[chore]: Bump github.com/KimMachineGun/automemlimit from 0.2.4 to 0.2.5 (#1666)

Bumps [github.com/KimMachineGun/automemlimit](https://github.com/KimMachineGun/automemlimit) from 0.2.4 to 0.2.5.
- [Release notes](https://github.com/KimMachineGun/automemlimit/releases)
- [Commits](https://github.com/KimMachineGun/automemlimit/compare/v0.2.4...v0.2.5)

---
updated-dependencies:
- dependency-name: github.com/KimMachineGun/automemlimit
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

vendor/github.com/cilium/ebpf/asm/instruction.go

@@ -8,8 +8,10 @@ import (
 	"fmt"
 	"io"
 	"math"
+	"sort"
 	"strings"
 
+	"github.com/cilium/ebpf/internal/sys"
 	"github.com/cilium/ebpf/internal/unix"
 )
 
@@ -19,6 +21,10 @@ const InstructionSize = 8
 // RawInstructionOffset is an offset in units of raw BPF instructions.
 type RawInstructionOffset uint64
 
+var ErrUnreferencedSymbol = errors.New("unreferenced symbol")
+var ErrUnsatisfiedMapReference = errors.New("unsatisfied map reference")
+var ErrUnsatisfiedProgramReference = errors.New("unsatisfied program reference")
+
 // Bytes returns the offset of an instruction in bytes.
 func (rio RawInstructionOffset) Bytes() uint64 {
 	return uint64(rio) * InstructionSize
@@ -26,50 +32,57 @@ func (rio RawInstructionOffset) Bytes() uint64 {
 
 // Instruction is a single eBPF instruction.
 type Instruction struct {
-	OpCode    OpCode
-	Dst       Register
-	Src       Register
-	Offset    int16
-	Constant  int64
-	Reference string
-	Symbol    string
-}
+	OpCode   OpCode
+	Dst      Register
+	Src      Register
+	Offset   int16
+	Constant int64
 
-// Sym creates a symbol.
-func (ins Instruction) Sym(name string) Instruction {
-	ins.Symbol = name
-	return ins
+	// Metadata contains optional metadata about this instruction.
+	Metadata Metadata
 }
 
 // Unmarshal decodes a BPF instruction.
 func (ins *Instruction) Unmarshal(r io.Reader, bo binary.ByteOrder) (uint64, error) {
-	var bi bpfInstruction
-	err := binary.Read(r, bo, &bi)
-	if err != nil {
+	data := make([]byte, InstructionSize)
+	if _, err := io.ReadFull(r, data); err != nil {
 		return 0, err
 	}
 
-	ins.OpCode = bi.OpCode
-	ins.Offset = bi.Offset
-	ins.Constant = int64(bi.Constant)
-	ins.Dst, ins.Src, err = bi.Registers.Unmarshal(bo)
-	if err != nil {
-		return 0, fmt.Errorf("can't unmarshal registers: %s", err)
+	ins.OpCode = OpCode(data[0])
+
+	regs := data[1]
+	switch bo {
+	case binary.LittleEndian:
+		ins.Dst, ins.Src = Register(regs&0xF), Register(regs>>4)
+	case binary.BigEndian:
+		ins.Dst, ins.Src = Register(regs>>4), Register(regs&0xf)
 	}
 
-	if !bi.OpCode.isDWordLoad() {
+	ins.Offset = int16(bo.Uint16(data[2:4]))
+	// Convert to int32 before widening to int64
+	// to ensure the signed bit is carried over.
+	ins.Constant = int64(int32(bo.Uint32(data[4:8])))
+
+	if !ins.OpCode.IsDWordLoad() {
 		return InstructionSize, nil
 	}
 
