Flush Crossgen2 R2R output stream before generating native PDB by Copilot · Pull Request #131607 · dotnet/runtime

Copilot · 2026-07-30T18:09:55Z

Crossgen2-generated native PDBs (*.ni.pdb) had an all-zero PDB-info GUID after the migration from R2RPEBuilder to PEObjectWriter, so the PDB could not satisfy the DLL's symbol-server lookup key and msdl symbol lookup failed for .NET 11 preview SDK R2R symbols.

Root cause

In ReadyToRunObjectWriter.EmitReadyToRunObjects, the output FileStream was declared with a method-scoped using, so it stayed open while SymbolFileBuilder.SavePdb ran. SavePdb → PdbWriter.WritePDBDataHelper reads the finished image back from disk (File.Copy(dllPath, ...)) to feed DIA. Since FileStream buffers writes until disposed, DIA read an incomplete on-disk image with a zeroed CodeView/RSDS GUID, producing a PDB whose identity didn't match the DLL.

Changes

ReadyToRunObjectWriter.cs: Scope the object emission in a nested using block so the stream is flushed and closed before any symbol file (PDB/PerfMap) reads the image from disk. Capture stream.Length inside the block for the map builder, which was the only remaining consumer of the open stream.

long outputFileSize;
using (FileStream stream = new FileStream(_objectFilePath, FileMode.Create))
{
    objectWriter.EmitObject(stream, _nodes, dumper: null, logger);
    outputFileSize = stream.Length;
}
// ... SavePdb / SavePerfMap now read a fully-flushed image

Notes

No regression test is added here: native PDB generation goes through DIA, which is Windows-only, and there is no cross-platform crossgen2 PDB test infrastructure to extend.

Fixes Crossgen2-generated native PDBs have zero PDB-info GUID after ObjectWriter migration #131605

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azure-pipelines · 2026-07-30T18:10:15Z

Azure Pipelines: 16 pipeline(s) were filtered out due to trigger conditions. There may be pipelines that require an authorized user to comment /azp run to run.

The FileStream that ReadyToRunObjectWriter writes the R2R image into was kept open (via a method-scoped `using`) while SymbolFileBuilder.SavePdb read the image back from disk to generate the native PDB. Because the FileStream buffers writes until disposed, the PDB writer could observe an incomplete image with a zeroed CodeView/RSDS GUID, producing native PDBs whose PDB-info GUID did not match the DLL. Close the stream (capturing the file size for the map builder) before generating symbol files. Co-authored-by: elinor-fung <47805090+elinor-fung@users.noreply.github.com>

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azure-pipelines · 2026-07-30T18:58:57Z

Azure Pipelines: Successfully started running 3 pipeline(s). 13 pipeline(s) were filtered out due to trigger conditions. There may be pipelines that require an authorized user to comment /azp run to run.

elinor-fung · 2026-07-30T19:01:57Z

No regression test is added here: native PDB generation goes through DIA, which is Windows-only, and there is no cross-platform crossgen2 PDB test infrastructure to extend.

@copilot We already have PdbChecker. Can we update that to also validate the PDB and image match?

Extend PdbChecker to optionally take the crossgen2 output image via a new `--image <file>` argument. When supplied, it reads the image's CodeView/RSDS debug record and verifies the DIA-reported PDB-info GUID/age is nonzero and matches the image identity, regressing the zero-GUID native PDB bug. Wire the crossgen2 R2R test PDB check to pass the output image. Co-authored-by: elinor-fung <47805090+elinor-fung@users.noreply.github.com>

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Avoid silently skipping validation and returning success when a PDB file argument is omitted but --image is supplied. Co-authored-by: elinor-fung <47805090+elinor-fung@users.noreply.github.com>

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Copilot · 2026-07-30T19:10:18Z

No regression test is added here: native PDB generation goes through DIA, which is Windows-only, and there is no cross-platform crossgen2 PDB test infrastructure to extend.

@copilot We already ha...

Done. PdbChecker now takes an optional --image <file> argument: when supplied it reads the image's CodeView/RSDS debug record and verifies the DIA-reported PDB-info GUID/age is nonzero and matches the image identity, failing otherwise. The crossgen2 R2R test PDB check in CLRTest.CrossGen.targets now passes the output image, so this runs as a regression guard for the zero-GUID bug.

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elinor-fung · 2026-07-30T19:49:17Z

        }
-        MSDiaSymbolReader reader = new MSDiaSymbolReader(args[0]);
+
+        string? pdbFile = null;


@copilot We can still require the pdb file to be args[0] (like it did before)

Done — the PDB file is back to args[0], with --image and symbol names parsed from the remaining args.

