// Copyright 2018 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 xcoff implements access to XCOFF (Extended Common Object File Format) files.
package xcoff
import (
"debug/dwarf"
"encoding/binary"
"fmt"
"io"
"os"
"strings"
)
// SectionHeader holds information about an XCOFF section header.
type SectionHeader struct {
Name string
VirtualAddress uint64
Size uint64
Type uint32
Relptr uint64
Nreloc uint32
}
type Section struct {
SectionHeader
Relocs []Reloc
io.ReaderAt
sr *io.SectionReader
}
// AuxiliaryCSect holds information about an XCOFF symbol in an AUX_CSECT entry.
type AuxiliaryCSect struct {
Length int64
StorageMappingClass int
SymbolType int
}
// AuxiliaryFcn holds information about an XCOFF symbol in an AUX_FCN entry.
type AuxiliaryFcn struct {
Size int64
}
type Symbol struct {
Name string
Value uint64
SectionNumber int
StorageClass int
AuxFcn AuxiliaryFcn
AuxCSect AuxiliaryCSect
}
type Reloc struct {
VirtualAddress uint64
Symbol *Symbol
Signed bool
InstructionFixed bool
Length uint8
Type uint8
}
// ImportedSymbol holds information about an imported XCOFF symbol.
type ImportedSymbol struct {
Name string
Library string
}
// FileHeader holds information about an XCOFF file header.
type FileHeader struct {
TargetMachine uint16
}
// A File represents an open XCOFF file.
type File struct {
FileHeader
Sections []*Section
Symbols []*Symbol
StringTable []byte
LibraryPaths []string
closer io.Closer
}
// Open opens the named file using os.Open and prepares it for use as an XCOFF 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
}
// Section returns the first section with the given name, or nil if no such
// section exists.
// Xcoff have section's name limited to 8 bytes. Some sections like .gosymtab
// can be trunked but this method will still find them.
func (f *File) Section(name string) *Section {
for _, s := range f.Sections {
if s.Name == name || (len(name) > 8 && s.Name == name[:8]) {
return s
}
}
return nil
}
// SectionByType returns the first section in f with the
// given type, or nil if there is no such section.
func (f *File) SectionByType(typ uint32) *Section {
for _, s := range f.Sections {
if s.Type == typ {
return s
}
}
return nil
}
// cstring converts ASCII byte sequence b to string.
// It stops once it finds 0 or reaches end of b.
func cstring(b []byte) string {
var i int
for i = 0; i < len(b) && b[i] != 0; i++ {
}
return string(b[:i])
}
// getString extracts a string from an XCOFF string table.
func getString(st []byte, offset uint32) (string, bool) {
if offset < 4 || int(offset) >= len(st) {
return "", false
}
return cstring(st[offset:]), true
}
// NewFile creates a new File for accessing an XCOFF binary in an underlying reader.
func NewFile(r io.ReaderAt) (*File, error) {
sr := io.NewSectionReader(r, 0, 1<<63-1)
// Read XCOFF target machine
var magic uint16
if err := binary.Read(sr, binary.BigEndian, &magic); err != nil {
return nil, err
}
if magic != U802TOCMAGIC && magic != U64_TOCMAGIC {
return nil, fmt.Errorf("unrecognised XCOFF magic: 0x%x", magic)
}
f := new(File)
f.TargetMachine = magic
// Read XCOFF file header
if _, err := sr.Seek(0, os.SEEK_SET); err != nil {
return nil, err
}
var nscns uint16
var symptr uint64
var nsyms int32
var opthdr uint16
var hdrsz int
switch f.TargetMachine {
case U802TOCMAGIC:
fhdr := new(FileHeader32)
if err := binary.Read(sr, binary.BigEndian, fhdr); err != nil {
return nil, err
}
nscns = fhdr.Fnscns
symptr = uint64(fhdr.Fsymptr)
nsyms = fhdr.Fnsyms
opthdr = fhdr.Fopthdr
hdrsz = FILHSZ_32
case U64_TOCMAGIC:
fhdr := new(FileHeader64)
if err := binary.Read(sr, binary.BigEndian, fhdr); err != nil {
return nil, err
}
nscns = fhdr.Fnscns
symptr = fhdr.Fsymptr
nsyms = fhdr.Fnsyms
opthdr = fhdr.Fopthdr
hdrsz = FILHSZ_64
}
if symptr == 0 || nsyms <= 0 {
return nil, fmt.Errorf("no symbol table")
}
// Read string table (located right after symbol table).
