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build: add __page_aligned_data and __page_aligned_bss

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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: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Jeremy Fitzhardinge 2008-05-28 15:02:14 +01:00 committed by Ingo Molnar
parent 1ecd27657b
commit a7bf0bd5e6
3 changed files with 6 additions and 3 deletions
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2
arch/x86/kernel/setup64.c
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@ -40,7 +40,7 @@ EXPORT_SYMBOL(_cpu_pda);
struct desc_ptr idt_descr = { 256 * 16 - 1, (unsigned long) idt_table };
char boot_cpu_stack[IRQSTACKSIZE] __attribute__((section(".bss.page_aligned")));
char boot_cpu_stack[IRQSTACKSIZE] __page_aligned_bss;
unsigned long __supported_pte_mask __read_mostly = ~0UL;
EXPORT_SYMBOL_GPL(__supported_pte_mask);

3
arch/x86/mm/ioremap.c
View file

@ -394,8 +394,7 @@ static int __init early_ioremap_debug_setup(char *str)
early_param("early_ioremap_debug", early_ioremap_debug_setup);
static __initdata int after_paging_init;
static pte_t bm_pte[PAGE_SIZE/sizeof(pte_t)]
__section(.bss.page_aligned);
static pte_t bm_pte[PAGE_SIZE/sizeof(pte_t)] __page_aligned_bss;
static inline pmd_t * __init early_ioremap_pmd(unsigned long addr)
{

4
include/linux/linkage.h
View file

@ -1,6 +1,7 @@
#ifndef _LINUX_LINKAGE_H
#define _LINUX_LINKAGE_H
#include <linux/compiler.h>
#include <asm/linkage.h>
#ifdef __cplusplus
@ -17,6 +18,9 @@
# define asmregparm
#endif
#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
* untouched by the compiler by keeping them live until the end.