Use FNV instead of maphash as the hasher for soong. am: d5133cfc64

Original change: https://android-review.googlesource.com/c/platform/build/blueprint/+/3107009

Change-Id: I2f0c454f7b473af96b1bcef9d6b12426a76e4185
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>

context.go

@@ -4159,7 +4159,7 @@ func (c *Context) VerifyProvidersWereUnchanged() []error {
 			for m := range toProcess {
 				for i, provider := range m.providers {
 					if provider != nil {
-						hash, err := proptools.HashProvider(provider)
+						hash, err := proptools.CalculateHash(provider)
 						if err != nil {
 							errors = append(errors, fmt.Errorf("provider %q on module %q was modified after being set, and no longer hashable afterwards: %s", providerRegistry[i].typ, m.Name(), err.Error()))
 							continue

proptools/hash_provider.go

@@ -18,32 +18,31 @@ import (
 	"cmp"
 	"encoding/binary"
 	"fmt"
-	"hash/maphash"
+	"hash"
+	"hash/fnv"
 	"math"
 	"reflect"
 	"sort"
+	"unsafe"
 )
 
-var seed maphash.Seed = maphash.MakeSeed()
-
 // byte to insert between elements of lists, fields of structs/maps, etc in order
 // to try and make sure the hash is different when values are moved around between
 // elements. 36 is arbitrary, but it's the ascii code for a record separator
 var recordSeparator []byte = []byte{36}
 
-func HashProvider(provider interface{}) (uint64, error) {
-	hasher := maphash.Hash{}
-	hasher.SetSeed(seed)
+func CalculateHash(value interface{}) (uint64, error) {
+	hasher := fnv.New64()
 	ptrs := make(map[uintptr]bool)
-	v := reflect.ValueOf(provider)
+	v := reflect.ValueOf(value)
 	var err error
 	if v.IsValid() {
-		err = hashProviderInternal(&hasher, v, ptrs)
+		err = calculateHashInternal(hasher, v, ptrs)
 	}
 	return hasher.Sum64(), err
 }
 
