runtime: make iface/eface handling more type safe

Change compiler-invoked interface functions to directly take
iface/eface parameters instead of fInterface/interface{} to avoid
needing to always convert.

For the handful of functions that legitimately need to take an
interface{} parameter, add efaceOf to type-safely convert *interface{}
to *eface.

Change-Id: I8928761a12fd3c771394f36adf93d3006a9fcf39
Reviewed-on: https://go-review.googlesource.com/16166
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

9 files changed, 99 insertions, 142 deletions

diff --git a/src/runtime/alg.go b/src/runtime/alg.go
index bb2f2b8ddb..95173495c3 100644
--- a/src/runtime/alg.go
+++ b/src/runtime/alg.go
@@ -226,18 +226,12 @@ func strequal(p, q unsafe.Pointer) bool {
 	return *(*string)(p) == *(*string)(q)
 }
 func interequal(p, q unsafe.Pointer) bool {
-	return ifaceeq(*(*interface {
-		f()
-	})(p), *(*interface {
-		f()
-	})(q))
+	return ifaceeq(*(*iface)(p), *(*iface)(q))
 }
 func nilinterequal(p, q unsafe.Pointer) bool {
-	return efaceeq(*(*interface{})(p), *(*interface{})(q))
+	return efaceeq(*(*eface)(p), *(*eface)(q))
 }
-func efaceeq(p, q interface{}) bool {
-	x := (*eface)(unsafe.Pointer(&p))
-	y := (*eface)(unsafe.Pointer(&q))
+func efaceeq(x, y eface) bool {
 	t := x._type
 	if t != y._type {
 		return false
@@ -254,11 +248,7 @@ func efaceeq(p, q interface{}) bool {
 	}
 	return eq(x.data, y.data)
 }
-func ifaceeq(p, q interface {
-	f()
-}) bool {
-	x := (*iface)(unsafe.Pointer(&p))
-	y := (*iface)(unsafe.Pointer(&q))
+func ifaceeq(x, y iface) bool {
 	xtab := x.tab
 	if xtab != y.tab {
 		return false
diff --git a/src/runtime/error.go b/src/runtime/error.go
index 4280306ac5..de07bcb643 100644
--- a/src/runtime/error.go
+++ b/src/runtime/error.go
@@ -4,8 +4,6 @@
 
 package runtime
 
-import "unsafe"
-
 // The Error interface identifies a run time error.
 type Error interface {
 	error
@@ -57,7 +55,7 @@ type stringer interface {
 }
 
 func typestring(x interface{}) string {
-	e := (*eface)(unsafe.Pointer(&x))
+	e := efaceOf(&x)
 	return *e._type._string
 }
 
diff --git a/src/runtime/export_test.go b/src/runtime/export_test.go
index 5c1394899a..d94fcb3bae 100644
--- a/src/runtime/export_test.go
+++ b/src/runtime/export_test.go
@@ -127,7 +127,7 @@ var BigEndian = _BigEndian
 // For benchmarking.
 
 func BenchSetType(n int, x interface{}) {
-	e := *(*eface)(unsafe.Pointer(&x))
+	e := *efaceOf(&x)
 	t := e._type
 	var size uintptr
 	var p unsafe.Pointer
diff --git a/src/runtime/heapdump.go b/src/runtime/heapdump.go
index 96aca9c1b7..0344330e4d 100644
--- a/src/runtime/heapdump.go
+++ b/src/runtime/heapdump.go
@@ -379,7 +379,7 @@ func dumpgoroutine(gp *g) {
 		dumpint(tagPanic)
 		dumpint(uint64(uintptr(unsafe.Pointer(p))))
 		dumpint(uint64(uintptr(unsafe.Pointer(gp))))
-		eface := (*eface)(unsafe.Pointer(&p.arg))
+		eface := efaceOf(&p.arg)
 		dumpint(uint64(uintptr(unsafe.Pointer(eface._type))))
 		dumpint(uint64(uintptr(unsafe.Pointer(eface.data))))
 		dumpint(0) // was p->defer, no longer recorded
diff --git a/src/runtime/iface.go b/src/runtime/iface.go
index f04cec0076..58c422a528 100644
--- a/src/runtime/iface.go
+++ b/src/runtime/iface.go
@@ -15,13 +15,6 @@ var (
 	hash      [hashSize]*itab
 )
 
