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authorDave Martin <dave.martin@linaro.org>2010-11-29 19:43:24 +0100
committerRussell King <rmk+kernel@arm.linux.org.uk>2010-11-30 13:44:24 +0000
commit4f79a5dd7c3e316e2230dc0ee665c40a39023a81 (patch)
tree38ba4294db39a53c40dda2540392eabaf98ae23e
parent077248fcce5edabb1b77ba3269e6c72341769d94 (diff)
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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>
-rw-r--r--arch/arm/kernel/head.S4
1 files changed, 4 insertions, 0 deletions
diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
index dd6b369ac69..591c097c89a 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