From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 39153 invoked by alias); 29 Nov 2017 00:59:46 -0000 Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org Received: (qmail 39144 invoked by uid 89); 29 Nov 2017 00:59:46 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-0.7 required=5.0 tests=BAYES_00,KAM_LAZY_DOMAIN_SECURITY,KB_WAM_FROM_NAME_SINGLEWORD,SPF_HELO_PASS,T_RP_MATCHES_RCVD autolearn=no version=3.3.2 spammy=clarifying, sk:minimal, obey X-HELO: mx1.redhat.com Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Wed, 29 Nov 2017 00:59:44 +0000 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 4CE6DC0567B3; Wed, 29 Nov 2017 00:59:43 +0000 (UTC) Received: from localhost (unused-10-15-17-193.yyz.redhat.com [10.15.17.193]) by smtp.corp.redhat.com (Postfix) with ESMTPS id ED56A5C6C5; Wed, 29 Nov 2017 00:59:42 +0000 (UTC) From: Sergio Durigan Junior To: Pedro Alves Cc: Yao Qi , Joel Brobecker , "gdb-patches\@sourceware.org" Subject: Re: [PATCH v2] Add support for the --readnever command-line option (DWARF only) References: <1467838463-15786-1-git-send-email-brobecker@adacore.com> <87o9ntddb6.fsf_-_@redhat.com> <2cb6d01b-b40b-0a73-2df4-65f4e2094731@redhat.com> <87efoodi79.fsf@redhat.com> <87a7zc9syx.fsf@redhat.com> <874lpj8lta.fsf@redhat.com> <8bd72067-dbb3-4c7f-1934-87df87c6f358@redhat.com> Date: Wed, 29 Nov 2017 00:59:00 -0000 In-Reply-To: <8bd72067-dbb3-4c7f-1934-87df87c6f358@redhat.com> (Pedro Alves's message of "Mon, 27 Nov 2017 19:13:11 +0000") Message-ID: <87y3mplx1d.fsf@redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-IsSubscribed: yes X-SW-Source: 2017-11/txt/msg00749.txt.bz2 On Monday, November 27 2017, Pedro Alves wrote: > On 11/24/2017 08:26 PM, Sergio Durigan Junior wrote: >> On Friday, November 24 2017, Pedro Alves wrote: >> >>> On 11/24/2017 04:54 AM, Sergio Durigan Junior wrote: >>>> On Thursday, November 23 2017, Pedro Alves wrote: >>>> >>>>> On 11/23/2017 05:21 PM, Sergio Durigan Junior wrote: >>>>> >>>>>>>> +This option is currently limited to debug information in DWARF format. >>>>>>>> +For all other format, this option has no effect. >>>>>>> >>>>>>> How hard would it be to just make it work? There's only stabs and mdebug >>>>>>> left, I think? There should be a single a function somewhere that we can >>>>>>> add an early return. And then we don't need to document this limitation... >>>>>>> >>>>>>> For example, in elf_symfile_read, we could just skip the elf_locate_sections >>>>>>> call. In coffread.c we could skip reading stabs right after >>>>>>> bfd_map_over_sections (abfd, coff_locate_sections....); >>>>>>> >>>>>>> Looking for: >>>>>>> >>>>>>> $ grep -h "^[a-z]*_build_psymtabs" gdb/ >>>>>>> coffstab_build_psymtabs (struct objfile *objfile, >>>>>>> elfstab_build_psymtabs (struct objfile *objfile, asection *stabsect, >>>>>>> stabsect_build_psymtabs (struct objfile *objfile, char *stab_name, >>>>>>> mdebug_build_psymtabs (minimal_symbol_reader &reader, >>>>>>> elfmdebug_build_psymtabs (struct objfile *objfile, >>>>>>> >>>>>>> finds all the relevant places. >>>>>>> >>>>>>> Maybe it wouldn't be that hard to make this be an objfile flag >>>>>>> afterall (like OBJF_READNOW is). That'd make it possible >>>>>>> to add the location "-readnever" counterpart switch to add-symbol-file >>>>>>> too, BTW: >>>>> >>>>> I meant "logical" instead of "location". I was staring at >>>>> gdb/location.c at that time. :-P >>>>> >>>>>>> >>>>>>> symfile.c: if (strcmp (arg, "-readnow") == 0) >>>>>>> symfile.c: else if (strcmp (arg, "-readnow") == 0) >>>>>> >>>>>> Hm, I'll look into this. Just to make it clear: the idea is to have >>>>>> both a --readnever global option and also a OBJF_READNEVER specific to >>>>>> each objfile? >>>>> >>>>> Sure, the idea is to do something similar to what's done for --readnow. >>>> >>>> Sorry, but I guess I need a few more details on this. >>>> >>>> The way I understand the code at elf_symfile_read, the very first thing >>>> to do would be to check if OBJF_READNEVER is set and return early if it >>>> is. But it seems that you're proposing something a bit different when >>>> you say that we should "... just skip the elf_locate_sections call." It >>>> doesn't seem to me that is worth continuing on that function if >>>> OBJF_READNEVER is present. >>> >>> No, you