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Full Discussion: problem in SIGSEGV signal handling
Top Forums Programming problem in SIGSEGV signal handling Post 302332592 by Corona688 on Thursday 9th of July 2009 02:19:51 PM
Old 07-09-2009
It's not going to rewind your code back to the beginning of that line when the interrupt returns. It'll jump back into where the segfault happened, deep inside libc, which already has a copy of the variable that won't change when you change j. So, that's not going to work.

There's also a problem with calling library calls inside a signal handler. What if, for instance, a SIGSEGV happened right inside malloc(), causing a second malloc() to be called before the first one has finished? The heap may not even be in a valid state at that moment, or may be left in an invalid state when the second one returns. Nothing but system calls are signal-safe unless specifically written to avoid signal interference, and even then, not all system calls.

I also forsee another problem with this design of yours. The signal has no way to know what size buffer is needed. Why not just do this instead?

Code:
int main(void)
{
  j=strdup("hello\n");
}

This creates a correct-sized buffer containing "hello\n" for you. You can free it with free() later.
 

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LEARN ABOUT BSD

siginterrupt

SIGINTERRUPT(3) 					     Library Functions Manual						   SIGINTERRUPT(3)

NAME

       siginterrupt - allow signals to interrupt system calls

SYNOPSIS

       siginterrupt(sig, flag);
       int sig, flag;

DESCRIPTION

       Siginterrupt  is used to change the system call restart behavior when a system call is interrupted by the specified signal.  If the flag is
       false (0), then system calls will be restarted if they are interrupted by the specified signal and no data has been transferred yet.   Sys-
       tem call restart is the default behavior on 4.2 BSD.

       If  the flag is true (1), then restarting of system calls is disabled.  If a system call is interrupted by the specified signal and no data
       has been transferred, the system call will return -1 with errno set to EINTR.  Interrupted system calls that have started transferring data
       will  return the amount of data actually transferred.  System call interrupt is the signal behavior found on 4.1 BSD and AT&T System V UNIX
       systems.

       Note that the new 4.2 BSD signal handling semantics are not altered in  any  other  way.   Most	notably,  signal  handlers  always  remain
       installed  until  explicitly changed by a subsequent sigvec(2) call, and the signal mask operates as documented in sigvec(2).  Programs may
       switch between restartable and interruptible system call operation as often as desired in the execution of a program.

       Issuing a siginterrupt(3) call during the execution of a signal handler will cause the new action to take place on the next  signal  to	be
       caught.

NOTES

       This  library  routine uses an extension of the sigvec(2) system call that is not available in 4.2BSD, hence it should not be used if back-
       ward compatibility is needed.

RETURN VALUE

       A 0 value indicates that the call succeeded.  A -1 value indicates that an invalid signal number has been supplied.

SEE ALSO

       sigvec(2), sigblock(2), sigpause(2), sigsetmask(2).

4.3 Berkeley Distribution					   May 15, 1985 						   SIGINTERRUPT(3)
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