--- /dev/null
+// Copyright 2013 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 goobj implements reading of Go object files and archives.
+//
+// TODO(rsc): Decide where this package should live. (golang.org/issue/6932)
+// TODO(rsc): Decide the appropriate integer types for various fields.
+// TODO(rsc): Write tests. (File format still up in the air a little.)
+package goobj
+
+import (
+ "bufio"
+ "bytes"
+ "errors"
+ "fmt"
+ "io"
+ "strconv"
+)
+
+// A SymKind describes the kind of memory represented by a symbol.
+type SymKind int
+
+// This list is taken from include/link.h.
+
+// Defined SymKind values.
+// TODO(rsc): Give idiomatic Go names.
+// TODO(rsc): Reduce the number of symbol types in the object files.
+const (
+ _ SymKind = iota
+
+ // readonly, executable
+ STEXT
+ SELFRXSECT
+
+ // readonly, non-executable
+ STYPE
+ SSTRING
+ SGOSTRING
+ SGOFUNC
+ SRODATA
+ SFUNCTAB
+ STYPELINK
+ SSYMTAB // TODO: move to unmapped section
+ SPCLNTAB
+ SELFROSECT
+
+ // writable, non-executable
+ SMACHOPLT
+ SELFSECT
+ SMACHO // Mach-O __nl_symbol_ptr
+ SMACHOGOT
+ SNOPTRDATA
+ SINITARR
+ SDATA
+ SWINDOWS
+ SBSS
+ SNOPTRBSS
+ STLSBSS
+
+ // not mapped
+ SXREF
+ SMACHOSYMSTR
+ SMACHOSYMTAB
+ SMACHOINDIRECTPLT
+ SMACHOINDIRECTGOT
+ SFILE
+ SFILEPATH
+ SCONST
+ SDYNIMPORT
+ SHOSTOBJ
+)
+
+// A Sym is a named symbol in an object file.
+type Sym struct {
+ SymID // symbol identifier (name and version)
+ Kind SymKind // kind of symbol
+ DupOK bool // are duplicate definitions okay?
+ Size int // size of corresponding data
+ Type SymID // symbol for Go type information
+ Data Data // memory image of symbol
+ Reloc []Reloc // relocations to apply to Data
+ Func *Func // additional data for functions
+}
+
+// A SymID - the combination of Name and Version - uniquely identifies
+// a symbol within a package.
+type SymID struct {
+ // Name is the name of a symbol.
+ Name string
+
+ // Version is zero for symbols with global visibility.
+ // Symbols with only file visibility (such as file-level static
+ // declarations in C) have a non-zero version distinguising
+ // a symbol in one file from a symbol of the same name
+ // in another file
+ Version int
+}
+
+// A Data is a reference to data stored in an object file.
+// It records the offset and size of the data, so that a client can
+// read the data only if necessary.
+type Data struct {
+ Offset int64
+ Size int64
+}
+
+// A Reloc describes a relocation applied to a memory image to refer
+// to an address within a particular symbol.
+type Reloc struct {
+ // The bytes at [Offset, Offset+Size) within the memory image
+ // should be updated to refer to the address Add bytes after the start
+ // of the symbol Sym.
+ Offset int
+ Size int
+ Sym SymID
+ Add int
+
+ // The Type records the form of address expected in the bytes
+ // described by the previous fields: absolute, PC-relative, and so on.
+ // TODO(rsc): The interpretation of Type is not exposed by this package.
+ Type int
+}
+
+// A Var describes a variable in a function stack frame: a declared
+// local variable, an input argument, or an output result.
+type Var struct {
+ // The combination of Name, Kind, and Offset uniquely
+ // identifies a variable in a function stack frame.
+ // Using fewer of these - in particular, using only Name - does not.
+ Name string // Name of variable.
+ Kind int // TODO(rsc): Define meaning.
+ Offset int // Frame offset. TODO(rsc): Define meaning.
+
+ Type SymID // Go type for variable.
+}
+
+// Func contains additional per-symbol information specific to functions.
+type Func struct {
+ Args int // size in bytes of of argument frame: inputs and outputs
+ Frame int // size in bytes of local variable frame
+ Var []Var // detail about local variables
+ PCSP Data // PC → SP offset map
+ PCFile Data // PC → file number map (index into File)
+ PCLine Data // PC → line number map
+ PCData []Data // PC → runtime support data map
+ FuncData []FuncData // non-PC-specific runtime support data
+ File []string // paths indexed by PCFile
+}
+
+// TODO: Add PCData []byte and PCDataIter (similar to liblink).
