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Message-ID: <bfdd914c-4c3a-9af7-d530-f57f3532c3d5@huawei.com>
Date: Fri, 28 Nov 2025 11:34:31 +0800
From: Jinjie Ruan <ruanjinjie@...wei.com>
To: Kevin Brodsky <kevin.brodsky@....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>, <charlie@...osinc.com>,
<akpm@...ux-foundation.org>, <ldv@...ace.io>, <macro@...am.me.uk>,
<deller@....de>, <mark.rutland@....com>, <efault@....de>, <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>, <linux-arm-kernel@...ts.infradead.org>,
<linux-kernel@...r.kernel.org>, <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH v8 11/12] arm64: entry: Convert to generic entry
On 2025/11/27 21:31, Kevin Brodsky wrote:
> On 26/11/2025 08:14, Jinjie Ruan wrote:
>> Currently, x86, Riscv, Loongarch use the generic entry which makes
>> maintainers' work easier and codes more elegant. arm64 has already
>> switched to the generic IRQ entry, so completely convert arm64 to use
>> the generic entry infrastructure from kernel/entry/*.
>>
>> The changes are below:
>> - Remove TIF_SYSCALL_* flag, _TIF_WORK_MASK, _TIF_SYSCALL_WORK,
>
> _TIF_WORK_MASK is now removed in patch 1.
>
>> and remove has_syscall_work(), as _TIF_SYSCALL_WORK is equal with
>> SYSCALL_WORK_ENTER.
>>
>> [...]
>>
>> +static __always_inline void arch_ptrace_report_syscall_exit(struct pt_regs *regs,
>> + int step)
>> +{
>> + unsigned long saved_reg;
>> + int regno;
>> +
>> + saved_reg = ptrace_save_reg(regs, PTRACE_SYSCALL_EXIT, ®no);
>> + if (!step) {
>
> A difference I noticed here is that the generic report_single_step()
> always returns false if SYSCALL_EMU is set. I don't know if the
> combination of SYSCALL_EMU and SINGLESTEP is meaningful, but if it is
> then I think that's a behaviour change.
commit 64eb35f701f0 ("ptrace: Migrate TIF_SYSCALL_EMU to use
SYSCALL_WORK flag") has changed the following code:
Therefore, the original logic returns false in these cases for
report_single_step() :
- Only _TIF_SYSCALL_EMU is set.
- Both _TIF_SINGLESTEP and _TIF_SYSCALL_EMU are set.
- Neither TIF_SINGLESTEP nor _TIF_SYSCALL_EMU is set;
#define SYSEMU_STEP (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU)
static inline bool report_single_step(unsigned long ti_work)
{
return (ti_work & SYSEMU_STEP) == _TIF_SINGLESTEP;
}
I think the "returns false if SYSCALL_EMU is set" behaviour is correct
according to the Man's Manual， both PTRACE_SYSEMU and
PTRACE_SYSEMU_SINGLESTEP need to report the syscal only once on syscall
entry.
“For PTRACE_SYSEMU, continue and stop on entry to the next
system call, which will not be executed. See the
documentation on syscall-stops below. For
PTRACE_SYSEMU_SINGLESTEP, do the same but also singlestep
if not a system call. “
Link：https://man7.org/linux/man-pages/man2/ptrace.2.html
>
>> + ptrace_report_syscall_exit(regs, 0);
>> + regs->regs[regno] = saved_reg;
>> + } else {
>> + regs->regs[regno] = saved_reg;
>> +
>> + /*
>> + * Signal a pseudo-step exception since we are stepping but
>> + * tracer modifications to the registers may have rewound the
>> + * state machine.
