[PATCH] ARM: mxc: Correct data alignment in headsmp.S for CONFIG_THUMB2_KERNEL

Dave Martin dave.martin at linaro.org
Tue Nov 16 08:13:37 EST 2010

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

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.

Applies cleanly on v2.6.37-rc1.

Signed-off-by: Dave Martin <dave.martin at linaro.org>
 arch/arm/plat-mxc/ssi-fiq.S |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/arch/arm/plat-mxc/ssi-fiq.S b/arch/arm/plat-mxc/ssi-fiq.S
index 4ddce56..8397a2d 100644
--- a/arch/arm/plat-mxc/ssi-fiq.S
+++ b/arch/arm/plat-mxc/ssi-fiq.S
@@ -124,6 +124,8 @@ imx_ssi_fiq_start:
 		@ return from FIQ
 		subs	pc, lr, #4
+		.align
 		.word 0x0

More information about the linux-arm-kernel mailing list