/>`__
.. [OpenCL] `The OpenCL Specification Version 2.0 <http://www.khronos.org/registry/cl/specs/opencl-2.0.pdf>`__
.. [HRF] `Heterogeneous-race-free Memory Models <http://benedictgaster.org/wp-content/uploads/2014/01/asplos269-FINAL.pdf>`__
.. [CLANG-ATTR] `Attributes in Clang <https://clang.llvm.org/docs/AttributeReference.html>`__
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