-func hashProviderInternal(hasher *maphash.Hash, v reflect.Value, ptrs map[uintptr]bool) error {
+func calculateHashInternal(hasher hash.Hash64, v reflect.Value, ptrs map[uintptr]bool) error {
 	var int64Array [8]byte
 	int64Buf := int64Array[:]
 	binary.LittleEndian.PutUint64(int64Buf, uint64(v.Kind()))
@@ -55,7 +54,7 @@ func hashProviderInternal(hasher *maphash.Hash, v reflect.Value, ptrs map[uintpt
 		hasher.Write(int64Buf)
 		for i := 0; i < v.NumField(); i++ {
 			hasher.Write(recordSeparator)
-			err := hashProviderInternal(hasher, v.Field(i), ptrs)
+			err := calculateHashInternal(hasher, v.Field(i), ptrs)
 			if err != nil {
 				return fmt.Errorf("in field %s: %s", v.Type().Field(i).Name, err.Error())
 			}
@@ -77,12 +76,12 @@ func hashProviderInternal(hasher *maphash.Hash, v reflect.Value, ptrs map[uintpt
 		})
 		for i := 0; i < v.Len(); i++ {
 			hasher.Write(recordSeparator)
-			err := hashProviderInternal(hasher, keys[indexes[i]], ptrs)
+			err := calculateHashInternal(hasher, keys[indexes[i]], ptrs)
 			if err != nil {
 				return fmt.Errorf("in map: %s", err.Error())
 			}
 			hasher.Write(recordSeparator)
-			err = hashProviderInternal(hasher, keys[indexes[i]], ptrs)
+			err = calculateHashInternal(hasher, keys[indexes[i]], ptrs)
 			if err != nil {
 				return fmt.Errorf("in map: %s", err.Error())
 			}
@@ -92,7 +91,7 @@ func hashProviderInternal(hasher *maphash.Hash, v reflect.Value, ptrs map[uintpt
 		hasher.Write(int64Buf)
 		for i := 0; i < v.Len(); i++ {
 			hasher.Write(recordSeparator)
-			err := hashProviderInternal(hasher, v.Index(i), ptrs)
+			err := calculateHashInternal(hasher, v.Index(i), ptrs)
 			if err != nil {
 				return fmt.Errorf("in %s at index %d: %s", v.Kind().String(), i, err.Error())
 			}
@@ -103,15 +102,16 @@ func hashProviderInternal(hasher *maphash.Hash, v reflect.Value, ptrs map[uintpt
 			hasher.Write(int64Buf[:1])
 			return nil
 		}
-		addr := v.Pointer()
-		binary.LittleEndian.PutUint64(int64Buf, uint64(addr))
+		// Hardcoded value to indicate it is a pointer
+		binary.LittleEndian.PutUint64(int64Buf, uint64(0x55))
 		hasher.Write(int64Buf)
+		addr := v.Pointer()
 		if _, ok := ptrs[addr]; ok {
 			// We could make this an error if we want to disallow pointer cycles in the future
 			return nil
 		}
 		ptrs[addr] = true
-		err := hashProviderInternal(hasher, v.Elem(), ptrs)
+		err := calculateHashInternal(hasher, v.Elem(), ptrs)
 		if err != nil {
 			return fmt.Errorf("in pointer: %s", err.Error())
 		}
@@ -122,13 +122,20 @@ func hashProviderInternal(hasher *maphash.Hash, v reflect.Value, ptrs map[uintpt
 		} else {
 			// The only way get the pointer out of an interface to hash it or check for cycles
 			// would be InterfaceData(), but that's deprecated and seems like it has undefined behavior.
-			err := hashProviderInternal(hasher, v.Elem(), ptrs)
+			err := calculateHashInternal(hasher, v.Elem(), ptrs)
 			if err != nil {
 				return fmt.Errorf("in interface: %s", err.Error())
 			}
 		}
 	case reflect.String:
-		hasher.WriteString(v.String())
+		strLen := len(v.String())
+		if strLen == 0 {
+			// unsafe.StringData is unspecified in this case
+			int64Buf[0] = 0
+			hasher.Write(int64Buf[:1])
+			return nil
+		}
+		hasher.Write(unsafe.Slice(unsafe.StringData(v.String()), strLen))
 	case reflect.Bool:
 		if v.Bool() {
 			int64Buf[0] = 1
@@ -146,7 +153,7 @@ func hashProviderInternal(hasher *maphash.Hash, v reflect.Value, ptrs map[uintpt
 		binary.LittleEndian.PutUint64(int64Buf, math.Float64bits(v.Float()))
 		hasher.Write(int64Buf)
 	default:
-		return fmt.Errorf("providers may only contain primitives, strings, arrays, slices, structs, maps, and pointers, found: %s", v.Kind().String())
+		return fmt.Errorf("data may only contain primitives, strings, arrays, slices, structs, maps, and pointers, found: %s", v.Kind().String())
 	}
 	return nil
 }

proptools/hash_provider_test.go

@@ -5,9 +5,9 @@ import (
 	"testing"
 )
 
-func mustHash(t *testing.T, provider interface{}) uint64 {
+func mustHash(t *testing.T, data interface{}) uint64 {
 	t.Helper()
-	result, err := HashProvider(provider)
+	result, err := CalculateHash(data)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -15,11 +15,11 @@ func mustHash(t *testing.T, provider interface{}) uint64 {
 }
 