offset := symptr + uint64(nsyms)*SYMESZ
if _, err := sr.Seek(int64(offset), os.SEEK_SET); err != nil {
return nil, err
}
// The first 4 bytes contain the length (in bytes).
var l uint32
if err := binary.Read(sr, binary.BigEndian, &l); err != nil {
return nil, err
}
if l > 4 {
if _, err := sr.Seek(int64(offset), os.SEEK_SET); err != nil {
return nil, err
}
f.StringTable = make([]byte, l)
if _, err := io.ReadFull(sr, f.StringTable); err != nil {
return nil, err
}
}
// Read section headers
if _, err := sr.Seek(int64(hdrsz)+int64(opthdr), os.SEEK_SET); err != nil {
return nil, err
}
f.Sections = make([]*Section, nscns)
for i := 0; i < int(nscns); i++ {
var scnptr uint64
s := new(Section)
switch f.TargetMachine {
case U802TOCMAGIC:
shdr := new(SectionHeader32)
if err := binary.Read(sr, binary.BigEndian, shdr); err != nil {
return nil, err
}
s.Name = cstring(shdr.Sname[:])
s.VirtualAddress = uint64(shdr.Svaddr)
s.Size = uint64(shdr.Ssize)
scnptr = uint64(shdr.Sscnptr)
s.Type = shdr.Sflags
s.Relptr = uint64(shdr.Srelptr)
s.Nreloc = uint32(shdr.Snreloc)
case U64_TOCMAGIC:
shdr := new(SectionHeader64)
if err := binary.Read(sr, binary.BigEndian, shdr); err != nil {
return nil, err
}
s.Name = cstring(shdr.Sname[:])
s.VirtualAddress = shdr.Svaddr
s.Size = shdr.Ssize
scnptr = shdr.Sscnptr
s.Type = shdr.Sflags
s.Relptr = shdr.Srelptr
s.Nreloc = shdr.Snreloc
}
r2 := r
if scnptr == 0 { // .bss must have all 0s
r2 = zeroReaderAt{}
}
s.sr = io.NewSectionReader(r2, int64(scnptr), int64(s.Size))
s.ReaderAt = s.sr
f.Sections[i] = s
}
// Symbol map needed by relocation
var idxToSym = make(map[int]*Symbol)
// Read symbol table
if _, err := sr.Seek(int64(symptr), os.SEEK_SET); err != nil {
return nil, err
}
f.Symbols = make([]*Symbol, 0)
for i := 0; i < int(nsyms); i++ {
var numaux int
var ok, needAuxFcn bool
sym := new(Symbol)
switch f.TargetMachine {
case U802TOCMAGIC:
se := new(SymEnt32)
if err := binary.Read(sr, binary.BigEndian, se); err != nil {
return nil, err
}
numaux = int(se.Nnumaux)
sym.SectionNumber = int(se.Nscnum)
sym.StorageClass = int(se.Nsclass)
sym.Value = uint64(se.Nvalue)
needAuxFcn = se.Ntype&SYM_TYPE_FUNC != 0 && numaux > 1
zeroes := binary.BigEndian.Uint32(se.Nname[:4])
if zeroes != 0 {
sym.Name = cstring(se.Nname[:])
} else {
offset := binary.BigEndian.Uint32(se.Nname[4:])
sym.Name, ok = getString(f.StringTable, offset)
if !ok {
goto skip
}
}
case U64_TOCMAGIC:
se := new(SymEnt64)
if err := binary.Read(sr, binary.BigEndian, se); err != nil {
return nil, err
}
numaux = int(se.Nnumaux)
sym.SectionNumber = int(se.Nscnum)
sym.StorageClass = int(se.Nsclass)
sym.Value = se.Nvalue
needAuxFcn = se.Ntype&SYM_TYPE_FUNC != 0 && numaux > 1
sym.Name, ok = getString(f.StringTable, se.Noffset)
if !ok {
goto skip
}
}
if sym.StorageClass != C_EXT && sym.StorageClass != C_WEAKEXT && sym.StorageClass != C_HIDEXT {
goto skip
}
// Must have at least one csect auxiliary entry.
