SIGSEGV signal handling in a child process

Question

I have a program that creates a fork that uses execve to run a program that have a SegFault and exit after catching the signal. In my signal handler, I should obtain "Segmentation fault (Core dumped)" but nothing is written. So I'm asking : how to handle a segfault signal in a child process ? My code is the following :

int     child_management(char **env, char **arguments)
{
  char  **paths;
  char  *current_path;
  char  *target_path;
  int   found;
  int   i;

  i = -1;
  found = 0;
  paths = get_paths(env);
  if (execve(arguments[0], arguments, env) == -1)
    {
      while (paths[++i] != NULL)
        {
          current_path = my_strcat(paths[i], "/");
          target_path = my_strcat(current_path, arguments[0]);
          found = (execve(target_path, arguments, env) == -1 && found == 0) ? 0 : 1;
          free(current_path);
          free(target_path);
        }
      if (!found && !is_existing_builtin(arguments[0]))
        my_printf("%s: Command not found.\n", arguments[0]);
    }
  free(arguments);
  free(paths);
  if (signal(SIGSEGV, segf_handler) == SIG_ERR);
  exit(0);
}

void    segf_handler()
{
  my_printf("Segmentation fault (Core dumped)\n");
}

int     execute_program(char *str, char **av, char **env)
{
  pid_t pid;
  char  **arguments;

  pid = fork();
  arguments = my_str_explode(str, ' ');
  if (pid > 0)
    {
      parent_management(pid, arguments, env);
    }
  else if (pid == 0)
    {
      child_management(env, arguments);
    }
}

Please notice that I am doing an exercice and I'm not allowed to use another function than signal so don't tell me about sigaction

Perhaps your `my_printf` is broken? Or the segfault is not happening? BTW, if `execve` is successful you will never get to the `signal` function at all... — Eugene Sh., Jan 18 '17 at 16:52
Even with a normal printf, it doesn't work. And if I launch the specified program with bash, it segfaults ! — Orionss, Jan 18 '17 at 16:54
As I said in the update: `execve` is not returning if successful. — Eugene Sh., Jan 18 '17 at 16:55
Thanks but if you relook at the code you'll see that signal is out of the condition statement. — Orionss, Jan 18 '17 at 16:56
You call `execve` **before** you call `signal`. Do you agree? — Eugene Sh., Jan 18 '17 at 17:19
Like this: http://stackoverflow.com/questions/7339664/c-catch-a-segfault-in-exec-which-was-run-in-a-child-process BTW, I think it's a duplicate... — Eugene Sh., Jan 18 '17 at 17:23
Nop, like I said, I have to use signal function. I can't use any other function... — Orionss, Jan 18 '17 at 17:25
What is this `if`-statement for: `if (signal(SIGSEGV, segf_handler) == SIG_ERR);` — alk, Jan 18 '17 at 17:31
It's a a precaution because when my problem will be solved, I suppose that I'll need it. — Orionss, Jan 18 '17 at 17:31
The moment an `exec*()` was successful any signal handler established by the process calling the `exec*()` function is gone, as the successful call to `exec*()` replaced the whole process with the process `exec*()`ed — alk, Jan 18 '17 at 17:32

score 3 · Accepted Answer · answered Jan 18 '17 at 17:38

3

You can't catch the SEGV signal inside the child because calling execve replaces the code running in the child with that program.

You can however catch the CHLD signal in the parent when the child process dies. You'll need to examine the status returned from wait() to see how/why it died though.

answered Jan 18 '17 at 17:38

Chris Turner

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This solved my problem because it caused me to ask someone to know if I could use the macros and I could ! Thanks ! – Orionss Jan 18 '17 at 17:49

SIGSEGV signal handling in a child process

1 Answers1