From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yb1-xb2d.google.com (mail-yb1-xb2d.google.com [IPv6:2607:f8b0:4864:20::b2d]) by sourceware.org (Postfix) with ESMTPS id A27493858D1E for ; Tue, 5 Apr 2022 16:22:46 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org A27493858D1E Received: by mail-yb1-xb2d.google.com with SMTP id l36so16757352ybj.12 for ; Tue, 05 Apr 2022 09:22:46 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=wqHyIsMOSkMHTF7UO67DFgVpjkSAMD1uumEw66HmyG0=; b=plkm1xqPDEEvPABgFol4i39xbbxLxYl2mQLYKM/EZ8trXgYrXZ2N0nhNGsWDBLXgTs bX89EC1d/MaIojAcHA4m1vDSpUdk+N3VoUvIE/vgrgT06bE6JRsO7e5MHgEC2N7AzkV5 D1vtzce2CFq5NHJCGclmjGPkksu1WF22jxaCOA7HeblsulvzWNZF5iQdiHj/3ogBsThG 1K7xgRpIX36/MZdn23tsSBfvvzvWBF01+clK+lN0MuHYxTyXIkELxI1OVb+s0kDDKHDq /sC5zzUmR9n8vYBl/cqllVVIKlSncBDLtkT/+kQiNFPW2VmknKh5KzMTWhyd3lrnzQaG blIQ== X-Gm-Message-State: AOAM532LNvpN+kECGwokmwy9fVjfJgZWzqcrWvOrd6t6KACUV/zg+Ni9 ATt1Z/ChlfXy/V6wj1YmFlBT/o20Xy0a4+4lVzH3eWeUTThFQA== X-Google-Smtp-Source: ABdhPJzGlV5oqTS5NDBvaNdb/0NCMecebaTD8YkiyPpBWdg/UNiN/j0eYnGXTxLW89L6G82BRnLGdpGl9rsamQLbql4= X-Received: by 2002:a25:bdd4:0:b0:63d:e354:c550 with SMTP id g20-20020a25bdd4000000b0063de354c550mr3214142ybk.63.1649175765871; Tue, 05 Apr 2022 09:22:45 -0700 (PDT) MIME-Version: 1.0 References: <20220330050729.2176630-1-maskray@google.com> <0295bfe2-2f44-c15e-1628-acaf94fc407c@linaro.org> <20220330162311.pwg52gcrr5vnlabe@google.com> <7e7fdfdc-ddc8-cf5a-0525-f927b4ae1e39@linaro.org> <20220331034302.rzcu6gllo7ltkhjh@google.com> <20220404155703.vefk66cwnsnkhsih@google.com> <22f8e3aa-5af9-93a2-65fc-1889674103d6@linaro.org> In-Reply-To: <22f8e3aa-5af9-93a2-65fc-1889674103d6@linaro.org> From: =?UTF-8?B?RsSBbmctcnXDrCBTw7JuZw==?= Date: Tue, 5 Apr 2022 10:22:34 -0600 Message-ID: Subject: Re: [PATCH] Remove fno-unit-at-a-time make variable To: Adhemerval Zanella Cc: libc-alpha@sourceware.org Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-17.9 required=5.0 tests=BAYES_00, DKIMWL_WL_MED, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, ENV_AND_HDR_SPF_MATCH, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP, T_SCC_BODY_TEXT_LINE, USER_IN_DEF_DKIM_WL, USER_IN_DEF_SPF_WL autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 05 Apr 2022 16:22:48 -0000 On Tue, Apr 5, 2022 at 8:35 AM Adhemerval Zanella wrote: > > > > On 04/04/2022 12:57, Fangrui Song wrote: > > > > On 2022-03-31, Adhemerval Zanella wrote: > >> > >> > >> On 31/03/2022 00:43, Fangrui Song wrote: > >>> On 2022-03-30, Adhemerval Zanella wrote: > >>>> > >>>> > >>>> On 30/03/2022 13:23, Fangrui Song wrote: > >>>>> On 2022-03-30, Adhemerval Zanella wrote: > >>>>>> > >>>>>> > >>>>>> On 30/03/2022 02:07, Fangrui Song wrote: > >>>>>>> 795985e4e751 in 2003 added -fno-unit-at-a-time to errlist.c and > >>>>>>> siglist.c to "avoid reordering assembler output". -fno-toplevel-reorder > >>>>>>> is a rough replacement for this legacy option > >>>>>>> (https://sourceware.org/pipermail/gcc-patches/2006-January/186801.html). > >>>>>>> > >>>>>>> The reordering requirement does not seem to be needed any longer. > >>>>>> > >>>>>> We still need them for otherwise DEFINE_COMPAT_ERRLIST used on errlist-compat.c > >>>>>> does not create _sys_errlist and _sys_siglist with expected sizes defined by > >>>>>> glibc ABI. > >>>>>> > >>>>>> I am trying to fix without resorting to compiler options. > >>>>> > >>>>> DEFINE_COMPAT_ERRLIST does not expand to code/data, just