Call into PerfMap logic exclusively in preemptive mode by davidwrighton · Pull Request #129019 · dotnet/runtime

davidwrighton · 2026-06-04T22:18:07Z

This PR makes the PerfMap apis available on Windows, where our contracts work, and provides stub implementations which have the appropriate contracts. Then, I went through the codebase and found the places where we would need to transition to preemptive to make it all safe. As I found a number of the codepaths were actually GC_NOTRIGGER code paths, I pushed the work upstream until the logic primarily converted was all calls to entrypoint apis, and all non-allow creation calls to FindOrCreateAssociatedMethodDesc

This probably isn't suitable for backport to fix the customer reported issue, but is a reason to avoid implementing the deferred PerfMap writing logic, and simply implement the UNSAFE_ANYMODE lock that @hoyosjs first investigated as a fix, since its significant downsides can be mitigated with this work in future releases.

NOTE: this is draft as I'm expecting that I missed a few places where we need transition, and I need to investigate if there is a perf impact on reflection.

…ere Contracts are supported)

…e various techniques for getting an entrypoint, and FindAssociatedMethodDesc are called in preemptive code. This has the effect that the PerfMap::LogStubs logic is always called in preemptive mode, and thus taking the critical section in it won't trigger a GC transition.

dotnet-policy-service · 2026-06-04T22:20:03Z

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Pull request overview

This PR updates CoreCLR VM call paths and contracts so PerfMap-related entrypoints (and a set of closely-related MethodDesc/slot resolution APIs) are only invoked in preemptive GC mode, and it removes many FEATURE_PERFMAP include/usage guards by providing always-available PerfMap APIs (with stubs when the feature is off).

Changes:

Introduces/uses conditional GCX_PREEMP / GCX_MAYBE_PREEMP transitions around stub generation and MethodDesc entrypoint resolution to satisfy PerfMap and related contract requirements.
Removes #ifdef FEATURE_PERFMAP wrappers at many call sites and centralizes “no-feature” behavior via stubbed PerfMap APIs.
Adjusts multiple VM contracts (e.g., MODE_ANY → MODE_PREEMPTIVE) and refactors some call helpers / delegate QCall plumbing accordingly.

Reviewed changes

Copilot reviewed 44 out of 44 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/coreclr/vm/virtualcallstub.cpp	Wraps stub generation with conditional preemptive transitions; unguards PerfMap logging.
src/coreclr/vm/threads.cpp	Unguards PerfMap logging for write barrier copy stubs.
src/coreclr/vm/stublink.cpp	Unguards PerfMap logging for emitted stubs.
src/coreclr/vm/runtimehandles.cpp	Narrows cooperative transitions in QCalls; adds preemptive transition for wrapper-stub unwrap.
src/coreclr/vm/riscv64/stubs.cpp	Unguards dynamic helper PerfMap logging macro.
src/coreclr/vm/reflectioninvocation.cpp	Moves call-target retrieval into a preemptive region.
src/coreclr/vm/readytoruninfo.cpp	Unguards PerfMap logging for dynamic helper precodes.
src/coreclr/vm/qcall.h	Adds `ObjectHandleOnStack::IsNull()` helper.
src/coreclr/vm/prestub.cpp	Unguards PerfMap logging; adds preemptive transition in dynamic helper worker path.
src/coreclr/vm/precode.cpp	Unguards PerfMap logging for various precode allocations.
src/coreclr/vm/perfmap.h	Adds stub PerfMap class under `!FEATURE_PERFMAP`; keeps real implementation under feature.
src/coreclr/vm/methodtable.inl	Changes GetMethodDescForSlot contract to `MODE_PREEMPTIVE`.
src/coreclr/vm/methodtable.cpp	Shifts several contracts to `MODE_PREEMPTIVE`; adds local coop regions for managed ref access.
src/coreclr/vm/method.hpp	Removes declaration of `FindOrCreateExactClassMethod`.
src/coreclr/vm/method.cpp	Broad contract/mode changes and added coop subregions for `OBJECTREF` access.
src/coreclr/vm/loongarch64/stubs.cpp	Unguards dynamic helper PerfMap logging macro.
src/coreclr/vm/jitinterface.cpp	Unguards PerfMap header include.
src/coreclr/vm/jithelpers.cpp	Adds preemptive transition before virtualized call target resolution.
src/coreclr/vm/interpexec.cpp	Adds preemptive transitions around virtualized MethodDesc resolution in interpreter.
src/coreclr/vm/i386/cgenx86.cpp	Unguards dynamic helper PerfMap logging macro.
src/coreclr/vm/genmeth.cpp	Removes helper API; adjusts contracts for instantiation/associated MethodDesc creation.
src/coreclr/vm/fptrstubs.cpp	Adds preemptive transition earlier in FuncPtr stub creation path.
src/coreclr/vm/eventing/eventpipe/ds-rt-coreclr.h	Updates contracts around perfmap enable path.
src/coreclr/vm/dllimportcallback.cpp	Unguards PerfMap logging and updates mode contracts for UM entry thunk paths.
src/coreclr/vm/dispatchinfo.cpp	Reorders GC mode transitions; shifts GetMemberInfoMap contract to preemptive.
src/coreclr/vm/customattribute.cpp	Precomputes ctor call target in preemptive mode and uses new callsite ctor.
src/coreclr/vm/corhost.cpp	Wraps `GetSingleCallableAddrOfCode` in preemptive region.
src/coreclr/vm/comutilnative.cpp	Avoids holding `OBJECTREF` across regions; uses MethodTable* in preemptive mode.
src/coreclr/vm/comdelegate.h	Changes QCall signature for `Delegate_AdjustTarget`.
src/coreclr/vm/comdelegate.cpp	Adds preemptive transitions around method desc association/entrypoint resolution; updates AdjustTarget QCall.
src/coreclr/vm/comconnectionpoints.cpp	Caches entrypoints in preemptive mode before invoking managed entrypoints.
src/coreclr/vm/comcallablewrapper.cpp	Changes a contract to `MODE_PREEMPTIVE`.
src/coreclr/vm/codeman.h	Adds a stub `ReportStubBlock` with preemptive-mode contract when perfmap is off.
src/coreclr/vm/codeman.cpp	Unguards PerfMap logging for jump stub emission.
src/coreclr/vm/class.cpp	Updates boxing/unboxing entrypoint helpers to `MODE_PREEMPTIVE`.
src/coreclr/vm/ceemain.cpp	Unguards PerfMap header include.
src/coreclr/vm/callhelpers.h	Refactors `MethodDescCallSite` to take an explicit `PCODE` call target.
src/coreclr/vm/callhelpers.cpp	Adjusts default ctor invocation to precompute callable entrypoint in preemptive region.
src/coreclr/vm/assembly.cpp	Wraps `GetSingleCallableAddrOfCode` in preemptive region for main entry.
src/coreclr/vm/arm64/stubs.cpp	Unguards dynamic helper PerfMap logging macro.
src/coreclr/vm/arm/stubs.cpp	Unguards dynamic helper PerfMap logging macro.
src/coreclr/vm/amd64/cgenamd64.cpp	Unguards dynamic helper PerfMap logging macro; modifies END macro behavior.
src/coreclr/System.Private.CoreLib/src/System/Delegate.CoreCLR.cs	Updates AdjustTarget interop to pass MethodTable* and keep target alive.
src/coreclr/debug/ee/funceval.cpp	Adds preemptive transitions around call target resolution for func-eval.

