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=-8.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,USER_AGENT_GIT 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 59111ECDE3D for ; Fri, 19 Oct 2018 12:49:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0859D214C2 for ; Fri, 19 Oct 2018 12:49:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="cdWw8+Vs" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0859D214C2 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727615AbeJSUzn (ORCPT ); Fri, 19 Oct 2018 16:55:43 -0400 Received: from mail-pl1-f193.google.com ([209.85.214.193]:34658 "EHLO mail-pl1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727189AbeJSUzm (ORCPT ); Fri, 19 Oct 2018 16:55:42 -0400 Received: by mail-pl1-f193.google.com with SMTP id f18-v6so15844519plr.1; Fri, 19 Oct 2018 05:49:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=bOm0HRmT/HL5EepHWbPNNUnvLKgst+PQQHeTsNhkPAY=; b=cdWw8+VsBI86IcDArWiR6DpHu07W/NCuIEyixrOcoNHxsP28FzRLgJso8uPIna9/fy 2kJ6xQw/UIOTuJU2NgRXwMCs1dc31mElYwdE5HcLoAdMK7yvGBvB/KCMVNl+rbT8jW9d wB7yhld+7PX5iSpoQO8lL0EQLJwlYT46r582MiNKDNMnBlvEszDTE+q7uVX357hTFrYt ZB4uCONhfPWn7dp0Uiclc5K8LWOtZms9Fl1L7x00AAk82HBjvEZhlVpsrPQ4CXM+z27m /rREhz1OZgIrQmp+ffFhwSWOep/wOco5dAw3YmwPVF29ce4If7NO0Gl+2bK1LlG/jb14 3Wrg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=bOm0HRmT/HL5EepHWbPNNUnvLKgst+PQQHeTsNhkPAY=; b=lERzTOV70M/jdqNehyZPFjTVAUilur1W/XUyjvaySZDvfhw/B5xJgKGcTVXGxn0Wtl r6OprFrnaBxLughxabaDSlrCcS0Q2R7t3HbtWc/EptkAgyqRbEgve7ry3VzWSbi869Y3 A74tzuSJNCwhHLyrLKgpN+uSXmefwFuG49vMa/tJ2iBouOTkL0r52TGM6fmKrKUUwjHi s71MOcqZB03byNMWaBDbqp70i/gQHzYs0MCGQRmn/lW11qpNouYCYz4gVIwn+y73mtXJ ZZh2v++rlTQIpoYcBe8jDt1P0uN6+ZWkpGsXc44aKJONVb2RU1UlyBvC4XVI9rbbVS0W rWpQ== X-Gm-Message-State: ABuFfogel92YNDUFljC50zktnHfJxJ878Km7EE+5cX0nc/0jpaHJ66aE LHYTctAJaurVHBwhaXffuMk= X-Google-Smtp-Source: ACcGV63lQ++xgpge5a4+5IgmRhl8IM1qUJsIhp3WFWDgw9MDcUJlRgzEayX+41yHaVanS/iPVQDQPA== X-Received: by 2002:a17:902:6843:: with SMTP id f3-v6mr33968645pln.64.1539953383858; Fri, 19 Oct 2018 05:49:43 -0700 (PDT) Received: from vultr.guest ([2001:19f0:6001:4ff6:5400:1ff:feb7:a195]) by smtp.gmail.com with ESMTPSA id o131-v6sm33640679pgo.53.2018.10.19.05.49.42 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 19 Oct 2018 05:49:43 -0700 (PDT) From: Du Changbin To: yamada.masahiro@socionext.com, michal.lkml@markovi.net, tglx@linutronix.de, mingo@redhat.com, linux@armlinux.org.uk, akpm@linux-foundation.org Cc: rostedt@goodmis.org, x86@kernel.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-sparse@vger.kernel.org, robin.murphy@arm.com, Du Changbin Subject: [PATCH v2 4/4] kernel hacking: new config CC_OPTIMIZE_FOR_DEBUGGING to apply GCC -Og optimization Date: Fri, 19 Oct 2018 12:49:21 +0000 Message-Id: <20181019124921.13780-5-changbin.du@gmail.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20181019124921.13780-1-changbin.du@gmail.com> References: <20181019124921.13780-1-changbin.du@gmail.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This will apply GCC '-Og' optimization level which is supported since GCC 4.8. This optimization level offers a reasonable level of optimization while maintaining fast compilation and a good debugging experience. It is similar to '-O1' while perferring to keep debug ability over runtime speed. If enabling this option breaks your kernel, you should either disable this or find a fix (mostly in the arch code). Currently this option has only been tested on x86_64 and arm platform. This option can satisfy people who was searching for a method to disable compiler optimizations so to achieve better kernel debugging experience with kgdb or qemu. The main problem of '-Og' is we must not use __attribute__((error(msg))). The compiler will report error though the call to error function still can be optimize out. So we must fallback to array tricky. Comparison of vmlinux size: a bit smaller. w/o CONFIG_CC_OPTIMIZE_FOR_DEBUGGING $ size vmlinux text data bss dec hex filename 22665554 9709674 2920908 35296136 21a9388 vmlinux w/ CONFIG_CC_OPTIMIZE_FOR_DEBUGGING $ size vmlinux text data bss dec hex filename 21499032 10102758 2920908 34522698 20ec64a vmlinux Comparison of system performance: a bit drop (~6%). This benchmark of kernel compilation is suggested by Ingo Molnar. https://lkml.org/lkml/2018/5/2/74 Preparation: Set cpufreq to 'performance'. for ((cpu=0; cpu<120; cpu++)); do G=/sys/devices/system/cpu/cpu$cpu/cpufreq/scaling_governor [ -f $G ] && echo performance > $G done w/o CONFIG_CC_OPTIMIZE_FOR_DEBUGGING $ perf stat --repeat 5 --null --pre '\ cp -a kernel ../kernel.copy.