linux-kernel - Re: [PATCH 02/10] x86: Convert BUG() to use unreachable()

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Date:	Thu, 10 Sep 2009 18:13:07 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"H. Peter Anvin" <hpa@...or.com>
cc:	David Daney <ddaney@...iumnetworks.com>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	Roland McGrath <roland@...hat.com>
Subject: Re: [PATCH 02/10] x86: Convert BUG() to use unreachable()

On Thu, 10 Sep 2009, H. Peter Anvin wrote:

> On 09/10/2009 04:56 PM, David Daney wrote:
> > Use the new unreachable() macro instead of for(;;);.  When
> > allyesconfig is built with a GCC-4.5 snapshot on i686 the size of the
> > text segment is reduced by 3987 bytes (from 6827019 to 6823032).
> > 
> > Signed-off-by: David Daney <ddaney@...iumnetworks.com>
> > CC: Thomas Gleixner <tglx@...utronix.de>
> > CC: Ingo Molnar <mingo@...hat.com>
> > CC: "H. Peter Anvin" <hpa@...or.com>
> > CC: x86@...nel.org
> 
> Acked-by: H. Peter Anvin <hpa@...or.com>
> 
> ... although of course this clashes with Roland McGrath's patchset for
> the same thing which I applied earlier.  I have to say I like
> unreachable() in lower case better though...

I like David's version a bit better, since it takes care of more 
architectures, and also because it avoids that butt-ugly special case for 
gcc-4.4.1-RH-relase-10 backporting this feature.

I realize that the RH backport thing is good for testing now, but at the 
same time, it really does look nasty. I wonder if we could add some 
config-time compiler feature testing - so that you'd not have a version 
test at all, but a CONFIG_BUILTIN_UNREACHABLE.

There are other cases where that kind of config-time testing could be 
useful, and we could avoid doing various gcc checks dynamically from 
within 'make' (along with checking for known-buggy versions etc).

And yeah, it looks better in lower case. That said, I don't care _that_ 
much, and people can fight it out. 

		Linus
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