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Disable MSVC runtime stack checks in janet_ffi_win64

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The MSVC /RTCs argument instrument alloca() to prepend stack allocations
with metadata used to check for memory corruption during the function
prologue. This causes stack-based FFI arguments in janet_ffi_win64 to
become mis-aligned, and also for the alloca()-prepended header to be
corrupted leading to a fatal exception.
This commit is contained in:
Benjamin Roberts
2025-12-01 15:37:09 -05:00
parent 73334f3485
commit a85689312a
1 changed files with 13 additions and 0 deletions
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13
src/core/ffi.c
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@@ -1344,6 +1344,15 @@ typedef double (win64_variant_f_ffif)(double, double, uint64_t, double);
typedef double (win64_variant_f_fffi)(double, double, double, uint64_t);
typedef double (win64_variant_f_ffff)(double, double, double, double);
/* MSVC stack frame runtime error checking (/RTCs) prepends alloca() allocations with an _RTC_ALLOCA_NODE
* header; misalligning stack-based FFI arguments and causing the memmove() (by stack_shift) to corrupt
* the _RTC_ALLOCA_NODE header.
*
* We turn off the RTC-instrumented alloca() and adding of _RTC_CheckStackVars to function prologue just
* for janet_ffi_win64() */
#ifdef __MSVC_RUNTIME_CHECKS
#pragma runtime_checks( "s", off )
#endif
static Janet janet_ffi_win64(JanetFFISignature *signature, void *function_pointer, const Janet *argv) {
union {
uint64_t integer;
@@ -1493,6 +1502,10 @@ static Janet janet_ffi_win64(JanetFFISignature *signature, void *function_pointe
return janet_ffi_read_one(ret_mem, signature->ret.type, JANET_FFI_MAX_RECUR);
}
#ifdef __MSVC_RUNTIME_CHECKS
// Restore stack frame runtime error checking (/RTCs) if it was enabled.
#pragma runtime_checks ( "s", restore )
#endif
#endif