Signal() Implementation

Signal() Implementation

[Firas Cheaib]

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Under signal/signal.c the comment header states the following:

/* Set the handler for the signal SIG to HANDLER,
returning the old handler, or SIG_ERR on error. */

Yet the function doesn't return the old handler at any point, it only returns SIG_ERR.
Is my understanding correct? If so, is the comment wrong and should be corrected?
I understand that using signal() is to be avoided and I should use sigaction instead.

__sighandler_t
signal (int sig, __sighandler_t handler)
{
__set_errno (ENOSYS);
return SIG_ERR;}

Thanks,
-Firas

Re: Signal() Implementation

[Joe Simmons-Talbott]

On Thu, May 11, 2023 at 01:44:48PM +0000, Firas Cheaib wrote:
> Under signal/signal.c the comment header states the following:
> 
> /* Set the handler for the signal SIG to HANDLER,
> returning the old handler, or SIG_ERR on error. */
> 
> Yet the function doesn't return the old handler at any point, it only returns SIG_ERR.
> Is my understanding correct? If so, is the comment wrong and should be corrected?
> I understand that using signal() is to be avoided and I should use sigaction instead.
> 
> __sighandler_t
> signal (int sig, __sighandler_t handler)
> {
> __set_errno (ENOSYS);
> return SIG_ERR;}

This is a stub function the actual implementation is elsewhere.  It
looks like it is __sysv_signal() in sysdeps/posix/sysv_signal.c.  Both
have the same comment which seems to be a clue as to the requirements in
signal/signal.c

Thanks,
Joe