powerpc problem with .data.page_aligned -> __page_aligned_data conversion

Tim Abbott tabbott at ksplice.com
Fri Oct 16 03:37:20 EST 2009

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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