$(date +%s); \ rm -rf *; \ git checkout .; \ echo 1 > /proc/sys/vm/drop_caches; \ find ../kernel* -type f | xargs cat >/dev/null; \ make -j kernel >/dev/null; \ make clean >/dev/null 2>&1; \ sync '\ \ make -j8 >/dev/null Performance counter stats for 'make -j8' (5 runs): 219.764246652 seconds time elapsed ( +- 0.78% ) w/ CONFIG_CC_OPTIMIZE_FOR_DEBUGGING $ perf stat --repeat 5 --null --pre '\ cp -a kernel ../kernel.copy.$(date +%s); \ rm -rf *; \ git checkout .; \ echo 1 > /proc/sys/vm/drop_caches; \ find ../kernel* -type f | xargs cat >/dev/null; \ make -j kernel >/dev/null; \ make clean >/dev/null 2>&1; \ sync '\ \ make -j8 >/dev/null Performance counter stats for 'make -j8' (5 runs): 233.574187771 seconds time elapsed ( +- 0.19% ) Signed-off-by: Du Changbin Acked-by: Steven Rostedt (VMware) --- Makefile | 5 +++++ include/linux/compiler-gcc.h | 2 +- include/linux/compiler.h | 2 +- init/Kconfig | 19 +++++++++++++++++++ 4 files changed, 26 insertions(+), 2 deletions(-) diff --git a/Makefile b/Makefile index 757d6507cb5c..ea908cfe8594 100644 --- a/Makefile +++ b/Makefile @@ -657,6 +657,10 @@ KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation) KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow) KBUILD_CFLAGS += $(call cc-disable-warning, int-in-bool-context) +ifdef CONFIG_CC_OPTIMIZE_FOR_DEBUGGING +KBUILD_CFLAGS += $(call cc-option, -Og) +KBUILD_CFLAGS += $(call cc-disable-warning,maybe-uninitialized,) +else ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE KBUILD_CFLAGS += $(call cc-option,-Oz,-Os) KBUILD_CFLAGS += $(call cc-disable-warning,maybe-uninitialized,) @@ -667,6 +671,7 @@ else KBUILD_CFLAGS += -O2 endif endif +endif KBUILD_CFLAGS += $(call cc-ifversion, -lt, 0409, \ $(call cc-disable-warning,maybe-uninitialized,)) diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h index 4d36b27214fd..2a76f7c64b54 100644 --- a/include/linux/compiler-gcc.h +++ b/include/linux/compiler-gcc.h @@ -85,7 +85,7 @@ #define __compiletime_object_size(obj) __builtin_object_size(obj, 0) -#ifndef __CHECKER__ +#if !defined(__CHECKER__) && !defined(CONFIG_CC_OPTIMIZE_FOR_DEBUGGING) #define __compiletime_warning(message) __attribute__((warning(message))) #define __compiletime_error(message) __attribute__((error(message))) diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 681d866efb1e..9385c62e9f00 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -320,7 +320,7 @@ static inline void *offset_to_ptr(const int *off) * sparse see a constant array size without breaking compiletime_assert on old * versions of GCC (e.g. 4.2.4), so hide the array from sparse altogether. */ -# ifndef __CHECKER__ +# if !defined(__CHECKER__) && !defined(CONFIG_CC_OPTIMIZE_FOR_DEBUGGING) # define __compiletime_error_fallback(condition) \ do { ((void)sizeof(char[1 - 2 * condition])); } while (0) # endif diff --git a/init/Kconfig b/init/Kconfig index 1e234e2f1cba..b01c7c654570 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -1081,6 +1081,25 @@ config CC_OPTIMIZE_FOR_SIZE If unsure, say N. +config CC_OPTIMIZE_FOR_DEBUGGING + bool "Optimize for better debugging experience (-Og)" + select NO_AUTO_INLINE + help + This will apply GCC '-Og' optimization level which is supported + since GCC 4.8. This optimization level offers a reasonable level + of optimization while maintaining fast compilation and a good + debugging experience. It is similar to '-O1' while preferring to + keep debug ability over runtime speed. The overall performance + will drop a bit (~6%). + + Use only if you want to debug the kernel, especially if you want + to have better kernel debugging experience with gdb facilities + like kgdb or qemu. If enabling this option breaks your kernel, + you should either disable this or find a fix (mostly in the arch + code). + + If unsure, select N. + endchoice config HAVE_LD_DEAD_CODE_DATA_ELIMINATION -- 2.17.1