>> + */
>> + ptrace_report_syscall_exit(regs, 1);
>> + }
>> +}
>> +
>> +#define arch_ptrace_report_syscall_exit arch_ptrace_report_syscall_exit
>> +
>> #endif /* _ASM_ARM64_ENTRY_COMMON_H */
>> diff --git a/arch/arm64/include/asm/syscall.h b/arch/arm64/include/asm/syscall.h
>> index 6225981fbbdb..f705ba2bb6fd 100644
>> --- a/arch/arm64/include/asm/syscall.h
>> +++ b/arch/arm64/include/asm/syscall.h
>> @@ -9,6 +9,9 @@
>> #include <linux/compat.h>
>> #include <linux/err.h>
>>
>> +#include <asm/compat.h>
>> +#include <asm/vdso.h>
>> +
>> typedef long (*syscall_fn_t)(const struct pt_regs *regs);
>>
>> extern const syscall_fn_t sys_call_table[];
>> @@ -114,12 +117,21 @@ static inline int syscall_get_arch(struct task_struct *task)
>> return AUDIT_ARCH_AARCH64;
>> }
>>
>> -static inline bool has_syscall_work(unsigned long flags)
>> +static inline bool arch_syscall_is_vdso_sigreturn(struct pt_regs *regs)
>> {
>> - return unlikely(flags & _TIF_SYSCALL_WORK);
>> + unsigned long sigtramp;
>> +
>> +#ifdef CONFIG_COMPAT
>> + if (is_compat_task()) {
>> + unsigned long vdso = (unsigned long)current->mm->context.sigpage;
>
> Might as well call it sigpage (separate from the vDSO on arm32).
>
>> +
>> + return (regs->pc >= vdso && regs->pc < (vdso + PAGE_SIZE));
>
> Nit: no need for parentheses around the expression to return.
>
>> + }
>> +#endif
>> + sigtramp = (unsigned long)VDSO_SYMBOL(current->mm->context.vdso, sigtramp);
>> + return regs->pc == (sigtramp + 8);
>> }
>>
>> -int syscall_trace_enter(struct pt_regs *regs, long syscall, unsigned long flags);
>> -void syscall_exit_to_user_mode_prepare(struct pt_regs *regs);
>> +#define ARCH_SYSCALL_WORK_EXIT (_TIF_SECCOMP | _TIF_SYSCALL_EMU)
>>
>> #endif /* __ASM_SYSCALL_H */
>> diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
>> index ff4998fa1844..d3142b5d1b9c 100644
>> --- a/arch/arm64/include/asm/thread_info.h
>> +++ b/arch/arm64/include/asm/thread_info.h
>> @@ -43,6 +43,7 @@ struct thread_info {
>> void *scs_sp;
>> #endif
>> u32 cpu;
>> + unsigned long syscall_work; /* SYSCALL_WORK_ flags */
>> };
>>
>> #define thread_saved_pc(tsk) \
>> @@ -65,11 +66,8 @@ void arch_setup_new_exec(void);
>> #define TIF_UPROBE 5 /* uprobe breakpoint or singlestep */
>> #define TIF_MTE_ASYNC_FAULT 6 /* MTE Asynchronous Tag Check Fault */
>> #define TIF_NOTIFY_SIGNAL 7 /* signal notifications exist */
>> -#define TIF_SYSCALL_TRACE 8 /* syscall trace active */
>> -#define TIF_SYSCALL_AUDIT 9 /* syscall auditing */
>> -#define TIF_SYSCALL_TRACEPOINT 10 /* syscall tracepoint for ftrace */
>> -#define TIF_SECCOMP 11 /* syscall secure computing */
>> -#define TIF_SYSCALL_EMU 12 /* syscall emulation active */
>> +#define TIF_SECCOMP 11 /* syscall secure computing */
>> +#define TIF_SYSCALL_EMU 12 /* syscall emulation active */
>
> These seem to have reappeared in v8 for some reason?
v8 add "ARCH_SYSCALL_WORK_EXIT" to be defined as "SECCOMP | SYSCALL_EMU"
to keep the arm64 behaviour unchanged as mentioned in v7.