reordeable directives: > >>>>> > >>>>> > >>>>> .globl __GLIBC_2_1_sys_errlist > >>>>> .set __GLIBC_2_1_sys_errlist, _sys_errlist_internal > >>>>> .type __GLIBC_2_1_sys_errlist,@object > >>>>> .size __GLIBC_2_1_sys_errlist, 1000 > >>>>> .globl __GLIBC_2_1__sys_errlist > >>>>> .set __GLIBC_2_1__sys_errlist, _sys_errlist_internal > >>>>> .type __GLIBC_2_1__sys_errlist,@object > >>>>> .size __GLIBC_2_1__sys_errlist, 1000 > >>>>> .symver __GLIBC_2_1_sys_nerr, sys_nerr@GLIBC_2.2.5 > >>>>> .symver __GLIBC_2_1__sys_nerr, _sys_nerr@GLIBC_2.2.5 > >>>>> .symver __GLIBC_2_1_sys_errlist, sys_errlist@GLIBC_2.2.5 > >>>>> .symver __GLIBC_2_1__sys_errlist, _sys_errlist@GLIBC_2.2.5 > >>>>> .globl __GLIBC_2_3_sys_errlist > >>>>> .set __GLIBC_2_3_sys_errlist, _sys_errlist_internal > >>>>> .type __GLIBC_2_3_sys_errlist,@object > >>>>> .size __GLIBC_2_3_sys_errlist, 1008 > >>>>> .globl __GLIBC_2_3__sys_errlist > >>>>> .set __GLIBC_2_3__sys_errlist, _sys_errlist_internal > >>>>> .type __GLIBC_2_3__sys_errlist,@object > >>>>> .size __GLIBC_2_3__sys_errlist, 1008 > >>>>> .symver __GLIBC_2_3_sys_nerr, sys_nerr@GLIBC_2.3 > >>>>> .symver __GLIBC_2_3__sys_nerr, _sys_nerr@GLIBC_2.3 > >>>>> .symver __GLIBC_2_3_sys_errlist, sys_errlist@GLIBC_2.3 > >>>>> .symver __GLIBC_2_3__sys_errlist, _sys_errlist@GLIBC_2.3 > >>>>> .globl __GLIBC_2_4_sys_errlist > >>>>> > >>>>> I do not know whether GCC would reorder these macros. Even yes, > >>>>> that'd just change the .symtab entries in the relocatable object file. > >>>>> The linker behavior remains the same with reordering. > >>>> > >>>> It does not seem to, just remove the -fno-unit-at-a-time and issue make > >>>> check-abi and you will see that object size for the compat symbols > >>>> reference to _sys_err_internal instead of the define compat ones. > >>> > >>> I see. I think this is a brittle behavior in GNU assembler. Filed > >>> https://sourceware.org/bugzilla/show_bug.cgi?id=29012 with detailed > >>> information. I have created a patch but I know that will not solve > >>> glibc's problem :( > >> > >> It would be good to have this fixes, but unfortunately we need a way > >> to handle this on older binutils. I am kind worried that the only > >> possible way to actually fix this without resorting to any compiler > >> flags is coding the array definitions in assembly direct... > > > > The GNU assembler issue has been fixed https://sourceware.org/bugzilla/show_bug.cgi?id=29012 > > (milestone 2.39, way larger than the current required version: 2.25) > > > > Switching to assembly output doesn't seem bad :-) > > > > If you keep the compiler driver option but need to refactor the nearby > > code, you may drop -fno-unit-at-a-time. It was added in 2006 (somewhere > > between GCC 4.1 and 4.4), while glibc requires GCC>=6.2. > > Good to know we won't need to rely on compiler flags to get the expected > correct asm directives. I am still struggling to get a fix without resorting > to compiler flags, but without much success. Trying to move it to assembly > might be tricky, I am not sure if the data directives would be architecture > agnostic. Many directives are architecture-independent: https://sourceware.org/binutils/docs/as/Pseudo-Ops.html#Pseudo-Ops binutils-gdb/gas/read.c:346 The `portable[]` array. To support Clang, no refactoring is probably needed: just change fno_unit_at_a_time to only specify -fno-toplevel-reorder (and rename it), not th legacy -fno-unit-at-a-time.