The PDB File Format

Introduction

PDB (Program Database) is a file format invented by Microsoft and which contains debug information that can be consumed by debuggers and other tools. Since officially supported APIs exist on Windows for querying debug information from PDBs even without the user understanding the internals of the file format, a large ecosystem of tools has been built for Windows to consume this format. In order for Clang to be able to generate programs that can interoperate with these tools, it is necessary for us to generate PDB files ourselves.

At the same time, LLVM has a long history of being able to cross-compile from any platform to any platform, and we wish for the same to be true here. So it is necessary for us to understand the PDB file format at the byte-level so that we can generate PDB files entirely on our own.

This manual describes what we know about the PDB file format today. The layout of the file, the various streams contained within, the format of individual records within, and more.

We would like to extend our heartfelt gratitude to Microsoft, without whom we would not be where we are today. Much of the knowledge contained within this manual was learned through reading code published by Microsoft on their GitHub repo.

File Layout

Important

Unless otherwise specified, all numeric values are encoded in little endian. If you see a type such as uint16_t or uint64_t going forward, always assume it is little endian!

The MSF Container

A PDB file is an MSF (Multi-Stream Format) file. An MSF file is a “file system within a file”. It contains multiple streams (aka files) which can represent arbitrary data, and these streams are divided into blocks which may not necessarily be contiguously laid out within the MSF container file. Additionally, the MSF contains a stream directory (aka MFT) which describes how the streams (files) are laid out within the MSF.

For more information about the MSF container format, stream directory, and block layout, see The MSF File Format.

Streams

The PDB format contains a number of streams which describe various information such as the types, symbols, source files, and compilands (e.g. object files) of a program, as well as some additional streams containing hash tables that are used by debuggers and other tools to provide fast lookup of records and types by name, and various other information about how the program was compiled such as the specific toolchain used, and more. A summary of streams contained in a PDB file is as follows:

Name

Stream Index

Contents

Old Directory

  • Fixed Stream Index 0

  • Previous MSF Stream Directory

PDB Stream

  • Fixed Stream Index 1

  • Basic File Information

  • Fields to match EXE to this PDB

  • Map of named streams to stream indices

TPI Stream

  • Fixed Stream Index 2

  • CodeView Type Records

  • Index of TPI Hash Stream

DBI Stream

  • Fixed Stream Index 3

  • Module/Compiland Information

  • Indices of individual module streams

  • Indices of public / global streams

  • Section Contribution Information

  • Source File Information

  • References to streams containing FPO / PGO Data