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| author | Dave Martin <dave.martin@linaro.org> | 2010-11-29 19:43:24 +0100 |
|---|---|---|
| committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2010-11-30 14:44:24 +0100 |
| commit | 4f79a5dd7c3e316e2230dc0ee665c40a39023a81 (patch) | |
| tree | 38ba4294db39a53c40dda2540392eabaf98ae23e /arch/arm/kernel/head.S | |
| parent | ARM: 6499/1: Thumb-2: Correct data alignment for CONFIG_THUMB2_KERNEL in boot... (diff) | |
| download | linux-4f79a5dd7c3e316e2230dc0ee665c40a39023a81.tar.xz linux-4f79a5dd7c3e316e2230dc0ee665c40a39023a81.zip | |
ARM: 6500/1: Thumb-2: Correct data alignment for CONFIG_THUMB2_KERNEL in kernel/head.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/kernel/head.S')
| -rw-r--r-- | arch/arm/kernel/head.S | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S index dd6b369ac69c..591c097c89ab 100644 --- a/arch/arm/kernel/head.S +++ b/arch/arm/kernel/head.S @@ -262,6 +262,7 @@ __create_page_tables: mov pc, lr ENDPROC(__create_page_tables) .ltorg + .align __enable_mmu_loc: .long . .long __enable_mmu @@ -308,6 +309,8 @@ ENTRY(__secondary_switched) b secondary_start_kernel ENDPROC(__secondary_switched) + .align + .type __secondary_data, %object __secondary_data: .long . @@ -413,6 +416,7 @@ __fixup_smp_on_up: mov pc, lr ENDPROC(__fixup_smp) + .align 1: .word . .word __smpalt_begin .word __smpalt_end |