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Fix false-positive assertion in CheckRegDisplaySP due to stale cached stack limit #126740

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Fix false-positive assertion in CheckRegDisplaySP due to stale cached stack limit #126740

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Copilot Apr 10, 2026
34ee568
Fix stale cached stack limit assertion in CheckRegDisplaySP
Copilot Apr 10, 2026
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7 changes: 7 additions & 0 deletions src/coreclr/vm/threads.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5687,7 +5687,14 @@ void CheckRegDisplaySP (REGDISPLAY *pRD)
if (pRD->SP && pRD->_pThread)
{
#ifndef NO_FIXED_STACK_LIMIT
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@jkotas jkotas Apr 10, 2026

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NO_FIXED_STACK_LIMIT is working around the same problem, just for Musl. If we find a better way to fix this, we should delete NO_FIXED_STACK_LIMIT.

// Use GetStackLowerBound() instead of GetCachedStackLimit() — on Linux the stack grows on demand
// and the cached limit can be stale if the stack has grown past the initially committed boundary.
// GetStackLowerBound() is only available in non-DAC builds.
#ifndef DACCESS_COMPILE
_ASSERTE(pRD->_pThread->IsExecutingOnAltStack() || PTR_VOID(pRD->SP) >= pRD->_pThread->GetStackLowerBound());
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@jkotas jkotas Apr 10, 2026

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PAL is caching the cache limits as well:

runtime/src/coreclr/pal/src/thread/thread.cpp

Lines 2396 to 2405 in 6adf63b

CPalThread::GetCachedStackBase()
{
_ASSERT_MSG(this == InternalGetCurrentThread(), "CPalThread::GetStackBase called from foreign thread");
if (m_stackBase == NULL)
{
m_stackBase = GetStackBase();
}
return m_stackBase;
. This is still going to use cached stack limit as far as I can tell.

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@jkotas jkotas Apr 10, 2026

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I think we will need to pass a bool flag all the way to the PAL to fetch non-cached stack limits.

Also, we make sure to use the cached stack limits most of the time to make this check cheap.

#else
_ASSERTE(pRD->_pThread->IsExecutingOnAltStack() || PTR_VOID(pRD->SP) >= pRD->_pThread->GetCachedStackLimit());
#endif // DACCESS_COMPILE
#endif // NO_FIXED_STACK_LIMIT
_ASSERTE(pRD->_pThread->IsExecutingOnAltStack() || PTR_VOID(pRD->SP) < pRD->_pThread->GetCachedStackBase());
}
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