gtsocial-umbx

instruction.go (22359B)

---

 package asm
 
 import (
 	"crypto/sha1"
 	"encoding/binary"
 	"encoding/hex"
 	"errors"
 	"fmt"
 	"io"
 	"math"
 	"sort"
 	"strings"
 
 	"github.com/cilium/ebpf/internal/sys"
 	"github.com/cilium/ebpf/internal/unix"
 )
 
 // InstructionSize is the size of a BPF instruction in bytes
 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
 }
 
 // Instruction is a single eBPF instruction.
 type Instruction struct {
 	OpCode   OpCode
 	Dst      Register
 	Src      Register
 	Offset   int16
 	Constant int64
 
 	// 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) {
 	data := make([]byte, InstructionSize)
 	if _, err := io.ReadFull(r, data); err != nil {
 		return 0, 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)
 	}
 
 	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
 	}
 
 	// 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")
 	}
 
 	// 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")
 	}
 
 	cons1 := uint32(ins.Constant)
 	cons2 := int32(bo.Uint32(data[4:8]))
 	ins.Constant = int64(cons2)<<32 | int64(cons1)
 
 	return 2 * InstructionSize, nil
 }
 
 // Marshal encodes a BPF instruction.
 func (ins Instruction) Marshal(w io.Writer, bo binary.ByteOrder) (uint64, error) {
 	if ins.OpCode == InvalidOpCode {
 		return 0, errors.New("invalid opcode")
 	}
 
 	isDWordLoad := ins.OpCode.IsDWordLoad()
 
 	cons := int32(ins.Constant)
 	if isDWordLoad {
 		// Encode least significant 32bit first for 64bit operations.
 		cons = int32(uint32(ins.Constant))
 	}
 
 	regs, err := newBPFRegisters(ins.Dst, ins.Src, bo)
 	if err != nil {
 		return 0, fmt.Errorf("can't marshal registers: %s", err)
 	}
 
 	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
 	}
 
 	if !isDWordLoad {
 		return InstructionSize, 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
 }
 
 // AssociateMap associates a Map with this Instruction.
 //
 // 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)
 }
 
 // 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() {
 		return fmt.Errorf("%s is not a 64 bit load", ins.OpCode)
 	}
 
 	if ins.Src != PseudoMapValue {
 		return errors.New("not a direct load from a map")
 	}
 
 	fd := uint64(ins.Constant) & math.MaxUint32
 	ins.Constant = int64(uint64(offset)<<32 | fd)
 	return nil
 }
 
 func (ins *Instruction) mapOffset() uint32 {
 	return uint32(uint64(ins.Constant) >> 32)
 }
 
 // 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 {
 	return ins.OpCode == LoadImmOp(DWord) && (ins.Src == PseudoMapFD || ins.Src == PseudoMapValue)
 }
 
 // IsFunctionCall returns true if the instruction calls another BPF function.
 //
 // This is not the same thing as a BPF helper call.
 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' {
 		fmt.Fprintf(f, "{UNRECOGNIZED: %c}", c)
 		return
 	}
 
 	op := ins.OpCode
 
 	if op == InvalidOpCode {
 		fmt.Fprint(f, "INVALID")
 		return
 	}
 
 	// Omit trailing space for Exit
 	if op.JumpOp() == Exit {
 		fmt.Fprint(f, op)
 		return
 	}
 
 	if ins.IsLoadFromMap() {
 		fd := ins.mapFd()
 		m := ins.Map()
 		switch ins.Src {
 		case PseudoMapFD:
 			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:
 			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(); {
 	case cls.isLoadOrStore():
 		switch op.Mode() {
 		case ImmMode:
 			fmt.Fprintf(f, "dst: %s imm: %d", ins.Dst, ins.Constant)
 		case AbsMode:
 			fmt.Fprintf(f, "imm: %d", ins.Constant)
 		case IndMode:
 			fmt.Fprintf(f, "dst: %s src: %s imm: %d", ins.Dst, ins.Src, ins.Constant)
 		case MemMode:
 			fmt.Fprintf(f, "dst: %s src: %s off: %d imm: %d", ins.Dst, ins.Src, ins.Offset, ins.Constant)
 		case XAddMode:
 			fmt.Fprintf(f, "dst: %s src: %s", ins.Dst, ins.Src)
 		}
 
 	case cls.IsALU():
 		fmt.Fprintf(f, "dst: %s ", ins.Dst)
 		if op.ALUOp() == Swap || op.Source() == ImmSource {
 			fmt.Fprintf(f, "imm: %d", ins.Constant)
 		} else {
 			fmt.Fprintf(f, "src: %s", ins.Src)
 		}
 
 	case cls.IsJump():
 		switch jop := op.JumpOp(); jop {
 		case Call:
 			if ins.Src == PseudoCall {
 				// bpf-to-bpf call
 				fmt.Fprint(f, ins.Constant)
 			} else {
 				fmt.Fprint(f, BuiltinFunc(ins.Constant))
 			}
 
 		default:
 			fmt.Fprintf(f, "dst: %s off: %d ", ins.Dst, ins.Offset)
 			if op.Source() == ImmSource {
 				fmt.Fprintf(f, "imm: %d", ins.Constant)
 			} else {
 				fmt.Fprintf(f, "src: %s", ins.Src)
 			}
 		}
 	}
 
