Index: sys/cddl/dev/dtrace/aarch64/dtrace_subr.c
===================================================================
--- sys/cddl/dev/dtrace/aarch64/dtrace_subr.c
+++ sys/cddl/dev/dtrace/aarch64/dtrace_subr.c
@@ -49,6 +49,7 @@
 extern dtrace_id_t	dtrace_probeid_error;
 extern int (*dtrace_invop_jump_addr)(struct trapframe *);
 extern void dtrace_getnanotime(struct timespec *tsp);
+extern void dtrace_getnanouptime(struct timespec *tsp);
 
 int dtrace_invop(uintptr_t, struct trapframe *, uintptr_t);
 void dtrace_invop_init(void);
@@ -163,7 +164,7 @@
 {
 	struct timespec curtime;
 
-	nanouptime(&curtime);
+	dtrace_getnanouptime(&curtime);
 
 	return (curtime.tv_sec * 1000000000UL + curtime.tv_nsec);
 
Index: sys/cddl/dev/dtrace/arm/dtrace_subr.c
===================================================================
--- sys/cddl/dev/dtrace/arm/dtrace_subr.c
+++ sys/cddl/dev/dtrace/arm/dtrace_subr.c
@@ -54,6 +54,7 @@
 extern dtrace_id_t	dtrace_probeid_error;
 extern int (*dtrace_invop_jump_addr)(struct trapframe *);
 extern void dtrace_getnanotime(struct timespec *tsp);
+extern void dtrace_getnanouptime(struct timespec *tsp);
 
 int dtrace_invop(uintptr_t, struct trapframe *, uintptr_t);
 void dtrace_invop_init(void);
@@ -174,7 +175,7 @@
 {
 	struct	timespec curtime;
 
-	nanouptime(&curtime);
+	dtrace_getnanouptime(&curtime);
 
 	return (curtime.tv_sec * 1000000000UL + curtime.tv_nsec);
 
Index: sys/cddl/dev/dtrace/riscv/dtrace_subr.c
===================================================================
--- sys/cddl/dev/dtrace/riscv/dtrace_subr.c
+++ sys/cddl/dev/dtrace/riscv/dtrace_subr.c
@@ -52,6 +52,7 @@
 extern dtrace_id_t	dtrace_probeid_error;
 extern int (*dtrace_invop_jump_addr)(struct trapframe *);
 extern void dtrace_getnanotime(struct timespec *tsp);
+extern void dtrace_getnanouptime(struct timespec *tsp);
 
 int dtrace_invop(uintptr_t, struct trapframe *);
 void dtrace_invop_init(void);
@@ -165,7 +166,7 @@
 {
 	struct timespec curtime;
 
-	nanouptime(&curtime);
+	dtrace_getnanouptime(&curtime);
 
 	return (curtime.tv_sec * 1000000000UL + curtime.tv_nsec);
 
Index: sys/cddl/dev/fbt/aarch64/fbt_isa.c
===================================================================
--- sys/cddl/dev/fbt/aarch64/fbt_isa.c
+++ sys/cddl/dev/fbt/aarch64/fbt_isa.c
@@ -96,6 +96,22 @@
 	if (fbt_excluded(name))
 		return (0);
 
+	/*
+	 * Instrumenting certain exception handling functions can lead to FBT
+	 * recursion, so exclude from instrumentation.
+	 */
+	 if (strcmp(name, "handle_el1h_sync") == 0 ||
+	    strcmp(name, "do_el1h_sync") == 0)
+		return (1);
+
+	/*
+	 * Some assembly language function implementations lack proper
+	 * prologues and epilogues, which can confuse the current FBT
+	 * implementation (which would ideally detect this directly).
+	 */
+	if (strcmp(name, "memcpy") == 0 || strcmp(name, "bcopy") == 0)
+		return (1);
+
 	instr = (uint32_t *)(symval->value);
 	limit = (uint32_t *)(symval->value + symval->size);
 
Index: sys/cddl/dev/fbt/fbt.c
===================================================================
--- sys/cddl/dev/fbt/fbt.c
+++ sys/cddl/dev/fbt/fbt.c
@@ -127,6 +127,17 @@
 		return (1);
 	}
 
+	/*
+	 * Omit instrumentation of functions that are probably in DDB.  It
+	 * makes it too hard to debug broken FBT.
+	 *
+	 * NB: kdb_enter() can be excluded, but its call to printf() can't be.
+	 * This is generally OK since we're not yet in debugging context.
+	 */
+	if (strncmp(name, "db_", 3) == 0 ||
+	    strncmp(name, "kdb_", 4) == 0)
+		return (1);
+
 	/*
 	 * Lock owner methods may be called from probe context.
 	 */
Index: sys/kern/kern_tc.c
===================================================================
--- sys/kern/kern_tc.c
+++ sys/kern/kern_tc.c
@@ -146,6 +146,7 @@
 static void cpu_tick_calibrate(int);
 
 void dtrace_getnanotime(struct timespec *tsp);
+void dtrace_getnanouptime(struct timespec *tsp);
 
 static int
 sysctl_kern_boottime(SYSCTL_HANDLER_ARGS)
@@ -997,6 +998,20 @@
 	GETTHMEMBER(tsp, th_nanotime);
 }
 
+/*
+ * This is a clone of getnanouptime used for time since boot.
+ * The dtrace_ prefix prevents fbt from creating probes for
+ * it so an uptime that can be safely used in all fbt probes.
+ */
+void
+dtrace_getnanouptime(struct timespec *tsp)
+{
+	struct bintime bt;
+
+	GETTHMEMBER(&bt, th_offset);
+	bintime2timespec(&bt, tsp);
+}
+
 /*
  * System clock currently providing time to the system. Modifiable via sysctl
  * when the FFCLOCK option is defined.