Golang cmd-internal-obj.Bread类(方法)实例源码

func ldobjfile(ctxt *Link, f *obj.Biobuf, pkg string, length int64, pn string) {
	start := obj.Boffset(f)
	ctxt.IncVersion()
	var buf [8]uint8
	obj.Bread(f, buf[:])
	if string(buf[:]) != startmagic {
		log.Fatalf("%s: invalid file start %x %x %x %x %x %x %x %x", pn, buf[0], buf[1], buf[2], buf[3], buf[4], buf[5], buf[6], buf[7])
	}
	c := obj.Bgetc(f)
	if c != 1 {
		log.Fatalf("%s: invalid file version number %d", pn, c)
	}

	var lib string
	for {
		lib = rdstring(f)
		if lib == "" {
			break
		}
		addlib(ctxt, pkg, pn, lib)
	}

	ctxt.CurRefs = []*LSym{nil} // zeroth ref is nil
	for {
		c, err := f.Peek(1)
		if err != nil {
			log.Fatalf("%s: peeking: %v", pn, err)
		}
		if c[0] == 0xff {
			obj.Bgetc(f)
			break
		}
		readref(ctxt, f, pkg, pn)
	}

	dataLength := rdint64(f)
	data := make([]byte, dataLength)
	obj.Bread(f, data)

	for {
		c, err := f.Peek(1)
		if err != nil {
			log.Fatalf("%s: peeking: %v", pn, err)
		}
		if c[0] == 0xff {
			break
		}
		readsym(ctxt, f, &data, pkg, pn)
	}

	buf = [8]uint8{}
	obj.Bread(f, buf[:])
	if string(buf[:]) != endmagic {
		log.Fatalf("%s: invalid file end", pn)
	}

	if obj.Boffset(f) != start+length {
		log.Fatalf("%s: unexpected end at %d, want %d", pn, int64(obj.Boffset(f)), int64(start+length))
	}
}

// hostArchive reads an archive file holding host objects and links in
// required objects.  The general format is the same as a Go archive
// file, but it has an armap listing symbols and the objects that
// define them.  This is used for the compiler support library
// libgcc.a.
func hostArchive(name string) {
	f, err := obj.Bopenr(name)
	if err != nil {
		if os.IsNotExist(err) {
			// It's OK if we don't have a libgcc file at all.
			return
		}
		Exitf("cannot open file %s: %v", name, err)
	}
	defer obj.Bterm(f)

	magbuf := make([]byte, len(ARMAG))
	if obj.Bread(f, magbuf) != len(magbuf) {
		Exitf("file %s too short", name)
	}

	var arhdr ArHdr
	l := nextar(f, obj.Boffset(f), &arhdr)
	if l <= 0 {
		Exitf("%s missing armap", name)
	}

	var armap archiveMap
	if arhdr.name == "/" || arhdr.name == "/SYM64/" {
		armap = readArmap(name, f, arhdr)
	} else {
		Exitf("%s missing armap", name)
	}

	loaded := make(map[uint64]bool)
	any := true
	for any {
		var load []uint64
		for s := Ctxt.Allsym; s != nil; s = s.Allsym {
			for _, r := range s.R {
				if r.Sym != nil && r.Sym.Type&obj.SMASK == obj.SXREF {
					if off := armap[r.Sym.Name]; off != 0 && !loaded[off] {
						load = append(load, off)
						loaded[off] = true
					}
				}
			}
		}

		for _, off := range load {
			l := nextar(f, int64(off), &arhdr)
			if l <= 0 {
				Exitf("%s missing archive entry at offset %d", name, off)
			}
			pname := fmt.Sprintf("%s(%s)", name, arhdr.name)
			l = atolwhex(arhdr.size)

			h := ldobj(f, "libgcc", l, pname, name, ArchiveObj)
			obj.Bseek(f, h.off, 0)
			h.ld(f, h.pkg, h.length, h.pn)
		}

		any = len(load) > 0
	}
}

// rdsymName reads a symbol name, replacing all "". with pkg.
func rdsymName(f *obj.Biobuf, pkg string) string {
	n := rdint(f)
	if n == 0 {
		rdint64(f)
		return ""
	}

	if len(rdBuf) < n {
		rdBuf = make([]byte, n, 2*n)
	}
	origName := rdBuf[:n]
	obj.Bread(f, origName)
	adjName := rdBuf[n:n]
	for {
		i := bytes.Index(origName, emptyPkg)
		if i == -1 {
			adjName = append(adjName, origName...)
			break
		}
		adjName = append(adjName, origName[:i]...)
		adjName = append(adjName, pkg...)
		adjName = append(adjName, '.')
		origName = origName[i+len(emptyPkg):]
	}
	name := string(adjName)
	if len(adjName) > len(rdBuf) {
		rdBuf = adjName // save the larger buffer for reuse
	}
	return name
}

