signals/t_sigaltstack.c

This is signals/t_sigaltstack.c (Listing 21-3, page 436), an example from the book, The Linux Programming Interface.

The source code file is copyright 2022, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

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/* t_sigaltstack.c

   Demonstrate the use of sigaltstack() to handle a signal on an alternate
   signal stack.
*/
#define _GNU_SOURCE             /* Get strsignal() declaration from <string.h> */
#include <string.h>
#include <signal.h>
#include "tlpi_hdr.h"
static void
sigsegvHandler(int sig)
{
    int x;

    /* UNSAFE: This handler uses non-async-signal-safe functions
       (printf(), strsignal(), fflush(); see Section 21.1.2) */

    printf("Caught signal %d (%s)\n", sig, strsignal(sig));
    printf("Top of handler stack near     %10p\n", (void *) &x);
    fflush(NULL);

    _exit(EXIT_FAILURE);                /* Can't return after SIGSEGV */
}
/* The following stops 'gcc -Wall' complaining that "control reaches
   end of non-void function" because we don't follow the call to
   overflowStack() stack in main() with a call to exit(). */

#ifdef __GNUC__
static void
overflowStack(int callNum) __attribute__ ((__noreturn__));
#endif
static void             /* A recursive function that overflows the stack */
overflowStack(int callNum)
{
    char a[100000];                     /* Make this stack frame large */

    printf("Call %4d - top of stack near %10p\n", callNum, &a[0]);
    overflowStack(callNum+1);
}
int
main(int argc, char *argv[])
{
    stack_t sigstack;
    struct sigaction sa;
    int j;

    printf("Top of standard stack is near %10p\n", (void *) &j);

    /* Allocate alternate stack and inform kernel of its existence */

    sigstack.ss_sp = malloc(SIGSTKSZ);
    if (sigstack.ss_sp == NULL)
        errExit("malloc");

    sigstack.ss_size = SIGSTKSZ;
    sigstack.ss_flags = 0;
    if (sigaltstack(&sigstack, NULL) == -1)
        errExit("sigaltstack");
    printf("Alternate stack is at         %10p-%p\n",
            sigstack.ss_sp, (char *) sbrk(0) - 1);

    sa.sa_handler = sigsegvHandler;     /* Establish handler for SIGSEGV */
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = SA_ONSTACK;           /* Handler uses alternate stack */
    if (sigaction(SIGSEGV, &sa, NULL) == -1)
        errExit("sigaction");

    overflowStack(1);
}

 

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