Index: sys/amd64/amd64/trap.c
===================================================================
--- sys/amd64/amd64/trap.c
+++ sys/amd64/amd64/trap.c
@@ -829,16 +829,18 @@
 }
 
 int
-cpu_fetch_syscall_args(struct thread *td, struct syscall_args *sa)
+cpu_fetch_syscall_args(struct thread *td)
 {
 	struct proc *p;
 	struct trapframe *frame;
 	register_t *argp;
+	struct syscall_args *sa;
 	caddr_t params;
 	int reg, regcnt, error;
 
 	p = td->td_proc;
 	frame = td->td_frame;
+	sa = &td->td_sa;
 	reg = 0;
 	regcnt = 6;
 
@@ -889,7 +891,6 @@
 void
 amd64_syscall(struct thread *td, int traced)
 {
-	struct syscall_args sa;
 	int error;
 	ksiginfo_t ksi;
 
@@ -899,7 +900,7 @@
 		/* NOT REACHED */
 	}
 #endif
-	error = syscallenter(td, &sa);
+	error = syscallenter(td);
 
 	/*
 	 * Traced syscall.
@@ -915,15 +916,16 @@
 
 	KASSERT(PCB_USER_FPU(td->td_pcb),
 	    ("System call %s returning with kernel FPU ctx leaked",
-	     syscallname(td->td_proc, sa.code)));
+	     syscallname(td->td_proc, td->td_sa.code)));
 	KASSERT(td->td_pcb->pcb_save == get_pcb_user_save_td(td),
 	    ("System call %s returning with mangled pcb_save",
-	     syscallname(td->td_proc, sa.code)));
+	     syscallname(td->td_proc, td->td_sa.code)));
 	KASSERT(td->td_md.md_invl_gen.gen == 0,
 	    ("System call %s returning with leaked invl_gen %lu",
-	    syscallname(td->td_proc, sa.code), td->td_md.md_invl_gen.gen));
+	    syscallname(td->td_proc, td->td_sa.code),
+	    td->td_md.md_invl_gen.gen));
 
-	syscallret(td, error, &sa);
+	syscallret(td, error);
 
 	/*
 	 * If the user-supplied value of %rip is not a canonical
Index: sys/amd64/cloudabi32/cloudabi32_sysvec.c
===================================================================
--- sys/amd64/cloudabi32/cloudabi32_sysvec.c
+++ sys/amd64/cloudabi32/cloudabi32_sysvec.c
@@ -90,11 +90,15 @@
 }
 
 static int
-cloudabi32_fetch_syscall_args(struct thread *td, struct syscall_args *sa)
+cloudabi32_fetch_syscall_args(struct thread *td)
 {
-	struct trapframe *frame = td->td_frame;
+	struct trapframe *frame;
+	struct syscall_args *sa;
 	int error;
 
+	frame = td->td_frame;
+	sa = &td->td_sa;
+
 	/* Obtain system call number. */
 	sa->code = frame->tf_rax;
 	if (sa->code >= CLOUDABI32_SYS_MAXSYSCALL)
Index: sys/amd64/cloudabi64/cloudabi64_sysvec.c
===================================================================
--- sys/amd64/cloudabi64/cloudabi64_sysvec.c
+++ sys/amd64/cloudabi64/cloudabi64_sysvec.c
@@ -87,9 +87,13 @@
 }
 
 static int
-cloudabi64_fetch_syscall_args(struct thread *td, struct syscall_args *sa)
+cloudabi64_fetch_syscall_args(struct thread *td)
 {
-	struct trapframe *frame = td->td_frame;
+	struct trapframe *frame;
+	struct syscall_args *sa;
+
+	frame = td->td_frame;
+	sa = &td->td_sa;
 
