llvm-mirror/docs/PDB/CodeViewSymbols.rst

=====================================
CodeView Symbol Records
=====================================


.. contents::
   :local:

.. _symbols_intro:

Introduction
============

This document describes the usage and serialization format of the various
CodeView symbol records that LLVM understands.  Like
:doc:`CodeView Type Records <CodeViewTypes>`, we describe only the important
types which are generated by modern C++ toolchains.

Record Categories
=================

Symbol records share one major similarity with :doc:`type records <CodeViewTypes>`:
They start with the same :ref:`record prefix <leaf_types>`, which we will not describe
again (refer to the previous link for a description).  As a result of this, a sequence
of symbol records can be processed with largely the same code as that which processes
type records.  There are several important differences between symbol and type records:

* Symbol records only appear in the :doc:`PublicStream`, :doc:`GlobalStream`, and
  :doc:`Module Info Streams <ModiStream>`.
* Type records only appear in the :doc:`TPI & IPI streams <TpiStream>`.
* While types are referenced from other CodeView records via :ref:`type indices <type_indices>`,
  symbol records are referenced by the byte offset of the record in the stream that it appears
  in.
* Types can reference types (via type indices), and symbols can reference both types (via type
  indices) and symbols (via offsets), but types can never reference symbols.
* There is no notion of :ref:`Leaf Records <leaf_types>` and :ref:`Member Records <member_types>`
  as there are with types.  Every symbol record describes is own length.
* Certain special symbol records begin a "scope".  For these records, all following records
  up until the next ``S_END`` record are "children" of this symbol record.  For example,
  given a symbol record which describes a certain function, all local variables of this
  function would appear following the function up until the corresponding ``S_END`` record.

Finally, there are three general categories of symbol record, grouped by where they are legal
to appear in a PDB file.  Public Symbols (which appear only in the
:doc:`publics stream <PublicStream>`), Global Symbols (which appear only in the
:doc:`globals stream <GlobalStream>`) and module symbols (which appear in the
:doc:`module info stream <ModiStream>`).


.. _public_symbols:

Public Symbols
--------------

Public symbols are the CodeView equivalent of DWARF ``.debug_pubnames``.  There
is one public symbol record for every function or variable in the program that
has a mangled name.  The :doc:`Publics Stream <PublicStream>`, which contains these
records, additionally contains a hash table that allows one to quickly locate a
record by mangled name.

S_PUB32 (0x110e)
^^^^^^^^^^^^^^^^

There is only type of public symbol, an ``S_PUB32`` which describes a mangled
name, a flag indicating what kind of symbol it is (e.g. function, variable), and
the symbol's address.  The :ref:`dbi_section_map_substream` of the
:doc:`DBI Stream <DbiStream>` can be consulted to determine what module this address
corresponds to, and from there that module's :doc:`module debug stream <ModiStream>`
can be consulted to locate full information for the symbol with the given address.

.. _global_symbols:

Global Symbols
--------------

While there is one :ref:`public symbol <public_symbols>` for every symbol in the
program with `external` linkage, there is one global symbol for every symbol in the
program with linkage (including internal linkage).  As a result, global symbols do
not describe a mangled name *or* an address, since symbols with internal linkage
need not have any mangling at all, and also may not have an address.  Thus, all
global symbols simply refer directly to the full symbol record via a module/offset
combination.

Similarly to :ref:`public symbols <public_symbols>`, all global symbols are contained
in a single :doc:`Globals Stream <GlobalStream>`, which contains a hash table mapping
fully qualified name to the corresponding record in the globals stream (which as
mentioned, then contains information allowing one to locate the full record in the
corresponding module symbol stream).

Note that a consequence and limitation of this design is that program-wide lookup
by anything other than an exact textually matching fully-qualified name of whatever
the compiler decided to emit is impractical.  This differs from DWARF, where even
though we don't necessarily have O(1) lookup by basename within a given scope (including
O(1) scope, we at least have O(n) access within a given scope).

.. important::
   Program-wide lookup of names by anything other than an exact textually matching fully
   qualified name is not possible.


