Add source info to perfmap/jitdump by a74nh · Pull Request #126836 · dotnet/runtime

a74nh · 2026-04-13T14:09:12Z

Add PerfMapSymbolReader and GetInfoForMethod in System.Private.CoreLib to read PDB/embedded PDB sequence points for perfmap/jitdump.
Retarget the native delegate creation to System.Diagnostics.StackTrace from SOS.NETCore
Add JIT_CODE_DEBUG_INFO records using managed debug info, gated behind config variable

* Add PerfMapSymbolReader and GetInfoForMethod in System.Private.CoreLib to read PDB/embedded PDB sequence points for perfmap/jitdump. * Retarget the native delegate creation to System.Diagnostics.StackTrace from SOS.NETCore * Add JIT_CODE_DEBUG_INFO records using managed debug info, gated behind config variable

dotnet-policy-service · 2026-04-13T14:10:26Z

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Copilot

Pull request overview

This PR adds source/line debug-info support to perfmap/jitdump by introducing a managed PDB sequence-point reader and wiring CoreCLR’s perfmap/jitdump pipeline to emit JIT_CODE_DEBUG_INFO records (gated by a new config knob).

Changes:

Add PerfMapSymbolReader (System.Diagnostics.StackTrace) to read sequence points from associated/embedded Portable PDBs for a given method token.
Retarget native delegate creation to System.Diagnostics.StackTrace.GetInfoForMethod in System.Private.CoreLib and add re-entrancy guards.
Extend jitdump logging to optionally emit JIT_CODE_DEBUG_INFO records and plumb debug-info payloads from perfmap.cpp into PAL_PerfJitDump_LogMethod.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/libraries/System.Diagnostics.StackTrace/src/System/Diagnostics/PerfMapSymbolReader.cs	New managed helper to read sequence points from associated/embedded PDBs into a native buffer.
src/libraries/System.Diagnostics.StackTrace/src/System.Diagnostics.StackTrace.csproj	Include new source file in the StackTrace library build.
src/libraries/System.Diagnostics.StackTrace/src/ILLink/ILLink.Descriptors.LibraryBuild.xml	Preserve `PerfMapSymbolReader` for trimming scenarios.
src/coreclr/vm/perfmap.h	Add `s_EmitDebugInfo` toggle for debug-info emission.
src/coreclr/vm/perfmap.cpp	Build/emit serialized jitdump debug-info payload from managed sequence points when enabled.
src/coreclr/vm/gdbjithelpers.h	Update debug-info delegate signature to return `int` and take `MethodDebugInfo*`.
src/coreclr/vm/gdbjit.cpp	Add re-entrancy guard and update delegate invocation for new signature.
src/coreclr/pal/src/misc/perfjitdump.cpp	Add `JIT_CODE_DEBUG_INFO` record support and extend logging API to accept debug/unwind payloads + sizes.
src/coreclr/pal/inc/pal.h	Update `PAL_PerfJitDump_LogMethod` signature to include debug/unwind payload sizes and const pointers.
src/coreclr/inc/clrconfigvalues.h	Add `PerfMapEmitDebugInfo` config knob.
src/coreclr/dlls/mscoree/exports.cpp	Create the native delegate against `System.Private.CoreLib` / `System.Diagnostics.StackTrace.GetInfoForMethod`.

src/coreclr/vm/perfmap.cpp

src/libraries/System.Diagnostics.StackTrace/src/System/Diagnostics/PerfMapSymbolReader.cs

+        /// <summary>
+        /// Populate a native buffer with sequence points for the specified method token using the assembly's associated or embedded PDB.
+        /// </summary>
+        /// <returns>true if at least one sequence point was written; otherwise false.</returns>
+        internal static bool GetInfoForMethod([MarshalAs(UnmanagedType.LPUTF8Str)] string assemblyPath, int methodToken, IntPtr points, int size)
+        {
+            if (string.IsNullOrEmpty(assemblyPath) || points == IntPtr.Zero || size <= 0)
+            {
+                return false;
+            }


a74nh · 2026-04-13T14:22:14Z

This PR is useful for any tool or developer that uses linux perf to analyse .NET applications. Specifically, support is being added for use by Arm Performix, with the aim of using this to help migrate users.