-// fInterface is our standard non-empty interface.  We use it instead
-// of interface{f()} in function prototypes because gofmt insists on
-// putting lots of newlines in the otherwise concise interface{f()}.
-type fInterface interface {
-	f()
-}
-
 func getitab(inter *interfacetype, typ *_type, canfail bool) *itab {
 	if len(inter.mhdr) == 0 {
 		throw("internal error - misuse of itab")
@@ -128,17 +121,16 @@ func typ2Itab(t *_type, inter *interfacetype, cache **itab) *itab {
 	return tab
 }
 
-func convT2E(t *_type, elem unsafe.Pointer, x unsafe.Pointer) (e interface{}) {
+func convT2E(t *_type, elem unsafe.Pointer, x unsafe.Pointer) (e eface) {
 	if raceenabled {
 		raceReadObjectPC(t, elem, getcallerpc(unsafe.Pointer(&t)), funcPC(convT2E))
 	}
 	if msanenabled {
 		msanread(elem, t.size)
 	}
-	ep := (*eface)(unsafe.Pointer(&e))
 	if isDirectIface(t) {
-		ep._type = t
-		typedmemmove(t, unsafe.Pointer(&ep.data), elem)
+		e._type = t
+		typedmemmove(t, unsafe.Pointer(&e.data), elem)
 	} else {
 		if x == nil {
 			x = newobject(t)
@@ -146,13 +138,13 @@ func convT2E(t *_type, elem unsafe.Pointer, x unsafe.Pointer) (e interface{}) {
 		// TODO: We allocate a zeroed object only to overwrite it with
 		// actual data.  Figure out how to avoid zeroing.  Also below in convT2I.
 		typedmemmove(t, x, elem)
-		ep._type = t
-		ep.data = x
+		e._type = t
+		e.data = x
 	}
 	return
 }
 
-func convT2I(t *_type, inter *interfacetype, cache **itab, elem unsafe.Pointer, x unsafe.Pointer) (i fInterface) {
+func convT2I(t *_type, inter *interfacetype, cache **itab, elem unsafe.Pointer, x unsafe.Pointer) (i iface) {
 	if raceenabled {
 		raceReadObjectPC(t, elem, getcallerpc(unsafe.Pointer(&t)), funcPC(convT2I))
 	}
@@ -164,17 +156,16 @@ func convT2I(t *_type, inter *interfacetype, cache **itab, elem unsafe.Pointer,
 		tab = getitab(inter, t, false)
 		atomicstorep(unsafe.Pointer(cache), unsafe.Pointer(tab))
 	}
-	pi := (*iface)(unsafe.Pointer(&i))
 	if isDirectIface(t) {
-		pi.tab = tab
-		typedmemmove(t, unsafe.Pointer(&pi.data), elem)
+		i.tab = tab
+		typedmemmove(t, unsafe.Pointer(&i.data), elem)
 	} else {
 		if x == nil {
 			x = newobject(t)
 		}
 		typedmemmove(t, x, elem)
-		pi.tab = tab
-		pi.data = x
+		i.tab = tab
+		i.data = x
 	}
 	return
 }
@@ -187,9 +178,8 @@ func panicdottype(have, want, iface *_type) {
 	panic(&TypeAssertionError{*iface._string, haveString, *want._string, ""})
 }
 
