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

[Jeremy Fitzhardinge]

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@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Paul Mundt <lethal@xxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
---
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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