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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 OPENSOLARIS

stack_violation

stack_violation(3C)					   Standard C Library Functions 				       stack_violation(3C)

NAME

       stack_violation - determine stack boundary violation event

SYNOPSIS

       #include <ucontext.h>

       int stack_violation(int sig, const siginfo_t *sip,
	    const ucontext_t *ucp);

DESCRIPTION

       The  stack_violation()  function  returns a boolean value indicating whether the signal, sig, and accompanying signal information, sip, and
       saved context, ucp, represent a stack boundary violation event or a stack overflow.

RETURN VALUES

       The stack_violation() function returns 0 if the signal does not represent a stack boundary violation event and 1 if the signal does  repre-
       sent a stack boundary violation event.

ERRORS

       No errors are defined.

EXAMPLES

       Example 1 Set up a signal handler to run on an alternate stack.

       The  following  example	sets  up a signal handler for SIGSEGV to run on an alternate signal stack. For each signal it handles, the handler
       emits a message to indicate if the signal was produced due to a stack boundary violation.

	 #include <stdlib.h>
	 #include <unistd.h>
	 #include <ucontext.h>
	 #include <signal.h>

	 static void
	 handler(int sig, siginfo_t *sip, void *p)
	 {
		 ucontext_t *ucp = p;
		 const char *str;

		 if (stack_violation(sig, sip, ucp))
			 str = "stack violation.
";
		 else
			 str = "no stack violation.
";

		 (void) write(STDERR_FILENO, str, strlen(str));

		 exit(1);
	 }

	 int
	 main(int argc, char **argv)
	 {
		 struct sigaction sa;
		 stack_t altstack;

		 altstack.ss_size = SIGSTKSZ;
		 altstack.ss_sp = malloc(SIGSTKSZ);
		 altstack.ss_flags = 0;

		 (void) sigaltstack(&altstack, NULL);

		 sa.sa_sigaction = handler;
		 (void) sigfillset(&sa.sa_mask);
		 sa.sa_flags = SA_ONSTACK | SA_SIGINFO;
		 (void) sigaction(SIGSEGV, &sa, NULL);

		 /*
		  * The application is now set up to use stack_violation(3C).
		  */

		 return(0);
	 }

USAGE

       An application typically uses stack_violation() in a signal handler that has been installed for SIGSEGV using sigaction(2) with the SA_SIG-
       INFO flag set and is configured to run on an alternate signal stack.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Evolving			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |Async-Signal-Safe 	   |
       +-----------------------------+-----------------------------+

SEE ALSO

       sigaction(2), sigaltstack(2), stack_getbounds(3C), stack_inbounds(3C), stack_setbounds(3C), attributes(5)

SunOS 5.11							    18 Jul 2002 					       stack_violation(3C)
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