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Unified Diff: debug/elf/file.go

Issue 81660043: code review 81660043: ogle: fork all the debug packages (Closed)
Patch Set: diff -r ecb70517b100 https://code.google.com/p/ogle Created 10 years ago
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Index: debug/elf/file.go
===================================================================
new file mode 100644
--- /dev/null
+++ b/debug/elf/file.go
@@ -0,0 +1,828 @@
+// Copyright 2009 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 elf implements access to ELF object files.
+package elf
+
+import (
+ "bytes"
+ "encoding/binary"
+ "errors"
+ "fmt"
+ "io"
+ "os"
+
+ "code.google.com/p/ogle/debug/dwarf"
+)
+
+// TODO: error reporting detail
+
+/*
+ * Internal ELF representation
+ */
+
+// A FileHeader represents an ELF file header.
+type FileHeader struct {
+ Class Class
+ Data Data
+ Version Version
+ OSABI OSABI
+ ABIVersion uint8
+ ByteOrder binary.ByteOrder
+ Type Type
+ Machine Machine
+ Entry uint64
+}
+
+// A File represents an open ELF file.
+type File struct {
+ FileHeader
+ Sections []*Section
+ Progs []*Prog
+ closer io.Closer
+ gnuNeed []verneed
+ gnuVersym []byte
+}
+
+// A SectionHeader represents a single ELF section header.
+type SectionHeader struct {
+ Name string
+ Type SectionType
+ Flags SectionFlag
+ Addr uint64
+ Offset uint64
+ Size uint64
+ Link uint32
+ Info uint32
+ Addralign uint64
+ Entsize uint64
+}
+
+// A Section represents a single section in an ELF 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 ELF section.
+func (s *Section) Data() ([]byte, error) {
+ dat := make([]byte, s.sr.Size())
+ n, err := s.sr.ReadAt(dat, 0)
+ if n == len(dat) {
+ err = nil
+ }
+ return dat[0:n], err
+}
+
+// stringTable reads and returns the string table given by the
+// specified link value.
+func (f *File) stringTable(link uint32) ([]byte, error) {
+ if link <= 0 || link >= uint32(len(f.Sections)) {
+ return nil, errors.New("section has invalid string table link")
+ }
+ return f.Sections[link].Data()
+}
+
+// Open returns a new ReadSeeker reading the ELF section.
+func (s *Section) Open() io.ReadSeeker { return io.NewSectionReader(s.sr, 0, 1<<63-1) }
+
+// A ProgHeader represents a single ELF program header.
+type ProgHeader struct {
+ Type ProgType
+ Flags ProgFlag
+ Off uint64
+ Vaddr uint64
+ Paddr uint64
+ Filesz uint64
+ Memsz uint64
+ Align uint64
+}
+
+// A Prog represents a single ELF program header in an ELF binary.
+type Prog struct {
+ ProgHeader
+
+ // 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
+}
+
+// Open returns a new ReadSeeker reading the ELF program body.
+func (p *Prog) Open() io.ReadSeeker { return io.NewSectionReader(p.sr, 0, 1<<63-1) }
+
+// A Symbol represents an entry in an ELF symbol table section.
+type Symbol struct {
+ Name string
+ Info, Other byte
+ Section SectionIndex
+ Value, Size uint64
+}
+
+/*
+ * ELF reader
+ */
+
+type FormatError struct {
+ off int64
+ msg string
+ val interface{}
+}
+
+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 an ELF 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
+}
+
+// SectionByType returns the first section in f with the
+// given type, or nil if there is no such section.
+func (f *File) SectionByType(typ SectionType) *Section {
+ for _, s := range f.Sections {
+ if s.Type == typ {
+ return s
+ }
+ }
+ return nil
+}
+
+// NewFile creates a new File for accessing an ELF binary in an underlying reader.
