doppio% cat /sys/src/libc/386/setjmp.s
TEXT	longjmp(SB), $0
	MOVL	r+4(FP), AX
	CMPL	AX, $0
	JNE	ok		/* ansi: "longjmp(0) => longjmp(1)" */
	MOVL	$1, AX		/* bless their pointed heads */
	...