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Merged
VSadov merged 3 commits into from
Feb 18, 2022
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Use CopyContext to restore saved context on X86 #65490

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Use CopyContext to restore saved context on X86
VSadov Feb 17, 2022
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VSadov Feb 18, 2022
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VSadov Feb 18, 2022
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8 changes: 7 additions & 1 deletion src/coreclr/vm/threadsuspend.cpp
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Expand Up @@ -2577,7 +2577,13 @@ int RedirectedHandledJITCaseExceptionFilter(
pFrame->Pop();

// Copy the saved context record into the EH context;
ReplaceExceptionContextRecord(pExcepPtrs->ContextRecord, pCtx);
// NB: cannot use ReplaceExceptionContextRecord here.
// these contexts may contain extended registers and may have different format
// for reasons such as alignment or context compaction
//
// REVIEW: CopyContext may fail. in theory. How should we handle that? FailFast?

@davidwrighton davidwrighton Feb 18, 2022

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Yes, FailFast is appropriate for failure here.

@davidwrighton davidwrighton Feb 18, 2022

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However, be careful calling new functions from this function. If they have destructors and the compiler chooses to inline them, the runtime will start crashing.

@VSadov VSadov Feb 18, 2022 •
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I was thinking of code like:

            if (!CopyContext(pTarget, pTarget->ContextFlags, pCtx))
            {
                STRESS_LOG1(LF_SYNC, LL_ERROR, "ERROR: Could not set context record, lastError = 0x%x\n", GetLastError());
                ThrowLastError();
            }

Would that fit here?

It is highly unlikely that copy would fail, but it'd be nice to have some diagnostics if that start happenning.

CONTEXT* pTarget = pExcepPtrs->ContextRecord;
CopyContext(pTarget, pTarget->ContextFlags, pCtx);

@janvorli janvorli Feb 17, 2022

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It seems it would make sense to modify the ReplaceExceptionContextRecord to use CopyContext instead.

@VSadov VSadov Feb 17, 2022

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I was not sure if ReplaceExceptionContextRecord can be used outside of Windows. Can it?

@filipnavara filipnavara Feb 17, 2022 •
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It's not readily obvious but it's always guarded by HOST_WINDOWS and/or !TARGET_UNIX so it looks Windows-only. CopyContext is available on Windows 7 SP1+ which is the minimum target at the moment so that should be fine too.

@VSadov VSadov Feb 17, 2022

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I also wonder if ReplaceExceptionContextRecord needs to handle extended context at all if suspension resume switches completely to the RtlRestoreContext plan.

@VSadov VSadov Feb 17, 2022 •
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I was not sure if ReplaceExceptionContextRecord can be used outside of Windows. Can it?

I have tried moving the fix into ReplaceExceptionContextRecord and that did not build on Linux, so that answers this.


DWORD espValue = pCtx->Esp;

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