diff options
author | Dave Martin <dave.martin@linaro.org> | 2010-11-29 13:43:24 -0500 |
---|---|---|
committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2010-11-30 08:44:24 -0500 |
commit | 4f79a5dd7c3e316e2230dc0ee665c40a39023a81 (patch) | |
tree | 38ba4294db39a53c40dda2540392eabaf98ae23e /arch | |
parent | 077248fcce5edabb1b77ba3269e6c72341769d94 (diff) |
ARM: 6500/1: Thumb-2: Correct data alignment for CONFIG_THUMB2_KERNEL in kernel/head.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.
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')
-rw-r--r-- | 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 dd6b369ac69c..591c097c89ab 100644 --- a/arch/arm/kernel/head.S +++ b/arch/arm/kernel/head.S | |||
@@ -262,6 +262,7 @@ __create_page_tables: | |||
262 | mov pc, lr | 262 | mov pc, lr |
263 | ENDPROC(__create_page_tables) | 263 | ENDPROC(__create_page_tables) |
264 | .ltorg | 264 | .ltorg |
265 | .align | ||
265 | __enable_mmu_loc: | 266 | __enable_mmu_loc: |
266 | .long . | 267 | .long . |
267 | .long __enable_mmu | 268 | .long __enable_mmu |
@@ -308,6 +309,8 @@ ENTRY(__secondary_switched) | |||
308 | b secondary_start_kernel | 309 | b secondary_start_kernel |
309 | ENDPROC(__secondary_switched) | 310 | ENDPROC(__secondary_switched) |
310 | 311 | ||
312 | .align | ||
313 | |||
311 | .type __secondary_data, %object | 314 | .type __secondary_data, %object |
312 | __secondary_data: | 315 | __secondary_data: |
313 | .long . | 316 | .long . |
@@ -413,6 +416,7 @@ __fixup_smp_on_up: | |||
413 | mov pc, lr | 416 | mov pc, lr |
414 | ENDPROC(__fixup_smp) | 417 | ENDPROC(__fixup_smp) |
415 | 418 | ||
419 | .align | ||
416 | 1: .word . | 420 | 1: .word . |
417 | .word __smpalt_begin | 421 | .word __smpalt_begin |
418 | .word __smpalt_end | 422 | .word __smpalt_end |