linux-kernel - Re: [PATCH 1/6] headers

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Date:	Fri, 5 Jun 2009 21:48:06 +0100
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	Jaswinder Singh Rajput <jaswinder@...nel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Catalin Marinas <catalin.marinas@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-arm-kernel@...ts.arm.linux.org.uk
Subject: Re: [PATCH 1/6] headers_check fix: arm, hwcap.h

On Thu, Jun 04, 2009 at 10:16:49PM +0200, Sam Ravnborg wrote:
> On Thu, Jun 04, 2009 at 01:53:07PM +0100, Russell King wrote:
> > On Thu, Jun 04, 2009 at 05:57:56PM +0530, Jaswinder Singh Rajput wrote:
> > > fix the following 'make headers_check' warning:
> > 
> > I think headers_check needs fixing - there's nothing wrong with the
> > code as it presently stands except the tools obviously can't properly
> > parse C preprocessor statements.
> 
> You are correct that headers_ceck is limited here and this patch
> take some valid code and refactor it to make it headers_check compatible.

Okay, here's the question:

Does userspace require anything in the ifdef __ASSEMBLY__ bits?

In any case, passing -D__KERNEL__ or -U__KERNEL__ allows unifdef to
do the right thing.

The problem which unifdef has is that if it finds a symbol in an
evaluation that it doesn't know about, it fails the expansion
entirely, rather than checking whether the expansion always results
in something which should be omitted.  In other words:

#if defined(__KERNEL__) && (<unknown>)

results in basically an "unknown" answer from the evaluator, where
we can see perfectly well that the expansion can never be true if
__KERNEL__ is never set.

So, the trivial answer to the problem if:

#if defined(__KERNEL__) && something-depending-on-__ASSEMBLY__

is to tell unifdef whether we want __ASSEMBLY__ defined or not defined.
This does shut up the headers_install warning from ARMs hwdef.h.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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