+
+// A FuncData is a single function-specific data value.
+type FuncData struct {
+ Sym SymID // symbol holding data
+ Offset int64 // offset into symbol for funcdata pointer
+}
+
+// A Package is a parsed Go object file or archive defining a Go package.
+type Package struct {
+ ImportPath string // import path denoting this package
+ Imports []string // packages imported by this package
+ Syms []*Sym // symbols defined by this package
+ MaxVersion int // maximum Version in any SymID in Syms
+}
+
+var (
+ archiveHeader = []byte("!<arch>\n")
+ archiveMagic = []byte("`\n")
+ goobjHeader = []byte("go objec") // truncated to size of archiveHeader
+
+ errCorruptArchive = errors.New("corrupt archive")
+ errTruncatedArchive = errors.New("truncated archive")
+ errNotArchive = errors.New("unrecognized archive format")
+
+ errCorruptObject = errors.New("corrupt object file")
+ errTruncatedObject = errors.New("truncated object file")
+ errNotObject = errors.New("unrecognized object file format")
+)
+
+// An objReader is an object file reader.
+type objReader struct {
+ p *Package
+ b *bufio.Reader
+ f io.ReadSeeker
+ err error
+ offset int64
+ limit int64
+ tmp [256]byte
+ pkg string
+}
+
+// init initializes r to read package p from f.
+func (r *objReader) init(f io.ReadSeeker, p *Package) {
+ r.f = f
+ r.p = p
+ r.offset, _ = f.Seek(0, 1)
+ r.limit, _ = f.Seek(0, 2)
+ f.Seek(r.offset, 0)
+ r.b = bufio.NewReader(f)
+}
+
+// error records that an error occurred.
+// It returns only the first error, so that an error
+// caused by an earlier error does not discard information
+// about the earlier error.
+func (r *objReader) error(err error) error {
+ if r.err == nil {
+ if err == io.EOF {
+ err = io.ErrUnexpectedEOF
+ }
+ r.err = err
+ }
+ // panic("corrupt") // useful for debugging
+ return r.err
+}
+
+// readByte reads and returns a byte from the input file.
+// On I/O error or EOF, it records the error but returns byte 0.
+// A sequence of 0 bytes will eventually terminate any
+// parsing state in the object file. In particular, it ends the
+// reading of a varint.
+func (r *objReader) readByte() byte {
+ if r.err != nil {
+ return 0
+ }
+ if r.offset >= r.limit {
+ r.error(io.ErrUnexpectedEOF)
+ return 0
+ }
+ b, err := r.b.ReadByte()
+ if err != nil {
+ if err == io.EOF {
+ err = io.ErrUnexpectedEOF
+ }
+ r.error(err)
+ b = 0
+ } else {
+ r.offset++
+ }
+ return b
+}
+
+// read reads exactly len(b) bytes from the input file.
+// If an error occurs, read returns the error but also
+// records it, so it is safe for callers to ignore the result
+// as long as delaying the report is not a problem.
+func (r *objReader) readFull(b []byte) error {
+ if r.err != nil {
+ return r.err
+ }
+ if r.offset+int64(len(b)) > r.limit {
+ return r.error(io.ErrUnexpectedEOF)
+ }
+ n, err := io.ReadFull(r.b, b)
+ r.offset += int64(n)
+ if err != nil {
+ return r.error(err)
+ }
+ return nil
+}
+
+// readInt reads a zigzag varint from the input file.
+func (r *objReader) readInt() int {
+ var u uint64
+
+ for shift := uint(0); ; shift += 7 {
+ if shift >= 64 {
+ r.error(errCorruptObject)
+ return 0
+ }
+ c := r.readByte()
+ u |= uint64(c&0x7F) << shift
+ if c&0x80 == 0 {
+ break
+ }
+ }
+
+ v := int64(u>>1) ^ (int64(u) << 63 >> 63)
+ if int64(int(v)) != v {
+ r.error(errCorruptObject) // TODO
+ return 0
+ }
+ return int(v)
+}
+
+// readString reads a length-delimited string from the input file.
