How to use Ptrace on Linux to print Call Stack of Other Processes of C++

i am working on an application which needs call stack of all executing processes on Linux. i am trying to use ptrace but not able to go ahead with it because the steps i need to follow in my code are not clear to me.

i also tryied backtrace, but its use is limmited to current process.

could some one guide me on the same.

Thanks, Sandeep

Take a look at the pstack code. pstack is available on ubuntu lucid.

This code is taken from HP UX man page of ptrace. Hope this is useful.

The following example illustrates the use of some of the ptrace() calls by a tracing process.

 #include <stdio.h>
 #include <signal.h>
 #include <sys/wait.h>
 #include <sys/ptrace.h>
 #define BUFSIZ  1024
 #define MAXPATH 1024

 pid_t           npid, cpid, pid;
 int             status, errors=0, pathlength;
 ptrace_event_t  *event_addr;
 ptrace_state_t  *state_addr;
 char            *buf_addr;
 size_t          event_len, state_len;
 int             filed[2];

 child()
 {
     int n, bar;

     close(filed[1]);
     /* Wait for parent to write to pipe */
     while ((n = read(filed[0], &bar, BUFSIZ)) == 0);

     /* Now the child can exec. */
     if (execlp("ls", "ls", (char *)0) < 0)   /* error during exec */
             printf("Child: exec failed\n");
     exit(0);
 }

 parent()
 {
     close(filed[0]);

     /* Before child does an exec, attach it and set its event flag. */
     if (ptrace(PT_ATTACH,pid))  /* failed to attach process */
         printf("Parent: Failed to attach child\n");
     if (pid != wait(&status))   /* wait failed */
         printf("Parent: attach failed with wrong wait status\n");
     if (!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGTRAP))
         printf("Parent: SIGTRAP didn't stop child\n");

     /*
      * The child process has now stopped.  Set its event flag indicating
      * that it needs to trigger on a PTRACE_EXEC event.
      */
     event_addr->pe_set_event = PTRACE_EXEC;
     if (ptrace(PT_SET_EVENT_MASK, pid, event_addr, event_len))
         printf("Parent: PT_SET_EVENT_MASK ptrace request failed\n");
     if (pid != wait(&status))   /* wait failed */
         printf("Parent: wait() failed with wrong wait status\n");

     /*
      * Send the child a message so it can break out of the while loop.
      * Get it running so it can exec.
      */
     write(filed[1], "now run", 7);
     if (ptrace(PT_CONTIN, pid, 1, 0) != 0)
         printf("Parent: failed to get child process running\n");
     /*
      * Wait for the traced child to stop after the exec system call in
      * response to an exec event set in its ptrace_event structure.
      */
     if (pid != (npid = wait(&status)))   /* wait failed */
       printf("Parent: wait() failed with wrong status\n");
   if (!WIFSTOPPED(status))
       printf("Parent: invalid wait() completion\n");

   /*
    * Child has stopped; fetch its process state and examine state
    * information.
    */
   if (ptrace(PT_GET_PROCESS_STATE, pid, state_addr, state_len) < 0)
       printf("Parent: PT_GET_PROCESS_STATE ptrace request failed\n");
   if (pid != wait(&status))   /* wait failed */
       printf("Parent: wait() failed with wrong wait status\n");

   /* Check if the pathlength value returned is non-zero */
   if ((pathlength = state_addr->pe_path_len) == 0)

            printf("Parent: zero length pathname returned\n");

        /* Fetch exec'd file pathname and store it in the buffer. */
        if (ptrace(PT_GET_PROCESS_PATHNAME, pid, buf_addr, (pathlength+1))
            < 0){
            printf("Parent: Failed to get exec pathname\n");
        } else {
            printf("Parent: the exec pathname is %s\n", buf_addr);
            if (pid != wait(&status))   /* wait failed */
                printf("Parent: wait() failed with wrong status\n");
        }
    }

    main()
    {
        event_len = sizeof(ptrace_event_t);
        state_len = sizeof(ptrace_state_t);
        event_addr = calloc(event_len, 1);
        state_addr = calloc(state_len, 1);
        buf_addr = calloc(MAXPATH, 1);
        pipe(filed);
        switch (pid = fork()) {
            case -1:
                exit(1);
            case 0:
                child();
                break;
            default:
                parent();
                break;
        }
    }