src/debug/plan9obj/file.go - go - Git at Google

 // Copyright 2014 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 /*
 Package plan9obj implements access to Plan 9 a.out object files.

 # Security

 This package is not designed to be hardened against adversarial inputs, and is
 outside the scope of https://go.dev/security/policy. In particular, only basic
 validation is done when parsing object files. As such, care should be taken when
 parsing untrusted inputs, as parsing malformed files may consume significant
 resources, or cause panics.
 */
 package plan9obj

 import (
 	"encoding/binary"
 	"errors"
 	"fmt"
 	"internal/saferio"
 	"io"
 	"os"
 )

 // A FileHeader represents a Plan 9 a.out file header.
 type FileHeader struct {
 	Magic       uint32
 	Bss         uint32
 	Entry       uint64
 	PtrSize     int
 	LoadAddress uint64
 	HdrSize     uint64
 }

 // A File represents an open Plan 9 a.out file.
 type File struct {
 	FileHeader
 	Sections []*Section
 	closer   io.Closer
 }

 // A SectionHeader represents a single Plan 9 a.out section header.
 // This structure doesn't exist on-disk, but eases navigation
 // through the object file.
 type SectionHeader struct {
 	Name   string
 	Size   uint32
 	Offset uint32
 }

 // A Section represents a single section in a Plan 9 a.out file.
 type Section struct {
 	SectionHeader

 	// Embed ReaderAt for ReadAt method.
 	// Do not embed SectionReader directly
 	// to avoid having Read and Seek.
 	// If a client wants Read and Seek it must use
 	// Open() to avoid fighting over the seek offset
 	// with other clients.
 	io.ReaderAt
 	sr *io.SectionReader
 }

 // Data reads and returns the contents of the Plan 9 a.out section.
 func (s *Section) Data() ([]byte, error) {
 	return saferio.ReadDataAt(s.sr, uint64(s.Size), 0)
 }

 // Open returns a new ReadSeeker reading the Plan 9 a.out section.
 func (s *Section) Open() io.ReadSeeker { return io.NewSectionReader(s.sr, 0, 1<<63-1) }

 // A Symbol represents an entry in a Plan 9 a.out symbol table section.
 type Sym struct {
 	Value uint64
 	Type  rune
 	Name  string
 }

 /*
  * Plan 9 a.out reader
  */

 // formatError is returned by some operations if the data does
 // not have the correct format for an object file.
 type formatError struct {
 	off int
 	msg string
 	val any
 }

 func (e *formatError) Error() string {
 	msg := e.msg
 	if e.val != nil {
 		msg += fmt.Sprintf(" '%v'", e.val)
 	}
 	msg += fmt.Sprintf(" in record at byte %#x", e.off)
 	return msg
 }

 // Open opens the named file using [os.Open] and prepares it for use as a Plan 9 a.out binary.
 func Open(name string) (*File, error) {
 	f, err := os.Open(name)
 	if err != nil {
 		return nil, err
 	}
 	ff, err := NewFile(f)
 	if err != nil {
 		f.Close()
 		return nil, err
 	}
 	ff.closer = f
 	return ff, nil
 }

 // Close closes the [File].
 // If the [File] was created using [NewFile] directly instead of [Open],
 // Close has no effect.
 func (f *File) Close() error {
 	var err error
 	if f.closer != nil {
 		err = f.closer.Close()
 		f.closer = nil
 	}
 	return err
 }

 func parseMagic(magic []byte) (uint32, error) {
 	m := binary.BigEndian.Uint32(magic)
 	switch m {
 	case Magic386, MagicAMD64, MagicARM:
 		return m, nil
 	}
 	return 0, &formatError{0, "bad magic number", magic}
 }

 // NewFile creates a new [File] for accessing a Plan 9 binary in an underlying reader.
 // The Plan 9 binary is expected to start at position 0 in the ReaderAt.
 func NewFile(r io.ReaderAt) (*File, error) {
 	sr := io.NewSectionReader(r, 0, 1<<63-1)
 	// Read and decode Plan 9 magic
 	var magic [4]byte
 	if _, err := r.ReadAt(magic[:], 0); err != nil {
 		return nil, err
 	}
 	_, err := parseMagic(magic[:])
 	if err != nil {
 		return nil, err
 	}

 	ph := new(prog)
 	if err := binary.Read(sr, binary.BigEndian, ph); err != nil {
 		return nil, err
 	}

 	f := &File{FileHeader: FileHeader{
 		Magic:       ph.Magic,
 		Bss:         ph.Bss,
 		Entry:       uint64(ph.Entry),
 		PtrSize:     4,
 		LoadAddress: 0x1000,
 		HdrSize:     4 * 8,
 	}}

