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

[Will Deacon <will@kernel.org>]

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?

Will