From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 26624 invoked by alias); 10 Dec 2004 23:01:18 -0000 Mailing-List: contact gdb-patches-help@sources.redhat.com; run by ezmlm Precedence: bulk List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sources.redhat.com Received: (qmail 26086 invoked from network); 10 Dec 2004 23:00:55 -0000 Received: from unknown (HELO legolas.inter.net.il) (192.114.186.24) by sourceware.org with SMTP; 10 Dec 2004 23:00:55 -0000 Received: from zaretski (IGLD-83-130-247-149.inter.net.il [83.130.247.149]) by legolas.inter.net.il (MOS 3.5.5-GR) with ESMTP id DHS15188 (AUTH halo1); Sat, 11 Dec 2004 00:59:58 +0200 (IST) Date: Fri, 10 Dec 2004 23:06:00 -0000 From: "Eli Zaretskii" To: Daniel Jacobowitz Message-ID: <01c4df0c$Blat.v2.2.2$244dda20@zahav.net.il> Content-Transfer-Encoding: 7BIT Content-Type: text/plain; charset=ISO-8859-1 CC: jjohnstn@redhat.com, gdb-patches@sources.redhat.com In-reply-to: <20041210191015.GA18430@nevyn.them.org> (message from Daniel Jacobowitz on Fri, 10 Dec 2004 14:10:15 -0500) Subject: Re: [RFA]: Modified Watchthreads Patch Reply-to: Eli Zaretskii References: <41B8E16D.6070505@redhat.com> <20041210191015.GA18430@nevyn.them.org> X-SW-Source: 2004-12/txt/msg00281.txt.bz2 > Date: Fri, 10 Dec 2004 14:10:15 -0500 > From: Daniel Jacobowitz > Cc: gdb-patches@sources.redhat.com > > 1) I can see that it will be a bit of work to rearrange i386-linux to > use this, but it should be doable. Do you know offhand of any > i386-specific problems other than inserting watchpoints for all > threads? The design of the x86 watchpoint support explicitly assumes that watchpoints are not thread-local. If we want to lift that limitation, I think the x86-specific code needs to be redesigned. Someone who knows way more than I do about x86 threads and how the debug registers are handled by the relevant kernels in the presence of threads, should present a clean replacement design that deals with thread-local watchpoints. Small modifications like inserting watchpoints for all threads and other similar patchwork will simply not cut it, IMHO. Observe: > 2) What should to_stopped_by_watchpoint do in the presence of multiple > threads? It looks like it relies on inferior_ptid being the thread > which stopped at a watchpoint; I'm worried that that may not be > consistently true in a heavily threaded application. Maybe it should > iterate over all threads. > > The to_stopped_data_address has its own problems with threads; but the > case of handling hitting two watchpoints at once, I think, we can leave > for another day. These two are just the tip of the iceberg, but already you discovered that the two cornerstones of the GDB watchpoint support do not work reliably in multithreaded programs. We should redesign the x86 watchpoint support instead of taking the evolutionary approach, which will leave us with messy, unmaintainable, and buggy code.