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

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Message-Id: <201310182151.AGF16889.SQOFJOtVLFFMHO@I-love.SAKURA.ne.jp>
Date:	Fri, 18 Oct 2013 21:51:04 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	mingo@...nel.org
Cc:	peterz@...radead.org, maarten.lankhorst@...onical.com,
	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.

Peter Zijlstra wrote:
> 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 :-/
> 

I see. Ingo, would you send this patch via your tree?
Then, I'll post a patch for 3.11-stable which differs white spaces.
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