Re: [RFC PATCH v2 2/2] LoongArch: No need to call RESTORE_ALL_AND_RET for all syscalls

[Tiezhu Yang]

On 06/15/2022 02:57 PM, hev wrote:
> Hello,
>
> On Wed, Jun 15, 2022 at 2:38 PM Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> wrote:
> > In handle_syscall, it is unnecessary to call RESTORE_ALL_AND_RET
> > for all syscalls.
> >
> > (1) If syscall number is __NR_clone and __NR_clone3,
> >     call RESTORE_STATIC_SOME_SP_AND_RET.
> > (2) If syscall number is __NR_rt_sigreturn and __NR_rt_sigsuspend,
> >     call RESTORE_TEMP_SOME_SP_AND_RET.
> > (3) The other syscalls call RESTORE_SOME_SP_AND_RET.
> >
> > With this patch, it can reduce many load instructions.
> >
> > Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
> > ---
> >  arch/loongarch/include/asm/stackframe.h | 17 +++++++++++++++++
> >  arch/loongarch/kernel/entry.S           | 24 +++++++++++++++++++++++-
> >  2 files changed, 40 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/loongarch/include/asm/stackframe.h b/arch/loongarch/include/asm/stackframe.h
> > index 4ca9530..52649a5f 100644
> > --- a/arch/loongarch/include/asm/stackframe.h
> > +++ b/arch/loongarch/include/asm/stackframe.h
> > @@ -216,4 +216,21 @@
> >         RESTORE_SP_AND_RET \docfi
> >         .endm
> >
> > +       .macro  RESTORE_SOME_SP_AND_RET docfi=0
> > +       RESTORE_SOME \docfi
> > +       RESTORE_SP_AND_RET \docfi
> > +       .endm
> > +
> > +       .macro  RESTORE_STATIC_SOME_SP_AND_RET docfi=0
> > +       RESTORE_STATIC \docfi
> > +       RESTORE_SOME \docfi
> > +       RESTORE_SP_AND_RET \docfi
> > +       .endm
> > +
> > +       .macro  RESTORE_TEMP_SOME_SP_AND_RET docfi=0
> > +       RESTORE_TEMP \docfi
> > +       RESTORE_SOME \docfi
> > +       RESTORE_SP_AND_RET \docfi
> > +       .endm
> > +
> >  #endif /* _ASM_STACKFRAME_H */
> > diff --git a/arch/loongarch/kernel/entry.S b/arch/loongarch/kernel/entry.S
> > index 53ce2cb..58fe507 100644
> > --- a/arch/loongarch/kernel/entry.S
> > +++ b/arch/loongarch/kernel/entry.S
> > @@ -79,7 +79,29 @@ SYM_FUNC_START(handle_syscall)
> >         move    a0, sp
> >         bl      do_syscall
> >
> > -       RESTORE_ALL_AND_RET
> > +       /*
> > +        * Syscall number held in a7 which is stored in PT_R11.
> > +        * If syscall number is __NR_clone and __NR_clone3,
> > +        * call RESTORE_STATIC_SOME_SP_AND_RET.
> > +        * If syscall number is __NR_rt_sigreturn and __NR_rt_sigsuspend,
> > +        * call RESTORE_TEMP_SOME_SP_AND_RET.
> > +        * The other syscalls call RESTORE_SOME_SP_AND_RET.
> > +        */
> > +       cfi_ld  t3, PT_R11
>
> I think PT_R11 may be overwritten by the signal handler and the
> syscall number is now lost.

Thank you. Let me use TI_SYSCALL. I will send RFC v3 patch later.

arch/loongarch/include/asm/thread_info.h
struct thread_info {
	struct task_struct	*task;		/* main task structure */
	unsigned long		flags;		/* low level flags */
	unsigned long		tp_value;	/* thread pointer */
	__u32			cpu;		/* current CPU */
	int			preempt_count;	/* 0 => preemptible, <0 => BUG */
	struct pt_regs		*regs;
	unsigned long		syscall;	/* syscall number */
	unsigned long		syscall_work;	/* SYSCALL_WORK_ flags */
};

> > +       li.w    t4, __NR_clone
> > +       beq     t3, t4, 3f
> > +       li.w    t4, __NR_clone3
> > +       beq     t3, t4, 3f
> > +       li.w    t4, __NR_rt_sigreturn
> > +       beq     t3, t4, 4f
> > +       li.w    t4, __NR_rt_sigsuspend
> > +       beq     t3, t4, 4f
> > +
> > +       RESTORE_SOME_SP_AND_RET
> > +3:
> > +       RESTORE_STATIC_SOME_SP_AND_RET
> > +4:
> > +       RESTORE_TEMP_SOME_SP_AND_RET
> >  SYM_FUNC_END(handle_syscall)
> >
> >  SYM_CODE_START(ret_from_fork)
> > --
> > 2.1.0
>
> Best regards,
> hev