if numaux < 1 || i+numaux >= int(nsyms) {
goto skip
}
if sym.SectionNumber > int(nscns) {
goto skip
}
if sym.SectionNumber == 0 {
sym.Value = 0
} else {
sym.Value -= f.Sections[sym.SectionNumber-1].VirtualAddress
}
idxToSym[i] = sym
// If this symbol is a function, it must retrieve its size from
// its AUX_FCN entry.
// It can happend that a function symbol doesn't have any AUX_FCN.
// In this case, needAuxFcn is false and their size will be set to 0
if needAuxFcn {
switch f.TargetMachine {
case U802TOCMAGIC:
aux := new(AuxFcn32)
if err := binary.Read(sr, binary.BigEndian, aux); err != nil {
return nil, err
}
sym.AuxFcn.Size = int64(aux.Xfsize)
case U64_TOCMAGIC:
aux := new(AuxFcn64)
if err := binary.Read(sr, binary.BigEndian, aux); err != nil {
return nil, err
}
sym.AuxFcn.Size = int64(aux.Xfsize)
}
}
// Read csect auxiliary entry (by convention, it is the last).
if !needAuxFcn {
if _, err := sr.Seek(int64(numaux-1)*SYMESZ, os.SEEK_CUR); err != nil {
return nil, err
}
}
i += numaux
numaux = 0
switch f.TargetMachine {
case U802TOCMAGIC:
aux := new(AuxCSect32)
if err := binary.Read(sr, binary.BigEndian, aux); err != nil {
return nil, err
}
sym.AuxCSect.SymbolType = int(aux.Xsmtyp & 0x7)
sym.AuxCSect.StorageMappingClass = int(aux.Xsmclas)
sym.AuxCSect.Length = int64(aux.Xscnlen)
case U64_TOCMAGIC:
aux := new(AuxCSect64)
if err := binary.Read(sr, binary.BigEndian, aux); err != nil {
return nil, err
}
sym.AuxCSect.SymbolType = int(aux.Xsmtyp & 0x7)
sym.AuxCSect.StorageMappingClass = int(aux.Xsmclas)
sym.AuxCSect.Length = int64(aux.Xscnlenhi)<<32 | int64(aux.Xscnlenlo)
}
f.Symbols = append(f.Symbols, sym)
skip:
i += numaux // Skip auxiliary entries
if _, err := sr.Seek(int64(numaux)*SYMESZ, os.SEEK_CUR); err != nil {
return nil, err
}
}
// Read relocations
// Only for .data or .text section
for _, sect := range f.Sections {
if sect.Type != STYP_TEXT && sect.Type != STYP_DATA {
continue
}
sect.Relocs = make([]Reloc, sect.Nreloc)
if sect.Relptr == 0 {
continue
}
if _, err := sr.Seek(int64(sect.Relptr), os.SEEK_SET); err != nil {
return nil, err
}
for i := uint32(0); i < sect.Nreloc; i++ {
switch f.TargetMachine {
case U802TOCMAGIC:
rel := new(Reloc32)
if err := binary.Read(sr, binary.BigEndian, rel); err != nil {
return nil, err
}
sect.Relocs[i].VirtualAddress = uint64(rel.Rvaddr)
sect.Relocs[i].Symbol = idxToSym[int(rel.Rsymndx)]
sect.Relocs[i].Type = rel.Rtype
sect.Relocs[i].Length = rel.Rsize&0x3F + 1
if rel.Rsize&0x80 == 1 {
sect.Relocs[i].Signed = true
}
if rel.Rsize&0x40 == 1 {
sect.Relocs[i].InstructionFixed = true
}
case U64_TOCMAGIC:
rel := new(Reloc64)
if err := binary.Read(sr, binary.BigEndian, rel); err != nil {
return nil, err
}
sect.Relocs[i].VirtualAddress = rel.Rvaddr
sect.Relocs[i].Symbol = idxToSym[int(rel.Rsymndx)]
sect.Relocs[i].Type = rel.Rtype
sect.Relocs[i].Length = rel.Rsize&0x3F + 1
if rel.Rsize&0x80 == 1 {
sect.Relocs[i].Signed = true
}
if rel.Rsize&0x40 == 1 {
sect.Relocs[i].InstructionFixed = true
}
}
}
}
return f, nil
}
// zeroReaderAt is ReaderAt that reads 0s.
