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168 lines
8.9 KiB
ReStructuredText
168 lines
8.9 KiB
ReStructuredText
=====================================
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The PDB File Format
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=====================================
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.. contents::
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:local:
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.. _pdb_intro:
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Introduction
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============
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PDB (Program Database) is a file format invented by Microsoft and which contains
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debug information that can be consumed by debuggers and other tools. Since
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officially supported APIs exist on Windows for querying debug information from
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PDBs even without the user understanding the internals of the file format, a
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large ecosystem of tools has been built for Windows to consume this format. In
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order for Clang to be able to generate programs that can interoperate with these
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tools, it is necessary for us to generate PDB files ourselves.
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At the same time, LLVM has a long history of being able to cross-compile from
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any platform to any platform, and we wish for the same to be true here. So it
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is necessary for us to understand the PDB file format at the byte-level so that
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we can generate PDB files entirely on our own.
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This manual describes what we know about the PDB file format today. The layout
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of the file, the various streams contained within, the format of individual
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records within, and more.
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We would like to extend our heartfelt gratitude to Microsoft, without whom we
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would not be where we are today. Much of the knowledge contained within this
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manual was learned through reading code published by Microsoft on their `GitHub
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repo <https://github.com/Microsoft/microsoft-pdb>`__.
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.. _pdb_layout:
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File Layout
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===========
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.. important::
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Unless otherwise specified, all numeric values are encoded in little endian.
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If you see a type such as ``uint16_t`` or ``uint64_t`` going forward, always
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assume it is little endian!
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.. toctree::
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:hidden:
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MsfFile
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PdbStream
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TpiStream
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DbiStream
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ModiStream
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PublicStream
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GlobalStream
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HashStream
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CodeViewSymbols
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CodeViewTypes
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.. _msf:
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The MSF Container
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-----------------
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A PDB file is really just a special case of an MSF (Multi-Stream Format) file.
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An MSF file is actually a miniature "file system within a file". It contains
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multiple streams (aka files) which can represent arbitrary data, and these
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streams are divided into blocks which may not necessarily be contiguously
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laid out within the file (aka fragmented). Additionally, the MSF contains a
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stream directory (aka MFT) which describes how the streams (files) are laid
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out within the MSF.
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For more information about the MSF container format, stream directory, and
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block layout, see :doc:`MsfFile`.
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.. _streams:
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Streams
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-------
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The PDB format contains a number of streams which describe various information
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such as the types, symbols, source files, and compilands (e.g. object files)
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of a program, as well as some additional streams containing hash tables that are
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used by debuggers and other tools to provide fast lookup of records and types
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by name, and various other information about how the program was compiled such
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as the specific toolchain used, and more. A summary of streams contained in a
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PDB file is as follows:
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+--------------------+------------------------------+-------------------------------------------+
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| Name | Stream Index | Contents |
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+====================+==============================+===========================================+
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| Old Directory | - Fixed Stream Index 0 | - Previous MSF Stream Directory |
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+--------------------+------------------------------+-------------------------------------------+
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| PDB Stream | - Fixed Stream Index 1 | - Basic File Information |
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| | | - Fields to match EXE to this PDB |
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| | | - Map of named streams to stream indices |
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+--------------------+------------------------------+-------------------------------------------+
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| TPI Stream | - Fixed Stream Index 2 | - CodeView Type Records |
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| | | - Index of TPI Hash Stream |
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+--------------------+------------------------------+-------------------------------------------+
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| DBI Stream | - Fixed Stream Index 3 | - Module/Compiland Information |
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| | | - Indices of individual module streams |
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| | | - Indices of public / global streams |
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| | | - Section Contribution Information |
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| | | - Source File Information |
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| | | - FPO / PGO Data |
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+--------------------+------------------------------+-------------------------------------------+
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| IPI Stream | - Fixed Stream Index 4 | - CodeView Type Records |
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| | | - Index of IPI Hash Stream |
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+--------------------+------------------------------+-------------------------------------------+
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| /LinkInfo | - Contained in PDB Stream | - Unknown |
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| | Named Stream map | |
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+--------------------+------------------------------+-------------------------------------------+
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| /src/headerblock | - Contained in PDB Stream | - Unknown |
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| | Named Stream map | |
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+--------------------+------------------------------+-------------------------------------------+
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| /names | - Contained in PDB Stream | - PDB-wide global string table used for |
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| | Named Stream map | string de-duplication |
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+--------------------+------------------------------+-------------------------------------------+
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| Module Info Stream | - Contained in DBI Stream | - CodeView Symbol Records for this module |
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| | - One for each compiland | - Line Number Information |
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+--------------------+------------------------------+-------------------------------------------+
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| Public Stream | - Contained in DBI Stream | - Public (Exported) Symbol Records |
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| | | - Index of Public Hash Stream |
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+--------------------+------------------------------+-------------------------------------------+
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| Global Stream | - Contained in DBI Stream | - Global Symbol Records |
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| | | - Index of Global Hash Stream |
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+--------------------+------------------------------+-------------------------------------------+
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| TPI Hash Stream | - Contained in TPI Stream | - Hash table for looking up TPI records |
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| | | by name |
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+--------------------+------------------------------+-------------------------------------------+
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| IPI Hash Stream | - Contained in IPI Stream | - Hash table for looking up IPI records |
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| | | by name |
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+--------------------+------------------------------+-------------------------------------------+
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More information about the structure of each of these can be found on the
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following pages:
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:doc:`PdbStream`
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Information about the PDB Info Stream and how it is used to match PDBs to EXEs.
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:doc:`TpiStream`
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Information about the TPI stream and the CodeView records contained within.
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:doc:`DbiStream`
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Information about the DBI stream and relevant substreams including the Module Substreams,
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source file information, and CodeView symbol records contained within.
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:doc:`ModiStream`
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Information about the Module Information Stream, of which there is one for each compilation
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unit and the format of symbols contained within.
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:doc:`PublicStream`
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Information about the Public Symbol Stream.
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:doc:`GlobalStream`
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Information about the Global Symbol Stream.
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:doc:`HashStream`
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Information about the Hash Table stream, and how it can be used to quickly look up records
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by name.
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CodeView
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========
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CodeView is another format which comes into the picture. While MSF defines
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the structure of the overall file, and PDB defines the set of streams that
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appear within the MSF file and the format of those streams, CodeView defines
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the format of **symbol and type records** that appear within specific streams.
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Refer to the pages on :doc:`CodeViewSymbols` and :doc:`CodeViewTypes` for
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more information about the CodeView format.
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