Fix CopyOSContext on amd64 #120300
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Fix CopyOSContext on amd64 #120300
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The CopyOSContext was skipping floating point registers on amd64. There was an obsolete comment that on some older Windows, the vector registers are not present in the context. I've found to be a problem when porting nativeAOT EH to CoreCLR and to make the context flags correct, I've removed the CONTEXT_FLOATING_POINT from the ContextFlags. But it now turned out that it prevents EH from correctly restoring non-volatile floating point registers after a catch. Since he ContextFlags don't contain the CONTEXT_FLOATING_POINT, the floating point registers were not restored during the resume. This change fixes it by removing the amd64 specific handling and always copying the whole CONTEXT structure. It just masks off the CONTEXT_XSTATE, as the XSTATE is stored out of the basic CONTEXT. Close dotnet#118564
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Pull Request Overview
Fix ensures floating point (non-volatile) registers are preserved/restored on AMD64 during exception handling by copying the full CONTEXT instead of omitting floating point parts.
- Removes legacy partial copy logic specific to older AMD64 Windows platforms.
- Adjusts ContextFlags post-copy to exclude XSTATE (stored separately).
jkotas
approved these changes
Oct 1, 2025
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/backport to release/10.0 |
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Started backporting to release/10.0: https://github.com/dotnet/runtime/actions/runs/18197632320 |
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The CopyOSContext was skipping floating point registers on amd64. There was an obsolete comment that on some older Windows, the vector registers are not present in the context. I've found to be a problem when porting nativeAOT EH to CoreCLR and to make the context flags correct, I've removed the CONTEXT_FLOATING_POINT from the ContextFlags. But it now turned out that it prevents EH from correctly restoring non-volatile floating point registers after a catch. Since he ContextFlags don't contain the CONTEXT_FLOATING_POINT, the floating point registers were not restored during the resume.
This change fixes it by removing the amd64 specific handling and always copying the whole CONTEXT structure. It just masks off the CONTEXT_XSTATE, as the XSTATE is stored out of the basic CONTEXT.
Close #118564