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From: chris@umcp-cs.UUCP (Chris Torek)
Newsgroups: net.unix-wizards
Subject: Re: Bug iwith setjmp/longjmp on Vax
Message-ID: <43@umcp-cs.UUCP>
Date: Fri, 7-Jun-85 23:00:59 EDT
Article-I.D.: umcp-cs.43
Posted: Fri Jun  7 23:00:59 1985
Date-Received: Tue, 11-Jun-85 02:40:38 EDT
References: <44700008@gypsy.UUCP>
Organization: U of Maryland, Computer Science Dept., College Park, MD
Lines: 26

Your code has a nasty little no-no in it: it longjmp's after the stack
environment in which the setjmp was done has been deallocated.  No
surprise it fails ``at random''.  Watch:

--------#include <setjmp.h>
--------static jmp_buf env;
--------int mode;
--------main() {
active: env=uninit, mode=0, main()
--------	foo();
[expand foo()]
[]------foo() {
active: env=uninit, mode=0, main(), foo()
[]------	mode = setjmp(env);
active: env=foo(), mode=0, main(), foo()
[]------	if (mode != 0) magic();
[]------}
[return to main()]
active: env=foo() [defunct], mode=0, main()
--------	longjmp(env, 1);

Oops.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 4251)
UUCP:	seismo!umcp-cs!chris
CSNet:	chris@umcp-cs		ARPA:	chris@maryland