 	/* Obtain system call number. */
 	sa->code = frame->tf_rax;
Index: sys/amd64/ia32/ia32_syscall.c
===================================================================
--- sys/amd64/ia32/ia32_syscall.c
+++ sys/amd64/ia32/ia32_syscall.c
@@ -105,16 +105,18 @@
 }
 
 int
-ia32_fetch_syscall_args(struct thread *td, struct syscall_args *sa)
+ia32_fetch_syscall_args(struct thread *td)
 {
 	struct proc *p;
 	struct trapframe *frame;
+	struct syscall_args *sa;
 	caddr_t params;
 	u_int32_t args[8], tmp;
 	int error, i;
 
 	p = td->td_proc;
 	frame = td->td_frame;
+	sa = &td->td_sa;
 
 	params = (caddr_t)frame->tf_rsp + sizeof(u_int32_t);
 	sa->code = frame->tf_rax;
@@ -175,7 +177,6 @@
 ia32_syscall(struct trapframe *frame)
 {
 	struct thread *td;
-	struct syscall_args sa;
 	register_t orig_tf_rflags;
 	int error;
 	ksiginfo_t ksi;
@@ -184,7 +185,7 @@
 	td = curthread;
 	td->td_frame = frame;
 
-	error = syscallenter(td, &sa);
+	error = syscallenter(td);
 
 	/*
 	 * Traced syscall.
@@ -198,7 +199,7 @@
 		trapsignal(td, &ksi);
 	}
 
-	syscallret(td, error, &sa);
+	syscallret(td, error);
 }
 
 static void
Index: sys/amd64/linux/linux_sysvec.c
===================================================================
--- sys/amd64/linux/linux_sysvec.c
+++ sys/amd64/linux/linux_sysvec.c
@@ -126,7 +126,7 @@
 static void	linux_vdso_install(void *param);
 static void	linux_vdso_deinstall(void *param);
 static void	linux_set_syscall_retval(struct thread *td, int error);
-static int	linux_fetch_syscall_args(struct thread *td, struct syscall_args *sa);
+static int	linux_fetch_syscall_args(struct thread *td);
 static void	linux_exec_setregs(struct thread *td, struct image_params *imgp,
 		    u_long stack);
 static int	linux_vsyscall(struct thread *td);
@@ -217,13 +217,15 @@
 }
 
 static int
-linux_fetch_syscall_args(struct thread *td, struct syscall_args *sa)
+linux_fetch_syscall_args(struct thread *td)
 {
 	struct proc *p;
 	struct trapframe *frame;
+	struct syscall_args *sa;
 
 	p = td->td_proc;
 	frame = td->td_frame;
+	sa = &td->td_sa;
 
 	sa->args[0] = frame->tf_rdi;
 	sa->args[1] = frame->tf_rsi;
Index: sys/amd64/linux32/linux32_sysvec.c
===================================================================
--- sys/amd64/linux32/linux32_sysvec.c
+++ sys/amd64/linux32/linux32_sysvec.c
@@ -725,13 +725,15 @@
 }
 
 static int
-linux32_fetch_syscall_args(struct thread *td, struct syscall_args *sa)
+linux32_fetch_syscall_args(struct thread *td)
 {
 	struct proc *p;
 	struct trapframe *frame;
+	struct syscall_args *sa;
 
 	p = td->td_proc;
 	frame = td->td_frame;
+	sa = &td->td_sa;
 
 	sa->args[0] = frame->tf_rbx;
 	sa->args[1] = frame->tf_rcx;
Index: sys/compat/ia32/ia32_util.h
===================================================================
--- sys/compat/ia32/ia32_util.h
+++ sys/compat/ia32/ia32_util.h
@@ -50,7 +50,7 @@
 #define	IA32_MAXVMEM	0			/* Unlimited */
 
 struct syscall_args;
-int ia32_fetch_syscall_args(struct thread *td, struct syscall_args *sa);
+int ia32_fetch_syscall_args(struct thread *td);
 void ia32_set_syscall_retval(struct thread *, int);
 void ia32_fixlimit(struct rlimit *rl, int which);
 
Index: sys/i386/cloudabi32/cloudabi32_sysvec.c
===================================================================
--- sys/i386/cloudabi32/cloudabi32_sysvec.c
+++ sys/i386/cloudabi32/cloudabi32_sysvec.c
@@ -85,11 +85,15 @@
 }
 
 static int
-cloudabi32_fetch_syscall_args(struct thread *td, struct syscall_args *sa)
+cloudabi32_fetch_syscall_args(struct thread *td)
 {
-	struct trapframe *frame = td->td_frame;
+	struct trapframe *frame;
+	struct syscall_args *sa;
 	int error;
 
