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Full Discussion: Signal Handler Hangs
Top Forums Programming Signal Handler Hangs Post 302404202 by sree_ec on Tuesday 16th of March 2010 12:38:37 AM
Old 03-16-2010
Signal Handler Hangs
Hi,

I have a problem with signal handler algorithm in linux. My code is hanging ( It is continuously looping inside the signal handler) . I am pasting my code here...
Please provide me some help regarding this. I googled many places and wrote this code.. but doesnt seem to be working without exit(0).. but i guess this is not the right way. What could be wrong?

Code:
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>

struct sigaction oldHandler;

void myHandler(int sig,  siginfo_t *siginfo, void *context) {
// if i have not written any code inside this function, the program will give a feel of hang( this functions is getting continuously called
        if(siginfo->si_code == SEGV_MAPERR)
        {
                write(1,"address not mapped to object",strlen("address not mapped to object"));
        }
        else if (siginfo->si_code == SEGV_ACCERR)
        {
                write(1,"invalid permissions for mapped object",strlen("invalid permissions for mapped object"));
        }

       write(1,"\n",1);

 //        exit(0); if this exit(0) is not present, program will get continuous calls to this signal handler
        return;
}

int main(int argc, char *argv[]) {

    /* Install mySignalHandler for SIGSEGV */
    struct sigaction sigAct;
    int              status = 0;
    char *addr = NULL;

    sigAct.sa_handler   = 0;
    sigAct.sa_sigaction = myHandler;
    sigfillset(&sigAct.sa_mask);
    sigAct.sa_flags = SA_SIGINFO;

    status = sigaction(SIGSEGV, &sigAct, &oldHandler);
    if (status != 0) {
        perror("Failed to install handler for signal SIGSEGV");
        exit(1);
    }
#if 1
    /* This will invoke the signal handler */
// addr = malloc(strlen("Hello"));
     strcpy(addr,"Hello");
    printf("%s\n",addr);

#endif
        printf("Returning from main\n");
    return 0;
}

 

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LEARN ABOUT LINUX

bsd_signal

BSD_SIGNAL(3)						     Linux Programmer's Manual						     BSD_SIGNAL(3)

NAME

       bsd_signal - signal handling with BSD semantics

SYNOPSIS

       #define _XOPEN_SOURCE
       #include <signal.h>

       typedef void (*sighandler_t)(int);

       sighandler_t bsd_signal(int signum, sighandler_t handler);

DESCRIPTION

       The bsd_signal() function takes the same arguments, and performs the same task, as signal(2).

       The  difference between the two is that bsd_signal() is guaranteed to provide reliable signal semantics, that is: a) the disposition of the
       signal is not reset to the default when the handler is invoked; b) delivery of further instances of the signal is blocked while the  signal
       handler is executing; and c) if the handler interrupts a blocking system call, then the system call is automatically restarted.	A portable
       application cannot rely on signal(2) to provide these guarantees.

RETURN VALUE

       The bsd_signal() function returns the previous value of the signal handler, or SIG_ERR on error.

ERRORS

       As for signal(2).

CONFORMING TO

       4.2BSD, POSIX.1-2001.  POSIX.1-2008 removes the specification of bsd_signal(), recommending the use of sigaction(2) instead.

NOTES

       Use of bsd_signal() should be avoided; use sigaction(2) instead.

       On modern Linux systems, bsd_signal() and signal(2) are equivalent.  But on older systems, signal(2) provided unreliable signal	semantics;
       see signal(2) for details.

       The use of sighandler_t is a GNU extension; this type is only defined if the _GNU_SOURCE feature test macro is defined.

SEE ALSO

       sigaction(2), signal(2), sysv_signal(3), feature_test_macros(7), signal(7)

COLOPHON

       This  page is part of release 3.27 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

								    2009-03-15							     BSD_SIGNAL(3)
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