variable: return *btf.Var from Variable{Spec}.Type()

In the initial design, we decided to return the inner type from .Type(), but
I forgot the outer btf.Var was needed to access decl tags set on the variable.

Returning a *Var here is the most convenient way of accessing the tags, otherwise
the caller would need to find the underlying map and parse the datasec manually,
which goes against what this API aims to solve.

Instead of the initial idea of returning a btf.Var as btf.Type, this now returns
btf.Var directly.

Signed-off-by: Timo Beckers <[email protected]>

elf_reader.go

@@ -1239,7 +1239,7 @@ func (ec *elfCode) loadDataSections() error {
 						return fmt.Errorf("data section %s: variable %s size in datasec (%d) doesn't match ELF symbol size (%d)", sec.Name, name, v.Size, ev.size)
 					}
 
-					ev.t = vt.Type
+					ev.t = vt
 				}
 			}
 		}

variable.go

@@ -19,7 +19,7 @@ type VariableSpec struct {
 	size   uint64
 
 	m *MapSpec
-	t btf.Type
+	t *btf.Var
 }
 
 // Set sets the value of the VariableSpec to the provided input using the host's
@@ -81,8 +81,12 @@ func (s *VariableSpec) Constant() bool {
 	return s.m.readOnly()
 }
 
-// Type returns the BTF Type of the variable.
-func (s *VariableSpec) Type() btf.Type {
+// Type returns the [btf.Var] representing the variable in its data section.
+// This is useful for inspecting the variable's decl tags and the type
+// information of the inner type.
+//
+// Returns nil if the original ELF object did not contain BTF information.
+func (s *VariableSpec) Type() *btf.Var {
 	return s.t
 }
 
@@ -122,12 +126,12 @@ type Variable struct {
 	name   string
 	offset uint64
 	size   uint64
-	t      btf.Type
+	t      *btf.Var
 
 	mm *Memory
 }
 
-func newVariable(name string, offset, size uint64, t btf.Type, mm *Memory) (*Variable, error) {
+func newVariable(name string, offset, size uint64, t *btf.Var, mm *Memory) (*Variable, error) {
 	if mm != nil {
 		if int(offset+size) > mm.Size() {
 			return nil, fmt.Errorf("offset %d(+%d) is out of bounds", offset, size)
@@ -159,8 +163,12 @@ func (v *Variable) ReadOnly() bool {
 	return v.mm.ReadOnly()
 }
 
-// Type returns the BTF Type of the variable.
-func (v *Variable) Type() btf.Type {
+// Type returns the [btf.Var] representing the variable in its data section.
+// This is useful for inspecting the variable's decl tags and the type
+// information of the inner type.
+//
+// Returns nil if the original ELF object did not contain BTF information.
+func (v *Variable) Type() *btf.Var {
 	return v.t
 }
 

variable_test.go

@@ -111,7 +111,7 @@ func TestVariable(t *testing.T) {
 
 	typ := obj.BSS.Type()
 	qt.Assert(t, qt.IsNotNil(typ))
-	i, ok := btf.As[*btf.Int](typ)
+	i, ok := btf.As[*btf.Int](typ.Type)
 	qt.Assert(t, qt.IsTrue(ok))
 	qt.Assert(t, qt.Equals(i.Size, 4))