From: Dave Martin Date: Tue, 30 Nov 2010 12:04:36 +0000 (+0100) Subject: ARM: 6507/1: RealView: Correct data alignment in headsmp.S for CONFIG_THUMB2_KERNEL X-Git-Tag: firefly_0821_release~7613^2~3283^2~7 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=725ca4adaea07460accd4622d44bcc7eaa34da09;p=firefly-linux-kernel-4.4.55.git ARM: 6507/1: RealView: 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: Will Deacon Signed-off-by: Dave Martin Acked-by: Catalin Marinas Signed-off-by: Russell King --- diff --git a/arch/arm/mach-realview/headsmp.S b/arch/arm/mach-realview/headsmp.S index 4075473cf68a..b34be4554d40 100644 --- a/arch/arm/mach-realview/headsmp.S +++ b/arch/arm/mach-realview/headsmp.S @@ -35,5 +35,6 @@ pen: ldr r7, [r6] */ b secondary_startup + .align 1: .long . .long pen_release