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>

arch/arm/kernel/head.S

@@ -262,6 +262,7 @@ __create_page_tables:
 	mov	pc, lr
 ENDPROC(__create_page_tables)
 	.ltorg
+	.align
 __enable_mmu_loc:
 	.long	.
 	.long	__enable_mmu
@@ -308,6 +309,8 @@ ENTRY(__secondary_switched)
 	b	secondary_start_kernel
 ENDPROC(__secondary_switched)
 
+	.align
+
 	.type	__secondary_data, %object
 __secondary_data:
 	.long	.
@@ -413,6 +416,7 @@ __fixup_smp_on_up:
 	mov	pc, lr
 ENDPROC(__fixup_smp)
 
+	.align
 1:	.word	.
 	.word	__smpalt_begin
 	.word	__smpalt_end