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Source file src/cmd/link/internal/ld/symtab.go

Documentation: cmd/link/internal/ld

  // Inferno utils/6l/span.c
  // https://bitbucket.org/inferno-os/inferno-os/src/default/utils/6l/span.c
  //
  //	Copyright © 1994-1999 Lucent Technologies Inc.  All rights reserved.
  //	Portions Copyright © 1995-1997 C H Forsyth (forsyth@terzarima.net)
  //	Portions Copyright © 1997-1999 Vita Nuova Limited
  //	Portions Copyright © 2000-2007 Vita Nuova Holdings Limited (www.vitanuova.com)
  //	Portions Copyright © 2004,2006 Bruce Ellis
  //	Portions Copyright © 2005-2007 C H Forsyth (forsyth@terzarima.net)
  //	Revisions Copyright © 2000-2007 Lucent Technologies Inc. and others
  //	Portions Copyright © 2009 The Go Authors. All rights reserved.
  //
  // Permission is hereby granted, free of charge, to any person obtaining a copy
  // of this software and associated documentation files (the "Software"), to deal
  // in the Software without restriction, including without limitation the rights
  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  // copies of the Software, and to permit persons to whom the Software is
  // furnished to do so, subject to the following conditions:
  //
  // The above copyright notice and this permission notice shall be included in
  // all copies or substantial portions of the Software.
  //
  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  // THE SOFTWARE.
  
  package ld
  
  import (
  	"cmd/internal/objabi"
  	"cmd/internal/sys"
  	"fmt"
  	"path/filepath"
  	"strings"
  )
  
  // Symbol table.
  
  func putelfstr(s string) int {
  	if len(Elfstrdat) == 0 && s != "" {
  		// first entry must be empty string
  		putelfstr("")
  	}
  
  	off := len(Elfstrdat)
  	Elfstrdat = append(Elfstrdat, s...)
  	Elfstrdat = append(Elfstrdat, 0)
  	return off
  }
  
  func putelfsyment(off int, addr int64, size int64, info int, shndx int, other int) {
  	if elf64 {
  		Thearch.Lput(uint32(off))
  		Cput(uint8(info))
  		Cput(uint8(other))
  		Thearch.Wput(uint16(shndx))
  		Thearch.Vput(uint64(addr))
  		Thearch.Vput(uint64(size))
  		Symsize += ELF64SYMSIZE
  	} else {
  		Thearch.Lput(uint32(off))
  		Thearch.Lput(uint32(addr))
  		Thearch.Lput(uint32(size))
  		Cput(uint8(info))
  		Cput(uint8(other))
  		Thearch.Wput(uint16(shndx))
  		Symsize += ELF32SYMSIZE
  	}
  }
  
  var numelfsym int = 1 // 0 is reserved
  
  var elfbind int
  
  func putelfsym(ctxt *Link, x *Symbol, s string, t SymbolType, addr int64, go_ *Symbol) {
  	var typ int
  
  	switch t {
  	default:
  		return
  
  	case TextSym:
  		typ = STT_FUNC
  
  	case DataSym, BSSSym:
  		typ = STT_OBJECT
  
  	case UndefinedSym:
  		// ElfType is only set for symbols read from Go shared libraries, but
  		// for other symbols it is left as STT_NOTYPE which is fine.
  		typ = int(x.ElfType)
  
  	case TLSSym:
  		typ = STT_TLS
  	}
  
  	size := x.Size
  	if t == UndefinedSym {
  		size = 0
  	}
  
  	xo := x
  	for xo.Outer != nil {
  		xo = xo.Outer
  	}
  
  	var elfshnum int
  	if xo.Type == SDYNIMPORT || xo.Type == SHOSTOBJ {
  		elfshnum = SHN_UNDEF
  	} else {
  		if xo.Sect == nil {
  			Errorf(x, "missing section in putelfsym")
  			return
  		}
  		if xo.Sect.Elfsect == nil {
  			Errorf(x, "missing ELF section in putelfsym")
  			return
  		}
  		elfshnum = xo.Sect.Elfsect.shnum
  	}
  
  	// One pass for each binding: STB_LOCAL, STB_GLOBAL,
  	// maybe one day STB_WEAK.
  	bind := STB_GLOBAL
  
  	if x.Version != 0 || (x.Type&SHIDDEN != 0) || x.Attr.Local() {
  		bind = STB_LOCAL
  	}
  
