From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 22621 invoked by alias); 18 Oct 2012 10:42:25 -0000 Received: (qmail 22613 invoked by uid 22791); 18 Oct 2012 10:42:24 -0000 X-SWARE-Spam-Status: No, hits=-7.8 required=5.0 tests=AWL,BAYES_00,KHOP_RCVD_UNTRUST,KHOP_THREADED,RCVD_IN_DNSWL_HI,RCVD_IN_HOSTKARMA_W,RP_MATCHES_RCVD,SPF_HELO_PASS X-Spam-Check-By: sourceware.org Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Thu, 18 Oct 2012 10:42:16 +0000 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id q9IAgB8O028716 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Thu, 18 Oct 2012 06:42:11 -0400 Received: from [127.0.0.1] (ovpn01.gateway.prod.ext.ams2.redhat.com [10.39.146.11]) by int-mx09.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id q9IAg9cP012936; Thu, 18 Oct 2012 06:42:10 -0400 Message-ID: <507FDD00.1000309@redhat.com> Date: Thu, 18 Oct 2012 10:42:00 -0000 From: Pedro Alves User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:16.0) Gecko/20121009 Thunderbird/16.0 MIME-Version: 1.0 To: Yao Qi CC: Michal Lesniewski , gdb@sourceware.org Subject: Re: Implementation of different software breakpoint kinds in gdb server References: <000001cdad12$1e2b1950$5a814bf0$%lesniewski@samsung.com> <507FD526.5080604@redhat.com> <507FD9CB.7060805@codesourcery.com> In-Reply-To: <507FD9CB.7060805@codesourcery.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Mailing-List: contact gdb-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-owner@sourceware.org X-SW-Source: 2012-10/txt/msg00081.txt.bz2 On 10/18/2012 11:28 AM, Yao Qi wrote: > On 10/18/2012 06:08 PM, Pedro Alves wrote: >> Offhand, the main issues with tracepoints on ARM are: >> >> #1 - gdbserver needs to know how to step over the tracepoints, without gdb's intervention. >> >> #2 - ARM can't hw single-step, so that needs to be done the hard way, with breakpoints >> (a.k.a., software single-step). >> All the logic to do that is in gdb. This conflicts with #1. >> >> So we'd need to teach gdbserver to software single-step. Maybe it's possible >> to tell offline all the possible destinations of an instruction, so we could still >> leave that logic in gdb, but I suspect not. > > I am wondering that it might be relatively easier to implement fast tracepoint in which step-over is not needed, if finding a jumppad is not a problem :) Maybe. :-) The "move out of jumppad" logic uses single-stepping. I guess we could come up with something clever to avoid it. Related, linux_fast_tracepoint_collecting logic assumes it can identify a thread from its tls base / thread area. And this assumes you can retrieve this address without an infcall. This is possible on x86. Don't know about ARM (well, in an ABI-stable way). -- Pedro Alves