From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS,T_DKIMWL_WL_HIGH,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AAC12C43387 for ; Sat, 22 Dec 2018 17:41:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7ADCA21A4E for ; Sat, 22 Dec 2018 17:41:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1545500471; bh=82FABdOcM/G57Ts+ncPpj6ZRoj15+5MHDq5fs9nJRgA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=V8jiqC1fAyYR9N1KSqJPzlHlY8qnxL71zQ56L5u7dMWyPWBd3u2z8Q3TKre/E1vCA YmWe8NcK80q5KR0rzyRUGPF0FrDa4b1mxsxbSKxo4qJbBx7DADoezmIWV7B0JiKS7z rtgMfs1KyOP+Dx3pUw3vwzRGZW4kemj2wERt1TVo= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2392707AbeLVRlK (ORCPT ); Sat, 22 Dec 2018 12:41:10 -0500 Received: from mail-pg1-f195.google.com ([209.85.215.195]:45292 "EHLO mail-pg1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389669AbeLVRlG (ORCPT ); Sat, 22 Dec 2018 12:41:06 -0500 Received: by mail-pg1-f195.google.com with SMTP id y4so3915576pgc.12 for ; Sat, 22 Dec 2018 09:41:05 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=7Z0vnExjIgk37sqhQmoWZs4Kim5TjQ4s7J2aCJgLvag=; b=fbW7dLpyKL5omEs29udrnAtO1bqyX2Y8/pTcfPEKx7qlP9tEIpL3kv6DNpUiPaGUxH DgGtGf/cdmDTgIZWTc3xOXsCELtKqQuP9X/NwGpXpqnSN7wRrhmzX7iDBT74lR2wLnpd B88e2EI6dg9eATxTBHkPbdILX6Y3WMN/eR0oiXp+mX0VfluWaid4Jdi0ox9QwwajuB10 1R9HpcaKlrc/B3sRajmUVRUs1uHFmlBLViUlGlrQD6gH1dmzULS2WmQt3LpMpCicEsCy ZfHJ31eAh8+Gamdm2bZvqUb+U4TisJBYa0niWkTG29GyK1qNrXeAQVptHHTIw2ytgieM jj2Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to:user-agent; bh=7Z0vnExjIgk37sqhQmoWZs4Kim5TjQ4s7J2aCJgLvag=; b=HGEopw6X217TuorMhx9A2VvIpUaD1Mu6dJsahxH2IpnppObOm0zNC/9Pff77zCaAZT 8kHSccykD9HNIAjmd8Im1hwQmfzN9adK7GZSZQWETgvRu3igYVijzs9fHdN/my99MKjr 9UW2mHHOSpxAkeK7Tzomjf5Qj+cXu/irD24xQY6RG9TZ3NK3FB/Z5On7TvksIZjYXU76 3enGf2hqaQ3vABC0pZogNpdxyFCPNZiCfyt1LCtJPeZWI1Hvjp04LnppR4j498EJSVle evIldbsVppAxDSrgrGowuodY0r+nMAqK3jr5G116BC84dd8lr8yZxfjtnbTpkQWsf7Jj Qdlw== X-Gm-Message-State: AJcUukdgCHlRmPzAhyxCkL6qcZ6wjX4DnZrRXxcDDoVCyB9TORKzVgA3 G9ZDgQpO4SP/h1f7WkGbb2cMoXGY X-Google-Smtp-Source: AFSGD/X6IIlERyarqF/4HT7Ci9Aev+cdyN9Gu5VtEUPxOSuQjODwCeh+Ttoui7qhIm1Fprl48pYUWQ== X-Received: by 2002:a62:6f88:: with SMTP id k130mr6600236pfc.234.1545488657863; Sat, 22 Dec 2018 06:24:17 -0800 (PST) Received: from danjae.aot.lge.com ([182.210.106.196]) by smtp.gmail.com with ESMTPSA id r66sm39427518pfk.157.2018.12.22.06.24.14 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sat, 22 Dec 2018 06:24:17 -0800 (PST) Date: Sat, 22 Dec 2018 23:24:11 +0900 From: Namhyung Kim To: Steven Rostedt Cc: LKML , Linus Torvalds , Ingo Molnar , Andrew Morton , Greg Kroah-Hartman , Joe Perches , Masami Hiramatsu , Tom Zanussi , Andreas Schwab , kernel-team@lge.com Subject: Re: [PATCH v4] string.h: Add str_has_prefix() helper function Message-ID: <20181222142411.GA10058@danjae.aot.lge.com> References: <20181221231924.4583e90b@vmware.local.home> <20181222093346.GB7610@danjae.aot.lge.com> <20181222072404.27a7e9a3@vmware.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20181222072404.27a7e9a3@vmware.local.home> User-Agent: Mutt/1.11.1 (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Dec 22, 2018 at 07:24:04AM -0500, Steven Rostedt wrote: > On Sat, 22 Dec 2018 18:33:46 +0900 > Namhyung Kim wrote: > > > > +static __always_inline size_t str_has_prefix(const char *str, const char *prefix) > > > +{ > > > + size_t len = strlen(prefix); > > > + return strncmp(str, prefix, len) == 0 ? len : 0; > > > > As it already knows the length (and it needs to use it for return > > value), isn't it (slightly) better using memcmp() instead? > > No, because we don't know the length of str. > > > [ str = "h\0[bad memory]" ] > > > str_has_prefix(str, "TEST THIS BIG STRING AT FRONT") > > > If we use memcmp(), then we are testing way after str has ended, and > that can cause a memory fault. I don't know what's the bad memory causing memory fault but anyway memcpy() should stop at the NUL character first as it's different, no? Thanks, Namhyung