[release/8.0-staging] Fix hardware exception context extraction on Rosetta #107199
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The recently added AVX support in hardware exception handling path on macOS x64 has introduced a problem when running under Rosetta. When we extract the floating point part of the context of the failing thread, the thread can have AVX or AVX512 active, or none of these. The code accidentally leaves CONTEXT_XSTATE set on the context even when no AVX was enabled on the thread. Rosetta doesn't support AVX, so having CONTEXT_XSTATE set in the context flags can lead to later call to RtlRestoreContext attempting to set ymm registers using instructions that Rosetta cannot emulate and the app crashes due to that. This doesn't happen in .NET 9, since we always clear the CONTEXT_XSTATE before exception handling stack unwinding. But in .NET 8, this causes stack overflow under Rosetta, since the attemt to execute the ymm instruction triggers the hardware exception handling again and again.
jeffschwMSFT
approved these changes
Aug 30, 2024
jkotas
approved these changes
Aug 30, 2024
rbhanda
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Friendly reminder that Code Complete for the October Release is September 9. If we want this fix to be included in that release, please merge this PR before that date. |
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Code complete is today. If this is ready, please merge it to include in the October Release. |
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Backport of #107188 to release/8.0-staging
/cc @janvorli
Customer Impact
The recently added AVX support in hardware exception handling path on macOS x64 that was also backported to .NET 8 has introduced a problem when running under Rosetta. Hardware exception handling always crashes when running as x64 under Rosetta emulation on arm64 macOS. The reason is that we try to set YMM registers and AVX instructions are not emulated by Rosetta.
Regression
Introduced in 8.0.8 by #104818
Testing
Directed test of a testing application where the issue got revealed and also running all coreclr tests under Rosetta.
Risk
Low, the change just removes CONTEXT_XSTATE flag from the captured context of the hardware exception location when the OS returns context without AVX.