 func TestHashingMapGetsSameResults(t *testing.T) {
-	provider := map[string]string{"foo": "bar", "baz": "qux"}
-	first := mustHash(t, provider)
-	second := mustHash(t, provider)
-	third := mustHash(t, provider)
-	fourth := mustHash(t, provider)
+	data := map[string]string{"foo": "bar", "baz": "qux"}
+	first := mustHash(t, data)
+	second := mustHash(t, data)
+	third := mustHash(t, data)
+	fourth := mustHash(t, data)
 	if first != second || second != third || third != fourth {
 		t.Fatal("Did not get the same result every time for a map")
 	}
@@ -28,28 +28,28 @@ func TestHashingMapGetsSameResults(t *testing.T) {
 func TestHashingNonSerializableTypesFails(t *testing.T) {
 	testCases := []struct {
 		name string
-		provider interface{}
+		data interface{}
 	}{
 		{
 			name: "function pointer",
-			provider: []func(){nil},
+			data: []func(){nil},
 		},
 		{
 			name: "channel",
-			provider: []chan int{make(chan int)},
+			data: []chan int{make(chan int)},
 		},
 		{
 			name: "list with non-serializable type",
-			provider: []interface{}{"foo", make(chan int)},
+			data: []interface{}{"foo", make(chan int)},
 		},
 	}
 	for _, testCase := range testCases {
 		t.Run(testCase.name, func(t *testing.T) {
-			_, err := HashProvider(testCase)
+			_, err := CalculateHash(testCase)
 			if err == nil {
 				t.Fatal("Expected hashing error but didn't get one")
 			}
-			expected := "providers may only contain primitives, strings, arrays, slices, structs, maps, and pointers"
+			expected := "data may only contain primitives, strings, arrays, slices, structs, maps, and pointers"
 			if !strings.Contains(err.Error(), expected) {
 				t.Fatalf("Expected %q, got %q", expected, err.Error())
 			}
@@ -60,31 +60,31 @@ func TestHashingNonSerializableTypesFails(t *testing.T) {
 func TestHashSuccessful(t *testing.T) {
 	testCases := []struct {
 		name string
-		provider interface{}
+		data interface{}
 	}{
 		{
 			name: "int",
-			provider: 5,
+			data: 5,
 		},
 		{
 			name: "string",
-			provider: "foo",
+			data: "foo",
 		},
 		{
 			name: "*string",
-			provider: StringPtr("foo"),
+			data: StringPtr("foo"),
 		},
 		{
 			name: "array",
-			provider: [3]string{"foo", "bar", "baz"},
+			data: [3]string{"foo", "bar", "baz"},
 		},
 		{
 			name: "slice",
-			provider: []string{"foo", "bar", "baz"},
+			data: []string{"foo", "bar", "baz"},
 		},
 		{
 			name: "struct",
-			provider: struct {
+			data: struct {
 				foo string
 				bar int
 			}{
@@ -94,19 +94,35 @@ func TestHashSuccessful(t *testing.T) {
 		},
 		{
 			name: "map",
-			provider: map[string]int{
+			data: map[string]int{
 				"foo": 3,
 				"bar": 4,
 			},
 		},
 		{
 			name: "list of interfaces with different types",
-			provider: []interface{}{"foo", 3, []string{"bar", "baz"}},
+			data: []interface{}{"foo", 3, []string{"bar", "baz"}},
 		},
 	}
 	for _, testCase := range testCases {
 		t.Run(testCase.name, func(t *testing.T) {
-			mustHash(t, testCase.provider)
+			mustHash(t, testCase.data)
 		})
 	}
 }
+
+func TestHashingDereferencePointers(t *testing.T) {
+	str1 := "this is a hash test for pointers"
+	str2 := "this is a hash test for pointers"
+	data := []struct {
+		content *string
+	}{
+		{content: &str1},
+		{content: &str2},
+	}
+	first := mustHash(t, data[0])
+	second := mustHash(t, data[1])
+	if first != second {
+		t.Fatal("Got different results for the same string")
+	}
+}

provider.go

@@ -158,7 +158,7 @@ func (c *Context) setProvider(m *moduleInfo, provider *providerKey, value any) {
 		if m.providerInitialValueHashes == nil {
 			m.providerInitialValueHashes = make([]uint64, len(providerRegistry))
 		}
-		hash, err := proptools.HashProvider(value)
+		hash, err := proptools.CalculateHash(value)
 		if err != nil {
 			panic(fmt.Sprintf("Can't set value of provider %s: %s", provider.typ, err.Error()))
 		}