Example output of perf annotate showing the line numbers from an example C# that was run through perf:

This PR was entirely written by codex. I've spent some time testing and reviewing the code. It looks sensible and works for me, however I don't claim to be familiar with some of these areas of CoreCLR.

@JulieLeeMSFT @dhartglassMSFT

a74nh · 2026-04-13T15:43:18Z

Still need to add tests. But, taking this out of draft to get some comments to see if this is in the right direction

Copilot

Pull request overview

This PR adds managed symbol-reading support to enrich perfmap/jitdump output with source/line information by reading Portable PDB sequence points, and wires the runtime to use this new managed helper when emitting perfmap/jitdump data.

Changes:

Add PerfMapSymbolReader (System.Diagnostics.StackTrace) and a CoreLib StackTrace.GetInfoForMethod unmanaged callback to retrieve sequence points from associated/embedded Portable PDBs.
Extend perfmap/jitdump plumbing to optionally emit JIT_CODE_DEBUG_INFO records (gated by PerfMapEmitDebugInfo) and update PAL jitdump logging to accept a debug-info payload.
Retarget the runtime delegate creation from SOS to System.Private.CoreLib / System.Diagnostics.StackTrace for debug-info retrieval.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/libraries/System.Diagnostics.StackTrace/src/System/Diagnostics/PerfMapSymbolReader.cs	New managed helper to read Portable PDB sequence points and fill a native buffer.
src/libraries/System.Diagnostics.StackTrace/src/System.Diagnostics.StackTrace.csproj	Includes the new `PerfMapSymbolReader.cs` in the build.
src/libraries/System.Diagnostics.StackTrace/src/ILLink/ILLink.Descriptors.LibraryBuild.xml	Preserves `PerfMapSymbolReader` for trimming scenarios.
src/coreclr/vm/perfmap.h	Adds `s_EmitDebugInfo` configuration flag.
src/coreclr/vm/perfmap.cpp	Emits optional jitdump debug-info payload and passes it to PAL jitdump logging.
src/coreclr/vm/gdbjithelpers.h	Updates the managed debug-info delegate signature to use a pointer and `int` return.
src/coreclr/vm/gdbjit.cpp	Adds re-entrancy guard and updates delegate invocation to new signature.
src/coreclr/System.Private.CoreLib/src/System/Diagnostics/StackTrace.CoreCLR.cs	Adds unmanaged callback (`GetInfoForMethod`) and UnsafeAccessor bridge into System.Diagnostics.StackTrace.
src/coreclr/pal/src/misc/perfjitdump.cpp	Adds `JIT_CODE_DEBUG_INFO` record support and extends `LogMethod` parameters.
src/coreclr/pal/inc/pal.h	Updates `PAL_PerfJitDump_LogMethod` signature to include debug/unwind buffers + sizes.
src/coreclr/inc/clrconfigvalues.h	Adds `PerfMapEmitDebugInfo` config value.
src/coreclr/dlls/mscoree/exports.cpp	Retargets delegate creation to `System.Diagnostics.StackTrace.GetInfoForMethod` and enables it for FEATURE_PERFMAP too.

src/coreclr/System.Private.CoreLib/src/System/Diagnostics/StackTrace.CoreCLR.cs

src/libraries/System.Diagnostics.StackTrace/src/System/Diagnostics/PerfMapSymbolReader.cs

src/coreclr/vm/gdbjit.cpp

src/coreclr/vm/perfmap.cpp

JulieLeeMSFT · 2026-04-13T17:12:32Z

@noahfalk, @brianrob, @steveisok, PTAL if it aligns with our diagnostics story. This change is related to the Performix tool supporting source annotation.

