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arm64: switch to relative exception tables

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Instead of using absolute addresses for both the exception location
and the fixup, use offsets relative to the exception table entry values.
Not only does this cut the size of the exception table in half, it is
also a prerequisite for KASLR, since absolute exception table entries
are subject to dynamic relocation, which is incompatible with the sorting
of the exception table that occurs at build time.

This patch also introduces the _ASM_EXTABLE preprocessor macro (which
exists on x86 as well) and its _asm_extable assembly counterpart, as
shorthands to emit exception table entries.

Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Ard Biesheuvel
2016-01-01 15:02:12 +01:00
committed by Catalin Marinas
parent a272858a3c
commit 6c94f27ac8
8 changed files with 43 additions and 51 deletions
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7
arch/arm64/include/asm/word-at-a-time.h
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@@ -16,6 +16,8 @@
#ifndef __ASM_WORD_AT_A_TIME_H
#define __ASM_WORD_AT_A_TIME_H
#include <asm/uaccess.h>
#ifndef __AARCH64EB__
#include <linux/kernel.h>
@@ -81,10 +83,7 @@ static inline unsigned long load_unaligned_zeropad(const void *addr)
#endif
" b 2b\n"
" .popsection\n"
" .pushsection __ex_table,\"a\"\n"
" .align 3\n"
" .quad 1b, 3b\n"
" .popsection"
_ASM_EXTABLE(1b, 3b)
: "=&r" (ret), "=&r" (offset)
: "r" (addr), "Q" (*(unsigned long *)addr));