Unprivileged objNameAllowsDot, return *btf.Var from Variable{Spec}.Type()

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
 				}
 			}
 		}

syscalls.go

@@ -179,10 +179,18 @@ var haveObjName = internal.NewFeatureTest("object names", func() error {
 		MapName:    sys.NewObjName("feature_test"),
 	}
 
+	// Tolerate EPERM as this runs during ELF loading which is potentially
+	// unprivileged. Only EINVAL is conclusive, thrown from CHECK_ATTR.
 	fd, err := sys.MapCreate(&attr)
-	if err != nil {
+	if errors.Is(err, unix.EPERM) {
+		return nil
+	}
+	if errors.Is(err, unix.EINVAL) {
 		return internal.ErrNotSupported
 	}
+	if err != nil {
+		return err
+	}
 
 	_ = fd.Close()
 	return nil
@@ -201,10 +209,19 @@ var objNameAllowsDot = internal.NewFeatureTest("dot in object names", func() err
 		MapName:    sys.NewObjName(".test"),
 	}
 
+	// Tolerate EPERM, otherwise MapSpec.Name has its dots removed when run by
+	// unprivileged tools. (bpf2go, other code gen). Only EINVAL is conclusive,
+	// thrown from bpf_obj_name_cpy().
 	fd, err := sys.MapCreate(&attr)
-	if err != nil {
+	if errors.Is(err, unix.EPERM) {
+		return nil
+	}
+	if errors.Is(err, unix.EINVAL) {
 		return internal.ErrNotSupported
 	}
+	if err != nil {
+		return err
+	}
 
 	_ = fd.Close()
 	return nil

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
@@ -75,14 +75,28 @@ func (s *VariableSpec) Size() uint64 {
 	return s.size
 }
 
+// MapName returns the name of the underlying MapSpec.
+func (s *VariableSpec) MapName() string {
+	return s.m.Name
+}
+
+// Offset returns the offset of the variable in the underlying MapSpec.
+func (s *VariableSpec) Offset() uint64 {
+	return s.offset
+}
+
 // Constant returns true if the VariableSpec represents a variable that is
 // read-only from the perspective of the BPF program.
 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 +136,12 @@ 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 +173,12 @@ 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))