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SubjectRe: [RFC PATCH v2 2/2] LoongArch: No need to call RESTORE_ALL_AND_RET for all syscalls
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On 06/15/2022 02:57 PM, hev wrote:
> 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.
>

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
>

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