Re: [PATCH v7 03/11] arm64/ptrace: Refator el0_svc_common()

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

In subject: s/refator/refactor/

Also nit: this is less about ptrace than about syscall entry, so maybe
"arm64/syscall:"?

On 17/11/2025 14:30, Jinjie Ruan wrote:
> Compared to the generic entry code, arm64 terminate the process

s/terminate/terminates/ (similar observation for other commit messages)

> after report_syscall_exit() if the syscall is issued within
> a restartable sequence.

Presumably this implies that forcing SIGSEGV before or after calling the
tracing handlers makes no difference, if so it should be clarified.

> In preparation for moving arm64 over to the generic entry code,
> refactor el0_svc_common() as below:
>
> - Extract syscall_exit_to_user_mode_prepare() to replace the
>   the combination of read_thread_flags() and syscall_trace_exit(),
>   also move the syscall exit check logic into it.
>
> - Move rseq_syscall() ahead, so the CONFIG_DEBUG_RSEQ check is
>   not needed.
>
> - Move has_syscall_work() helper into asm/syscall.h, which will be
>   reused by ptrace.c.
>
> Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
> ---
>  arch/arm64/include/asm/syscall.h |  7 ++++++-
>  arch/arm64/kernel/ptrace.c       | 10 +++++++++-
>  arch/arm64/kernel/syscall.c      | 26 +++++---------------------
>  3 files changed, 20 insertions(+), 23 deletions(-)
>
> diff --git a/arch/arm64/include/asm/syscall.h b/arch/arm64/include/asm/syscall.h
> index d69f590a989b..6225981fbbdb 100644
> --- a/arch/arm64/include/asm/syscall.h
> +++ b/arch/arm64/include/asm/syscall.h
> @@ -114,7 +114,12 @@ static inline int syscall_get_arch(struct task_struct *task)
>  	return AUDIT_ARCH_AARCH64;
>  }
>  
> +static inline bool has_syscall_work(unsigned long flags)
> +{
> +	return unlikely(flags & _TIF_SYSCALL_WORK);
> +}
> +
>  int syscall_trace_enter(struct pt_regs *regs, long syscall, unsigned long flags);
> -void syscall_trace_exit(struct pt_regs *regs, unsigned long flags);
> +void syscall_exit_to_user_mode_prepare(struct pt_regs *regs);
>  
>  #endif	/* __ASM_SYSCALL_H */
> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
> index bbb868f6b292..95984bbf53db 100644
> --- a/arch/arm64/kernel/ptrace.c
> +++ b/arch/arm64/kernel/ptrace.c
> @@ -2403,7 +2403,7 @@ int syscall_trace_enter(struct pt_regs *regs, long syscall, unsigned long flags)
>  	return regs->syscallno;
>  }
>  
> -void syscall_trace_exit(struct pt_regs *regs, unsigned long flags)
> +static void syscall_trace_exit(struct pt_regs *regs, unsigned long flags)
>  {
>  	audit_syscall_exit(regs);
>  
> @@ -2412,8 +2412,16 @@ void syscall_trace_exit(struct pt_regs *regs, unsigned long flags)
>  
>  	if (flags & (_TIF_SYSCALL_TRACE | _TIF_SINGLESTEP))
>  		report_syscall_exit(regs);
> +}
> +
> +void syscall_exit_to_user_mode_prepare(struct pt_regs *regs)
> +{
> +	unsigned long flags = read_thread_flags();
>  
>  	rseq_syscall(regs);
> +
> +	if (has_syscall_work(flags) || flags & _TIF_SINGLESTEP)
> +		syscall_trace_exit(regs, flags);

Since we're trying to align as much with the generic code as possible,
we might as well rename this function to syscall_exit_work() as well.

>  }
>  
>  /*
> diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
> index 6e3fe760e0bb..9713b038d750 100644
> --- a/arch/arm64/kernel/syscall.c
> +++ b/arch/arm64/kernel/syscall.c
> @@ -65,11 +65,6 @@ static void invoke_syscall(struct pt_regs *regs, unsigned int scno,
>  	choose_random_kstack_offset(get_random_u16());
>  }
>  
> -static inline bool has_syscall_work(unsigned long flags)
> -{
> -	return unlikely(flags & _TIF_SYSCALL_WORK);
> -}
> -
>  static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
>  			   const syscall_fn_t syscall_table[])
>  {
> @@ -125,26 +120,15 @@ 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, regs->syscallno, flags);
> -		if (scno == NO_SYSCALL)
> -			goto trace_exit;

Why not keep the goto instead of duplicating the call? It could be
renamed if necessary.

- Kevin

> +		if (scno == NO_SYSCALL) {
> +			syscall_exit_to_user_mode_prepare(regs);
> +			return;
> +		}
>  	}
>  
>  	invoke_syscall(regs, scno, sc_nr, syscall_table);
>  
> -	/*
> -	 * The tracing status may have changed under our feet, so we have to
> -	 * check again. However, if we were tracing entry, then we always trace
> -	 * exit regardless, as the old entry assembly did.
> -	 */
> -	if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) {
> -		flags = read_thread_flags();
> -		if (!has_syscall_work(flags) && !(flags & _TIF_SINGLESTEP))
> -			return;
> -	}
> -
> -trace_exit:
> -	flags = read_thread_flags();
> -	syscall_trace_exit(regs, flags);
> +	syscall_exit_to_user_mode_prepare(regs);
>  }
>  
>  void do_el0_svc(struct pt_regs *regs)