Index: sys/arm64/arm64/exception.S
===================================================================
--- sys/arm64/arm64/exception.S
+++ sys/arm64/arm64/exception.S
@@ -25,6 +25,9 @@
  *
  */
 
+#include "opt_ddb.h"
+#include "opt_stack.h"
+
 #include <machine/asm.h>
 #include <machine/armreg.h>
 __FBSDID("$FreeBSD$");
@@ -33,6 +36,13 @@
 
 	.text
 
+#if defined(KDTRACE_HOOKS) || defined(STACK)
+#define	EXTRA_FRAME_SPACE	(8 * 2)
+#define	SAVE_FP
+#else
+#define	EXTRA_FRAME_SPACE	0
+#endif
+
 /*
  * This is limited to 28 instructions as it's placed in the exception vector
  * slot that is 32 instructions long. We need one for the branch, and three
@@ -43,7 +53,7 @@
 	mov	x18, sp
 	sub	sp, sp, #128
 .endif
-	sub	sp, sp, #(TF_SIZE)
+	sub	sp, sp, #(TF_SIZE + EXTRA_FRAME_SPACE)
 	stp	x28, x29, [sp, #(TF_X + 28 * 8)]
 	stp	x26, x27, [sp, #(TF_X + 26 * 8)]
 	stp	x24, x25, [sp, #(TF_X + 24 * 8)]
@@ -60,6 +70,17 @@
 	stp	x2,  x3,  [sp, #(TF_X + 2  * 8)]
 	stp	x0,  x1,  [sp, #(TF_X + 0  * 8)]
 	mrs	x10, elr_el1
+#if defined(SAVE_FP)
+	/*
+	 * Save a stack frame so the in-kernel stack unwinder can get past
+	 * the exception.
+	 */
+.if \el == 1
+	stp	x29, x10,  [sp, #(TF_SIZE)]
+.else
+	stp	xzr, xzr,  [sp, #(TF_SIZE)]
+.endif
+#endif
 	mrs	x11, spsr_el1
 	mrs	x12, esr_el1
 .if \el == 0
@@ -69,7 +90,9 @@
 	stp	w11, w12, [sp, #(TF_SPSR)]
 	stp	x18,  lr, [sp, #(TF_SP)]
 	mrs	x18, tpidr_el1
+#if defined(SAVE_FP)
 	add	x29, sp, #(TF_SIZE)
+#endif
 .endm
 
 .macro	save_registers el
@@ -158,7 +181,7 @@
 	ldr	     x29, [sp, #(TF_X + 29 * 8)]
 .endif
 .if \el == 0
-	add	sp, sp, #(TF_SIZE)
+	add	sp, sp, #(TF_SIZE + EXTRA_FRAME_SPACE)
 .else
 	mov	sp, x18
 	mrs	x18, tpidr_el1