Signal handler for SIGSEGV.

[vashwath]

Hi all,
In my current project I am using signals for error handling. Since I
cannot show full code, I have just shown important piece of code which
is relevant.

void sigsegenv()
{
printf("\n\n ********** F D S Message ***********\n\n ");
printf("\n\n ********** S E G M E N T A T I O N F A U L T
inside F D S ***********\n\n ");
exit(-1);
}
int main(void)
{
............
...........
signal ( SIGSEGV ,sigsegenv);
...........
...........
}

I think this might give some idea about what is happening.
My signal handler is not catching SIGSEGV always. Some time it is
catching sometimes not. Please let me know what am I doing wrong

[Walter Roberson]

In article <11************ **********@o13g 2000cwo.googleg roups.com>,
<va******@redif fmail.com> wrote:

In my current project I am using signals for error handling. Since I
cannot show full code, I have just shown important piece of code which
is relevant. void sigsegenv()
{
printf("\n\n ********** F D S Message ***********\n\n ");
printf("\n\n ********** S E G M E N T A T I O N F A U L T
inside F D S ***********\n\n ");
exit(-1);
} int main(void)
{
...........
..........
signal ( SIGSEGV ,sigsegenv);
..........
..........
}
You cannot use printf() inside a signal handler.

In standard C, other than calling exit, resetting the signal handler,
or a *very* small number of other things, all you can do is set
a volatile variable of sig_atomic_t .
I think this might give some idea about what is happening.
My signal handler is not catching SIGSEGV always. Some time it is
catching sometimes not. Please let me know what am I doing wrong

What evidence have you found that the handler is not catching SIGSEGV ?
If it is just that the printf() are not occuring, then you might
be encountering the restrictions on what you can do in a handler.

--
All is vanity. -- Ecclesiastes

[Madhav]

Walter Roberson wrote:

You cannot use printf() inside a signal handler.

In standard C, other than calling exit, resetting the signal handler,
or a *very* small number of other things, all you can do is set
a volatile variable of sig_atomic_t .

Could you please tell me about restrictions on signal handlers or where
I can find more info about restrictions on signal handlers?

Thanks,
Madhav.

[Richard Heathfield]

Madhav said:

Walter Roberson wrote:

You cannot use printf() inside a signal handler.

In standard C, other than calling exit, resetting the signal handler,
or a *very* small number of other things, all you can do is set
a volatile variable of sig_atomic_t .
Could you please tell me about restrictions on signal handlers

He just did.
or where I can find more info about restrictions on signal handlers?

That's the whole thing.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)

[vashwath]

> In standard C, other than calling exit, resetting the signal handler,

or a *very* small number of other things, all you can do is set
a volatile variable of sig_atomic_t .
Can I invoke longjmp in signal handler?
Actually, In our project we have to return status to the scheduler(Some
what like scheduler) which will execute our program. The scheduler is
in JAVA. The values I should return is 0 (if everything is fine) or
50(warning, If not a very serious error has occurred) or 99(If some
serious error has occurred like segmentation fault).I was thinking to
use longjmp inside signal handler and jump to main and then return
appropriate error status. What evidence have you found that the handler is not catching SIGSEGV ?

Programming terminated due to segmentation fault.

[Richard Heathfield]

va******@rediff mail.com said:

In standard C, other than calling exit, resetting the signal handler,
or a *very* small number of other things, all you can do is set
a volatile variable of sig_atomic_t .

Can I invoke longjmp in signal handler?

Not with well-defined behaviour, no.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)

[vashwath]

Richard Heathfield wrote:

va******@rediff mail.com said:

In standard C, other than calling exit, resetting the signal handler,
or a *very* small number of other things, all you can do is set
a volatile variable of sig_atomic_t .

Can I invoke longjmp in signal handler?

Not with well-defined behaviour, no.

Is it possible to return certain value to the calling program from
signal handler?My aim is to exit gracefully and to return the
predefined values to the scheduler, which invokes my program.Note that
scheduler is coded using JAVA.
OK, let me put it in a better eay. This is what happens in our project

JAVA progam calls list of C programs. C programs should return the
status(0, 50 or 100) to JAVA. I somehow want to return the status to
JAVA program if there is a segmentation fault. I don't want to exit
from signal handler
..

[Richard Heathfield]

va******@rediff mail.com said:

Richard Heathfield wrote:

va******@rediff mail.com said:

>> In standard C, other than calling exit, resetting the signal handler,
>> or a *very* small number of other things, all you can do is set
>> a volatile variable of sig_atomic_t .
>>
> Can I invoke longjmp in signal handler?

Not with well-defined behaviour, no.

Is it possible to return certain value to the calling program from
signal handler?

No. Signal handlers have the form void handler(int); and thus do not return
a value. You can, however, use the signal handler to modify a file scope
object of type sig_atomic_t.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)

[Flash Gordon]

Richard Heathfield wrote:

va******@rediff mail.com said:

Richard Heathfield wrote:

va******@rediff mail.com said:

> In standard C, other than calling exit, resetting the signal handler,
> or a *very* small number of other things, all you can do is set
> a volatile variable of sig_atomic_t .
>
Can I invoke longjmp in signal handler?
Not with well-defined behaviour, no.

Is it possible to return certain value to the calling program from
signal handler?

No. Signal handlers have the form void handler(int); and thus do not return
a value. You can, however, use the signal handler to modify a file scope
object of type sig_atomic_t.

I think he meant return a value to the program that invoked his C
program, not return a value in to his program. If I read him right, then
calling exit from within the signal handler might be the way to go,
although whether doing exit(99) is valid is system dependant.
--
Flash Gordon
Living in interesting times.
Although my email address says spam, it is real and I read it.

[Eric Sosman]

Walter Roberson wrote:

In article <11************ **********@o13g 2000cwo.googleg roups.com>,
<va******@redif fmail.com> wrote:

In my current project I am using signals for error handling. Since I
cannot show full code, I have just shown important piece of code which
is relevant.

void sigsegenv()
{
printf("\n\n ********** F D S Message ***********\n\n ");
printf("\n\n ********** S E G M E N T A T I O N F A U L T
inside F D S ***********\n\n ");
exit(-1);
}

int main(void)
{
...........
..........
signal ( SIGSEGV ,sigsegenv);
..........
..........
}

You cannot use printf() inside a signal handler.

In standard C, other than calling exit, resetting the signal handler,
or a *very* small number of other things, all you can do is set
a volatile variable of sig_atomic_t .

Calling exit() in a signal handler is impermissible.
Perhaps you mean _Exit(), a function introduced in C99;
see 7.14.1.1/5. Handlers for signals that were generated
by raise() or abort() are not subject to these restrictions;
handlers for all other signals must respect them.

--
Eric Sosman
es*****@acm-dot-org.invalid