+	frame = td->td_frame;
+	sa = &td->td_sa;
+
 	/* Obtain system call number. */
 	sa->code = frame->tf_eax;
 	if (sa->code >= CLOUDABI32_SYS_MAXSYSCALL)
Index: sys/i386/i386/trap.c
===================================================================
--- sys/i386/i386/trap.c
+++ sys/i386/i386/trap.c
@@ -1012,16 +1012,18 @@
 }
 
 int
-cpu_fetch_syscall_args(struct thread *td, struct syscall_args *sa)
+cpu_fetch_syscall_args(struct thread *td)
 {
 	struct proc *p;
 	struct trapframe *frame;
+	struct syscall_args *sa;
 	caddr_t params;
 	long tmp;
 	int error;
 
 	p = td->td_proc;
 	frame = td->td_frame;
+	sa = &td->td_sa;
 
 	params = (caddr_t)frame->tf_esp + sizeof(int);
 	sa->code = frame->tf_eax;
@@ -1082,7 +1084,6 @@
 syscall(struct trapframe *frame)
 {
 	struct thread *td;
-	struct syscall_args sa;
 	register_t orig_tf_eflags;
 	int error;
 	ksiginfo_t ksi;
@@ -1099,7 +1100,7 @@
 	td = curthread;
 	td->td_frame = frame;
 
-	error = syscallenter(td, &sa);
+	error = syscallenter(td);
 
 	/*
 	 * Traced syscall.
@@ -1115,10 +1116,10 @@
 
 	KASSERT(PCB_USER_FPU(td->td_pcb),
 	    ("System call %s returning with kernel FPU ctx leaked",
-	     syscallname(td->td_proc, sa.code)));
+	     syscallname(td->td_proc, td->td_sa.code)));
 	KASSERT(td->td_pcb->pcb_save == get_pcb_user_save_td(td),
 	    ("System call %s returning with mangled pcb_save",
-	     syscallname(td->td_proc, sa.code)));
+	     syscallname(td->td_proc, td->td_sa.code)));
 
-	syscallret(td, error, &sa);
+	syscallret(td, error);
 }
Index: sys/i386/linux/linux_sysvec.c
===================================================================
--- sys/i386/linux/linux_sysvec.c
+++ sys/i386/linux/linux_sysvec.c
@@ -850,13 +850,15 @@
 }
 
 static int
-linux_fetch_syscall_args(struct thread *td, struct syscall_args *sa)
+linux_fetch_syscall_args(struct thread *td)
 {
 	struct proc *p;
 	struct trapframe *frame;
+	struct syscall_args *sa;
 
 	p = td->td_proc;
 	frame = td->td_frame;
+	sa = &td->td_sa;
 
 	sa->code = frame->tf_eax;
 	sa->args[0] = frame->tf_ebx;
Index: sys/kern/init_main.c
===================================================================
--- sys/kern/init_main.c
+++ sys/kern/init_main.c
@@ -360,8 +360,7 @@
 #endif
 
 static int
-null_fetch_syscall_args(struct thread *td __unused,
-    struct syscall_args *sa __unused)
+null_fetch_syscall_args(struct thread *td __unused)
 {
 
 	panic("null_fetch_syscall_args");
Index: sys/kern/kern_fork.c
===================================================================
--- sys/kern/kern_fork.c
+++ sys/kern/kern_fork.c
@@ -1099,7 +1099,7 @@
 		 */
 		PROC_LOCK(p);
 		td->td_dbgflags |= TDB_SCX;
-		_STOPEVENT(p, S_SCX, td->td_dbg_sc_code);
+		_STOPEVENT(p, S_SCX, td->td_sa.code);
 		if ((p->p_ptevents & PTRACE_SCX) != 0 ||
 		    (td->td_dbgflags & TDB_BORN) != 0)
 			ptracestop(td, SIGTRAP, NULL);
Index: sys/kern/kern_sig.c
===================================================================
--- sys/kern/kern_sig.c
+++ sys/kern/kern_sig.c
@@ -150,6 +150,10 @@
 SYSCTL_INT(_kern_sigqueue, OID_AUTO, alloc_fail, CTLFLAG_RD,
     &signal_alloc_fail, 0, "signals failed to be allocated");
 
