linux-kernel - Re: powerpc problem with .data.page_aligned -> __page_aligned

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Message-ID: <alpine.DEB.1.10.0910151229340.25434@dr-wily.mit.edu>
Date:	Thu, 15 Oct 2009 12:37:20 -0400 (EDT)
From:	Tim Abbott <tabbott@...lice.com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
cc:	sam@...nborg.org, linuxppc-dev@...ts.ozlabs.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: powerpc problem with .data.page_aligned -> __page_aligned_data
 conversion

On Thu, 15 Oct 2009, Benjamin Herrenschmidt wrote:

> For some weird reason, our gcc until 4.3 (fixed in 4.3) had the weird
> idea that the alignment attribute should not be allowed to force an
> alignment greater than 32k. If attempted, it would warn -and- crop the
> alignment to 32k.
[...]
> This has a few issues for us:
> 
> 	- The patch that converted bits of powerpc to the new macro break since
> it now hits that bug

Hi Ben,

Just to make sure I understand the nature of the problem, is the current 
breakage that gcc < 4.3 will _warn_ on any compilation units on ppc64 that 
use __page_aligned data, or something worse?

The cropping is clearly a potential problem, but I read the rest of your 
email as saying that the cropping of the alignment isn't actually a 
problem with the current kernel because the kernel is currently only using 
the macro with things whose size is divisible by PAGE_SIZE.  However, I am 
not sure how to reconcile that with using the word "break" above...

	-Tim Abbott
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