+// The ELF 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 ELF identifier
+ var ident [16]uint8
+ if _, err := r.ReadAt(ident[0:], 0); err != nil {
+ return nil, err
+ }
+ if ident[0] != '\x7f' || ident[1] != 'E' || ident[2] != 'L' || ident[3] != 'F' {
+ return nil, &FormatError{0, "bad magic number", ident[0:4]}
+ }
+
+ f := new(File)
+ f.Class = Class(ident[EI_CLASS])
+ switch f.Class {
+ case ELFCLASS32:
+ case ELFCLASS64:
+ // ok
+ default:
+ return nil, &FormatError{0, "unknown ELF class", f.Class}
+ }
+
+ f.Data = Data(ident[EI_DATA])
+ switch f.Data {
+ case ELFDATA2LSB:
+ f.ByteOrder = binary.LittleEndian
+ case ELFDATA2MSB:
+ f.ByteOrder = binary.BigEndian
+ default:
+ return nil, &FormatError{0, "unknown ELF data encoding", f.Data}
+ }
+
+ f.Version = Version(ident[EI_VERSION])
+ if f.Version != EV_CURRENT {
+ return nil, &FormatError{0, "unknown ELF version", f.Version}
+ }
+
+ f.OSABI = OSABI(ident[EI_OSABI])
+ f.ABIVersion = ident[EI_ABIVERSION]
+
+ // Read ELF file header
+ var phoff int64
+ var phentsize, phnum int
+ var shoff int64
+ var shentsize, shnum, shstrndx int
+ shstrndx = -1
+ switch f.Class {
+ case ELFCLASS32:
+ hdr := new(Header32)
+ sr.Seek(0, os.SEEK_SET)
+ if err := binary.Read(sr, f.ByteOrder, hdr); err != nil {
+ return nil, err
+ }
+ f.Type = Type(hdr.Type)
+ f.Machine = Machine(hdr.Machine)
+ f.Entry = uint64(hdr.Entry)
+ if v := Version(hdr.Version); v != f.Version {
+ return nil, &FormatError{0, "mismatched ELF version", v}
+ }
+ phoff = int64(hdr.Phoff)
+ phentsize = int(hdr.Phentsize)
+ phnum = int(hdr.Phnum)
+ shoff = int64(hdr.Shoff)
+ shentsize = int(hdr.Shentsize)
+ shnum = int(hdr.Shnum)
+ shstrndx = int(hdr.Shstrndx)
+ case ELFCLASS64:
+ hdr := new(Header64)
+ sr.Seek(0, os.SEEK_SET)
+ if err := binary.Read(sr, f.ByteOrder, hdr); err != nil {
+ return nil, err
+ }
+ f.Type = Type(hdr.Type)
+ f.Machine = Machine(hdr.Machine)
+ f.Entry = uint64(hdr.Entry)
+ if v := Version(hdr.Version); v != f.Version {
+ return nil, &FormatError{0, "mismatched ELF version", v}
+ }
+ phoff = int64(hdr.Phoff)
+ phentsize = int(hdr.Phentsize)
+ phnum = int(hdr.Phnum)
+ shoff = int64(hdr.Shoff)
+ shentsize = int(hdr.Shentsize)
+ shnum = int(hdr.Shnum)
+ shstrndx = int(hdr.Shstrndx)
+ }
+
+ if shnum > 0 && shoff > 0 && (shstrndx < 0 || shstrndx >= shnum) {
+ return nil, &FormatError{0, "invalid ELF shstrndx", shstrndx}
+ }
+
+ // Read program headers
+ f.Progs = make([]*Prog, phnum)
+ for i := 0; i < phnum; i++ {
+ off := phoff + int64(i)*int64(phentsize)
+ sr.Seek(off, os.SEEK_SET)
+ p := new(Prog)
+ switch f.Class {
+ case ELFCLASS32:
+ ph := new(Prog32)
+ if err := binary.Read(sr, f.ByteOrder, ph); err != nil {
+ return nil, err
+ }
+ p.ProgHeader = ProgHeader{
+ Type: ProgType(ph.Type),
+ Flags: ProgFlag(ph.Flags),
+ Off: uint64(ph.Off),
+ Vaddr: uint64(ph.Vaddr),
+ Paddr: uint64(ph.Paddr),
+ Filesz: uint64(ph.Filesz),
+ Memsz: uint64(ph.Memsz),
+ Align: uint64(ph.Align),
+ }
+ case ELFCLASS64:
+ ph := new(Prog64)
+ if err := binary.Read(sr, f.ByteOrder, ph); err != nil {
