diff --git a/src/runtime/asm_386.s b/src/runtime/asm_386.s
index 54d5eaa014..5ca26a2d5f 100644
--- a/src/runtime/asm_386.s
+++ b/src/runtime/asm_386.s
@@ -704,6 +704,8 @@ TEXT ·asmcgocall(SB),NOSPLIT,$0-12
 	MOVL	g(CX), DI
 	CMPL	SI, DI
 	JEQ	noswitch
+	CMPL	DI, m_gsignal(BP)
+	JEQ	noswitch
 	CALL	gosave<>(SB)
 	get_tls(CX)
 	MOVL	SI, g(CX)
diff --git a/src/runtime/defs_darwin.go b/src/runtime/defs_darwin.go
index bedaf99961..e3a25c5312 100644
--- a/src/runtime/defs_darwin.go
+++ b/src/runtime/defs_darwin.go
@@ -17,6 +17,7 @@ package runtime
 #define __DARWIN_UNIX03 0
 #include <mach/mach.h>
 #include <mach/message.h>
+#include <mach/mach_time.h>
 #include <sys/types.h>
 #include <sys/time.h>
 #include <errno.h>
@@ -184,3 +185,5 @@ type Kevent C.struct_kevent
 
 type Pthread C.pthread_t
 type PthreadAttr C.pthread_attr_t
+
+type MachTimebaseInfo C.mach_timebase_info_data_t
diff --git a/src/runtime/defs_darwin_386.go b/src/runtime/defs_darwin_386.go
index 51c6340dfa..7f8ae9c934 100644
--- a/src/runtime/defs_darwin_386.go
+++ b/src/runtime/defs_darwin_386.go
@@ -395,3 +395,7 @@ type pthreadattr struct {
 	X__sig    int32
 	X__opaque [36]int8
 }
+type machTimebaseInfo struct {
+	numer uint32
+	denom uint32
+}
diff --git a/src/runtime/defs_darwin_amd64.go b/src/runtime/defs_darwin_amd64.go
index d1483e7db5..f35b90a5fa 100644
--- a/src/runtime/defs_darwin_amd64.go
+++ b/src/runtime/defs_darwin_amd64.go
@@ -398,3 +398,7 @@ type pthreadattr struct {
 	X__sig    int64
 	X__opaque [56]int8
 }
+type machTimebaseInfo struct {
+	numer uint32
+	denom uint32
+}
diff --git a/src/runtime/stubs3.go b/src/runtime/stubs3.go
index 7570dcaeb2..5c0786e411 100644
--- a/src/runtime/stubs3.go
+++ b/src/runtime/stubs3.go
@@ -7,6 +7,7 @@
 // +build !windows
 // +build !nacl
 // +build !freebsd
+// +build !darwin
 
 package runtime
 
diff --git a/src/runtime/stubs4.go b/src/runtime/stubs4.go
new file mode 100644
index 0000000000..ad0e48e455
--- /dev/null
+++ b/src/runtime/stubs4.go
@@ -0,0 +1,9 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build darwin,arm darwin,arm64
+
+package runtime
+
+func nanotime() int64
diff --git a/src/runtime/sys_darwin.go b/src/runtime/sys_darwin.go
index 8757486e22..3bdd1f2b16 100644
--- a/src/runtime/sys_darwin.go
+++ b/src/runtime/sys_darwin.go
@@ -124,6 +124,28 @@ func open(name *byte, mode, perm int32) (ret int32) {
 }
 func open_trampoline()
 
+//go:nosplit
+//go:cgo_unsafe_args
+func nanotime() int64 {
+	var r struct {
+		t            int64  // raw timer
+		numer, denom uint32 // conversion factors. nanoseconds = t * numer / denom.
+	}
+	asmcgocall(unsafe.Pointer(funcPC(nanotime_trampoline)), unsafe.Pointer(&r))
+	// Note: Apple seems unconcerned about overflow here. See
+	// https://developer.apple.com/library/content/qa/qa1398/_index.html
+	// Note also, numer == denom == 1 is common.
+	t := r.t
+	if r.numer != 1 {
+		t *= int64(r.numer)
+	}
+	if r.denom != 1 {
+		t /= int64(r.denom)
+	}
+	return t
+}
+func nanotime_trampoline()
+
 // Not used on Darwin, but must be defined.
 func exitThread(wait *uint32) {
 }
@@ -150,6 +172,9 @@ func exitThread(wait *uint32) {
 //go:cgo_import_dynamic libc_error __error "/usr/lib/libSystem.B.dylib"
 //go:cgo_import_dynamic libc_usleep usleep "/usr/lib/libSystem.B.dylib"
 
+//go:cgo_import_dynamic libc_mach_timebase_info mach_timebase_info "/usr/lib/libSystem.B.dylib"
+//go:cgo_import_dynamic libc_mach_absolute_time mach_absolute_time "/usr/lib/libSystem.B.dylib"
+
 // Magic incantation to get libSystem actually dynamically linked.
 // TODO: Why does the code require this?  See cmd/compile/internal/ld/go.go:210
 //go:cgo_import_dynamic _ _ "/usr/lib/libSystem.B.dylib"
diff --git a/src/runtime/sys_darwin_386.s b/src/runtime/sys_darwin_386.s
index 16ca3e06ae..44a686f400 100644
--- a/src/runtime/sys_darwin_386.s
+++ b/src/runtime/sys_darwin_386.s
@@ -311,13 +311,37 @@ TEXT time·now(SB),NOSPLIT,$0-20
 	MOVL	DX, nsec+8(FP)
 	RET
 
