• Dave Martin's avatar
    ARM: 6507/1: RealView: Correct data alignment in headsmp.S for CONFIG_THUMB2_KERNEL · 725ca4ad
    Dave Martin authored
    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>
    725ca4ad
headsmp.S 906 Bytes