btf: Add decl tags for functions

btf/ext_info.go

@@ -145,7 +145,7 @@ func AssignMetadataToInstructions(
 //
 // If an instruction has an [asm.Comment], it will be synthesized into a mostly
 // empty line info.
-func MarshalExtInfos(insns asm.Instructions, b *Builder) (funcInfos, lineInfos []byte, _ error) {
+func MarshalExtInfos(insns asm.Instructions, b *Builder, types *Spec) (funcInfos, lineInfos []byte, _ error) {
 	iter := insns.Iterate()
 	for iter.Next() {
 		if iter.Ins.Source() != nil || FuncMetadata(iter.Ins) != nil {
@@ -166,6 +166,24 @@ marshal:
 			if err := fi.marshal(&fiBuf, b); err != nil {
 				return nil, nil, fmt.Errorf("write func info: %w", err)
 			}
+			if types != nil {
+				iter := types.Iterate()
+				for iter.Next() {
+					if t, ok := iter.Type.(*declTag); ok {
+						tfn, ok := t.Type.(*Func)
+						if !ok {
+							continue
+						}
+						if fn.Name != tfn.Name {
+							continue
+						}
+						_, err := b.Add(&declTag{fn, t.Value, t.Index})
+						if err != nil {
+							return nil, nil, fmt.Errorf("write decl tag: %w", err)
+						}
+					}
+				}
+			}
 		}
 
 		if source := iter.Ins.Source(); source != nil {

collection.go

@@ -529,7 +529,7 @@ func (cl *collectionLoader) loadProgram(progName string) (*Program, error) {
 		}
 	}
 
-	prog, err := newProgramWithOptions(progSpec, cl.opts.Programs)
+	prog, err := newProgramWithOptions(progSpec, cl.opts.Programs, cl.coll.Types)
 	if err != nil {
 		return nil, fmt.Errorf("program %s: %w", progName, err)
 	}

prog.go

@@ -219,7 +219,7 @@ func NewProgramWithOptions(spec *ProgramSpec, opts ProgramOptions) (*Program, er
 		return nil, errors.New("can't load a program from a nil spec")
 	}
 
-	prog, err := newProgramWithOptions(spec, opts)
+	prog, err := newProgramWithOptions(spec, opts, nil)
 	if errors.Is(err, asm.ErrUnsatisfiedMapReference) {
 		return nil, fmt.Errorf("cannot load program without loading its whole collection: %w", err)
 	}
@@ -235,7 +235,7 @@ var (
 	kfuncBadCall = []byte(fmt.Sprintf("invalid func unknown#%d\n", kfuncCallPoisonBase))
 )
 
-func newProgramWithOptions(spec *ProgramSpec, opts ProgramOptions) (*Program, error) {
+func newProgramWithOptions(spec *ProgramSpec, opts ProgramOptions, types *btf.Spec) (*Program, error) {
 	if len(spec.Instructions) == 0 {
 		return nil, errors.New("instructions cannot be empty")
 	}
@@ -307,7 +307,7 @@ func newProgramWithOptions(spec *ProgramSpec, opts ProgramOptions) (*Program, er
 	if errExtInfos == nil {
 		// Only add func and line info if the kernel supports it. This allows
 		// BPF compiled with modern toolchains to work on old kernels.
-		fib, lib, err := btf.MarshalExtInfos(insns, &b)
+		fib, lib, err := btf.MarshalExtInfos(insns, &b, types)
 		if err != nil {
 			return nil, fmt.Errorf("marshal ext_infos: %w", err)
 		}