Copilot

Pull request overview

This PR adds source/line mapping support for perfmap/jitdump by introducing a managed symbol reader (Portable PDB / embedded PDB) and wiring it into CoreCLR’s perfmap and jitdump emission paths on Unix.

Changes:

Add PerfMapSymbolReader in System.Diagnostics.StackTrace and preserve it for trimming so CoreCLR can query Portable PDB sequence points.
Retarget the native debug-info delegate from SOS.NETCore to System.Private.CoreLib (System.Diagnostics.StackTrace.GetInfoForMethod) and adjust native delegate signatures/call sites.
Emit JIT_CODE_DEBUG_INFO records into jitdump (gated by the new PerfMapEmitDebugInfo config).

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/libraries/System.Diagnostics.StackTrace/src/System/Diagnostics/PerfMapSymbolReader.cs	New managed reader to extract sequence points from associated/embedded Portable PDBs.
src/libraries/System.Diagnostics.StackTrace/src/System.Diagnostics.StackTrace.csproj	Includes the new `PerfMapSymbolReader.cs` in the build.
src/libraries/System.Diagnostics.StackTrace/src/ILLink/ILLink.Descriptors.LibraryBuild.xml	Ensures `PerfMapSymbolReader` is preserved under trimming.
src/coreclr/vm/perfmap.h	Adds `s_EmitDebugInfo` config flag.
src/coreclr/vm/perfmap.cpp	Generates and logs serialized jitdump debug-info payloads when enabled.
src/coreclr/vm/gdbjithelpers.h	Updates delegate signature to use pointer + int return.
src/coreclr/vm/gdbjit.cpp	Adds reentrancy guard and updates delegate usage; attempts to handle missing locals.
src/coreclr/pal/src/misc/perfjitdump.cpp	Extends jitdump logging to optionally write `JIT_CODE_DEBUG_INFO` records and adjusts API.
src/coreclr/pal/inc/pal.h	Updates `PAL_PerfJitDump_LogMethod` signature to include buffer + size pairs.
src/coreclr/inc/clrconfigvalues.h	Adds `PerfMapEmitDebugInfo` config value.
src/coreclr/dlls/mscoree/exports.cpp	Retargets delegate creation to CoreLib StackTrace method and widens feature guard.
src/coreclr/System.Private.CoreLib/src/System/Diagnostics/StackTrace.CoreCLR.cs	Adds `UnmanagedCallersOnly` callback and UnsafeAccessor bridge to the library symbol reader.

src/coreclr/System.Private.CoreLib/src/System/Diagnostics/StackTrace.CoreCLR.cs

src/coreclr/vm/gdbjit.cpp

noahfalk · 2026-04-14T11:24:26Z

I'm hesitant that trying to do this source resolution at runtime will necessarily give the overall scenario characteristics you are looking for but we should discuss.

Do you expect all PDBs for relevant modules to be present on the disk when the application is running? Deploying PDBs is not typical for .NET apps and most other .NET profiling scenarios I can think of don't rely on this. You would need every developer who wants to use the profiler to do some manual deployment steps and/or create custom builds.
How much interference from the profiling code are you willing to tolerate? Searching for PDBs, loading them into memory, and parsing them is going to execute down different non-trivial codepaths and allocate a bunch of memory.
For self-contained apps I don't recall if anything is going to ensure the PDB parsing logic is always linked in. We'd need to investigate that or accept that on some apps it just wouldn't work.

The alternative that I've seen other profilers do is PDB/source resolution as a post-processing step after the trace is collected rather than at runtime. It requires at runtime capturing IP->IL offset mappings, then later using PDBs to convert IL -> source line info. Its probably a bit more complex to create initially but gives a higher fidelity result and supports acquiring symbols out-of-band such as from a symbol server. A couple possibilities on how that could be built:

if there is a way to smuggle IL information into a jitdump file it could be post-processed. I'm not aware that jitdump supports storing that kind of data so probably what this really means is creating a custom file format initially that turns into a valid jitdump after post-processing.
instead of trying to leverage the runtime's jitdump file writing capability we could use completely different mechanisms to write the initial file such as an EventPipe trace or a custom profiling plugin.

a74nh · 2026-04-14T13:17:09Z

I'm hesitant that trying to do this source resolution at runtime will necessarily give the overall scenario characteristics you are looking for but we should discuss.

