linux-kernel - Re: [PATCH for 3.12] mutex: Avoid gcc version dependent __builtin_constant

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Date:	Thu, 17 Oct 2013 13:02:15 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Maarten Lankhorst <maarten.lankhorst@...onical.com>
Cc:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	mingo@...nel.org, imirkin@...m.mit.edu,
	linux-kernel@...r.kernel.org, daniel.vetter@...ll.ch,
	robdclark@...il.com
Subject: Re: [PATCH for 3.12] mutex: Avoid gcc version dependent
 __builtin_constant_p() usage.

On Thu, Oct 17, 2013 at 12:54:21PM +0200, Maarten Lankhorst wrote:
> op 17-10-13 12:52, Peter Zijlstra schreef:
> > On Thu, Oct 17, 2013 at 07:45:29PM +0900, Tetsuo Handa wrote:
> >> Commit 040a0a37 "mutex: Add support for wound/wait style locks" used
> >> "!__builtin_constant_p(p == NULL)" but gcc 3.x cannot handle such expression
> >> correctly, leading to boot failure when built with CONFIG_DEBUG_MUTEXES=y.
> > So I completely forgot all about this, but wouldn't something like:
> >
> >  !(__builtin_constant_p(p) && p == NULL)
> >
> > Not also work and generate the same code?
> >
> See earlier discussion. It was already answered why that was undesirable. ;)

OK; I forgot if we covered that particular option.. I so hate this
patch; but I'm afraid we'll have to take it :-/
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