diff --git a/cpu/cpu.go b/cpu/cpu.go
index e3a2c4c8..679e78c2 100644
--- a/cpu/cpu.go
+++ b/cpu/cpu.go
@@ -94,3 +94,33 @@ var PPC64 struct {
 	IsPOWER9 bool // ISA v3.00 (POWER9)
 	_        CacheLinePad
 }
+
+// S390X contains the supported CPU features of the current IBM Z
+// (s390x) platform. If the current platform is not IBM Z then all
+// feature flags are false.
+//
+// S390X is padded to avoid false sharing. Further HasVX is only set
+// if the OS supports vector registers in addition to the STFLE
+// feature bit being set.
+var S390X struct {
+	_         CacheLinePad
+	HasZARCH  bool // z/Architecture mode is active [mandatory]
+	HasSTFLE  bool // store facility list extended
+	HasLDISP  bool // long (20-bit) displacements
+	HasEIMM   bool // 32-bit immediates
+	HasDFP    bool // decimal floating point
+	HasETF3EH bool // ETF-3 enhanced
+	HasMSA    bool // message security assist (CPACF)
+	HasAES    bool // KM-AES{128,192,256} functions
+	HasAESCBC bool // KMC-AES{128,192,256} functions
+	HasAESCTR bool // KMCTR-AES{128,192,256} functions
+	HasAESGCM bool // KMA-GCM-AES{128,192,256} functions
+	HasGHASH  bool // KIMD-GHASH function
+	HasSHA1   bool // K{I,L}MD-SHA-1 functions
+	HasSHA256 bool // K{I,L}MD-SHA-256 functions
+	HasSHA512 bool // K{I,L}MD-SHA-512 functions
+	HasSHA3   bool // K{I,L}MD-SHA3-{224,256,384,512} and K{I,L}MD-SHAKE-{128,256} functions
+	HasVX     bool // vector facility
+	HasVXE    bool // vector-enhancements facility 1
+	_         CacheLinePad
+}
diff --git a/cpu/cpu_gc_s390x.go b/cpu/cpu_gc_s390x.go
new file mode 100644
index 00000000..568bcd03
--- /dev/null
+++ b/cpu/cpu_gc_s390x.go
@@ -0,0 +1,21 @@
+// Copyright 2019 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 !gccgo
+
+package cpu
+
+// haveAsmFunctions reports whether the other functions in this file can
+// be safely called.
+func haveAsmFunctions() bool { return true }
+
+// The following feature detection functions are defined in cpu_s390x.s.
+// They are likely to be expensive to call so the results should be cached.
+func stfle() facilityList
+func kmQuery() queryResult
+func kmcQuery() queryResult
+func kmctrQuery() queryResult
+func kmaQuery() queryResult
+func kimdQuery() queryResult
+func klmdQuery() queryResult
diff --git a/cpu/cpu_gccgo_s390x.go b/cpu/cpu_gccgo_s390x.go
new file mode 100644
index 00000000..aa986f77
--- /dev/null
+++ b/cpu/cpu_gccgo_s390x.go
@@ -0,0 +1,22 @@
+// Copyright 2019 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 gccgo
+
+package cpu
+
+// haveAsmFunctions reports whether the other functions in this file can
+// be safely called.
+func haveAsmFunctions() bool { return false }
+
+// TODO(mundaym): the following feature detection functions are currently
+// stubs. See https://golang.org/cl/162887 for how to fix this.
+// They are likely to be expensive to call so the results should be cached.
+func stfle() facilityList     { panic("not implemented for gccgo") }
+func kmQuery() queryResult    { panic("not implemented for gccgo") }
+func kmcQuery() queryResult   { panic("not implemented for gccgo") }
+func kmctrQuery() queryResult { panic("not implemented for gccgo") }
+func kmaQuery() queryResult   { panic("not implemented for gccgo") }
+func kimdQuery() queryResult  { panic("not implemented for gccgo") }
+func klmdQuery() queryResult  { panic("not implemented for gccgo") }
diff --git a/cpu/cpu_linux_s390x.go b/cpu/cpu_linux_s390x.go
new file mode 100644
index 00000000..d579eaef
--- /dev/null
+++ b/cpu/cpu_linux_s390x.go
@@ -0,0 +1,161 @@
+// Copyright 2019 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.
+
+package cpu
+
+const cacheLineSize = 256
+
+const (
+	// bit mask values from /usr/include/bits/hwcap.h
+	hwcap_ZARCH  = 2
+	hwcap_STFLE  = 4
+	hwcap_MSA    = 8
+	hwcap_LDISP  = 16
+	hwcap_EIMM   = 32
+	hwcap_DFP    = 64
+	hwcap_ETF3EH = 256
+	hwcap_VX     = 2048
+	hwcap_VXE    = 8192
+)
+
+// bitIsSet reports whether the bit at index is set. The bit index
+// is in big endian order, so bit index 0 is the leftmost bit.
