C++ Get File Name and Line Number of "Segmentation Fault" Linux x64

Question

Without running GDB, but only the program itself.

edit: i've already seen such program but i can't figure how to do that myself :(

Answer 1

Tommie deserves credit for solving this.

I've detached his answer from GDB by using the somewhat standard backtrace utility from <execinfo.h>.

static void dumpstack(void){
    static void *backbuf[ 50 ];
    int levels;

    levels = backtrace( backbuf, 50 );
    backtrace_symbols_fd( backbuf, levels, STDERR_FILENO );

    return;
}

You can try opening a file and writing instead of STDERR_FILENO, but I'd avoid such heavy lifting in a crashed process.

On my system, the output looks like this:

Shadow:code dkrauss$ ./dumpy 
0   dumpy                               0x0000000100000d81 dumpstack + 25
1   dumpy                               0x0000000100000d18 signal_handler + 47
2   libSystem.B.dylib                   0x00007fff86b1766a _sigtramp + 26
3   ???                                 0x0000000000000000 0x0 + 0
4   dumpy                               0x0000000100000a18 start + 52
FATAL: Segmentation Fault

So, it doesn't give file name + line number, but it does give function name + code offset, which you can translate easily enough.

Answer 2

Hmmm... you could try doing it this way...

struct sigaction g_sigact;

void panic(const char *fmt, ...){
    char buf[PANICBUF_LEN];
    va_list argptr;
    va_start(argptr, fmt);
    vsprintf(buf, fmt, argptr);
    va_end(argptr);
    fprintf(stderr, "%s\n", buf);
    exit(-1);
}
void init_signals(void){
    g_sigact.sa_handler = signal_handler;
    sigemptyset(&g_sigact.sa_mask);
    g_sigact.sa_flags = 0;
    sigaction(SIGINT, &g_sigact, (struct sigaction *)NULL);

    sigaddset(&g_sigact.sa_mask, SIGSEGV);
    sigaction(SIGSEGV, &g_sigact, (struct sigaction *)NULL);

    sigaddset(&g_sigact.sa_mask, SIGBUS);
    sigaction(SIGBUS, &g_sigact, (struct sigaction *)NULL);

    sigaddset(&g_sigact.sa_mask, SIGQUIT);
    sigaction(SIGQUIT, &g_sigact, (struct sigaction *)NULL);

    sigaddset(&g_sigact.sa_mask, SIGHUP);
    sigaction(SIGHUP, &g_sigact, (struct sigaction *)NULL);

    sigaddset(&g_sigact.sa_mask, SIGKILL);
    sigaction(SIGKILL, &g_sigact, (struct sigaction *)NULL);
}

static void signal_handler(int sig){
    if (sig == SIGHUP) g_keepRunning = 0;
    if (sig == SIGSEGV || sig == SIGBUS){
        dumpstack();
        panic("FATAL: %s Fault\n", (sig == SIGSEGV) ? "Segmentation" : ((sig == SIGBUS) ? "Bus" : "Unknown"));
    }
    if ((sig == SIGQUIT || (sig == SIGKILL) || (sig == SIGINT)) ;
}

static void dumpstack(void){
    /* Got this routine from http://www.whitefang.com/unix/faq_toc.html
    ** Section 6.5. Modified to redirect to file to prevent clutter
    */
    char dbx[160];
    sprintf(dbx, "echo -ne 'detach\n' | gdb --eval-command=where --pid=%d > %d.dump", getpid(), getpid());
    system(dbx);
    return;
}

When a segmentation fault is trapped, dumpstack gets invoked and prints the most recent stack-trace up to the point when it segmentation faulted and gets redirected to a file with a numeric pid of the process....

Answer 3

Why exactly do you not want to run gdb? You can detect the location of segfaults very easily if you use it.