linux-kernel - Re: [PATCH V4 08/17] riscv: compat: syscall: Add compat_sys_call

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Date:   Sun, 30 Jan 2022 12:32:29 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Guo Ren <guoren@...nel.org>
Cc:     Arnd Bergmann <arnd@...db.de>, Palmer Dabbelt <palmer@...belt.com>,
        Anup Patel <anup@...infault.org>,
        gregkh <gregkh@...uxfoundation.org>,
        liush <liush@...winnertech.com>, Wei Fu <wefu@...hat.com>,
        Drew Fustini <drew@...gleboard.org>,
        Wang Junqiang <wangjunqiang@...as.ac.cn>,
        Christoph Hellwig <hch@....de>,
        Christoph Hellwig <hch@...radead.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        linux-csky@...r.kernel.org,
        linux-s390 <linux-s390@...r.kernel.org>,
        sparclinux <sparclinux@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Parisc List <linux-parisc@...r.kernel.org>,
        "open list:BROADCOM NVRAM DRIVER" <linux-mips@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Guo Ren <guoren@...ux.alibaba.com>
Subject: Re: [PATCH V4 08/17] riscv: compat: syscall: Add compat_sys_call_table
 implementation

On Sun, Jan 30, 2022 at 6:54 AM Guo Ren <guoren@...nel.org> wrote:
> On Sun, Jan 30, 2022 at 6:41 AM Arnd Bergmann <arnd@...db.de> wrote:
> >
> > I would make these endian-specific, and reverse them on big-endian
> > architectures. That way it
> > should be possible to share them across all compat architectures
> > without needing the override
> > option.
> I hope it could be another patch. Because it's not clear to
> _LITTLE_ENDIAN definition in archs.
>
> eg: Names could be __ORDER_LITTLE_ENDIAN__ CPU_LITTLE_ENDIAN
> SYS_SUPPORTS_LITTLE_ENDIAN __LITTLE_ENDIAN
>
> riscv is little-endian, but no any LITTLE_ENDIAN definition.
>
> So let's keep them in the patch, first, Thx

The correct way to do it is to check for CONFIG_CPU_BIG_ENDIAN,
which works on all architectures. Since nothing else selects the
__ARCH_WANT_COMPAT_* symbols, there is also no risk for
regressions, so just use this and leave the #ifndef compat_arg_u64
check in place.

      Arnd