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| author | Dave Martin <dave.martin@linaro.org> | 2010-11-29 21:43:23 +0300 |
|---|---|---|
| committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2010-11-30 16:44:24 +0300 |
| commit | 077248fcce5edabb1b77ba3269e6c72341769d94 (patch) | |
| tree | 99a3ef92054ef39e63d39c56673f4db4c84c803d /arch/arm/boot | |
| parent | 7eb25ebee894ba2f8a591a83e45accc091ced19f (diff) | |
| download | linux-077248fcce5edabb1b77ba3269e6c72341769d94.tar.xz | |
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/arm/boot')
| -rw-r--r-- | arch/arm/boot/bootp/init.S | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/arm/boot/bootp/init.S b/arch/arm/boot/bootp/init.S index 8b0de41c3dcb..78b508075161 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 |