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([2804:431:c7cb:a6c0:26f4:3c2a:73ae:3e2]) by smtp.gmail.com with ESMTPSA id u7-20020a05687036c700b000da4bcdae42sm5499549oak.13.2022.04.05.09.40.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 05 Apr 2022 09:40:13 -0700 (PDT) Message-ID: <4570fa06-24b0-873a-09b6-d57c85dd1191@linaro.org> Date: Tue, 5 Apr 2022 13:40:10 -0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Subject: Re: [PATCH] Remove fno-unit-at-a-time make variable Content-Language: en-US To: =?UTF-8?B?RsSBbmctcnXDrCBTw7JuZw==?= Cc: libc-alpha@sourceware.org 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> From: Adhemerval Zanella In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-6.2 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, NICE_REPLY_A, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP, T_SCC_BODY_TEXT_LINE 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 16:40:17 -0000 On 05/04/2022 13:22, Fāng-ruì Sòng wrote: > 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. I think we can make it work with asciz directive. > > 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. Afaik llvm does not support -fno-toplevel-reorder