From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 32343 invoked by alias); 20 Mar 2012 02:03:31 -0000 Received: (qmail 32207 invoked by uid 22791); 20 Mar 2012 02:03:30 -0000 X-SWARE-Spam-Status: No, hits=-1.8 required=5.0 tests=AWL,BAYES_00 X-Spam-Check-By: sourceware.org Received: from relay1.mentorg.com (HELO relay1.mentorg.com) (192.94.38.131) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Tue, 20 Mar 2012 02:03:07 +0000 Received: from svr-orw-exc-10.mgc.mentorg.com ([147.34.98.58]) by relay1.mentorg.com with esmtp id 1S9oPi-00057r-Q1 from Luis_Gustavo@mentor.com for gdb-patches@sourceware.org; Mon, 19 Mar 2012 19:03:06 -0700 Received: from NA1-MAIL.mgc.mentorg.com ([147.34.98.181]) by SVR-ORW-EXC-10.mgc.mentorg.com with Microsoft SMTPSVC(6.0.3790.4675); Mon, 19 Mar 2012 19:03:03 -0700 Received: from [0.0.0.0] ([172.16.63.104]) by NA1-MAIL.mgc.mentorg.com with Microsoft SMTPSVC(6.0.3790.4675); Mon, 19 Mar 2012 19:03:05 -0700 Message-ID: <4F67E54C.1010904@mentor.com> Date: Tue, 20 Mar 2012 02:03:00 -0000 From: Luis Gustavo Reply-To: "Gustavo, Luis" User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.27) Gecko/20120216 Lightning/1.0b2 Thunderbird/3.1.19 MIME-Version: 1.0 To: gdb-patches@sourceware.org Subject: [PATCH] Fix displaced stepping for remote targets Content-Type: multipart/mixed; boundary="------------090400000703040404020508" X-IsSubscribed: yes 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 X-SW-Source: 2012-03/txt/msg00728.txt.bz2 This is a multi-part message in MIME format. --------------090400000703040404020508 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Content-length: 1770 Hi, While debugging a remote target that supports hardware single-stepping with a GDB that supports displaced stepping, i've ran into the following problem... When reaching a breakpoint, GDB should take care of relocating the instruction underneath that breakpoint to the scratch space where it will be executed out-of-line. If a target supports hw single-stepping for displaced stepping, GDB should just send a vCont;s packet to tell the target to step a single instruction. In my case, GDB was always sending a vCont;c instead. I've tracked it down to infrun.c:resume, where we have this check: if (gdbarch_cannot_step_breakpoint (gdbarch)) { /* Most targets can step a breakpoint instruction, thus executing it normally. But if this one cannot, just continue and we will hit it anyway. */ if (step && breakpoint_inserted_here_p (aspace, pc)) step = 0; } My target can't step breakpoints and, if we're doing displaced stepping, it's because we're trying to step off a breakpoint, thus breakpoint_inserted_here_p returns true, and we disable single-stepping by setting step to 0. It seems to me we need to update the PC prior to calling breakpoint_inserted_here_p since the displaced stepping machinery adjusted the old PC to point to the space in the scratch area. That way we can properly command the target to step the displaced instruction and we can check for breakpoints at the real execution place. The following patch fixes this by pushing the if block further down in the code and taking care of updating PC if displaced stepping is being used. I've regtested this on x86 and everything looks OK. This also makes GDB send vCont;s now. Ok? Luis --------------090400000703040404020508 Content-Type: text/x-patch; name="0001-fix_remote_displaced_stepping.diff" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="0001-fix_remote_displaced_stepping.diff" Content-length: 1885 2012-03-19 Luis Machado * infrun.c (resume): Change order of statements and update PC to the real PC in case of displaced stepping. Index: HEAD-git/gdb/infrun.c =================================================================== --- HEAD-git.orig/gdb/infrun.c 2012-03-19 20:40:57.589621232 -0300 +++ HEAD-git/gdb/infrun.c 2012-03-19 22:12:08.729898472 -0300 @@ -1884,15 +1884,6 @@ a command like `return' or `jump' to con resume_ptid = inferior_ptid; } - if (gdbarch_cannot_step_breakpoint (gdbarch)) - { - /* Most targets can step a breakpoint instruction, thus - executing it normally. But if this one cannot, just - continue and we will hit it anyway. */ - if (step && breakpoint_inserted_here_p (aspace, pc)) - step = 0; - } - if (debug_displaced && use_displaced_stepping (gdbarch) && tp->control.trap_expected) @@ -1902,12 +1893,25 @@ a command like `return' or `jump' to con CORE_ADDR actual_pc = regcache_read_pc (resume_regcache); gdb_byte buf[4]; + /* Update pc to reflect the new address from which we will execute + instructions due to displaced stepping. */ + pc = actual_pc; + fprintf_unfiltered (gdb_stdlog, "displaced: run %s: ", paddress (resume_gdbarch, actual_pc)); read_memory (actual_pc, buf, sizeof (buf)); displaced_step_dump_bytes (gdb_stdlog, buf, sizeof (buf)); } + if (gdbarch_cannot_step_breakpoint (gdbarch)) + { + /* Most targets can step a breakpoint instruction, thus + executing it normally. But if this one cannot, just + continue and we will hit it anyway. */ + if (step && breakpoint_inserted_here_p (aspace, pc)) + step = 0; + } + /* Install inferior's terminal modes. */ target_terminal_inferior (); --------------090400000703040404020508--