From: Guo Ren <guoren@kernel.org>
To: Jisheng Zhang <jszhang3@mail.ustc.edu.cn>
Cc: "Arnd Bergmann" <arnd@arndb.de>,
"Palmer Dabbelt" <palmer@dabbelt.com>,
"Anup Patel" <anup.patel@wdc.com>,
gregkh <gregkh@linuxfoundation.org>,
liush <liush@allwinnertech.com>, "Wei Fu" <wefu@redhat.com>,
"Drew Fustini" <drew@beagleboard.org>,
"Wang Junqiang" <wangjunqiang@iscas.ac.cn>,
"Wei Wu (吴伟)" <lazyparser@gmail.com>,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
linux-riscv <linux-riscv@lists.infradead.org>,
linux-csky@vger.kernel.org, "Guo Ren" <guoren@linux.alibaba.com>
Subject: Re: [PATCH 00/13] riscv: compat: Add COMPAT mode support for rv64
Date: Sun, 26 Dec 2021 20:38:23 +0800 [thread overview]
Message-ID: <CAJF2gTRHND1F_-5+Euzy-UdRRdg2oAXDY4dt8_5p9JxsHDSe6Q@mail.gmail.com> (raw)
In-Reply-To: <20211226162223.795f9417@xhacker>
On Sun, Dec 26, 2021 at 4:36 PM Jisheng Zhang <jszhang3@mail.ustc.edu.cn> wrote:
>
> On Wed, 22 Dec 2021 20:59:30 +0800
> Guo Ren <guoren@kernel.org> wrote:
>
> > On Wed, Dec 22, 2021 at 2:10 AM Arnd Bergmann <arnd@arndb.de> wrote:
> > >
> > > On Tue, Dec 21, 2021 at 5:35 PM <guoren@kernel.org> wrote:
> > > >
> > > > From: Guo Ren <guoren@linux.alibaba.com>
> > > >
> > > > Currently, most 64-bit architectures (x86, parisc, powerpc, arm64,
> > > > s390, mips, sparc) have supported COMPAT mode. But they all have
> > > > history issues and can't use standard linux unistd.h. RISC-V would
> > > > be first standard __SYSCALL_COMPAT user of include/uapi/asm-generic
> > > > /unistd.h.
> > > >
> > > > The patchset are based on v5.16-rc6, you can compare rv64-compat32
> > > > v.s. rv32-whole in qemu with following step:
> > >
> > > Looks good overall, see my individual replies for minor comments I had.
> > Thx for the review :)
> >
> > >
> > > I think there is a bigger question to answer though, which is whether this is
> > > actually a useful feature for rv64. In general, there are two reasons for
> > > wanting compat mode:
> > >
> > > a) compatibility with existing binaries and distros
> > >
> > > b) reducing the memory footprint of user space in a memory constrained
> > > environment, either deeply embedded or in a container.
> > >
> > > For the other architectures, a) is clearly the main driver, but equally so
> > > this is not the case on riscv, which does not have any legacy 32-bit
> > > code. Without that, adding compat mode would mainly introduce a
> > > second ABI to a lot of environments that at the moment only need to
> > > support one, and that adds complexity to the implementation and
> > > the extra attack surface of the second syscall ABI when an exploit
> > > may be possible only in compat mode.
> > >
> > > There is still some benefit in b), but it would need to be weighed
> > > against the downsides above. Can you explain in more detail what
> > > use cases you have in mind, and which CPU cores actually support
> > > this mode?
> > The most reason is about b), see our customer's product:
> > https://www.cnx-software.com/2021/10/25/allwinner-d1s-f133-risc-v-processor-64mb-ddr2/
> >
> > So I think all our next generation rv64 cores should support
> > compat-mode. Compare to releasing rv32-full core, rv64 compat-mode is
> > very cheap for our CPU design.
> >
> > You would get the answer when our new generation CPU is announced and it's soon.
> >
>
> What about adding RV64 ILP32 support instead? This don't need HW side
> modifications so can benefit all RV64.
ILP32 is another topic in C Language Data Type Models and it couldn't
replace the standard rv32 ecosystem.