+static int	kern_lognosys = 0;
+SYSCTL_INT(_kern, OID_AUTO, lognosys, CTLFLAG_RWTUN, &kern_lognosys, 0,
+    "Log invalid syscalls");
+
 SYSINIT(signal, SI_SUB_P1003_1B, SI_ORDER_FIRST+3, sigqueue_start, NULL);
 
 /*
@@ -3568,11 +3572,16 @@
 int
 nosys(struct thread *td, struct nosys_args *args)
 {
-	struct proc *p = td->td_proc;
+	struct proc *p;
+
+	p = td->td_proc;
 
 	PROC_LOCK(p);
 	tdsignal(td, SIGSYS);
 	PROC_UNLOCK(p);
+	if (kern_lognosys)
+		uprintf("pid %d comm %s: nosys %d\n", p->p_pid, p->p_comm,
+		    td->td_sa.code);
 	return (ENOSYS);
 }
 
Index: sys/kern/kern_thread.c
===================================================================
--- sys/kern/kern_thread.c
+++ sys/kern/kern_thread.c
@@ -80,9 +80,9 @@
     "struct thread KBI td_flags");
 _Static_assert(offsetof(struct thread, td_pflags) == 0xfc,
     "struct thread KBI td_pflags");
-_Static_assert(offsetof(struct thread, td_frame) == 0x410,
+_Static_assert(offsetof(struct thread, td_frame) == 0x408,
     "struct thread KBI td_frame");
-_Static_assert(offsetof(struct thread, td_emuldata) == 0x4b8,
+_Static_assert(offsetof(struct thread, td_emuldata) == 0x4b0,
     "struct thread KBI td_emuldata");
 _Static_assert(offsetof(struct proc, p_flag) == 0xb0,
     "struct proc KBI p_flag");
@@ -100,9 +100,9 @@
     "struct thread KBI td_flags");
 _Static_assert(offsetof(struct thread, td_pflags) == 0xa4,
     "struct thread KBI td_pflags");
-_Static_assert(offsetof(struct thread, td_frame) == 0x2c8,
+_Static_assert(offsetof(struct thread, td_frame) == 0x2c0,
     "struct thread KBI td_frame");
-_Static_assert(offsetof(struct thread, td_emuldata) == 0x314,
+_Static_assert(offsetof(struct thread, td_emuldata) == 0x30c,
     "struct thread KBI td_emuldata");
 _Static_assert(offsetof(struct proc, p_flag) == 0x68,
     "struct proc KBI p_flag");
Index: sys/kern/subr_syscall.c
===================================================================
--- sys/kern/subr_syscall.c
+++ sys/kern/subr_syscall.c
@@ -53,13 +53,15 @@
 #include <security/audit/audit.h>
 
 static inline int
-syscallenter(struct thread *td, struct syscall_args *sa)
+syscallenter(struct thread *td)
 {
 	struct proc *p;
+	struct syscall_args *sa;
 	int error, traced;
 
 	VM_CNT_INC(v_syscall);
 	p = td->td_proc;
+	sa = &td->td_sa;
 