+ return nil, err
+ }
+ p.ProgHeader = ProgHeader{
+ Type: ProgType(ph.Type),
+ Flags: ProgFlag(ph.Flags),
+ Off: uint64(ph.Off),
+ Vaddr: uint64(ph.Vaddr),
+ Paddr: uint64(ph.Paddr),
+ Filesz: uint64(ph.Filesz),
+ Memsz: uint64(ph.Memsz),
+ Align: uint64(ph.Align),
+ }
+ }
+ p.sr = io.NewSectionReader(r, int64(p.Off), int64(p.Filesz))
+ p.ReaderAt = p.sr
+ f.Progs[i] = p
+ }
+
+ // Read section headers
+ f.Sections = make([]*Section, shnum)
+ names := make([]uint32, shnum)
+ for i := 0; i < shnum; i++ {
+ off := shoff + int64(i)*int64(shentsize)
+ sr.Seek(off, os.SEEK_SET)
+ s := new(Section)
+ switch f.Class {
+ case ELFCLASS32:
+ sh := new(Section32)
+ if err := binary.Read(sr, f.ByteOrder, sh); err != nil {
+ return nil, err
+ }
+ names[i] = sh.Name
+ s.SectionHeader = SectionHeader{
+ Type: SectionType(sh.Type),
+ Flags: SectionFlag(sh.Flags),
+ Addr: uint64(sh.Addr),
+ Offset: uint64(sh.Off),
+ Size: uint64(sh.Size),
+ Link: uint32(sh.Link),
+ Info: uint32(sh.Info),
+ Addralign: uint64(sh.Addralign),
+ Entsize: uint64(sh.Entsize),
+ }
+ case ELFCLASS64:
+ sh := new(Section64)
+ if err := binary.Read(sr, f.ByteOrder, sh); err != nil {
+ return nil, err
+ }
+ names[i] = sh.Name
+ s.SectionHeader = SectionHeader{
+ Type: SectionType(sh.Type),
+ Flags: SectionFlag(sh.Flags),
+ Offset: uint64(sh.Off),
+ Size: uint64(sh.Size),
+ Addr: uint64(sh.Addr),
+ Link: uint32(sh.Link),
+ Info: uint32(sh.Info),
+ Addralign: uint64(sh.Addralign),
+ Entsize: uint64(sh.Entsize),
+ }
+ }
+ s.sr = io.NewSectionReader(r, int64(s.Offset), int64(s.Size))
+ s.ReaderAt = s.sr
+ f.Sections[i] = s
+ }
+
+ if len(f.Sections) == 0 {
+ return f, nil
+ }
+
+ // Load section header string table.
+ shstrtab, err := f.Sections[shstrndx].Data()
+ if err != nil {
+ return nil, err
+ }
+ for i, s := range f.Sections {
+ var ok bool
+ s.Name, ok = getString(shstrtab, int(names[i]))
+ if !ok {
+ return nil, &FormatError{shoff + int64(i*shentsize), "bad section name index", names[i]}
+ }
+ }
+
+ return f, nil
+}
+
+// getSymbols returns a slice of Symbols from parsing the symbol table
+// with the given type, along with the associated string table.
+func (f *File) getSymbols(typ SectionType) ([]Symbol, []byte, error) {
+ switch f.Class {
+ case ELFCLASS64:
+ return f.getSymbols64(typ)
+
+ case ELFCLASS32:
+ return f.getSymbols32(typ)
+ }
+
+ return nil, nil, errors.New("not implemented")
+}
+
+func (f *File) getSymbols32(typ SectionType) ([]Symbol, []byte, error) {
+ symtabSection := f.SectionByType(typ)
+ if symtabSection == nil {
+ return nil, nil, errors.New("no symbol section")
+ }
+
+ data, err := symtabSection.Data()
+ if err != nil {
+ return nil, nil, errors.New("cannot load symbol section")
+ }
+ symtab := bytes.NewReader(data)
+ if symtab.Len()%Sym32Size != 0 {
+ return nil, nil, errors.New("length of symbol section is not a multiple of SymSize")
+ }
+
+ strdata, err := f.stringTable(symtabSection.Link)
+ if err != nil {
+ return nil, nil, errors.New("cannot load string table section")
+ }
+
+ // The first entry is all zeros.
