reflect: ensure uniqueness of type descriptors on AIX.

On AIX, duplication of type descriptors can occur if one is
declared in the libgo and one in the Go program being compiled.
The AIX linker isn't able to merge them together as Linux one does.
One solution is to always load libgo first but that needs a huge mechanism in
gcc core. Thus, this patch ensures that the duplication isn't visible
for the end user.

In reflect and internal/reflectlite, the comparison of rtypes is made on their
name and not only on their addresses.

In reflect, toType() function is using a canonicalization map to force rtypes
having the same rtype.String() to return the same Type. This can't be made in
internal/reflectlite as it needs sync package. But, for now, it doesn't matter
as internal/reflectlite is not widely used.

Fixes golang/go#39276

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/260158

7 files changed, 157 insertions, 29 deletions

diff --git a/libgo/go/internal/reflectlite/eqtype.go b/libgo/go/internal/reflectlite/eqtype.go
new file mode 100644
index 0000000..a03cf1c
--- /dev/null
+++ b/libgo/go/internal/reflectlite/eqtype.go
@@ -0,0 +1,12 @@
+// Copyright 2020 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 !aix !gccgo
+
+package reflectlite
+
+// rtypeEqual returns true if both types are identical.
+func rtypeEqual(t1, t2 *rtype) bool {
+	return t1 == t2
+}
diff --git a/libgo/go/internal/reflectlite/eqtype_aix_gccgo.go b/libgo/go/internal/reflectlite/eqtype_aix_gccgo.go
new file mode 100644
index 0000000..38b507f
--- /dev/null
+++ b/libgo/go/internal/reflectlite/eqtype_aix_gccgo.go
@@ -0,0 +1,26 @@
+// Copyright 2020 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 aix,gccgo
+
+// AIX linker isn't able to merge identical type descriptors coming from
+// different objects. Thus, two rtypes might have two different pointers
+// even if they are the same. Thus, instead of pointer equality, string
+// field is checked.
+
+package reflectlite
+
+// rtypeEqual returns true if both types are identical.
+func rtypeEqual(t1, t2 *rtype) bool {
+	switch {
+	case t1 == t2:
+		return true
+	case t1 == nil || t2 == nil:
+		return false
+	case t1.kind != t2.kind || t1.hash != t2.hash:
+		return false
+	default:
+		return t1.String() == t2.String()
+	}
+}
diff --git a/libgo/go/internal/reflectlite/type.go b/libgo/go/internal/reflectlite/type.go
index e700a55..1609a06 100644
--- a/libgo/go/internal/reflectlite/type.go
+++ b/libgo/go/internal/reflectlite/type.go
@@ -539,7 +539,7 @@ func implements(T, V *rtype) bool {
 		for j := 0; j < len(v.methods); j++ {
 			tm := &t.methods[i]
 			vm := &v.methods[j]
-			if *vm.name == *tm.name && (vm.pkgPath == tm.pkgPath || (vm.pkgPath != nil && tm.pkgPath != nil && *vm.pkgPath == *tm.pkgPath)) && toType(vm.typ).common() == toType(tm.typ).common() {
+			if *vm.name == *tm.name && (vm.pkgPath == tm.pkgPath || (vm.pkgPath != nil && tm.pkgPath != nil && *vm.pkgPath == *tm.pkgPath)) && rtypeEqual(toType(vm.typ).common(), toType(tm.typ).common()) {
 				if i++; i >= len(t.methods) {
 					return true
 				}
@@ -556,7 +556,7 @@ func implements(T, V *rtype) bool {
 	for j := 0; j < len(v.methods); j++ {
 		tm := &t.methods[i]
 		vm := &v.methods[j]
-		if *vm.name == *tm.name && (vm.pkgPath == tm.pkgPath || (vm.pkgPath != nil && tm.pkgPath != nil && *vm.pkgPath == *tm.pkgPath)) && toType(vm.mtyp).common() == toType(tm.typ).common() {
+		if *vm.name == *tm.name && (vm.pkgPath == tm.pkgPath || (vm.pkgPath != nil && tm.pkgPath != nil && *vm.pkgPath == *tm.pkgPath)) && rtypeEqual(toType(vm.mtyp).common(), toType(tm.typ).common()) {
 			if i++; i >= len(t.methods) {
 				return true
 			}
@@ -572,7 +572,7 @@ func implements(T, V *rtype) bool {
 // and the ideal constant rules (no ideal constants at run time).
 func directlyAssignable(T, V *rtype) bool {
 	// x's type V is identical to T?
-	if T == V {
+	if rtypeEqual(T, V) {
 		return true
 	}
 
