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

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Message-ID: <87r5e4lab7.fsf@basil.nowhere.org>
Date:	Mon, 29 Nov 2010 10:59:40 +0100
From:	Andi Kleen <andi@...stfloor.org>
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

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.

>
> 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 ? 

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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