Re: [PATCH v10 04/16] arm64/ptrace: Refactor syscall_trace_enter/exit()

[Jinjie Ruan <ruanjinjie@huawei.com>]

On 2026/1/27 0:42, Will Deacon wrote:
> On Mon, Dec 22, 2025 at 07:47:25PM +0800, Jinjie Ruan wrote:
>> The generic syscall entry code has the following form, which use
>> the input syscall work flag and syscall number:
>>
>> | syscall_trace_enter(struct pt_regs *regs, long syscall,
>> |		      unsigned long work)
>> |
>> | syscall_exit_work(struct pt_regs *regs, unsigned long work)
>>
>> In preparation for moving arm64 over to the generic entry code,
>> refactor syscall_trace_enter/exit() to also pass thread flags, and
>> get syscall number by syscall_get_nr() helper.
>>
>> No functional changes.
>>
>> Reviewed-by: Kevin Brodsky <kevin.brodsky@arm.com>
>> Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
>> ---
>>  arch/arm64/include/asm/syscall.h |  4 ++--
>>  arch/arm64/kernel/ptrace.c       | 25 ++++++++++++++++---------
>>  arch/arm64/kernel/syscall.c      |  5 +++--
>>  3 files changed, 21 insertions(+), 13 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/syscall.h b/arch/arm64/include/asm/syscall.h
>> index 5e4c7fc44f73..cef1d9ce6e1b 100644
>> --- a/arch/arm64/include/asm/syscall.h
>> +++ b/arch/arm64/include/asm/syscall.h
>> @@ -120,7 +120,7 @@ static inline int syscall_get_arch(struct task_struct *task)
>>  	return AUDIT_ARCH_AARCH64;
>>  }
>>  
>> -int syscall_trace_enter(struct pt_regs *regs);
>> -void syscall_trace_exit(struct pt_regs *regs);
>> +int syscall_trace_enter(struct pt_regs *regs, long syscall, unsigned long flags);
>> +void syscall_trace_exit(struct pt_regs *regs, unsigned long flags);
>>  
>>  #endif	/* __ASM_SYSCALL_H */
>> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
>> index f333791ffba6..79762ff33945 100644
>> --- a/arch/arm64/kernel/ptrace.c
>> +++ b/arch/arm64/kernel/ptrace.c
>> @@ -2407,9 +2407,8 @@ static void report_syscall_exit(struct pt_regs *regs)
>>  	}
>>  }
>>  
>> -int syscall_trace_enter(struct pt_regs *regs)
>> +int syscall_trace_enter(struct pt_regs *regs, long syscall, unsigned long flags)
>>  {
>> -	unsigned long flags = read_thread_flags();
>>  	int ret;
>>  
>>  	if (flags & (_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE)) {
>> @@ -2422,19 +2421,27 @@ int syscall_trace_enter(struct pt_regs *regs)
>>  	if (secure_computing() == -1)
>>  		return NO_SYSCALL;
>>  
>> -	if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
>> -		trace_sys_enter(regs, regs->syscallno);
>> +	/* Either of the above might have changed the syscall number */
>> +	syscall = syscall_get_nr(current, regs);
> 
> I understand that you're gradually making the arch code more similar to
> the core code so that we can switch over to it, but I'm struggling to
> understand why syscall_trace_enter() takes the 'syscall' argument.
> 
> Even the core code just seems to use it as a local variable, which it
> overrides before it ever uses it. What am I missing?

Hi,

You're absolutely right. The 'syscall' parameter is indeed treated as a
local variable and gets overridden before any real use. Should we
refactor to remove the parameter entirely in generic entry?

Regards,
Jinjie

> 
> Will
>