-	var bi2 bpfInstruction
-	if err := binary.Read(r, bo, &bi2); err != nil {
+	// Pull another instruction from the stream to retrieve the second
+	// half of the 64-bit immediate value.
+	if _, err := io.ReadFull(r, data); err != nil {
 		// No Wrap, to avoid io.EOF clash
 		return 0, errors.New("64bit immediate is missing second half")
 	}
-	if bi2.OpCode != 0 || bi2.Offset != 0 || bi2.Registers != 0 {
+
+	// Require that all fields other than the value are zero.
+	if bo.Uint32(data[0:4]) != 0 {
 		return 0, errors.New("64bit immediate has non-zero fields")
 	}
-	ins.Constant = int64(uint64(uint32(bi2.Constant))<<32 | uint64(uint32(bi.Constant)))
+
+	cons1 := uint32(ins.Constant)
+	cons2 := int32(bo.Uint32(data[4:8]))
+	ins.Constant = int64(cons2)<<32 | int64(cons1)
 
 	return 2 * InstructionSize, nil
 }
@@ -80,7 +93,7 @@ func (ins Instruction) Marshal(w io.Writer, bo binary.ByteOrder) (uint64, error)
 		return 0, errors.New("invalid opcode")
 	}
 
-	isDWordLoad := ins.OpCode.isDWordLoad()
+	isDWordLoad := ins.OpCode.IsDWordLoad()
 
 	cons := int32(ins.Constant)
 	if isDWordLoad {
@@ -93,14 +106,12 @@ func (ins Instruction) Marshal(w io.Writer, bo binary.ByteOrder) (uint64, error)
 		return 0, fmt.Errorf("can't marshal registers: %s", err)
 	}
 
-	bpfi := bpfInstruction{
-		ins.OpCode,
-		regs,
-		ins.Offset,
-		cons,
-	}
-
-	if err := binary.Write(w, bo, &bpfi); err != nil {
+	data := make([]byte, InstructionSize)
+	data[0] = byte(ins.OpCode)
+	data[1] = byte(regs)
+	bo.PutUint16(data[2:4], uint16(ins.Offset))
+	bo.PutUint32(data[4:8], uint32(cons))
+	if _, err := w.Write(data); err != nil {
 		return 0, err
 	}
 
@@ -108,45 +119,83 @@ func (ins Instruction) Marshal(w io.Writer, bo binary.ByteOrder) (uint64, error)
 		return InstructionSize, nil
 	}
 
-	bpfi = bpfInstruction{
-		Constant: int32(ins.Constant >> 32),
-	}
-
-	if err := binary.Write(w, bo, &bpfi); err != nil {
+	// The first half of the second part of a double-wide instruction
+	// must be zero. The second half carries the value.
+	bo.PutUint32(data[0:4], 0)
+	bo.PutUint32(data[4:8], uint32(ins.Constant>>32))
+	if _, err := w.Write(data); err != nil {
 		return 0, err
 	}
 
 	return 2 * InstructionSize, nil
 }
 
-// RewriteMapPtr changes an instruction to use a new map fd.
+// AssociateMap associates a Map with this Instruction.
 //
-// Returns an error if the instruction doesn't load a map.
-func (ins *Instruction) RewriteMapPtr(fd int) error {
-	if !ins.OpCode.isDWordLoad() {
-		return fmt.Errorf("%s is not a 64 bit load", ins.OpCode)
-	}
-
-	if ins.Src != PseudoMapFD && ins.Src != PseudoMapValue {
+// Implicitly clears the Instruction's Reference field.
+//
+// Returns an error if the Instruction is not a map load.
+func (ins *Instruction) AssociateMap(m FDer) error {
+	if !ins.IsLoadFromMap() {
 		return errors.New("not a load from a map")
 	}
 
