in  IPNet
	out IPNet
}{
	{IPNet{IP: v4addr, Mask: v4mask}, IPNet{IP: v4addr, Mask: v4mask}},
	{IPNet{IP: v4addr, Mask: v4mappedv6mask}, IPNet{IP: v4addr, Mask: v4mask}},
	{IPNet{IP: v4mappedv6addr, Mask: v4mappedv6mask}, IPNet{IP: v4addr, Mask: v4mask}},
	{IPNet{IP: v4mappedv6addr, Mask: v6mask}, IPNet{IP: v4addr, Mask: v4maskzero}},
	{IPNet{IP: v4addr, Mask: v6mask}, IPNet{IP: v4addr, Mask: v4maskzero}},

		},
		{
			name:          "private v6 mapped v4Addr 10/8",
			ip:            private6mapped4a,
			globalUnicast: true,
			private:       true,
		},
		{
			name:          "private v6 mapped v4Addr 172.16/12",
			ip:            private6mapped4b,
			globalUnicast: true,
			private:       true,
		},
		{
			name:          "private v6 mapped v4Addr 192.168/16",
			ip:            private6mapped4c,

		// If main section has no bits, nothing to relocate.
		if sect.Vaddr >= sect.Seg.Vaddr+sect.Seg.Filelen {
			return 0
		}
		sect.Reloff = uint64(ctxt.Out.Offset())
		for i, s := range syms {
			if !ldr.AttrReachable(s) {
				continue
			}
			if uint64(ldr.SymValue(s)) >= sect.Vaddr {
				syms = syms[i:]
				break
			}
		}
		eaddr := int64(sect.Vaddr + sect.Length)
		for _, s := range syms {

		offset := sect.Vaddr - Segtext.Vaddr + Segtext.Fileoff
		// Handle text sections with Codeblk
		if sect.Name == ".text" {
			writeParallel(&wg, f, ctxt, offset, sect.Vaddr, sect.Length)
		} else {
			writeParallel(&wg, datblk, ctxt, offset, sect.Vaddr, sect.Length)
		}
	}

	if Segrodata.Filelen > 0 {
		writeParallel(&wg, datblk, ctxt, Segrodata.Fileoff, Segrodata.Vaddr, Segrodata.Filelen)
	}

		// address where the first byte of the segment is loaded
		// (loadSegment.Vaddr). A file offset fx maps to a virtual (symbol) address
		// sx = fx - loadSegment.Off + loadSegment.Vaddr.
		//
		// Thus, a runtime virtual address x maps to a symbol address
		// sx = x - start + offset - loadSegment.Off + loadSegment.Vaddr.
		return start - offset + loadSegment.Off - loadSegment.Vaddr, nil
	}

	}
	if addr == 0 || eaddr < addr {
		return nil
	}
	size := eaddr - addr
	data := make([]byte, size)
	for _, prog := range f.elf.Progs {
		if prog.Vaddr <= addr && addr+size-1 <= prog.Vaddr+prog.Filesz-1 {
			if _, err := prog.ReadAt(data, int64(addr-prog.Vaddr)); err != nil {
				return nil
			}
			return data
		}
	}
	return nil

	ctxt.xdefine("runtime.noptrdata", sym.SNOPTRDATA, int64(noptr.Vaddr))
	ctxt.xdefine("runtime.enoptrdata", sym.SNOPTRDATA, int64(noptr.Vaddr+noptr.Length))
	ctxt.xdefine("runtime.bss", sym.SBSS, int64(bss.Vaddr))
	ctxt.xdefine("runtime.ebss", sym.SBSS, int64(bss.Vaddr+bss.Length))
	ctxt.xdefine("runtime.data", sym.SDATA, int64(data.Vaddr))

}

type ldMachoCmd struct {
	type_ int
	off   uint32
	size  uint32
	seg   ldMachoSeg
	sym   ldMachoSymtab
	dsym  ldMachoDysymtab
}

type ldMachoSeg struct {
	name     string
	vmaddr   uint64
	vmsize   uint64
	fileoff  uint32
	filesz   uint32
	maxprot  uint32
	initprot uint32
	nsect    uint32
	flags    uint32
	sect     []ldMachoSect
}

type ldMachoSect struct {
	name    string

		msect.align++
	}
	msect.addr = sect.Vaddr
	msect.size = sect.Length

	if sect.Vaddr < sect.Seg.Vaddr+sect.Seg.Filelen {
		// data in file
		if sect.Length > sect.Seg.Vaddr+sect.Seg.Filelen-sect.Vaddr {
			Errorf(nil, "macho cannot represent section %s crossing data and bss", sect.Name)
		}
		msect.off = uint32(sect.Seg.Fileoff + sect.Vaddr - sect.Seg.Vaddr)
	} else {
		msect.off = 0

type Segment struct {
	Rwx      uint8  // permission as usual unix bits (5 = r-x etc)
	Vaddr    uint64 // virtual address
	Length   uint64 // length in memory
	Fileoff  uint64 // file offset
	Filelen  uint64 // length on disk
	Sections []*Section
}

type Section struct {
	Rwx     uint8
	Extnum  int16
	Align   int32
	Name    string
	Vaddr   uint64
	Length  uint64
	Seg     *Segment
	Elfsect interface{} // an *ld.ElfShdr