linux-kernel - Re: [PATCH 2/5] bitops: compile time optimization for hweight

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Message-ID: <1266490310.26719.185.camel@laptop>
Date:	Thu, 18 Feb 2010 11:51:50 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Michal Marek <mmarek@...e.cz>
Cc:	"H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...64.org>,
	linux-kbuild <linux-kbuild@...r.kernel.org>,
	Borislav Petkov <petkovbb@...glemail.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jamie Lokier <jamie@...reable.org>,
	Roland Dreier <rdreier@...co.com>,
	Al Viro <viro@...IV.linux.org.uk>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>, Brian Gerst <brgerst@...il.com>
Subject: Re: [PATCH 2/5] bitops: compile time optimization for
 hweight_long(CONSTANT)

On Wed, 2010-02-17 at 14:57 +0100, Michal Marek wrote:
> On 12.2.2010 20:05, H. Peter Anvin wrote:
> > On 02/12/2010 09:47 AM, Borislav Petkov wrote:
> >>
> >> However, this is generic code and for the above to work we have to
> >> enforce x86-specific CFLAGS for it. What is the preferred way to do
> >> that?
> >>
> > 
> > That's a question for Michal and the kbuild list.  Michal?
> 
> (I was offline last week).
> 
> The _preferred_ way probably is not to do it :), but otherwise you can
> set CFLAGS_hweight.o depending on CONFIG_X86(_32|_64), just like you do
> in arch/x86/lib/Makefile already.

I guess one way to achieve that is to create a arch/x86/lib/hweight.c
that includes lib/hweight.c and give the x86 one special compile flags
and not build the lib on.

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