From patchwork Sun Nov 12 09:18:00 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Alejandro Colomar X-Patchwork-Id: 79628 Return-Path: X-Original-To: patchwork@sourceware.org Delivered-To: patchwork@sourceware.org Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id 195EE3858CD1 for ; Sun, 12 Nov 2023 09:18:41 +0000 (GMT) X-Original-To: libc-alpha@sourceware.org Delivered-To: libc-alpha@sourceware.org Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by sourceware.org (Postfix) with ESMTPS id D2CE63858C50 for ; Sun, 12 Nov 2023 09:18:06 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org D2CE63858C50 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=kernel.org Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=kernel.org ARC-Filter: OpenARC Filter v1.0.0 sourceware.org D2CE63858C50 Authentication-Results: server2.sourceware.org; arc=none smtp.remote-ip=2604:1380:4641:c500::1 ARC-Seal: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1699780688; cv=none; b=NDVLKfOsz7/mHwkQJL2RCk98ecpI/Wok5foczkSfyr1I5AXUq6G0aahUqOj1v58+DOg6YdH7c8LBiVv7bmkr8RGgO9XO9gAA8uhSwB8xRlp2IGIcDAQbVJ4uIlHgDoDwh2jewJGWrVvIbDIeeyk/wvB494g3MEbrt6Olz4tLZ80= ARC-Message-Signature: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1699780688; c=relaxed/simple; bh=4OZ5pjlZcOR5C1mMy/ZMLW5UGIj/eQsxRwe+fNCiBwQ=; h=DKIM-Signature:Date:From:To:Subject:Message-ID:MIME-Version; b=SfyXvPR7RT4jCLQABV/7noFS2buD8jl1GkFeQ6mSZs3iWzcIzCnmHB2yKTgImoCXjwOOdstvXL2pM2n5r3EmLbHxwcHFkzH0M8D7eBQYKDwig25sTJo5Pgk1/qCi2SKetEfqsaSX8km9iE8BS4fxKsbedpADmtuqZ+Oj18T58XQ= ARC-Authentication-Results: i=1; server2.sourceware.org Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by dfw.source.kernel.org (Postfix) with ESMTP id 30F8B60C2C; Sun, 12 Nov 2023 09:18:06 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1DA06C433C8; Sun, 12 Nov 2023 09:18:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1699780685; bh=4OZ5pjlZcOR5C1mMy/ZMLW5UGIj/eQsxRwe+fNCiBwQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=K7U32jJf3Ol59lo24w9UxsPoZbVkqZLuCB2kHDLSXt6uTUhFGY+FlipEmmKNzVgO2 vviuui4yAkODSHm7yeaupebbs3/ThSjJMsDJO7TvGhaDvK9Rc1qoPCY0vW8sKz51Gx A1p3ad6EOaKsCInNWcvPxn9qEZmsPgvuoBTgZgnynDLJFh0I8iohptXlW0Hc8gR6oI qlUyaHxf7gg9SrNwU8uS5tojo1ueumRMaEyNAypLKOGh+yqT4DxWi7G/52/sNXNMvj hRWQz+IsAYqUlHIoO+fnkIWhswcGThq2q53pki2e3EkeyW1SfqvJQ26YWvv0AaJzPt 8nHrUD7i1IL+Q== Date: Sun, 12 Nov 2023 10:18:00 +0100 From: Alejandro Colomar To: linux-man@vger.kernel.org Cc: Alejandro Colomar , libc-alpha@sourceware.org, Paul Eggert , Jonny Grant , DJ Delorie , Matthew House , Oskari Pirhonen , Thorsten Kukuk , Adhemerval Zanella Netto , Zack Weinberg , "G. Branden Robinson" , Carlos O'Donell , Xi Ruoyao , Stefan Puiu , Andreas Schwab Subject: [PATCH 1/2] string_copying.7: BUGS: *cat(3) functions aren't always bad Message-ID: <20231112091748.6906-3-alx@kernel.org> References: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-Mailer: git-send-email 2.42.0 X-Spam-Status: No, score=-9.8 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, SPF_HELO_NONE, SPF_PASS, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: libc-alpha-bounces+patchwork=sourceware.org@sourceware.org The compiler will sometimes optimize them to normal *cpy(3) functions, since the length of dst is usually known, if the previous *cpy(3) is visible to the compiler. And they provide for cleaner code. If you know that they'll get optimized, you could use them. Cc: Paul Eggert Cc: Jonny Grant Cc: DJ Delorie Cc: Matthew House Cc: Oskari Pirhonen Cc: Thorsten Kukuk Cc: Adhemerval Zanella Netto Cc: Zack Weinberg Cc: "G. Branden Robinson" Cc: Carlos O'Donell Cc: Xi Ruoyao Cc: Stefan Puiu Cc: Andreas Schwab Signed-off-by: Alejandro Colomar --- man7/string_copying.7 | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/man7/string_copying.7 b/man7/string_copying.7 index 1637ebc91..0254fbba6 100644 --- a/man7/string_copying.7 +++ b/man7/string_copying.7 @@ -592,8 +592,14 @@ .SH BUGS All catenation functions share the same performance problem: .UR https://www.joelonsoftware.com/\:2001/12/11/\:back\-to\-basics/ Shlemiel the painter .UE . +As a mitigation, +compilers are able to transform some calls to catenation functions +into normal copy functions, +since +.I strlen(dst) +is usually a byproduct of the previous copy. .\" ----- EXAMPLES :: -------------------------------------------------/ .SH EXAMPLES The following are examples of correct use of each of these functions. .\" ----- EXAMPLES :: stpcpy(3) ---------------------------------------/