Re: [PATCH V5 13/21] riscv: compat: process: Add UXL_32 support in start_thread

[Guo Ren]

On Wed, Feb 23, 2022 at 9:42 AM Palmer Dabbelt <palmer@xxxxxxxxxxx> wrote:
>
> On Tue, 01 Feb 2022 07:05:37 PST (-0800), guoren@xxxxxxxxxx wrote:
> > From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> >
> > 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@xxxxxxxxxxxxxxxxx>
> > Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
> > Cc: Arnd Bergmann <arnd@xxxxxxxx>
> > Cc: Palmer Dabbelt <palmer@xxxxxxxxxxx>
> > ---
> >  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 long pc,
> >       }
> >       regs->epc = pc;
> >       regs->sp = sp;
> > +
> > +#ifdef CONFIG_COMPAT
> > +     if (is_compat_task())
> > +             regs->status |= 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=32)?  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 = （regs->status & ~SR_UXL) | SR_UXL_32;
+     else
+.            regs->status = （regs->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=64 on
> CONFIG_COMPAT=n 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=y).



-- 
Best Regards
 Guo Ren

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