diff --git a/sys/arch/amd64/amd64/process_machdep.c b/sys/arch/amd64/amd64/process_machdep.c
index 58e215187d30..e5e0e10a1d78 100644
--- a/sys/arch/amd64/amd64/process_machdep.c
+++ b/sys/arch/amd64/amd64/process_machdep.c
@@ -283,12 +283,28 @@ process_set_pc(struct lwp *l, void *addr)
 }
 
 #ifdef __HAVE_PTRACE_MACHDEP
+static int
+process_machdep_read_tlsbase(struct lwp *l, __greg_t *reg)
+{
+
+	*reg = (__greg_t)(uintptr_t)l->l_private;
+
+	return 0;
+}
+
 static int
 process_machdep_read_xstate(struct lwp *l, struct xstate *regs)
 {
 	return process_read_xstate(l, regs);
 }
 
+static int
+process_machdep_write_tlsbase(struct lwp *l, const __greg_t *reg)
+{
+
+	return lwp_setprivate(l, (void *)(uintptr_t)*reg);
+}
+
 static int
 process_machdep_write_xstate(struct lwp *l, const struct xstate *regs)
 {
@@ -370,6 +386,31 @@ ptrace_machdep_dorequest(
 		MODULE_HOOK_CALL(netbsd32_process_doxmmregs_hook,
 		    (l, lt, addr, write), EINVAL, error);
 		return error;
+
+	case PT_SETTLSBASE:
+		write = 1;
+
+		/* FALLTHROUGH */
+	case PT_GETTLSBASE:
+		/* write = 0 done above. */
+		if (!process_machdep_validtlsbase(lt->l_proc))
+			return EINVAL;
+		error = proc_vmspace_getref(l->l_proc, &vm);
+		if (error) {
+			return error;
+		}
+		iov.iov_base = addr;
+		iov.iov_len = sizeof(__greg_t);
+		uio.uio_iov = &iov;
+		uio.uio_iovcnt = 1;
+		uio.uio_offset = 0;
+		uio.uio_resid = sizeof(__greg_t);
+		uio.uio_rw = write ? UIO_WRITE : UIO_READ;
+		uio.uio_vmspace = vm;
+		error = process_machdep_dotlsbase(l, lt, &uio);
+		uvmspace_free(vm);
+		return error;
+
 	}
 
 #ifdef DIAGNOSTIC
@@ -380,9 +421,54 @@ ptrace_machdep_dorequest(
 }
 
 /*
- * The following functions are used by both ptrace(2) and procfs.
+ * The following functions are used by ptrace(2).
  */
 
+int
+process_machdep_dotlsbase(struct lwp *curl, struct lwp *l, struct uio *uio)
+	/* curl:		tracer */
+	/* l:			traced */
+{
+	int error;
+	__greg_t r;
+	char *kv;
+	int kl;
+
+	kl = sizeof(r);
+	kv = (char *) &r;
+
+	kv += uio->uio_offset;
+	kl -= uio->uio_offset;
+	if (kl > uio->uio_resid)
+		kl = uio->uio_resid;
+
+	if (kl < 0)
+		error = EINVAL;
+	else
+		error = process_machdep_read_tlsbase(l, &r);
+	if (error == 0)
+		error = uiomove(kv, kl, uio);
+	if (error == 0 && uio->uio_rw == UIO_WRITE) {
+		if (l->l_proc->p_stat != SSTOP)
+			error = EBUSY;
+		else
+			error = process_machdep_write_tlsbase(l, &r);
+	}
+
+	uio->uio_offset = 0;
+	return error;
+}
+
+int
+process_machdep_validtlsbase(struct proc *p)
+{
+
+	if (p->p_flag & PK_SYSTEM)
+		return 0;
+
+	return 1;
+}
+
 int
 process_machdep_doxstate(struct lwp *curl, struct lwp *l, struct uio *uio)
 	/* curl:		 tracer */
diff --git a/sys/arch/amd64/include/ptrace.h b/sys/arch/amd64/include/ptrace.h
index 8820ed8f9061..73f3a11d486a 100644
--- a/sys/arch/amd64/include/ptrace.h
+++ b/sys/arch/amd64/include/ptrace.h
@@ -54,6 +54,8 @@
 #define	PT_GETXMMREGS		(PT_FIRSTMACH + 11)
 #define	PT_SETXMMREGS		(PT_FIRSTMACH + 12)
 #endif
+#define	PT_GETTLSBASE	(PT_FIRSTMACH + 13)
+#define	PT_SETTLSBASE	(PT_FIRSTMACH + 14)
 
 /* We have machine-dependent process tracing needs. */
 #define	__HAVE_PTRACE_MACHDEP
@@ -69,7 +71,11 @@
 	"PT_SETSTEP", \
 	"PT_CLEARSTEP", \
 	"PT_GETXSTATE", \
-	"PT_SETXSTATE"
+	"PT_SETXSTATE", \
+	"PT_GETXMMREGS", \
+	"PT_SETXMMREGS", \
+	"PT_GETTLSBASE", \
+	"PT_SETTLSBASE"
 
 #include <machine/reg.h>
 #define PTRACE_REG_PC(r)	(r)->regs[_REG_RIP]
@@ -94,11 +100,16 @@
 	case PT_GETXSTATE:						\
 	case PT_SETXSTATE:						\
 	case PT_GETXMMREGS:						\
-	case PT_SETXMMREGS:
+	case PT_SETXMMREGS:						\
+	case PT_GETTLSBASE:						\
+	case PT_SETTLSBASE:
 
 int process_machdep_doxstate(struct lwp *, struct lwp *, struct uio *);
 int process_machdep_validfpu(struct proc *);
 
