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

On Wed, Jun 15, 2022 at 2:38 PM Tiezhu Yang <yangtiezhu@loongson.cn> 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@loongson.cn>
> ---
> 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.

> + 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

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