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

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Date:	Mon, 29 Nov 2010 16:18:09 +0800
From:	microcai <microcai@...oraproject.org>
To:	unlisted-recipients:; (no To-header on input)
Cc:	Hui Zhu <teawater@...il.com>, linux-kernel@...r.kernel.org,
	gdb@...rceware.org, hellogcc@...elists.org
Subject: Re: [PATCH] Built kernel without -O2 option

2010/11/29 Américo Wang <xiyou.wangcong@...il.com>:
> 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.
>
> Also, what is size of vmlinux before applying your patch and after that?
> Does it increase too much?
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