+int process_machdep_dotlsbase(struct lwp *, struct lwp *, struct uio *);
+int process_machdep_validtlsbase(struct proc *);
+
 #include <sys/module_hook.h>
 MODULE_HOOK(netbsd32_process_doxmmregs_hook, int,
     (struct lwp *, struct lwp *, void *, bool));
diff --git a/tests/lib/libc/sys/t_ptrace_wait.c b/tests/lib/libc/sys/t_ptrace_wait.c
index 76088a3e60d8..1a727a87911e 100644
--- a/tests/lib/libc/sys/t_ptrace_wait.c
+++ b/tests/lib/libc/sys/t_ptrace_wait.c
@@ -4379,7 +4379,7 @@ BYTES_TRANSFER_EOF(bytes_transfer_eof_piod_write_d, "PIOD_WRITE_D")
 
 /// ----------------------------------------------------------------------------
 
-#if defined(HAVE_GPREGS) || defined(HAVE_FPREGS)
+#if defined(HAVE_GPREGS) || defined(HAVE_FPREGS) || defined(HAVE_TLSBASE)
 static void
 access_regs(const char *regset, const char *aux)
 {
@@ -4396,6 +4396,9 @@ access_regs(const char *regset, const char *aux)
 #if defined(HAVE_FPREGS)
 	struct fpreg fpr;
 #endif
+#if defined(HAVE_TLSBASE)
+	register_t r;
+#endif
 	
 #if !defined(HAVE_GPREGS)
 	if (strcmp(regset, "regs") == 0)
@@ -4407,6 +4410,11 @@ access_regs(const char *regset, const char *aux)
 		atf_tc_fail("Impossible test scenario!");
 #endif
 
+#if !defined(HAVE_TLSBASE)
+	if (strcmp(regset, "tlsbase") == 0)
+		atf_tc_fail("Impossible test scenario!");
+#endif
+
 	DPRINTF("Before forking process PID=%d\n", getpid());
 	SYSCALL_REQUIRE((child = fork()) != -1);
 	if (child == 0) {
@@ -4468,6 +4476,21 @@ access_regs(const char *regset, const char *aux)
 	}
 #endif
 
+#if defined(HAVE_TLSBASE)
+	if (strcmp(regset, "tlsbase") == 0) {
+		DPRINTF("Call GETTLSBASE for the child process\n");
+		SYSCALL_REQUIRE(ptrace(PT_GETTLSBASE, child, &r, 0) != -1);
+
+		DPRINTF("Retrieved TLSBASE register: %" PRIxREGISTER "\n", r);
+
+		if (strcmp(aux, "settlsbase") == 0) {
+			DPRINTF("Call SETTLSBASE for the child\n");
+			SYSCALL_REQUIRE(
+			    ptrace(PT_SETTLSBASE, child, &r, 0) != -1);
+		}
+	}
+#endif
+
 	DPRINTF("Before resuming the child process where it left off and "
 	    "without signal to be sent\n");
 	SYSCALL_REQUIRE(ptrace(PT_CONTINUE, child, (void *)1, 0) != -1);
@@ -4508,6 +4531,10 @@ ACCESS_REGS(access_regs6, "regs", "setregs")
 ACCESS_REGS(access_fpregs1, "fpregs", "getfpregs")
 ACCESS_REGS(access_fpregs2, "fpregs", "setfpregs")
 #endif
+#if defined(HAVE_TLSBASE)
+ACCESS_REGS(access_tlsbase1, "tlsbase", "gettlsbase")
+ACCESS_REGS(access_tlsbase2, "tlsbase", "settlsbase")
+#endif
 
 /// ----------------------------------------------------------------------------
 
@@ -8169,6 +8196,9 @@ ATF_TP_ADD_TCS(tp)
 	ATF_TP_ADD_TC_HAVE_FPREGS(tp, access_fpregs1);
 	ATF_TP_ADD_TC_HAVE_FPREGS(tp, access_fpregs2);
 
+	ATF_TP_ADD_TC_HAVE_TLSBASE(tp, access_tlsbase1);
+	ATF_TP_ADD_TC_HAVE_TLSBASE(tp, access_tlsbase2);
+
 	ATF_TP_ADD_TC_PT_STEP(tp, step1);
 	ATF_TP_ADD_TC_PT_STEP(tp, step2);
 	ATF_TP_ADD_TC_PT_STEP(tp, step3);
diff --git a/tests/lib/libc/sys/t_ptrace_wait.h b/tests/lib/libc/sys/t_ptrace_wait.h
index a840de3da27c..ecf5818901d7 100644
--- a/tests/lib/libc/sys/t_ptrace_wait.h
+++ b/tests/lib/libc/sys/t_ptrace_wait.h
@@ -207,6 +207,12 @@ do {									\
 #define HAVE_DBREGS
 #endif
 
+/* Add guards for TLSBASE register */
+#if defined(PT_GETTLSBASE)		\
+    && defined(PT_SETTLSBASE)
+#define HAVE_TLSBASE
+#endif
+
 /*
  * If waitid(2) returns because one or more processes have a state change to
  * report, 0 is returned.  If an error is detected, a value of -1 is returned
@@ -722,6 +728,12 @@ find_event_count(struct lwp_event_count list[], lwpid_t lwp, size_t max_lwps)
 #define ATF_TP_ADD_TC_HAVE_DBREGS(a,b)
 #endif
 
+#if defined(HAVE_TLSBASE)
+#define ATF_TP_ADD_TC_HAVE_TLSBASE(a,b) ATF_TP_ADD_TC(a,b)
+#else
+#define ATF_TP_ADD_TC_HAVE_TLSBASE(a,b)
+#endif
+
 #if defined(PT_STEP)
 #define ATF_TP_ADD_TC_PT_STEP(a,b)	ATF_TP_ADD_TC(a,b)
 #else