linux-kernel - Re: [PATCH 4/6] Add support for LZO-compressed kernels for ARM

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Date:	Fri, 7 Aug 2009 13:50:03 +0200
From:	Matthieu CASTET <matthieu.castet@...rot.com>
To:	Albin Tonnerre <albin.tonnerre@...e-electrons.com>
CC:	Alain Knaff <alain@...ff.lu>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	"sam@...nborg.org" <sam@...nborg.org>,
	"hpa@...or.com" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-embedded@...r.kernel.org" <linux-embedded@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [PATCH 4/6] Add support for LZO-compressed kernels for ARM

Albin Tonnerre a écrit :
> On Fri, Aug 07, 2009 at 11:36:56AM +0200, Alain Knaff wrote :
>> On 08/07/09 11:24, Albin Tonnerre wrote:
> 
>>> Regards,
> 
>> Could it be that the patches that remove division (zutil.h and inflate.c)
>> have somehow not been applied?
> 
> Indeed, they've not been applied. However, I'd rather try to understand why
> exactly this is an issue when compiling with -Os and not -O2 instead of working
> around it by removing the divisions.
> 
Look at the generated code.

Arm doesn't have division instruction.
May be at -Os gcc emit a call to the software division, but at -O2 it
manage to optimise the division (transform it in shift, inline some
builtin, ...).


Matthieu
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