[release/10.0] Fix SampleType field in ThreadSample event from Sample Profiler #124084
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…Profiler Backport of dotnet#124019 to release/10.0 ## Customer Impact - [X] Customer reported - [ ] Found internally The SampleType field in ThreadSample events from SampleProfiler was always reporting EP_SAMPLE_PROFILER_SAMPLE_TYPE_EXTERNAL even when threads were executing managed code. This causes incorrect profiling data for customers using diagnostics tools that rely on this event. Fixes dotnet#123996 ## Regression - [X] Yes - [ ] No This regressed in .NET 9 when SuspendAllThreads was ported from NativeAOT to CoreCLR (commit 00a8973). ## Testing The fix was verified by building CoreCLR with Debug/Checked configuration which validates the asmconstants offsets via compile-time assertions. ## Risk Low The change is minimal and self-contained: - Adds a new thread state flag (TS_SuspensionTrapped) using a previously unused bit - Sets/clears the flag in RareDisablePreemptiveGC when threads voluntarily suspend - Uses the flag instead of the removed m_gcModeOnSuspension field for sample type detection - The change is pay-for-play: only threads that were actually executing managed code participate
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Pull request overview
This PR is a backport of #124019 to the release/10.0 branch, fixing a regression in the SampleProfiler's ThreadSample event. In .NET 9+, the SampleType field incorrectly reported all samples as EP_SAMPLE_PROFILER_SAMPLE_TYPE_EXTERNAL instead of properly distinguishing managed code execution (EP_SAMPLE_PROFILER_SAMPLE_TYPE_MANAGED). The regression occurred when SuspendAllThreads was ported from NativeAOT to CoreCLR in commit 00a8973.
Changes:
- Introduces a new thread state flag
TS_SuspensionTrappedto track when threads voluntarily suspend while in managed (cooperative) mode - Removes the obsolete
m_gcModeOnSuspensionfield and related methods from the Thread class - Updates assembly offset constants for ARM64 and AMD64 platforms to reflect the reduced Thread structure size
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.
Show a summary per file
| File | Description |
|---|---|
| src/coreclr/vm/threads.h | Adds TS_SuspensionTrapped flag using previously unused bit 0x00000002; removes m_gcModeOnSuspension field and its accessor methods |
| src/coreclr/vm/threadsuspend.cpp | Sets TS_SuspensionTrapped when thread traps for suspension in cooperative mode; clears flag on resume |
| src/coreclr/vm/eventing/eventpipe/ep-rt-coreclr.cpp | Uses HasThreadState(TS_SuspensionTrapped) to determine sample type instead of deleted GetGCModeOnSuspension() |
| src/coreclr/vm/arm64/asmconstants.h | Adjusts m_pInterpThreadContext offset down by 8 bytes (0xb78→0xb70 Unix, 0xba0→0xb98 non-Unix) due to removed field |
| src/coreclr/vm/amd64/asmconstants.h | Adjusts m_pInterpThreadContext offset down by 8 bytes (0xb50→0xb48 Unix, 0xba8→0xba0 non-Unix) due to removed field |
steveisok
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jkotas
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Feb 6, 2026
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Backport of #124019 to release/10.0
Customer Impact
The SampleType field in ThreadSample events from SampleProfiler was always reporting EP_SAMPLE_PROFILER_SAMPLE_TYPE_EXTERNAL even when threads were executing managed code. This causes incorrect profiling data for customers using diagnostics tools that rely on this event.
Fixes #123996
Regression
This regressed in .NET 9 when SuspendAllThreads was ported from NativeAOT to CoreCLR (commit 00a8973).
Testing
Manual
Risk
Low
The change is minimal and self-contained: