From patchwork Sun Oct 28 13:09:45 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Changbin Du X-Patchwork-Id: 10658609 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 2E6D81751 for ; Sun, 28 Oct 2018 13:10:43 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 1B77129D03 for ; Sun, 28 Oct 2018 13:10:43 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 1974229D34; Sun, 28 Oct 2018 13:10:43 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.0 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FROM,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 656ED29D03 for ; Sun, 28 Oct 2018 13:10:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727756AbeJ1VzM (ORCPT ); Sun, 28 Oct 2018 17:55:12 -0400 Received: from mail-pf1-f196.google.com ([209.85.210.196]:40387 "EHLO mail-pf1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726548AbeJ1VzL (ORCPT ); Sun, 28 Oct 2018 17:55:11 -0400 Received: by mail-pf1-f196.google.com with SMTP id g21-v6so2681460pfi.7; Sun, 28 Oct 2018 06:10:35 -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=+j4XlDFq4raU553LDUaUCt5+jy/FBKWbgmTWsZs9/w4=; b=ZcZBVTU89pzNt3vBNg6lVDMrt64t8JhHC/0QMzrER553066hxt39E1B+2UPNQ1CWhP 8v2Srqy/Yq86tkFT0eLx4mC/cdct4Rnrr7omJ/gsVPv8WxtIjs9QCE7NbNWLzElqVLzV Jweu+ZO6fkhSsXFPGne13D87/uAow5Sndz8G5BTRLmso+V9aUlySPUt4/YGPhS/6qZ9h U095NfJJa34DSdKEjJZy3VsaGm6860estcI6578dO9vw7pPuYG5AttvngxaYbyHfUeJv 7+lb5IBXlUrdp6aoq1UOGGiTY45kTlxBk1mkyemOkyJqD8eLC0Yu8/sCeZH3rf3EtU7+ omvA== 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=+j4XlDFq4raU553LDUaUCt5+jy/FBKWbgmTWsZs9/w4=; b=chdgAukOJVKuvWYWkJoCF+J1Yfg3e3DWoh3uSSh64Vuyr4Q0NSUn/YNqpaE7zQz4oT ESkip4ys26X644QM+8a12Vb5Df25ZDyiLRuzMbTpr4l9YLufquW2fTRn9+S52pyVCz/J JjVwqy1dGSePXczh86mvvWX9RLELL0b8+/J040hYE/h23KXHUMA0Zdsu1kKMPan60Gz+ 4j6hZweOJqri059fVqPSAc6LJHKbwE2nKtLGUATGg83bYsX8eR8hPwEbkC4BWNAiImtY 1ID3G10uOBI7jJKhCEnTF+mZmRz9ZjNxmlHZ+kXyAk2CGvAY1WNTdsrWEjnefi0uINa4 ElNA== X-Gm-Message-State: AGRZ1gIfshElXjDEJ5pts9H3bjPl3Ct/hSfnQ8TjsxcEVHVovC+XKJof 5DBF4DWkgUx/rV5YZaD09zU= X-Google-Smtp-Source: AJdET5fvHJQDAmPn9R6YowSIM8HbjBhm2D9STevLO7cEgHL7LQu7zx+lqCgO6PEB40iV3xLLy4Kjsw== X-Received: by 2002:a62:b24e:: with SMTP id x75-v6mr6183101pfe.148.1540732235340; Sun, 28 Oct 2018 06:10:35 -0700 (PDT) Received: from vultr.guest ([2001:19f0:6001:4ff6:5400:1ff:feb7:a195]) by smtp.gmail.com with ESMTPSA id e3-v6sm24520585pgc.71.2018.10.28.06.10.34 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 28 Oct 2018 06:10:34 -0700 (PDT) From: Changbin Du To: yamada.masahiro@socionext.com, michal.lkml@markovi.net, tglx@linutronix.de, mingo@redhat.com, linux@armlinux.org.uk, akpm@linux-foundation.org, gregkh@linuxfoundation.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, Changbin Du Subject: [PATCH v3 4/4] kernel hacking: new config CC_OPTIMIZE_FOR_DEBUGGING to apply GCC -Og optimization Date: Sun, 28 Oct 2018 13:09:45 +0000 Message-Id: <20181028130945.23581-5-changbin.du@gmail.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20181028130945.23581-1-changbin.du@gmail.com> References: <20181028130945.23581-1-changbin.du@gmail.com> Sender: linux-kbuild-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kbuild@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP 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: Changbin Du Acked-by: Steven Rostedt (VMware) Cc: Masahiro Yamada --- v3: o make CC_OPTIMIZE_FOR_DEBUGGING depends on $(cc-option,-Og) o reflect CONFIG_CC_OPTIMIZE_FOR_DEBUGGING in tiny.config --- Makefile | 5 +++++ include/linux/compiler-gcc.h | 2 +- include/linux/compiler.h | 2 +- init/Kconfig | 20 ++++++++++++++++++++ kernel/configs/tiny.config | 1 + 5 files changed, 28 insertions(+), 2 deletions(-) diff --git a/Makefile b/Makefile index 04beb822ddfc..10de245a3325 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 += -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 90ddfefb6c2b..4832c98c7885 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 1921545c6351..3836397bf477 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -350,7 +350,7 @@ 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 a4112e95724a..0fb9c0b5f1a1 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -1105,6 +1105,26 @@ config CC_OPTIMIZE_FOR_SIZE If unsure, say N. +config CC_OPTIMIZE_FOR_DEBUGGING + bool "Optimize for better debugging experience (-Og)" + depends on $(cc-option,-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 diff --git a/kernel/configs/tiny.config b/kernel/configs/tiny.config index 7fa0c4ae6394..599ea86b0800 100644 --- a/kernel/configs/tiny.config +++ b/kernel/configs/tiny.config @@ -1,5 +1,6 @@ # CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE is not set CONFIG_CC_OPTIMIZE_FOR_SIZE=y +# CONFIG_CC_OPTIMIZE_FOR_DEBUGGING is not set # CONFIG_KERNEL_GZIP is not set # CONFIG_KERNEL_BZIP2 is not set # CONFIG_KERNEL_LZMA is not set