From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gdb-return-15691-listarch-gdb=sources.redhat.com@sources.redhat.com>
Received: (qmail 6043 invoked by alias); 28 Sep 2003 22:35:35 -0000
Mailing-List: contact gdb-help@sources.redhat.com; run by ezmlm
Precedence: bulk
List-Subscribe: <mailto:gdb-subscribe@sources.redhat.com>
List-Archive: <http://sources.redhat.com/ml/gdb/>
List-Post: <mailto:gdb@sources.redhat.com>
List-Help: <mailto:gdb-help@sources.redhat.com>, <http://sources.redhat.com/ml/#faqs>
Sender: gdb-owner@sources.redhat.com
Received: (qmail 6036 invoked from network); 28 Sep 2003 22:35:34 -0000
Received: from unknown (HELO localhost.redhat.com) (65.49.0.121)
  by sources.redhat.com with SMTP; 28 Sep 2003 22:35:34 -0000
Received: from redhat.com (localhost [127.0.0.1])
	by localhost.redhat.com (Postfix) with ESMTP
	id 036DB2B89; Sun, 28 Sep 2003 18:35:24 -0400 (EDT)
Message-ID: <3F77622C.8090403@redhat.com>
Date: Sun, 28 Sep 2003 22:45:00 -0000
From: Andrew Cagney <ac131313@redhat.com>
User-Agent: Mozilla/5.0 (X11; U; NetBSD macppc; en-US; rv:1.0.2) Gecko/20030820
X-Accept-Language: en-us, en
MIME-Version: 1.0
To: Michael Elizabeth Chastain <mec@shout.net>,
	aurelien.chanudet@enst.fr
Cc: gdb@sources.redhat.com
Subject: Re: process attaching gdb to itself
References: <200309282225.h8SMP9Rf026649@duracef.shout.net>
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Transfer-Encoding: 7bit
X-SW-Source: 2003-09/txt/msg00354.txt.bz2

> Hello,
> 
>   char cmd [256];
>   sprintf (cmd, "gdb attach %d", getpid ());
>   system (cmd);
> 
> 'system' waits for the program that it calls to finish.
> Thus, your program is waiting for gdb to finish before it
> does anything.
> 
> Try the appended program which uses raw fork/exec.
> It works for me on red hat linux 8, native i686-pc-linux-gnu.
> 
> If you try to do this in production code then you are likely
> to run into a blizzard of race conditions, error cases,
> and signal handling problems.  If you are doing this as a learning
> experience, that's great -- read up on 'man fork' and
> 'man execlp', and check out a book on Linux systems programming.

Is the kernel Linux?  JeffJ and I just discovered that:

$ sleep 1000
^Z
PID 1234 suspended
$ gdb sleep 1234
...
(gdb)

works on BSD but fails on GNU/Linux.  When doing an attach, BSD always 
generates something for wait4 to consume. GNU/Linux does not, leaving 
GDB stuck in wait4 :-(

Andrew