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

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Date:	Tue, 7 Apr 2009 07:50:38 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
cc:	David Woodhouse <dwmw2@...radead.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, 7 Apr 2009, Ingo Molnar wrote:
> 
> Switch it to a braced group statement.

No, the way to do that is to just clean it up (or in the worst case just 
add another set of parenthesis, not a statement expression).

That said, whoever made "if()" a macro should be shot. That 
PROFILE_ALL_BRANCHES thing is crazy, crazy.

Anyway, in this case, I think

>  #define for_each_active_iommu(i, drhd)					\
>  	list_for_each_entry(drhd, &dmar_drhd_units, list)		\
> -		if (i=drhd->iommu, drhd->ignored) {} else
> +		if (({i=drhd->iommu, drhd->ignored;})) {} else

Just do it like

	if ( (i=drhd->iommu, drhd->ignored) ) {} else

is still not pretty, but better than using ({..}) I think. And just a 
single set of parenthesis will protect the macro expansion.

But that '#define if(cond)' for the branch profiling is really the core 
problem there. Wow. I never realized quite _how_ ugly tricks it played.

		Linus
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