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Top Forums Programming catching all signals in a single handler Post 58959 by xtrix on Monday 6th of December 2004 11:31:34 AM
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);
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");
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;

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RAISE_DEFAULT_SIGNAL(3) 				   BSD Library Functions Manual 				   RAISE_DEFAULT_SIGNAL(3)

raise_default_signal -- raise the default signal handler LIBRARY
System Utilities Library (libutil, -lutil) SYNOPSIS
#include <util.h> int raise_default_signal(int sig); DESCRIPTION
The raise_default_signal() function raises the default signal handler for the signal sig. This function may be used by a user-defined signal handler router to ensure that a parent process receives the correct notification of a process termination by a signal. This can be used to avoid a common programming mistake when terminating a process from a custom SIGINT or SIGQUIT signal handler. The operations performed are: 1. Block all signals, using sigprocmask(2). 2. Set the signal handler for signal sig to the default signal handler (SIG_DFL). 3. raise(3) signal sig. 4. Unblock signal sig to deliver it. 5. Restore the original signal mask and handler, even if there was a failure. See signal(7) for a table of signals and default actions. The raise_default_signal() function should be async-signal-safe. RETURN VALUES
Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and the global variable errno is set to indicate the error. ERRORS
The raise_default_signal() function may fail and set errno for any of the errors specified for the functions sigemptyset(3), sigfillset(3), sigaddset(3), sigprocmask(2), sigaction(2), or raise(3). SEE ALSO
sigaction(2), sigprocmask(2), raise(3), signal(7) HISTORY
The raise_default_signal() function first appeared in NetBSD 5.0. BSD
September 25, 2007 BSD

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