From mboxrd@z Thu Jan 1 00:00:00 1970 From: Fangrui Song Subject: Re: [PATCH v3 2/9] vmlinux.lds.h: Add .symtab, .strtab, and .shstrtab to STABS_DEBUG Date: Wed, 24 Jun 2020 10:26:20 -0700 Message-ID: <20200624172620.654hhjetiyzpgoxw@google.com> References: <20200624014940.1204448-1-keescook@chromium.org> <20200624014940.1204448-3-keescook@chromium.org> <20200624153930.GA1337895@rani.riverdale.lan> <20200624161643.73x6navnwryckuit@google.com> <20200624171121.GA1377921@rani.riverdale.lan> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Return-path: Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49956 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2405517AbgFXR0Y (ORCPT ); Wed, 24 Jun 2020 13:26:24 -0400 Received: from mail-pj1-x1041.google.com (mail-pj1-x1041.google.com [IPv6:2607:f8b0:4864:20::1041]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C64F5C0613ED for ; Wed, 24 Jun 2020 10:26:24 -0700 (PDT) Received: by mail-pj1-x1041.google.com with SMTP id d6so1425254pjs.3 for ; Wed, 24 Jun 2020 10:26:24 -0700 (PDT) Content-Disposition: inline In-Reply-To: <20200624171121.GA1377921@rani.riverdale.lan> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Arvind Sankar Cc: Kees Cook , Will Deacon , Catalin Marinas , Mark Rutland , Ard Biesheuvel , Peter Collingbourne , James Morse , Borislav Petkov , Thomas Gleixner , Ingo Molnar , Russell King , Masahiro Yamada , Nick Desaulniers , Nathan Chancellor , Arnd Bergmann , x86@kernel.org, clang-built-linux@googlegroups.com, linux-arch@vger.kernel.org, linux-efi@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org On 2020-06-24, Arvind Sankar wrote: >On Wed, Jun 24, 2020 at 09:16:43AM -0700, Fangrui Song wrote: >> >> On 2020-06-24, Arvind Sankar wrote: >> >On Tue, Jun 23, 2020 at 06:49:33PM -0700, Kees Cook wrote: >> >> When linking vmlinux with LLD, the synthetic sections .symtab, .strtab, >> >> and .shstrtab are listed as orphaned. Add them to the STABS_DEBUG section >> >> so there will be no warnings when --orphan-handling=warn is used more >> >> widely. (They are added above comment as it is the more common >> > >> >Nit 1: is "after .comment" better than "above comment"? It's above in the >> >sense of higher file offset, but it's below in readelf output. >> >> I mean this order:) >> >> .comment >> .symtab >> .shstrtab >> .strtab >> >> This is the case in the absence of a linker script if at least one object file has .comment (mostly for GCC/clang version information) or the linker is LLD which adds a .comment >> >> >Nit 2: These aren't actually debugging sections, no? Is it better to add >> >a new macro for it, and is there any plan to stop LLD from warning about >> >them? >> >> https://reviews.llvm.org/D75149 "[ELF] --orphan-handling=: don't warn/error for unused synthesized sections" >> described that .symtab .shstrtab .strtab are different in GNU ld. >> Since many other GNU ld synthesized sections (.rela.dyn .plt ...) can be renamed or dropped >> via output section descriptions, I don't understand why the 3 sections >> can't be customized. > >So IIUC, lld will now warn about .rela.dyn etc only if they're non-empty? HEAD and future 11.0.0 will not warn about unused synthesized sections like .rela.dyn For most synthesized sections, empty = unused. >> >> I created a feature request: https://sourceware.org/bugzilla/show_bug.cgi?id=26168 >> (If this is supported, it is a consistent behavior to warn for orphan >> .symtab/.strtab/.shstrtab >> >> There may be 50% chance that the maintainer decides that "LLD diverges" >> I would disagree: there is no fundamental problems with .symtab/.strtab/.shstrtab which make them special in output section descriptions or orphan handling.) >> > >.shstrtab is a little special in that it can't be discarded if the ELF >file contains any sections at all. But yeah, there's no reason they >can't be renamed or placed in a custom location in the file. https://sourceware.org/pipermail/binutils/2020-March/000179.html proposes -z nosectionheader. With this option, I believe .shstrtab is not needed. /DISCARD/ : { *(.shstrtab) } should achieve a similar effect.