[go-marshal] Add dynamic tag in go_marshal.

This makes it easier to implement dynamically sized types in go-marshal. You
really only need to implement MarshalBytes, UnmarshalBytes and SizeBytes to
implement the entire interface.

By using the `dynamic` tag, the autogenerator will generate the rest of the
methods for us.

This change also simplifies how KernelIPTGetEntries implements Marshallable
using the newly added utility.

PiperOrigin-RevId: 356397114

1 files changed, 19 insertions, 0 deletions

diff --git a/tools/go_marshal/test/marshal_test.go b/tools/go_marshal/test/marshal_test.go
index a00f9a684..b0091dc64 100644
--- a/tools/go_marshal/test/marshal_test.go
+++ b/tools/go_marshal/test/marshal_test.go
@@ -28,6 +28,7 @@ import (
 
 	"github.com/google/go-cmp/cmp"
 	"gvisor.dev/gvisor/pkg/marshal"
+	"gvisor.dev/gvisor/pkg/marshal/primitive"
 	"gvisor.dev/gvisor/pkg/syserror"
 	"gvisor.dev/gvisor/pkg/usermem"
 	"gvisor.dev/gvisor/tools/go_marshal/analysis"
@@ -513,3 +514,21 @@ func TestLimitedSliceMarshalling(t *testing.T) {
 		})
 	}
 }
+
+func TestDynamicType(t *testing.T) {
+	t12 := test.Type12Dynamic{
+		X: 32,
+		Y: []primitive.Int64{5, 6, 7},
+	}
+
+	var m marshal.Marshallable
+	m = &t12 // Ensure that all methods were generated.
+	b := make([]byte, m.SizeBytes())
+	m.MarshalBytes(b)
+
+	var res test.Type12Dynamic
+	res.UnmarshalBytes(b)
+	if !reflect.DeepEqual(t12, res) {
+		t.Errorf("dynamic type is not same after marshalling and unmarshalling: before = %+v, after = %+v", t12, res)
+	}
+}