w64: Fix definition of setjmp

The default definition of setjmp which is implemented in MinGW-w64
cannot be used with programs like QEMU which call longjmp from
code without structured exception handling (SEH).

This code therefore disables stack unwinding.

We could also implement SEH for QEMU's generated JIT code, but
that is much more difficult. Stack unwinding would also cost
execution time.

Signed-off-by: Stefan Weil <sw@weilnetz.de>

qemu-os-win32.h

@@ -56,6 +56,15 @@
 # define EWOULDBLOCK  WSAEWOULDBLOCK
 #endif
 
+#if defined(_WIN64)
+/* On w64, setjmp is implemented by _setjmp which needs a second parameter.
+ * If this parameter is NULL, longjump does no stack unwinding.
+ * That is what we need for QEMU. Passing the value of register rsp (default)
+ * lets longjmp try a stack unwinding which will crash with generated code. */
+# undef setjmp
+# define setjmp(env) _setjmp(env, NULL)
+#endif
+
 /* Declaration of ffs() is missing in MinGW's strings.h. */
 int ffs(int i);