-// func nanotime() int64
-TEXT runtime·nanotime(SB),NOSPLIT,$0
-	CALL	runtime·now(SB)
-	SUBL	runtime·startNano(SB), AX
-	SBBL	runtime·startNano+4(SB), DX
-	MOVL	AX, ret_lo+0(FP)
-	MOVL	DX, ret_hi+4(FP)
+GLOBL timebase<>(SB),NOPTR,$(machTimebaseInfo__size)
+
+TEXT runtime·nanotime_trampoline(SB),NOSPLIT,$0
+	PUSHL	BP
+	MOVL	SP, BP
+	SUBL	$8+(machTimebaseInfo__size+15)/16*16, SP
+	CALL	libc_mach_absolute_time(SB)
+	MOVL	16+(machTimebaseInfo__size+15)/16*16(SP), CX
+	MOVL	AX, 0(CX)
+	MOVL	DX, 4(CX)
+	MOVL	timebase<>+machTimebaseInfo_denom(SB), DI // atomic read
+	MOVL	timebase<>+machTimebaseInfo_numer(SB), SI
+	TESTL	DI, DI
+	JNE	initialized
+
+	LEAL	4(SP), AX
+	MOVL	AX, 0(SP)
+	CALL	libc_mach_timebase_info(SB)
+	MOVL	4+machTimebaseInfo_numer(SP), SI
+	MOVL	4+machTimebaseInfo_denom(SP), DI
+
+	MOVL	SI, timebase<>+machTimebaseInfo_numer(SB)
+	MOVL	DI, AX
+	XCHGL	AX, timebase<>+machTimebaseInfo_denom(SB) // atomic write
+	MOVL	16+(machTimebaseInfo__size+15)/16*16(SP), CX
+
+initialized:
+	MOVL	SI, 8(CX)
+	MOVL	DI, 12(CX)
+	MOVL	BP, SP
+	POPL	BP
 	RET
 
 TEXT runtime·sigprocmask(SB),NOSPLIT,$0
diff --git a/src/runtime/sys_darwin_amd64.s b/src/runtime/sys_darwin_amd64.s
index e48145a450..24db7f52cd 100644
--- a/src/runtime/sys_darwin_amd64.s
+++ b/src/runtime/sys_darwin_amd64.s
@@ -110,33 +110,35 @@ TEXT runtime·madvise_trampoline(SB), NOSPLIT, $0
 #define	v17_gtod_scale		0xe8
 #define	v17_gtod_tkspersec	0xf0
 
-TEXT runtime·nanotime(SB),NOSPLIT,$0-8
-	MOVQ	$0x7fffffe00000, BP	/* comm page base */
-	// Loop trying to take a consistent snapshot
-	// of the time parameters.
-timeloop:
-	MOVL	nt_generation(BP), R9
-	TESTL	R9, R9
-	JZ	timeloop
-	RDTSC
-	MOVQ	nt_tsc_base(BP), R10
-	MOVL	nt_scale(BP), R11
-	MOVQ	nt_ns_base(BP), R12
-	CMPL	nt_generation(BP), R9
-	JNE	timeloop
+GLOBL timebase<>(SB),NOPTR,$(machTimebaseInfo__size)
 
-	// Gathered all the data we need. Compute monotonic time:
-	//	((tsc - nt_tsc_base) * nt_scale) >> 32 + nt_ns_base
-	// The multiply and shift extracts the top 64 bits of the 96-bit product.
-	SHLQ	$32, DX
-	ADDQ	DX, AX
-	SUBQ	R10, AX
-	MULQ	R11
-	SHRQ	$32, AX:DX
-	ADDQ	R12, AX
-	MOVQ	runtime·startNano(SB), CX
-	SUBQ	CX, AX
-	MOVQ	AX, ret+0(FP)
+TEXT runtime·nanotime_trampoline(SB),NOSPLIT,$0
+	PUSHQ	BP
+	MOVQ	SP, BP
+	MOVQ	DI, BX
+	CALL	libc_mach_absolute_time(SB)
+	MOVQ	AX, 0(BX)
+	MOVL	timebase<>+machTimebaseInfo_numer(SB), SI
+	MOVL	timebase<>+machTimebaseInfo_denom(SB), DI // atomic read
+	TESTL	DI, DI
+	JNE	initialized
+
+	SUBQ	$(machTimebaseInfo__size+15)/16*16, SP
+	MOVQ	SP, DI
+	CALL	libc_mach_timebase_info(SB)
+	MOVL	machTimebaseInfo_numer(SP), SI
+	MOVL	machTimebaseInfo_denom(SP), DI
+	ADDQ	$(machTimebaseInfo__size+15)/16*16, SP
+
+	MOVL	SI, timebase<>+machTimebaseInfo_numer(SB)
+	MOVL	DI, AX
+	XCHGL	AX, timebase<>+machTimebaseInfo_denom(SB) // atomic write
+
+initialized:
+	MOVL	SI, 8(BX)
+	MOVL	DI, 12(BX)
+	MOVQ	BP, SP
+	POPQ	BP
 	RET
 
 TEXT time·now(SB), NOSPLIT, $32-24