Date: Tue, 15 Sep 1998 07:16:00 -0500 (EST) From: Alfred Perlstein <bright@hotjobs.com> To: Konrad Heuer <kheuer@gwdu60.gwdg.de> Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: Catching SIGSEGV Message-ID: <Pine.BSF.3.96.980915071330.21829D-100000@bright.fx.genx.net> In-Reply-To: <Pine.BSF.3.96.980915114921.5972A-100000@gwdu60.gwdg.de>
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i had to write a short test program, but simply when SIGSEGV is caught it
seems that the return address is set to as to try to "retry" the operation
that failed. take a look at the output of this program:
#include <signal.h>
int nsegv = 0;
int ptr;
int zero = 0;
int *inv = 0;
void sighdl ( int sig )
{
ptr = &zero;
printf("%x\n",inv);fflush(0);
inv++; /* remove this to see 0 vs behaviour */
nsegv++;
}
int main( )
{
int buf;
signal(SIGSEGV, sighdl);
ptr = *(++inv); /* note this only happens once, put the ++ after and
it starts at 0 rather than 4 */
buf = ptr;
return 1;
}
it compiles with a warning... sue me i'm up 24hrs :P
Alfred Perlstein - Programmer, HotJobs Inc. - www.hotjobs.com
-- There are operating systems, and then there's FreeBSD.
-- http://www.freebsd.org/ 3.0-current
On Tue, 15 Sep 1998, Konrad Heuer wrote:
>
> May I ask my question here although it's not correlated to FreeBSD
> development?
>
> I write a program which shall run under FreeBSD and want to catch SIGSEGV
> to count these events. So the program is like this:
>
> int nsegv = 0;
> int *ptr;
> int zero = 0;
>
> void sighdl ( int sig )
> {
> ptr = &zero;
> nsegv++;
> }
>
> int dowork ( )
> {
> int buf;
>
> signal(SIGSEGV, sighdl);
>
> ptr = InvalidAddress;
> buf = *ptr;
> }
>
> Ok, the signal handler gets called, ptr will be reset to a legal address,
> but nevertheless after returning from the signal handler it will be called
> again immediately resulting in an infinite loop.
>
> Where's my mistake? What can I do to prevent that loop?
> Thanks for any reply.
>
> Regards
> Konrad Heuer
>
> // Gesellschaft fuer wissenschaftliche Datenverarbeitung mbH
> // Goettingen (GWDG), Am Fassberg, D-37077 Goettingen, Germany
> //
> // kheuer@gwdu60.gwdg.de
>
>
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