From: Nick Hu <nickhu@andestech.com>
To: Paul Walmsley <paul.walmsley@sifive.com>
Cc: "Palmer Dabbelt" <palmer@sifive.com>,
"Christoph Hellwig" <hch@infradead.org>,
"Alan Quey-Liang Kao(高魁良)" <alankao@andestech.com>,
"aou@eecs.berkeley.edu" <aou@eecs.berkeley.edu>,
"green.hu@gmail.com" <green.hu@gmail.com>,
"deanbo422@gmail.com" <deanbo422@gmail.com>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"linux-riscv@lists.infradead.org"
<linux-riscv@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"aryabinin@virtuozzo.com" <aryabinin@virtuozzo.com>,
"glider@google.com" <glider@google.com>,
"dvyukov@google.com" <dvyukov@google.com>,
"Anup Patel" <Anup.Patel@wdc.com>,
"Greg KH" <gregkh@linuxfoundation.org>,
"alexios.zavras@intel.com" <alexios.zavras@intel.com>,
"Atish Patra" <Atish.Patra@wdc.com>,
"離職Zong Zong-Xian Li(李宗憲)" <zong@andestech.com>,
"kasan-dev@googlegroups.com" <kasan-dev@googlegroups.com>
Subject: Re: [PATCH 1/2] riscv: Add memmove string operation.
Date: Thu, 15 Aug 2019 11:12:25 +0800 [thread overview]
Message-ID: <20190815031225.GA5666@andestech.com> (raw)
In-Reply-To: <alpine.DEB.2.21.9999.1908141002500.18249@viisi.sifive.com>
Hi Paul,
On Wed, Aug 14, 2019 at 10:03:39AM -0700, Paul Walmsley wrote:
> Hi Nick,
>
> On Wed, 14 Aug 2019, Nick Hu wrote:
>
> > On Wed, Aug 14, 2019 at 10:22:15AM +0800, Paul Walmsley wrote:
> > > 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:
> > > >
> > > > 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?
> >
> > KASAN has its own string operations(memcpy/memmove/memset) because it needs to
> > hook some code to check memory region. It would undefined the original string
> > operations and called the string operations with the prefix '__'. But the
> > generic string operations didn't declare with the prefix. Other archs with
> > KASAN support like arm64 and xtensa all have their own string operations and
> > defined with the prefix.
>
> Thanks for the explanation. What do you think about Palmer's idea to
> define a generic C set of KASAN string operations, derived from the newlib
> code?
>
>
> - Paul
That sounds good to me. But it should be another topic. We need to investigate
it further about replacing something generic and fundamental in lib/string.c
with newlib C functions. Some blind spots may exist. So I suggest, let's
consider KASAN for now.
Nick
next prev parent reply other threads:[~2019-08-15 3:13 UTC|newest]
Thread overview: 19+ 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
2019-08-14 3:27 ` Nick Hu
[not found] ` <alpine.DEB.2.21.9999.1908141002500.18249@viisi.sifive.com>
2019-08-15 3:12 ` Nick Hu [this message]
[not found] ` <alpine.DEB.2.21.9999.1908151124450.18249@viisi.sifive.com>
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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