add callback based constant editor

constant_editor.go

@@ -17,6 +17,8 @@ type ConstantEditor struct {
 	// Value - Value to write in the eBPF bytecode. When using the asm load method, the Value has to be a `uint64`.
 	Value interface{}
 
+	ValueCallback func(prog *ebpf.ProgramSpec) interface{}
+
 	// FailOnMissing - If FailOMissing is set to true, the constant edition process will return an error if the constant
 	// was missing in at least one program
 	FailOnMissing bool
@@ -29,6 +31,13 @@ type ConstantEditor struct {
 	ProbeIdentificationPairs []ProbeIdentificationPair
 }
 
+func (ce *ConstantEditor) GetValue(prog *ebpf.ProgramSpec) interface{} {
+	if ce.ValueCallback != nil {
+		return ce.ValueCallback(prog)
+	}
+	return ce.Value
+}
+
 // editConstants - newEditor the programs in the CollectionSpec with the provided constant editors. Tries with the BTF global
 // variable first, and fall back to the asm method if BTF is not available.
 func (m *Manager) editConstants() error {
@@ -40,7 +49,7 @@ func (m *Manager) editConstants() error {
 				continue
 			}
 			constant := map[string]interface{}{
-				editor.Name: editor.Value,
+				editor.Name: editor.GetValue(nil), // in BTF mode, we don't have access to the constant name
 			}
 			if err := m.collectionSpec.RewriteConstants(constant); err != nil && editor.FailOnMissing {
 				return err
@@ -88,7 +97,7 @@ func (m *Manager) editConstants() error {
 				edit = newEditor(&prog.Instructions)
 			}
 
-			if err := m.editConstantWithEditor(edit, constantEditor); err != nil {
+			if err := m.editConstantWithEditor(prog, edit, constantEditor); err != nil {
 				return fmt.Errorf("couldn't edit %s in %s: %w", constantEditor.Name, section, err)
 			}
 		}
@@ -100,11 +109,11 @@ func (m *Manager) editConstants() error {
 // editConstant - newEditor the provided program with the provided constant using the asm method.
 func (m *Manager) editConstant(prog *ebpf.ProgramSpec, editor ConstantEditor) error {
 	edit := newEditor(&prog.Instructions)
-	return m.editConstantWithEditor(edit, editor)
+	return m.editConstantWithEditor(prog, edit, editor)
 }
 
-func (m *Manager) editConstantWithEditor(edit *editor, editor ConstantEditor) error {
-	data, ok := (editor.Value).(uint64)
+func (m *Manager) editConstantWithEditor(prog *ebpf.ProgramSpec, edit *editor, editor ConstantEditor) error {
+	data, ok := (editor.GetValue(prog)).(uint64)
 	if !ok {
 		return fmt.Errorf("with the asm method, the constant value has to be of type uint64")
 	}