 	if ph.Magic&Magic64 != 0 {
 		if err := binary.Read(sr, binary.BigEndian, &f.Entry); err != nil {
 			return nil, err
 		}
 		f.PtrSize = 8
 		f.LoadAddress = 0x200000
 		f.HdrSize += 8
 	}

 	var sects = []struct {
 		name string
 		size uint32
 	}{
 		{"text", ph.Text},
 		{"data", ph.Data},
 		{"syms", ph.Syms},
 		{"spsz", ph.Spsz},
 		{"pcsz", ph.Pcsz},
 	}

 	f.Sections = make([]*Section, 5)

 	off := uint32(f.HdrSize)

 	for i, sect := range sects {
 		s := new(Section)
 		s.SectionHeader = SectionHeader{
 			Name:   sect.name,
 			Size:   sect.size,
 			Offset: off,
 		}
 		off += sect.size
 		s.sr = io.NewSectionReader(r, int64(s.Offset), int64(s.Size))
 		s.ReaderAt = s.sr
 		f.Sections[i] = s
 	}

 	return f, nil
 }

 func walksymtab(data []byte, ptrsz int, fn func(sym) error) error {
 	var order binary.ByteOrder = binary.BigEndian
 	var s sym
 	p := data
 	for len(p) >= 4 {
 		// Symbol type, value.
 		if len(p) < ptrsz {
 			return &formatError{len(data), "unexpected EOF", nil}
 		}
 		// fixed-width value
 		if ptrsz == 8 {
 			s.value = order.Uint64(p[0:8])
 			p = p[8:]
 		} else {
 			s.value = uint64(order.Uint32(p[0:4]))
 			p = p[4:]
 		}

 		if len(p) < 1 {
 			return &formatError{len(data), "unexpected EOF", nil}
 		}
 		typ := p[0] & 0x7F
 		s.typ = typ
 		p = p[1:]

 		// Name.
 		var i int
 		var nnul int
 		for i = 0; i < len(p); i++ {
 			if p[i] == 0 {
 				nnul = 1
 				break
 			}
 		}
 		switch typ {
 		case 'z', 'Z':
 			p = p[i+nnul:]
 			for i = 0; i+2 <= len(p); i += 2 {
 				if p[i] == 0 && p[i+1] == 0 {
 					nnul = 2
 					break
 				}
 			}
 		}
 		if len(p) < i+nnul {
 			return &formatError{len(data), "unexpected EOF", nil}
 		}
 		s.name = p[0:i]
 		i += nnul
 		p = p[i:]

 		fn(s)
 	}
 	return nil
 }

 // newTable decodes the Go symbol table in data,
 // returning an in-memory representation.
 func newTable(symtab []byte, ptrsz int) ([]Sym, error) {
 	var n int
 	err := walksymtab(symtab, ptrsz, func(s sym) error {
 		n++
 		return nil
 	})
 	if err != nil {
 		return nil, err
 	}

 	fname := make(map[uint16]string)
 	syms := make([]Sym, 0, n)
 	err = walksymtab(symtab, ptrsz, func(s sym) error {
 		n := len(syms)
 		syms = syms[0 : n+1]
 		ts := &syms[n]
 		ts.Type = rune(s.typ)
 		ts.Value = s.value
 		switch s.typ {
 		default:
 			ts.Name = string(s.name)
 		case 'z', 'Z':
 			for i := 0; i < len(s.name); i += 2 {
 				eltIdx := binary.BigEndian.Uint16(s.name[i : i+2])
 				elt, ok := fname[eltIdx]
 				if !ok {
 					return &formatError{-1, "bad filename code", eltIdx}
 				}
 				if n := len(ts.Name); n > 0 && ts.Name[n-1] != '/' {
 					ts.Name += "/"
 				}
 				ts.Name += elt
 			}
 		}
 		switch s.typ {
 		case 'f':
 			fname[uint16(s.value)] = ts.Name
 		}
 		return nil
 	})
 	if err != nil {
 		return nil, err
 	}

 	return syms, nil
 }

 // ErrNoSymbols is returned by [File.Symbols] if there is no such section
 // in the File.
 var ErrNoSymbols = errors.New("no symbol section")

 // Symbols returns the symbol table for f.
 func (f *File) Symbols() ([]Sym, error) {
 	symtabSection := f.Section("syms")
 	if symtabSection == nil {
 		return nil, ErrNoSymbols
 	}

 	symtab, err := symtabSection.Data()
 	if err != nil {
 		return nil, errors.New("cannot load symbol section")
 	}

 	return newTable(symtab, f.PtrSize)
 }

 // Section returns a section with the given name, or nil if no such
 // section exists.
 func (f *File) Section(name string) *Section {
 	for _, s := range f.Sections {
 		if s.Name == name {
 			return s
 		}
 	}
 	return nil
 }
	// Copyright 2014 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	/*
	Package plan9obj implements access to Plan 9 a.out object files.

