Date: Wed, 22 Oct 1997 13:59:25 -0700 (PDT) From: tadhunt@bell-labs.com To: freebsd-gnats-submit@FreeBSD.ORG Subject: i386/4826: libc_r, buggy setjmp implementation (rookie error) Message-ID: <199710222059.NAA27302@hub.freebsd.org> Resent-Message-ID: <199710222100.OAA27386@hub.freebsd.org>
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>Number: 4826
>Category: i386
>Synopsis: libc_r, buggy setjmp implementation (rookie error)
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: freebsd-bugs
>State: open
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Wed Oct 22 14:00:01 PDT 1997
>Last-Modified:
>Originator: Tad Hunt
>Organization:
Lucent Technologies, Bell Labs
>Release: 2.2.5-971018-BETA
>Environment:
doesn't matter. It's not specific to a particular version of FreeBSD,
it's incorrect implementation of a library...
>Description:
I was looking at the libc_r implementation of setjmp
(lib/libc_r/uthread/uthread_setjmp.c) from (FreeBSD-2.2.5-101897)
from lib/libc_r/uthread/uthread_setjmp.c:
int
setjmp(jmp_buf env)
{
return (_thread_sys_setjmp(env));
}
where _thread_sys_setjmp is implemented in lib/libc/i386/gen/setjmp.S
as something like the following:
#ifdef _THREAD_SAFE
ENTRY(_thread_sys_setjmp)
#else
ENTRY(setjmp)
#endif
[... essentially the same implementation for both cases, except
for some signal stuff]
In the case of threaded programs calling setjmp() (instead of calling
_thread_sys_setjmp()) the wrong environment gets saved in the jmp_buf.
When longjmp does it's work, it returns into setjmp() (instead of returning
into the caller of setjmp(). Essentially the following is happening:
jmp_buf foo;
main()
{
bar();
longjmp(foo, 1);
}
bar()
{
setjmp(foo);
}
-Tad
>How-To-Repeat:
% gcc -static foo.c -lc_r
% ./a.out
Memory Fault (core dumped)
%
foo.c:
#include <pthread.h>
#include <setjmp.h>
jmp_buf j;
void
main(void)
{
if(setjmp(j)) {
printf("setjmp returned the second time\n");
exit(1);
}
longjmp(j, 69);
}
>Fix:
diff lib/libc/i386/gen/setjmp.orig.S lib/libc/i386/gen/setjmp.S
59,30d58
< #else
< ENTRY(setjmp)
61a60
> ENTRY(setjmp)
>Audit-Trail:
>Unformatted:
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