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elinor-fung · 2026-07-30T19:58:38Z

+    /// match the CodeView / RSDS debug record embedded in the output image. This guards
+    /// against native PDBs whose identity does not satisfy the image's symbol-server lookup key.
+    /// </summary>
+    private static void ValidatePdbMatchesImage(MSDiaSymbolReader reader, string imageFile)


@copilot can we just make MSDiaSymbol reader use loadAndValidateDataFromPdb if we have an image?

Done. MSDiaSymbolReader now reads the image's CodeView/RSDS GUID+age and calls loadAndValidateDataFromPdb when an image is provided, so DIA performs the identity match (and rejects the all-zero-GUID PDB) instead of comparing manually in Program.cs.

Note
This comment was generated by GitHub Copilot.

…taFromPdb Keep the PDB file as the first positional argument. When --image is supplied, MSDiaSymbolReader reads the image's CodeView/RSDS identity and loads the PDB via DIA's loadAndValidateDataFromPdb, which throws when the PDB-info GUID/age don't match the image (including the all-zero GUID regression), instead of comparing identities manually in Program.cs. Co-authored-by: elinor-fung <47805090+elinor-fung@users.noreply.github.com>

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Co-authored-by: elinor-fung <47805090+elinor-fung@users.noreply.github.com>

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elinor-fung · 2026-07-30T20:12:22Z

+    /// <summary>
+    /// PDB-info identity GUID as reported by DIA for the PDB file.
+    /// </summary>
+    public Guid PdbGuid { get; }
+
+    /// <summary>
+    /// PDB-info age as reported by DIA for the PDB file.
+    /// </summary>
+    public uint PdbAge { get; }
+
+    public MSDiaSymbolReader(string pdbFile, string? imageFile = null)


@copilot remove these properties. All we do is print out the GUID and age in the constructor.

Removed the PdbGuid/PdbAge properties; the GUID and age are now local variables printed in the constructor (809f5c6).

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Co-authored-by: elinor-fung <47805090+elinor-fung@users.noreply.github.com>

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Co-authored-by: Elinor Fung <elfung@microsoft.com>

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Files reviewed: 4/4 changed files
Comments generated: 1

            Console.WriteLine("PDB file:       {0}", pdbFile);
+            Console.WriteLine("PDB GUID:       {0}", pdbGuid);
+            IDiaSymbol globalScope = _diaSession.globalScope;
+            Console.WriteLine("PDB file:       {0}", pdbFile);
+            Console.WriteLine("PDB GUID:       {0}", globalScope.guid);
+            Console.WriteLine("PDB age:        {0}", globalScope.age);
            Console.WriteLine("Total symbols:  {0}", symbolsTotal);
            Console.WriteLine("Public symbols: {0}", _pdbSymbols.Count);


Initial plan

44ad1a3

Copilot AI assigned Copilot and elinor-fung Jul 30, 2026

Copilot AI review requested due to automatic review settings July 30, 2026 18:09

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Copilot AI linked an issue Jul 30, 2026 that may be closed by this pull request

Crossgen2-generated native PDBs have zero PDB-info GUID after ObjectWriter migration #131605

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Copilot AI review requested due to automatic review settings July 30, 2026 18:15

Copilot AI reviewed Jul 30, 2026

Copilot AI changed the title ~~[WIP] Fix zero PDB-info GUID in Crossgen2-generated native PDBs~~ Flush Crossgen2 R2R output stream before generating native PDB Jul 30, 2026

Copilot finished work on behalf of elinor-fung July 30, 2026 18:16

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github-actions Bot added the area-crossgen2-coreclr only use for closed issues label Jul 30, 2026

jkoritzinsky approved these changes Jul 30, 2026

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elinor-fung marked this pull request as ready for review July 30, 2026 18:58

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PdbChecker: error when --image is given without a PDB file

631b0c0

Avoid silently skipping validation and returning success when a PDB file argument is omitted but --image is supplied. Co-authored-by: elinor-fung <47805090+elinor-fung@users.noreply.github.com>

Copilot AI review requested due to automatic review settings July 30, 2026 19:10

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Copilot AI review requested due to automatic review settings July 30, 2026 20:05

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PdbChecker: document sig=0 for RSDS (PDB 7.0) validation

d013216

Co-authored-by: elinor-fung <47805090+elinor-fung@users.noreply.github.com>

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Remove PdbGuid/PdbAge properties from MSDiaSymbolReader, use locals

809f5c6

Co-authored-by: elinor-fung <47805090+elinor-fung@users.noreply.github.com>

Copilot AI review requested due to automatic review settings July 30, 2026 20:29

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Comment thread src/coreclr/tools/PdbChecker/MSDiaSymbolReader.cs Outdated

Comment thread src/coreclr/tools/PdbChecker/MSDiaSymbolReader.cs Outdated

Comment thread src/coreclr/tools/PdbChecker/MSDiaSymbolReader.cs Outdated

Apply batched suggestions from code review

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Co-authored-by: Elinor Fung <elfung@microsoft.com>

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Copilot AI commented Jul 30, 2026 •

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