 	td->td_pticks = 0;
 	if (td->td_cowgen != p->p_cowgen)
@@ -72,7 +74,7 @@
 			td->td_dbgflags |= TDB_SCE;
 		PROC_UNLOCK(p);
 	}
-	error = (p->p_sysent->sv_fetch_syscall_args)(td, sa);
+	error = (p->p_sysent->sv_fetch_syscall_args)(td);
 #ifdef KTRACE
 	if (KTRPOINT(td, KTR_SYSCALL))
 		ktrsyscall(sa->code, sa->narg, sa->args);
@@ -86,8 +88,6 @@
 		STOPEVENT(p, S_SCE, sa->narg);
 		if (p->p_flag & P_TRACED) {
 			PROC_LOCK(p);
-			td->td_dbg_sc_code = sa->code;
-			td->td_dbg_sc_narg = sa->narg;
 			if (p->p_ptevents & PTRACE_SCE)
 				ptracestop((td), SIGTRAP, NULL);
 			PROC_UNLOCK(p);
@@ -97,11 +97,7 @@
 			 * Reread syscall number and arguments if
 			 * debugger modified registers or memory.
 			 */
-			error = (p->p_sysent->sv_fetch_syscall_args)(td, sa);
-			PROC_LOCK(p);
-			td->td_dbg_sc_code = sa->code;
-			td->td_dbg_sc_narg = sa->narg;
-			PROC_UNLOCK(p);
+			error = (p->p_sysent->sv_fetch_syscall_args)(td);
 #ifdef KTRACE
 			if (KTRPOINT(td, KTR_SYSCALL))
 				ktrsyscall(sa->code, sa->narg, sa->args);
@@ -163,9 +159,10 @@
 }
 
 static inline void
-syscallret(struct thread *td, int error, struct syscall_args *sa)
+syscallret(struct thread *td, int error)
 {
 	struct proc *p, *p2;
+	struct syscall_args *sa;
 	ksiginfo_t ksi;
 	int traced, error1;
 
@@ -173,6 +170,7 @@
 	    ("fork() did not clear TDP_FORKING upon completion"));
 
 	p = td->td_proc;
+	sa = &td->td_sa;
 	if ((trap_enotcap || (p->p_flag2 & P2_TRAPCAP) != 0) &&
 	    IN_CAPABILITY_MODE(td)) {
 		error1 = (td->td_pflags & TDP_NERRNO) == 0 ? error :
Index: sys/kern/sys_process.c
===================================================================
--- sys/kern/sys_process.c
+++ sys/kern/sys_process.c
@@ -586,6 +586,7 @@
 		struct ptrace_lwpinfo32 pl32;
 		struct ptrace_vm_entry32 pve32;
 #endif
+		char args[nitems(td->td_sa.args) * sizeof(register_t)];
 		int ptevents;
 	} r;
 	void *addr;
@@ -606,6 +607,7 @@
 	case PT_GETFPREGS:
 	case PT_GETDBREGS:
 	case PT_LWPINFO:
+	case PT_GET_SC_ARGS:
 		break;
 	case PT_SETREGS:
 		error = COPYIN(uap->addr, &r.reg, sizeof r.reg);
@@ -663,6 +665,10 @@
 		/* NB: The size in uap->data is validated in kern_ptrace(). */
 		error = copyout(&r.pl, uap->addr, uap->data);
 		break;
+	case PT_GET_SC_ARGS:
+		error = copyout(td->td_sa.args, uap->addr, MIN(uap->data,
+		    sizeof(r.args)));
+		break;
 	}
 
 	return (error);
@@ -739,6 +745,7 @@
 	case PT_GET_EVENT_MASK:
 	case PT_SET_EVENT_MASK:
 	case PT_DETACH:
+	case PT_GET_SC_ARGS:
 		sx_xlock(&proctree_lock);
 		proctree_locked = 1;
 		break;
@@ -1009,6 +1016,28 @@
 		    p->p_pid, p->p_ptevents, tmp);
 		p->p_ptevents = tmp;
 		break;
+
+	case PT_GET_SC_ARGS:
+		CTR1(KTR_PTRACE, "PT_GET_SC_ARGS: pid %d", p->p_pid);
+		if ((td2->td_dbgflags & (TDB_SCE | TDB_SCX)) == 0
+#ifdef COMPAT_FREEBSD32
+		    || !safe
+#endif
+		    ) {
+			error = EINVAL;
+			break;
+		}
+		bzero(addr, sizeof(td2->td_sa.args));
+#ifdef COMPAT_FREEBSD32
+		if (wrap32)
+			for (num = 0; num < nitems(td2->td_sa.args); num++)
+				((uint32_t *)addr)[num] = (uint32_t)
+				    td2->td_sa.args[num];
+		else
+#endif
+			bcopy(td2->td_sa.args, addr, td2->td_sa.narg *
+			    sizeof(register_t));
+		break;
 		
