tests: do not cast pointers to uintptr

uintptr is not tracked by the GC, while any pointer type (including
unsafe.Pointer) is tracked. Make sure to only cast pointers to uintptr
when absolutely necessary.

This fixes a bug found in #3162.

tests/runtime_wasi/malloc_test.go

@@ -23,13 +23,13 @@ func libc_calloc(nmemb, size uintptr) unsafe.Pointer
 //export realloc
 func libc_realloc(ptr unsafe.Pointer, size uintptr) unsafe.Pointer
 
-func getFilledBuffer_malloc() uintptr {
+func getFilledBuffer_malloc() unsafe.Pointer {
 	ptr := libc_malloc(5)
 	fillPanda(ptr)
-	return uintptr(ptr)
+	return ptr
 }
 
-func getFilledBuffer_calloc() uintptr {
+func getFilledBuffer_calloc() unsafe.Pointer {
 	ptr := libc_calloc(2, 5)
 	fillPanda(ptr)
 	*(*byte)(unsafe.Add(ptr, 5)) = 'b'
@@ -37,23 +37,23 @@ func getFilledBuffer_calloc() uintptr {
 	*(*byte)(unsafe.Add(ptr, 7)) = 'a'
 	*(*byte)(unsafe.Add(ptr, 8)) = 'r'
 	*(*byte)(unsafe.Add(ptr, 9)) = 's'
-	return uintptr(ptr)
+	return ptr
 }
 
-func getFilledBuffer_realloc() uintptr {
+func getFilledBuffer_realloc() unsafe.Pointer {
 	origPtr := getFilledBuffer_malloc()
-	ptr := libc_realloc(unsafe.Pointer(origPtr), 9)
+	ptr := libc_realloc(origPtr, 9)
 	*(*byte)(unsafe.Add(ptr, 5)) = 'b'
 	*(*byte)(unsafe.Add(ptr, 6)) = 'e'
 	*(*byte)(unsafe.Add(ptr, 7)) = 'a'
 	*(*byte)(unsafe.Add(ptr, 8)) = 'r'
-	return uintptr(ptr)
+	return ptr
 }
 
-func getFilledBuffer_reallocNil() uintptr {
+func getFilledBuffer_reallocNil() unsafe.Pointer {
 	ptr := libc_realloc(nil, 5)
 	fillPanda(ptr)
-	return uintptr(ptr)
+	return ptr
 }
 
 func fillPanda(ptr unsafe.Pointer) {
@@ -64,10 +64,10 @@ func fillPanda(ptr unsafe.Pointer) {
 	*(*byte)(unsafe.Add(ptr, 4)) = 'a'
 }
 
-func checkFilledBuffer(t *testing.T, ptr uintptr, content string) {
+func checkFilledBuffer(t *testing.T, ptr unsafe.Pointer, content string) {
 	t.Helper()
 	buf := *(*string)(unsafe.Pointer(&reflect.StringHeader{
-		Data: ptr,
+		Data: uintptr(ptr),
 		Len:  uintptr(len(content)),
 	}))
 	if buf != content {
@@ -78,7 +78,7 @@ func checkFilledBuffer(t *testing.T, ptr uintptr, content string) {
 func TestMallocFree(t *testing.T) {
 	tests := []struct {
 		name      string
-		getBuffer func() uintptr
+		getBuffer func() unsafe.Pointer
 		content   string
 	}{
 		{
@@ -121,7 +121,7 @@ func TestMallocFree(t *testing.T) {
 
 			checkFilledBuffer(t, bufPtr, tt.content)
 
-			libc_free(unsafe.Pointer(bufPtr))
+			libc_free(bufPtr)
 		})
 	}
 }