From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 34026 invoked by alias); 24 Nov 2017 20:27:01 -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 34015 invoked by uid 89); 24 Nov 2017 20:27:01 -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= 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; Fri, 24 Nov 2017 20:26:59 +0000 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 48CB84E4C2; Fri, 24 Nov 2017 20:26:58 +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 C8A216198D; Fri, 24 Nov 2017 20:26:57 +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> Date: Fri, 24 Nov 2017 20:27:00 -0000 In-Reply-To: (Pedro Alves's message of "Fri, 24 Nov 2017 13:17:54 +0000") Message-ID: <874lpj8lta.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/msg00623.txt.bz2 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. 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/