 	case PT_STEP:
 	case PT_CONTINUE:
@@ -1347,8 +1376,8 @@
 		pl->pl_siglist = td2->td_siglist;
 		strcpy(pl->pl_tdname, td2->td_name);
 		if ((td2->td_dbgflags & (TDB_SCE | TDB_SCX)) != 0) {
-			pl->pl_syscall_code = td2->td_dbg_sc_code;
-			pl->pl_syscall_narg = td2->td_dbg_sc_narg;
+			pl->pl_syscall_code = td2->td_sa.code;
+			pl->pl_syscall_narg = td2->td_sa.narg;
 		} else {
 			pl->pl_syscall_code = 0;
 			pl->pl_syscall_narg = 0;
Index: sys/sys/proc.h
===================================================================
--- sys/sys/proc.h
+++ sys/sys/proc.h
@@ -142,6 +142,7 @@
  *      j - locked by proc slock
  *      k - only accessed by curthread
  *	k*- only accessed by curthread and from an interrupt
+ *	kx- only accessed by curthread and by debugger
  *      l - the attaching proc or attaching proc parent
  *      m - Giant
  *      n - not locked, lazy
@@ -296,8 +297,6 @@
 	u_char		td_pri_class;	/* (t) Scheduling class. */
 	u_char		td_user_pri;	/* (t) User pri from estcpu and nice. */
 	u_char		td_base_user_pri; /* (t) Base user pri */
-	u_int		td_dbg_sc_code;	/* (c) Syscall code to debugger. */
-	u_int		td_dbg_sc_narg;	/* (c) Syscall arg count to debugger.*/
 	uintptr_t	td_rb_list;	/* (k) Robust list head. */
 	uintptr_t	td_rbp_list;	/* (k) Robust priv list head. */
 	uintptr_t	td_rb_inact;	/* (k) Current in-action mutex loc. */
@@ -342,6 +341,7 @@
 	int		td_lastcpu;	/* (t) Last cpu we were on. */
 	int		td_oncpu;	/* (t) Which cpu we are on. */
 	void		*td_lkpi_task;	/* LinuxKPI task struct pointer */
+	struct syscall_args td_sa;	/* (kx) */
 };
 
 struct thread0_storage {
@@ -1053,7 +1053,7 @@
 void	cpu_exit(struct thread *);
 void	exit1(struct thread *, int, int) __dead2;
 void	cpu_copy_thread(struct thread *td, struct thread *td0);
-int	cpu_fetch_syscall_args(struct thread *td, struct syscall_args *sa);
+int	cpu_fetch_syscall_args(struct thread *td);
 void	cpu_fork(struct thread *, struct proc *, struct thread *, int);
 void	cpu_fork_kthread_handler(struct thread *, void (*)(void *), void *);
 void	cpu_set_syscall_retval(struct thread *, int);
Index: sys/sys/ptrace.h
===================================================================
--- sys/sys/ptrace.h
+++ sys/sys/ptrace.h
@@ -69,6 +69,8 @@
 #define	PT_GET_EVENT_MASK 25	/* get mask of optional events */
 #define	PT_SET_EVENT_MASK 26	/* set mask of optional events */
 
+#define	PT_GET_SC_ARGS	27	/* fetch syscall args */
+
 #define PT_GETREGS      33	/* get general-purpose registers */
 #define PT_SETREGS      34	/* set general-purpose registers */
 #define PT_GETFPREGS    35	/* get floating-point registers */
Index: sys/sys/sysent.h
===================================================================
--- sys/sys/sysent.h
+++ sys/sys/sysent.h
@@ -119,8 +119,7 @@
 	u_long		*sv_maxssiz;
 	u_int		sv_flags;
 	void		(*sv_set_syscall_retval)(struct thread *, int);
-	int		(*sv_fetch_syscall_args)(struct thread *, struct
-			    syscall_args *);
+	int		(*sv_fetch_syscall_args)(struct thread *);
 	const char	**sv_syscallnames;
 	vm_offset_t	sv_timekeep_base;
 	vm_offset_t	sv_shared_page_base;