linux-kernel - Re: [patch 2/8] compiler-gcc.h: add more comments to RELOC

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Date:	Wed, 14 Jan 2009 19:33:32 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Rusty Russell <rusty@...tcorp.com.au>
cc:	Christoph Lameter <cl@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, akpm@...ux-foundation.org,
	andi@...stfloor.org, ak@...ux.intel.com, rth@...ddle.net,
	sfr@...b.auug.org.au, travis@....com, linux-kernel@...r.kernel.org
Subject: Re: [patch 2/8] compiler-gcc.h: add more comments to RELOC_HIDE



On Thu, 15 Jan 2009, Rusty Russell wrote:

> On Tuesday 13 January 2009 04:03:49 Christoph Lameter wrote:
> > But that is not what is occurring. We do not do &var + LARGE_OFFSET.
> > Instead one does
> > 
> > 	((void *)&var) + LARGE_OFFSET
> > 
> > or
> > 	((unsigned long)&var) + LARGE_OFFSET
> > 
> > The cast should cause the C compiler to drop all assumptions about size.
> 
> No, and that's the point.  Sorry, at this point you need to talk to a gcc expert.  As I have said, I did and I believe what he told me.

Yeah, I personally believe in the "should cause the C compiler" part, but 
gcc doesn't work that way. It will remember where the value came from, 
even when the pointer has been cast to something else.

			Linus
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