From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from simark.ca (simark.ca [158.69.221.121]) by sourceware.org (Postfix) with ESMTPS id 4A6483861030 for ; Thu, 6 Aug 2020 15:01:40 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 4A6483861030 Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=simark.ca Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=simark@simark.ca Received: from [10.0.0.11] (173-246-6-90.qc.cable.ebox.net [173.246.6.90]) (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 EC71A1E594; Thu, 6 Aug 2020 11:01:39 -0400 (EDT) Subject: Re: [PATCH v3 7/7] amd64_analyze_prologue: use target_read_code instead of read_code To: Victor Collod , gdb-patches@sourceware.org References: <0cc93067-1313-6434-4330-61a21736376f@simark.ca> <20200624012857.31849-1-vcollod@nvidia.com> <20200624012857.31849-8-vcollod@nvidia.com> From: Simon Marchi Message-ID: Date: Thu, 6 Aug 2020 11:01:31 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200624012857.31849-8-vcollod@nvidia.com> Content-Type: text/plain; charset=utf-8 Content-Language: fr Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-9.5 required=5.0 tests=BAYES_00, GIT_PATCH_0, KAM_DMARC_STATUS, NICE_REPLY_A, SPF_HELO_PASS, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) 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, 06 Aug 2020 15:01:41 -0000 On 2020-06-23 9:28 p.m., Victor Collod via Gdb-patches wrote: > Using target_read_code enables gracefuly handling error cases. Can you expand a bit why you think it's more graceful? > > 2020-06-23 Victor Collod > > * amd64-tdep.c (amd64_analyze_prologue): Use target_read_code > instead of read_code. > --- > gdb/amd64-tdep.c | 19 ++++++++++++++----- > 1 file changed, 14 insertions(+), 5 deletions(-) > > diff --git a/gdb/amd64-tdep.c b/gdb/amd64-tdep.c > index 901733cf443..7f70c1d0d8d 100644 > --- a/gdb/amd64-tdep.c > +++ b/gdb/amd64-tdep.c > @@ -2394,9 +2394,15 @@ amd64_analyze_prologue (struct gdbarch *gdbarch, > else > pc = amd64_analyze_stack_align (pc, current_pc, cache); > > - read_code (pc, buf, 4); > - /* Check for the `endbr64' instruction and skip it if found. */ > - if (memcmp (buf, endbr64, sizeof (endbr64)) == 0) > + /* Try to read enough bytes to check for `endbr64'. */ > + if (target_read_code (pc, buf, 4) != 0) > + { > + /* If it fails, read just enough data for `pushq %rbp'. */ > + if (target_read_code (pc, buf, 1) != 0) > + return pc; > + } > + /* If reading succeeded, check for the `endbr64' instruction and skip it if found. */ > + else if (memcmp (buf, endbr64, sizeof (endbr64)) == 0) Personally, I find this "try to read 4 else try to read 1" approach less clear and less intuitive than the "read 1 byte and read more if needed approach". Simon