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Fix SIGILL crash on ARM64 platforms with SME but no SVE #127398

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Fix SIGILL crash on ARM64 platforms with SME but no SVE #127398

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65d64d8
Fix SIGILL crash on ARM64 platforms with SME but no SVE (dotnet/runti…
Apr 24, 2026
5bf6f17
Address review feedback: remove redundant assert, derive vq from sve->vl
Apr 24, 2026
3dd6e51
Address review feedback: clean up dead code and improve assertions
Apr 24, 2026
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8 changes: 0 additions & 8 deletions src/coreclr/pal/src/arch/arm64/context2.S
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Original file line number Diff line number Diff line change
Expand Up @@ -296,11 +296,3 @@ LEAF_END RestoreCompleteContext, _TEXT

#endif // __APPLE__

// Incoming:
// None
//
.arch_extension sve
LEAF_ENTRY CONTEXT_GetSveLengthFromOS, _TEXT
rdvl x0, 1
ret lr
LEAF_END CONTEXT_GetSveLengthFromOS, _TEXT
15 changes: 0 additions & 15 deletions src/coreclr/pal/src/include/pal/context.h
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Expand Up @@ -1622,21 +1622,6 @@ DWORD CONTEXTGetExceptionCodeForSignal(const siginfo_t *siginfo,

#endif // HAVE_MACH_EXCEPTIONS else

#if defined(HOST_ARM64)
/*++
Function :
CONTEXT_GetSveLengthFromOS
Gets the SVE vector length
Parameters :
None
Return value :
The SVE vector length in bytes
--*/
DWORD64
CONTEXT_GetSveLengthFromOS(
);
#endif // HOST_ARM64

#ifdef __cplusplus
}
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17 changes: 13 additions & 4 deletions src/coreclr/pal/src/thread/context.cpp
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Expand Up @@ -896,11 +896,17 @@ void CONTEXTToNativeContext(CONST CONTEXT *lpContext, native_context_t *native)
if (sve && sve->head.size >= SVE_SIG_CONTEXT_SIZE(sve_vq_from_vl(sve->vl)))
{
//TODO-SVE: This only handles vector lengths of 128bits.
if (CONTEXT_GetSveLengthFromOS() == 16)
// Use sve->vl from the signal frame to avoid SIGILL on platforms that
// provide an SVE context record without supporting SVE instructions
// (e.g. Apple M4 with SME streaming SVE under Virtualization.Framework).
if (sve->vl == 16)
{
_ASSERT((lpContext->XStateFeaturesMask & XSTATE_MASK_ARM64_SVE) == XSTATE_MASK_ARM64_SVE);

Comment on lines +902 to 905
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Copilot AI Apr 24, 2026

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In CONTEXTToNativeContext, the SVE block later derives vq from lpContext->Vl and relies only on an _ASSERTE to ensure lpContext->Vl == sve->vl. Since _ASSERTE is compiled out in non-debug builds, a mismatch in release could make the subsequent offset calculations write to the wrong locations in the signal frame. Consider computing vq from sve->vl (the actual frame layout) and using a non-assert runtime check for equality before writing, otherwise skip updating the SVE region.

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uint16_t vq = sve_vq_from_vl(lpContext->Vl);
// Derive vq from the signal frame's vl (the authoritative layout)
// rather than lpContext->Vl, to ensure offset calculations always
// match the actual frame even in non-debug builds.
uint16_t vq = sve_vq_from_vl(sve->vl);

// Vector length should not have changed.
_ASSERTE(lpContext->Vl == sve->vl);
Expand Down Expand Up @@ -1255,9 +1261,12 @@ void CONTEXTFromNativeContext(const native_context_t *native, LPCONTEXT lpContex
if (sve && sve->head.size >= SVE_SIG_CONTEXT_SIZE(sve_vq_from_vl(sve->vl)))
{
//TODO-SVE: This only handles vector lengths of 128bits.
if (CONTEXT_GetSveLengthFromOS() == 16)
// Use sve->vl from the signal frame to avoid SIGILL on platforms that
// provide an SVE context record without supporting SVE instructions
// (e.g. Apple M4 with SME streaming SVE under Virtualization.Framework).
if (sve->vl == 16)
{
_ASSERTE((sve->vl > 0) && (sve->vl % 16 == 0));
_ASSERTE(sve->head.size >= SVE_SIG_CONTEXT_SIZE(sve_vq_from_vl(16)));
lpContext->Vl = sve->vl;

uint16_t vq = sve_vq_from_vl(sve->vl);
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