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Use index [4] instead of [3] to save MXCSR in case cf-protection is enabled #70

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Merged
neboat merged 1 commit into from
Feb 20, 2026
Merged

Use index [4] instead of [3] to save MXCSR in case cf-protection is enabled #70

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4 changes: 3 additions & 1 deletion runtime/jmpbuf.h
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Original file line number Diff line number Diff line change
Expand Up @@ -27,7 +27,9 @@ typedef void *jmpbuf[JMPBUF_SIZE];

#if defined __i386__ || defined __x86_64__
// We use an otherwise unused entry in the jmpbuf to store MXCSR
#define JMPBUF_MXCSR(ctx) (ctx)[3]
// [0], [1], [2] hold fp, pc, sp.
// When cf-protection is enabled, [3] holds the shadow stack.
#define JMPBUF_MXCSR(ctx) (ctx)[4]
/**
* @brief Get MXCSR from jump buffer in__cilkrts_stack_frame. X86 and X86_64
* only.
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