	# Security

	This package is not designed to be hardened against adversarial inputs, and is
	outside the scope of https://go.dev/security/policy. In particular, only basic
	validation is done when parsing object files. As such, care should be taken when
	parsing untrusted inputs, as parsing malformed files may consume significant
	resources, or cause panics.
	*/
	package plan9obj

	import (
	"encoding/binary"
	"errors"
	"fmt"
	"internal/saferio"
	"io"
	"os"
	)

	// A FileHeader represents a Plan 9 a.out file header.
	type FileHeader struct {
	Magic uint32
	Bss uint32
	Entry uint64
	PtrSize int
	LoadAddress uint64
	HdrSize uint64
	}

	// A File represents an open Plan 9 a.out file.
	type File struct {
	FileHeader
	Sections []*Section
	closer io.Closer
	}

	// A SectionHeader represents a single Plan 9 a.out section header.
	// This structure doesn't exist on-disk, but eases navigation
	// through the object file.
	type SectionHeader struct {
	Name string
	Size uint32
	Offset uint32
	}

	// A Section represents a single section in a Plan 9 a.out file.
	type Section struct {
	SectionHeader

	// Embed ReaderAt for ReadAt method.
	// Do not embed SectionReader directly
	// to avoid having Read and Seek.
	// If a client wants Read and Seek it must use
	// Open() to avoid fighting over the seek offset
	// with other clients.
	io.ReaderAt
	sr *io.SectionReader
	}

	// Data reads and returns the contents of the Plan 9 a.out section.
	func (s *Section) Data() ([]byte, error) {
	return saferio.ReadDataAt(s.sr, uint64(s.Size), 0)
	}

	// Open returns a new ReadSeeker reading the Plan 9 a.out section.
	func (s *Section) Open() io.ReadSeeker { return io.NewSectionReader(s.sr, 0, 1<<63-1) }

	// A Symbol represents an entry in a Plan 9 a.out symbol table section.
	type Sym struct {
	Value uint64
	Type rune
	Name string
	}

	/*
	* Plan 9 a.out reader
	*/

	// formatError is returned by some operations if the data does
	// not have the correct format for an object file.
	type formatError struct {
	off int
	msg string
	val any
	}

	func (e *formatError) Error() string {
	msg := e.msg
	if e.val != nil {
	msg += fmt.Sprintf(" '%v'", e.val)
	}
	msg += fmt.Sprintf(" in record at byte %#x", e.off)
	return msg
	}

	// Open opens the named file using [os.Open] and prepares it for use as a Plan 9 a.out binary.
	func Open(name string) (*File, error) {
	f, err := os.Open(name)
	if err != nil {
	return nil, err
	}
	ff, err := NewFile(f)
	if err != nil {
	f.Close()
	return nil, err
	}
	ff.closer = f
	return ff, nil
	}

	// Close closes the [File].
	// If the [File] was created using [NewFile] directly instead of [Open],
	// Close has no effect.
	func (f *File) Close() error {
	var err error
	if f.closer != nil {
	err = f.closer.Close()
	f.closer = nil
	}
	return err
	}

	func parseMagic(magic []byte) (uint32, error) {
	m := binary.BigEndian.Uint32(magic)
	switch m {
	case Magic386, MagicAMD64, MagicARM:
	return m, nil
	}
	return 0, &formatError{0, "bad magic number", magic}
	}

	// NewFile creates a new [File] for accessing a Plan 9 binary in an underlying reader.
	// The Plan 9 binary is expected to start at position 0 in the ReaderAt.
	func NewFile(r io.ReaderAt) (*File, error) {
	sr := io.NewSectionReader(r, 0, 1<<63-1)
	// Read and decode Plan 9 magic
	var magic [4]byte
	if _, err := r.ReadAt(magic[:], 0); err != nil {
	return nil, err
	}
	_, err := parseMagic(magic[:])
	if err != nil {
	return nil, err
	}

	ph := new(prog)
	if err := binary.Read(sr, binary.BigEndian, ph); err != nil {
	return nil, err
	}

