linux-kernel - [PATCH 1/2] make page-aligned data and bss less fragile

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Message-ID: <483EB37F.7090902@goop.org>
Date:	Thu, 29 May 2008 14:45:35 +0100
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	x86@...nel.org
Subject: [PATCH 1/2] make page-aligned data and bss less fragile

Making a variable page-aligned by using
__attribute__((section(".data.page_aligned"))) is fragile because if
sizeof(variable) is not also a multiple of page size, it leaves
variables in the remainder of the section unaligned.

This patch introduces two new qualifiers, __page_aligned_data and
__page_aligned_bss to set the section *and* the alignment of
variables.  This makes page-aligned variables more robust because the
linker will make sure they're aligned properly.  Unfortunately it
requires *all* page-aligned data to use these macros...

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Paul Mundt <lethal@...ux-sh.org>
Cc: Paul Mackerras <paulus@...ba.org>
---
 include/linux/linkage.h |    8 ++++++++
 1 file changed, 8 insertions(+)

===================================================================
--- a/include/linux/linkage.h
+++ b/include/linux/linkage.h
@@ -1,6 +1,7 @@
 #ifndef _LINUX_LINKAGE_H
 #define _LINUX_LINKAGE_H
 
+#include <linux/compiler.h>
 #include <asm/linkage.h>
 
 #define notrace __attribute__((no_instrument_function))
@@ -18,6 +19,13 @@
 #ifndef asmregparm
 # define asmregparm
 #endif
+
+/*
+ * Mark a variable page aligned, and put it in an appropriate page
+ * aligned section.
+ */
+#define __page_aligned_data	__section(.data.page_aligned) __aligned(PAGE_SIZE)
+#define __page_aligned_bss	__section(.bss.page_aligned) __aligned(PAGE_SIZE)
 
 /*
  * This is used by architectures to keep arguments on the stack


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