>
>> #define TIF_PATCH_PENDING 13 /* pending live patching update */
>> #define TIF_MEMDIE 18 /* is terminating due to OOM killer */
>> #define TIF_FREEZE 19
>> @@ -92,24 +90,16 @@ void arch_setup_new_exec(void);
>> #define _TIF_NEED_RESCHED_LAZY (1 << TIF_NEED_RESCHED_LAZY)
>> #define _TIF_NOTIFY_RESUME (1 << TIF_NOTIFY_RESUME)
>> #define _TIF_FOREIGN_FPSTATE (1 << TIF_FOREIGN_FPSTATE)
>> -#define _TIF_SYSCALL_TRACE (1 << TIF_SYSCALL_TRACE)
>> -#define _TIF_SYSCALL_AUDIT (1 << TIF_SYSCALL_AUDIT)
>> -#define _TIF_SYSCALL_TRACEPOINT (1 << TIF_SYSCALL_TRACEPOINT)
>> #define _TIF_SECCOMP (1 << TIF_SECCOMP)
>> #define _TIF_SYSCALL_EMU (1 << TIF_SYSCALL_EMU)
>
> Ditto.
>
>> #define _TIF_PATCH_PENDING (1 << TIF_PATCH_PENDING)
>> #define _TIF_UPROBE (1 << TIF_UPROBE)
>> -#define _TIF_SINGLESTEP (1 << TIF_SINGLESTEP)
>> #define _TIF_32BIT (1 << TIF_32BIT)
>> #define _TIF_SVE (1 << TIF_SVE)
>> #define _TIF_MTE_ASYNC_FAULT (1 << TIF_MTE_ASYNC_FAULT)
>> #define _TIF_NOTIFY_SIGNAL (1 << TIF_NOTIFY_SIGNAL)
>> #define _TIF_TSC_SIGSEGV (1 << TIF_TSC_SIGSEGV)
>>
>> -#define _TIF_SYSCALL_WORK (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
>> - _TIF_SYSCALL_TRACEPOINT | _TIF_SECCOMP | \
>> - _TIF_SYSCALL_EMU)
>> -
>> #ifdef CONFIG_SHADOW_CALL_STACK
>> #define INIT_SCS \
>> .scs_base = init_shadow_call_stack, \
>> diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c
>> index 29307642f4c9..e67643a70405 100644
>> --- a/arch/arm64/kernel/debug-monitors.c
>> +++ b/arch/arm64/kernel/debug-monitors.c
>> @@ -385,11 +385,18 @@ void user_enable_single_step(struct task_struct *task)
>>
>> if (!test_and_set_ti_thread_flag(ti, TIF_SINGLESTEP))
>> set_regs_spsr_ss(task_pt_regs(task));
>> +
>> + /*
>> + * Ensure that a trap is triggered once stepping out of a system
>> + * call prior to executing any user instruction.
>> + */
>> + set_task_syscall_work(task, SYSCALL_EXIT_TRAP);
>> }
>> NOKPROBE_SYMBOL(user_enable_single_step);
>>
>> void user_disable_single_step(struct task_struct *task)
>> {
>> clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
>> + clear_task_syscall_work(task, SYSCALL_EXIT_TRAP);
>> }
>> NOKPROBE_SYMBOL(user_disable_single_step);
>> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
>> index c2bd0130212d..9e3b39e207d1 100644
>> --- a/arch/arm64/kernel/ptrace.c
>> +++ b/arch/arm64/kernel/ptrace.c
>> @@ -42,9 +42,6 @@
>> #include <asm/traps.h>
>> #include <asm/system_misc.h>
>>
>> -#define CREATE_TRACE_POINTS
>> -#include <trace/events/syscalls.h>
>> -
>> struct pt_regs_offset {
>> const char *name;
>> int offset;
>> @@ -2312,141 +2309,6 @@ long arch_ptrace(struct task_struct *child, long request,
>> return ptrace_request(child, request, addr, data);
>> }
>>
>> -enum ptrace_syscall_dir {
>> - PTRACE_SYSCALL_ENTER = 0,
>> - PTRACE_SYSCALL_EXIT,
>> -};
>> -
>> -static inline unsigned long ptrace_save_reg(struct pt_regs *regs,
>> - enum ptrace_syscall_dir dir,
>> - int *regno)
>> -{
>> - unsigned long saved_reg;
>> -
>> - /*
>> - * We have some ABI weirdness here in the way that we handle syscall
>> - * exit stops because we indicate whether or not the stop has been
>> - * signalled from syscall entry or syscall exit by clobbering a general
>> - * purpose register (ip/r12 for AArch32, x7 for AArch64) in the tracee
>> - * and restoring its old value after the stop. This means that:
>> - *
>> - * - Any writes by the tracer to this register during the stop are
>> - * ignored/discarded.
