TEXT ·Syscall6(SB),NOSPLIT,$0-44
	JMP	syscall·Syscall6(SB)

TEXT ·RawSyscall(SB),NOSPLIT,$0-28
	JMP	syscall·RawSyscall(SB)

TEXT ·RawSyscall6(SB),NOSPLIT,$0-40
	JMP	syscall·RawSyscall6(SB)

TEXT ·seek(SB),NOSPLIT,$0-36

	}
	return
}

func seek(fd int, offset int64, whence int) (int64, syscall.Errno) {
	var newoffset int64
	offsetLow := uint32(offset & 0xffffffff)
	offsetHigh := uint32((offset >> 32) & 0xffffffff)
	_, _, err := Syscall6(SYS__LLSEEK, uintptr(fd), uintptr(offsetHigh), uintptr(offsetLow), uintptr(unsafe.Pointer(&newoffset)), uintptr(whence), 0)
	return newoffset, err
}

}

// Underlying system call writes to newoffset via pointer.
// Implemented in assembly to avoid allocation.
func seek(fd int, offset int64, whence int) (newoffset int64, err Errno)

func Seek(fd int, offset int64, whence int) (newoffset int64, err error) {
	newoffset, errno := seek(fd, offset, whence)
	if errno != 0 {
		return 0, errno
	}
	return newoffset, nil
}

TEXT	·Syscall6(SB),NOSPLIT,$0-88
	JMP	syscall·Syscall6(SB)

TEXT ·RawSyscall(SB),NOSPLIT,$0-56
	JMP	syscall·RawSyscall(SB)

TEXT	·RawSyscall6(SB),NOSPLIT,$0-80
	JMP	syscall·RawSyscall6(SB)

TEXT ·seek(SB),NOSPLIT,$0-56
	JMP	syscall·seek(SB)

TEXT ·exit(SB),NOSPLIT,$8-8

      sinkBuffer.write(maskKey)

      if (length > 0) {
        val payloadStart = sinkBuffer.size
        sinkBuffer.write(payload)

        sinkBuffer.readAndWriteUnsafe(maskCursor!!)
        maskCursor.seek(payloadStart)
        toggleMask(maskCursor, maskKey)
        maskCursor.close()
      }
    } else {
      sinkBuffer.writeByte(b1)
      sinkBuffer.write(payload)
    }

    sink.flush()
  }

	return t, nil
}

// typeUnitReader is a typeReader for a tagTypeUnit.
type typeUnitReader struct {
	d   *Data
	tu  *typeUnit
	b   buf
	err error
}

// Seek to a new position in the type unit.
func (tur *typeUnitReader) Seek(off Offset) {
	tur.err = nil
	doff := off - tur.tu.off
	if doff < 0 || doff >= Offset(len(tur.tu.data)) {

	MOVSQ
	MOVSQ
	SYSCALL
	MOVQ	AX, r1+56(FP)
	MOVQ	AX, r2+64(FP)
	MOVQ	AX, err+72(FP)
	RET

#define SYS_SEEK 39	/* from zsysnum_plan9.go */

//func seek(placeholder uintptr, fd int, offset int64, whence int) (newoffset int64, err string)
TEXT ·seek(SB),NOSPLIT,$48-56
	NO_LOCAL_POINTERS
	LEAQ	newoffset+32(FP), AX
	MOVQ	AX, placeholder+0(FP)

	// copy args down
	LEAQ	placeholder+0(FP), SI

  CHECK(v2_reader_ != nullptr);
  CHECK(v2_reader_->status().ok());

  // First pass: filters out the entries of the slices.
  std::unordered_set<string> filtered_keys;
  BundleEntryProto entry;
  v2_reader_->Seek(kHeaderEntryKey);
  for (v2_reader_->Next(); v2_reader_->Valid(); v2_reader_->Next()) {
    CHECK(entry.ParseFromArray(v2_reader_->value().data(),
                               v2_reader_->value().size()))

	// of the transfer was reported correctly, and that the destination
	// file contains exactly the bytes we expect it to contain.
	dstoff, err := dst.Seek(0, io.SeekCurrent)
	if err != nil {
		t.Fatal(err)
	}
	srcoff, err := src.Seek(0, io.SeekCurrent)
	if err != nil {
		t.Fatal(err)
	}
	if dstoff != srcoff {
		t.Errorf("offsets differ: dstoff = %d, srcoff = %d", dstoff, srcoff)
	}

}

func closefd(fd uintptr) {
	syscall.Close(syscall.Handle(fd))
}

func preadn(fd uintptr, buf []byte, off int) error {
	whence := seekStart
	if off < 0 {
		whence = seekEnd
	}
	if _, err := syscall.Seek(syscall.Handle(fd), int64(off), whence); err != nil {
		return err
	}
	for len(buf) > 0 {
		m, err := syscall.Read(syscall.Handle(fd), buf)
		if m <= 0 {
			if err == nil {
				return errors.New("short read")
			}