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=-1.0 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS 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 50C6EC43387 for ; Fri, 21 Dec 2018 22:20:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1B25421920 for ; Fri, 21 Dec 2018 22:20:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404603AbeLUWUa (ORCPT ); Fri, 21 Dec 2018 17:20:30 -0500 Received: from smtprelay0037.hostedemail.com ([216.40.44.37]:40566 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1730887AbeLUWU3 (ORCPT ); Fri, 21 Dec 2018 17:20:29 -0500 Received: from filter.hostedemail.com (clb03-v110.bra.tucows.net [216.40.38.60]) by smtprelay02.hostedemail.com (Postfix) with ESMTP id B98213A91; Fri, 21 Dec 2018 22:20:28 +0000 (UTC) X-Session-Marker: 6A6F6540706572636865732E636F6D X-HE-Tag: frame06_78561ece8b74c X-Filterd-Recvd-Size: 5031 Received: from XPS-9350.home (unknown [47.151.153.53]) (Authenticated sender: joe@perches.com) by omf02.hostedemail.com (Postfix) with ESMTPA; Fri, 21 Dec 2018 22:20:26 +0000 (UTC) Message-ID: <84199633fd49db573c9ba71f1992936422e907d4.camel@perches.com> Subject: Re: [for-next][PATCH 23/24] string.h: Add strncmp_prefix() helper macro From: Joe Perches To: Steven Rostedt , Andreas Schwab Cc: Linus Torvalds , Linux List Kernel Mailing , Ingo Molnar , Andrew Morton , Namhyung Kim , Masami Hiramatsu , Tom Zanussi , Greg Kroah-Hartman Date: Fri, 21 Dec 2018 14:20:25 -0800 In-Reply-To: <20181221160826.34c544e6@gandalf.local.home> References: <20181221175618.968519903@goodmis.org> <20181221175659.208858193@goodmis.org> <20181221144054.20bdeb33@gandalf.local.home> <20181221153526.5e6055ca@gandalf.local.home> <077eeb8b09baebe78822819b5f15d671b738a2b2.camel@perches.com> <20181221155435.38a9a221@gandalf.local.home> <871s6ad2br.fsf@igel.home> <20181221160826.34c544e6@gandalf.local.home> Content-Type: text/plain; charset="ISO-8859-1" User-Agent: Evolution 3.30.1-1build1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2018-12-21 at 16:08 -0500, Steven Rostedt wrote: > On Fri, 21 Dec 2018 21:58:32 +0100 > Andreas Schwab wrote: > > > > > Well, perhaps I can just remove the ending ones. I get paranoid with > > > macro variables, and tend to over do it so that there's no question. > > > > Why not make it an inline function? > > Matters if that removes the strlen(const) optimization. I could try it > and see what happens. Using static inline bool str_has_prefix(const char *str, const char prefix[]) { return !strncmp(str, prefix, strlen(prefix)); } eliminates the strlen with gcc 4.8 (oldest I still have) $ cat lib/test_module.c * This module emits "Hello, world" on printk when loaded. * * It is designed to be used for basic evaluation of the module loading * subsystem (for example when validating module signing/verification). It * lacks any extra dependencies, and will not normally be loaded by the * system unless explicitly requested by name. */ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt #include #include #include static inline bool str_has_prefix(const char *str, const char prefix[]) { return !strncmp(str, prefix, strlen(prefix)); } bool test_str_has_prefix(const char *foo) { return str_has_prefix("TomJonesPrefix", foo); } bool test_str_has_prefix_TomJones(void) { return str_has_prefix("TomJonesPrefix", "TomJones"); } $ make CC=/usr/bin/gcc-4.8 lib/test_module.o $ objdump -d -s lib/test_module.o lib/test_module.o: file format elf64-x86-64 Contents of section .text: 0000 534889fb e8000000 00b90f00 00004883 SH............H. 0010 f80f4889 df480f4e c848c7c6 00000000 ..H..H.N.H...... 0020 4839c9f3 a65b0f94 c0c3660f 1f440000 H9...[....f..D.. 0030 b8010000 00c3 ...... Contents of section .rodata.str1.1: 0000 546f6d4a 6f6e6573 50726566 697800 TomJonesPrefix. Contents of section .comment: 0000 00474343 3a202855 62756e74 7520342e .GCC: (Ubuntu 4. 0010 382e352d 34756275 6e747539 2920342e 8.5-4ubuntu9) 4. 0020 382e3500 8.5. Contents of section .orc_unwind_ip: 0000 00000000 00000000 00000000 00000000 ................ 0010 00000000 00000000 ........ Contents of section .orc_unwind: 0000 08000000 05001000 00000500 08000000 ................ 0010 05000000 00000000 08000000 05000000 ................ 0020 00000000 .... Disassembly of section .text: 0000000000000000 : 0: 53 push %rbx 1: 48 89 fb mov %rdi,%rbx 4: e8 00 00 00 00 callq 9 9: b9 0f 00 00 00 mov $0xf,%ecx e: 48 83 f8 0f cmp $0xf,%rax 12: 48 89 df mov %rbx,%rdi 15: 48 0f 4e c8 cmovle %rax,%rcx 19: 48 c7 c6 00 00 00 00 mov $0x0,%rsi 20: 48 39 c9 cmp %rcx,%rcx 23: f3 a6 repz cmpsb %es:(%rdi),%ds:(%rsi) 25: 5b pop %rbx 26: 0f 94 c0 sete %al 29: c3 retq 2a: 66 0f 1f 44 00 00 nopw 0x0(%rax,%rax,1) 0000000000000030 : 30: b8 01 00 00 00 mov $0x1,%eax 35: c3 retq