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[AMDGPU] DWARF Proposal For Heterogeneous Debugging

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- Add introduction to DWARF Proposal For Heterogeneous Debugging.

Differential Revision: https://reviews.llvm.org/D70523
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docs/AMDGPUDwarfProposalForHeterogeneousDebugging.rst
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.. _amdgpu-proposal-for-heterogeneous-debugging:
.. _amdgpu-dwarf-proposal-for-heterogeneous-debugging:
******************************************
DWARF Proposal For Heterogeneous Debugging
@ -13,9 +13,76 @@ DWARF Proposal For Heterogeneous Debugging
[:ref:`DWARF <amdgpu-dwarf-DWARF>`] to support heterogeneous debugging. It is
not currently fully implemented and is subject to change.
.. _amdgpu-dwarf-introduction:
Introduction
============
AMD [:ref:`AMD <amdgpu-dwarf-AMD>`] has been working on supporting heterogeneous
computing through the AMD Radeon Open Compute Platform (ROCm) [:ref:`AMD-ROCm
<amdgpu-dwarf-AMD-ROCm>`]. A heterogeneous computing program can be written in a
high level language such as C++ or Fortran with OpenMP pragmas, OpenCL, or HIP
(a portable C++ programming environment for heterogeneous computing [:ref:`HIP
<amdgpu-dwarf-HIP>`]). A heterogeneous compiler and runtime allows a program to
execute on multiple devices within the same native process. Devices could
include CPUs, GPUs, DSPs, FPGAs, or other special purpose accelerators.
Currently HIP programs execute on systems with CPUs and GPUs.
ROCm is fully open sourced and includes contributions to open source projects
such as LLVM for compilation [:ref:`LLVM <amdgpu-dwarf-LLVM>`] and GDB for
debugging [:ref:`GDB <amdgpu-dwarf-GDB>`], as well as collaboration with other
third party projects such as the GCC compiler [:ref:`GCC <amdgpu-dwarf-GCC>`]
and the Perforce TotalView HPC debugger [:ref:`Perforce-TotalView
<amdgpu-dwarf-Perforce-TotalView>`].
To support debugging heterogeneous programs several features that are not
provided by current DWARF Version 5 [:ref:`DWARF <amdgpu-dwarf-DWARF>`] have
been identified. This document contains a collection of proposals to address
providing those features.
The :ref:`amdgpu-dwarf-motivation` section describes the issues that are being
addressed for heterogeneous computing. That is followed by the
:ref:`amdgpu-dwarf-proposed-changes-relative-to-dwarf-version-5` section
containing the proposed textual changes relative to the DWARF Version 5
standard. Then there is an :ref:`amdgpu-dwarf-examples` section that links to
the AMD GPU specific usage of the features in the proposal that includes an
example. Finally, there is a :ref:`amdgpu-dwarf-references` section. There are a
number of notes included that raise open questions, or provide alternative
approaches considered. The draft proposal seeks to be general in nature and
backwards compatible with DWARF Version 5. Its goal is to be applicable to
meeting the needs of any heterogeneous system and not be vendor or architecture
specific.
A fundamental aspect of the draft proposal is that it allows DWARF expression
location descriptions as stack elements. The draft proposal is based on DWARF
Version 5 and maintains compatibility with DWARF Version 5. After attempting
several alternatives, the current thinking is that such an addition to DWARF
Version 5 is the simplest and cleanest way to support debugging optimized GPU
code. It also appears to be generally useful and may be able to address other
reported DWARF issues, as well as being helpful in providing better optimization
support for non-GPU code.
General feedback on this draft proposal is sought, together with suggestions on
how to clarify, simplify, or organize it before submitting it as a formal DWARF
proposal. The current draft proposal is large and may need to be split into
separate proposals before formal submission. Any suggestions on how best to do
that are appreciated. However, at the initial review stage it is believed there
is value in presenting a unified proposal as there are mutual dependencies
between the various parts that would not be as apparent if it was broken up into
separate independent proposals.
We are in the process of modifying LLVM and GDB to support this draft proposal
which is providing experience and insights. We plan to upstream the changes to
those projects for any final form of the proposal.
The author very much appreciates the input provided so far by many others which
has been incorporated into this current version.
.. _amdgpu-dwarf-motivation:
Motivation
==========
This document proposes a set of backwards compatible extensions to DWARF Version
5 [:ref:`DWARF <amdgpu-dwarf-DWARF>`] for consideration of inclusion into a
future DWARF Version 6 standard to support heterogeneous debugging.
@ -3753,12 +3820,16 @@ debugger information entries.
* ``DW_AT_LLVM_lanes``
============================= =============================
.. _amdgpu-dwarf-examples:
Examples
========
The AMD GPU specific usage of the features in the proposal, including examples,
is available at :ref:`amdgpu-dwarf-debug-information`.
.. _amdgpu-dwarf-references:
References
==========