+	ins.Metadata.Set(referenceMeta{}, nil)
+	ins.Metadata.Set(mapMeta{}, m)
+
+	return nil
+}
+
+// RewriteMapPtr changes an instruction to use a new map fd.
+//
+// Returns an error if the instruction doesn't load a map.
+//
+// Deprecated: use AssociateMap instead. If you cannot provide a Map,
+// wrap an fd in a type implementing FDer.
+func (ins *Instruction) RewriteMapPtr(fd int) error {
+	if !ins.IsLoadFromMap() {
+		return errors.New("not a load from a map")
+	}
+
+	ins.encodeMapFD(fd)
+
+	return nil
+}
+
+func (ins *Instruction) encodeMapFD(fd int) {
 	// Preserve the offset value for direct map loads.
 	offset := uint64(ins.Constant) & (math.MaxUint32 << 32)
 	rawFd := uint64(uint32(fd))
 	ins.Constant = int64(offset | rawFd)
-	return nil
 }
 
-func (ins *Instruction) mapPtr() uint32 {
-	return uint32(uint64(ins.Constant) & math.MaxUint32)
+// MapPtr returns the map fd for this instruction.
+//
+// The result is undefined if the instruction is not a load from a map,
+// see IsLoadFromMap.
+//
+// Deprecated: use Map() instead.
+func (ins *Instruction) MapPtr() int {
+	// If there is a map associated with the instruction, return its FD.
+	if fd := ins.Metadata.Get(mapMeta{}); fd != nil {
+		return fd.(FDer).FD()
+	}
+
+	// Fall back to the fd stored in the Constant field
+	return ins.mapFd()
+}
+
+// mapFd returns the map file descriptor stored in the 32 least significant
+// bits of ins' Constant field.
+func (ins *Instruction) mapFd() int {
+	return int(int32(ins.Constant))
 }
 
 // RewriteMapOffset changes the offset of a direct load from a map.
 //
 // Returns an error if the instruction is not a direct load.
 func (ins *Instruction) RewriteMapOffset(offset uint32) error {
-	if !ins.OpCode.isDWordLoad() {
+	if !ins.OpCode.IsDWordLoad() {
 		return fmt.Errorf("%s is not a 64 bit load", ins.OpCode)
 	}
 
@@ -163,10 +212,10 @@ func (ins *Instruction) mapOffset() uint32 {
 	return uint32(uint64(ins.Constant) >> 32)
 }
 
-// isLoadFromMap returns true if the instruction loads from a map.
+// IsLoadFromMap returns true if the instruction loads from a map.
 //
 // This covers both loading the map pointer and direct map value loads.
-func (ins *Instruction) isLoadFromMap() bool {
+func (ins *Instruction) IsLoadFromMap() bool {
 	return ins.OpCode == LoadImmOp(DWord) && (ins.Src == PseudoMapFD || ins.Src == PseudoMapValue)
 }
 
@@ -177,6 +226,29 @@ func (ins *Instruction) IsFunctionCall() bool {
 	return ins.OpCode.JumpOp() == Call && ins.Src == PseudoCall
 }
 
+// IsLoadOfFunctionPointer returns true if the instruction loads a function pointer.
+func (ins *Instruction) IsLoadOfFunctionPointer() bool {
+	return ins.OpCode.IsDWordLoad() && ins.Src == PseudoFunc
+}
+
+// IsFunctionReference returns true if the instruction references another BPF
+// function, either by invoking a Call jump operation or by loading a function
+// pointer.
+func (ins *Instruction) IsFunctionReference() bool {
+	return ins.IsFunctionCall() || ins.IsLoadOfFunctionPointer()
+}
+
+// IsBuiltinCall returns true if the instruction is a built-in call, i.e. BPF helper call.
+func (ins *Instruction) IsBuiltinCall() bool {
+	return ins.OpCode.JumpOp() == Call && ins.Src == R0 && ins.Dst == R0
+}
+
+// IsConstantLoad returns true if the instruction loads a constant of the
+// given size.
+func (ins *Instruction) IsConstantLoad(size Size) bool {
+	return ins.OpCode == LoadImmOp(size) && ins.Src == R0 && ins.Offset == 0
+}
+
 // Format implements fmt.Formatter.
 func (ins Instruction) Format(f fmt.State, c rune) {
 	if c != 'v' {
@@ -197,22 +269,31 @@ func (ins Instruction) Format(f fmt.State, c rune) {
 		return
 	}
 
