linux-kernel - Re: __packed vs. __attribute_

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Message-ID: <20110623150209.GA12413@x4.trippels.de>
Date:	Thu, 23 Jun 2011 17:02:09 +0200
From:	Markus Trippelsdorf <markus@...ppelsdorf.de>
To:	Nick Bowler <nbowler@...iptictech.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Mike Frysinger <vapier@...too.org>,
	Sam Ravnborg <sam@...nborg.org>,
	Artem Bityutskiy <Artem.Bityutskiy@...ia.com>
Subject: Re: __packed vs. __attribute__((packed)) in kernel headers

On 2011.06.23 at 09:42 -0400, Nick Bowler wrote:
> On 2011-06-22 08:34 +0200, Markus Trippelsdorf wrote:
> > One possible solution would be to let the "scripts/headers_install.pl"
> > script automatically substitute __packed with __attribute__((packed)):
> > 
> > diff --git a/scripts/headers_install.pl b/scripts/headers_install.pl
> > index efb3be1..e0dc065 100644
> > --- a/scripts/headers_install.pl
> > +++ b/scripts/headers_install.pl
> > @@ -35,6 +35,7 @@ foreach my $file (@files) {
> >  		$line =~ s/([\s(])__iomem\s/$1/g;
> >  		$line =~ s/\s__attribute_const__\s/ /g;
> >  		$line =~ s/\s__attribute_const__$//g;
> > +		$line =~ s/\s__packed/__attribute__((packed))/g;
> >  		$line =~ s/^#include <linux\/compiler.h>//;
> >  		$line =~ s/(^|\s)(inline)\b/$1__$2__/g;
> >  		$line =~ s/(^|\s)(asm)\b(\s|[(]|$)/$1__$2__$3/g;
> > 
> > Any thoughts?
> 
> Without any comment on the approach itself, the above change will eat a
> space character before __packed, which may break the header by merging a
> preceding token into the __attribute__.  It may also change instances of
> __packed that occur as a prefix of a longer token.
> 
> Note that the __attribute_const__ lines above it take some care to avoid
> both of these situations.

Yes, you're right. But the patch was meant as a rough proof of concept
and not as the final implementation. 

I'm not an expert of Perl regular expressions, but maybe this:
 $line =~ s/\s__packed;$/ __attribute__((packed));/g
is a little bit closer to the intention?

-- 
Markus
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