linux-kernel - Fix for asm warning in head

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Message-ID: <20080602212106.GA25959@tsunami.ccur.com>
Date:	Mon, 2 Jun 2008 17:21:06 -0400
From:	Joe Korty <joe.korty@...r.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Hugh Dickins <hugh@...itas.com>, Theodore Tso <tytso@....edu>,
	Gabriel C <nix.or.die@...glemail.com>,
	Keith Packard <keithp@...thp.com>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Eric Anholt <eric@...olt.net>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	bugme-daemon@...zilla.kernel.org, airlied@...ux.ie,
	"Barnes, Jesse" <jesse.barnes@...el.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Fix for asm warning in head_32.S

On Mon, May 19, 2008 at 04:10:02PM -0700, Linus Torvalds wrote:
> It also causes these warnings on 32-bit PAE:
> 
> 	  AS      arch/x86/kernel/head_32.o
> 	arch/x86/kernel/head_32.S: Assembler messages:
> 	arch/x86/kernel/head_32.S:225: Warning: left operand is a bignum; integer 0 assumed
> 	arch/x86/kernel/head_32.S:609: Warning: left operand is a bignum; integer 0 assumed
> 
> and I do not see why (the end result seems to be identical).



Fix head_32.S gcc bignum warnings when CONFIG_PAE=y.

    arch/x86/kernel/head_32.S: Assembler messages:
    arch/x86/kernel/head_32.S:225: Warning: left operand is a bignum; integer 0 assumed
    arch/x86/kernel/head_32.S:609: Warning: left operand is a bignum; integer 0 assumed

The assembler was stumbling over the 64-bit constant 0x100000000 in the
KPMDS #define.

Testing: a cmp(1) on head_32.o before and after shows the binary is unchanged.

Signed-off-by: Joe Korty <joe.korty@...r.com

Index: a/arch/x86/kernel/head_32.S
===================================================================
--- a.orig/arch/x86/kernel/head_32.S	2008-06-02 16:51:20.000000000 -0400
+++ a/arch/x86/kernel/head_32.S	2008-06-02 16:54:05.000000000 -0400
@@ -189,7 +189,7 @@
 	 * this stage.
 	 */
 
-#define KPMDS ((0x100000000-__PAGE_OFFSET) >> 30) /* Number of kernel PMDs */
+#define KPMDS (((-__PAGE_OFFSET) >> 30) & 3) /* Number of kernel PMDs */
 
 	xorl %ebx,%ebx				/* %ebx is kept at zero */
 
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