-	if ins.isLoadFromMap() {
-		fd := int32(ins.mapPtr())
+	if ins.IsLoadFromMap() {
+		fd := ins.mapFd()
+		m := ins.Map()
 		switch ins.Src {
 		case PseudoMapFD:
-			fmt.Fprintf(f, "LoadMapPtr dst: %s fd: %d", ins.Dst, fd)
+			if m != nil {
+				fmt.Fprintf(f, "LoadMapPtr dst: %s map: %s", ins.Dst, m)
+			} else {
+				fmt.Fprintf(f, "LoadMapPtr dst: %s fd: %d", ins.Dst, fd)
+			}
 
 		case PseudoMapValue:
-			fmt.Fprintf(f, "LoadMapValue dst: %s, fd: %d off: %d", ins.Dst, fd, ins.mapOffset())
+			if m != nil {
+				fmt.Fprintf(f, "LoadMapValue dst: %s, map: %s off: %d", ins.Dst, m, ins.mapOffset())
+			} else {
+				fmt.Fprintf(f, "LoadMapValue dst: %s, fd: %d off: %d", ins.Dst, fd, ins.mapOffset())
+			}
 		}
 
 		goto ref
 	}
 
 	fmt.Fprintf(f, "%v ", op)
-	switch cls := op.Class(); cls {
-	case LdClass, LdXClass, StClass, StXClass:
+	switch cls := op.Class(); {
+	case cls.isLoadOrStore():
 		switch op.Mode() {
 		case ImmMode:
 			fmt.Fprintf(f, "dst: %s imm: %d", ins.Dst, ins.Constant)
@@ -226,7 +307,7 @@ func (ins Instruction) Format(f fmt.State, c rune) {
 			fmt.Fprintf(f, "dst: %s src: %s", ins.Dst, ins.Src)
 		}
 
-	case ALU64Class, ALUClass:
+	case cls.IsALU():
 		fmt.Fprintf(f, "dst: %s ", ins.Dst)
 		if op.ALUOp() == Swap || op.Source() == ImmSource {
 			fmt.Fprintf(f, "imm: %d", ins.Constant)
@@ -234,7 +315,7 @@ func (ins Instruction) Format(f fmt.State, c rune) {
 			fmt.Fprintf(f, "src: %s", ins.Src)
 		}
 
-	case JumpClass:
+	case cls.IsJump():
 		switch jop := op.JumpOp(); jop {
 		case Call:
 			if ins.Src == PseudoCall {
@@ -255,34 +336,171 @@ func (ins Instruction) Format(f fmt.State, c rune) {
 	}
 
 ref:
-	if ins.Reference != "" {
-		fmt.Fprintf(f, " <%s>", ins.Reference)
+	if ins.Reference() != "" {
+		fmt.Fprintf(f, " <%s>", ins.Reference())
 	}
 }
 