  	// In external linking mode, we have to invoke gcc with -rdynamic
  	// to get the exported symbols put into the dynamic symbol table.
  	// To avoid filling the dynamic table with lots of unnecessary symbols,
  	// mark all Go symbols local (not global) in the final executable.
  	// But when we're dynamically linking, we need all those global symbols.
  	if !ctxt.DynlinkingGo() && Linkmode == LinkExternal && !x.Attr.CgoExportStatic() && elfshnum != SHN_UNDEF {
  		bind = STB_LOCAL
  	}
  
  	if Linkmode == LinkExternal && elfshnum != SHN_UNDEF {
  		addr -= int64(xo.Sect.Vaddr)
  	}
  	other := STV_DEFAULT
  	if x.Type&SHIDDEN != 0 {
  		other = STV_HIDDEN
  	}
  	if SysArch.Family == sys.PPC64 && typ == STT_FUNC && x.Attr.Shared() && x.Name != "runtime.duffzero" && x.Name != "runtime.duffcopy" {
  		// On ppc64 the top three bits of the st_other field indicate how
  		// many instructions separate the global and local entry points. In
  		// our case it is two instructions, indicated by the value 3.
  		// The conditions here match those in preprocess in
  		// cmd/internal/obj/ppc64/obj9.go, which is where the
  		// instructions are inserted.
  		other |= 3 << 5
  	}
  
  	// When dynamically linking, we create Symbols by reading the names from
  	// the symbol tables of the shared libraries and so the names need to
  	// match exactly. Tools like DTrace will have to wait for now.
  	if !ctxt.DynlinkingGo() {
  		// Rewrite · to . for ASCII-only tools like DTrace (sigh)
  		s = strings.Replace(s, "·", ".", -1)
  	}
  
  	if ctxt.DynlinkingGo() && bind == STB_GLOBAL && elfbind == STB_LOCAL && x.Type == STEXT {
  		// When dynamically linking, we want references to functions defined
  		// in this module to always be to the function object, not to the
  		// PLT. We force this by writing an additional local symbol for every
  		// global function symbol and making all relocations against the
  		// global symbol refer to this local symbol instead (see
  		// (*Symbol).ElfsymForReloc). This is approximately equivalent to the
  		// ELF linker -Bsymbolic-functions option, but that is buggy on
  		// several platforms.
  		putelfsyment(putelfstr("local."+s), addr, size, STB_LOCAL<<4|typ&0xf, elfshnum, other)
  		x.LocalElfsym = int32(numelfsym)
  		numelfsym++
  		return
  	} else if bind != elfbind {
  		return
  	}
  
  	putelfsyment(putelfstr(s), addr, size, bind<<4|typ&0xf, elfshnum, other)
  	x.Elfsym = int32(numelfsym)
  	numelfsym++
  }
  
  func putelfsectionsym(s *Symbol, shndx int) {
  	putelfsyment(0, 0, 0, STB_LOCAL<<4|STT_SECTION, shndx, 0)
  	s.Elfsym = int32(numelfsym)
  	numelfsym++
  }
  
  func Asmelfsym(ctxt *Link) {
  	// the first symbol entry is reserved
  	putelfsyment(0, 0, 0, STB_LOCAL<<4|STT_NOTYPE, 0, 0)
  
  	dwarfaddelfsectionsyms(ctxt)
  
  	// Some linkers will add a FILE sym if one is not present.
  	// Avoid having the working directory inserted into the symbol table.
  	// It is added with a name to avoid problems with external linking
  	// encountered on some versions of Solaris. See issue #14957.
  	putelfsyment(putelfstr("go.go"), 0, 0, STB_LOCAL<<4|STT_FILE, SHN_ABS, 0)
  	numelfsym++
  
  	elfbind = STB_LOCAL
  	genasmsym(ctxt, putelfsym)
  
  	elfbind = STB_GLOBAL
  	elfglobalsymndx = numelfsym
  	genasmsym(ctxt, putelfsym)
  }
  
  func putplan9sym(ctxt *Link, x *Symbol, s string, typ SymbolType, addr int64, go_ *Symbol) {
  	t := int(typ)
  	switch typ {
  	case TextSym, DataSym, BSSSym:
  		if x.Version != 0 {
  			t += 'a' - 'A'
  		}
  		fallthrough
  
  	case AutoSym, ParamSym, FileSym, FrameSym:
  		l := 4
  		if Headtype == objabi.Hplan9 && SysArch.Family == sys.AMD64 && !Flag8 {
  			Lputb(uint32(addr >> 32))
  			l = 8
  		}
  