COMPAT is a common framework in Linux (7 arches have been supported),
so let rv64 support COMPAT mode is considerable.
Customers would choose ILP32 / RV32-compat by themself and that
depends on which one has a better ecosystem.
>
> Thanks
>
> > Currently, only qemu supports rv64 compact mode, that is my colleague
> > (LIU Zhi Wei) contributed.
>
--
Best Regards
Guo Ren
ML: https://lore.kernel.org/linux-csky/
next prev parent reply other threads:[~2021-12-26 12:38 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-21 16:35 [PATCH 00/13] riscv: compat: Add COMPAT mode support for rv64 guoren
2021-12-21 16:35 ` [PATCH 01/13] syscalls: compat: Fix the missing part for __SYSCALL_COMPAT guoren
2021-12-21 17:08 ` Arnd Bergmann
2021-12-22 11:16 ` Guo Ren
2021-12-22 11:24 ` Arnd Bergmann
2021-12-24 6:52 ` Christoph Hellwig
2021-12-21 16:35 ` [PATCH 02/13] riscv: Fixup difference with defconfig guoren
2021-12-21 17:09 ` Arnd Bergmann
2021-12-22 11:34 ` Guo Ren
2021-12-22 11:44 ` Arnd Bergmann
2021-12-22 13:06 ` Guo Ren
2021-12-22 13:30 ` Arnd Bergmann
2021-12-23 2:12 ` Guo Ren
2021-12-21 16:35 ` [PATCH 03/13] riscv: compat: Add basic compat date type implementation guoren
2021-12-21 17:12 ` Arnd Bergmann
2021-12-22 12:03 ` Guo Ren
2021-12-22 12:46 ` Arnd Bergmann
2021-12-26 15:33 ` Guo Ren
2021-12-24 6:53 ` Christoph Hellwig
2021-12-24 9:28 ` Guo Ren
2021-12-21 16:35 ` [PATCH 04/13] riscv: compat: Re-implement TASK_SIZE for COMPAT_32BIT guoren
2021-12-21 16:35 ` [PATCH 05/13] riscv: compat: syscall: Add compat_sys_call_table implementation guoren
2021-12-21 17:15 ` Arnd Bergmann
2021-12-22 12:43 ` Guo Ren
2021-12-22 13:21 ` Arnd Bergmann
2021-12-22 14:00 ` Arnd Bergmann
2021-12-24 9:42 ` Guo Ren
2021-12-21 16:35 ` [PATCH 06/13] riscv: compat: syscall: Add entry.S implementation guoren
2021-12-21 16:35 ` [PATCH 07/13] riscv: compat: Add elf.h implementation guoren
2021-12-21 16:35 ` [PATCH 08/13] riscv: compat: Add COMPAT Kbuild skeletal support guoren
2021-12-21 17:21 ` Arnd Bergmann
2021-12-22 12:06 ` Guo Ren
2021-12-24 6:54 ` Christoph Hellwig
2021-12-21 16:35 ` [PATCH 09/13] riscv: compat: init: Add hw-cap detect in setup_arch guoren
2021-12-21 16:35 ` [PATCH 10/13] riscv: compat: vdso: Add rv32 VDSO base code implementation guoren
2021-12-21 16:35 ` [PATCH 11/13] riscv: compat: vdso: Add setup additional pages implementation guoren
2021-12-21 16:35 ` [PATCH 12/13] riscv: compat: signal: Add rt_frame implementation guoren
2021-12-21 16:35 ` [PATCH 13/13] riscv: compat: ptrace: Add compat_arch_ptrace implement guoren
2021-12-21 17:38 ` [PATCH 00/13] riscv: compat: Add COMPAT mode support for rv64 Arnd Bergmann
2021-12-22 12:59 ` Guo Ren
2021-12-22 13:29 ` Arnd Bergmann
2021-12-26 8:22 ` Jisheng Zhang
2021-12-26 12:38 ` Guo Ren [this message]
2021-12-26 20:31 ` Arnd Bergmann
2021-12-27 1:16 ` Guo Ren
2021-12-27 2:29 ` Jessica Clarke
2021-12-28 10:45 ` Guo Ren
2021-12-22 12:00 ` Guo Ren
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