+func (ins Instruction) equal(other Instruction) bool {
+	return ins.OpCode == other.OpCode &&
+		ins.Dst == other.Dst &&
+		ins.Src == other.Src &&
+		ins.Offset == other.Offset &&
+		ins.Constant == other.Constant
+}
+
+// Size returns the amount of bytes ins would occupy in binary form.
+func (ins Instruction) Size() uint64 {
+	return uint64(InstructionSize * ins.OpCode.rawInstructions())
+}
+
+type symbolMeta struct{}
+
+// WithSymbol marks the Instruction as a Symbol, which other Instructions
+// can point to using corresponding calls to WithReference.
+func (ins Instruction) WithSymbol(name string) Instruction {
+	ins.Metadata.Set(symbolMeta{}, name)
+	return ins
+}
+
+// Sym creates a symbol.
+//
+// Deprecated: use WithSymbol instead.
+func (ins Instruction) Sym(name string) Instruction {
+	return ins.WithSymbol(name)
+}
+
+// Symbol returns the value ins has been marked with using WithSymbol,
+// otherwise returns an empty string. A symbol is often an Instruction
+// at the start of a function body.
+func (ins Instruction) Symbol() string {
+	sym, _ := ins.Metadata.Get(symbolMeta{}).(string)
+	return sym
+}
+
+type referenceMeta struct{}
+
+// WithReference makes ins reference another Symbol or map by name.
+func (ins Instruction) WithReference(ref string) Instruction {
+	ins.Metadata.Set(referenceMeta{}, ref)
+	return ins
+}
+
+// Reference returns the Symbol or map name referenced by ins, if any.
+func (ins Instruction) Reference() string {
+	ref, _ := ins.Metadata.Get(referenceMeta{}).(string)
+	return ref
+}
+
+type mapMeta struct{}
+
+// Map returns the Map referenced by ins, if any.
+// An Instruction will contain a Map if e.g. it references an existing,
+// pinned map that was opened during ELF loading.
+func (ins Instruction) Map() FDer {
+	fd, _ := ins.Metadata.Get(mapMeta{}).(FDer)
+	return fd
+}
+
+type sourceMeta struct{}
+
+// WithSource adds source information about the Instruction.
+func (ins Instruction) WithSource(src fmt.Stringer) Instruction {
+	ins.Metadata.Set(sourceMeta{}, src)
+	return ins
+}
+
+// Source returns source information about the Instruction. The field is
+// present when the compiler emits BTF line info about the Instruction and
+// usually contains the line of source code responsible for it.
+func (ins Instruction) Source() fmt.Stringer {
+	str, _ := ins.Metadata.Get(sourceMeta{}).(fmt.Stringer)
+	return str
+}
+
+// A Comment can be passed to Instruction.WithSource to add a comment
+// to an instruction.
+type Comment string
+
+func (s Comment) String() string {
+	return string(s)
+}
+
+// FDer represents a resource tied to an underlying file descriptor.
+// Used as a stand-in for e.g. ebpf.Map since that type cannot be
+// imported here and FD() is the only method we rely on.
+type FDer interface {
+	FD() int
+}
+
 // Instructions is an eBPF program.
 type Instructions []Instruction
 
+// Unmarshal unmarshals an Instructions from a binary instruction stream.
+// All instructions in insns are replaced by instructions decoded from r.
+func (insns *Instructions) Unmarshal(r io.Reader, bo binary.ByteOrder) error {
+	if len(*insns) > 0 {
+		*insns = nil
+	}
+
+	var offset uint64
+	for {
+		var ins Instruction
+		n, err := ins.Unmarshal(r, bo)
+		if errors.Is(err, io.EOF) {
+			break
+		}
+		if err != nil {
+			return fmt.Errorf("offset %d: %w", offset, err)
+		}
+
+		*insns = append(*insns, ins)
+		offset += n
+	}
+
+	return nil
+}
+
+// Name returns the name of the function insns belongs to, if any.
+func (insns Instructions) Name() string {
+	if len(insns) == 0 {
+		return ""
+	}
+	return insns[0].Symbol()
+}
+
 func (insns Instructions) String() string {
 	return fmt.Sprint(insns)
 }
 
