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| author | Dave Martin <dave.martin@linaro.org> | 2010-11-29 21:43:25 +0300 |
|---|---|---|
| committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2010-11-30 16:44:25 +0300 |
| commit | 6323875db20fd8ca8c8fbbd608bc377f2d4c8cf5 (patch) | |
| tree | 585f1108cc59a4a77b8fd0295be040726de750df /arch/arm | |
| parent | 4f79a5dd7c3e316e2230dc0ee665c40a39023a81 (diff) | |
| download | linux-6323875db20fd8ca8c8fbbd608bc377f2d4c8cf5.tar.xz | |
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>
Diffstat (limited to 'arch/arm')
| -rw-r--r-- | 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 53cbe2225153..9b9ff5d949fd 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 |