  		Lputb(uint32(addr))
  		Cput(uint8(t + 0x80)) /* 0x80 is variable length */
  
  		var i int
  
  		/* skip the '<' in filenames */
  		if t == FileSym {
  			s = s[1:]
  		}
  		for i = 0; i < len(s); i++ {
  			Cput(s[i])
  		}
  		Cput(0)
  
  		Symsize += int32(l) + 1 + int32(i) + 1
  
  	default:
  		return
  	}
  }
  
  func Asmplan9sym(ctxt *Link) {
  	genasmsym(ctxt, putplan9sym)
  }
  
  var symt *Symbol
  
  var encbuf [10]byte
  
  func Wputb(w uint16) { Cwrite(Append16b(encbuf[:0], w)) }
  func Lputb(l uint32) { Cwrite(Append32b(encbuf[:0], l)) }
  func Vputb(v uint64) { Cwrite(Append64b(encbuf[:0], v)) }
  
  func Wputl(w uint16) { Cwrite(Append16l(encbuf[:0], w)) }
  func Lputl(l uint32) { Cwrite(Append32l(encbuf[:0], l)) }
  func Vputl(v uint64) { Cwrite(Append64l(encbuf[:0], v)) }
  
  func Append16b(b []byte, v uint16) []byte {
  	return append(b, uint8(v>>8), uint8(v))
  }
  func Append16l(b []byte, v uint16) []byte {
  	return append(b, uint8(v), uint8(v>>8))
  }
  
  func Append32b(b []byte, v uint32) []byte {
  	return append(b, uint8(v>>24), uint8(v>>16), uint8(v>>8), uint8(v))
  }
  func Append32l(b []byte, v uint32) []byte {
  	return append(b, uint8(v), uint8(v>>8), uint8(v>>16), uint8(v>>24))
  }
  
  func Append64b(b []byte, v uint64) []byte {
  	return append(b, uint8(v>>56), uint8(v>>48), uint8(v>>40), uint8(v>>32),
  		uint8(v>>24), uint8(v>>16), uint8(v>>8), uint8(v))
  }
  
  func Append64l(b []byte, v uint64) []byte {
  	return append(b, uint8(v), uint8(v>>8), uint8(v>>16), uint8(v>>24),
  		uint8(v>>32), uint8(v>>40), uint8(v>>48), uint8(v>>56))
  }
  
  type byPkg []*Library
  
  func (libs byPkg) Len() int {
  	return len(libs)
  }
  
  func (libs byPkg) Less(a, b int) bool {
  	return libs[a].Pkg < libs[b].Pkg
  }
  
  func (libs byPkg) Swap(a, b int) {
  	libs[a], libs[b] = libs[b], libs[a]
  }
  
  // Create a table with information on the text sections.
  
  func textsectionmap(ctxt *Link) uint32 {
  
  	t := ctxt.Syms.Lookup("runtime.textsectionmap", 0)
  	t.Type = SRODATA
  	t.Attr |= AttrReachable
  	nsections := int64(0)
  
  	for _, sect := range Segtext.Sections {
  		if sect.Name == ".text" {
  			nsections++
  		} else {
  			break
  		}
  	}
  	Symgrow(t, 3*nsections*int64(SysArch.PtrSize))
  
  	off := int64(0)
  	n := 0
  
  	// The vaddr for each text section is the difference between the section's
  	// Vaddr and the Vaddr for the first text section as determined at compile
  	// time.
  
  	// The symbol for the first text section is named runtime.text as before.
  	// Additional text sections are named runtime.text.n where n is the
  	// order of creation starting with 1. These symbols provide the section's
  	// address after relocation by the linker.
  
  	textbase := Segtext.Sections[0].Vaddr
  	for _, sect := range Segtext.Sections {
  		if sect.Name != ".text" {
  			break
  		}
  		off = setuint(ctxt, t, off, sect.Vaddr-textbase)
  		off = setuint(ctxt, t, off, sect.Length)
  		if n == 0 {
  			s := ctxt.Syms.ROLookup("runtime.text", 0)
  			if s == nil {
  				Errorf(nil, "Unable to find symbol runtime.text\n")
  			}
  			off = setaddr(ctxt, t, off, s)
  
