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authorDave Martin <dave.martin@linaro.org>2010-11-29 19:43:25 +0100
committerRussell King <rmk+kernel@arm.linux.org.uk>2010-11-30 13:44:25 +0000
commit6323875db20fd8ca8c8fbbd608bc377f2d4c8cf5 (patch)
tree585f1108cc59a4a77b8fd0295be040726de750df
parent4f79a5dd7c3e316e2230dc0ee665c40a39023a81 (diff)
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ARM: 6501/1: Thumb-2: Correct data alignment for CONFIG_THUMB2_KERNEL in mm/proc-v7.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. 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. 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>
-rw-r--r--arch/arm/mm/proc-v7.S4
1 files changed, 2 insertions, 2 deletions
diff --git a/arch/arm/mm/proc-v7.S b/arch/arm/mm/proc-v7.S
index 53cbe222515..9b9ff5d949f 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