| // 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" |
| "debug/dwarf" |
| "encoding/binary" |
| "fmt" |
| "io" |
| "os" |
| ) |
| |
| // 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 |
| } |
| |
| // A File represents an open ELF file. |
| type File struct { |
| FileHeader |
| Sections []*Section |
| Progs []*Prog |
| closer io.Closer |
| } |
| |
| // 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, os.Error) { |
| dat := make([]byte, s.sr.Size()) |
| n, err := s.sr.ReadAt(dat, 0) |
| return dat[0:n], err |
| } |
| |
| // 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 |
| 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 uint32 |
| Info, Other byte |
| Section uint32 |
| Value, Size uint64 |
| } |
| |
| /* |
| * ELF reader |
| */ |
| |
| type FormatError struct { |
| off int64 |
| msg string |
| val interface{} |
| } |
| |
| func (e *FormatError) String() 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, os.Error) { |
| f, err := os.Open(name, os.O_RDONLY, 0) |
| 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() os.Error { |
| var err os.Error |
| if f.closer != nil { |
| err = f.closer.Close() |
| f.closer = nil |
| } |
| return err |
| } |
| |
| // 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, os.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 shoff int64 |
| var shentsize, shnum, shstrndx int |
| shstrndx = -1 |
| switch f.Class { |
| case ELFCLASS32: |
| hdr := new(Header32) |
| sr.Seek(0, 0) |
| if err := binary.Read(sr, f.ByteOrder, hdr); err != nil { |
| return nil, err |
| } |
| f.Type = Type(hdr.Type) |
| f.Machine = Machine(hdr.Machine) |
| if v := Version(hdr.Version); v != f.Version { |
| return nil, &FormatError{0, "mismatched ELF version", v} |
| } |
| shoff = int64(hdr.Shoff) |
| shentsize = int(hdr.Shentsize) |
| shnum = int(hdr.Shnum) |
| shstrndx = int(hdr.Shstrndx) |
| case ELFCLASS64: |
| hdr := new(Header64) |
| sr.Seek(0, 0) |
| if err := binary.Read(sr, f.ByteOrder, hdr); err != nil { |
| return nil, err |
| } |
| f.Type = Type(hdr.Type) |
| f.Machine = Machine(hdr.Machine) |
| if v := Version(hdr.Version); v != f.Version { |
| return nil, &FormatError{0, "mismatched ELF version", v} |
| } |
| shoff = int64(hdr.Shoff) |
| shentsize = int(hdr.Shentsize) |
| shnum = int(hdr.Shnum) |
| shstrndx = int(hdr.Shstrndx) |
| } |
| if shstrndx < 0 || shstrndx >= shnum { |
| return nil, &FormatError{0, "invalid ELF shstrndx", shstrndx} |
| } |
| |
| // Read program headers |
| // TODO |
| |
| // 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, 0) |
| 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 |
| } |
| |
| // Load section header string table. |
| s := f.Sections[shstrndx] |
| shstrtab := make([]byte, s.Size) |
| if _, err := r.ReadAt(shstrtab, int64(s.Offset)); 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 |
| } |
| |
| func (f *File) getSymbols() ([]Symbol, os.Error) { |
| switch f.Class { |
| case ELFCLASS64: |
| return f.getSymbols64() |
| } |
| |
| return nil, os.ErrorString("not implemented") |
| } |
| |
| // GetSymbols returns a slice of Symbols from parsing the symbol table. |
| func (f *File) getSymbols64() ([]Symbol, os.Error) { |
| var symtabSection *Section |
| for _, section := range f.Sections { |
| if section.Type == SHT_SYMTAB { |
| symtabSection = section |
| break |
| } |
| } |
| |
| if symtabSection == nil { |
| return nil, os.ErrorString("no symbol section") |
| } |
| |
| data, err := symtabSection.Data() |
| if err != nil { |
| return nil, os.ErrorString("cannot load symbol section") |
| } |
| symtab := bytes.NewBuffer(data) |
| if symtab.Len()%Sym64Size != 0 { |
| return nil, os.ErrorString("length of symbol section is not a multiple of Sym64Size") |
| } |
| |
| // The first entry is all zeros. |
| var skip [Sym64Size]byte |
| symtab.Read(skip[0:]) |
| |
| symbols := make([]Symbol, symtab.Len()/Sym64Size) |
| |
| i := 0 |
| var sym Sym64 |
| for symtab.Len() > 0 { |
| binary.Read(symtab, f.ByteOrder, &sym) |
| symbols[i].Name = sym.Name |
| symbols[i].Info = sym.Info |
| symbols[i].Other = sym.Other |
| symbols[i].Section = uint32(sym.Shndx) |
| symbols[i].Value = sym.Value |
| symbols[i].Size = sym.Size |
| i++ |
| } |
| |
| return symbols, 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) os.Error { |
| if f.Class == ELFCLASS64 && f.Machine == EM_X86_64 { |
| return f.applyRelocationsAMD64(dst, rels) |
| } |
| |
| return os.ErrorString("not implemented") |
| } |
| |
| func (f *File) applyRelocationsAMD64(dst []byte, rels []byte) os.Error { |
| if len(rels)%Sym64Size != 0 { |
| return os.ErrorString("length of relocation section is not a multiple of Sym64Size") |
| } |
| |
| symbols, err := f.getSymbols() |
| if err != nil { |
| return err |
| } |
| |
| b := bytes.NewBuffer(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 >= uint64(len(symbols)) { |
| continue |
| } |
| sym := &symbols[symNo] |
| 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, os.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] |
| return dwarf.New(abbrev, nil, nil, info, nil, nil, nil, str) |
| } |
