Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1751620Ab0K2IZG (ORCPT <rfc822;w@1wt.eu>);
	Mon, 29 Nov 2010 03:25:06 -0500
Received: from mail-wy0-f174.google.com ([74.125.82.174]:52042 "EHLO
	mail-wy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1750959Ab0K2IZF convert rfc822-to-8bit (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Mon, 29 Nov 2010 03:25:05 -0500
DomainKey-Signature: a=rsa-sha1; c=nofws;
        d=gmail.com; s=gamma;
        h=mime-version:in-reply-to:references:from:date:message-id:subject:to
         :cc:content-type:content-transfer-encoding;
        b=IKxlpX4KJZelDMmr6oXUpdXs1O5+kXtlcAsw8A15ZynDIs7h4cCUiRmBBWKSA/pyyL
         4zkHU7cu/We2BRwF5W6kMvmm+moNO0x3/6zEpj1xjTUnNv3ONWkLcCGoU0OFwTzRGHRL
         kfg4zWTFV36J7uutgEGX0Tv33azYWtJ8eaRJY=
MIME-Version: 1.0
In-Reply-To: <20101129081619.GD5218@cr0.nay.redhat.com>
References: <AANLkTimewZ4QhxzL2vOYYV85pegy8Fu6Rb4XUAPqGUXS@mail.gmail.com> <20101129081619.GD5218@cr0.nay.redhat.com>
From: Hui Zhu <teawater@gmail.com>
Date: Mon, 29 Nov 2010 16:24:42 +0800
Message-ID: <AANLkTinnJjqmXmbpAYmV9Tsc0VJV=WDM+GY6Gi1cJFCB@mail.gmail.com>
Subject: Re: [PATCH] Built kernel without -O2 option
To: =?ISO-8859-1?Q?Am=E9rico_Wang?= <xiyou.wangcong@gmail.com>
Cc: linux-kernel@vger.kernel.org, gdb@sourceware.org, hellogcc@freelists.org
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 8BIT
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 2090
Lines: 60

On Mon, Nov 29, 2010 at 16:16, Am?rico Wang <xiyou.wangcong@gmail.com> 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 = <value optimized out>
>>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

And I will try to find more of these type files.

>
> Also, what is size of vmlinux before applying your patch and after that?
> Does it increase too much?
>

Before the patch:
ls -alh vmlinuz-2.6.37-rc3+
-rw-r--r-- 1 root root 4.1M 2010-11-25 12:02 vmlinuz-2.6.37-rc3+
ls -alh b26no/vmlinux
-rwxr-xr-x 1 teawater teawater 135M 2010-11-25 13:31 b26no/vmlinux

After the patch:
ls -alh vmlinuz-2.6.37-rc3debug+
-rw-r--r-- 1 root root 4.6M 2010-11-25 14:02 vmlinuz-2.6.37-rc3debug+
ls -alh b26/vmlinux
-rwxr-xr-x 1 teawater teawater 140M 2010-11-25 11:14 b26/vmlinux

Thanks,
Hui
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/