Messages in this thread | | | Date | Tue, 13 Aug 2019 19:22:15 -0700 (PDT) | From | Paul Walmsley <> | Subject | Re: [PATCH 1/2] riscv: Add memmove string operation. |
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On Tue, 13 Aug 2019, Palmer Dabbelt wrote:
> 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.
There's a generic memmove implementation in the kernel already:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/string.h#n362
Nick, could you tell us more about why the generic memmove() isn't suitable?
- Paul
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