CODEWITHSUNDEEP
ceclipsegdbforkeclipse-cdt
Bush
Bush

Reputation: 2533

Debug fork() in eclipse cdt

I'm trying to debug some fork() mechanism with eclipse cdt (Juno). I wrote the program in C.

  if( -1 == (pid = fork()) ) /* error */
    goto cleanup;
  else if ( 0 == pid ) /* child */
  {
    execlp("gcc", "gcc", cFilePath, "-o" , GCC_OUTPUT_FILE_NAME, NULL);
    goto cleanup; /* Arrives here only on error! */
  }
  else if (pid > 0) /* parent - checks: correct pid returns, returns normally, with exit status = 0*/
  {
      returnedpid = wait(exitStatus);
      if( pid != returnedpid || exitStatus == NULL || !WIFEXITED(*exitStatus) || !WEXITSTATUS(*exitStatus) )
          goto cleanup;
  }

I tried to add "set follow-fork-mode child" as said here: http://unix.derkeiler.com/Newsgroups/comp.unix.programmer/2006-02/msg00435.html

1. How can I debug the code section where (0==pid)?

2. When I get to the wait statement, the debugger just return immediately, isn't wait() suppose to suspend till the child returns? Why is it return immediately?

Upvotes: 12

Views: 7094

Answers (4)

jouge
jouge

Reputation: 13

Just to add to the perfect answer of @dbrank0, the Debug Configuration window is located under the Run menu. You can find the mentioned configurations under the Debugger tab. enter image description here

Upvotes: 0

Serg Kryvonos
Serg Kryvonos

Reputation: 4677

  1. In debug configuration window -> Debugger -> Check "Automatically debug forked processes"
  2. Open breakpoint window -> View menu -> Add Event Breakpoint C/C++ -> "fork called"
  3. Now once the event breakpoint occurred, press F6 -> you'll see new process in debug window
  4. Choose new process and press F6 - You are in the child
  5. Enjoy

Upvotes: 1

dbrank0
dbrank0

Reputation: 9476

Your problems are probably due to "detach-on-fork" being set to off. DSF sets this by default (it's also gdb's default).

1) Put a breakpoint onto lines with "execlp..." and "returnedpid =...". 2) In debug configuration enable "non-stop mode" and "automatically debug forked process". 3) Start debug session. You will hit a breakpoint either in child or parent. Now see debug view.

Debug view

You will notice your binary shows two threads.

4) Click on one or the other (lines with main() in above image) to switch debug context.

Upvotes: 15

user2180705
user2180705

Reputation: 21

It might be because the init process reaps the child before you go to wait. Try blocking sigchld as you go into fork and then unblock the signals after your forks/execs. Maybe that should give you some idea as to what is exactly happening.

Using sigprocmask should help you.

Upvotes: 1

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