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JSC: detect AVX on Darwin instead of assuming it (fixes SIGILL on pre-AVX Macs) #478

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WolfgangFahl wants to merge 2 commits into from
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JSC: detect AVX on Darwin instead of assuming it (fixes SIGILL on pre-AVX Macs) #478

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7302dea
JSC: detect AVX on Darwin instead of assuming it
WolfgangFahl Aug 20, 2026
0e9bb7f
JSC: use the generic probe trampoline selection on Darwin
WolfgangFahl Aug 22, 2026
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27 changes: 11 additions & 16 deletions Source/JavaScriptCore/assembler/MacroAssemblerX86_64.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -40,10 +40,8 @@ namespace JSC {

JSC_DECLARE_NOEXCEPT_JIT_OPERATION(ctiMasmProbeTrampoline, void, ());
JSC_ANNOTATE_JIT_OPERATION_PROBE(ctiMasmProbeTrampoline);
#if !OS(DARWIN)
JSC_DECLARE_NOEXCEPT_JIT_OPERATION(ctiMasmProbeTrampolineAVX, void, ());
JSC_ANNOTATE_JIT_OPERATION_PROBE(ctiMasmProbeTrampolineAVX);
#endif

// The following are offsets for Probe::State fields accessed by the ctiMasmProbeTrampoline stub.

Expand Down Expand Up @@ -193,7 +191,6 @@ static_assert(sizeof(Probe::State) == PROBE_SIZE, "Probe::State::size's matches
"vmovaps " STRINGIZE_VALUE_OF(PROBE_CPU_XMM14_VECTOR_OFFSET) "(%rbp), %xmm14" "\n" \
"vmovaps " STRINGIZE_VALUE_OF(PROBE_CPU_XMM15_VECTOR_OFFSET) "(%rbp), %xmm15" "\n"

#if !OS(DARWIN)
#define PROBE_XMM_SAVE_MOVAPS \
"movaps %xmm0, " STRINGIZE_VALUE_OF(PROBE_CPU_XMM0_VECTOR_OFFSET) "(%rsp)" "\n" \
"movaps %xmm1, " STRINGIZE_VALUE_OF(PROBE_CPU_XMM1_VECTOR_OFFSET) "(%rsp)" "\n" \
Expand Down Expand Up @@ -229,7 +226,6 @@ static_assert(sizeof(Probe::State) == PROBE_SIZE, "Probe::State::size's matches
"movaps " STRINGIZE_VALUE_OF(PROBE_CPU_XMM13_VECTOR_OFFSET) "(%rbp), %xmm13" "\n" \
"movaps " STRINGIZE_VALUE_OF(PROBE_CPU_XMM14_VECTOR_OFFSET) "(%rbp), %xmm14" "\n" \
"movaps " STRINGIZE_VALUE_OF(PROBE_CPU_XMM15_VECTOR_OFFSET) "(%rbp), %xmm15" "\n"
#endif // !OS(DARWIN)

#if COMPILER(MSVC)
#define ASM_PREVIOUS_SECTION
Expand Down Expand Up @@ -404,19 +400,13 @@ __asm__( \
ASM_PREVIOUS_SECTION \
);

#if OS(DARWIN)
// On macOS, all x86_64 CPUs support AVX. Use vmovaps unconditionally.
DEFINE_PROBE_TRAMPOLINE(ctiMasmProbeTrampoline, PROBE_XMM_SAVE_VMOVAPS, PROBE_XMM_RESTORE_VMOVAPS,
ctiMasmProbeTrampolineCopyLoop, ctiMasmProbeTrampolineProbeStateIsSafe, ctiMasmProbeTrampolineRestoreRegisters)
#else
// On Linux/Windows, AVX may not be available. Provide two trampolines:
// AVX may not be available. Provide two trampolines:
// - ctiMasmProbeTrampoline: uses movaps (SSE, always available on x86_64)
// - ctiMasmProbeTrampolineAVX: uses vmovaps (requires AVX)
DEFINE_PROBE_TRAMPOLINE(ctiMasmProbeTrampoline, PROBE_XMM_SAVE_MOVAPS, PROBE_XMM_RESTORE_MOVAPS,
ctiMasmProbeTrampolineCopyLoop, ctiMasmProbeTrampolineProbeStateIsSafe, ctiMasmProbeTrampolineRestoreRegisters)
DEFINE_PROBE_TRAMPOLINE(ctiMasmProbeTrampolineAVX, PROBE_XMM_SAVE_VMOVAPS, PROBE_XMM_RESTORE_VMOVAPS,
ctiMasmProbeTrampolineAVXCopyLoop, ctiMasmProbeTrampolineAVXProbeStateIsSafe, ctiMasmProbeTrampolineAVXRestoreRegisters)
#endif

// What code is emitted for the probe?
// ==================================
Expand Down Expand Up @@ -464,14 +454,10 @@ void MacroAssembler::probe(Probe::Function function, void* arg)
push(RegisterID::eax);
push(RegisterID::eax);

#if OS(DARWIN)
move(TrustedImmPtr(reinterpret_cast<void*>(ctiMasmProbeTrampoline)), RegisterID::eax);
#else
if (supportsAVX())
move(TrustedImmPtr(reinterpret_cast<void*>(ctiMasmProbeTrampolineAVX)), RegisterID::eax);
else
move(TrustedImmPtr(reinterpret_cast<void*>(ctiMasmProbeTrampoline)), RegisterID::eax);
#endif

push(RegisterID::edx);
move(TrustedImmPtr(reinterpret_cast<void*>(function)), RegisterID::edx);
Expand Down Expand Up @@ -517,7 +503,16 @@ void MacroAssemblerX86_64::collectCPUFeatures()
s_sse4_2CheckState = (cpuid[2] & (1 << 20)) ? CPUIDCheckState::Set : CPUIDCheckState::Clear;
s_popcntCheckState = (cpuid[2] & (1 << 23)) ? CPUIDCheckState::Set : CPUIDCheckState::Clear;
#if OS(DARWIN)
s_avxCheckState = CPUIDCheckState::Set;
// Every Mac Apple shipped with an x86_64 CPU newer than 2011 has AVX,
// but Westmere Mac Pros (5,1) run macOS 14 via OpenCore and do not.
// Ask the OS rather than assuming; the SSE fallbacks behind
// supportsAVX() already exist and are what those machines need.
{
uint32_t avxVal = 0;
size_t avxValSize = sizeof(avxVal);
int avxRc = sysctlbyname("hw.optional.avx1_0", &avxVal, &avxValSize, nullptr, 0);
s_avxCheckState = (avxRc >= 0 && avxVal) ? CPUIDCheckState::Set : CPUIDCheckState::Clear;
}
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#else
// Per the Intel SDM, AVX is usable only when:
// 1. CPUID.1:ECX.AVX[bit 28] = 1 (CPU supports AVX)
Expand Down