-// RewriteMapPtr rewrites all loads of a specific map pointer to a new fd.
+// Size returns the amount of bytes insns would occupy in binary form.
+func (insns Instructions) Size() uint64 {
+	var sum uint64
+	for _, ins := range insns {
+		sum += ins.Size()
+	}
+	return sum
+}
+
+// AssociateMap updates all Instructions that Reference the given symbol
+// to point to an existing Map m instead.
 //
-// Returns an error if the symbol isn't used, see IsUnreferencedSymbol.
-func (insns Instructions) RewriteMapPtr(symbol string, fd int) error {
+// Returns ErrUnreferencedSymbol error if no references to symbol are found
+// in insns. If symbol is anything else than the symbol name of map (e.g.
+// a bpf2bpf subprogram), an error is returned.
+func (insns Instructions) AssociateMap(symbol string, m FDer) error {
 	if symbol == "" {
 		return errors.New("empty symbol")
 	}
 
-	found := false
+	var found bool
 	for i := range insns {
 		ins := &insns[i]
-		if ins.Reference != symbol {
+		if ins.Reference() != symbol {
 			continue
 		}
 
-		if err := ins.RewriteMapPtr(fd); err != nil {
+		if err := ins.AssociateMap(m); err != nil {
 			return err
 		}
 
@@ -290,7 +508,40 @@ func (insns Instructions) RewriteMapPtr(symbol string, fd int) error {
 	}
 
 	if !found {
-		return &unreferencedSymbolError{symbol}
+		return fmt.Errorf("symbol %s: %w", symbol, ErrUnreferencedSymbol)
+	}
+
+	return nil
+}
+
+// RewriteMapPtr rewrites all loads of a specific map pointer to a new fd.
+//
+// Returns ErrUnreferencedSymbol if the symbol isn't used.
+//
+// Deprecated: use AssociateMap instead.
+func (insns Instructions) RewriteMapPtr(symbol string, fd int) error {
+	if symbol == "" {
+		return errors.New("empty symbol")
+	}
+
+	var found bool
+	for i := range insns {
+		ins := &insns[i]
+		if ins.Reference() != symbol {
+			continue
+		}
+
+		if !ins.IsLoadFromMap() {
+			return errors.New("not a load from a map")
+		}
+
+		ins.encodeMapFD(fd)
+
+		found = true
+	}
+
+	if !found {
+		return fmt.Errorf("symbol %s: %w", symbol, ErrUnreferencedSymbol)
 	}
 
 	return nil
@@ -302,31 +553,61 @@ func (insns Instructions) SymbolOffsets() (map[string]int, error) {
 	offsets := make(map[string]int)
 
 	for i, ins := range insns {
-		if ins.Symbol == "" {
+		if ins.Symbol() == "" {
 			continue
 		}
 
-		if _, ok := offsets[ins.Symbol]; ok {
-			return nil, fmt.Errorf("duplicate symbol %s", ins.Symbol)
+		if _, ok := offsets[ins.Symbol()]; ok {
+			return nil, fmt.Errorf("duplicate symbol %s", ins.Symbol())
 		}
 
-		offsets[ins.Symbol] = i
+		offsets[ins.Symbol()] = i
 	}
 
 	return offsets, nil
 }
 
+// FunctionReferences returns a set of symbol names these Instructions make
+// bpf-to-bpf calls to.
+func (insns Instructions) FunctionReferences() []string {
+	calls := make(map[string]struct{})
+	for _, ins := range insns {
+		if ins.Constant != -1 {
+			// BPF-to-BPF calls have -1 constants.
+			continue
+		}
+
+		if ins.Reference() == "" {
+			continue
+		}
+
+		if !ins.IsFunctionReference() {
+			continue
+		}
+
+		calls[ins.Reference()] = struct{}{}
+	}
+
+	result := make([]string, 0, len(calls))
+	for call := range calls {
+		result = append(result, call)
+	}
+
+	sort.Strings(result)
+	return result
+}
+
 // ReferenceOffsets returns the set of references and their offset in
 // the instructions.
 func (insns Instructions) ReferenceOffsets() map[string][]int {
 	offsets := make(map[string][]int)
 
 	for i, ins := range insns {
-		if ins.Reference == "" {
+		if ins.Reference() == "" {
 			continue
 		}
 