  		} else {
  			s := ctxt.Syms.Lookup(fmt.Sprintf("runtime.text.%d", n), 0)
  			if s == nil {
  				Errorf(nil, "Unable to find symbol runtime.text.%d\n", n)
  			}
  			off = setaddr(ctxt, t, off, s)
  		}
  		n++
  	}
  	return uint32(n)
  }
  
  func (ctxt *Link) symtab() {
  	dosymtype(ctxt)
  
  	// Define these so that they'll get put into the symbol table.
  	// data.c:/^address will provide the actual values.
  	ctxt.xdefine("runtime.text", STEXT, 0)
  
  	ctxt.xdefine("runtime.etext", STEXT, 0)
  	ctxt.xdefine("runtime.itablink", SRODATA, 0)
  	ctxt.xdefine("runtime.eitablink", SRODATA, 0)
  	ctxt.xdefine("runtime.rodata", SRODATA, 0)
  	ctxt.xdefine("runtime.erodata", SRODATA, 0)
  	ctxt.xdefine("runtime.types", SRODATA, 0)
  	ctxt.xdefine("runtime.etypes", SRODATA, 0)
  	ctxt.xdefine("runtime.noptrdata", SNOPTRDATA, 0)
  	ctxt.xdefine("runtime.enoptrdata", SNOPTRDATA, 0)
  	ctxt.xdefine("runtime.data", SDATA, 0)
  	ctxt.xdefine("runtime.edata", SDATA, 0)
  	ctxt.xdefine("runtime.bss", SBSS, 0)
  	ctxt.xdefine("runtime.ebss", SBSS, 0)
  	ctxt.xdefine("runtime.noptrbss", SNOPTRBSS, 0)
  	ctxt.xdefine("runtime.enoptrbss", SNOPTRBSS, 0)
  	ctxt.xdefine("runtime.end", SBSS, 0)
  	ctxt.xdefine("runtime.epclntab", SRODATA, 0)
  	ctxt.xdefine("runtime.esymtab", SRODATA, 0)
  
  	// garbage collection symbols
  	s := ctxt.Syms.Lookup("runtime.gcdata", 0)
  
  	s.Type = SRODATA
  	s.Size = 0
  	s.Attr |= AttrReachable
  	ctxt.xdefine("runtime.egcdata", SRODATA, 0)
  
  	s = ctxt.Syms.Lookup("runtime.gcbss", 0)
  	s.Type = SRODATA
  	s.Size = 0
  	s.Attr |= AttrReachable
  	ctxt.xdefine("runtime.egcbss", SRODATA, 0)
  
  	// pseudo-symbols to mark locations of type, string, and go string data.
  	var symtype *Symbol
  	var symtyperel *Symbol
  	if UseRelro() && (Buildmode == BuildmodeCArchive || Buildmode == BuildmodeCShared || Buildmode == BuildmodePIE) {
  		s = ctxt.Syms.Lookup("type.*", 0)
  
  		s.Type = STYPE
  		s.Size = 0
  		s.Attr |= AttrReachable
  		symtype = s
  
  		s = ctxt.Syms.Lookup("typerel.*", 0)
  
  		s.Type = STYPERELRO
  		s.Size = 0
  		s.Attr |= AttrReachable
  		symtyperel = s
  	} else if !ctxt.DynlinkingGo() {
  		s = ctxt.Syms.Lookup("type.*", 0)
  
  		s.Type = STYPE
  		s.Size = 0
  		s.Attr |= AttrReachable
  		symtype = s
  		symtyperel = s
  	}
  
  	groupSym := func(name string, t SymKind) *Symbol {
  		s := ctxt.Syms.Lookup(name, 0)
  		s.Type = t
  		s.Size = 0
  		s.Attr |= AttrLocal | AttrReachable
  		return s
  	}
  	var (
  		symgostring = groupSym("go.string.*", SGOSTRING)
  		symgofunc   = groupSym("go.func.*", SGOFUNC)
  		symgcbits   = groupSym("runtime.gcbits.*", SGCBITS)
  	)
  
  	var symgofuncrel *Symbol
  	if !ctxt.DynlinkingGo() {
  		if UseRelro() {
  			symgofuncrel = groupSym("go.funcrel.*", SGOFUNCRELRO)
  		} else {
  			symgofuncrel = symgofunc
  		}
  	}
  
  	symitablink := ctxt.Syms.Lookup("runtime.itablink", 0)
  	symitablink.Type = SITABLINK
  
