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From: moore%cdr.utah.edu@wasatch.UUCP (Tim Moore)
Newsgroups: comp.lang.c
Subject: Re: Behaviour of setjmp/longjmp and registers
Message-ID: <944@wasatch.UUCP>
Date: 20 Jan 89 21:21:19 GMT
References: <25@torsqnt.UUCP>
Sender: news@wasatch.UUCP
Reply-To: moore%cdr.utah.edu.UUCP@wasatch.UUCP (Tim Moore)
Organization: University of Utah, Computer Science Dept.
Lines: 36

In article <25@torsqnt.UUCP> david@torsqnt.UUCP (David Haynes) writes:

	#include <setjmp.h>
	
	main()
	{
		register int j;
		jmp_buf env;
	
		j = 1;
		if(setjmp(env) == 1) {
			printf("j = %d\n", j);
			exit(1);
		}
		printf("j = %d\n", j);
		j += 3;
		longjmp(env, 1);
	}
	
	Sequent, Ultrix and Vax C give results of j = 1, j = 4.
	Gcc gives a result of j = 1, j = 1.
	What does the ANSI standard say about this?
	
	-david-

Gcc follows the ANSI standard which, when strictly interpreted, says
that "the only automatic variables guaranteed to remain valid are
those declared volatile" (quoted from the gcc manual). Traditional
compilers put local variables in the stack in functions that call
setjump. If you look at the assembly code output of  Sequent,
Ultrix, Vax C, and gcc with the "-traditional" flag you will see that
j isn't really being stored in a register.
			-Tim Moore
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