 #define BEGIN_DYNAMIC_HELPER_EMIT(size) \
    BEGIN_DYNAMIC_HELPER_EMIT_WORKER(size) \
    PerfMap::LogStubs(__FUNCTION__, "DynamicHelper", (PCODE)p, size, PerfMapStubType::Individual);
-#else
-#define BEGIN_DYNAMIC_HELPER_EMIT(size) BEGIN_DYNAMIC_HELPER_EMIT_WORKER(size)
-#endif

 #define END_DYNAMIC_HELPER_EMIT() \
-    _ASSERTE(pStart + cb == p); \
-    while (p < pStart + cbAligned) *p++ = X86_INSTR_INT3; \
    ClrFlushInstructionCache(pStartRX, cbAligned); \
    return (PCODE)pStartRX


        [LibraryImport(RuntimeHelpers.QCall, EntryPoint = "Delegate_AdjustTarget")]
-        private static partial IntPtr AdjustTarget(ObjectHandleOnStack target, IntPtr methodPtr);
+        private static partial IntPtr AdjustTarget(MethodTable* targetMT, IntPtr methodPtr);



    CONTRACT(MethodDesc*)
    {
+        MODE_PREEMPTIVE;
        THROWS;
-        if (allowCreate) { GC_TRIGGERS; } else { GC_NOTRIGGER; }
+        if (allowCreate) { MODE_PREEMPTIVE; } else { MODE_ANY; }
        if (!allowCreate) { SUPPORTS_DAC; }
        INJECT_FAULT(COMPlusThrowOM(););


jkotas · 2026-06-05T02:05:17Z

Switching more C/C++ loader code that does heavy lifting to preemptive mode is general goodness.

The test failures are related and needs fixing:

Fatal error.
Internal CLR error. (0x80131506 (COR_E_EXECUTIONENGINE))
   at System.Delegate.BindToMethodInfo(System.Object, System.IRuntimeMethodInfo, System.RuntimeType, System.DelegateBindingFlags)
   at System.Delegate.CreateDelegateInternal(System.RuntimeType, System.Reflection.RuntimeMethodInfo, System.Object, System.DelegateBindingFlags)

davidwrighton added 2 commits June 4, 2026 14:37

Make incorrect PerfMap usage trigger contract failures on Windows (wh…

99f405d

…ere Contracts are supported)

Copilot AI review requested due to automatic review settings June 4, 2026 22:18

github-actions Bot added the area-VM-coreclr label Jun 4, 2026

Copilot started reviewing on behalf of davidwrighton June 4, 2026 22:18 View session

davidwrighton requested review from hoyosjs and jkotas June 4, 2026 22:18

dotnet-policy-service Bot assigned davidwrighton Jun 4, 2026

Copilot AI reviewed Jun 4, 2026

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Update genmeth.cpp

e1f7ef1

This was referenced Jun 5, 2026

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Call into PerfMap logic exclusively in preemptive mode#129019

Call into PerfMap logic exclusively in preemptive mode#129019
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Pull request overview

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jkotas commented Jun 5, 2026

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