Example on how to dump stack trace on SIGUSR2, useful if program gets stuck

unwindtest.c

/*
 * unwindtest.c
 * Copyright (C) 2017 Adrian Perez <aperez@igalia.com>
 *
 * Distributed under terms of the MIT license.
 */

#define _GNU_SOURCE
#include <ucontext.h>
#include <dlfcn.h>
#include <signal.h>
#include <inttypes.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>


static void
context_backtrace (ucontext_t *context)
{
    unsigned frame_number = 0;

    void *ip = NULL;
    void **bp = NULL;

#if defined(REG_RIP)
    ip = (void*) context->uc_mcontext.gregs[REG_RIP];
    bp = (void**) context->uc_mcontext.gregs[REG_RBP];
#elif defined(REG_EIP)
    ip = (void*) context->uc_mcontext.gregs[REG_EIP];
    bp = (void**) context->uc_mcontext.gregs[REG_EBP];
#endif

    while (bp && ip) {
        Dl_info dlinfo;
        if (!dladdr (ip, &dlinfo))
            break;

        const char *symbol = dlinfo.dli_sname;

        fprintf (stderr, "% 2d: %p <%s+%lu> (%s)\n",
                 ++frame_number,
                 ip,
                 symbol ? symbol : "(?)",
                 (uintptr_t) ip - (uintptr_t) dlinfo.dli_saddr,
                 dlinfo.dli_fname);

        if (dlinfo.dli_sname && strcmp (dlinfo.dli_sname, "main") == 0)
            break;

        ip = bp[1];
        bp = (void**) bp[0];
    }
}


#define BACKTRACE( )             \
    do {                         \
        ucontext_t uc;           \
        getcontext (&uc);        \
        context_backtrace (&uc); \
    } while (0)


static void
handle_signal (int signum, siginfo_t *info, void *context)
{
    context_backtrace ((ucontext_t*) context);
}

void h (void) { BACKTRACE (); }
void g (void) { h (); }
void f (void) { g (); }

void lh (void) {
    static volatile int x = 1;
    while (x) /* noop */;
}
void lg (void) { lh (); }
void lf (void) { lg (); }

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

    struct sigaction sa = { 0, };
    sa.sa_sigaction = handle_signal;
    sa.sa_flags = SA_SIGINFO | SA_RESTART | SA_NODEFER;
    sigaction (SIGUSR2, &sa, NULL);
    printf ("PID: %lu\n", (unsigned long) getpid ());

    lf ();
    return EXIT_SUCCESS;
}