can't return early the very first thing, because >>> --readnever is supposed to skip _debug_ info, not ELF/minimal symbols... >>> So the "return early" would have to be _after_ the >>> elf_read_minimal_symbols call: >> >> Hm, OK, it makes sense and I confess I thought "why is Pedro mentioning >> elf_symfile_read if the feature is about skipping DWARF, not ELF?". >> >>> static void >>> elf_symfile_read (struct objfile *objfile, symfile_add_flags symfile_flags) >>> { >>> bfd *abfd = objfile->obfd; >>> struct elfinfo ei; >>> >>> memset ((char *) &ei, 0, sizeof (ei)); >>> bfd_map_over_sections (abfd, elf_locate_sections, (void *) & ei); >>> >>> elf_read_minimal_symbols (objfile, symfile_flags, &ei); >>> >>> I don't know whether we can reorder that. Maybe we can. >>> >>> When I looked at this quickly yesterday, I saw that elf_location_sections >>> is what finds the stabs and mdebug sections: >>> >>> static void >>> elf_locate_sections (bfd *ignore_abfd, asection *sectp, void *eip) >>> { >>> struct elfinfo *ei; >>> >>> ei = (struct elfinfo *) eip; >>> if (strcmp (sectp->name, ".stab") == 0) >>> { >>> ei->stabsect = sectp; >>> } >>> else if (strcmp (sectp->name, ".mdebug") == 0) >>> { >>> ei->mdebugsect = sectp; >>> } >>> } >>> >>> and it seemed to be that skipping the section location would make >>> the parts of elf_symfile_read that actually read the symbols >>> be no-ops, because the stabsect/mdebusect pointers would be NULL. >>> >>> But if returning early or something else works, that's fine. >> >> OK, thanks for clarifying. >> >>>> As for the *_build_psymtabs functions, I am doing exactly that: if >>>> objfile->flags contains OBJF_READNEVER, then just return and do nothing. >>> >>> Sure, that should work too. It's just the difference between >>> skipping checking whether debug info is available (skipping before >>> calling into those), vs letting gdb do the work to figure out whether >>> debug info is available, but then ignore it. >>> The grep for "*_build_psymtabs" was intended as a pointer to find >>> what the relevant code is, including to look at the code that >>> is calling those functions, see if there's something to be done there. >> >> I think it makes more sense, logically speaking, to not mess with >> elf_symfile_read and instead modify the *_build_psymtabs functions. > > Yet, somehow that logic didn't carry to the DWARF reader > changes? ;-) dwarf2_has_info is the place that checks > whether the objfile has DWARF sections, > see dwarf2_per_objfile::dwarf2_per_objfile. > So for DWARF, the patch is checking for readnever _before_ > dwarf2_build_psymtabs is reached, by essentially skipping > the "locate_sections" call. You're right, I never thought about making the changes for DWARF. > A small advantage of checking before is that you can skip a little bit > more work. See the comment in elf_read_minimal_symbols about skipping > work unless stabs, or this bit here: > > if (info->stabsects) > { > if (!info->stabstrsect) > { > error (_("The debugging information in `%s' is corrupted.\nThe " > "file has a `.stabs' section, but no `.stabstr' section."), > name); > } > ... > > It's really not a bit deal, but to me it'd be more > consistent have all readers do the same logically. Understood. I switched the logic and now I'm doing all the work on elf_symfile_read (and consequently dwarf2_has_info, which now is the right place to put the checks on). I wasn't sure if I should modify other *_symfile_read functions to obey the setting, so I left them alone. > On another note: there's a symbol_file_add_separate call at the tail > end of elf_symfile_read, where we seem to read separate info. It seems > like that'd end up reading debug info, with "add-symbol-file -readnever"? > Same in read_symbols, I guess. Or is OBJF_READNEVER etc. somehow > propagated to the separate objfile? "add-symbol-file -readnever" doesn't get propagated, the only thing that does is the "--readnever" global option. symbol_file_add_separate calls symbol_file_add_with_addrs (responsible for created the objfile), so I now propagate the OBJF_READNEVER flag if the main objfile has it. I'll submit a new version soon. Thanks, -- Sergio GPG key ID: 237A 54B1 0287 28BF 00EF 31F4 D0EB 7628 65FC 5E36 Please send encrypted e-mail if possible http://sergiodj.net/