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[release/10.0] Don't crash when walking callstack roots in the debugger - #136161
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Changeset 1fa1745 introduced a stack walking regression where we will crash trying to unwind/report registers. The real fix here is in cgenamd64.cpp/excep.cpp, which will point the context to a local copy before we try to use it. I've also added some changes in gcinfodecoder.cpp that aren't strictly necessary but would have avoided the problem to begin with. Fixes #124401.
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Backport of #124402 to release/10.0
Fixes #135590
/cc @max-charlamb @leculver
Customer Impact
Reported in #135590 on .NET 10.0.12. Debugger and diagnostics tools crash with a native SIGSEGV inside
libmscordaccorewhen the DAC walks stack roots. Examples are ClrMDEnumerateStackRoots()on a live process, anddotnet-dumpclrstack -gc/gcrooton Linux amd64 dumps. Expected: stack roots are enumerated. Actual: the tool process crashes. This affects any tool built on the DAC stack-root enumeration (dotnet-dump, ClrMD-based tools, and memory/heap analysis in debuggers).Regression
Introduced by #108480 ("Improve software exception handling performance", 1fa1745), which has been in release/10.0 since 10.0.0-preview.1. A partial fix (1a5af14) handled x86 only. This change covers the remaining architectures.
Testing
Verified locally on Linux x64 Release, using an unmodified 10.0.12 runtime and swapping only
libmscordaccore.so. The repro is the one from #135590 (live ClrMDEnumerateStackRoots()under load):GetStackSlot(GC_FRAMEREG_REL) dereferencingpCurrentContextPointers->Rbp, an unmapped target-process address, while the local context copy was valid.Risk
Low. The change only affects
DACCESS_COMPILEcode (SoftwareExceptionFrame/FaultingExceptionFrameUpdateRegDisplay). It makes the DAC register pointers refer to the localpRD->pCurrentContextcopy instead of target memory. The runtime (non-DAC) paths are unchanged. It is the same diff that has been on main since #124402.IMPORTANT: This backport targets
release/10.0(no-stagingsuffix), as required for .NET 10+.