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From:   Guo Ren <guoren@kernel.org>
Date:   Wed, 23 Feb 2022 17:21:59 +0800
Message-ID: <CAJF2gTQd_5Ei9RDUg5uYAAjf0+idCqUtxdemb0CEMsxq7m3+UA@mail.gmail.com>
Subject: Re: [PATCH V5 13/21] riscv: compat: process: Add UXL_32 support in start_thread
To:     Palmer Dabbelt <palmer@dabbelt.com>
Cc:     Arnd Bergmann <arnd@arndb.de>, Anup Patel <anup@brainfault.org>,
        Greg KH <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>
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On Wed, Feb 23, 2022 at 9:42 AM Palmer Dabbelt <palmer@dabbelt.com> wrote:
>
> On Tue, 01 Feb 2022 07:05:37 PST (-0800), guoren@kernel.org wrote:
> > From: Guo Ren <guoren@linux.alibaba.com>
> >
> > If the current task is in COMPAT mode, set SR_UXL_32 in status for
> > returning userspace. We need CONFIG _COMPAT to prevent compiling
> > errors with rv32 defconfig.
> >
> > Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> > Signed-off-by: Guo Ren <guoren@kernel.org>
> > Cc: Arnd Bergmann <arnd@arndb.de>
> > Cc: Palmer Dabbelt <palmer@dabbelt.com>
> > ---
> >  arch/riscv/kernel/process.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
> > index 03ac3aa611f5..1a666ad299b4 100644
> > --- a/arch/riscv/kernel/process.c
> > +++ b/arch/riscv/kernel/process.c
> > @@ -97,6 +97,11 @@ void start_thread(struct pt_regs *regs, unsigned lon=
g pc,
> >       }
> >       regs->epc =3D pc;
> >       regs->sp =3D sp;
> > +
> > +#ifdef CONFIG_COMPAT
> > +     if (is_compat_task())
> > +             regs->status |=3D SR_UXL_32;
>
> Not sure if I'm just misunderstanding the bit ops here, but aren't we
> trying to set the UXL field to 1 (for UXL=3D32)?  That should be a bit
> field set op, not just an OR.
You are right, I would modify like this:
+     if (is_compat_task())
+             regs->status =3D =EF=BC=88regs->status & ~SR_UXL) | SR_UXL_32=
;
+     else
+.            regs->status =3D =EF=BC=88regs->status & ~SR_UXL) | SR_UXL_64=
;


>
> > +#endif
> >  }
> >
> >  void flush_thread(void)
>
> Additionally: this isn't really an issue so much with this patch, but it
> does bring up that we're relying on someone else to have set UXL=3D64 on
> CONFIG_COMPAT=3Dn systems.  I don't see that in any spec anywhere, so we
> should really be setting UXL in Linux for all systems (ie, not just those=
 with
> COMPAT=3Dy).


--=20
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/