-func assertI2T(t *_type, i fInterface, r unsafe.Pointer) {
-	ip := (*iface)(unsafe.Pointer(&i))
-	tab := ip.tab
+func assertI2T(t *_type, i iface, r unsafe.Pointer) {
+	tab := i.tab
 	if tab == nil {
 		panic(&TypeAssertionError{"", "", *t._string, ""})
 	}
@@ -198,16 +188,15 @@ func assertI2T(t *_type, i fInterface, r unsafe.Pointer) {
 	}
 	if r != nil {
 		if isDirectIface(t) {
-			writebarrierptr((*uintptr)(r), uintptr(ip.data))
+			writebarrierptr((*uintptr)(r), uintptr(i.data))
 		} else {
-			typedmemmove(t, r, ip.data)
+			typedmemmove(t, r, i.data)
 		}
 	}
 }
 
-func assertI2T2(t *_type, i fInterface, r unsafe.Pointer) bool {
-	ip := (*iface)(unsafe.Pointer(&i))
-	tab := ip.tab
+func assertI2T2(t *_type, i iface, r unsafe.Pointer) bool {
+	tab := i.tab
 	if tab == nil || tab._type != t {
 		if r != nil {
 			memclr(r, uintptr(t.size))
@@ -216,27 +205,26 @@ func assertI2T2(t *_type, i fInterface, r unsafe.Pointer) bool {
 	}
 	if r != nil {
 		if isDirectIface(t) {
-			writebarrierptr((*uintptr)(r), uintptr(ip.data))
+			writebarrierptr((*uintptr)(r), uintptr(i.data))
 		} else {
-			typedmemmove(t, r, ip.data)
+			typedmemmove(t, r, i.data)
 		}
 	}
 	return true
 }
 
-func assertE2T(t *_type, e interface{}, r unsafe.Pointer) {
-	ep := (*eface)(unsafe.Pointer(&e))
-	if ep._type == nil {
+func assertE2T(t *_type, e eface, r unsafe.Pointer) {
+	if e._type == nil {
 		panic(&TypeAssertionError{"", "", *t._string, ""})
 	}
-	if ep._type != t {
-		panic(&TypeAssertionError{"", *ep._type._string, *t._string, ""})
+	if e._type != t {
+		panic(&TypeAssertionError{"", *e._type._string, *t._string, ""})
 	}
 	if r != nil {
 		if isDirectIface(t) {
-			writebarrierptr((*uintptr)(r), uintptr(ep.data))
+			writebarrierptr((*uintptr)(r), uintptr(e.data))
 		} else {
-			typedmemmove(t, r, ep.data)
+			typedmemmove(t, r, e.data)
 		}
 	}
 }
@@ -244,101 +232,89 @@ func assertE2T(t *_type, e interface{}, r unsafe.Pointer) {
 var testingAssertE2T2GC bool
 
 // The compiler ensures that r is non-nil.
-func assertE2T2(t *_type, e interface{}, r unsafe.Pointer) bool {
+func assertE2T2(t *_type, e eface, r unsafe.Pointer) bool {
 	if testingAssertE2T2GC {
 		GC()
 	}
-	ep := (*eface)(unsafe.Pointer(&e))
-	if ep._type != t {
+	if e._type != t {
 		memclr(r, uintptr(t.size))
 		return false
 	}
 	if isDirectIface(t) {
-		writebarrierptr((*uintptr)(r), uintptr(ep.data))
+		writebarrierptr((*uintptr)(r), uintptr(e.data))
 	} else {
-		typedmemmove(t, r, ep.data)
+		typedmemmove(t, r, e.data)
 	}
 	return true
 }
 
-func convI2E(i fInterface) (r interface{}) {
-	ip := (*iface)(unsafe.Pointer(&i))
-	tab := ip.tab
+func convI2E(i iface) (r eface) {
+	tab := i.tab
 	if tab == nil {
 		return
 	}
-	rp := (*eface)(unsafe.Pointer(&r))
-	rp._type = tab._type
-	rp.data = ip.data
+	r._type = tab._type
+	r.data = i.data
 	return
 }
 
