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 4F2E8383E832 for ; Sun, 21 Jun 2020 11:38:43 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 4F2E8383E832 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 022F21E79B; Sun, 21 Jun 2020 07:38:42 -0400 (EDT) Subject: Re: [PATCH v2 2/2] Refactor amd64_analyze_prologue To: Victor Collod , gdb-patches@sourceware.org References: <0c2e7c13-3a10-0f83-955b-e08dcd628d17@simark.ca> <20200611225455.9354-1-vcollod@nvidia.com> <20200611225455.9354-3-vcollod@nvidia.com> From: Simon Marchi Message-ID: <0cc93067-1313-6434-4330-61a21736376f@simark.ca> Date: Sun, 21 Jun 2020 07:38:42 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: <20200611225455.9354-3-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, 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: Sun, 21 Jun 2020 11:38:44 -0000 On 2020-06-11 6:54 p.m., Victor Collod via Gdb-patches wrote: > * merge op and the buf array, which were both used for storing code > * invert conditions to avoid long nested ifs > * use target_read_code instead of read_code to gracefully handle errors > * `if (current_pc <= pc)' felt backwards, as current_pc doesn't change, > and the test could be described as "stop if pc went past current_pc" I'd appreciate if you could do one patch per change here. They'd each be more trivial to review and ensure they are ok. > 2020-06-11 Victor Collod > > * amd64-tdep.c (amd64_analyze_prologue): Make the function more readable. > --- > gdb/amd64-tdep.c | 93 ++++++++++++++++++++++++++---------------------- > 1 file changed, 50 insertions(+), 43 deletions(-) > > diff --git a/gdb/amd64-tdep.c b/gdb/amd64-tdep.c > index 0ce9fbc2997..6c1a4a138de 100644 > --- a/gdb/amd64-tdep.c > +++ b/gdb/amd64-tdep.c > @@ -2374,7 +2374,6 @@ amd64_analyze_prologue (struct gdbarch *gdbarch, > CORE_ADDR pc, CORE_ADDR current_pc, > struct amd64_frame_cache *cache) > { > - enum bfd_endian byte_order = gdbarch_byte_order (gdbarch); > /* The `endbr64` instruction. */ > static const gdb_byte endbr64[4] = { 0xf3, 0x0f, 0x1e, 0xfa }; > /* There are two variations of movq %rsp, %rbp. */ > @@ -2384,10 +2383,10 @@ amd64_analyze_prologue (struct gdbarch *gdbarch, > static const gdb_byte mov_esp_ebp_1[2] = { 0x89, 0xe5 }; > static const gdb_byte mov_esp_ebp_2[2] = { 0x8b, 0xec }; > > - gdb_byte buf[3]; > - gdb_byte op; > + gdb_byte buf[4]; > > - if (current_pc <= pc) > + /* Analysis must not go past current_pc */ Take the habit of starting each comment with a capital letter, finishing with a period and two spaces (unless it's not really a sentence, like `/* no-op */`). > + if (pc >= current_pc) > return current_pc; > > if (gdbarch_ptr_bit (gdbarch) == 32) > @@ -2395,57 +2394,65 @@ amd64_analyze_prologue (struct gdbarch *gdbarch, > else > pc = amd64_analyze_stack_align (pc, current_pc, cache); > > - op = read_code_unsigned_integer (pc, 1, byte_order); > - > - /* Check for the `endbr64` instruction, skip it if found. */ > - if (op == 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) > { > - read_code (pc + 1, buf, 3); > + pc += sizeof (endbr64); > + /* If we went past the allowed bound, stop */ > + if (pc >= current_pc) > + return current_pc; For readability, please add an empty line after return statements, when there is another statement after it. Thanks, Simon