+ var skip [Sym32Size]byte
+ symtab.Read(skip[:])
+
+ symbols := make([]Symbol, symtab.Len()/Sym32Size)
+
+ i := 0
+ var sym Sym32
+ for symtab.Len() > 0 {
+ binary.Read(symtab, f.ByteOrder, &sym)
+ str, _ := getString(strdata, int(sym.Name))
+ symbols[i].Name = str
+ symbols[i].Info = sym.Info
+ symbols[i].Other = sym.Other
+ symbols[i].Section = SectionIndex(sym.Shndx)
+ symbols[i].Value = uint64(sym.Value)
+ symbols[i].Size = uint64(sym.Size)
+ i++
+ }
+
+ return symbols, strdata, nil
+}
+
+func (f *File) getSymbols64(typ SectionType) ([]Symbol, []byte, error) {
+ symtabSection := f.SectionByType(typ)
+ if symtabSection == nil {
+ return nil, nil, errors.New("no symbol section")
+ }
+
+ data, err := symtabSection.Data()
+ if err != nil {
+ return nil, nil, errors.New("cannot load symbol section")
+ }
+ symtab := bytes.NewReader(data)
+ if symtab.Len()%Sym64Size != 0 {
+ return nil, nil, errors.New("length of symbol section is not a multiple of Sym64Size")
+ }
+
+ strdata, err := f.stringTable(symtabSection.Link)
+ if err != nil {
+ return nil, nil, errors.New("cannot load string table section")
+ }
+
+ // The first entry is all zeros.
+ var skip [Sym64Size]byte
+ symtab.Read(skip[:])
+
+ symbols := make([]Symbol, symtab.Len()/Sym64Size)
+
+ i := 0
+ var sym Sym64
+ for symtab.Len() > 0 {
+ binary.Read(symtab, f.ByteOrder, &sym)
+ str, _ := getString(strdata, int(sym.Name))
+ symbols[i].Name = str
+ symbols[i].Info = sym.Info
+ symbols[i].Other = sym.Other
+ symbols[i].Section = SectionIndex(sym.Shndx)
+ symbols[i].Value = sym.Value
+ symbols[i].Size = sym.Size
+ i++
+ }
+
+ return symbols, strdata, nil
+}
+
+// getString extracts a string from an ELF string table.
+func getString(section []byte, start int) (string, bool) {
+ if start < 0 || start >= len(section) {
+ return "", false
+ }
+
+ for end := start; end < len(section); end++ {
+ if section[end] == 0 {
+ return string(section[start:end]), true
+ }
+ }
+ return "", false
+}
+
+// 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
+}
+
+// applyRelocations applies relocations to dst. rels is a relocations section
+// in RELA format.
+func (f *File) applyRelocations(dst []byte, rels []byte) error {
+ if f.Class == ELFCLASS64 && f.Machine == EM_X86_64 {
+ return f.applyRelocationsAMD64(dst, rels)
+ }
+
+ return errors.New("not implemented")
+}
+
+func (f *File) applyRelocationsAMD64(dst []byte, rels []byte) error {
+ if len(rels)%Sym64Size != 0 {
+ return errors.New("length of relocation section is not a multiple of Sym64Size")
+ }
+
+ symbols, _, err := f.getSymbols(SHT_SYMTAB)
+ if err != nil {
+ return err
+ }
+
+ b := bytes.NewReader(rels)
+ var rela Rela64
+
+ for b.Len() > 0 {
+ binary.Read(b, f.ByteOrder, &rela)
+ symNo := rela.Info >> 32
+ t := R_X86_64(rela.Info & 0xffff)
+
+ if symNo == 0 || symNo > uint64(len(symbols)) {
+ continue
+ }
+ sym := &symbols[symNo-1]
+ if SymType(sym.Info&0xf) != STT_SECTION {
+ // We don't handle non-section relocations for now.
