From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp.polymtl.ca (smtp.polymtl.ca [132.207.4.11]) by sourceware.org (Postfix) with ESMTPS id AE5E73858C27 for ; Thu, 29 Jul 2021 19:36:18 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org AE5E73858C27 Received: from simark.ca (simark.ca [158.69.221.121]) (authenticated bits=0) by smtp.polymtl.ca (8.14.7/8.14.7) with ESMTP id 16TJaC5L024854 (version=TLSv1/SSLv3 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 29 Jul 2021 15:36:17 -0400 DKIM-Filter: OpenDKIM Filter v2.11.0 smtp.polymtl.ca 16TJaC5L024854 Received: from [10.0.0.11] (192-222-157-6.qc.cable.ebox.net [192.222.157.6]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by simark.ca (Postfix) with ESMTPSA id 81AB31E4A3; Thu, 29 Jul 2021 15:36:12 -0400 (EDT) Subject: Re: [PATCH] Fix displaced stepping watchpoint check order To: Luis Machado , gdb-patches@sourceware.org References: <20210608154230.354202-1-luis.machado@linaro.org> From: Simon Marchi Message-ID: Date: Thu, 29 Jul 2021 15:36:12 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: <20210608154230.354202-1-luis.machado@linaro.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Poly-FromMTA: (simark.ca [158.69.221.121]) at Thu, 29 Jul 2021 19:36:12 +0000 X-Spam-Status: No, score=-10.1 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, NICE_REPLY_A, RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL, SPF_HELO_PASS, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: gdb-patches@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gdb-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 29 Jul 2021 19:36:20 -0000 I think this is ok, but in all honestly I don't completely understand how the interaction between watchpoints and displaced stepping is expected to work. Just some nits: On 2021-06-08 11:42 a.m., Luis Machado via Gdb-patches wrote: > When checking the stopped data address, I noticed, under some circumstances, > that the instruction at PC wasn't the expected one. This happens because the > displaced stepping machinery restores the buffer before checking if the > instruction executed successfully, which in turn calls the watchpoint check. > > I guess this was never noticed because stopped data address checks usually > don't need to fetch the instruction at PC, but AArch64 needs to do it from > now on. Can you clarify what you mean by "from now on"? Can you indicate what change you are referring to? > > We should check if the instruction executed successfully before we restore the > scratchpad contents. > > Regression tested on aarch64-linux/Ubuntu 20.04. > > gdb/ChangeLog: > > YYYY-MM-DD Luis Machado > > * displaced-stepping.c (displaced_step_buffers::finish): Move check > upwards. > --- > gdb/displaced-stepping.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/gdb/displaced-stepping.c b/gdb/displaced-stepping.c > index 59b78c22f6a..06324d523d8 100644 > --- a/gdb/displaced-stepping.c > +++ b/gdb/displaced-stepping.c > @@ -227,6 +227,11 @@ displaced_step_buffers::finish (gdbarch *arch, thread_info *thread, > > ULONGEST len = gdbarch_max_insn_length (arch); > > + /* Check if the execution was successful before restoring the buffer > + contents. */ > + bool instruction_executed_successfully > + = displaced_step_instruction_executed_successfully (arch, sig); Maybe extend the comment to say "why". Right now I think it just states what is in plain sight when looking at the code, I think it would be more useful if it said why it's important to do that. Simon