+func (r *objReader) readString() string {
+ n := r.readInt()
+ buf := make([]byte, n)
+ r.readFull(buf)
+ return string(buf)
+}
+
+// readSymID reads a SymID from the input file.
+func (r *objReader) readSymID() SymID {
+ name, vers := r.readString(), r.readInt()
+
+ // An individual object file only records version 0 (extern) or 1 (static).
+ // To make static symbols unique across all files being read, we
+ // replace version 1 with the version corresponding to the current
+ // file number. The number is incremented on each call to parseObject.
+ if vers != 0 {
+ vers = r.p.MaxVersion
+ }
+
+ return SymID{name, vers}
+}
+
+// readData reads a data reference from the input file.
+func (r *objReader) readData() Data {
+ n := r.readInt()
+ d := Data{Offset: r.offset, Size: int64(n)}
+ r.skip(int64(n))
+ return d
+}
+
+// skip skips n bytes in the input.
+func (r *objReader) skip(n int64) {
+ if n < 0 {
+ r.error(fmt.Errorf("debug/goobj: internal error: misuse of skip"))
+ }
+ if n < int64(len(r.tmp)) {
+ // Since the data is so small, a just reading from the buffered
+ // reader is better than flushing the buffer and seeking.
+ r.readFull(r.tmp[:n])
+ } else if n <= int64(r.b.Buffered()) {
+ // Even though the data is not small, it has already been read.
+ // Advance the buffer instead of seeking.
+ for n > int64(len(r.tmp)) {
+ r.readFull(r.tmp[:])
+ n -= int64(len(r.tmp))
+ }
+ r.readFull(r.tmp[:n])
+ } else {
+ // Seek, giving up buffered data.
+ _, err := r.f.Seek(r.offset+n, 0)
+ if err != nil {
+ r.error(err)
+ }
+ r.offset += n
+ r.b.Reset(r.f)
+ }
+}
+
+// Parse parses an object file or archive from r,
+// assuming that its import path is pkgpath.
+func Parse(r io.ReadSeeker, pkgpath string) (*Package, error) {
+ p := new(Package)
+ p.ImportPath = pkgpath
+
+ var rd objReader
+ rd.init(r, p)
+ err := rd.readFull(rd.tmp[:8])
+ if err != nil {
+ if err == io.EOF {
+ err = io.ErrUnexpectedEOF
+ }
+ return nil, err
+ }
+
+ switch {
+ default:
+ return nil, errNotObject
+
+ case bytes.Equal(rd.tmp[:8], archiveHeader):
+ if err := rd.parseArchive(); err != nil {
+ return nil, err
+ }
+ case bytes.Equal(rd.tmp[:8], goobjHeader):
+ if err := rd.parseObject(goobjHeader); err != nil {
+ return nil, err
+ }
+ }
+
+ return p, nil
+}
+
+// trimSpace removes trailing spaces from b and returns the corresponding string.
+// This effectively parses the form used in archive headers.
+func trimSpace(b []byte) string {
+ return string(bytes.TrimRight(b, " "))
+}
+
+// parseArchive parses a Unix archive of Go object files.
+// TODO(rsc): Need to skip non-Go object files.
+// TODO(rsc): Maybe record table of contents in r.p so that
+// linker can avoid having code to parse archives too.
+func (r *objReader) parseArchive() error {
+ for r.offset < r.limit {
+ if err := r.readFull(r.tmp[:60]); err != nil {
+ return err
+ }
+ data := r.tmp[:60]
+
+ // Each file is preceded by this text header (slice indices in first column):
+ // 0:16 name
+ // 16:28 date
+ // 28:34 uid
+ // 34:40 gid
+ // 40:48 mode
+ // 48:58 size
+ // 58:60 magic - `\n
+ // We only care about name, size, and magic.
+ // The fields are space-padded on the right.
+ // The size is in decimal.
+ // The file data - size bytes - follows the header.
+ // Headers are 2-byte aligned, so if size is odd, an extra padding
+ // byte sits between the file data and the next header.
+ // The file data that follows is padded to an even number of bytes:
+ // if size is odd, an extra padding byte is inserted betw the next header.
