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Message-ID: <57c2c83c-9eea-40e0-9f95-47f21b1c75be@arm.com>
Date: Tue, 18 Nov 2025 18:10:44 +0100
From: Kevin Brodsky <kevin.brodsky@....com>
To: Jinjie Ruan <ruanjinjie@...wei.com>, catalin.marinas@....com,
will@...nel.org, oleg@...hat.com, tglx@...utronix.de, peterz@...radead.org,
luto@...nel.org, shuah@...nel.org, kees@...nel.org, wad@...omium.org,
akpm@...ux-foundation.org, ldv@...ace.io, macro@...am.me.uk, deller@....de,
mark.rutland@....com, song@...nel.org, mbenes@...e.cz, ryan.roberts@....com,
ada.coupriediaz@....com, anshuman.khandual@....com, broonie@...nel.org,
pengcan@...inos.cn, dvyukov@...gle.com, kmal@...k.li, lihongbo22@...wei.com,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v7 03/11] arm64/ptrace: Refator el0_svc_common()
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@...wei.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)
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