-func assertI2E(inter *interfacetype, i fInterface, r *interface{}) {
-	ip := (*iface)(unsafe.Pointer(&i))
-	tab := ip.tab
+func assertI2E(inter *interfacetype, i iface, r *eface) {
+	tab := i.tab
 	if tab == nil {
 		// explicit conversions require non-nil interface value.
 		panic(&TypeAssertionError{"", "", *inter.typ._string, ""})
 	}
-	rp := (*eface)(unsafe.Pointer(r))
-	rp._type = tab._type
-	rp.data = ip.data
+	r._type = tab._type
+	r.data = i.data
 	return
 }
 
 // The compiler ensures that r is non-nil.
-func assertI2E2(inter *interfacetype, i fInterface, r *interface{}) bool {
-	ip := (*iface)(unsafe.Pointer(&i))
-	tab := ip.tab
+func assertI2E2(inter *interfacetype, i iface, r *eface) bool {
+	tab := i.tab
 	if tab == nil {
 		return false
 	}
-	rp := (*eface)(unsafe.Pointer(r))
-	rp._type = tab._type
-	rp.data = ip.data
+	r._type = tab._type
+	r.data = i.data
 	return true
 }
 
-func convI2I(inter *interfacetype, i fInterface) (r fInterface) {
-	ip := (*iface)(unsafe.Pointer(&i))
-	tab := ip.tab
+func convI2I(inter *interfacetype, i iface) (r iface) {
+	tab := i.tab
 	if tab == nil {
 		return
 	}
-	rp := (*iface)(unsafe.Pointer(&r))
 	if tab.inter == inter {
-		rp.tab = tab
-		rp.data = ip.data
+		r.tab = tab
+		r.data = i.data
 		return
 	}
-	rp.tab = getitab(inter, tab._type, false)
-	rp.data = ip.data
+	r.tab = getitab(inter, tab._type, false)
+	r.data = i.data
 	return
 }
 
-func assertI2I(inter *interfacetype, i fInterface, r *fInterface) {
-	ip := (*iface)(unsafe.Pointer(&i))
-	tab := ip.tab
+func assertI2I(inter *interfacetype, i iface, r *iface) {
+	tab := i.tab
 	if tab == nil {
 		// explicit conversions require non-nil interface value.
 		panic(&TypeAssertionError{"", "", *inter.typ._string, ""})
 	}
-	rp := (*iface)(unsafe.Pointer(r))
 	if tab.inter == inter {
-		rp.tab = tab
-		rp.data = ip.data
+		r.tab = tab
+		r.data = i.data
 		return
 	}
-	rp.tab = getitab(inter, tab._type, false)
-	rp.data = ip.data
+	r.tab = getitab(inter, tab._type, false)
+	r.data = i.data
 }
 
-func assertI2I2(inter *interfacetype, i fInterface, r *fInterface) bool {
-	ip := (*iface)(unsafe.Pointer(&i))
-	tab := ip.tab
+func assertI2I2(inter *interfacetype, i iface, r *iface) bool {
+	tab := i.tab
 	if tab == nil {
 		if r != nil {
-			*r = nil
+			*r = iface{}
 		}
 		return false
 	}
@@ -346,68 +322,62 @@ func assertI2I2(inter *interfacetype, i fInterface, r *fInterface) bool {
 		tab = getitab(inter, tab._type, true)
 		if tab == nil {
 			if r != nil {
-				*r = nil
+				*r = iface{}
 			}
 			return false
 		}
 	}
 	if r != nil {
-		rp := (*iface)(unsafe.Pointer(r))
-		rp.tab = tab
-		rp.data = ip.data
+		r.tab = tab
+		r.data = i.data
 	}
 	return true
 }
 
