linux-kernel - Re: linux-next: build failure

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Message-ID: <alpine.LFD.1.10.0807290927240.3334@nehalem.linux-foundation.org>
Date:	Tue, 29 Jul 2008 09:33:10 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	David Miller <davem@...emloft.net>, linux-next@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Travis <travis@....com>
Subject: Re: linux-next: build failure

On Tue, 29 Jul 2008, Ingo Molnar wrote:
> 
> the fix is simple enough.
> 
> but the question is, wont it generate huge artificial stackframes with 
> CONFIG_MAXSMP and NR_CPUS=4096?

Quite the reverse.

The "address-of statement expression" is the one that is more likely to 
generate artificial stack-frames because of a temporary variable (of 
course, I wouldn't count on it, since statement expressions are gcc 
extensions, and as such the gcc people could make up any semantics they 
want to them, including just defining that a statement expression with 
an lvalue value is the same lvalue rather than any temporary). 

In contrast, "address-of lvalue" is _guaranteed_ to not do anything stupid 
like that, and gives just the address-of.

Oh, and I was wrong about the &*x losing the 'const'. It doesn't. So I 
think Stephen's patch is fine after all - if somebody tries to modify the 
end result through the pointer, it will give a big compiler warning.

			Linus
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