linux-kernel - Re: [PATCH -next 4/7] riscv: syscall: Don't clobber s0 when syscall

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Date:   Wed, 21 Sep 2022 10:16:03 +0800
From:   Guo Ren <guoren@...nel.org>
To:     Chen Zhongjin <chenzhongjin@...wei.com>
Cc:     linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-perf-users@...r.kernel.org, paul.walmsley@...ive.com,
        palmer@...belt.com, aou@...s.berkeley.edu, peterz@...radead.org,
        mingo@...hat.com, acme@...nel.org, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, namhyung@...nel.org,
        jolsa@...nel.org, nsaenzju@...hat.com, frederic@...nel.org,
        changbin.du@...el.com, vincent.chen@...ive.com, ardb@...nel.org,
        mhiramat@...nel.org, rostedt@...dmis.org, keescook@...omium.org,
        catalin.marinas@....com
Subject: Re: [PATCH -next 4/7] riscv: syscall: Don't clobber s0 when syscall

On Wed, Sep 21, 2022 at 9:30 AM Guo Ren <guoren@...nel.org> wrote:
>
> On Tue, Sep 20, 2022 at 11:15 PM Chen Zhongjin <chenzhongjin@...wei.com> wrote:
> >
> > syscall uses s0 to load address of sys_call_table.
> >
> > Since now we uses s0 to save pt_regs for unwinding, clobber
> > s0 can make unwinder treat s0 as pt_regs address. Use s1 for
> > this job.
> This patch does not make sense. Why couldn't we use s1 for pt_regs?
Seems s0->fp can't be replaced. I take back the question.

>
> No need to modify the entry.S here.
>
> >
> > Signed-off-by: Chen Zhongjin <chenzhongjin@...wei.com>
> > ---
> >  arch/riscv/kernel/entry.S | 20 ++++++++++----------
> >  1 file changed, 10 insertions(+), 10 deletions(-)
> >
> > diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> > index ecb15c7430b4..a3b14a649782 100644
> > --- a/arch/riscv/kernel/entry.S
> > +++ b/arch/riscv/kernel/entry.S
> > @@ -205,33 +205,33 @@ handle_syscall:
> >  check_syscall_nr:
> >         /* Check to make sure we don't jump to a bogus syscall number. */
> >         li t0, __NR_syscalls
> > -       la s0, sys_ni_syscall
> > +       la s1, sys_ni_syscall
> >         /*
> >          * Syscall number held in a7.
> >          * If syscall number is above allowed value, redirect to ni_syscall.
> >          */
> >         bgeu a7, t0, 3f
> >  #ifdef CONFIG_COMPAT
> > -       REG_L s0, PT_STATUS(sp)
> > -       srli s0, s0, SR_UXL_SHIFT
> > -       andi s0, s0, (SR_UXL >> SR_UXL_SHIFT)
> > +       REG_L s1, PT_STATUS(sp)
> > +       srli s1, s1, SR_UXL_SHIFT
> > +       andi s1, s1, (SR_UXL >> SR_UXL_SHIFT)
> >         li t0, (SR_UXL_32 >> SR_UXL_SHIFT)
> > -       sub t0, s0, t0
> > +       sub t0, s1, t0
> >         bnez t0, 1f
> >
> >         /* Call compat_syscall */
> > -       la s0, compat_sys_call_table
> > +       la s1, compat_sys_call_table
> >         j 2f
> >  1:
> >  #endif
> >         /* Call syscall */
> > -       la s0, sys_call_table
> > +       la s1, sys_call_table
> >  2:
> >         slli t0, a7, RISCV_LGPTR
> > -       add s0, s0, t0
> > -       REG_L s0, 0(s0)
> > +       add s1, s1, t0
> > +       REG_L s1, 0(s1)
> >  3:
> > -       jalr s0
> > +       jalr s1
> >
> >  ret_from_syscall:
> >         /* Set user a0 to kernel a0 */
> > --
> > 2.17.1
> >
>
>
> --
> Best Regards
>  Guo Ren



-- 
Best Regards
 Guo Ren