From 4f79a5dd7c3e316e2230dc0ee665c40a39023a81 Mon Sep 17 00:00:00 2001 From: Dave Martin Date: Mon, 29 Nov 2010 19:43:24 +0100 Subject: 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 Signed-off-by: Dave Martin Acked-by: Catalin Marinas Signed-off-by: Russell King --- arch/arm/kernel/head.S | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'arch') 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 -- cgit v1.2.3