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Fix arm64 fragment unwinding #92678

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merged 1 commit into from
Sep 27, 2023
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Fix arm64 fragment unwinding #92678

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63 changes: 21 additions & 42 deletions src/coreclr/vm/codeman.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -920,35 +920,6 @@ BOOL IsFunctionFragment(TADDR baseAddress, PTR_RUNTIME_FUNCTION pFunctionEntry)
#endif
}

// When we have fragmented unwind we usually want to refer to the
// unwind record that includes the prolog. We can find it by searching
// back in the sequence of unwind records.
PTR_RUNTIME_FUNCTION FindRootEntry(PTR_RUNTIME_FUNCTION pFunctionEntry, TADDR baseAddress)
{
LIMITED_METHOD_DAC_CONTRACT;

PTR_RUNTIME_FUNCTION pRootEntry = pFunctionEntry;

if (pRootEntry != NULL)
{
// Walk backwards in the RUNTIME_FUNCTION array until we find a non-fragment.
// We're guaranteed to find one, because we require that a fragment live in a function or funclet
// that has a prolog, which will have non-fragment .xdata.
while (true)
{
if (!IsFunctionFragment(baseAddress, pRootEntry))
{
// This is not a fragment; we're done
break;
}

--pRootEntry;
}
}

return pRootEntry;
}

#endif // EXCEPTION_DATA_SUPPORTS_FUNCTION_FRAGMENTS


Expand Down Expand Up @@ -1134,12 +1105,30 @@ TADDR IJitManager::GetFuncletStartAddress(EECodeInfo * pCodeInfo)
#endif

TADDR baseAddress = pCodeInfo->GetModuleBase();
TADDR funcletStartAddress = baseAddress + RUNTIME_FUNCTION__BeginAddress(pFunctionEntry);

#if defined(EXCEPTION_DATA_SUPPORTS_FUNCTION_FRAGMENTS)
pFunctionEntry = FindRootEntry(pFunctionEntry, baseAddress);
#endif // EXCEPTION_DATA_SUPPORTS_FUNCTION_FRAGMENTS
// Is the RUNTIME_FUNCTION a fragment? If so, we need to walk backwards until we find the first
// non-fragment RUNTIME_FUNCTION, and use that one. This happens when we have very large functions
// and multiple RUNTIME_FUNCTION entries per function or funclet. However, all but the first will
// have the "F" bit set in the unwind data, indicating a fragment (with phantom prolog unwind codes).

TADDR funcletStartAddress = baseAddress + RUNTIME_FUNCTION__BeginAddress(pFunctionEntry);
for (;;)
{
if (!IsFunctionFragment(baseAddress, pFunctionEntry))
{
// This is not a fragment; we're done
break;
}

// We found a fragment. Walk backwards in the RUNTIME_FUNCTION array until we find a non-fragment.
// We're guaranteed to find one, because we require that a fragment live in a function or funclet
// that has a prolog, which will have non-fragment .xdata.
--pFunctionEntry;

funcletStartAddress = baseAddress + RUNTIME_FUNCTION__BeginAddress(pFunctionEntry);
}
#endif // EXCEPTION_DATA_SUPPORTS_FUNCTION_FRAGMENTS

return funcletStartAddress;
}
Expand Down Expand Up @@ -4133,8 +4122,6 @@ void EEJitManager::NibbleMapSetUnlocked(HeapList * pHp, TADDR pCode, BOOL bSet)
#endif // !DACCESS_COMPILE

#if defined(FEATURE_EH_FUNCLETS)
// Note: This returns the root unwind record (the one that describes the prolog)
// in cases where there is fragmented unwind.
PTR_RUNTIME_FUNCTION EEJitManager::LazyGetFunctionEntry(EECodeInfo * pCodeInfo)
{
CONTRACTL {
Expand Down Expand Up @@ -4163,14 +4150,6 @@ PTR_RUNTIME_FUNCTION EEJitManager::LazyGetFunctionEntry(EECodeInfo * pCodeInfo)

if (RUNTIME_FUNCTION__BeginAddress(pFunctionEntry) <= address && address < RUNTIME_FUNCTION__EndAddress(pFunctionEntry, baseAddress))
{

#if defined(EXCEPTION_DATA_SUPPORTS_FUNCTION_FRAGMENTS) && (defined(TARGET_ARM64) || defined(TARGET_LOONGARCH64) || defined(TARGET_RISCV64))
// If we might have fragmented unwind, and we're on ARM64/LoongArch64,
// make sure to returning the root record,
// as the trailing records don't have prolog unwind codes.
pFunctionEntry = FindRootEntry(pFunctionEntry, baseAddress);
#endif

return pFunctionEntry;
}
}
Expand Down
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