-		offsets[ins.Reference] = append(offsets[ins.Reference], i)
+		offsets[ins.Reference()] = append(offsets[ins.Reference()], i)
 	}
 
 	return offsets
@@ -337,7 +618,7 @@ func (insns Instructions) ReferenceOffsets() map[string][]int {
 // You can control indentation of symbols by
 // specifying a width. Setting a precision controls the indentation of
 // instructions.
-// The default character is a tab, which can be overriden by specifying
+// The default character is a tab, which can be overridden by specifying
 // the ' ' space flag.
 func (insns Instructions) Format(f fmt.State, c rune) {
 	if c != 's' && c != 'v' {
@@ -377,20 +658,36 @@ func (insns Instructions) Format(f fmt.State, c rune) {
 
 	iter := insns.Iterate()
 	for iter.Next() {
-		if iter.Ins.Symbol != "" {
-			fmt.Fprintf(f, "%s%s:\n", symIndent, iter.Ins.Symbol)
+		if iter.Ins.Symbol() != "" {
+			fmt.Fprintf(f, "%s%s:\n", symIndent, iter.Ins.Symbol())
+		}
+		if src := iter.Ins.Source(); src != nil {
+			line := strings.TrimSpace(src.String())
+			if line != "" {
+				fmt.Fprintf(f, "%s%*s; %s\n", indent, offsetWidth, " ", line)
+			}
 		}
 		fmt.Fprintf(f, "%s%*d: %v\n", indent, offsetWidth, iter.Offset, iter.Ins)
 	}
-
-	return
 }
 
 // Marshal encodes a BPF program into the kernel format.
+//
+// insns may be modified if there are unresolved jumps or bpf2bpf calls.
+//
+// Returns ErrUnsatisfiedProgramReference if there is a Reference Instruction
+// without a matching Symbol Instruction within insns.
 func (insns Instructions) Marshal(w io.Writer, bo binary.ByteOrder) error {
+	if err := insns.encodeFunctionReferences(); err != nil {
+		return err
+	}
+
+	if err := insns.encodeMapPointers(); err != nil {
+		return err
+	}
+
 	for i, ins := range insns {
-		_, err := ins.Marshal(w, bo)
-		if err != nil {
+		if _, err := ins.Marshal(w, bo); err != nil {
 			return fmt.Errorf("instruction %d: %w", i, err)
 		}
 	}
@@ -405,7 +702,7 @@ func (insns Instructions) Marshal(w io.Writer, bo binary.ByteOrder) error {
 func (insns Instructions) Tag(bo binary.ByteOrder) (string, error) {
 	h := sha1.New()
 	for i, ins := range insns {
-		if ins.isLoadFromMap() {
+		if ins.IsLoadFromMap() {
 			ins.Constant = 0
 		}
 		_, err := ins.Marshal(h, bo)
@@ -416,6 +713,95 @@ func (insns Instructions) Tag(bo binary.ByteOrder) (string, error) {
 	return hex.EncodeToString(h.Sum(nil)[:unix.BPF_TAG_SIZE]), nil
 }
 
