From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pj1-x1034.google.com (mail-pj1-x1034.google.com [IPv6:2607:f8b0:4864:20::1034]) by sourceware.org (Postfix) with ESMTPS id B1D133858416 for ; Thu, 21 Oct 2021 20:07:52 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org B1D133858416 Received: by mail-pj1-x1034.google.com with SMTP id ls18so1315522pjb.3 for ; Thu, 21 Oct 2021 13:07:52 -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=2kyIpPai0pPNghjV34dH0h2w3WaKVpZZphJaVIToJoE=; b=bCG7s8iOnSeHJ5QzJwLbz/hUXkQrATAbSQGkxAYmjHI8ivCXAAOrhU4JBNrwlHTZB8 w07hEt/mrAWf2leh5aerhlJP8+MAIajMInz6bhDoKUachrdNpiNdhPMzk+zO3GuwHDVQ Jhyy2bXRFkakQWlVAUJ9ZApy8L/hYDCQdvJiin622S2h+fFWQIjnAC+6kFa2KCOZBbJX WH0zmEF56PaXW6x7QsjPOHDQwdLhWJscig8iAConWqO7qWXz2oLoI9LXRWZzQXRpg3YW HC7r45zR5Nn6O0HqZyJfWEStsv1syedUL/bNtoS2xE33Nqyl7LwU8gehpN/6tHNjyPmR zL/Q== X-Gm-Message-State: AOAM533n+O0xvtI9bneeEWvzhH788/o+7RpjHIyujhBXSxuSJbfwFb8m FI5PkMXJnQVOLl1pkvHyefePJl9qcP4u/NBCk/Y= X-Google-Smtp-Source: ABdhPJxY1F3Xro8MN2a08hT7rxv2JnT/q7VVuO6Npj2jY8yLbgaJQIkdg47cm1lAgFC6C49Js1K49hlpWTil91Fg9RY= X-Received: by 2002:a17:902:cec9:b0:13f:17c2:8f14 with SMTP id d9-20020a170902cec900b0013f17c28f14mr7191735plg.66.1634846871723; Thu, 21 Oct 2021 13:07:51 -0700 (PDT) MIME-Version: 1.0 References: <20210927203827.2852935-1-goldstein.w.n@gmail.com> <20210929151743.3351092-1-goldstein.w.n@gmail.com> <8ee11473-cdfd-3dbe-47a1-dffddc996b34@linaro.org> In-Reply-To: From: "H.J. Lu" Date: Thu, 21 Oct 2021 13:07:15 -0700 Message-ID: Subject: Re: [PATCH v7] String: Add support for __memcmpeq() ABI on all targets To: Noah Goldstein Cc: Adhemerval Zanella , GNU C Library Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-3023.7 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, 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: Thu, 21 Oct 2021 20:07:54 -0000 On Thu, Oct 21, 2021 at 1:02 PM Noah Goldstein via Libc-alpha wrote: > > On Thu, Oct 21, 2021 at 2:33 PM Adhemerval Zanella > wrote: > > > > > > > > On 29/09/2021 12:17, Noah Goldstein via Libc-alpha wrote: > > > No bug. > > > > > > This commit adds support for __memcmpeq() as a new ABI for all > > > targets. In this commit __memcmpeq() is implemented only as an alias > > > to the corresponding targets memcmp() implementation. __memcmpeq() is > > > added as a new symbol starting with GLIBC_2.35 and defined in string.h > > > with comments explaining its behavior. Basic tests that it is callable > > > and works where added in string/tester.c > > > > > > As discussed in the proposal "Add new ABI '__memcmpeq()' to libc" > > > __memcmpeq() is essentially a reserved namespace for bcmp(). The means > > > is shares the same specifications as memcmp() except the return value > > > for non-equal byte sequences is any non-zero value. This is less > > > strict than memcmp()'s return value specification and can be better > > > optimized when a boolean return is all that is needed. > > > > > > __memcmpeq() is meant to only be called by compilers if they can prove > > > that the return value of a memcmp() call is only used for its boolean > > > value. > > > > > > > Should we export memcmpeq() as a GNU extension as well? > > > > > All tests in string/tester.c passed. As well build succeeds on > > > x86_64-linux-gnu target. > > > > This patch requires a NEWS entry for the new symbol and most likely > > a manual entry to describe its semantic. > > My understanding is that since we are only exporting this symbol for > compiler use (to optimize boolean use of 'memcmp()') we weren't > planning to add a manual entry. > > > > > I also think we should model a new testing based on test-memcmp.c > > to check for multiple alignments and random inputs. > > In this patch __memcmpeq is always just memcmp which is tested. > > In my followup patch (once this one gets through) to add separate > implementations for x86_64 I add tests. Would it be better to include > those tests in this patchset? I think we should add it now since someone can add IFUNC for a non x86-64 target before x86-64 one is landed. With __memcmpeq, bcmp should be an alias of __memcmpeq, not memcmp. -- H.J.