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authorDave Martin <dave.martin@linaro.org>2010-11-29 19:43:23 +0100
committerRussell King <rmk+kernel@arm.linux.org.uk>2010-11-30 13:44:24 +0000
commit077248fcce5edabb1b77ba3269e6c72341769d94 (patch)
tree99a3ef92054ef39e63d39c56673f4db4c84c803d /arch
parent7eb25ebee894ba2f8a591a83e45accc091ced19f (diff)
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ARM: 6499/1: Thumb-2: Correct data alignment for CONFIG_THUMB2_KERNEL in bootp/init.S
Directives such as .long and .word do not magically cause the assembler location counter to become aligned in gas. As a result, using these directives in code sections can result in misaligned data words when building a Thumb-2 kernel (CONFIG_THUMB2_KERNEL). This is a Bad Thing, since the ABI permits the compiler to assume that fundamental types of word size or above are word- aligned when accessing them from C. If the data is not really word-aligned, this can cause impaired performance and stray alignment faults in some circumstances. In general, the following rules should be applied when using data word declaration directives inside code sections: * .quad and .double: .align 3 * .long, .word, .single, .float: .align (or .align 2) * .short: No explicit alignment required, since Thumb-2 instructions are always 2 or 4 bytes in size. immediately after an instruction. Reviewed-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Dave Martin <dave.martin@linaro.org> Acked-by: Catalin Marinas <catalin.marinas@arm.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'arch')
-rw-r--r--arch/arm/boot/bootp/init.S2
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/arm/boot/bootp/init.S b/arch/arm/boot/bootp/init.S
index 8b0de41c3dc..78b50807516 100644
--- a/arch/arm/boot/bootp/init.S
+++ b/arch/arm/boot/bootp/init.S
@@ -73,6 +73,8 @@ move: ldmia r4!, {r7 - r10} @ move 32-bytes at a time
.size _start, . - _start
+ .align
+
.type data,#object
data: .word initrd_start @ source initrd address
.word initrd_phys @ destination initrd address