type zeroReaderAt struct{}
// ReadAt writes len(p) 0s into p.
func (w zeroReaderAt) ReadAt(p []byte, off int64) (n int, err error) {
for i := range p {
p[i] = 0
}
return len(p), nil
}
// Data reads and returns the contents of the XCOFF section s.
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[:n], err
}
// CSect reads and returns the contents of a csect.
func (f *File) CSect(name string) []byte {
for _, sym := range f.Symbols {
if sym.Name == name && sym.AuxCSect.SymbolType == XTY_SD {
if i := sym.SectionNumber - 1; 0 <= i && i < len(f.Sections) {
s := f.Sections[i]
if sym.Value+uint64(sym.AuxCSect.Length) <= s.Size {
dat := make([]byte, sym.AuxCSect.Length)
_, err := s.sr.ReadAt(dat, int64(sym.Value))
if err != nil {
return nil
}
return dat
}
}
break
}
}
return nil
}
func (f *File) DWARF() (*dwarf.Data, error) {
// There are many other DWARF sections, but these
// are the ones the debug/dwarf package uses.
// Don't bother loading others.
var subtypes = [...]uint32{SSUBTYP_DWABREV, SSUBTYP_DWINFO, SSUBTYP_DWLINE, SSUBTYP_DWRNGES, SSUBTYP_DWSTR}
var dat [len(subtypes)][]byte
for i, subtype := range subtypes {
s := f.SectionByType(STYP_DWARF | subtype)
if s != nil {
b, err := s.Data()
if err != nil && uint64(len(b)) < s.Size {
return nil, err
}
dat[i] = b
}
}
abbrev, info, line, ranges, str := dat[0], dat[1], dat[2], dat[3], dat[4]
return dwarf.New(abbrev, nil, nil, info, line, nil, ranges, str)
}
// readImportID returns the import file IDs stored inside the .loader section.
