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catching all signals in a single handler


 
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# 1  
Old 12-06-2004
catching all signals in a single handler

Hi guys - got some questions... hope something helpfull will come out!!! I just want to catch every signal that can be caught and print some info by using only one handler.

I use the sigaction() function and only one instance of a sigaction struct as an argument to the sigaction() function.

1) If sigset_t sigaction.sa_mask is empty, things seem to work fine when i send signals to my process from the command line. However the shell sends an additional SIGCONT to my process for every signal that i send. Why is this happening?

2) If sigset_t sigaction.sa_mask is filled (meaning - from my point of view Smilie - that all signals should block while sig_handler's body is being executed) i get weird results. For example the scheduler (pid=0) is repeatedly sending a SIGBUS signal to my process. Why is this happening?

Thanx in advance, please have a look at the code...

P.S. This is a simplified version of the source code. In fact the program is multi-threaded. Anyway considering just one thread of execution, would this be right?

//----------------------------------------------------------------------------------
void sig_handler(int sig, siginfo_t * info, void * context)
{
FILE *f= fopen("signal_trap", "a");

if (sig == SIGILL || sig == SIGFPE || sig == SIGSEGV || sig == SIGBUS || sig == SIGCHLD || sig == SIGTRAP || sig == SIGPOLL)
fprintf(f, "Signal = %d, subcode = %d, pid = %d, uid = %d, address = %p, errno = %d\n", sig, info->si_code, info->si_pid, info->si_uid, info->si_addr, info->si_errno);
else
fprintf(f, "Signal = %d, pid = %d, uid = %d, address = %p, errno = %d\n", sig, info->si_pid, info->si_uid, info->si_addr, info->si_errno);

fprintf(f, "\n");
fclose(f);
}
//----------------------------------------------------------------------------------
int main()
{
struct sigaction act;
sigemptyset(&act.sa_mask); // or sigfillset(&act.sa_mask);
act.sa_flags = SA_SIGINFO;
act.sa_sigaction = sig_handler;

sigaction(SIGABRT, &act, 0);
sigaction(SIGALRM, &act, 0);
sigaction(SIGFPE, &act, 0);
sigaction(SIGHUP, &act, 0);
sigaction(SIGILL, &act, 0);
sigaction(SIGINT, &act, 0);
sigaction(SIGPIPE, &act, 0);

// blah blah blah - all available signals use struct sigaction act

return 0;
}
//----------------------------------------------------------------------------------
# 2  
Old 12-06-2004
When you a signal from pid 0, that is the kernel. It is sending a SIGBUS because your program has a bus error.
# 3  
Old 12-07-2004
not a very helpful answer.... what i am trying to find out is how sigemptyset and sigfillset affect sigaction when a single handler is used to catch all catchable signals. a process with pid = 0 is the sceduler or swapper, the father of all unix processes, which - of course - is part of the kernel. SIGBUS signals denote access to an undefined portion of a memory object and not bus errors...
# 4  
Old 12-09-2004
FWIW - SIGBUS is not precsiely what you described - you basically described SIGSEGV.

What Perderabo is telling you, politely, is that you have code errors.

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