From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from simark.ca by simark.ca with LMTP id OBTHCiQFx1+JWAAAWB0awg (envelope-from ) for ; Tue, 01 Dec 2020 22:08:20 -0500 Received: by simark.ca (Postfix, from userid 112) id 29F961F0AB; Tue, 1 Dec 2020 22:08:20 -0500 (EST) X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on simark.ca X-Spam-Level: X-Spam-Status: No, score=-1.1 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,MAILING_LIST_MULTI,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.2 Received: from sourceware.org (server2.sourceware.org [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 9C2B21E58D for ; Tue, 1 Dec 2020 22:08:19 -0500 (EST) Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id EAE00388C03B; Wed, 2 Dec 2020 03:08:18 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org EAE00388C03B DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1606878499; bh=VRZAt9cggC/idyWpHwYVFdgIwb9eo8yVVnFY7OIZ01E=; h=To:Subject:References:Date:In-Reply-To:List-Id:List-Unsubscribe: List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:Cc: From; b=TrW7u++b/IY5ietRQA6FI5GXP9qd7vb8YLCaD82gEKjjcU4H6MQ7+86sRIgFowEt7 hOWxbqw3RDf1Xg4DOkCdf1rdcc7rZaws/KuQUoEVacXFksJx0wM6CMjORQE7V1s5bq O4KTR7TDWTwSgOovYxYJLNmQJrALoQ0IZB73vgDo= Received: from mail.sergiodj.net (mail.sergiodj.net [IPv6:2607:5300:60:3666::3]) by sourceware.org (Postfix) with ESMTPS id 7D9943857033 for ; Wed, 2 Dec 2020 03:08:16 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 7D9943857033 Received: from localhost (bras-base-toroon1016w-grc-37-76-65-22-220.dsl.bell.ca [76.65.22.220]) by mail.sergiodj.net (Postfix) with ESMTPSA id CDCD2A0099; Tue, 1 Dec 2020 22:08:15 -0500 (EST) To: Simon Marchi Subject: Re: [PATCH v3] Search for DWZ files in debug-file-directories as well References: <20201114234842.2334396-1-sergiodj@sergiodj.net> <20201129010841.97294-1-sergiodj@sergiodj.net> <6ca067dc-6f81-3573-a3cf-712ac7371c5b@simark.ca> X-URL: http://blog.sergiodj.net Date: Tue, 01 Dec 2020 22:08:15 -0500 In-Reply-To: <6ca067dc-6f81-3573-a3cf-712ac7371c5b@simark.ca> (Simon Marchi's message of "Tue, 1 Dec 2020 09:45:49 -0500") Message-ID: <87a6uwewgw.fsf@paluero> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain 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: , From: Sergio Durigan Junior via Gdb-patches Reply-To: Sergio Durigan Junior Cc: Mark Wielaard , gdb-patches@sourceware.org Errors-To: gdb-patches-bounces@sourceware.org Sender: "Gdb-patches" On Tuesday, December 01 2020, Simon Marchi wrote: > 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. Thanks, I've just pushed the patch. > 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. Totally agreed. I'll see if I can come up with a testcase for this, and will submit it later. Thanks, -- Sergio GPG key ID: 237A 54B1 0287 28BF 00EF 31F4 D0EB 7628 65FC 5E36 Please send encrypted e-mail if possible https://sergiodj.net/