	f := &File{FileHeader: FileHeader{
	Magic: ph.Magic,
	Bss: ph.Bss,
	Entry: uint64(ph.Entry),
	PtrSize: 4,
	LoadAddress: 0x1000,
	HdrSize: 4 * 8,
	}}

	if ph.Magic&Magic64 != 0 {
	if err := binary.Read(sr, binary.BigEndian, &f.Entry); err != nil {
	return nil, err
	}
	f.PtrSize = 8
	f.LoadAddress = 0x200000
	f.HdrSize += 8
	}

	var sects = []struct {
	name string
	size uint32
	}{
	{"text", ph.Text},
	{"data", ph.Data},
	{"syms", ph.Syms},
	{"spsz", ph.Spsz},
	{"pcsz", ph.Pcsz},
	}

	f.Sections = make([]*Section, 5)

	off := uint32(f.HdrSize)

	for i, sect := range sects {
	s := new(Section)
	s.SectionHeader = SectionHeader{
	Name: sect.name,
	Size: sect.size,
	Offset: off,
	}
	off += sect.size
	s.sr = io.NewSectionReader(r, int64(s.Offset), int64(s.Size))
	s.ReaderAt = s.sr
	f.Sections[i] = s
	}

	return f, nil
	}

	func walksymtab(data []byte, ptrsz int, fn func(sym) error) error {
	var order binary.ByteOrder = binary.BigEndian
	var s sym
	p := data
	for len(p) >= 4 {
	// Symbol type, value.
	if len(p) < ptrsz {
	return &formatError{len(data), "unexpected EOF", nil}
	}
	// fixed-width value
	if ptrsz == 8 {
	s.value = order.Uint64(p[0:8])
	p = p[8:]
	} else {
	s.value = uint64(order.Uint32(p[0:4]))
	p = p[4:]
	}

	if len(p) < 1 {
	return &formatError{len(data), "unexpected EOF", nil}
	}
	typ := p[0] & 0x7F
	s.typ = typ
	p = p[1:]

	// Name.
	var i int
	var nnul int
	for i = 0; i < len(p); i++ {
	if p[i] == 0 {
	nnul = 1
	break
	}
	}
	switch typ {
	case 'z', 'Z':
	p = p[i+nnul:]
	for i = 0; i+2 <= len(p); i += 2 {
	if p[i] == 0 && p[i+1] == 0 {
	nnul = 2
	break
	}
	}
	}
	if len(p) < i+nnul {
	return &formatError{len(data), "unexpected EOF", nil}
	}
	s.name = p[0:i]
	i += nnul
	p = p[i:]

	fn(s)
	}
	return nil
	}

	// newTable decodes the Go symbol table in data,
	// returning an in-memory representation.
	func newTable(symtab []byte, ptrsz int) ([]Sym, error) {
	var n int
	err := walksymtab(symtab, ptrsz, func(s sym) error {
	n++
	return nil
	})
	if err != nil {
	return nil, err
	}

	fname := make(map[uint16]string)
	syms := make([]Sym, 0, n)
	err = walksymtab(symtab, ptrsz, func(s sym) error {
	n := len(syms)
	syms = syms[0 : n+1]
	ts := &syms[n]
	ts.Type = rune(s.typ)
	ts.Value = s.value
	switch s.typ {
	default:
	ts.Name = string(s.name)
	case 'z', 'Z':
	for i := 0; i < len(s.name); i += 2 {
	eltIdx := binary.BigEndian.Uint16(s.name[i : i+2])
	elt, ok := fname[eltIdx]
	if !ok {
	return &formatError{-1, "bad filename code", eltIdx}
	}
	if n := len(ts.Name); n > 0 && ts.Name[n-1] != '/' {
	ts.Name += "/"
	}
	ts.Name += elt
	}
	}
	switch s.typ {
	case 'f':
	fname[uint16(s.value)] = ts.Name
	}
	return nil
	})
	if err != nil {
	return nil, err
	}

	return syms, nil
	}

	// ErrNoSymbols is returned by [File.Symbols] if there is no such section
	// in the File.
	var ErrNoSymbols = errors.New("no symbol section")

	// Symbols returns the symbol table for f.
	func (f *File) Symbols() ([]Sym, error) {
	symtabSection := f.Section("syms")
	if symtabSection == nil {
	return nil, ErrNoSymbols
	}

	symtab, err := symtabSection.Data()
	if err != nil {
	return nil, errors.New("cannot load symbol section")
	}

	return newTable(symtab, f.PtrSize)
	}

	// Section returns a section with the given name, or nil if no such
	// section exists.
	func (f File) Section(name string) Section {
	for _, s := range f.Sections {
	if s.Name == name {
	return s
	}
	}
	return nil
	}