reflect: use int in StringHeader and SliceHeader on non-AVR platforms (#4156)

src/reflect/intw.go

@@ -0,0 +1,8 @@
+//go:build !avr
+
+package reflect
+
+// intw is an integer type, used in places where an int is typically required,
+// except architectures where the size of an int != word size.
+// See https://github.com/tinygo-org/tinygo/issues/1284.
+type intw = int

src/reflect/intw_avr.go

@@ -0,0 +1,8 @@
+//go:build avr
+
+package reflect
+
+// intw is an integer type, used in places where an int is typically required,
+// except architectures where the size of an int != word size.
+// See https://github.com/tinygo-org/tinygo/issues/1284.
+type intw = uintptr

src/reflect/intw_test.go

@@ -0,0 +1,30 @@
+//go:build !avr
+
+package reflect_test
+
+import (
+	"reflect"
+	"testing"
+	"unsafe"
+)
+
+// Verify that SliceHeader is the same size as a slice.
+var _ [unsafe.Sizeof([]byte{})]byte = [unsafe.Sizeof(reflect.SliceHeader{})]byte{}
+
+// TestSliceHeaderIntegerSize verifies that SliceHeader.Len and Cap are type int on non-AVR platforms.
+// See https://github.com/tinygo-org/tinygo/issues/1284.
+func TestSliceHeaderIntegerSize(t *testing.T) {
+	var h reflect.SliceHeader
+	h.Len = int(0)
+	h.Cap = int(0)
+}
+
+// Verify that StringHeader is the same size as a string.
+var _ [unsafe.Sizeof("hello")]byte = [unsafe.Sizeof(reflect.StringHeader{})]byte{}
+
+// TestStringHeaderIntegerSize verifies that StringHeader.Len and Cap are type int on non-AVR platforms.
+// See https://github.com/tinygo-org/tinygo/issues/1284.
+func TestStringHeaderIntegerSize(t *testing.T) {
+	var h reflect.StringHeader
+	h.Len = int(0)
+}

src/reflect/value.go

@@ -1578,8 +1578,8 @@ type funcHeader struct {
 
 type SliceHeader struct {
 	Data uintptr
-	Len  uintptr
+	Len  intw
-	Cap  uintptr
+	Cap  intw
 }
 
 // Slice header that matches the underlying structure. Used for when we switch
@@ -1592,7 +1592,7 @@ type sliceHeader struct {
 
 type StringHeader struct {
 	Data uintptr
-	Len  uintptr
+	Len  intw
 }
 
 // Like sliceHeader, this type is used internally to make sure pointer and
@@ -1602,6 +1602,16 @@ type stringHeader struct {
 	len  uintptr
 }
 
+// Verify SliceHeader and StringHeader sizes.
+// See https://github.com/tinygo-org/tinygo/pull/4156
+// and https://github.com/tinygo-org/tinygo/issues/1284.
+var (
+	_ [unsafe.Sizeof([]byte{})]byte = [unsafe.Sizeof(SliceHeader{})]byte{}
+	_ [unsafe.Sizeof([]byte{})]byte = [unsafe.Sizeof(sliceHeader{})]byte{}
+	_ [unsafe.Sizeof("")]byte       = [unsafe.Sizeof(StringHeader{})]byte{}
+	_ [unsafe.Sizeof("")]byte       = [unsafe.Sizeof(stringHeader{})]byte{}
+)
+
 type ValueError struct {
 	Method string
 	Kind   Kind

tests/runtime_wasi/malloc_test.go

@@ -67,7 +67,7 @@ func checkFilledBuffer(t *testing.T, ptr uintptr, content string) {
 	t.Helper()
 	buf := *(*string)(unsafe.Pointer(&reflect.StringHeader{
 		Data: ptr,
-		Len:  uintptr(len(content)),
+		Len:  len(content),
 	}))
 	if buf != content {
 		t.Errorf("expected %q, got %q", content, buf)