ld: Align the PDB DBI source-info substream
Ensure PDB DBI source-info substream size is a multiple of 4 bytes, zero-padding any excess.
This patch modifies the linker (ld) to align the size of the PDB DBI source-info substream to a four-byte boundary, zeroing out any padding. This change ensures compliance with the PDB format’s requirement for four-byte alignment and determinism in padding bytes. A test case is extended to verify this behavior.
- proposer
Proposes aligning the source-info substream size to four bytes and zeroing padding, citing PDB format requirements.
“Round the source-info substream size up to four bytes and zero the padding. Extend the test to exercise this case. docs/pdb/dbi_sources.md in https://github.com/microsoft/pdb-rs says: "Invariant: The size of the DBI Sources Substream (source_info_size) is a multiple of 4." and "Determinism: Alignment padding bytes are set to zero, if present."”
- reviewer
Asks a clarifying question about potential issues with MSYS2's environment variable handling for path conversions in test cases.
“The workaround of course isn't very nice, and in particular doesn't scale. The page you reference doesn't address at all whether e.g. some form of quoting would also help. That certainly depends on where exactly the conversion is being done.”
- reviewer
Follows up on a previous question, suggesting appending to an environment variable rather than overwriting it to maintain global settings.
“In case the user has set the env var globally, wouldn't you better append to it (and then restore) rather than fully overwriting (and then deleting)?”
- proposer
Acknowledges Jan Beulich's concern about environment variable handling and agrees to append to the variable instead of overwriting it.
“On 18.09.2026 11:42, Jan Beulich wrote: > On 18.09.2026 11:36, Oleg Tolmatcev wrote: >> Round the source-info substream size up to four bytes and zero the >> padding. Extend the test to exercise this case. >> >> docs/pdb/dbi_sources.md in https://github.com/microsoft/pdb-rs says: >> "Invariant: The size of the DBI Sources Substream (source_info_size) is >> a multiple of 4." and "Determinism: Ali…”
Technical Tradeoffs
- Ensures PDB compatibility and determinism by adhering to alignment requirements.
- Introduces minor overhead for alignment calculation and zeroing padding.
In Details
This change modifies ld/pdb.c to ensure that the size of the PDB DBI source-info substream is a multiple of 4 bytes, as required by the PDB format specification. It also ensures padding bytes are zeroed. The test suite is updated to cover this alignment.