Date: Thu, 21 Jun 2001 11:54:23 -0500 From: Alfred Perlstein <bright@sneakerz.org> To: Louis-Philippe Gagnon <louisphilippe@macadamian.com> Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: pthread/longjmp/signal problem Message-ID: <20010621115423.U4543@sneakerz.org> In-Reply-To: <0db001c0fa62$2b567800$2964a8c0@macadamian.com>; from louisphilippe@macadamian.com on Thu, Jun 21, 2001 at 10:55:10AM -0400 References: <0db001c0fa62$2b567800$2964a8c0@macadamian.com>
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* Louis-Philippe Gagnon <louisphilippe@macadamian.com> [010621 09:56] wrote:
> No reactions the first time, let's try again.
>
> I've encountered a problem in the interaction betwen signals, longjmp and
> pthreads; I'm hoping someone can help me make sense of it.
>
> I've been trying to implement a IsBadReadPtr-style function in FreeBSD by
> using signal handlers and longjmp/setjmp. It seemed to work as expected,
> until I started using the -pthread option to gcc (thus linking against
> libc_r). Now the function only works on the first call; subsequent calls
> hang on the segmentation fault.
>
> Here's an example of the kind of code that causes problems :
[snip]
ERRORS
If the contents of the env are corrupted, or correspond to an environment
that has already returned, the longjmp() routine calls the routine
longjmperror(3). If longjmperror() returns the program is aborted (see
abort(3)). The default version of longjmperror() prints the message
``longjmp botch'' to standard error and returns. User programs wishing
to exit more gracefully should write their own versions of
longjmperror().
> So the questions are :
> -Am I doing something obviously wrong?
I think so, I think you must reinit the 'env' like so:
reset:
if(sigsetjmp(env,1)) {
fprintf(stderr,"longjmp successful\n");
goto reset;
}
> -Is this a bug?
I think so, even with reinitializing the env structure it still hangs
for me as well:
before sigsegv
write(2,0x3fbff308,15) = 15 (0xf)
sigprocmask(0x3,0x280fb338,0x0) = 0 (0x0)
sigaltstack(0x28116d00,0x0) = 0 (0x0)
in handler
write(2,0x3fbfef98,11) = 11 (0xb)
sigprocmask(0x3,0x804997c,0x0) = 0 (0x0)
longjmp successful
write(2,0x3fbff308,19) = 19 (0x13)
sigprocmask(0x1,0x0,0x804997c) = 0 (0x0)
before sigsegv
write(2,0x3fbff308,15) = 15 (0xf)
sigreturn(0x8057e7c) = 0 (0x0)
sigreturn(0x8057e7c) = 0 (0x0)
sigreturn(0x8057e7c) = 0 (0x0)
sigreturn(0x8057e7c) = 0 (0x0)
> -Is this a known bug with a known workaround?
Not that I know of, I'll take a peek at the threading libraries, but
I'm not promising anything.
-Alfred
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