 ref:
 	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)
 }
 
 // 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 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")
 	}
 
 	var found bool
 	for i := range insns {
 		ins := &insns[i]
 		if ins.Reference() != symbol {
 			continue
 		}
 
 		if err := ins.AssociateMap(m); err != nil {
 			return err
 		}
 
 		found = true
 	}
 
 	if !found {
 		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
 }
 
 // SymbolOffsets returns the set of symbols and their offset in
 // the instructions.
 func (insns Instructions) SymbolOffsets() (map[string]int, error) {
 	offsets := make(map[string]int)
 
 	for i, ins := range insns {
 		if ins.Symbol() == "" {
 			continue
 		}
 
 		if _, ok := offsets[ins.Symbol()]; ok {
 			return nil, fmt.Errorf("duplicate symbol %s", ins.Symbol())
 		}
 
 		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() == "" {
 			continue
 		}
 
 		offsets[ins.Reference()] = append(offsets[ins.Reference()], i)
 	}
 
 	return offsets
 }
 
 // Format implements fmt.Formatter.
 //
 // 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 overridden by specifying
 // the ' ' space flag.
 func (insns Instructions) Format(f fmt.State, c rune) {
 	if c != 's' && c != 'v' {
 		fmt.Fprintf(f, "{UNKNOWN FORMAT '%c'}", c)
 		return
 	}
 
 	// Precision is better in this case, because it allows
 	// specifying 0 padding easily.
 	padding, ok := f.Precision()
 	if !ok {
 		padding = 1
 	}
 
 	indent := strings.Repeat("\t", padding)
 	if f.Flag(' ') {
 		indent = strings.Repeat(" ", padding)
 	}
 
 	symPadding, ok := f.Width()
 	if !ok {
 		symPadding = padding - 1
 	}
 	if symPadding < 0 {
 		symPadding = 0
 	}
 
 	symIndent := strings.Repeat("\t", symPadding)
 	if f.Flag(' ') {
 		symIndent = strings.Repeat(" ", symPadding)
 	}
 
 	// Guess how many digits we need at most, by assuming that all instructions
 	// are double wide.
 	highestOffset := len(insns) * 2
 	offsetWidth := int(math.Ceil(math.Log10(float64(highestOffset))))
 
 	iter := insns.Iterate()
 	for iter.Next() {
 		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)
 	}
 }
 
 // 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 {
 		if _, err := ins.Marshal(w, bo); err != nil {
 			return fmt.Errorf("instruction %d: %w", i, err)
 		}
 	}
 	return nil
 }
 
 // Tag calculates the kernel tag for a series of instructions.
 //
 // It mirrors bpf_prog_calc_tag in the kernel and so can be compared
 // to ProgramInfo.Tag to figure out whether a loaded program matches
 // certain instructions.
 func (insns Instructions) Tag(bo binary.ByteOrder) (string, error) {
 	h := sha1.New()
 	for i, ins := range insns {
 		if ins.IsLoadFromMap() {
 			ins.Constant = 0
 		}
 		_, err := ins.Marshal(h, bo)
 		if err != nil {
 			return "", fmt.Errorf("instruction %d: %w", i, err)
 		}
 	}
 	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.
 //
 // Modifying the instruction slice will lead to undefined behaviour.
 func (insns Instructions) Iterate() *InstructionIterator {
 	return &InstructionIterator{insns: insns}
 }
 
 // InstructionIterator iterates over a BPF program.
 type InstructionIterator struct {
 	insns Instructions
 	// The instruction in question.
 	Ins *Instruction
 	// The index of the instruction in the original instruction slice.
 	Index int
 	// The offset of the instruction in raw BPF instructions. This accounts
 	// for double-wide instructions.
 	Offset RawInstructionOffset
 }
 
 // Next returns true as long as there are any instructions remaining.
 func (iter *InstructionIterator) Next() bool {
 	if len(iter.insns) == 0 {
 		return false
 	}
 
 	if iter.Ins != nil {
 		iter.Index++
 		iter.Offset += RawInstructionOffset(iter.Ins.OpCode.rawInstructions())
 	}
 	iter.Ins = &iter.insns[0]
 	iter.insns = iter.insns[1:]
 	return true
 }
 
 type bpfRegisters uint8
 
 func newBPFRegisters(dst, src Register, bo binary.ByteOrder) (bpfRegisters, error) {
 	switch bo {
 	case binary.LittleEndian:
 		return bpfRegisters((src << 4) | (dst & 0xF)), nil
 	case binary.BigEndian:
 		return bpfRegisters((dst << 4) | (src & 0xF)), nil
 	default:
 		return 0, fmt.Errorf("unrecognized ByteOrder %T", bo)
 	}
 }
 
 // IsUnreferencedSymbol returns true if err was caused by
 // an unreferenced symbol.
 //
 // Deprecated: use errors.Is(err, asm.ErrUnreferencedSymbol).
 func IsUnreferencedSymbol(err error) bool {
 	return errors.Is(err, ErrUnreferencedSymbol)
 }