/*
 * look for the next file in an archive.
 * adapted from libmach.
 */
func nextar(bp *obj.Biobuf, off int64, a *ArHdr) int64 {
	if off&1 != 0 {
		off++
	}
	obj.Bseek(bp, off, 0)
	buf := make([]byte, SAR_HDR)
	if n := obj.Bread(bp, buf); n < len(buf) {
		if n >= 0 {
			return 0
		}
		return -1
	}

	a.name = artrim(buf[0:16])
	a.date = artrim(buf[16:28])
	a.uid = artrim(buf[28:34])
	a.gid = artrim(buf[34:40])
	a.mode = artrim(buf[40:48])
	a.size = artrim(buf[48:58])
	a.fmag = artrim(buf[58:60])

	arsize := atolwhex(a.size)
	if arsize&1 != 0 {
		arsize++
	}
	return int64(arsize) + SAR_HDR
}

func rdstring(f *obj.Biobuf) string {
	n := rdint(f)
	if len(rdBuf) < n {
		rdBuf = make([]byte, n)
	}
	obj.Bread(f, rdBuf[:n])
	return string(rdBuf[:n])
}

func macholoadsym(m *LdMachoObj, symtab *LdMachoSymtab) int {
	if symtab.sym != nil {
		return 0
	}

	strbuf := make([]byte, symtab.strsize)
	if obj.Bseek(m.f, m.base+int64(symtab.stroff), 0) < 0 || obj.Bread(m.f, strbuf) != len(strbuf) {
		return -1
	}

	symsize := 12
	if m.is64 {
		symsize = 16
	}
	n := int(symtab.nsym * uint32(symsize))
	symbuf := make([]byte, n)
	if obj.Bseek(m.f, m.base+int64(symtab.symoff), 0) < 0 || obj.Bread(m.f, symbuf) != len(symbuf) {
		return -1
	}
	sym := make([]LdMachoSym, symtab.nsym)
	p := symbuf
	var s *LdMachoSym
	var v uint32
	for i := 0; uint32(i) < symtab.nsym; i++ {
		s = &sym[i]
		v = m.e.Uint32(p)
		if v >= symtab.strsize {
			return -1
		}
		s.name = cstring(strbuf[v:])
		s.type_ = uint8(p[4])
		s.sectnum = uint8(p[5])
		s.desc = m.e.Uint16(p[6:])
		if m.is64 {
			s.value = m.e.Uint64(p[8:])
		} else {
			s.value = uint64(m.e.Uint32(p[8:]))
		}
		p = p[symsize:]
	}

	symtab.str = strbuf
	symtab.sym = sym
	return 0
}

func ldobjfile(ctxt *Link, f *obj.Biobuf, pkg string, length int64, pn string) {
	start := obj.Boffset(f)
	ctxt.Version++
	var buf [8]uint8
	obj.Bread(f, buf[:])
	if string(buf[:]) != startmagic {
		log.Fatalf("%s: invalid file start %x %x %x %x %x %x %x %x", pn, buf[0], buf[1], buf[2], buf[3], buf[4], buf[5], buf[6], buf[7])
	}
	c := obj.Bgetc(f)
	if c != 1 {
		log.Fatalf("%s: invalid file version number %d", pn, c)
	}

	var lib string
	for {
		lib = rdstring(f)
		if lib == "" {
			break
		}
		addlib(ctxt, pkg, pn, lib)
	}

	for {
		c, err := f.Peek(1)
		if err != nil {
			log.Fatalf("%s: peeking: %v", pn, err)
		}
		if c[0] == 0xff {
			break
		}
		readsym(ctxt, f, pkg, pn)
	}

	buf = [8]uint8{}
	obj.Bread(f, buf[:])
	if string(buf[:]) != endmagic {
		log.Fatalf("%s: invalid file end", pn)
	}

	if obj.Boffset(f) != start+length {
		log.Fatalf("%s: unexpected end at %d, want %d", pn, int64(obj.Boffset(f)), int64(start+length))
	}
}

