Re: [PATCH v8 11/12] arm64: entry: Convert to generic entry

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, &regno);
• 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.

• 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?

#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, &regno);
• 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, &regno);
• 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