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

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Message-ID: <20101129081619.GD5218@cr0.nay.redhat.com>
Date:	Mon, 29 Nov 2010 16:16:19 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Hui Zhu <teawater@...il.com>
Cc:	linux-kernel@...r.kernel.org, gdb@...rceware.org,
	hellogcc@...elists.org
Subject: Re: [PATCH] Built kernel without -O2 option

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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