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

On 2025/11/19 1:10, Kevin Brodsky wrote:

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:

quoted

Compared to the generic entry code, arm64 terminate the process

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

Will update it.

quoted

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.

It seems that it need a separate patch to clarify.

quoted

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 <redacted>
---
 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.

Yes, syscall_trace_exit() is very similar to syscall_exit_work().

quoted

 }
 
 /*

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.

That is good.

- Kevin

quoted

+		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)