From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 20566 invoked by alias); 19 Feb 2004 18:47:31 -0000 Mailing-List: contact gdb-help@sources.redhat.com; run by ezmlm Precedence: bulk List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-owner@sources.redhat.com Received: (qmail 20550 invoked from network); 19 Feb 2004 18:47:30 -0000 Received: from unknown (HELO nevyn.them.org) (66.93.172.17) by sources.redhat.com with SMTP; 19 Feb 2004 18:47:30 -0000 Received: from drow by nevyn.them.org with local (Exim 4.30 #1 (Debian)) id 1AttCs-0006rT-86; Thu, 19 Feb 2004 13:47:30 -0500 Date: Thu, 19 Feb 2004 18:47:00 -0000 From: Daniel Jacobowitz To: Dave Allan Cc: gdb@sources.redhat.com Subject: Re: execute_control_command may not remove its cleanups Message-ID: <20040219184730.GA26281@nevyn.them.org> Mail-Followup-To: Dave Allan , gdb@sources.redhat.com References: <1077204518.1305.1192.camel@hasufel.egenera.com> <20040219154016.GA24829@nevyn.them.org> <1077214912.1304.1351.camel@hasufel.egenera.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1077214912.1304.1351.camel@hasufel.egenera.com> User-Agent: Mutt/1.5.1i X-SW-Source: 2004-02/txt/msg00248.txt.bz2 On Thu, Feb 19, 2004 at 01:21:52PM -0500, Dave Allan wrote: > > > However, it seems from code inspection and the gdb internals > > > documentation that the call to do_cleanups ought to be unconditional. > > > Does that seem right? > > > > No, instead, the cleanup chain should always have an item on it. If > > make_cleanup is not called then old_chain will remain NULL, and > > do_cleanups (NULL) means "do all cleanups", not "do nothing". It looks > > to me like command_handler is responsible for there always being a > > cleanup on the chain: > > old_chain = make_cleanup (null_cleanup, 0); > > but maybe I'm mistaken about that; it's a bit far down the tree. > > I definitely understand that do_cleanups(NULL) will do all cleanups > which is not what's wanted here. The call is do_cleanups(old_chain), > though, so if there are cleanups on the chain already, they are > preserved. The problem isn't the do_cleanups call, it's the fact that > the do_cleanups call is conditional. The solution is to remove the if > (old_chain) statement and always do the cleanup. > > Given what's stated in the docs, that a function must always remove the > cleanups it creates, it would seem to me that regardless of the state of > cleanup_chain at the beginning of execute_control_command, whether it's > NULL or contains cleanups, we want to get back to that state before we > return. > > Looking at what cleanups execute_control_command puts on cleanup_chain, > that is correct. Either one or two cleanups are put on the chain where > arg is an automatic variable and function is free_current_contents. If > these cleanups aren't done before the stack frame is destroyed, > something undefined will later be freed when the cleanups are done. Think about this again. Both of those cleanups are conditionally created. If neither of them is created, old_chain will still be NULL. This will lead to running cleanups prematurely. If the cleanup chain is non-empty, things work OK. The alternative is null_cleanup. -- Daniel Jacobowitz MontaVista Software Debian GNU/Linux Developer