Merge pull request #1676 from tsujamin/msvc-runtime-stack-check-ffi-crash

Disable MSVC runtime stack checks in janet_ffi_win64

Author: bakpakin

src/core/ffi.c

@@ -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