Path: utzoo!attcan!uunet!ncrlnk!ncr-sd!hp-sdd!ucsdhub!sdcsvax!ucsd!rutgers!att!ulysses!andante!alice!ark
From: ark@alice.UUCP (Andrew Koenig)
Newsgroups: comp.lang.c
Subject: Re: Behaviour of setjmp/longjmp and registers
Message-ID: <8831@alice.UUCP>
Date: 25 Jan 89 18:10:44 GMT
References: <5771@phoenix.Princeton.EDU> <9467@ihlpb.ATT.COM>
Organization: AT&T Bell Laboratories, Liberty Corner NJ
Lines: 28

In article <9467@ihlpb.ATT.COM>, gregg@ihlpb.ATT.COM (Wonderly) writes:

> It strikes me that setjmp() could save all GP registers.  I know of at
> least one implementation were a jmp_buf is enough space for the entire
> register set.  longjmp() of course just reloads the registers grabs the
> return value passed, and jumps to the return address given to it (on the
> stack or elsewhere).  The expense is a consideration but the results are
> guaranteed in the cases I can think of.

Yup, that's what the folks thought who did the first VAX
implementation, too.

It doesn't work.  Consider this case:

	register x;
	jmp_buf j;

	x = 3;
	if (setjmp(j))
		{ stuff }
	x = 4;
	longjmp(j,1);

You will see that when `stuff' is executed, x will have been
restored to 3.
-- 
				--Andrew Koenig
				  ark@europa.att.com