+ if len(data) < 60 {
+ return errTruncatedArchive
+ }
+ if !bytes.Equal(data[58:60], archiveMagic) {
+ return errCorruptArchive
+ }
+ name := trimSpace(data[0:16])
+ size, err := strconv.ParseInt(trimSpace(data[48:58]), 10, 64)
+ if err != nil {
+ return errCorruptArchive
+ }
+ data = data[60:]
+ fsize := size + size&1
+ if fsize < 0 || fsize < size {
+ return errCorruptArchive
+ }
+ switch name {
+ case "__.SYMDEF", "__.GOSYMDEF", "__.PKGDEF":
+ r.skip(size)
+ default:
+ oldLimit := r.limit
+ r.limit = r.offset + size
+ if err := r.parseObject(nil); err != nil {
+ return fmt.Errorf("parsing archive member %q: %v", name, err)
+ }
+ r.skip(r.limit - r.offset)
+ r.limit = oldLimit
+ }
+ if size&1 != 0 {
+ r.skip(1)
+ }
+ }
+ return nil
+}
+
+// parseObject parses a single Go object file.
+// The prefix is the bytes already read from the file,
+// typically in order to detect that this is an object file.
+// The object file consists of a textual header ending in "\n!\n"
+// and then the part we want to parse begins.
+// The format of that part is defined in a comment at the top
+// of src/liblink/objfile.c.
+func (r *objReader) parseObject(prefix []byte) error {
+ // TODO(rsc): Maybe use prefix and the initial input to
+ // record the header line from the file, which would
+ // give the architecture and other version information.
+
+ r.p.MaxVersion++
+ var c1, c2, c3 byte
+ for {
+ c1, c2, c3 = c2, c3, r.readByte()
+ if c3 == 0 { // NUL or EOF, either is bad
+ return errCorruptObject
+ }
+ if c1 == '\n' && c2 == '!' && c3 == '\n' {
+ break
+ }
+ }
+
+ r.readFull(r.tmp[:8])
+ if !bytes.Equal(r.tmp[:8], []byte("\x00\x00go13ld")) {
+ return r.error(errCorruptObject)
+ }
+
+ // Direct package dependencies.
+ for {
+ s := r.readString()
+ if s == "" {
+ break
+ }
+ r.p.Imports = append(r.p.Imports, s)
+ }
+
+ // Symbols.
+ for {
+ if b := r.readByte(); b != 0xfe {
+ if b != 0xff {
+ return r.error(errCorruptObject)
+ }
+ break
+ }
+
+ typ := r.readInt()
+ s := &Sym{SymID: r.readSymID()}
+ r.p.Syms = append(r.p.Syms, s)
+ s.Kind = SymKind(typ)
+ s.DupOK = r.readInt() != 0
+ s.Size = r.readInt()
+ s.Type = r.readSymID()
+ s.Data = r.readData()
+ s.Reloc = make([]Reloc, r.readInt())
+ for i := range s.Reloc {
+ rel := &s.Reloc[i]
+ rel.Offset = r.readInt()
+ rel.Size = r.readInt()
+ rel.Type = r.readInt()
+ rel.Add = r.readInt()
+ r.readInt() // Xadd - ignored
+ rel.Sym = r.readSymID()
+ r.readSymID() // Xsym - ignored
+ }
+
+ if s.Kind == STEXT {
+ f := new(Func)
+ s.Func = f
+ f.Args = r.readInt()
+ f.Frame = r.readInt()
+ f.Var = make([]Var, r.readInt())
+ for i := range f.Var {
+ v := &f.Var[i]
+ v.Name = r.readSymID().Name
+ v.Offset = r.readInt()
+ v.Kind = r.readInt()
+ v.Type = r.readSymID()
+ }
+
+ f.PCSP = r.readData()
+ f.PCFile = r.readData()
+ f.PCLine = r.readData()
+ f.PCData = make([]Data, r.readInt())
+ for i := range f.PCData {
+ f.PCData[i] = r.readData()
+ }
+ f.FuncData = make([]FuncData, r.readInt())
+ for i := range f.FuncData {
+ f.FuncData[i].Sym = r.readSymID()
+ }
+ for i := range f.FuncData {
+ f.FuncData[i].Offset = int64(r.readInt()) // TODO
+ }
+ f.File = make([]string, r.readInt())
+ for i := range f.File {
+ f.File[i] = r.readSymID().Name
+ }
+ }
+ }
+
+ r.readFull(r.tmp[:7])
+ if !bytes.Equal(r.tmp[:7], []byte("\xffgo13ld")) {
+ return r.error(errCorruptObject)
+ }
+
+ return nil
+}