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Date: Wed, 15 Jan 2003 15:27:51 -0500
From: Daniel Jacobowitz <dan@debian.org>
To: Daniel Barlow <dan@telent.net>
Cc: linux-kernel@vger.kernel.org
Subject: Re: 2.4.x, can't ptrace a task created with clone() ?
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On Wed, Jan 15, 2003 at 04:34:58PM +0000, Daniel Barlow wrote:
> 
> Tested with 4.2.20 and 2.4.21-pre3, after PTRACE_ATTACHing to a
> process I created with clone(), wait() returns ECHILD .  strace
> of the parent shows
> 
> clone(child_stack=0x80599a8, flags=CLONE_VM) = 1292
> rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
> rt_sigaction(SIGCHLD, NULL, {SIG_DFL}, 8) = 0
> rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
> nanosleep({5, 0}, {5, 0})               = 0
> ptrace(PTRACE_ATTACH, 1292, 0, 0)       = 0
> --- SIGCHLD (Child exited) ---
> wait4(-1, 0xbffffbf0, 0, NULL)          = -1 ECHILD (No child processes)
> write(2, "waitpid: No child processes\n", 28) = 28
> 
> If I replace the clone in my test program with a fork, everything
> works as I expected.  Is this a bug, or are my expectations at fault?
> if the latter, how _do_ I attach to one of my cloned children?

You did attach.  But if you want to wait for a cloned child, you need
to use __WCLONE or __WALL.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer
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