From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 9076 invoked by alias); 15 May 2013 13:46:33 -0000 Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org Received: (qmail 9066 invoked by uid 89); 15 May 2013 13:46:32 -0000 X-Spam-SWARE-Status: No, score=-4.3 required=5.0 tests=AWL,BAYES_00,KHOP_THREADED,RCVD_IN_DNSWL_NONE,RCVD_IN_HOSTKARMA_NO,SPF_SOFTFAIL autolearn=no version=3.3.1 Received: from mtaout21.012.net.il (HELO mtaout21.012.net.il) (80.179.55.169) by sourceware.org (qpsmtpd/0.84/v0.84-167-ge50287c) with ESMTP; Wed, 15 May 2013 13:46:31 +0000 Received: from conversion-daemon.a-mtaout21.012.net.il by a-mtaout21.012.net.il (HyperSendmail v2007.08) id <0MMU00M00E2PFG00@a-mtaout21.012.net.il> for gdb-patches@sourceware.org; Wed, 15 May 2013 16:46:08 +0300 (IDT) Received: from HOME-C4E4A596F7 ([87.69.4.28]) by a-mtaout21.012.net.il (HyperSendmail v2007.08) with ESMTPA id <0MMU00M9GE8V9DI0@a-mtaout21.012.net.il>; Wed, 15 May 2013 16:46:08 +0300 (IDT) Date: Wed, 15 May 2013 13:46:00 -0000 From: Eli Zaretskii Subject: Re: [PATCH 3/5] range stepping: gdb In-reply-to: <519381E9.3020007@redhat.com> To: Pedro Alves Cc: gdb-patches@sourceware.org Reply-to: Eli Zaretskii Message-id: <83bo8c5pb7.fsf@gnu.org> References: <20130514191026.13213.39574.stgit@brno.lan> <20130514191047.13213.8476.stgit@brno.lan> <83k3n173ao.fsf@gnu.org> <5193621C.50603@redhat.com> <83ppws5w00.fsf@gnu.org> <519381E9.3020007@redhat.com> X-SW-Source: 2013-05/txt/msg00527.txt.bz2 > Date: Wed, 15 May 2013 13:39:05 +0100 > From: Pedro Alves > CC: gdb-patches@sourceware.org > > > Doesn't this mean that these two use cases are explicit exceptions > > from the rule that END is excluded? > > Nope. There's no exception. > > With: > > vCont ;r START,END > > #1 - The stub single-steps the thread. > #2 - Once the thread stops, the stub checks whether the thread > stopped in the [START,END) range. If so, goto #1. > It not, goto #3. > #3 - The stub reports to gdb that the thread stopped stepping. > > If it happens that START and END are the same, then #2 always > goes to #3. I'm simulating a naive reader, while you are replying to someone you consider an experienced code developer ;-) So we are talking past each other. When you say "END is the address of the first instruction beyond the step range", that means, simply put, that execution will always stop before it executes the instruction at END. IOW, the instruction at END will _not_ be executed. With that interpretation, a range [START,START) is _empty_ and will never execute any instructions at all. It is OK to use a different interpretation, but then we should either (a) describe the semantics differently to begin with, or (b) explain that [START,START) is an exception. You seem to object to (b), which then brings us back at (a), meaning that this text: > +@var{end} is the address of the first instruction beyond the step > +range, and @strong{not} the address of the last instruction within it. needs to be reworded, so as not to say that END is _beyond_ the range. If you want a specific response for the algorithm you show above, then I would ask why does GDB single-step the stub at all, when START and END are equal? The fact that we implemented this is a 'do-until' loop rather than a 'while' loop, i.e. test at the end instead of at the beginning, is an important implementation detail which must be present explicitly in the description of what this feature does. If you hide it behind the [a,b) notation, you get a problem you will need to explain, as we see. > When I said: > > "(This has the property that @var{start} == @var{end} single-steps > once, and only once, even if the instruction at @var{start} jumps to > @var{start}.)" > > I was trying to clarify the case of the instruction at START being: > > jump START > > Then, > > vCont ;r START,START > > always single-steps once, and only once, instead of > continuously single-stepping that instruction without > reporting to GDB. The very need you felt to explain this is already a clear sign that the original description is wrong.