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

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Message-ID: <AANLkTiktPFtCdYpZai-L_WCOpBrZYN5yN_V7GZ5tKGXG@mail.gmail.com>
Date:	Mon, 29 Nov 2010 16:47:14 +0800
From:	Hui Zhu <teawater@...il.com>
To:	hellogcc@...elists.org
Cc:	Américo Wang <xiyou.wangcong@...il.com>,
	linux-kernel@...r.kernel.org, gdb@...rceware.org
Subject: Re: [hellogcc] Re: [PATCH] Built kernel without -O2 option

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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