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

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Message-ID: <AANLkTimwnKamJ+UBO1CCn9Hb3PWGgFmC1c0iQr_KeyzO@mail.gmail.com>
Date:	Wed, 1 Dec 2010 20:52:16 +0800
From:	Hui Zhu <teawater@...il.com>
To:	Andi Kleen <andi@...stfloor.org>
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 17:59, Andi Kleen <andi@...stfloor.org> wrote:
> Hui Zhu <teawater@...il.com> writes:
>
>> 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.
>
> Really the right place to fix a lot of this would be gcc (and perhaps
> gdb). I suspect with some careful work the debugging experience
> for -O2 could be improved a lot.
> I also believe the latest gccs already have improvements in this area.
>

If you think they are OK, go get a new gcc and try.  :)

>>
>> 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.
>
>
> You need to at least keep aggressive inlining for header files,
> otherwise there will be too much code bloat and bad code.
>
> Like -O1 -finline-functions ?
>

If I can build OK, why I need add some options?

Thanks,
Hui
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