+func bitIsSet(bits []uint64, index uint) bool {
+	return bits[index/64]&((1<<63)>>(index%64)) != 0
+}
+
+// function is the code for the named cryptographic function.
+type function uint8
+
+const (
+	// KM{,A,C,CTR} function codes
+	aes128 function = 18 // AES-128
+	aes192 function = 19 // AES-192
+	aes256 function = 20 // AES-256
+
+	// K{I,L}MD function codes
+	sha1     function = 1  // SHA-1
+	sha256   function = 2  // SHA-256
+	sha512   function = 3  // SHA-512
+	sha3_224 function = 32 // SHA3-224
+	sha3_256 function = 33 // SHA3-256
+	sha3_384 function = 34 // SHA3-384
+	sha3_512 function = 35 // SHA3-512
+	shake128 function = 36 // SHAKE-128
+	shake256 function = 37 // SHAKE-256
+
+	// KLMD function codes
+	ghash function = 65 // GHASH
+)
+
+// queryResult contains the result of a Query function
+// call. Bits are numbered in big endian order so the
+// leftmost bit (the MSB) is at index 0.
+type queryResult struct {
+	bits [2]uint64
+}
+
+// Has reports whether the given functions are present.
+func (q *queryResult) Has(fns ...function) bool {
+	if len(fns) == 0 {
+		panic("no function codes provided")
+	}
+	for _, f := range fns {
+		if !bitIsSet(q.bits[:], uint(f)) {
+			return false
+		}
+	}
+	return true
+}
+
+// facility is a bit index for the named facility.
+type facility uint8
+
+const (
+	// cryptography facilities
+	msa4 facility = 77  // message-security-assist extension 4
+	msa8 facility = 146 // message-security-assist extension 8
+)
+
+// facilityList contains the result of an STFLE call.
+// Bits are numbered in big endian order so the
+// leftmost bit (the MSB) is at index 0.
+type facilityList struct {
+	bits [4]uint64
+}
+
+// Has reports whether the given facilities are present.
+func (s *facilityList) Has(fs ...facility) bool {
+	if len(fs) == 0 {
+		panic("no facility bits provided")
+	}
+	for _, f := range fs {
+		if !bitIsSet(s.bits[:], uint(f)) {
+			return false
+		}
+	}
+	return true
+}
+
+func doinit() {
+	// test HWCAP bit vector
+	has := func(featureMask uint) bool {
+		return hwCap&featureMask == featureMask
+	}
+
+	// mandatory
+	S390X.HasZARCH = has(hwcap_ZARCH)
+
+	// optional
+	S390X.HasSTFLE = has(hwcap_STFLE)
+	S390X.HasLDISP = has(hwcap_LDISP)
+	S390X.HasEIMM = has(hwcap_EIMM)
+	S390X.HasETF3EH = has(hwcap_ETF3EH)
+	S390X.HasDFP = has(hwcap_DFP)
+	S390X.HasMSA = has(hwcap_MSA)
+	S390X.HasVX = has(hwcap_VX)
+	if S390X.HasVX {
+		S390X.HasVXE = has(hwcap_VXE)
+	}
+
+	// We need implementations of stfle, km and so on
+	// to detect cryptographic features.
+	if !haveAsmFunctions() {
+		return
+	}
+
+	// optional cryptographic functions
+	if S390X.HasMSA {
+		aes := []function{aes128, aes192, aes256}
+
+		// cipher message
+		km, kmc := kmQuery(), kmcQuery()
+		S390X.HasAES = km.Has(aes...)
+		S390X.HasAESCBC = kmc.Has(aes...)
+		if S390X.HasSTFLE {
+			facilities := stfle()
+			if facilities.Has(msa4) {
+				kmctr := kmctrQuery()
+				S390X.HasAESCTR = kmctr.Has(aes...)
+			}
+			if facilities.Has(msa8) {
+				kma := kmaQuery()
+				S390X.HasAESGCM = kma.Has(aes...)
