Re: [PATCH 2 of 3] memcpy32 for x86_64

[Matt Mackall <mpm@selenic.com>]

On Tue, Dec 27, 2005 at 03:41:56PM -0800, Bryan O'Sullivan wrote:
> Introduce an x86_64-specific memcpy32 routine.  The routine is similar
> to memcpy, but is guaranteed to work in units of 32 bits at a time.
> 
> Signed-off-by: Bryan O'Sullivan <bos@pathscale.com>
> 
> diff -r 7b7b442a4d63 -r 042b7d9004ac arch/x86_64/kernel/x8664_ksyms.c
> --- a/arch/x86_64/kernel/x8664_ksyms.c	Tue Dec 27 15:41:48 2005 -0800
> +++ b/arch/x86_64/kernel/x8664_ksyms.c	Tue Dec 27 15:41:48 2005 -0800
> @@ -150,6 +150,8 @@
>  extern void * memcpy(void *,const void *,__kernel_size_t);
>  extern void * __memcpy(void *,const void *,__kernel_size_t);
>  
> +extern void memcpy32(void *,const void *,__kernel_size_t);

It's better to do an include here. Duplicating prototypes in .c files
is frowned upon (despite the fact that it's already done here).

> +
>  EXPORT_SYMBOL(memset);
>  EXPORT_SYMBOL(strlen);
>  EXPORT_SYMBOL(memmove);
> @@ -164,6 +166,8 @@
>  EXPORT_SYMBOL(memcpy);
>  EXPORT_SYMBOL(__memcpy);
>  
> +EXPORT_SYMBOL_GPL(memcpy32);
> +

We've been steadily moving towards grouping EXPORTs with function
definitions. Do *_ksyms.c exist solely to provide exports for
functions defined in assembly at this point? If so, perhaps we ought
to come up with a suitable export macro for asm files.

> diff -r 7b7b442a4d63 -r 042b7d9004ac arch/x86_64/lib/memcpy32.S
> --- /dev/null	Thu Jan  1 00:00:00 1970 +0000
> +++ b/arch/x86_64/lib/memcpy32.S	Tue Dec 27 15:41:48 2005 -0800
> @@ -0,0 +1,25 @@
> +/*
> + * Copyright (c) 2003, 2004, 2005 PathScale, Inc.
> + */
> +
> +/*
> + * memcpy32 - Copy a memory block, 32 bits at a time.
> + *
> + * Count is number of dwords; it need not be a qword multiple.
> + * Input:
> + * rdi destination
> + * rsi source
> + * rdx count
> + */
> +
> + 	.globl memcpy32
> +memcpy32:
> +	movl %edx,%ecx
> +	shrl $1,%ecx
> +	andl $1,%edx
> +	rep
> +	movsq
> +	movl %edx,%ecx
> +	rep
> +	movsd
> +	ret

Any reason this needs its own .S file? One wonders if the

        .p2align 4

in memcpy.S is appropriate here too. Splitting rep movsq across two
lines is a little weird to me too, but I see Andi did it too.

-- 
Mathematics is the supreme nostalgia of our time.