-func assertE2I(inter *interfacetype, e interface{}, r *fInterface) {
-	ep := (*eface)(unsafe.Pointer(&e))
-	t := ep._type
+func assertE2I(inter *interfacetype, e eface, r *iface) {
+	t := e._type
 	if t == nil {
 		// explicit conversions require non-nil interface value.
 		panic(&TypeAssertionError{"", "", *inter.typ._string, ""})
 	}
-	rp := (*iface)(unsafe.Pointer(r))
-	rp.tab = getitab(inter, t, false)
-	rp.data = ep.data
+	r.tab = getitab(inter, t, false)
+	r.data = e.data
 }
 
 var testingAssertE2I2GC bool
 
-func assertE2I2(inter *interfacetype, e interface{}, r *fInterface) bool {
+func assertE2I2(inter *interfacetype, e eface, r *iface) bool {
 	if testingAssertE2I2GC {
 		GC()
 	}
-	ep := (*eface)(unsafe.Pointer(&e))
-	t := ep._type
+	t := e._type
 	if t == nil {
 		if r != nil {
-			*r = nil
+			*r = iface{}
 		}
 		return false
 	}
 	tab := getitab(inter, t, true)
 	if tab == nil {
 		if r != nil {
-			*r = nil
+			*r = iface{}
 		}
 		return false
 	}
 	if r != nil {
-		rp := (*iface)(unsafe.Pointer(r))
-		rp.tab = tab
-		rp.data = ep.data
+		r.tab = tab
+		r.data = e.data
 	}
 	return true
 }
 
 //go:linkname reflect_ifaceE2I reflect.ifaceE2I
-func reflect_ifaceE2I(inter *interfacetype, e interface{}, dst *fInterface) {
+func reflect_ifaceE2I(inter *interfacetype, e eface, dst *iface) {
 	assertE2I(inter, e, dst)
 }
 
-func assertE2E(inter *interfacetype, e interface{}, r *interface{}) {
-	ep := (*eface)(unsafe.Pointer(&e))
-	if ep._type == nil {
+func assertE2E(inter *interfacetype, e eface, r *eface) {
+	if e._type == nil {
 		// explicit conversions require non-nil interface value.
 		panic(&TypeAssertionError{"", "", *inter.typ._string, ""})
 	}
@@ -415,28 +385,25 @@ func assertE2E(inter *interfacetype, e interface{}, r *interface{}) {
 }
 
 // The compiler ensures that r is non-nil.
-func assertE2E2(inter *interfacetype, e interface{}, r *interface{}) bool {
-	ep := (*eface)(unsafe.Pointer(&e))
-	if ep._type == nil {
-		*r = nil
+func assertE2E2(inter *interfacetype, e eface, r *eface) bool {
+	if e._type == nil {
+		*r = eface{}
 		return false
 	}
 	*r = e
 	return true
 }
 
-func ifacethash(i fInterface) uint32 {
-	ip := (*iface)(unsafe.Pointer(&i))
-	tab := ip.tab
+func ifacethash(i iface) uint32 {
+	tab := i.tab
 	if tab == nil {
 		return 0
 	}
 	return tab._type.hash
 }
 
-func efacethash(e interface{}) uint32 {
-	ep := (*eface)(unsafe.Pointer(&e))
-	t := ep._type
+func efacethash(e eface) uint32 {
+	t := e._type
 	if t == nil {
 		return 0
 	}
diff --git a/src/runtime/mbitmap.go b/src/runtime/mbitmap.go
index e7319c10de..33715f287b 100644
--- a/src/runtime/mbitmap.go
+++ b/src/runtime/mbitmap.go
@@ -1623,7 +1623,7 @@ func getgcmaskcb(frame *stkframe, ctxt unsafe.Pointer) bool {
 //go:linkname reflect_gcbits reflect.gcbits
 func reflect_gcbits(x interface{}) []byte {
 	ret := getgcmask(x)
-	typ := (*ptrtype)(unsafe.Pointer((*eface)(unsafe.Pointer(&x))._type)).elem
+	typ := (*ptrtype)(unsafe.Pointer(efaceOf(&x)._type)).elem
 	nptr := typ.ptrdata / ptrSize
 	for uintptr(len(ret)) > nptr && ret[len(ret)-1] == 0 {
 		ret = ret[:len(ret)-1]
@@ -1633,7 +1633,7 @@ func reflect_gcbits(x interface{}) []byte {
 