S_GDATA32
^^^^^^^^^^

S_GTHREAD32 (0x1113)
^^^^^^^^^^^^^^^^^^^^

S_PROCREF (0x1125)
^^^^^^^^^^^^^^^^^^

S_LPROCREF (0x1127)
^^^^^^^^^^^^^^^^^^^

S_GMANDATA (0x111d)
^^^^^^^^^^^^^^^^^^^

.. _module_symbols:

Module Symbols
--------------

S_END (0x0006)
^^^^^^^^^^^^^^

S_FRAMEPROC (0x1012)
^^^^^^^^^^^^^^^^^^^^

S_OBJNAME (0x1101)
^^^^^^^^^^^^^^^^^^

S_THUNK32 (0x1102)
^^^^^^^^^^^^^^^^^^

S_BLOCK32 (0x1103)
^^^^^^^^^^^^^^^^^^

S_LABEL32 (0x1105)
^^^^^^^^^^^^^^^^^^

S_REGISTER (0x1106)
^^^^^^^^^^^^^^^^^^^

S_BPREL32 (0x110b)
^^^^^^^^^^^^^^^^^^

S_LPROC32 (0x110f)
^^^^^^^^^^^^^^^^^^

S_GPROC32 (0x1110)
^^^^^^^^^^^^^^^^^^

S_REGREL32 (0x1111)
^^^^^^^^^^^^^^^^^^^

S_COMPILE2 (0x1116)
^^^^^^^^^^^^^^^^^^^

S_UNAMESPACE (0x1124)
^^^^^^^^^^^^^^^^^^^^^

S_TRAMPOLINE (0x112c)
^^^^^^^^^^^^^^^^^^^^^

S_SECTION (0x1136)
^^^^^^^^^^^^^^^^^^

S_COFFGROUP (0x1137)
^^^^^^^^^^^^^^^^^^^^

S_EXPORT (0x1138)
^^^^^^^^^^^^^^^^^

S_CALLSITEINFO (0x1139)
^^^^^^^^^^^^^^^^^^^^^^^

S_FRAMECOOKIE (0x113a)
^^^^^^^^^^^^^^^^^^^^^^

S_COMPILE3 (0x113c)
^^^^^^^^^^^^^^^^^^^

S_ENVBLOCK (0x113d)
^^^^^^^^^^^^^^^^^^^

S_LOCAL (0x113e)
^^^^^^^^^^^^^^^^

S_DEFRANGE (0x113f)
^^^^^^^^^^^^^^^^^^^

S_DEFRANGE_SUBFIELD (0x1140)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^

S_DEFRANGE_REGISTER (0x1141)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^

S_DEFRANGE_FRAMEPOINTER_REL (0x1142)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

S_DEFRANGE_SUBFIELD_REGISTER (0x1143)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

S_DEFRANGE_FRAMEPOINTER_REL_FULL_SCOPE (0x1144)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

S_DEFRANGE_REGISTER_REL (0x1145)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

S_LPROC32_ID (0x1146)
^^^^^^^^^^^^^^^^^^^^^

S_GPROC32_ID (0x1147)
^^^^^^^^^^^^^^^^^^^^^

S_BUILDINFO (0x114c)
^^^^^^^^^^^^^^^^^^^^

S_INLINESITE (0x114d)
^^^^^^^^^^^^^^^^^^^^^

S_INLINESITE_END (0x114e)
^^^^^^^^^^^^^^^^^^^^^^^^^

S_PROC_ID_END (0x114f)
^^^^^^^^^^^^^^^^^^^^^^

S_FILESTATIC (0x1153)
^^^^^^^^^^^^^^^^^^^^^

S_LPROC32_DPC (0x1155)
^^^^^^^^^^^^^^^^^^^^^^

S_LPROC32_DPC_ID (0x1156)
^^^^^^^^^^^^^^^^^^^^^^^^^

S_CALLEES (0x115a)
^^^^^^^^^^^^^^^^^^

S_CALLERS (0x115b)
^^^^^^^^^^^^^^^^^^

S_HEAPALLOCSITE (0x115e)
^^^^^^^^^^^^^^^^^^^^^^^^

S_FASTLINK (0x1167)
^^^^^^^^^^^^^^^^^^^

S_INLINEES (0x1168)
^^^^^^^^^^^^^^^^^^^

.. _module_and_global_symbols:

Symbols which can go in either/both of the module info stream & global stream
-----------------------------------------------------------------------------

S_CONSTANT (0x1107)
^^^^^^^^^^^^^^^^^^^

S_UDT (0x1108)
^^^^^^^^^^^^^^

S_LDATA32 (0x110c)
^^^^^^^^^^^^^^^^^^

S_LTHREAD32 (0x1112)
^^^^^^^^^^^^^^^^^^^^

S_LMANDATA (0x111c)
^^^^^^^^^^^^^^^^^^^

S_MANCONSTANT (0x112d)
^^^^^^^^^^^^^^^^^^^^^^