+ continue
+ }
+
+ switch t {
+ case R_X86_64_64:
+ if rela.Off+8 >= uint64(len(dst)) || rela.Addend < 0 {
+ continue
+ }
+ f.ByteOrder.PutUint64(dst[rela.Off:rela.Off+8], uint64(rela.Addend))
+ case R_X86_64_32:
+ if rela.Off+4 >= uint64(len(dst)) || rela.Addend < 0 {
+ continue
+ }
+ f.ByteOrder.PutUint32(dst[rela.Off:rela.Off+4], uint32(rela.Addend))
+ }
+ }
+
+ return nil
+}
+
+func (f *File) DWARF() (*dwarf.Data, error) {
+ // There are many other DWARF sections, but these
+ // are the required ones, and the debug/dwarf package
+ // does not use the others, so don't bother loading them.
+ var names = [...]string{"abbrev", "info", "str"}
+ var dat [len(names)][]byte
+ for i, name := range names {
+ name = ".debug_" + name
+ s := f.Section(name)
+ if s == nil {
+ continue
+ }
+ b, err := s.Data()
+ if err != nil && uint64(len(b)) < s.Size {
+ return nil, err
+ }
+ dat[i] = b
+ }
+
+ // If there's a relocation table for .debug_info, we have to process it
+ // now otherwise the data in .debug_info is invalid for x86-64 objects.
+ rela := f.Section(".rela.debug_info")
+ if rela != nil && rela.Type == SHT_RELA && f.Machine == EM_X86_64 {
+ data, err := rela.Data()
+ if err != nil {
+ return nil, err
+ }
+ err = f.applyRelocations(dat[1], data)
+ if err != nil {
+ return nil, err
+ }
+ }
+
+ abbrev, info, str := dat[0], dat[1], dat[2]
+ d, err := dwarf.New(abbrev, nil, nil, info, nil, nil, nil, str)
+ if err != nil {
+ return nil, err
+ }
+
+ // Look for DWARF4 .debug_types sections.
+ for i, s := range f.Sections {
+ if s.Name == ".debug_types" {
+ b, err := s.Data()
+ if err != nil && uint64(len(b)) < s.Size {
+ return nil, err
+ }
+
+ for _, r := range f.Sections {
+ if r.Type != SHT_RELA && r.Type != SHT_REL {
+ continue
+ }
+ if int(r.Info) != i {
+ continue
+ }
+ rd, err := r.Data()
+ if err != nil {
+ return nil, err
+ }
+ err = f.applyRelocations(b, rd)
+ if err != nil {
+ return nil, err
+ }
+ }
+
+ err = d.AddTypes(fmt.Sprintf("types-%d", i), b)
+ if err != nil {
+ return nil, err
+ }
+ }
+ }
+
+ return d, nil
+}
+
+// Symbols returns the symbol table for f.
+//
+// For compatibility with Go 1.0, Symbols omits the null symbol at index 0.
+// After retrieving the symbols as symtab, an externally supplied index x
+// corresponds to symtab[x-1], not symtab[x].
+func (f *File) Symbols() ([]Symbol, error) {
+ sym, _, err := f.getSymbols(SHT_SYMTAB)
+ return sym, err
+}
+
+type ImportedSymbol struct {
+ Name string
+ Version string
+ Library string
+}
+
+// ImportedSymbols returns the names of all symbols
+// referred to by the binary f that are expected to be
+// satisfied by other libraries at dynamic load time.
+// It does not return weak symbols.
+func (f *File) ImportedSymbols() ([]ImportedSymbol, error) {
+ sym, str, err := f.getSymbols(SHT_DYNSYM)
+ if err != nil {
+ return nil, err
+ }
+ f.gnuVersionInit(str)
+ var all []ImportedSymbol
+ for i, s := range sym {
+ if ST_BIND(s.Info) == STB_GLOBAL && s.Section == SHN_UNDEF {
+ all = append(all, ImportedSymbol{Name: s.Name})
+ f.gnuVersion(i, &all[len(all)-1])
+ }
+ }
+ return all, nil
+}
+
+type verneed struct {
+ File string
+ Name string
+}
+
+// gnuVersionInit parses the GNU version tables
+// for use by calls to gnuVersion.
+func (f *File) gnuVersionInit(str []byte) {
+ // Accumulate verneed information.
