Commit 618d9c8f authored by Dave Martin's avatar Dave Martin Committed by Russell King

ARM: 6508/1: vexpress: Correct data alignment in headsmp.S for CONFIG_THUMB2_KERNEL

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: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarDave Martin <dave.martin@linaro.org>
Acked-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
parent 725ca4ad
...@@ -35,5 +35,6 @@ pen: ldr r7, [r6] ...@@ -35,5 +35,6 @@ pen: ldr r7, [r6]
*/ */
b secondary_startup b secondary_startup
.align
1: .long . 1: .long .
.long pen_release .long pen_release
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