From mboxrd@z Thu Jan 1 00:00:00 1970 From: dave.martin@linaro.org (Dave Martin) Date: Tue, 16 Nov 2010 13:14:34 +0000 Subject: [PATCH 4/7] ARM: Thumb-2: Correct data alignment for CONFIG_THUMB2_KERNEL in kernel/head.S In-Reply-To: <1289913277-8822-1-git-send-email-dave.martin@linaro.org> References: <1289913277-8822-1-git-send-email-dave.martin@linaro.org> Message-ID: <1289913277-8822-4-git-send-email-dave.martin@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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. Applies cleanly on v2.6.37-rc1. Signed-off-by: Dave Martin Acked-by: Catalin Marinas Reviewed-by: Will Deacon --- 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 dd6b369..591c097 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 -- 1.7.1