// readArmap reads the archive symbol map.
func readArmap(filename string, f *obj.Biobuf, arhdr ArHdr) archiveMap {
	is64 := arhdr.name == "/SYM64/"
	wordSize := 4
	if is64 {
		wordSize = 8
	}

	l := atolwhex(arhdr.size)
	contents := make([]byte, l)
	if obj.Bread(f, contents) != int(l) {
		Exitf("short read from %s", filename)
	}

	var c uint64
	if is64 {
		c = binary.BigEndian.Uint64(contents)
	} else {
		c = uint64(binary.BigEndian.Uint32(contents))
	}
	contents = contents[wordSize:]

	ret := make(archiveMap)

	names := contents[c*uint64(wordSize):]
	for i := uint64(0); i < c; i++ {
		n := 0
		for names[n] != 0 {
			n++
		}
		name := string(names[:n])
		names = names[n+1:]

		// For Mach-O and PE/386 files we strip a leading
		// underscore from the symbol name.
		if goos == "darwin" || (goos == "windows" && goarch == "386") {
			if name[0] == '_' && len(name) > 1 {
				name = name[1:]
			}
		}

		var off uint64
		if is64 {
			off = binary.BigEndian.Uint64(contents)
		} else {
			off = uint64(binary.BigEndian.Uint32(contents))
		}
		contents = contents[wordSize:]

		ret[name] = off
	}

	return ret
}

func macholoaddsym(m *LdMachoObj, d *LdMachoDysymtab) int {
	n := int(d.nindirectsyms)

	p := make([]byte, n*4)
	if obj.Bseek(m.f, m.base+int64(d.indirectsymoff), 0) < 0 || obj.Bread(m.f, p) != len(p) {
		return -1
	}

	d.indir = make([]uint32, n)
	for i := 0; i < n; i++ {
		d.indir[i] = m.e.Uint32(p[4*i:])
	}
	return 0
}

func pemap(peobj *PeObj, sect *PeSect) int {
	if sect.base != nil {
		return 0
	}

	sect.base = make([]byte, sect.sh.SizeOfRawData)
	if sect.sh.PointerToRawData == 0 { // .bss doesn't have data in object file
		return 0
	}
	if obj.Bseek(peobj.f, int64(peobj.base)+int64(sect.sh.PointerToRawData), 0) < 0 || obj.Bread(peobj.f, sect.base) != len(sect.base) {
		return -1
	}

	return 0
}

func rddata(f *obj.Biobuf) []byte {
	var p []byte
	n := rdint(f)
	if n > rddataBufMax {
		p = make([]byte, n)
	} else {
		if len(rddataBuf) < n {
			rddataBuf = make([]byte, rddataBufMax)
		}
		p = rddataBuf[:n:n]
		rddataBuf = rddataBuf[n:]
	}
	obj.Bread(f, p)
	return p
}

func macholoadrel(m *LdMachoObj, sect *LdMachoSect) int {
	if sect.rel != nil || sect.nreloc == 0 {
		return 0
	}
	rel := make([]LdMachoRel, sect.nreloc)
	n := int(sect.nreloc * 8)
	buf := make([]byte, n)
	if obj.Bseek(m.f, m.base+int64(sect.reloff), 0) < 0 || obj.Bread(m.f, buf) != n {
		return -1
	}
	var p []byte
	var r *LdMachoRel
	var v uint32
	for i := 0; uint32(i) < sect.nreloc; i++ {
		r = &rel[i]
		p = buf[i*8:]
		r.addr = m.e.Uint32(p)

		// TODO(rsc): Wrong interpretation for big-endian bitfields?
		if r.addr&0x80000000 != 0 {
			// scatterbrained relocation
			r.scattered = 1

			v = r.addr >> 24
			r.addr &= 0xFFFFFF
			r.type_ = uint8(v & 0xF)
			v >>= 4
			r.length = 1 << (v & 3)
			v >>= 2
			r.pcrel = uint8(v & 1)
			r.value = m.e.Uint32(p[4:])
		} else {
			v = m.e.Uint32(p[4:])
			r.symnum = v & 0xFFFFFF
			v >>= 24
			r.pcrel = uint8(v & 1)
			v >>= 1
			r.length = 1 << (v & 3)
			v >>= 2
			r.extrn = uint8(v & 1)
			v >>= 1
			r.type_ = uint8(v)
		}
	}

