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

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Date:	Wed, 17 Feb 2010 18:31:04 +0100
From:	Michal Marek <mmarek@...e.cz>
To:	Borislav Petkov <bp@...64.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	linux-kbuild <linux-kbuild@...r.kernel.org>,
	Borislav Petkov <petkovbb@...glemail.com>,
	Peter Zijlstra <peterz@...radead.org>,
	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 17.2.2010 18:20, Borislav Petkov wrote:
> On Wed, Feb 17, 2010 at 02:57:42PM +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.
> 
> Wouldn't it be better if we had something like ARCH_CFLAGS_hweight.o
> which gets set in the arch Makefile instead?

We could, but is it worth it if there is only one potential user so far?
IMO just put the condition to lib/Makefile now and if there turn out to
be more cases like this, we can add support for ARCH_CFLAGS_foo.o then.

Michal
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