From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 23178 invoked by alias); 29 Nov 2010 21:07:29 -0000 Received: (qmail 23166 invoked by uid 22791); 29 Nov 2010 21:07:28 -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_KG X-Spam-Check-By: sourceware.org Received: from mail-gx0-f169.google.com (HELO mail-gx0-f169.google.com) (209.85.161.169) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Mon, 29 Nov 2010 21:07:22 +0000 Received: by gxk5 with SMTP id 5so2555867gxk.0 for ; Mon, 29 Nov 2010 13:07:20 -0800 (PST) MIME-Version: 1.0 Received: by 10.42.241.8 with SMTP id lc8mr1626932icb.95.1291064840372; Mon, 29 Nov 2010 13:07:20 -0800 (PST) Received: by 10.42.176.10 with HTTP; Mon, 29 Nov 2010 13:07:20 -0800 (PST) In-Reply-To: References: Date: Mon, 29 Nov 2010 21:07:00 -0000 Message-ID: Subject: Re: [PATCH] Built kernel without -O2 option From: Arnaud Lacombe To: Hui Zhu Cc: linux-kernel@vger.kernel.org, gdb@sourceware.org, hellogcc@freelists.org Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable 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/msg00130.txt.bz2 Hi, On Sun, Nov 28, 2010 at 10:56 PM, 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 > $3 =3D > And the code execution order is not right. > > This is becuase the Kernel is bult with gcc -O2. =A0Gcc will not > generate enough debug message with file with -O2. > So GDB cannot work very well with Linux kernel. > > So I make a patch that add a option in "Kernel hacking" called "Close > GCC optimization". =A0It will make kernel be built without -O2. > no, it does not, see below .. > I built and use it in i386 and x86_64. =A0I will try to make it OK in oth= er arch. > > And I will put new patch in here and > http://code.google.com/p/kgtp/downloads/list > > Thanks, > Hui > > Signed-off-by: Hui Zhu > --- > [...] > +ifdef CONFIG_CC_CLOSE_OPTIMIZATION > +CFLAGS_process_$(BITS).o =A0 =A0 =A0 +=3D -O2 > +CFLAGS_entry_$(BITS).o =A0 =A0 =A0 =A0 +=3D -O2 > +CFLAGS_traps.o =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 +=3D -O2 > +CFLAGS_i387.o =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0+=3D -O2 > +CFLAGS_xsave.o =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 +=3D -O2 > +CFLAGS_hpet.o =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0+=3D -O2 > +endif > > [...] > > --- a/lib/Kconfig.debug > +++ b/lib/Kconfig.debug > @@ -136,6 +136,14 @@ config DEBUG_SECTION_MISMATCH > =A0 =A0 =A0 =A0 =A0- Enable verbose reporting from modpost to help solving > =A0 =A0 =A0 =A0 =A0 =A0the section mismatches reported. > > +config CC_CLOSE_OPTIMIZATION > + =A0 =A0 =A0 bool "Close GCC optimization" > + =A0 =A0 =A0 default n > + =A0 =A0 =A0 help > + =A0 =A0 =A0 =A0 Enabling this option will let gcc build kernel without = "-O2". > + > + =A0 =A0 =A0 =A0 If unsure, say N. > + You are not consistent with yourself, you add an option saying "do not build the kernel with -O2" and yet, you add "-O2" flags for unknown reason all over the tree... - Arnaud