+ vn := f.SectionByType(SHT_GNU_VERNEED)
+ if vn == nil {
+ return
+ }
+ d, _ := vn.Data()
+
+ var need []verneed
+ i := 0
+ for {
+ if i+16 > len(d) {
+ break
+ }
+ vers := f.ByteOrder.Uint16(d[i : i+2])
+ if vers != 1 {
+ break
+ }
+ cnt := f.ByteOrder.Uint16(d[i+2 : i+4])
+ fileoff := f.ByteOrder.Uint32(d[i+4 : i+8])
+ aux := f.ByteOrder.Uint32(d[i+8 : i+12])
+ next := f.ByteOrder.Uint32(d[i+12 : i+16])
+ file, _ := getString(str, int(fileoff))
+
+ var name string
+ j := i + int(aux)
+ for c := 0; c < int(cnt); c++ {
+ if j+16 > len(d) {
+ break
+ }
+ // hash := f.ByteOrder.Uint32(d[j:j+4])
+ // flags := f.ByteOrder.Uint16(d[j+4:j+6])
+ other := f.ByteOrder.Uint16(d[j+6 : j+8])
+ nameoff := f.ByteOrder.Uint32(d[j+8 : j+12])
+ next := f.ByteOrder.Uint32(d[j+12 : j+16])
+ name, _ = getString(str, int(nameoff))
+ ndx := int(other)
+ if ndx >= len(need) {
+ a := make([]verneed, 2*(ndx+1))
+ copy(a, need)
+ need = a
+ }
+
+ need[ndx] = verneed{file, name}
+ if next == 0 {
+ break
+ }
+ j += int(next)
+ }
+
+ if next == 0 {
+ break
+ }
+ i += int(next)
+ }
+
+ // Versym parallels symbol table, indexing into verneed.
+ vs := f.SectionByType(SHT_GNU_VERSYM)
+ if vs == nil {
+ return
+ }
+ d, _ = vs.Data()
+
+ f.gnuNeed = need
+ f.gnuVersym = d
+}
+
+// gnuVersion adds Library and Version information to sym,
+// which came from offset i of the symbol table.
+func (f *File) gnuVersion(i int, sym *ImportedSymbol) {
+ // Each entry is two bytes.
+ i = (i + 1) * 2
+ if i >= len(f.gnuVersym) {
+ return
+ }
+ j := int(f.ByteOrder.Uint16(f.gnuVersym[i:]))
+ if j < 2 || j >= len(f.gnuNeed) {
+ return
+ }
+ n := &f.gnuNeed[j]
+ sym.Library = n.File
+ sym.Version = n.Name
+}
+
+// ImportedLibraries returns the names of all libraries
+// referred to by the binary f that are expected to be
+// linked with the binary at dynamic link time.
+func (f *File) ImportedLibraries() ([]string, error) {
+ return f.DynString(DT_NEEDED)
+}
+
+// DynString returns the strings listed for the given tag in the file's dynamic
+// section.
+//
+// The tag must be one that takes string values: DT_NEEDED, DT_SONAME, DT_RPATH, or
+// DT_RUNPATH.
+func (f *File) DynString(tag DynTag) ([]string, error) {
+ switch tag {
+ case DT_NEEDED, DT_SONAME, DT_RPATH, DT_RUNPATH:
+ default:
+ return nil, fmt.Errorf("non-string-valued tag %v", tag)
+ }
+ ds := f.SectionByType(SHT_DYNAMIC)
+ if ds == nil {
+ // not dynamic, so no libraries
+ return nil, nil
+ }
+ d, err := ds.Data()
+ if err != nil {
+ return nil, err
+ }
+ str, err := f.stringTable(ds.Link)
+ if err != nil {
+ return nil, err
+ }
+ var all []string
+ for len(d) > 0 {
+ var t DynTag
+ var v uint64
+ switch f.Class {
+ case ELFCLASS32:
+ t = DynTag(f.ByteOrder.Uint32(d[0:4]))
+ v = uint64(f.ByteOrder.Uint32(d[4:8]))
+ d = d[8:]
+ case ELFCLASS64:
+ t = DynTag(f.ByteOrder.Uint64(d[0:8]))
+ v = f.ByteOrder.Uint64(d[8:16])
+ d = d[16:]
+ }
+ if t == tag {
+ s, ok := getString(str, int(v))
+ if ok {
+ all = append(all, s)
+ }
+ }
+ }
+ return all, nil
+}
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