// Library name pattern is either path/base/member or base/member
func (f *File) readImportIDs(s *Section) ([]string, error) {
// Read loader header
if _, err := s.sr.Seek(0, os.SEEK_SET); err != nil {
return nil, err
}
var istlen uint32
var nimpid int32
var impoff uint64
switch f.TargetMachine {
case U802TOCMAGIC:
lhdr := new(LoaderHeader32)
if err := binary.Read(s.sr, binary.BigEndian, lhdr); err != nil {
return nil, err
}
istlen = lhdr.Listlen
nimpid = lhdr.Lnimpid
impoff = uint64(lhdr.Limpoff)
case U64_TOCMAGIC:
lhdr := new(LoaderHeader64)
if err := binary.Read(s.sr, binary.BigEndian, lhdr); err != nil {
return nil, err
}
istlen = lhdr.Listlen
nimpid = lhdr.Lnimpid
impoff = lhdr.Limpoff
}
// Read loader import file ID table
if _, err := s.sr.Seek(int64(impoff), os.SEEK_SET); err != nil {
return nil, err
}
table := make([]byte, istlen)
if _, err := io.ReadFull(s.sr, table); err != nil {
return nil, err
}
offset := 0
// First import file ID is the default LIBPATH value
libpath := cstring(table[offset:])
f.LibraryPaths = strings.Split(libpath, ":")
offset += len(libpath) + 3 // 3 null bytes
all := make([]string, 0)
for i := 1; i < int(nimpid); i++ {
impidpath := cstring(table[offset:])
offset += len(impidpath) + 1
impidbase := cstring(table[offset:])
offset += len(impidbase) + 1
impidmem := cstring(table[offset:])
offset += len(impidmem) + 1
var path string
if len(impidpath) > 0 {
path = impidpath + "/" + impidbase + "/" + impidmem
} else {
path = impidbase + "/" + impidmem
}
all = append(all, path)
}
return all, nil
}
// 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) {
s := f.SectionByType(STYP_LOADER)
if s == nil {
return nil, nil
}
// Read loader header
if _, err := s.sr.Seek(0, os.SEEK_SET); err != nil {
return nil, err
}
var stlen uint32
var stoff uint64
var nsyms int32
var symoff uint64
switch f.TargetMachine {
case U802TOCMAGIC:
lhdr := new(LoaderHeader32)
if err := binary.Read(s.sr, binary.BigEndian, lhdr); err != nil {
return nil, err
}
stlen = lhdr.Lstlen
stoff = uint64(lhdr.Lstoff)
nsyms = lhdr.Lnsyms
symoff = LDHDRSZ_32
case U64_TOCMAGIC:
lhdr := new(LoaderHeader64)
if err := binary.Read(s.sr, binary.BigEndian, lhdr); err != nil {
return nil, err
}
stlen = lhdr.Lstlen
stoff = lhdr.Lstoff
nsyms = lhdr.Lnsyms
symoff = lhdr.Lsymoff
}
// Read loader section string table
if _, err := s.sr.Seek(int64(stoff), os.SEEK_SET); err != nil {
return nil, err
}
st := make([]byte, stlen)
if _, err := io.ReadFull(s.sr, st); err != nil {
return nil, err
}
// Read imported libraries
libs, err := f.readImportIDs(s)
if err != nil {
return nil, err
}
// Read loader symbol table
if _, err := s.sr.Seek(int64(symoff), os.SEEK_SET); err != nil {
return nil, err
}
all := make([]ImportedSymbol, 0)
for i := 0; i < int(nsyms); i++ {
var name string
var ifile int32
var ok bool
switch f.TargetMachine {
case U802TOCMAGIC:
ldsym := new(LoaderSymbol32)
if err := binary.Read(s.sr, binary.BigEndian, ldsym); err != nil {
return nil, err
}
if ldsym.Lsmtype&0x40 == 0 {
continue // Imported symbols only
}
zeroes := binary.BigEndian.Uint32(ldsym.Lname[:4])
if zeroes != 0 {
name = cstring(ldsym.Lname[:])
} else {
offset := binary.BigEndian.Uint32(ldsym.Lname[4:])
name, ok = getString(st, offset)
if !ok {
continue
}
}
ifile = ldsym.Lifile
case U64_TOCMAGIC:
ldsym := new(LoaderSymbol64)
if err := binary.Read(s.sr, binary.BigEndian, ldsym); err != nil {
return nil, err
}
if ldsym.Lsmtype&0x40 == 0 {
continue // Imported symbols only
}
name, ok = getString(st, ldsym.Loffset)
if !ok {
continue
}
ifile = ldsym.Lifile
}
var sym ImportedSymbol
sym.Name = name
if ifile >= 1 && int(ifile) <= len(libs) {
sym.Library = libs[ifile-1]
}
all = append(all, sym)
}
return all, nil
}
// 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) {
s := f.SectionByType(STYP_LOADER)
if s == nil {
return nil, nil
}
all, err := f.readImportIDs(s)
return all, err
}