From mboxrd@z Thu Jan 1 00:00:00 1970 From: dave.martin@linaro.org (Dave Martin) Date: Tue, 16 Nov 2010 13:14:35 +0000 Subject: [PATCH 5/7] ARM: Thumb-2: Correct data alignment for CONFIG_THUMB2_KERNEL in mm/proc-v7.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: <1289913277-8822-5-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. In this specific case, we can achieve the desired alignment by forcing a 32-bit branch instruction using the W() macro, since the assembler location counter is already 32-bit aligned in this case. Applies cleanly on v2.6.37-rc1. Signed-off-by: Dave Martin Acked-by: Catalin Marinas Reviewed-by: Will Deacon --- arch/arm/mm/proc-v7.S | 4 ++-- 1 files changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/arm/mm/proc-v7.S b/arch/arm/mm/proc-v7.S index 53cbe22..9b9ff5d 100644 --- a/arch/arm/mm/proc-v7.S +++ b/arch/arm/mm/proc-v7.S @@ -381,7 +381,7 @@ __v7_ca9mp_proc_info: PMD_SECT_XN | \ PMD_SECT_AP_WRITE | \ PMD_SECT_AP_READ - b __v7_ca9mp_setup + W(b) __v7_ca9mp_setup .long cpu_arch_name .long cpu_elf_name .long HWCAP_SWP|HWCAP_HALF|HWCAP_THUMB|HWCAP_FAST_MULT|HWCAP_EDSP|HWCAP_TLS @@ -413,7 +413,7 @@ __v7_proc_info: PMD_SECT_XN | \ PMD_SECT_AP_WRITE | \ PMD_SECT_AP_READ - b __v7_setup + W(b) __v7_setup .long cpu_arch_name .long cpu_elf_name .long HWCAP_SWP|HWCAP_HALF|HWCAP_THUMB|HWCAP_FAST_MULT|HWCAP_EDSP|HWCAP_TLS -- 1.7.1