linux-kernel - Re: [RFC] [PATCH 2/16] x86_64: Assembly safe page.h and pgtable.h

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Date:	Mon, 13 Nov 2006 19:41:17 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Andi Kleen <ak@...e.de>
Cc:	vgoyal@...ibm.com,
	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	Reloc Kernel List <fastboot@...ts.osdl.org>, akpm@...l.org,
	hpa@...or.com, magnus.damm@...il.com, lwang@...hat.com,
	dzickus@...hat.com
Subject: Re: [RFC] [PATCH 2/16] x86_64: Assembly safe page.h and pgtable.h

Andi Kleen <ak@...e.de> writes:

>> 
>> I think we need these UL suffixes. Otherwise in some cases overflow
>> can take place and compiler emits warning.
>> 
>> For ex. in following definition I got rid of UL.
>> 
>> #define PGDIR_SIZE      (1 << PGDIR_SHIFT) 
>
> Yes for the shifts it is needed, but not for the unshifted constants.
> I think. At least when they're hex the compiler should chose the right
> type on its own.

Only if the high bit is set.  But it should chose a big enough type.
However there is no reason to play games and possibly out smart ourselves.
That is the point of the _AC() macro.  It adds the suffix only for
C code, and drops it for assembly.

Eric
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