>> - *
>> - * - The actual value of the register is not available during the stop,
>> - * so the tracer cannot save it and restore it later.
>> - *
>> - * - Syscall stops behave differently to seccomp and pseudo-step traps
>> - * (the latter do not nobble any registers).
>> - */
>> - *regno = (is_compat_task() ? 12 : 7);
>> - saved_reg = regs->regs[*regno];
>> - regs->regs[*regno] = dir;
>> -
>> - return saved_reg;
>> -}
>> -
>> -static int report_syscall_entry(struct pt_regs *regs)
>> -{
>> - unsigned long saved_reg;
>> - int regno, ret;
>> -
>> - saved_reg = ptrace_save_reg(regs, PTRACE_SYSCALL_ENTER, ®no);
>> - ret = ptrace_report_syscall_entry(regs);
>> - if (ret)
>> - forget_syscall(regs);
>> - regs->regs[regno] = saved_reg;
>> -
>> - return ret;
>> -}
>> -
>> -static void report_syscall_exit(struct pt_regs *regs)
>> -{
>> - unsigned long saved_reg;
>> - int regno;
>> -
>> - saved_reg = ptrace_save_reg(regs, PTRACE_SYSCALL_EXIT, ®no);
>> - if (!test_thread_flag(TIF_SINGLESTEP)) {
>> - ptrace_report_syscall_exit(regs, 0);
>> - regs->regs[regno] = saved_reg;
>> - } else {
>> - regs->regs[regno] = saved_reg;
>> -
>> - /*
>> - * Signal a pseudo-step exception since we are stepping but
>> - * tracer modifications to the registers may have rewound the
>> - * state machine.
>> - */
>> - ptrace_report_syscall_exit(regs, 1);
>> - }
>> -}
>> -
>> -static inline void syscall_enter_audit(struct pt_regs *regs, long syscall)
>> -{
>> - if (unlikely(audit_context())) {
>> - unsigned long args[6];
>> -
>> - syscall_get_arguments(current, regs, args);
>> - audit_syscall_entry(syscall, args[0], args[1], args[2], args[3]);
>> - }
>> -}
>> -
>> -int syscall_trace_enter(struct pt_regs *regs, long syscall, unsigned long flags)
>> -{
>> - int ret;
>> -
>> - if (flags & (_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE)) {
>> - ret = report_syscall_entry(regs);
>> - if (ret || (flags & _TIF_SYSCALL_EMU))
>> - return NO_SYSCALL;
>> - }
>> -
>> - /* Do the secure computing after ptrace; failures should be fast. */
>> - if (flags & _TIF_SECCOMP) {
>> - ret = __secure_computing();
>> - if (ret == -1)
>> - return NO_SYSCALL;
>> - }
>> -
>> - /* 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);
>> -
>> - /*
>> - * Probes or BPF hooks in the tracepoint may have changed the
>> - * system call number as well.
>> - */
>> - syscall = syscall_get_nr(current, regs);
>> - }
>> -
>> - syscall_enter_audit(regs, syscall);
>> -
>> - return ret ? : syscall;
>> -}
>> -
>> -static void syscall_exit_work(struct pt_regs *regs, unsigned long flags)
>> -{
>> - audit_syscall_exit(regs);
>> -
>> - if (flags & _TIF_SYSCALL_TRACEPOINT)
>> - trace_sys_exit(regs, syscall_get_return_value(current, regs));
>> -
>> - 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_exit_work(regs, flags);
>> -}
>
> Aside from the small change in arch_ptrace_report_syscall_exit(), these
> look exactly equivalent to the generic functions, so LGTM.
>
> - Kevin
>
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