From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by sourceware.org (Postfix) with ESMTPS id F21D83857C65 for ; Tue, 18 Jan 2022 12:00:30 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org F21D83857C65 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-139-udLWtZi9PF2xuM_S_0iLIA-1; Tue, 18 Jan 2022 07:00:27 -0500 X-MC-Unique: udLWtZi9PF2xuM_S_0iLIA-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D82141006AAC; Tue, 18 Jan 2022 12:00:25 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.39.192.198]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A4699752DC; Tue, 18 Jan 2022 12:00:23 +0000 (UTC) From: Florian Weimer To: Adhemerval Zanella Cc: "xuyang2018.jy@fujitsu.com" , Theodore Ts'o , "libc-alpha@sourceware.org" , "fstests@vger.kernel.org" Subject: Re: [PATCH] src/ext4_resize.c: set errno to 0 before the strtoull call References: <1642405014-3287-1-git-send-email-xuyang2018.jy@fujitsu.com> <61E6298D.80006@fujitsu.com> <61E64FED.2010906@fujitsu.com> <87wnixjndg.fsf@oldenburg.str.redhat.com> <496a3521-5a0c-b3ae-29bb-02fd0056525b@linaro.org> Date: Tue, 18 Jan 2022 13:00:20 +0100 In-Reply-To: <496a3521-5a0c-b3ae-29bb-02fd0056525b@linaro.org> (Adhemerval Zanella's message of "Tue, 18 Jan 2022 08:49:40 -0300") Message-ID: <87h7a1jlt7.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Spam-Status: No, score=-6.5 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_NONE, TXREP 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, 18 Jan 2022 12:00:32 -0000 * Adhemerval Zanella: > On 18/01/2022 08:26, Florian Weimer wrote: >> * Adhemerval Zanella: >> >>> >>> >>> On 18/01/2022 02:27, xuyang2018.jy--- via Libc-alpha wrote: >>>> on 2022/1/18 11:56, Theodore Ts'o wrote: >>>>> On Tue, Jan 18, 2022 at 02:43:26AM +0000, xuyang2018.jy@fujitsu.com wrote: >>>>>>> You're right of course, but out of curiosity, which C library are you >>>>>>> using? >>>>>> I use glibc-2.34. >>>>> >>>>> Hmm, ok. I'm using glibc 2.31, and in this particular program, errno >>>>> shouldn't have been set by any prior system call. I'm guessing maybe >>>>> it was something in crt0 which ended up setting errno? >>>> It maybe a glibc bug. >>>> I cc glibc mailing list and see whether they have met this problem. >>>> >>>> @Florian >>>> >>>> Now, I use glibc-2.34 and run the following program[1] but the errno is >>>> not 0 in the beginning. So is this a known bug on glibc-2.34(Theodore >>>> doesn't meet this problem on glicb-2.31)? >>>> >>>> [1]https://git.kernel.org/pub/scm/fs/xfs/xfstests-dev.git/tree/src/ext4_resize.c >>> >>> The errno should be only set on a failure, no function shall set errno >>> to 0 (it is a POSIX definition which glibc adheres). The application >>> need to explicitly set errno to 0 before the function call to check if >>> an error occurs. >> >> While this is true, I think errno should still be 0 at the start of the >> program. > > I think this is a implementation detail, I am not aware that either C or > POSIX now states it should initialized to any specific value (in fact, > POSIX at Issue 5 [1] has removed the 'The value of errno is 0 at program > start-up' on its description). It would be nice to stay compatible with that. > In any case, we set errno to be an uninitialized TLS variable. Unless we > have a bug on .tbss initialization I think the issue is somewhere else. I suspect it's some additional system call, which is why I requested strace output. Thanks, Florian