Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20220227162831.674483-1-guoren@kernel.org> <20220227162831.674483-14-guoren@kernel.org>
 <CAJF2gTSJFMg1YJ=dbaNyemNV4sc_3P=+_PrS=RD_Y2_xz3TzPA@mail.gmail.com>
 <509d2b62-7d52-bf5c-7a6c-213a740a5c00@codethink.co.uk> <CAJF2gTSkrm+Ek5i--TTikR2RDBUa6Eo72jwvszbj3uZg=Kxorg@mail.gmail.com>
In-Reply-To: <CAJF2gTSkrm+Ek5i--TTikR2RDBUa6Eo72jwvszbj3uZg=Kxorg@mail.gmail.com>
From:   Arnd Bergmann <arnd@arndb.de>
Date:   Sat, 12 Mar 2022 09:36:18 +0100
Message-ID: <CAK8P3a0LqTdEk53XpUV4xRKoiJ_AvLkJSbMabqBgk7KNxF_XxQ@mail.gmail.com>
Subject: Re: [PATCH V7 13/20] riscv: compat: process: Add UXL_32 support in start_thread
To:     Guo Ren <guoren@kernel.org>
Cc:     Ben Dooks <ben.dooks@codethink.co.uk>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Anup Patel <anup@brainfault.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        liush <liush@allwinnertech.com>, Wei Fu <wefu@redhat.com>,
        Drew Fustini <drew@beagleboard.org>,
        Wang Junqiang <wangjunqiang@iscas.ac.cn>,
        Christoph Hellwig <hch@lst.de>,
        linux-arch <linux-arch@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-riscv <linux-riscv@lists.infradead.org>,
        linux-csky@vger.kernel.org,
        linux-s390 <linux-s390@vger.kernel.org>,
        sparclinux <sparclinux@vger.kernel.org>,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
        Parisc List <linux-parisc@vger.kernel.org>,
        "open list:BROADCOM NVRAM DRIVER" <linux-mips@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        Guo Ren <guoren@linux.alibaba.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Sat, Mar 12, 2022 at 3:13 AM Guo Ren <guoren@kernel.org> wrote:
> On Fri, Mar 11, 2022 at 9:38 PM Ben Dooks <ben.dooks@codethink.co.uk> wrote:
> > On 11/03/2022 02:38, Guo Ren wrote:
> > >> --- a/arch/riscv/kernel/process.c
> > >> +++ b/arch/riscv/kernel/process.c
> > >> @@ -97,6 +97,11 @@ void start_thread(struct pt_regs *regs, unsigned long pc,
> > >>          }
> > >>          regs->epc = pc;
> > >>          regs->sp = sp;
> > >> +
> > > FIxup:
> > >
> > > + #ifdef CONFIG_COMPAT
> > >> +       if (is_compat_task())
> > >> +               regs->status = (regs->status & ~SR_UXL) | SR_UXL_32;
> > >> +       else
> > >> +               regs->status = (regs->status & ~SR_UXL) | SR_UXL_64;
> > > + #endif
> > >
> > > We still need "#ifdef CONFIG_COMPAT" here, because for rv32 we can't
> > > set SR_UXL at all. SR_UXL is BIT[32, 33].
> >
> > would an if (IS_ENABLED(CONFIG_COMPAT)) { } around the lot be better
> > than an #ifdef here?
>
> I don't think, seems #ifdef CONFIG_COMPAT is more commonly used in arch/*

We used to require an #ifdef check around is_compat_task(), so there are
a lot of stale #ifdefs that could be removed. In general, 'if (IS_ENABLED())'
is considered more readable than #ifdef inside of a function. In this case
there are a number of better ways to write the function if you want to get
into the details:

 - firstly, you should remove the #ifdef check around the definition of
   SR_UXL, otherwise the IS_ENABLED() check does not work.

 - you can use an 'if (!IS_ENABLED(CONFIG_COMPAT)) \\ return;' ahead of the
   assignment since that is at the end of  the function.

 - you can remove the bit masking since 'regs->status' is initialized above it,
   adding in only the one bit, shortening it to

    if (IS_ENABLED(CONFIG_COMPAT))
               regs->status |= is_compat_task()) ? SR_UXL_32 : SR_UXL_64;

 - to make this more logical, I would suggest always assigning the SR_UXL
   bits regardless of CONFIG_COMPAT, and instead make it something like

  if (IS_ENABLED(CONFIG_32BIT) || is_compat_task())
            regs->status = | SR_UXL_32;
  else
            regs->status = | SR_UXL_64;

       Arnd