  	symt = ctxt.Syms.Lookup("runtime.symtab", 0)
  	symt.Attr |= AttrLocal
  	symt.Type = SSYMTAB
  	symt.Size = 0
  	symt.Attr |= AttrReachable
  
  	nitablinks := 0
  
  	// assign specific types so that they sort together.
  	// within a type they sort by size, so the .* symbols
  	// just defined above will be first.
  	// hide the specific symbols.
  	for _, s := range ctxt.Syms.Allsym {
  		if !s.Attr.Reachable() || s.Attr.Special() || s.Type != SRODATA {
  			continue
  		}
  
  		switch {
  		case strings.HasPrefix(s.Name, "type."):
  			if !ctxt.DynlinkingGo() {
  				s.Attr |= AttrNotInSymbolTable
  			}
  			if UseRelro() {
  				s.Type = STYPERELRO
  				s.Outer = symtyperel
  			} else {
  				s.Type = STYPE
  				s.Outer = symtype
  			}
  
  		case strings.HasPrefix(s.Name, "go.importpath.") && UseRelro():
  			// Keep go.importpath symbols in the same section as types and
  			// names, as they can be referred to by a section offset.
  			s.Type = STYPERELRO
  
  		case strings.HasPrefix(s.Name, "go.itablink."):
  			nitablinks++
  			s.Type = SITABLINK
  			s.Attr |= AttrNotInSymbolTable
  			s.Outer = symitablink
  
  		case strings.HasPrefix(s.Name, "go.string."):
  			s.Type = SGOSTRING
  			s.Attr |= AttrNotInSymbolTable
  			s.Outer = symgostring
  
  		case strings.HasPrefix(s.Name, "runtime.gcbits."):
  			s.Type = SGCBITS
  			s.Attr |= AttrNotInSymbolTable
  			s.Outer = symgcbits
  
  		case strings.HasSuffix(s.Name, "·f"):
  			if !ctxt.DynlinkingGo() {
  				s.Attr |= AttrNotInSymbolTable
  			}
  			if UseRelro() {
  				s.Type = SGOFUNCRELRO
  				s.Outer = symgofuncrel
  			} else {
  				s.Type = SGOFUNC
  				s.Outer = symgofunc
  			}
  
  		case strings.HasPrefix(s.Name, "gcargs."),
  			strings.HasPrefix(s.Name, "gclocals."),
  			strings.HasPrefix(s.Name, "gclocals·"),
  			strings.HasPrefix(s.Name, "inltree."):
  			s.Type = SGOFUNC
  			s.Attr |= AttrNotInSymbolTable
  			s.Outer = symgofunc
  			s.Align = 4
  			liveness += (s.Size + int64(s.Align) - 1) &^ (int64(s.Align) - 1)
  		}
  	}
  
  	if Buildmode == BuildmodeShared {
  		abihashgostr := ctxt.Syms.Lookup("go.link.abihash."+filepath.Base(*flagOutfile), 0)
  		abihashgostr.Attr |= AttrReachable
  		abihashgostr.Type = SRODATA
  		hashsym := ctxt.Syms.Lookup("go.link.abihashbytes", 0)
  		Addaddr(ctxt, abihashgostr, hashsym)
  		adduint(ctxt, abihashgostr, uint64(hashsym.Size))
  	}
  	if Buildmode == BuildmodePlugin || ctxt.Syms.ROLookup("plugin.Open", 0) != nil {
  		for _, l := range ctxt.Library {
  			s := ctxt.Syms.Lookup("go.link.pkghashbytes."+l.Pkg, 0)
  			s.Attr |= AttrReachable
  			s.Type = SRODATA
  			s.Size = int64(len(l.hash))
  			s.P = []byte(l.hash)
  			str := ctxt.Syms.Lookup("go.link.pkghash."+l.Pkg, 0)
  			str.Attr |= AttrReachable
  			str.Type = SRODATA
  			Addaddr(ctxt, str, s)
  			adduint(ctxt, str, uint64(len(l.hash)))
  		}
  	}
  
  	nsections := textsectionmap(ctxt)
  