	sect.rel = rel
	return 0
}

func elfmap(elfobj *ElfObj, sect *ElfSect) (err error) {
	if sect.base != nil {
		return nil
	}

	if sect.off+sect.size > uint64(elfobj.length) {
		err = fmt.Errorf("elf section past end of file")
		return err
	}

	sect.base = make([]byte, sect.size)
	err = fmt.Errorf("short read")
	if obj.Bseek(elfobj.f, int64(uint64(elfobj.base)+sect.off), 0) < 0 || obj.Bread(elfobj.f, sect.base) != len(sect.base) {
		return err
	}

	return nil
}

func (p *importer) string() string {
	if p.debugFormat {
		p.marker('s')
	}

	if n := int(p.rawInt64()); n > 0 {
		if cap(p.buf) < n {
			p.buf = make([]byte, n)
		} else {
			p.buf = p.buf[:n]
		}
		r := obj.Bread(p.in, p.buf)
		p.read += r
		if r != n {
			Fatalf("read error: read %d bytes of %d", r, n)
		}
		return string(p.buf)
	}

	return ""
}

func rdsym(ctxt *Link, f *obj.Biobuf, pkg string) *LSym {
	n := int(rdint(f))
	if n == 0 {
		rdint(f)
		return nil
	}

	if len(symbuf) < n {
		symbuf = make([]byte, n)
	}
	obj.Bread(f, symbuf[:n])
	p := string(symbuf[:n])
	v := int(rdint(f))
	if v != 0 {
		v = ctxt.Version
	}
	s := Linklookup(ctxt, expandpkg(p, pkg), v)

	if v == 0 && s.Name[0] == '$' && s.Type == 0 {
		if strings.HasPrefix(s.Name, "$f32.") {
			x, _ := strconv.ParseUint(s.Name[5:], 16, 32)
			i32 := int32(x)
			s.Type = obj.SRODATA
			s.Local = true
			Adduint32(ctxt, s, uint32(i32))
			s.Reachable = false
		} else if strings.HasPrefix(s.Name, "$f64.") || strings.HasPrefix(s.Name, "$i64.") {
			x, _ := strconv.ParseUint(s.Name[5:], 16, 64)
			i64 := int64(x)
			s.Type = obj.SRODATA
			s.Local = true
			Adduint64(ctxt, s, uint64(i64))
			s.Reachable = false
		}
	}
	if v == 0 && strings.HasPrefix(s.Name, "runtime.gcbits.") {
		s.Local = true
	}
	return s
}

func ldpkg(f *obj.Biobuf, pkg string, length int64, filename string, whence int) {
	var p0, p1 int

	if Debug['g'] != 0 {
		return
	}

	if int64(int(length)) != length {
		fmt.Fprintf(os.Stderr, "%s: too much pkg data in %s\n", os.Args[0], filename)
		if Debug['u'] != 0 {
			errorexit()
		}
		return
	}

	// In a __.PKGDEF, we only care about the package name.
	// Don't read all the export data.
	if length > 1000 && whence == Pkgdef {
		length = 1000
	}

	bdata := make([]byte, length)
	if int64(obj.Bread(f, bdata)) != length {
		fmt.Fprintf(os.Stderr, "%s: short pkg read %s\n", os.Args[0], filename)
		if Debug['u'] != 0 {
			errorexit()
		}
		return
	}
	data := string(bdata)

	// first \n$$ marks beginning of exports - skip rest of line
	p0 = strings.Index(data, "\n$$")
	if p0 < 0 {
		if Debug['u'] != 0 && whence != ArchiveObj {
			Exitf("cannot find export data in %s", filename)
		}
		return
	}

	// \n$$B marks the beginning of binary export data - don't skip over the B
	p0 += 3
	for p0 < len(data) && data[p0] != '\n' && data[p0] != 'B' {
		p0++
	}

