linux-kernel - Re: [hellogcc] Re: [PATCH] Built kernel without -O2 option

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Date:	Mon, 29 Nov 2010 16:57:58 +0800
From:	Hui Zhu <teawater@...il.com>
To:	Steven <mqyoung@...il.com>
Cc:	hellogcc@...elists.org,
	Américo Wang <xiyou.wangcong@...il.com>,
	linux-kernel@...r.kernel.org, gdb@...rceware.org
Subject: Re: [hellogcc] Re: [PATCH] Built kernel without -O2 option

On Mon, Nov 29, 2010 at 16:55, Steven <mqyoung@...il.com> wrote:
> I replace -O2 with -O0 in Makefile of kernel source code root directory?
> I just do it and my gdb works well with this method.
>
> You mean it is not enough?
>
> Steven

Yes.

>
> On Mon, 2010-11-29 at 16:47 +0800, Hui Zhu wrote:
>> In this way, you will got a lot of error.
>>
>> Hui
>>
>> On Mon, Nov 29, 2010 at 16:41, 乔崇 <qiaochong@...ngson.cn> wrote:
>> > does not need change kernel,just write a shell mycc as bellow:
>> >
>> > #!/bin/sh
>> > gcc "$@" -O0
>> >
>> > then
>> >
>> > make CC=./mycc vmlinux
>> >
>> > Hui Zhu said
>> >
>> > On Mon, Nov 29, 2010 at 16:16, Américo Wang <xiyou.wangcong@...il.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
>> >
>> >
>> >
>> >
>> > --
>> >
>> > 乔崇 qiaochong@...ngson.cn
>> >
>> > 2010年 11月 29日 星期一 16:35:38 CST
>
>
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