ⓘ Program database is a proprietary file format for storing debugging information about a program. PDB files commonly have a.pdb extension. A PDB file is typicall ..

                                     

ⓘ Program database

Program database is a proprietary file format for storing debugging information about a program. PDB files commonly have a.pdb extension. A PDB file is typically created from source files during compilation. It stores a list of all symbols in a module with their addresses and possibly the name of the file and the line on which the symbol was declared. This symbol information is not stored in the module itself, because it takes up a lot of space.

                                     

1. Applications

When a program is debugged, the debugger loads debugging information from the PDB file and uses it to locate symbols or relate current execution state of a program source code. Microsoft Visual Studio uses PDB files as its primary file format for debugging information.

Another use of PDB files is in services that collect crash data from users and relate it to the specific parts of the source code that cause or are involved in the crash.

Microsoft compilers will, under appropriate options, store information in a single PDB about types found in the compiled sources. Debug information specific to each source is stored in the compiled object file, and contains references to types in the PDB. Each compilation will add to the PDB any types that are not already found there, so that references in already compiled object files remain valid.

The Microsoft linker, under appropriate options, builds a complete new PDB which combines the debug information found in its input modules, the types referenced by those modules, and other information generated by the linker. If the link is performed incrementally, an existing PDB is modified by adding replacing only the information pertaining to added or replaced modules, and adding any new types not already in the PDB.

PDB files are usually removed from the programs distribution package. They are used by developers during debugging to save time and gain insight.

                                     

2. Extracting information

The PDB format is documented here, information can be extracted from a PDB file using the DIA Debug Interface Access interfaces, available on Microsoft Windows. There are also third-party tools that can also extract information from PDB such as radare2 and pdbparse

                                     

3. Multiple stream format

The PDB is a single file which is logically composed of several sub-files, called streams. It is designed to optimize the process of making changes to the PDB, as performed by compiles and incremental links. Streams can be removed, added, or replaced without rewriting any other streams, and the changes to the metadata which describes the streams is minimized as well.

The PDB is organized in fixed-size pages, typically 1K, 2K, or 4K, numbered consecutively starting at 0.

Note: It is presumed that all numeric information e.g., stream and page numbers is stored in little-endian form, the native form for Intel x86 based processors. The pdbparse Python code makes this assumption.

                                     

3.1. Multiple stream format Stream

Each stream in the PDB occupies several pages, which arent necessarily consecutively numbered. The stream has a number and a length. The stream content is the concatenation of its pages, truncated to the streams length.

                                     

3.2. Multiple stream format Metadata format

The function of the PDB metadata is to identify all of the component streams, giving the length, and sequence of pages for each stream. Streams are numbered consecutively starting with 0. There is also a root stream, unnumbered, which contains some of the metadata.

                                     

3.3. Multiple stream format Version 2

Signature is "Microsoft C/C++ program database 2.00\r\n\032JG\0\0" 44 bytes.

Remainder of the header consists of:

  • reserved, 4 bytes.
  • Root stream page number list, 2 bytes per page, enough to cover the above Root stream size.
  • Start page, 2 bytes.
  • Page size, 4 bytes.
  • Root stream size, 4 bytes.
  • Number of file pages, 2 bytes.


                                     

3.4. Multiple stream format Version 7

Signature is "Microsoft C/C++ MSF 7.00\r\n\x1ADS\0\0\0" 32 bytes.

Remainder of the header consists of:

  • Allocation table pointer, 4 bytes. The meaning of this is unknown. There appears to be an allocation table, an array of 65.536 bits 8.192 bytes, located at the end of the PDB, and a 1-bit means a page that is not being used.
  • reserved, 4 bytes.
  • Number of file pages, 4 bytes.
  • Root stream size, 4 bytes.
  • Page number of the Root stream page number list. It does not indicate the location of the Root stream itself, only of the page containing the structure which points to its pages. At that page, the Root stream page number list indicates the pages where the Root stream is stored. It contains 4 bytes per page, enough to cover the above Root stream size.
  • Page size, 4 bytes.
                                     

3.5. Multiple stream format Root stream

The root stream describes all of the PDB streams starting with stream 0. Its contents vary with the PDB format version.

                                     

3.6. Multiple stream format Version 2

The root stream consists of:

  • Reserved, 4 bytes.
  • Reserved, 2 bytes.
  • Number of streams, 2 bytes.
  • Stream size, 4 bytes.
  • For each stream
  • For each stream
  • Stream page number list, 2 bytes per page, enough to cover above stream size.
                                     

3.7. Multiple stream format Version 7

The root stream consists of:

  • Number of streams, 4 bytes.
  • For each stream
  • Stream size, 4 bytes.
  • Stream page number list, 4 bytes per page, enough to cover above stream size.
  • For each stream
                                     

3.8. Multiple stream format Stream contents

Microsoft tools store different sorts of information in different numbered streams. Some stream numbers have a fixed information type associated with them, and other streams are identified in the aforementioned fixed type streams.

Stream 1 is used to verify that the PDB is the same file referred to in an executable or object file stream.

  • Total length of following names, 4 bytes. Followed by null-terminated character strings.
  • Version, 4 bytes.
  • Time date stamp, 4 bytes.
  • GUID, 16 bytes.
  • Age, 4 bytes. This is the number of times this PDB has been modified since its creation.

Stream 2 and stream 4 hold types information. Actual type records define types used in the program. The structure of these records can be found in the file cvinfo.h provided by Microsoft. There are two flavors of records, each with its own set of index numbers: type IDs and types; only types are stored in stream 2 and only type IDs are stored in stream 4. The indices are used to refer to these records from within symbol records and other type records.

  • Header size, 4 bytes.
  • A header
  • Minimum and maximum last + 1 index for type records 4 bytes each.
  • Version, 4 bytes.
  • Size of following data, 4 bytes, to the end of the stream.
  • Hash key, 4 bytes.
  • Buckets, 4 bytes.
  • Stream number, 2 bytes with 2 bytes padding.
  • HashVals, TiOff, and HashAdj, each composed of an offset and length, each 4 bytes.
  • Hash information
  • Type records, variable length, count = maximum - minimum from above header.

Stream 3 is a directory for other streams. Note, it is not present in Version 2, nor in a PDB produced by a compiler. The stream starts with a header which is padded to be 64 bytes in total

  • Symbol info.
  • Opened, 4 bytes.
  • CRCs for section data and relocations data, 4 bytes each.
  • Section number, 2 bytes + 2 bytes padding.
  • Module number, 2 bytes + 2 bytes padding.
  • Flags, 4 bytes.
  • Module information, variable length. Total size in above header. There is one of these for each object module used by the linker
  • Offset and size, 4 bytes each.
  • Padding to multiple of 4 bytes.
  • Symbols size, 4 bytes.
  • Old and new line number info sizes, 4 bytes each.
  • Number of source files, 2 bytes + 2 bytes padding.
  • niSource and niCompiler, 4 bytes each.
  • Flags, 2 bytes.
  • Object name, null terminated byte string.
  • Stream number, 2 bytes.
  • Offsets, 4 bytes.
  • Module name, null terminated byte string.
  • Stream numbers for Old Frame Pointer Omission, Exceptions, Fixups, Object Maps to and from Source, Section Headers, Token Ring IDs, Xdata, Pdata, New Frame Pointer Omission, and Section Header Origin. 2 bytes each.
  • Section contributions, section headers, file info, ts map, and EC info. Their sizes are found in the above header.
  • Debug header,
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