 // Returns GC type info for object p for testing.
 func getgcmask(ep interface{}) (mask []byte) {
-	e := *(*eface)(unsafe.Pointer(&ep))
+	e := *efaceOf(&ep)
 	p := e.data
 	t := e._type
 	// data or bss
diff --git a/src/runtime/mfinal.go b/src/runtime/mfinal.go
index a753ceda52..24f35d2163 100644
--- a/src/runtime/mfinal.go
+++ b/src/runtime/mfinal.go
@@ -187,7 +187,7 @@ func runfinq() {
 					if len(ityp.mhdr) != 0 {
 						// convert to interface with methods
 						// this conversion is guaranteed to succeed - we checked in SetFinalizer
-						assertE2I(ityp, *(*interface{})(frame), (*fInterface)(frame))
+						assertE2I(ityp, *(*eface)(frame), (*iface)(frame))
 					}
 				default:
 					throw("bad kind in runfinq")
@@ -264,7 +264,7 @@ func SetFinalizer(obj interface{}, finalizer interface{}) {
 		// (and we don't have the data structures to record them).
 		return
 	}
-	e := (*eface)(unsafe.Pointer(&obj))
+	e := efaceOf(&obj)
 	etyp := e._type
 	if etyp == nil {
 		throw("runtime.SetFinalizer: first argument is nil")
@@ -313,7 +313,7 @@ func SetFinalizer(obj interface{}, finalizer interface{}) {
 		}
 	}
 
-	f := (*eface)(unsafe.Pointer(&finalizer))
+	f := efaceOf(&finalizer)
 	ftyp := f._type
 	if ftyp == nil {
 		// switch to system stack and remove finalizer
@@ -347,7 +347,7 @@ func SetFinalizer(obj interface{}, finalizer interface{}) {
 			// ok - satisfies empty interface
 			goto okarg
 		}
-		if assertE2I2(ityp, obj, nil) {
+		if assertE2I2(ityp, *efaceOf(&obj), nil) {
 			goto okarg
 		}
 	}
diff --git a/src/runtime/print.go b/src/runtime/print.go
index 841e684eca..b0e503afe7 100644
--- a/src/runtime/print.go
+++ b/src/runtime/print.go
@@ -220,12 +220,10 @@ func printslice(s []byte) {
 	printpointer(unsafe.Pointer(sp.array))
 }
 
-func printeface(e interface{}) {
-	ep := (*eface)(unsafe.Pointer(&e))
-	print("(", ep._type, ",", ep.data, ")")
+func printeface(e eface) {
+	print("(", e._type, ",", e.data, ")")
 }
 
-func printiface(i fInterface) {
-	ip := (*iface)(unsafe.Pointer(&i))
-	print("(", ip.tab, ",", ip.data, ")")
+func printiface(i iface) {
+	print("(", i.tab, ",", i.data, ")")
 }
diff --git a/src/runtime/runtime2.go b/src/runtime/runtime2.go
index 97d5ed2752..d4e3758678 100644
--- a/src/runtime/runtime2.go
+++ b/src/runtime/runtime2.go
@@ -82,6 +82,10 @@ type eface struct {
 	data  unsafe.Pointer
 }
 
+func efaceOf(ep *interface{}) *eface {
+	return (*eface)(unsafe.Pointer(ep))
+}
+
 // The guintptr, muintptr, and puintptr are all used to bypass write barriers.
 // It is particularly important to avoid write barriers when the current P has
 // been released, because the GC thinks the world is stopped, and an