+			}
+		}
+
+		// compute message digest
+		kimd := kimdQuery() // intermediate (no padding)
+		klmd := klmdQuery() // last (padding)
+		S390X.HasSHA1 = kimd.Has(sha1) && klmd.Has(sha1)
+		S390X.HasSHA256 = kimd.Has(sha256) && klmd.Has(sha256)
+		S390X.HasSHA512 = kimd.Has(sha512) && klmd.Has(sha512)
+		S390X.HasGHASH = kimd.Has(ghash) // KLMD-GHASH does not exist
+		sha3 := []function{
+			sha3_224, sha3_256, sha3_384, sha3_512,
+			shake128, shake256,
+		}
+		S390X.HasSHA3 = kimd.Has(sha3...) && klmd.Has(sha3...)
+	}
+}
diff --git a/cpu/cpu_s390x.go b/cpu/cpu_s390x.go
deleted file mode 100644
index ce8a2289..00000000
--- a/cpu/cpu_s390x.go
+++ /dev/null
@@ -1,9 +0,0 @@
-// 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.
-
-package cpu
-
-const cacheLineSize = 256
-
-func doinit() {}
diff --git a/cpu/cpu_s390x.s b/cpu/cpu_s390x.s
new file mode 100644
index 00000000..e5037d92
--- /dev/null
+++ b/cpu/cpu_s390x.s
@@ -0,0 +1,57 @@
+// Copyright 2019 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 !gccgo
+
+#include "textflag.h"
+
+// func stfle() facilityList
+TEXT ·stfle(SB), NOSPLIT|NOFRAME, $0-32
+	MOVD $ret+0(FP), R1
+	MOVD $3, R0          // last doubleword index to store
+	XC   $32, (R1), (R1) // clear 4 doublewords (32 bytes)
+	WORD $0xb2b01000     // store facility list extended (STFLE)
+	RET
+
+// func kmQuery() queryResult
+TEXT ·kmQuery(SB), NOSPLIT|NOFRAME, $0-16
+	MOVD $0, R0         // set function code to 0 (KM-Query)
+	MOVD $ret+0(FP), R1 // address of 16-byte return value
+	WORD $0xB92E0024    // cipher message (KM)
+	RET
+
+// func kmcQuery() queryResult
+TEXT ·kmcQuery(SB), NOSPLIT|NOFRAME, $0-16
+	MOVD $0, R0         // set function code to 0 (KMC-Query)
+	MOVD $ret+0(FP), R1 // address of 16-byte return value
+	WORD $0xB92F0024    // cipher message with chaining (KMC)
+	RET
+
+// func kmctrQuery() queryResult
+TEXT ·kmctrQuery(SB), NOSPLIT|NOFRAME, $0-16
+	MOVD $0, R0         // set function code to 0 (KMCTR-Query)
+	MOVD $ret+0(FP), R1 // address of 16-byte return value
+	WORD $0xB92D4024    // cipher message with counter (KMCTR)
+	RET
+
+// func kmaQuery() queryResult
+TEXT ·kmaQuery(SB), NOSPLIT|NOFRAME, $0-16
+	MOVD $0, R0         // set function code to 0 (KMA-Query)
+	MOVD $ret+0(FP), R1 // address of 16-byte return value
+	WORD $0xb9296024    // cipher message with authentication (KMA)
+	RET
+
+// func kimdQuery() queryResult
+TEXT ·kimdQuery(SB), NOSPLIT|NOFRAME, $0-16
+	MOVD $0, R0         // set function code to 0 (KIMD-Query)
+	MOVD $ret+0(FP), R1 // address of 16-byte return value
+	WORD $0xB93E0024    // compute intermediate message digest (KIMD)
+	RET
+
+// func klmdQuery() queryResult
+TEXT ·klmdQuery(SB), NOSPLIT|NOFRAME, $0-16
+	MOVD $0, R0         // set function code to 0 (KLMD-Query)
+	MOVD $ret+0(FP), R1 // address of 16-byte return value
+	WORD $0xB93F0024    // compute last message digest (KLMD)
+	RET
diff --git a/cpu/cpu_test.go b/cpu/cpu_test.go
index c0d8f640..0433d552 100644
--- a/cpu/cpu_test.go
+++ b/cpu/cpu_test.go
@@ -55,3 +55,20 @@ func TestPPC64minimalFeatures(t *testing.T) {
 		}
 	}
 }
+
+func TestS390X(t *testing.T) {
+	if runtime.GOARCH != "s390x" {
+		return
+	}
+	if testing.Verbose() {
+		t.Logf("%+v\n", cpu.S390X)
+	}
+	// z/Architecture is mandatory
+	if !cpu.S390X.HasZARCH {
+		t.Error("HasZARCH expected true, got false")
+	}
+	// vector-enhancements require vector facility to be enabled
+	if cpu.S390X.HasVXE && !cpu.S390X.HasVX {
+		t.Error("HasVX expected true, got false (VXE is true)")
+	}
+}