@@ -599,7 +599,7 @@ func haveIdenticalType(T, V Type, cmpTags bool) bool {
 }
 
 func haveIdenticalUnderlyingType(T, V *rtype, cmpTags bool) bool {
-	if T == V {
+	if rtypeEqual(T, V) {
 		return true
 	}
 
diff --git a/libgo/go/reflect/eqtype.go b/libgo/go/reflect/eqtype.go
new file mode 100644
index 0000000..5639bc5
--- /dev/null
+++ b/libgo/go/reflect/eqtype.go
@@ -0,0 +1,24 @@
+// Copyright 2020 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 !aix !gccgo
+
+package reflect
+
+// rtypeEqual returns true if both rtypes are identical.
+func rtypeEqual(t1, t2 *rtype) bool {
+	return t1 == t2
+}
+
+// typeEqual returns true if both Types are identical.
+func typeEqual(t1, t2 Type) bool {
+	return t1 == t2
+}
+
+func toType(p *rtype) Type {
+	if p == nil {
+		return nil
+	}
+	return p
+}
diff --git a/libgo/go/reflect/eqtype_aix_gccgo.go b/libgo/go/reflect/eqtype_aix_gccgo.go
new file mode 100644
index 0000000..7afbf10
--- /dev/null
+++ b/libgo/go/reflect/eqtype_aix_gccgo.go
@@ -0,0 +1,74 @@
+// Copyright 2020 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 aix,gccgo
+
+// AIX linker isn't able to merge identical type descriptors coming from
+// different objects. Thus, two rtypes might have two different pointers
+// even if they are the same. Thus, instead of pointer equality, string
+// field is checked.
+
+package reflect
+
+import (
+	"sync"
+)
+
+// rtypeEqual returns true if both rtypes are identical.
+func rtypeEqual(t1, t2 *rtype) bool {
+	switch {
+	case t1 == t2:
+		return true
+	case t1 == nil || t2 == nil:
+		return false
+	case t1.kind != t2.kind || t1.hash != t2.hash:
+		return false
+	default:
+		return t1.String() == t2.String()
+	}
+}
+
+// typeEqual returns true if both Types are identical.
+func typeEqual(t1, t2 Type) bool {
+	return rtypeEqual(t1.common(), t2.common())
+}
+
+// toType converts from a *rtype to a Type that can be returned
+// to the client of package reflect. The only concern is that
+// a nil *rtype must be replaced by a nil Type.
+// On AIX, as type duplications can occur, it also ensure that
+// multiple *rtype for the same  type are coalesced into a single
+// Type.
+
+var canonicalType = make(map[string]Type)
+
+var canonicalTypeLock sync.RWMutex
+
+func canonicalize(t Type) Type {
+	if t == nil {
+		return nil
+	}
+	s := t.rawString()
+	canonicalTypeLock.RLock()
+	if r, ok := canonicalType[s]; ok {
+		canonicalTypeLock.RUnlock()
+		return r
+	}
+	canonicalTypeLock.RUnlock()
+	canonicalTypeLock.Lock()
+	if r, ok := canonicalType[s]; ok {
+		canonicalTypeLock.Unlock()
+		return r
+	}
+	canonicalType[s] = t
+	canonicalTypeLock.Unlock()
+	return t
+}
+
+func toType(p *rtype) Type {
+	if p == nil {
+		return nil
+	}
+	return canonicalize(p)
+}
diff --git a/libgo/go/reflect/type.go b/libgo/go/reflect/type.go
index 2ce1901f..73c09d4 100644
--- a/libgo/go/reflect/type.go
+++ b/libgo/go/reflect/type.go
@@ -1129,7 +1129,7 @@ func (t *rtype) ptrTo() *rtype {
 	// Look in known types.
 	s := "*" + *t.string
 	if tt := lookupType(s); tt != nil {
-		p := (*ptrType)(unsafe.Pointer(tt))
+		p := (*ptrType)(unsafe.Pointer(toType(tt).(*rtype)))
 		if p.elem == t {
 			pi, _ := ptrMap.LoadOrStore(t, p)
 			return &pi.(*ptrType).rtype
@@ -1158,7 +1158,9 @@ func (t *rtype) ptrTo() *rtype {
 	pp.ptrToThis = nil
 	pp.elem = t
 
-	pi, _ := ptrMap.LoadOrStore(t, &pp)
+	q := toType(&pp.rtype).(*rtype)
+	p := (*ptrType)(unsafe.Pointer(q))
+	pi, _ := ptrMap.LoadOrStore(t, p)
 	return &pi.(*ptrType).rtype
 }
 
@@ -1273,7 +1275,7 @@ func specialChannelAssignability(T, V *rtype) bool {
 // and the ideal constant rules (no ideal constants at run time).
 func directlyAssignable(T, V *rtype) bool {
 	// x's type V is identical to T?
-	if T == V {
+	if rtypeEqual(T, V) {
 		return true
 	}
 
@@ -1304,7 +1306,7 @@ func haveIdenticalType(T, V Type, cmpTags bool) bool {
 }
 
 func haveIdenticalUnderlyingType(T, V *rtype, cmpTags bool) bool {
-	if T == V {
+	if rtypeEqual(T, V) {
 		return true
 	}
 
