From: Paul Walmsley <paul.walmsley@sifive.com>
To: Palmer Dabbelt <palmer@sifive.com>
Cc: zong@andestech.com, aou@eecs.berkeley.edu, nickhu@andestech.com,
alankao@andestech.com, Atish Patra <Atish.Patra@wdc.com>,
Greg KH <gregkh@linuxfoundation.org>,
Anup Patel <Anup.Patel@wdc.com>,
linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com,
Christoph Hellwig <hch@infradead.org>,
alexios.zavras@intel.com, glider@google.com, green.hu@gmail.com,
aryabinin@virtuozzo.com, tglx@linutronix.de, deanbo422@gmail.com,
linux-riscv@lists.infradead.org, dvyukov@google.com
Subject: Re: [PATCH 1/2] riscv: Add memmove string operation.
Date: Tue, 13 Aug 2019 19:22:15 -0700 (PDT) [thread overview]
Message-ID: <alpine.DEB.2.21.9999.1908131921180.19217@viisi.sifive.com> (raw)
In-Reply-To: <mhng-ba92c635-7087-4783-baa5-2a111e0e2710@palmer-si-x1e>
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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next prev parent reply other threads:[~2019-08-14 2:22 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-07 7:19 [PATCH 0/2] KASAN support for RISC-V Nick Hu
2019-08-07 7:19 ` [PATCH 1/2] riscv: Add memmove string operation Nick Hu
2019-08-12 15:04 ` Christoph Hellwig
2019-08-13 23:50 ` Palmer Dabbelt
2019-08-14 2:22 ` Paul Walmsley [this message]
2019-08-14 3:27 ` Nick Hu
2019-08-14 17:03 ` Paul Walmsley
2019-08-15 3:12 ` Nick Hu
2019-08-15 18:27 ` Paul Walmsley
2019-08-19 6:29 ` Nick Hu
2019-08-14 18:33 ` Palmer Dabbelt
2019-08-22 15:59 ` Andrey Ryabinin
2019-08-27 9:07 ` Nick Hu
2019-08-27 9:33 ` Andrey Ryabinin
2019-08-28 3:06 ` Nick Hu
2019-08-07 7:19 ` [PATCH 2/2] riscv: Add KASAN support Nick Hu
2019-08-12 15:10 ` Christoph Hellwig
2019-08-14 7:44 ` Nick Hu
2019-08-22 17:08 ` Andrey Ryabinin
2019-09-03 15:08 ` Daniel Axtens
2019-09-04 2:24 ` Nick Hu
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