diff --git a/sys/arm64/arm64/support.S b/sys/arm64/arm64/support.S
--- a/sys/arm64/arm64/support.S
+++ b/sys/arm64/arm64/support.S
@@ -55,6 +55,48 @@
 	ret
 END(fsu_fault)
 
+#ifdef COMPAT_FREEBSD32
+ENTRY(swp_emulate_atomic)
+	adr	x6, fsu_fault		/* Load the fault handler */
+	mov	w5, #1
+	SET_FAULT_HANDLER(x6, x4)	/* And set it */
+	ENTER_USER_ACCESS(w6, x4)
+
+	/* Save off &val, we'll store the old value to it later. */
+	mov	x7, x1
+	ldr	w1, [x7]
+
+	cmp	x2, #0			/* is_swpb */
+	b.ne	2f
+
+	/* swp */
+1:	ldxr	w2, [x0]		/* Stash the old value in w2 */
+	stxr	w3, w1, [x0]		/* Store new value */
+	cbnz	w3, 1b			/* Success? */
+
+	mov	w0, w2			/* Return the old value */
+	b	3f
+
+	/* swpb */
+2:	ldxrb	w2, [x0]
+	stxrb	w3, w1, [x0]
+	cbnz	w3, 2b
+
+	mov	w0, w2
+
+3:	EXIT_USER_ACCESS(w6)
+	SET_FAULT_HANDLER(xzr, x6)
+
+	/*
+	 *  w0 has the value to be returned, stash it in
+	 * *val and return success.
+	 */
+	str	x0, [x7]
+	mov	x0, #0
+	ret
+END(swp_emulate_atomic)
+#endif
+
 /*
  * int casueword32_llsc(volatile uint32_t *, uint32_t, uint32_t *, uint32_t)
  */
diff --git a/sys/arm64/arm64/undefined.c b/sys/arm64/arm64/undefined.c
--- a/sys/arm64/arm64/undefined.c
+++ b/sys/arm64/arm64/undefined.c
@@ -41,10 +41,15 @@
 #include <sys/signalvar.h>
 #include <sys/sysent.h>
 
+#include <machine/atomic.h>
 #include <machine/frame.h>
+#include <machine/pcb.h>
 #include <machine/undefined.h>
 #include <machine/vmparam.h>
 
+#include <vm/vm.h>
+#include <vm/vm_extern.h>
+
 MALLOC_DEFINE(M_UNDEF, "undefhandler", "Undefined instruction handler data");
 
 struct undef_handler {
@@ -113,6 +118,63 @@
 	}
 	return 0;
 }
+
+extern int swp_emulate_atomic(vm_offset_t addr, uint32_t *val, bool is_swpb);
+
+static int
+swp_emulate(vm_offset_t va, uint32_t insn, struct trapframe *frame,
+    uint32_t esr)
+{
+	ksiginfo_t ksi;
+	struct thread *td;
+	vm_offset_t vaddr;
+	uint64_t *regs;
+	uint32_t val;
+	int Rn, Rd, Rm;
+	bool is_swpb;
+
+	td = curthread;
+
+	/* swp, swpb only */
+	if (!SV_PROC_FLAG(td->td_proc, SV_ILP32))
+		return (0);
+	else if ((insn & 0x0fb00ff0) != 0x01000090)
+		return (0);
+
+	Rn = (insn & 0xf0000) >> 16;
+	Rd = (insn & 0xf000) >> 12;
+	Rm = (insn & 0xf);
+
+	regs = frame->tf_x;
+	vaddr = regs[Rn] & 0xffffffff;
+	val = regs[Rm];
+
+	/* Enforce alignment for swp. */
+	is_swpb = (insn & 0x00400000) != 0;
+	if (!is_swpb && (vaddr & 3) != 0)
+		goto fault;
+
+	/*
+	 * vaddr is a 32-bit quantity, let it slide.
+	 */
+	if (swp_emulate_atomic(vaddr, &val, is_swpb) != 0)
+		goto fault;
+
+	regs[Rd] = val;
+
+	/* No thumb SWP/SWPB */
+	frame->tf_elr += 4; //INSN_SIZE;
+
+	return (1);
+fault:
+	ksiginfo_init_trap(&ksi);
+	ksi.ksi_signo = SIGSEGV;
+	ksi.ksi_code = SEGV_MAPERR;
+	ksi.ksi_addr = (void *)va;
+	trapsignal(td, &ksi);
+
+	return (1);
+}
 #endif
 
 void
@@ -125,6 +187,7 @@
 	install_undef_handler(false, id_aa64mmfr2_handler);
 #ifdef COMPAT_FREEBSD32
 	install_undef_handler(true, gdb_trapper);
+	install_undef_handler(true, swp_emulate);
 #endif
 }