From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 10577 invoked by alias); 29 Nov 2010 08:48:08 -0000 Received: (qmail 10569 invoked by uid 22791); 29 Nov 2010 08:48:08 -0000 X-SWARE-Spam-Status: No, hits=-1.9 required=5.0 tests=AWL,BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FROM,RCVD_IN_DNSWL_NONE,TW_CL,TW_KG X-Spam-Check-By: sourceware.org Received: from mail-qw0-f41.google.com (HELO mail-qw0-f41.google.com) (209.85.216.41) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Mon, 29 Nov 2010 08:48:04 +0000 Received: by qwi2 with SMTP id 2so1302878qwi.0 for ; Mon, 29 Nov 2010 00:48:02 -0800 (PST) Received: by 10.229.215.213 with SMTP id hf21mr4658403qcb.189.1291020482023; Mon, 29 Nov 2010 00:48:02 -0800 (PST) Received: from cr0.nay.redhat.com ([60.247.97.98]) by mx.google.com with ESMTPS id l14sm3061912qck.29.2010.11.29.00.47.58 (version=TLSv1/SSLv3 cipher=RC4-MD5); Mon, 29 Nov 2010 00:48:01 -0800 (PST) Date: Mon, 29 Nov 2010 08:48:00 -0000 From: =?utf-8?Q?Am=C3=A9rico?= Wang To: Hui Zhu Cc: =?utf-8?Q?Am=C3=A9rico?= Wang , linux-kernel@vger.kernel.org, gdb@sourceware.org, hellogcc@freelists.org Subject: Re: [PATCH] Built kernel without -O2 option Message-ID: <20101129085250.GF5218@cr0.nay.redhat.com> References: <20101129081619.GD5218@cr0.nay.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Mailing-List: contact gdb-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-owner@sourceware.org X-SW-Source: 2010-11/txt/msg00108.txt.bz2 On Mon, Nov 29, 2010 at 04:24:42PM +0800, Hui Zhu wrote: >On Mon, Nov 29, 2010 at 16:16, Américo Wang wrote: >> On Mon, Nov 29, 2010 at 11:56:15AM +0800, Hui Zhu wrote: >>>Hi, >>> >>>Now, there are a lot of ways to debug the Linux kernel with GDB, like >>>qemu, kgtp or kgdb and so on. >>>But the developer more like add a printk. It have a lot of reason, a big one is: >>>(gdb) p ret >>>$3 = >>>And the code execution order is not right. >>> >>>This is becuase the Kernel is bult with gcc -O2.  Gcc will not >>>generate enough debug message with file with -O2. >>>So GDB cannot work very well with Linux kernel. >>> >>>So I make a patch that add a option in "Kernel hacking" called "Close >>>GCC optimization".  It will make kernel be built without -O2. >>> >>>I built and use it in i386 and x86_64.  I will try to make it OK in other arch. >>> >> >> The problem is that some functions _have to_ be inlined and gcc without -O2 >> doesn't inline them. Have check all the cases? I doubt. > >If they really need O2, I set them to O2. >Actually, this is the main work, find out the file that need the O2. :) > >For example: >ifdef CONFIG_CC_CLOSE_OPTIMIZATION >CFLAGS_fpu.o += -O2 >CFLAGS_aesni-intel_glue.o += -O2 >CFLAGS_ghash-clmulni-intel_glue.o += -O2 >endif No, I didn't mean this, I meant some function that have to be inlined are those who only work when being inlined, e.g. current_text_addr(). I think it is not alone. :) Also, since many inline functions sit in hot-path, are there any performance regressions with your patch applied? BTW, you need to Cc kbuild for makefile changes like this.