  	// Information about the layout of the executable image for the
  	// runtime to use. Any changes here must be matched by changes to
  	// the definition of moduledata in runtime/symtab.go.
  	// This code uses several global variables that are set by pcln.go:pclntab.
  	moduledata := ctxt.Moduledata
  	// The pclntab slice
  	Addaddr(ctxt, moduledata, ctxt.Syms.Lookup("runtime.pclntab", 0))
  	adduint(ctxt, moduledata, uint64(ctxt.Syms.Lookup("runtime.pclntab", 0).Size))
  	adduint(ctxt, moduledata, uint64(ctxt.Syms.Lookup("runtime.pclntab", 0).Size))
  	// The ftab slice
  	Addaddrplus(ctxt, moduledata, ctxt.Syms.Lookup("runtime.pclntab", 0), int64(pclntabPclntabOffset))
  	adduint(ctxt, moduledata, uint64(pclntabNfunc+1))
  	adduint(ctxt, moduledata, uint64(pclntabNfunc+1))
  	// The filetab slice
  	Addaddrplus(ctxt, moduledata, ctxt.Syms.Lookup("runtime.pclntab", 0), int64(pclntabFiletabOffset))
  	adduint(ctxt, moduledata, uint64(len(ctxt.Filesyms))+1)
  	adduint(ctxt, moduledata, uint64(len(ctxt.Filesyms))+1)
  	// findfunctab
  	Addaddr(ctxt, moduledata, ctxt.Syms.Lookup("runtime.findfunctab", 0))
  	// minpc, maxpc
  	Addaddr(ctxt, moduledata, pclntabFirstFunc)
  	Addaddrplus(ctxt, moduledata, pclntabLastFunc, pclntabLastFunc.Size)
  	// pointers to specific parts of the module
  	Addaddr(ctxt, moduledata, ctxt.Syms.Lookup("runtime.text", 0))
  	Addaddr(ctxt, moduledata, ctxt.Syms.Lookup("runtime.etext", 0))
  	Addaddr(ctxt, moduledata, ctxt.Syms.Lookup("runtime.noptrdata", 0))
  	Addaddr(ctxt, moduledata, ctxt.Syms.Lookup("runtime.enoptrdata", 0))
  	Addaddr(ctxt, moduledata, ctxt.Syms.Lookup("runtime.data", 0))
  	Addaddr(ctxt, moduledata, ctxt.Syms.Lookup("runtime.edata", 0))
  	Addaddr(ctxt, moduledata, ctxt.Syms.Lookup("runtime.bss", 0))
  	Addaddr(ctxt, moduledata, ctxt.Syms.Lookup("runtime.ebss", 0))
  	Addaddr(ctxt, moduledata, ctxt.Syms.Lookup("runtime.noptrbss", 0))
  	Addaddr(ctxt, moduledata, ctxt.Syms.Lookup("runtime.enoptrbss", 0))
  	Addaddr(ctxt, moduledata, ctxt.Syms.Lookup("runtime.end", 0))
  	Addaddr(ctxt, moduledata, ctxt.Syms.Lookup("runtime.gcdata", 0))
  	Addaddr(ctxt, moduledata, ctxt.Syms.Lookup("runtime.gcbss", 0))
  	Addaddr(ctxt, moduledata, ctxt.Syms.Lookup("runtime.types", 0))
  	Addaddr(ctxt, moduledata, ctxt.Syms.Lookup("runtime.etypes", 0))
  
  	// text section information
  	Addaddr(ctxt, moduledata, ctxt.Syms.Lookup("runtime.textsectionmap", 0))
  	adduint(ctxt, moduledata, uint64(nsections))
  	adduint(ctxt, moduledata, uint64(nsections))
  
  	// The typelinks slice
  	typelinkSym := ctxt.Syms.Lookup("runtime.typelink", 0)
  	ntypelinks := uint64(typelinkSym.Size) / 4
  	Addaddr(ctxt, moduledata, typelinkSym)
  	adduint(ctxt, moduledata, ntypelinks)
  	adduint(ctxt, moduledata, ntypelinks)
  	// The itablinks slice
  	Addaddr(ctxt, moduledata, ctxt.Syms.Lookup("runtime.itablink", 0))
  	adduint(ctxt, moduledata, uint64(nitablinks))
  	adduint(ctxt, moduledata, uint64(nitablinks))
  	// The ptab slice
  	if ptab := ctxt.Syms.ROLookup("go.plugin.tabs", 0); ptab != nil && ptab.Attr.Reachable() {
  		ptab.Attr |= AttrLocal
  		ptab.Type = SRODATA
  