	// second marks end of exports / beginning of local data
	p1 = strings.Index(data[p0:], "\n$$\n")
	if p1 < 0 && whence == Pkgdef {
		p1 = len(data) - p0
	}
	if p1 < 0 {
		fmt.Fprintf(os.Stderr, "%s: cannot find end of exports in %s\n", os.Args[0], filename)
		if Debug['u'] != 0 {
			errorexit()
		}
		return
	}
	p1 += p0

	for p0 < p1 && data[p0] != 'B' && (data[p0] == ' ' || data[p0] == '\t' || data[p0] == '\n') {
		p0++
	}
	// don't check this section if we have binary (B) export data
	// TODO fix this eventually
	if p0 < p1 && data[p0] != 'B' {
		if !strings.HasPrefix(data[p0:], "package ") {
			fmt.Fprintf(os.Stderr, "%s: bad package section in %s - %.20s\n", os.Args[0], filename, data[p0:])
			if Debug['u'] != 0 {
				errorexit()
			}
			return
		}

		p0 += 8
		for p0 < p1 && (data[p0] == ' ' || data[p0] == '\t' || data[p0] == '\n') {
			p0++
		}
		pname := p0
		for p0 < p1 && data[p0] != ' ' && data[p0] != '\t' && data[p0] != '\n' {
			p0++
		}
		if Debug['u'] != 0 && whence != ArchiveObj && (p0+6 > p1 || !strings.HasPrefix(data[p0:], " safe\n")) {
			Exitf("load of unsafe package %s", filename)
		}

		name := data[pname:p0]
		for p0 < p1 && data[p0] != '\n' {
			p0++
		}
		if p0 < p1 {
			p0++
		}

		if pkg == "main" && name != "main" {
			Exitf("%s: not package main (package %s)", filename, name)
		}
	}

	// __.PKGDEF has no cgo section - those are in the C compiler-generated object files.
//.........这里部分代码省略.........

func objfile(lib *Library) {
	pkg := pathtoprefix(lib.Pkg)

	if Debug['v'] > 1 {
		fmt.Fprintf(&Bso, "%5.2f ldobj: %s (%s)\n", obj.Cputime(), lib.File, pkg)
	}
	Bso.Flush()
	var err error
	var f *obj.Biobuf
	f, err = obj.Bopenr(lib.File)
	if err != nil {
		Exitf("cannot open file %s: %v", lib.File, err)
	}

	magbuf := make([]byte, len(ARMAG))
	if obj.Bread(f, magbuf) != len(magbuf) || !strings.HasPrefix(string(magbuf), ARMAG) {
		/* load it as a regular file */
		l := obj.Bseek(f, 0, 2)

		obj.Bseek(f, 0, 0)
		ldobj(f, pkg, l, lib.File, lib.File, FileObj)
		obj.Bterm(f)

		return
	}

	/* skip over optional __.GOSYMDEF and process __.PKGDEF */
	off := obj.Boffset(f)

	var arhdr ArHdr
	l := nextar(f, off, &arhdr)
	var pname string
	if l <= 0 {
		Diag("%s: short read on archive file symbol header", lib.File)
		goto out
	}

	if strings.HasPrefix(arhdr.name, symname) {
		off += l
		l = nextar(f, off, &arhdr)
		if l <= 0 {
			Diag("%s: short read on archive file symbol header", lib.File)
			goto out
		}
	}

	if !strings.HasPrefix(arhdr.name, pkgname) {
		Diag("%s: cannot find package header", lib.File)
		goto out
	}

	if Buildmode == BuildmodeShared {
		before := obj.Boffset(f)
		pkgdefBytes := make([]byte, atolwhex(arhdr.size))
		obj.Bread(f, pkgdefBytes)
		hash := sha1.Sum(pkgdefBytes)
		lib.hash = hash[:]
		obj.Bseek(f, before, 0)
	}

	off += l

	if Debug['u'] != 0 {
		ldpkg(f, pkg, atolwhex(arhdr.size), lib.File, Pkgdef)
	}

	/*
	 * load all the object files from the archive now.
	 * this gives us sequential file access and keeps us
	 * from needing to come back later to pick up more
	 * objects.  it breaks the usual C archive model, but
	 * this is Go, not C.  the common case in Go is that
	 * we need to load all the objects, and then we throw away
	 * the individual symbols that are unused.
	 *
	 * loading every object will also make it possible to
	 * load foreign objects not referenced by __.GOSYMDEF.
	 */
	for {
		l = nextar(f, off, &arhdr)
		if l == 0 {
			break
		}
		if l < 0 {
			Exitf("%s: malformed archive", lib.File)
		}

		off += l

		pname = fmt.Sprintf("%s(%s)", lib.File, arhdr.name)
		l = atolwhex(arhdr.size)
		ldobj(f, pkg, l, pname, lib.File, ArchiveObj)
	}

out:
	obj.Bterm(f)
}

func rdstring(f *obj.Biobuf) string {
	n := rdint(f)
	p := make([]byte, n)
	obj.Bread(f, p)
	return string(p)
}

func ldelf(f *obj.Biobuf, pkg string, length int64, pn string) {
	if Debug['v'] != 0 {
		fmt.Fprintf(&Bso, "%5.2f ldelf %s\n", obj.Cputime(), pn)
	}

