linux-kernel - Re: [PATCH] intel-iommu: fix build with CONFIG_BRANCH

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Date:	Tue, 07 Apr 2009 05:44:23 -0700
From:	David Woodhouse <dwmw2@...radead.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	torvalds@...ux-foundation.org, iommu@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] intel-iommu: fix build with CONFIG_BRANCH_TRACER=y

On Tue, 2009-04-07 at 14:14 +0200, Ingo Molnar wrote:
> Well, i consider it a feature that it flags weird if (x, y) 
> constructs: and yes, these iterators you introduced, while they are 
> legit C, definitely count as 'weird'. If regular code was doing it, 
> not a loop abstraction, i'd call it non-obvious and borderline 
> broken straight away.
> 
> We should _never ever_ put comma statements into if () constructs 
> without a _really_ good reason - and if yes, we can flag that we 
> know what we are doing, via extra parentheses.

I disagree. I don't think we should be declaring valid C syntax as 'off
limits', however rare it is.

_Especially_ if it only actually fails with a fairly esoteric config
option set. That's just asking for build breakage.

> and if yes, we can flag that we know what we are doing, via extra 
> parentheses.

That's hardly much of a barrier. The requirement to sprinkle
gratuitous-looking extra parentheses around the place really isn't going
to give us much of a _benefit_ in return for the build breakage.

-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@...el.com                              Intel Corporation

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