  		nentries := uint64(len(ptab.P) / 8) // sizeof(nameOff) + sizeof(typeOff)
  		Addaddr(ctxt, moduledata, ptab)
  		adduint(ctxt, moduledata, nentries)
  		adduint(ctxt, moduledata, nentries)
  	} else {
  		adduint(ctxt, moduledata, 0)
  		adduint(ctxt, moduledata, 0)
  		adduint(ctxt, moduledata, 0)
  	}
  	if Buildmode == BuildmodePlugin {
  		addgostring(ctxt, moduledata, "go.link.thispluginpath", *flagPluginPath)
  
  		pkghashes := ctxt.Syms.Lookup("go.link.pkghashes", 0)
  		pkghashes.Attr |= AttrReachable
  		pkghashes.Attr |= AttrLocal
  		pkghashes.Type = SRODATA
  
  		for i, l := range ctxt.Library {
  			// pkghashes[i].name
  			addgostring(ctxt, pkghashes, fmt.Sprintf("go.link.pkgname.%d", i), l.Pkg)
  			// pkghashes[i].linktimehash
  			addgostring(ctxt, pkghashes, fmt.Sprintf("go.link.pkglinkhash.%d", i), string(l.hash))
  			// pkghashes[i].runtimehash
  			hash := ctxt.Syms.ROLookup("go.link.pkghash."+l.Pkg, 0)
  			Addaddr(ctxt, pkghashes, hash)
  		}
  		Addaddr(ctxt, moduledata, pkghashes)
  		adduint(ctxt, moduledata, uint64(len(ctxt.Library)))
  		adduint(ctxt, moduledata, uint64(len(ctxt.Library)))
  	} else {
  		adduint(ctxt, moduledata, 0) // pluginpath
  		adduint(ctxt, moduledata, 0)
  		adduint(ctxt, moduledata, 0) // pkghashes slice
  		adduint(ctxt, moduledata, 0)
  		adduint(ctxt, moduledata, 0)
  	}
  	if len(ctxt.Shlibs) > 0 {
  		thismodulename := filepath.Base(*flagOutfile)
  		switch Buildmode {
  		case BuildmodeExe, BuildmodePIE:
  			// When linking an executable, outfile is just "a.out". Make
  			// it something slightly more comprehensible.
  			thismodulename = "the executable"
  		}
  		addgostring(ctxt, moduledata, "go.link.thismodulename", thismodulename)
  
  		modulehashes := ctxt.Syms.Lookup("go.link.abihashes", 0)
  		modulehashes.Attr |= AttrReachable
  		modulehashes.Attr |= AttrLocal
  		modulehashes.Type = SRODATA
  
  		for i, shlib := range ctxt.Shlibs {
  			// modulehashes[i].modulename
  			modulename := filepath.Base(shlib.Path)
  			addgostring(ctxt, modulehashes, fmt.Sprintf("go.link.libname.%d", i), modulename)
  
  			// modulehashes[i].linktimehash
  			addgostring(ctxt, modulehashes, fmt.Sprintf("go.link.linkhash.%d", i), string(shlib.Hash))
  
  			// modulehashes[i].runtimehash
  			abihash := ctxt.Syms.Lookup("go.link.abihash."+modulename, 0)
  			abihash.Attr |= AttrReachable
  			Addaddr(ctxt, modulehashes, abihash)
  		}
  
  		Addaddr(ctxt, moduledata, modulehashes)
  		adduint(ctxt, moduledata, uint64(len(ctxt.Shlibs)))
  		adduint(ctxt, moduledata, uint64(len(ctxt.Shlibs)))
  	}
  
  	// The rest of moduledata is zero initialized.
  	// When linking an object that does not contain the runtime we are
  	// creating the moduledata from scratch and it does not have a
  	// compiler-provided size, so read it from the type data.
  	moduledatatype := ctxt.Syms.ROLookup("type.runtime.moduledata", 0)
  	moduledata.Size = decodetypeSize(ctxt.Arch, moduledatatype)
  	Symgrow(moduledata, moduledata.Size)
  
  	lastmoduledatap := ctxt.Syms.Lookup("runtime.lastmoduledatap", 0)
  	if lastmoduledatap.Type != SDYNIMPORT {
  		lastmoduledatap.Type = SNOPTRDATA
  		lastmoduledatap.Size = 0 // overwrite existing value
  		Addaddr(ctxt, lastmoduledatap, moduledata)
  	}
  }
  

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