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SubjectRe: [PATCH 1/2] riscv: Add memmove string operation.
On Mon, 12 Aug 2019 08:04:46 PDT (-0700), Christoph Hellwig wrote:
> On Wed, Aug 07, 2019 at 03:19:14PM +0800, Nick Hu wrote:
>> There are some features which need this string operation for compilation,
>> like KASAN. So the purpose of this porting is for the features like KASAN
>> which cannot be compiled without it.
>> KASAN's string operations would replace the original string operations and
>> call for the architecture defined string operations. Since we don't have
>> this in current kernel, this patch provides the implementation.
>> This porting refers to the 'arch/nds32/lib/memmove.S'.
> This looks sensible to me, although my stringop asm is rather rusty,
> so just an ack and not a real review-by:
> Acked-by: Christoph Hellwig <>

FWIW, we just write this in C everywhere else and rely on the compiler to
unroll the loops. I always prefer C to assembly when possible, so I'd prefer
if we just adopt the string code from newlib. We have a RISC-V-specific memcpy
in there, but just use the generic memmove.

Maybe the best bet here would be to adopt the newlib memcpy/memmove as generic
Linux functions? They're both in C so they should be fine, and they both look
faster than what's in lib/string.c. Then everyone would benefit and we don't
need this tricky RISC-V assembly. Also, from the look of it the newlib code is
faster because the inner loop is unrolled.

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