signal handling in C

[subramanian]

Consider the following code: segment violation is deliberately
generated to catch the SIGSEGV signal. The handler for this signal,
namely SIGSEGV_handler , is called. However after the handler is
finished, control does not return to the printf statement in main()
which is present after the strcpy statement. Instead Segmentation
violation error message is printed in Redhat Linux and the program is
aborted. In VC++, the SIGSEGV_handler is called and then the program
crashes. Is this the expected behaviour ?

void SIGSEGV_handler (int num);

int main(void)
{
char *str = NULL;

signal(SIGSEGV, SIGSEGV_handler );
strcpy(str, "TEST");
printf("After signal handling\n");

return 0;
}

void SIGSEGV_handler (int num)
{
printf("SIGSEGV _handler called with the argument %d\n", num);

return;
}

[Richard Bos]

Kohn Emil Dan <em***@cs.techn ion.ac.ilwrote:

On Fri, 15 Dec 2006, Chris Dollin wrote:

Using `longjmp` inside a signal handler in Standard C gives you
undefined behaviour (unless the signal was provoked by `abort`
or `raise`).

Can you point me where the standard mentions this?

7.14.1.1#5: "If the signal occurs other than as the result of calling
the abort or raise function, the behavior is undefined if ... the signal
handler calls any function in the standard library other than the abort
function, the _Exit function, or the signal function with the first
argument equal to the signal number corresponding to the signal that
caused the invocation of the handler."
longjmp() is a function in the standard library other than those three,
so calling it in a signal handler has UB unless the signal was caused by
abort() or raise().

Richard