Re: [PATCH v7 02/11] arm64/ptrace: Refactor syscall_trace_enter/exit()

[Kevin Brodsky <kevin.brodsky@arm.com>]

On 17/11/2025 14:30, Jinjie Ruan wrote:
> [...]
>
> @@ -2386,19 +2384,27 @@ 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);
> +
> +	if (test_thread_flag(TIF_SYSCALL_TRACEPOINT)) {
> +		trace_sys_enter(regs, syscall);
>  
> -	audit_syscall_entry(regs->syscallno, regs->orig_x0, regs->regs[1],
> +		/*
> +		 * Probes or BPF hooks in the tracepoint may have changed the
> +		 * system call number as well.
> +		 */
> +		 syscall = syscall_get_nr(current, regs);
> +	}
> +
> +	audit_syscall_entry(syscall, regs->orig_x0, regs->regs[1],
>  			    regs->regs[2], regs->regs[3]);
>  
>  	return regs->syscallno;

It would be good to align the return with the generic version as well.

>  }
>  
> -void syscall_trace_exit(struct pt_regs *regs)
> +void syscall_trace_exit(struct pt_regs *regs, unsigned long flags)
>  {
> -	unsigned long flags = read_thread_flags();
> -
>  	audit_syscall_exit(regs);
>  
>  	if (flags & _TIF_SYSCALL_TRACEPOINT)
> diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
> index aba7ca6bca2d..6e3fe760e0bb 100644
> --- a/arch/arm64/kernel/syscall.c
> +++ b/arch/arm64/kernel/syscall.c
> @@ -124,7 +124,7 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
>  		 */
>  		if (scno == NO_SYSCALL)
>  			syscall_set_return_value(current, regs, -ENOSYS, 0);
> -		scno = syscall_trace_enter(regs);
> +		scno = syscall_trace_enter(regs, regs->syscallno, flags);

Nit: could use scno instead of regs->syscallno.

- Kevin

>  		if (scno == NO_SYSCALL)
>  			goto trace_exit;
>  	}
> @@ -143,7 +143,8 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
>  	}
>  
>  trace_exit:
> -	syscall_trace_exit(regs);
> +	flags = read_thread_flags();
> +	syscall_trace_exit(regs, flags);
>  }
>  
>  void do_el0_svc(struct pt_regs *regs)