Capture build-id in module load events on Linux #116865
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Module load events on Windows carry a GUID of the matching PDB. This is used to verify the PDB that is used to analyze traces matches the one of the program. On Linux, we don't have PDBs and PDB GUID. Instead, we have build-id. Build-id is a binary blob of an unspecified length that is stored both in .debug files and in the program binary. Typically, it is 20 bytes (SHA-1). Since 20 is more than 16, it unfortunately doesn't fit in the space we have. The event however has two GUIDs. So use the space from the other event to store rest of the bits. Should be futureproof up to SHA-256.
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Tagging subscribers to this area: @agocke, @MichalStrehovsky, @jkotas |
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Pull Request Overview
This PR extends module load tracing on Linux to capture the ELF build-id (up to SHA-256) by repurposing the extra GUID field in module events.
- Expanded
PalGetPDBInfoto accept and zero-initialize apManagedGuidSignaturefor overflow build-id bytes. - Added a Linux-specific implementation in
PalUnix.cppthat iterates program headers to extract the GNU build-id into two GUIDs. - Updated
eventtrace.cppto pass the new managed GUID into module load events.
Reviewed Changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.
| File | Description |
|---|---|
| src/coreclr/nativeaot/Runtime/windows/PalCommon.cpp | Extended PalGetPDBInfo signature and initialized the new GUID |
| src/coreclr/nativeaot/Runtime/unix/PalUnix.cpp | Implemented ELF build-id extraction via dl_iterate_phdr |
| src/coreclr/nativeaot/Runtime/eventtrace.cpp | Passed the new managed GUID into module load ETW events |
| src/coreclr/nativeaot/Runtime/Pal.h | Updated PalGetPDBInfo declaration to include pManagedGuidSignature |
Comments suppressed due to low confidence (2)
src/coreclr/nativeaot/Runtime/eventtrace.cpp:382
- [nitpick] The variable dwAge is used to store the build-id length on Linux but retains its original name suggesting PDB age. Consider renaming dwAge to buildIdLength or a more descriptive name to reflect its dual purpose.
uint32_t dwAge;
src/coreclr/nativeaot/Runtime/Pal.h:164
- The function signature for PalGetPDBInfo has changed to include the pManagedGuidSignature parameter. Please update or add a documentation comment to describe the purpose and behavior of this new parameter.
void PalGetPDBInfo(HANDLE hOsHandle, GUID * pGuidSignature, _Out_ uint32_t * pdwAge, _Out_writes_z_(cchPath) WCHAR * wszPath, int32_t cchPath, GUID * pManagedGuidSignature);
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A general question on this: My understanding (and I could be very wrong on this) is that NativeAOT only emits one merged binary. If that's the case, are you expecting this event to be emitted once for the merged binary? If so, we may not need to do this at all - native profilers will get the build ID on their own through the OS mmap event and I'm not sure that eventpipe will ever need it. |
Yep, only one native binary. .NET native had a mode where there could be 3 native binaries. Assume I have an already running process and execute |
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/azp run runtime-nativeaot-outerloop |
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Azure Pipelines successfully started running 1 pipeline(s). |
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/ba-g unable to match the failure with #117015 that I just filed for some reason |
Module load events on Windows carry a GUID of the matching PDB. This is used to verify the PDB that is used to analyze traces matches the one of the program.
On Linux, we don't have PDBs and PDB GUID. Instead, we have build-id. Build-id is a binary blob of an unspecified length that is stored both in .debug files and in the program binary. Typically, it is 20 bytes (SHA-1). Since 20 is more than 16, it unfortunately doesn't fit in the space we have. Emit a new version of the event that can fit it.
Cc @brianrob @noahfalk @dotnet/ilc-contrib