btf: add Builder.Spec

When collecting and merging BTF types from multiple ELFs, it's convenient to be
able to query the resulting Spec in a single step. This commit adds the
Builder.Spec method to avoid having to write the BTF blob out to a file and
read it back from the filesystem.

Also add a test that checks if two identical types get correctly deduplicated
so they can be queried with AnyTypeByName afterwards.

Signed-off-by: Timo Beckers <timo@isovalent.com>

Author: ti-mo

btf/marshal.go

@@ -168,6 +168,19 @@ func (b *Builder) Add(typ Type) (TypeID, error) {
 	return id, nil
 }
 
+// Spec marshals the Builder's types and returns a new Spec to query them.
+//
+// The resulting Spec does not share any state with the Builder, subsequent
+// additions to the Builder will not affect the Spec.
+func (b *Builder) Spec() (*Spec, error) {
+	buf, err := b.Marshal(make([]byte, 0), nil)
+	if err != nil {
+		return nil, err
+	}
+
+	return loadRawSpec(buf, nil)
+}
+
 // Marshal encodes all types in the Marshaler into BTF wire format.
 //
 // opts may be nil.

btf/marshal_test.go

@@ -68,6 +68,22 @@ func TestBuilderAdd(t *testing.T) {
 	qt.Assert(t, qt.Equals(id, TypeID(3)))
 }
 
+func TestBuilderSpec(t *testing.T) {
+	b, err := NewBuilder([]Type{
+		&Int{Name: "foo", Size: 2},
+		&Int{Name: "foo", Size: 2},
+	}, &BuilderOptions{Deduplicate: true})
+	qt.Assert(t, qt.IsNil(err))
+
+	spec, err := b.Spec()
+	qt.Assert(t, qt.IsNil(err))
+
+	// With deduplication enabled, both ints should be merged into one,
+	// allowing queries with AnyTypeByName.
+	_, err = spec.AnyTypeByName("foo")
+	qt.Assert(t, qt.IsNil(err))
+}
+
 func TestRoundtripVMlinux(t *testing.T) {
 	types := typesFromSpec(t, vmlinuxSpec(t))