@@ -1449,7 +1451,7 @@ func ChanOf(dir ChanDir, t Type) Type {
 		s = "chan " + *typ.string
 	}
 	if tt := lookupType(s); tt != nil {
-		ch := (*chanType)(unsafe.Pointer(tt))
+		ch := (*chanType)(unsafe.Pointer(toType(tt).(*rtype)))
 		if ch.elem == typ && ch.dir == uintptr(dir) {
 			ti, _ := lookupCache.LoadOrStore(ckey, tt)
 			return ti.(Type)
@@ -1481,7 +1483,7 @@ func ChanOf(dir ChanDir, t Type) Type {
 	ch.uncommonType = nil
 	ch.ptrToThis = nil
 
-	ti, _ := lookupCache.LoadOrStore(ckey, &ch.rtype)
+	ti, _ := lookupCache.LoadOrStore(ckey, toType(&ch.rtype).(*rtype))
 	return ti.(Type)
 }
 
@@ -1508,7 +1510,7 @@ func MapOf(key, elem Type) Type {
 	// Look in known types.
 	s := "map[" + *ktyp.string + "]" + *etyp.string
 	if tt := lookupType(s); tt != nil {
-		mt := (*mapType)(unsafe.Pointer(tt))
+		mt := (*mapType)(unsafe.Pointer(toType(tt).(*rtype)))
 		if mt.key == ktyp && mt.elem == etyp {
 			ti, _ := lookupCache.LoadOrStore(ckey, tt)
 			return ti.(Type)
@@ -1559,7 +1561,7 @@ func MapOf(key, elem Type) Type {
 		mt.flags |= 16
 	}
 
-	ti, _ := lookupCache.LoadOrStore(ckey, &mt.rtype)
+	ti, _ := lookupCache.LoadOrStore(ckey, toType(&mt.rtype).(*rtype))
 	return ti.(Type)
 }
 
@@ -1648,7 +1650,7 @@ func FuncOf(in, out []Type, variadic bool) Type {
 	ft.string = &str
 	ft.uncommonType = nil
 	ft.ptrToThis = nil
-	return addToCache(&ft.rtype)
+	return addToCache(toType(&ft.rtype).(*rtype))
 }
 
 // funcStr builds a string representation of a funcType.
@@ -1909,7 +1911,7 @@ func SliceOf(t Type) Type {
 	// Look in known types.
 	s := "[]" + *typ.string
 	if tt := lookupType(s); tt != nil {
-		slice := (*sliceType)(unsafe.Pointer(tt))
+		slice := (*sliceType)(unsafe.Pointer(toType(tt).(*rtype)))
 		if slice.elem == typ {
 			ti, _ := lookupCache.LoadOrStore(ckey, tt)
 			return ti.(Type)
@@ -1930,7 +1932,7 @@ func SliceOf(t Type) Type {
 	slice.uncommonType = nil
 	slice.ptrToThis = nil
 
-	ti, _ := lookupCache.LoadOrStore(ckey, &slice.rtype)
+	ti, _ := lookupCache.LoadOrStore(ckey, toType(&slice.rtype).(*rtype))
 	return ti.(Type)
 }
 
@@ -2234,7 +2236,7 @@ func StructOf(fields []StructField) Type {
 
 	typ.uncommonType = nil
 	typ.ptrToThis = nil
-	return addToCache(&typ.rtype)
+	return addToCache(toType(&typ.rtype).(*rtype))
 }
 
 // runtimeStructField takes a StructField value passed to StructOf and
@@ -2330,7 +2332,7 @@ func ArrayOf(count int, elem Type) Type {
 	// Look in known types.
 	s := "[" + strconv.Itoa(count) + "]" + *typ.string
 	if tt := lookupType(s); tt != nil {
-		array := (*arrayType)(unsafe.Pointer(tt))
+		array := (*arrayType)(unsafe.Pointer(toType(tt).(*rtype)))
 		if array.elem == typ {
 			ti, _ := lookupCache.LoadOrStore(ckey, tt)
 			return ti.(Type)
@@ -2446,7 +2448,7 @@ func ArrayOf(count int, elem Type) Type {
 		array.kind &^= kindDirectIface
 	}
 
-	ti, _ := lookupCache.LoadOrStore(ckey, &array.rtype)
+	ti, _ := lookupCache.LoadOrStore(ckey, toType(&array.rtype).(*rtype))
 	return ti.(Type)
 }
 
@@ -2458,16 +2460,6 @@ func appendVarint(x []byte, v uintptr) []byte {
 	return x
 }
 
-// toType converts from a *rtype to a Type that can be returned
-// to the client of package reflect. The only concern is that
-// a nil *rtype must be replaced by a nil Type.
-func toType(p *rtype) Type {
-	if p == nil {
-		return nil
-	}
-	return p
-}
-
 // Look up a compiler-generated type descriptor.
 // Implemented in runtime.
 func lookupType(s string) *rtype
diff --git a/libgo/go/reflect/value.go b/libgo/go/reflect/value.go
index e60f84f..64f7432 100644
--- a/libgo/go/reflect/value.go
+++ b/libgo/go/reflect/value.go
@@ -1785,7 +1785,7 @@ type SliceHeader struct {
 }
 
 func typesMustMatch(what string, t1, t2 Type) {
-	if t1 != t2 {
+	if !typeEqual(t1, t2) {
 		panic(what + ": " + t1.String() + " != " + t2.String())
 	}
 }