	Ctxt.Version++
	base := int32(obj.Boffset(f))

	var add uint64
	var e binary.ByteOrder
	var elfobj *ElfObj
	var err error
	var flag int
	var hdr *ElfHdrBytes
	var hdrbuf [64]uint8
	var info uint64
	var is64 int
	var j int
	var n int
	var name string
	var p []byte
	var r []Reloc
	var rela int
	var rp *Reloc
	var rsect *ElfSect
	var s *LSym
	var sect *ElfSect
	var sym ElfSym
	var symbols []*LSym
	if obj.Bread(f, hdrbuf[:]) != len(hdrbuf) {
		goto bad
	}
	hdr = new(ElfHdrBytes)
	binary.Read(bytes.NewReader(hdrbuf[:]), binary.BigEndian, hdr) // only byte arrays; byte order doesn't matter
	if string(hdr.Ident[:4]) != "\x7FELF" {
		goto bad
	}
	switch hdr.Ident[5] {
	case ElfDataLsb:
		e = binary.LittleEndian

	case ElfDataMsb:
		e = binary.BigEndian

	default:
		goto bad
	}

	// read header
	elfobj = new(ElfObj)

	elfobj.e = e
	elfobj.f = f
	elfobj.base = int64(base)
	elfobj.length = length
	elfobj.name = pn

	is64 = 0
	if hdr.Ident[4] == ElfClass64 {
		is64 = 1
		hdr := new(ElfHdrBytes64)
		binary.Read(bytes.NewReader(hdrbuf[:]), binary.BigEndian, hdr) // only byte arrays; byte order doesn't matter
		elfobj.type_ = uint32(e.Uint16(hdr.Type[:]))
		elfobj.machine = uint32(e.Uint16(hdr.Machine[:]))
		elfobj.version = e.Uint32(hdr.Version[:])
		elfobj.phoff = e.Uint64(hdr.Phoff[:])
		elfobj.shoff = e.Uint64(hdr.Shoff[:])
		elfobj.flags = e.Uint32(hdr.Flags[:])
		elfobj.ehsize = uint32(e.Uint16(hdr.Ehsize[:]))
		elfobj.phentsize = uint32(e.Uint16(hdr.Phentsize[:]))
		elfobj.phnum = uint32(e.Uint16(hdr.Phnum[:]))
		elfobj.shentsize = uint32(e.Uint16(hdr.Shentsize[:]))
		elfobj.shnum = uint32(e.Uint16(hdr.Shnum[:]))
		elfobj.shstrndx = uint32(e.Uint16(hdr.Shstrndx[:]))
	} else {
		elfobj.type_ = uint32(e.Uint16(hdr.Type[:]))
		elfobj.machine = uint32(e.Uint16(hdr.Machine[:]))
		elfobj.version = e.Uint32(hdr.Version[:])
		elfobj.entry = uint64(e.Uint32(hdr.Entry[:]))
		elfobj.phoff = uint64(e.Uint32(hdr.Phoff[:]))
		elfobj.shoff = uint64(e.Uint32(hdr.Shoff[:]))
		elfobj.flags = e.Uint32(hdr.Flags[:])
		elfobj.ehsize = uint32(e.Uint16(hdr.Ehsize[:]))
		elfobj.phentsize = uint32(e.Uint16(hdr.Phentsize[:]))
		elfobj.phnum = uint32(e.Uint16(hdr.Phnum[:]))
		elfobj.shentsize = uint32(e.Uint16(hdr.Shentsize[:]))
		elfobj.shnum = uint32(e.Uint16(hdr.Shnum[:]))
		elfobj.shstrndx = uint32(e.Uint16(hdr.Shstrndx[:]))
	}

	elfobj.is64 = is64

	if uint32(hdr.Ident[6]) != elfobj.version {
		goto bad
	}

	if e.Uint16(hdr.Type[:]) != ElfTypeRelocatable {
		Diag("%s: elf but not elf relocatable object", pn)
		return
	}
//.........这里部分代码省略.........

func rddata(f *obj.Biobuf) []byte {
	n := rdint(f)
	p := make([]byte, n)
	obj.Bread(f, p)
	return p
}