From mboxrd@z Thu Jan 1 00:00:00 1970 From: dave.martin@linaro.org (Dave Martin) Date: Tue, 16 Nov 2010 13:14:32 +0000 Subject: [PATCH 2/7] ARM: vfp: Correct data alignment for CONFIG_THUMB2_KERNEL 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: <1289913277-8822-2-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/vfp/vfphw.S | 1 + 1 files changed, 1 insertions(+), 0 deletions(-) diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S index d66cead..9897dcf 100644 --- a/arch/arm/vfp/vfphw.S +++ b/arch/arm/vfp/vfphw.S @@ -206,6 +206,7 @@ ENTRY(vfp_save_state) mov pc, lr ENDPROC(vfp_save_state) + .align last_VFP_context_address: .word last_VFP_context -- 1.7.1