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

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Date:	Tue, 30 Nov 2010 17:31:06 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Mark Wielaard <mjw@...hat.com>
Cc:	Andi Kleen <andi@...stfloor.org>, Hui Zhu <teawater@...il.com>,
	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 11:12:16AM +0100, Mark Wielaard wrote:
>On Mon, 2010-11-29 at 10:59 +0100, Andi Kleen 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.
>
>The VTA branch was merged for GCC 4.5
>http://gcc.gnu.org/wiki/Var_Tracking_Assignments
>Which helps a lot with generating dwarf for previously "optimized out"
>values. There were also a couple of papers on generating even better
>debuginfo at the recent GCC Summit: http://gcc.gnu.org/wiki/summit2010
>
>Jakub Jelínek, Improving debug info for optimized away parameters
>http://gcc.gnu.org/wiki/summit2010?action=AttachFile&do=get&target=jelinek.pdf
>Alexandre Oliva, Consistent Views at Recommended Breakpoints
>http://gcc.gnu.org/wiki/summit2010?action=AttachFile&do=get&target=oliva.pdf
>

Cool! It would be much more convenient if this is solved by gcc.
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