From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from simark.ca by simark.ca with LMTP id AO7qA164wl8+cgAAWB0awg (envelope-from ) for ; Sat, 28 Nov 2020 15:51:42 -0500 Received: by simark.ca (Postfix, from userid 112) id 0E2931F0AB; Sat, 28 Nov 2020 15:51:42 -0500 (EST) X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on simark.ca X-Spam-Level: X-Spam-Status: No, score=0.2 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,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 A525B1E552 for ; Sat, 28 Nov 2020 15:51:41 -0500 (EST) Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id 1C39F3854830; Sat, 28 Nov 2020 20:51:41 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 1C39F3854830 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1606596701; bh=uiR3zyzL68LEQtDcOn80ERGMRz2CZ3o+JkjgKMpOb7U=; 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=sm8KyigDHKnJJXmPiIX075Vh1VJjxfLiUuhd5cT1ICaSXcM9OBFzPTApb7PGr1t8p eY7VpiN6DzPcptg+jrj5X4Ok7OC2eVT+eKjrVNWQcjjMWAcaqrMuXlqg3Aiqm2mv51 4C0FX3kZCkjDsf78JAK/JezwHo//Ls183hlyBHsw= Received: from mail.sergiodj.net (mail.sergiodj.net [IPv6:2607:5300:60:3666::3]) by sourceware.org (Postfix) with ESMTPS id B78153857C6F for ; Sat, 28 Nov 2020 20:51:38 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org B78153857C6F 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 09E45A00BB; Sat, 28 Nov 2020 15:51:38 -0500 (EST) To: Luis Machado Subject: Re: [PATCH v2] Search for DWZ files in debug-file-directories as well References: <20201114234842.2334396-1-sergiodj@sergiodj.net> <20201119022708.3627287-1-sergiodj@sergiodj.net> <30b3b6b7-704c-acb8-01ca-b0db0f5704ba@linaro.org> X-URL: http://blog.sergiodj.net Date: Sat, 28 Nov 2020 15:51:37 -0500 In-Reply-To: <30b3b6b7-704c-acb8-01ca-b0db0f5704ba@linaro.org> (Luis Machado's message of "Wed, 25 Nov 2020 13:58:52 -0300") Message-ID: <874kl919ye.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: Simon Marchi , Mark Wielaard , gdb-patches@sourceware.org Errors-To: gdb-patches-bounces@sourceware.org Sender: "Gdb-patches" On Wednesday, November 25 2020, Luis Machado wrote: > Hi, > > I like the idea of GDB trying harder to find a particular > file. Sometimes it is a bit frustrating to deal with GDB and hardcoded > paths. > > With that said, the code is a bit confusing as-is, maybe because there > is a lot of fiddling with the paths etc. > > I think putting the new code into a function with the appropriate name > would help here. Your choice. Thanks for the review. I will see about putting this code into a separate function. > In any case, it looks OK for me as-is. Just a nit below... > > On 11/18/20 11:27 PM, Sergio Durigan Junior via Gdb-patches wrote: >> Changes from v1: >> - Addressed Simon's comments (new comment explaining how we try to >> match for the current debug-file-directory; properly use >> .erase/.insert methods -- keeping in mind that they modify the >> string in-place). >> >> 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". >> 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. >> 2020-11-14 Sergio Durigan Junior >> * dwarf2/read.c (dwarf2_get_dwz_file): Convert 'filename' to a >> std::string. Implement ability to search for DWZ files in the >> debug-file-directories provided by the user as well. >> --- >> gdb/dwarf2/read.c | 73 +++++++++++++++++++++++++++++++++++++++++++---- >> 1 file changed, 67 insertions(+), 6 deletions(-) >> diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c >> index 3c59826291..c462b9bb2c 100644 >> --- a/gdb/dwarf2/read.c >> +++ b/gdb/dwarf2/read.c >> @@ -2190,7 +2190,7 @@ locate_dwz_sections (bfd *abfd, asection *sectp, dwz_file *dwz_file) >> struct dwz_file * >> dwarf2_get_dwz_file (dwarf2_per_bfd *per_bfd) >> { >> - const char *filename; >> + std::string filename; >> bfd_size_type buildid_len_arg; >> size_t buildid_len; >> bfd_byte *buildid; >> @@ -2216,19 +2216,17 @@ dwarf2_get_dwz_file (dwarf2_per_bfd *per_bfd) >> filename = data.get (); >> - std::string abs_storage; >> - if (!IS_ABSOLUTE_PATH (filename)) >> + if (!IS_ABSOLUTE_PATH (filename.c_str ())) >> { >> gdb::unique_xmalloc_ptr abs >> = gdb_realpath (bfd_get_filename (per_bfd->obfd)); >> - abs_storage = ldirname (abs.get ()) + SLASH_STRING + >> filename; >> - filename = abs_storage.c_str (); >> + filename = ldirname (abs.get ()) + SLASH_STRING + filename; >> } >> /* First try the file name given in the section. If that >> doesn't >> work, try to use the build-id instead. */ >> - gdb_bfd_ref_ptr dwz_bfd (gdb_bfd_open (filename, gnutarget)); >> + gdb_bfd_ref_ptr dwz_bfd (gdb_bfd_open (filename.c_str (), gnutarget)); >> if (dwz_bfd != NULL) >> { >> if (!build_id_verify (dwz_bfd.get (), buildid_len, buildid)) >> @@ -2238,6 +2236,69 @@ dwarf2_get_dwz_file (dwarf2_per_bfd *per_bfd) >> if (dwz_bfd == NULL) >> dwz_bfd = build_id_to_debug_bfd (buildid_len, buildid); >> + if (dwz_bfd == nullptr) >> + { >> + /* If the user has provided us with different >> + debug-file-directories, we can try them in order. */ >> + size_t dwz_pos = filename.find ("/.dwz/"); >> + >> + if (dwz_pos != std::string::npos) >> + { >> + std::vector> debugdir_vec >> + = dirnames_to_char_ptr_vec (debug_file_directory); >> + >> + for (const gdb::unique_xmalloc_ptr &debugdir : debugdir_vec) >> + { >> + /* The idea is to iterate over the >> + debug-file-directories provided by the user and >> + replace the hard-coded path in the "filename" by each >> + debug-file-directory. >> + >> + For example, suppose that filename is: >> + >> + /usr/lib/debug/.dwz/foo.dwz >> + >> + And suppose that we have "$HOME/bar" as the >> + debug-file-directory. We would then adjust filename >> + to look like: >> + >> + $HOME/bar/.dwz/foo.dwz >> + >> + which would hopefully allow us to find the alt debug >> + file. */ >> + std::string ddir = debugdir.get (); >> + >> + /* Check whether the beginning of FILENAME is DDIR. If >> + it is, then we are dealing with a file which we >> + already attempted to open before, so we just skip it >> + and continue processing the reamining > > remaining? Fixed. >> + debug-file-directories. */ > > debug-file-directories doesn't exist in the code. I suppose this > should be "debug file directories" or "debug-file-directory's"? OK, I see your rationale. I don't mind having debug-file-directories, but I replaced it with "debug file directories". Thanks for the review. -- Sergio GPG key ID: 237A 54B1 0287 28BF 00EF 31F4 D0EB 7628 65FC 5E36 Please send encrypted e-mail if possible https://sergiodj.net/