path: root/arch
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authorDave Martin <dave.martin@linaro.org>2010-11-30 13:05:10 +0100
committerRussell King <rmk+kernel@arm.linux.org.uk>2010-11-30 13:44:27 +0000
commit618d9c8f9e554b5eaaca3f8e55a28e1a928a8571 (patch)
treeeed55141c126d49aca9a5299e629f78d991ef07e /arch
parent725ca4adaea07460accd4622d44bcc7eaa34da09 (diff)
ARM: 6508/1: vexpress: Correct data alignment in headsmp.S for CONFIG_THUMB2_KERNEL
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')
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/arm/mach-vexpress/headsmp.S b/arch/arm/mach-vexpress/headsmp.S
index 8a78ff68e1e..7a3f0632947 100644
--- a/arch/arm/mach-vexpress/headsmp.S
+++ b/arch/arm/mach-vexpress/headsmp.S
@@ -35,5 +35,6 @@ pen: ldr r7, [r6]
b secondary_startup
+ .align
1: .long .
.long pen_release