libstacktrace/stacktrace.c

#include "stacktrace.h"
#include <signal.h>
#include <errno.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/syscall.h>
#include <unistd.h>
#include <stdio.h>

#define WRITE(s) do { if (write(2, s, my_strlen(s)) < 0) { perror("write"); } } while (0);

static size_t my_strlen(char* s)
{
  size_t length = 0;

  if (s != NULL) {
    while (*s++ != '\0') {
      length++;
    }
  }
  return length;
}


// We need this because sprintf() isn't safe to call from a signal handler.
static char *format_uint(unsigned int i)
{
  static char str[100];
  char *p = str + sizeof(str) - 1;
  *(--p) = '\0';
  do {
    *(--p) = '0' + (i % 10);
    i /= 10;
  } while (i > 0);
  return p;
}


static pid_t gettid(void)
{
  // According to 'man gettid', this function is not in libc, so you need
  // to call syscall() yourself.  Seems to be true.
  return syscall(__NR_gettid);
}


void stacktrace(void)
{
  pid_t pid, trace_tid = gettid();

  if ((pid = fork()) > 0) {
    // For some reason, if we call waitpid() here, gdb (7.3.1) isn't able to
    // get a valid stack trace.  If we use syscall(__NR_waitpid), then it
    // works fine.
#if defined(__MIPSEL__) || defined(_MIPSEB_)
    syscall(__NR_waitpid, pid, 0);
#endif
  } else if (pid == 0) {
    char *argv[] = {(char*)"stacktrace", format_uint(trace_tid), NULL};
    execv("/usr/bin/stacktrace", argv);
  } else {
    int e = errno;
    WRITE("ERROR: fork failed?!  code=");
    WRITE(format_uint(e));
  }
}


void stacktrace_sighandler(int sig)
{
  WRITE("\nExiting on signal ");
  WRITE(format_uint(sig));
  WRITE("\n");

  stacktrace();

  /*
   * We have to generate a signal *other* than the one we received, because
   * signals aren't re-entrant.  But we want a proper "die!" signal so that
   * we can still get a core dump.  Stack traces are nice, but so are cores
   * sometimes.
   */
  sig = (sig == SIGSEGV) ? SIGBUS : SIGSEGV;
  signal(sig, SIG_DFL);
  kill(getpid(), sig);

  // should never get here, but just in case...
  abort();
}


void stacktrace_setup(void)
{
  signal(SIGSEGV, stacktrace_sighandler);
  signal(SIGBUS, stacktrace_sighandler);
  signal(SIGFPE, stacktrace_sighandler);
  signal(SIGILL, stacktrace_sighandler);
}