Thanks.

Do you expect all PDBs for relevant modules to be present on the disk when the application is running? Deploying PDBs is not typical for .NET apps and most other .NET profiling scenarios I can think of don't rely on this. You would need every developer who wants to use the profiler to do some manual deployment steps and/or create custom builds.

Even if we did this as a post processing step instead (or in any other conceivable way) then the source code would need to be present at the point of processing.

This is all hidden behind an additional config variable (DOTNET_PerfMapEmitDebugInfo) which is off by default, so shouldn't cause any overhead for anyone who doesn't want this.

How much interference from the profiling code are you willing to tolerate? Searching for PDBs, loading them into memory, and parsing them is going to execute down different non-trivial codepaths and allocate a bunch of memory.

Agreed, this would be a concern as we want this to effect performance as little as possible.

This will overhead will happen at jit compilation time, not execution time. So mostly startup would be effected.

Looking at my test app, running it under Linux perf, with DOTNET_PerfMapEnabled=2 it took ~5.3 seconds. With DOTNET_PerfMapEmitDebugInfo=1 enabled too, it jumps to ~5.8 seconds (almost 10%). Increasing the internal loops in the test app took it to 44.8 secs and 45.3 seconds (now 1%).

Do you have an suggestions as to other ways to measure the impact?

Or at what level you'd consider this to be too much?

For self-contained apps I don't recall if anything is going to ensure the PDB parsing logic is always linked in. We'd need to investigate that or accept that on some apps it just wouldn't work.

Ok.

The alternative that I've seen other profilers do is PDB/source resolution as a post-processing step after the trace is collected rather than at runtime. It requires at runtime capturing IP->IL offset mappings, then later using PDBs to convert IL -> source line info. Its probably a bit more complex to create initially but gives a higher fidelity result and supports acquiring symbols out-of-band such as from a symbol server. A couple possibilities on how that could be built:

if there is a way to smuggle IL information into a jitdump file it could be post-processed. I'm not aware that jitdump supports storing that kind of data so probably what this really means is creating a custom file format initially that turns into a valid jitdump after post-processing.

Post processing would be a valid way of doing this

instead of trying to leverage the runtime's jitdump file writing capability we could use completely different mechanisms to write the initial file such as an EventPipe trace or a custom profiling plugin.

That would have the same issue that it'd be during runtime and so would effect performance?

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github-actions bot added the area-VM-coreclr label Apr 13, 2026

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a74nh added 2 commits April 13, 2026 15:23

array safe allocation for IL native map data

1c8baa5

fill the unused slots with a sentinel ilOffset

260baa0

a74nh marked this pull request as ready for review April 13, 2026 15:43

Copilot AI review requested due to automatic review settings April 13, 2026 15:43

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a74nh added 4 commits April 13, 2026 17:09

Explicity set locals and localsSize

a246dbe

Add try/catch

f6b729b

safer GetInfoForMethod

8bda1ba

Optimized the sequence point lookup

cb9e153

JulieLeeMSFT requested review from brianrob, noahfalk and steveisok April 13, 2026 17:10

JulieLeeMSFT assigned a74nh and noahfalk Apr 13, 2026

build-analysis bot mentioned this pull request Apr 13, 2026

System.Net.NameResolution.Tests DNS failures: Name or service not known #126641

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init vars in gdbjit

7a0ca38

Copilot AI review requested due to automatic review settings April 14, 2026 10:42

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src/coreclr/System.Private.CoreLib/src/System/Diagnostics/StackTrace.CoreCLR.cs Outdated Show resolved Hide resolved

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a74nh added 2 commits April 14, 2026 12:05

don't set locals to null

44c1fa9

Only consume locals if both pointer and size are valid

91866fa

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