From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from simark.ca by simark.ca with LMTP id 2KKoGyJXxl+qSAAAWB0awg (envelope-from ) for ; Tue, 01 Dec 2020 09:45:54 -0500 Received: by simark.ca (Postfix, from userid 112) id 644A01F0AB; Tue, 1 Dec 2020 09:45:54 -0500 (EST) X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on simark.ca X-Spam-Level: X-Spam-Status: No, score=0.3 required=5.0 tests=MAILING_LIST_MULTI,RDNS_NONE, URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.2 Received: from sourceware.org (unknown [8.43.85.97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by simark.ca (Postfix) with ESMTPS id 0ECD51E58E for ; Tue, 1 Dec 2020 09:45:54 -0500 (EST) Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id 5C7A13857C6D; Tue, 1 Dec 2020 14:45:53 +0000 (GMT) Received: from simark.ca (simark.ca [158.69.221.121]) by sourceware.org (Postfix) with ESMTPS id 52F703857C6D for ; Tue, 1 Dec 2020 14:45:50 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 52F703857C6D 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) server-digest SHA256) (No client certificate requested) by simark.ca (Postfix) with ESMTPSA id C754A1E58E; Tue, 1 Dec 2020 09:45:49 -0500 (EST) Subject: Re: [PATCH v3] Search for DWZ files in debug-file-directories as well To: Sergio Durigan Junior , gdb-patches@sourceware.org References: <20201114234842.2334396-1-sergiodj@sergiodj.net> <20201129010841.97294-1-sergiodj@sergiodj.net> From: Simon Marchi Message-ID: <6ca067dc-6f81-3573-a3cf-712ac7371c5b@simark.ca> Date: Tue, 1 Dec 2020 09:45:49 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <20201129010841.97294-1-sergiodj@sergiodj.net> Content-Type: text/plain; charset=utf-8 Content-Language: fr Content-Transfer-Encoding: 7bit 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: , Cc: Mark Wielaard Errors-To: gdb-patches-bounces@sourceware.org Sender: "Gdb-patches" On 2020-11-28 8:08 p.m., Sergio Durigan Junior via Gdb-patches wrote: > Changes from v2: > > - Put the new code into a new function. > > - The code now makes sure that the debug-file-directory being > processed ends with a directory separator, which makes things more > robust. > > - Minimized indentation level; fixed typos and improved code > readability by adding more comments. > > > When Debian (and Ubuntu) builds its binaries, it (still) doesn't use > dwz's "--relative" option. This causes their debuginfo files to > carry a .gnu_debugaltlink section containing a full pathname to the > DWZ alt debug file, like this: > > $ readelf -wk /usr/bin/cat > Contents of the .gnu_debugaltlink section: > > Separate debug info file: /usr/lib/debug/.dwz/x86_64-linux-gnu/coreutils.debug > Build-ID (0x14 bytes): > ee 76 5d 71 97 37 ce 46 99 44 32 bb e8 a9 1a ef 99 96 88 db > > Contents of the .gnu_debuglink section: > > Separate debug info file: 06d3bee37b8c7e67b31cb2689cb351102ae73b.debug > CRC value: 0x53267655 > > This usually works OK, because most of the debuginfo files installed > via apt will be present in /usr/lib/debug anyway. However, imagine > the following scenario: > > - You are using /usr/bin/cat, it crashes on you and generates a > corefile. > > - You don't want/need to "apt install" the debuginfo file for > coreutils from the repositories. Instead, you already have the > debuginfo files in a separate directory (e.g., $HOME/dbgsym). > > - You start GDB and "set debug-file-directory $HOME/dbgsym/usr/lib/debug". > You then get the following message: > > $ gdb -ex 'set debug-file-directory ./dbgsym/usr/lib/debug' -ex 'file /bin/cat' -ex 'core-file ./cat.core' > GNU gdb (Ubuntu 10.1-0ubuntu1) 10.1 > ... > Reading symbols from /bin/cat... > Reading symbols from /home/sergio/gdb/dbgsym/usr/lib/debug/.build-id/bc/06d3bee37b8c7e67b31cb2689cb351102ae73b.debug... > could not find '.gnu_debugaltlink' file for /home/sergio/gdb/dbgsym/usr/lib/debug/.build-id/bc/06d3bee37b8c7e67b31cb2689cb351102ae73b.debug > > This error happens because GDB is trying to locate the build-id > link (inside /home/sergio/gdb/dbgsym/usr/lib/debug/.build-id) for the > DWZ alt debug file, which doesn't exist. Arguably, this is a problem > with how dh_dwz works in Debian, and it's something I'm also planning > to tackle. But, back at the problem at hand. > > Besides not being able to find the build-id link in the directory > mentioned above, GDB also tried to open the DWZ alt file using its > filename. The problem here is that, since we don't have the distro's > debuginfo installed, it can't find anything under /usr/lib/debug that > satisfies it. > > It occurred to me that a good way to workaround this problem is to > actually try to locate the DWZ alt debug file inside the > debug-file-directories (that were likely provided by the user). So > this is what the proposed patch does. > > The idea here is simple: get the filename extracted from the > .gnu_debugaltlink section, and manipulate it in order to replace the > initial part of the path (everything before "/.dwz/") by whatever > debug-file-directories the user might have provided. > > I talked with Mark Wielaard and he agrees this is a sensible approach. > In fact, apparently this is something that eu-readelf also does. > > I regtested this code, and no regressions were found. > > 2020-11-28 Sergio Durigan Junior > > * dwarf2/read.c (dwz_search_other_debugdirs): New function. > (dwarf2_get_dwz_file): Convert 'filename' to a > std::string. Use dwz_search_other_debugdirs to search for DWZ > files in the debug-file-directories provided by the user as well. Thanks this is OK. I forgot to mention that before, but a test would be nice to make sure this feature doesn't break when doing changes to the DWARF reader. Simon