diff --git a/sys/cddl/dev/dtrace/aarch64/dtrace_isa.c b/sys/cddl/dev/dtrace/aarch64/dtrace_isa.c
--- a/sys/cddl/dev/dtrace/aarch64/dtrace_isa.c
+++ b/sys/cddl/dev/dtrace/aarch64/dtrace_isa.c
@@ -238,14 +238,37 @@
 	printf("IMPLEMENT ME: %s\n", __func__);
 }
 
-/*ARGSUSED*/
 uint64_t
-dtrace_getarg(int arg, int aframes)
+dtrace_getarg(int arg, int aframes __unused)
 {
+	struct trapframe *tf;
 
-	printf("IMPLEMENT ME: %s\n", __func__);
-
-	return (0);
+	/*
+	 * We only handle invop providers here.
+	 */
+	if ((tf = curthread->t_dtrace_trapframe) == NULL) {
+		DTRACE_CPUFLAG_SET(CPU_DTRACE_ILLOP);
+		return (0);
+	} else if (arg < 8) {
+		return (tf->tf_x[arg]);
+	} else {
+		uintptr_t p;
+		uint64_t val;
+
+		p = (tf->tf_sp + (arg - 8) * sizeof(uint64_t));
+		if ((p & 7) != 0) {
+			DTRACE_CPUFLAG_SET(CPU_DTRACE_BADALIGN);
+			cpu_core[curcpu].cpuc_dtrace_illval = p;
+			return (0);
+		}
+		if (!kstack_contains(curthread, p, sizeof(uint64_t))) {
+			DTRACE_CPUFLAG_SET(CPU_DTRACE_BADADDR);
+			cpu_core[curcpu].cpuc_dtrace_illval = p;
+			return (0);
+		}
+		memcpy(&val, (void *)p, sizeof(uint64_t));
+		return (val);
+	}
 }
 
 int