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Date:   Tue, 13 Aug 2019 16:50:58 -0700 (PDT)
Subject:     Re: [PATCH 1/2] riscv: Add memmove string operation.
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CC:     nickhu@andestech.com, alankao@andestech.com,
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        Atish Patra <Atish.Patra@wdc.com>, zong@andestech.com,
        kasan-dev@googlegroups.com
From:   Palmer Dabbelt <palmer@sifive.com>
To:     Christoph Hellwig <hch@infradead.org>
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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 <hch@lst.de>

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.