Re: [PATCH v13 RESEND 08/14] arm64/ptrace: Skip syscall exit reporting for PTRACE_SYSEMU_SINGLESTEP

[Linus Walleij]

On Tue, Mar 17, 2026 at 9:20 AM Jinjie Ruan <ruanjinjie@xxxxxxxxxx> wrote:

> Align the syscall exit reporting logic with the generic entry
> framework by skipping the exit stop when PTRACE_SYSEMU_SINGLESTEP is
> in effect.
>
> [Rationale]
> When a tracer uses PTRACE_SYSEMU_SINGLESTEP, both _TIF_SYSCALL_EMU
> and _TIF_SINGLESTEP flags are set. Currently, arm64 reports a syscall
> exit stop whenever _TIF_SINGLESTEP is set, regardless of the
> emulation state.
>
> However, as per the generic entry implementation (see
> include/linux/entry-common.h):
> "If SYSCALL_EMU is set, then the only reason to report is when SINGLESTEP
> is set (i.e. PTRACE_SYSEMU_SINGLESTEP). This syscall instruction has been
> already reported in syscall_trace_enter()."
>
> Since PTRACE_SYSEMU intercepts and skips the actual syscall
> execution, reporting a subsequent exit stop is redundant and
> inconsistent with the expected behavior of emulated system calls.
>
> [Changes]
> - Introduce report_single_step(): Add a helper to encapsulate the
>   logic for deciding whether to report a single-step stop at syscall
>   exit. It returns false if _TIF_SYSCALL_EMU is set, ensuring the
>   emulated syscall does not trigger a duplicate report.
>
> - Update syscall_exit_work(): Use the new helper to determine
>   the stepping state instead of directly checking _TIF_SINGLESTEP.
>
> [Impact]
> - PTRACE_SINGLESTEP: Continues to report exit stops for actual
>   instructions.
>
> - PTRACE_SYSEMU: Continues to skip exit stops.
>
> - PTRACE_SYSEMU_SINGLESTEP: Now correctly skips the redundant exit
>   stop, aligning arm64 with the generic entry infrastructure.
>
> Cc: Will Deacon <will@xxxxxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Signed-off-by: Jinjie Ruan <ruanjinjie@xxxxxxxxxx>

These small semantic glitches underscores the need to move
to generic entry.
Reviewed-by: Linus Walleij <linusw@xxxxxxxxxx>

Yours,
Linus Walleij