+// encodeFunctionReferences populates the Offset (or Constant, depending on
+// the instruction type) field of instructions with a Reference field to point
+// to the offset of the corresponding instruction with a matching Symbol field.
+//
+// Only Reference Instructions that are either jumps or BPF function references
+// (calls or function pointer loads) are populated.
+//
+// Returns ErrUnsatisfiedProgramReference if there is a Reference Instruction
+// without at least one corresponding Symbol Instruction within insns.
+func (insns Instructions) encodeFunctionReferences() error {
+	// Index the offsets of instructions tagged as a symbol.
+	symbolOffsets := make(map[string]RawInstructionOffset)
+	iter := insns.Iterate()
+	for iter.Next() {
+		ins := iter.Ins
+
+		if ins.Symbol() == "" {
+			continue
+		}
+
+		if _, ok := symbolOffsets[ins.Symbol()]; ok {
+			return fmt.Errorf("duplicate symbol %s", ins.Symbol())
+		}
+
+		symbolOffsets[ins.Symbol()] = iter.Offset
+	}
+
+	// Find all instructions tagged as references to other symbols.
+	// Depending on the instruction type, populate their constant or offset
+	// fields to point to the symbol they refer to within the insn stream.
+	iter = insns.Iterate()
+	for iter.Next() {
+		i := iter.Index
+		offset := iter.Offset
+		ins := iter.Ins
+
+		if ins.Reference() == "" {
+			continue
+		}
+
+		switch {
+		case ins.IsFunctionReference() && ins.Constant == -1:
+			symOffset, ok := symbolOffsets[ins.Reference()]
+			if !ok {
+				return fmt.Errorf("%s at insn %d: symbol %q: %w", ins.OpCode, i, ins.Reference(), ErrUnsatisfiedProgramReference)
+			}
+
+			ins.Constant = int64(symOffset - offset - 1)
+
+		case ins.OpCode.Class().IsJump() && ins.Offset == -1:
+			symOffset, ok := symbolOffsets[ins.Reference()]
+			if !ok {
+				return fmt.Errorf("%s at insn %d: symbol %q: %w", ins.OpCode, i, ins.Reference(), ErrUnsatisfiedProgramReference)
+			}
+
+			ins.Offset = int16(symOffset - offset - 1)
+		}
+	}
+
+	return nil
+}
+
+// encodeMapPointers finds all Map Instructions and encodes their FDs
+// into their Constant fields.
+func (insns Instructions) encodeMapPointers() error {
+	iter := insns.Iterate()
+	for iter.Next() {
+		ins := iter.Ins
+
+		if !ins.IsLoadFromMap() {
+			continue
+		}
+
+		m := ins.Map()
+		if m == nil {
+			continue
+		}
+
+		fd := m.FD()
+		if fd < 0 {
+			return fmt.Errorf("map %s: %w", m, sys.ErrClosedFd)
+		}
+
+		ins.encodeMapFD(m.FD())
+	}
+
+	return nil
+}
+
 // Iterate allows iterating a BPF program while keeping track of
 // various offsets.
 //
@@ -451,13 +837,6 @@ func (iter *InstructionIterator) Next() bool {
 	return true
 }
 
-type bpfInstruction struct {
-	OpCode    OpCode
-	Registers bpfRegisters
-	Offset    int16
-	Constant  int32
-}
-
 type bpfRegisters uint8
 
 func newBPFRegisters(dst, src Register, bo binary.ByteOrder) (bpfRegisters, error) {
@@ -471,28 +850,10 @@ func newBPFRegisters(dst, src Register, bo binary.ByteOrder) (bpfRegisters, erro
 	}
 }
 
-func (r bpfRegisters) Unmarshal(bo binary.ByteOrder) (dst, src Register, err error) {
-	switch bo {
-	case binary.LittleEndian:
-		return Register(r & 0xF), Register(r >> 4), nil
-	case binary.BigEndian:
-		return Register(r >> 4), Register(r & 0xf), nil
-	default:
-		return 0, 0, fmt.Errorf("unrecognized ByteOrder %T", bo)
-	}
-}
-
-type unreferencedSymbolError struct {
-	symbol string
-}
-
-func (use *unreferencedSymbolError) Error() string {
-	return fmt.Sprintf("unreferenced symbol %s", use.symbol)
-}
-
 // IsUnreferencedSymbol returns true if err was caused by
 // an unreferenced symbol.
+//
+// Deprecated: use errors.Is(err, asm.ErrUnreferencedSymbol).
 func IsUnreferencedSymbol(err error) bool {
-	_, ok := err.(*unreferencedSymbolError)
-	return ok
+	return errors.Is(err, ErrUnreferencedSymbol)
 }