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

Documentation: cmd/link/internal/ld

  // Derived from Inferno utils/6l/obj.c and utils/6l/span.c
  // https://bitbucket.org/inferno-os/inferno-os/src/default/utils/6l/obj.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/gcprog"
  	"cmd/internal/objabi"
  	"cmd/internal/sys"
  	"cmd/link/internal/sym"
  	"fmt"
  	"log"
  	"os"
  	"sort"
  	"strconv"
  	"strings"
  	"sync"
  )
  
  // isRuntimeDepPkg returns whether pkg is the runtime package or its dependency
  func isRuntimeDepPkg(pkg string) bool {
  	switch pkg {
  	case "runtime",
  		"sync/atomic": // runtime may call to sync/atomic, due to go:linkname
  		return true
  	}
  	return strings.HasPrefix(pkg, "runtime/internal/") && !strings.HasSuffix(pkg, "_test")
  }
  
  // Estimate the max size needed to hold any new trampolines created for this function. This
  // is used to determine when the section can be split if it becomes too large, to ensure that
  // the trampolines are in the same section as the function that uses them.
  func maxSizeTrampolinesPPC64(s *sym.Symbol, isTramp bool) uint64 {
  	// If Thearch.Trampoline is nil, then trampoline support is not available on this arch.
  	// A trampoline does not need any dependent trampolines.
  	if Thearch.Trampoline == nil || isTramp {
  		return 0
  	}
  
  	n := uint64(0)
  	for ri := range s.R {
  		r := &s.R[ri]
  		if r.Type.IsDirectJump() {
  			n++
  		}
  	}
  	// Trampolines in ppc64 are 4 instructions.
  	return n * 16
  }
  
  // detect too-far jumps in function s, and add trampolines if necessary
  // ARM, PPC64 & PPC64LE support trampoline insertion for internal and external linking
  // On PPC64 & PPC64LE the text sections might be split but will still insert trampolines
  // where necessary.
  func trampoline(ctxt *Link, s *sym.Symbol) {
  	if Thearch.Trampoline == nil {
  		return // no need or no support of trampolines on this arch
  	}
  
  	for ri := range s.R {
  		r := &s.R[ri]
  		if !r.Type.IsDirectJump() {
  			continue
  		}
  		if Symaddr(r.Sym) == 0 && r.Sym.Type != sym.SDYNIMPORT {
  			if r.Sym.File != s.File {
  				if !isRuntimeDepPkg(s.File) || !isRuntimeDepPkg(r.Sym.File) {
  					Errorf(s, "unresolved inter-package jump to %s(%s)", r.Sym, r.Sym.File)
  				}
  				// runtime and its dependent packages may call to each other.
  				// they are fine, as they will be laid down together.
  			}
  			continue
  		}
  
  		Thearch.Trampoline(ctxt, r, s)
  	}
  
  }
  
  // resolve relocations in s.
  func relocsym(ctxt *Link, s *sym.Symbol) {
  	for ri := int32(0); ri < int32(len(s.R)); ri++ {
  		r := &s.R[ri]
  		if r.Done {
  			// Relocation already processed by an earlier phase.
  			continue
  		}
  		r.Done = true
  		off := r.Off
  		siz := int32(r.Siz)
  		if off < 0 || off+siz > int32(len(s.P)) {
  			rname := ""
  			if r.Sym != nil {
  				rname = r.Sym.Name
  			}
  			Errorf(s, "invalid relocation %s: %d+%d not in [%d,%d)", rname, off, siz, 0, len(s.P))
  			continue
  		}
  
  		if r.Sym != nil && ((r.Sym.Type == 0 && !r.Sym.Attr.VisibilityHidden()) || r.Sym.Type == sym.SXREF) {
  			// When putting the runtime but not main into a shared library
  			// these symbols are undefined and that's OK.
  			if ctxt.BuildMode == BuildModeShared {
  				if r.Sym.Name == "main.main" || r.Sym.Name == "main.init" {
  					r.Sym.Type = sym.SDYNIMPORT
  				} else if strings.HasPrefix(r.Sym.Name, "go.info.") {
  					// Skip go.info symbols. They are only needed to communicate
  					// DWARF info between the compiler and linker.
  					continue
  				}
  			} else {
  				Errorf(s, "relocation target %s not defined", r.Sym.Name)
  				continue
  			}
  		}
  
  		if r.Type >= 256 {
  			continue
  		}
  		if r.Siz == 0 { // informational relocation - no work to do
  			continue
  		}
  		if r.Type == objabi.R_DWARFFILEREF {
  			// These should have been processed previously during
  			// line table writing.
  			Errorf(s, "orphan R_DWARFFILEREF reloc to %v", r.Sym.Name)
  			continue
  		}
  
  		// We need to be able to reference dynimport symbols when linking against
  		// shared libraries, and Solaris needs it always
  		if ctxt.HeadType != objabi.Hsolaris && r.Sym != nil && r.Sym.Type == sym.SDYNIMPORT && !ctxt.DynlinkingGo() && !r.Sym.Attr.SubSymbol() {
  			if !(ctxt.Arch.Family == sys.PPC64 && ctxt.LinkMode == LinkExternal && r.Sym.Name == ".TOC.") {
  				Errorf(s, "unhandled relocation for %s (type %d (%s) rtype %d (%s))", r.Sym.Name, r.Sym.Type, r.Sym.Type, r.Type, sym.RelocName(ctxt.Arch, r.Type))
  			}
  		}
  		if r.Sym != nil && r.Sym.Type != sym.STLSBSS && r.Type != objabi.R_WEAKADDROFF && !r.Sym.Attr.Reachable() {
  			Errorf(s, "unreachable sym in relocation: %s", r.Sym.Name)
  		}
  
  		// TODO(mundaym): remove this special case - see issue 14218.
  		if ctxt.Arch.Family == sys.S390X {
  			switch r.Type {
  			case objabi.R_PCRELDBL:
  				r.Type = objabi.R_PCREL
  				r.Variant = sym.RV_390_DBL
  			case objabi.R_CALL:
  				r.Variant = sym.RV_390_DBL
  			}
  		}
  
  		var o int64
  		switch r.Type {
  		default:
  			switch siz {
  			default:
  				Errorf(s, "bad reloc size %#x for %s", uint32(siz), r.Sym.Name)
  			case 1:
  				o = int64(s.P[off])
  			case 2:
  				o = int64(ctxt.Arch.ByteOrder.Uint16(s.P[off:]))
  			case 4:
  				o = int64(ctxt.Arch.ByteOrder.Uint32(s.P[off:]))
  			case 8:
  				o = int64(ctxt.Arch.ByteOrder.Uint64(s.P[off:]))
  			}
  			if !Thearch.Archreloc(ctxt, r, s, &o) {
  				Errorf(s, "unknown reloc to %v: %d (%s)", r.Sym.Name, r.Type, sym.RelocName(ctxt.Arch, r.Type))
  			}
  		case objabi.R_TLS_LE:
  			isAndroidX86 := objabi.GOOS == "android" && (ctxt.Arch.InFamily(sys.AMD64, sys.I386))
  
  			if ctxt.LinkMode == LinkExternal && ctxt.IsELF && !isAndroidX86 {
  				r.Done = false
  				if r.Sym == nil {
  					r.Sym = ctxt.Tlsg
  				}
  				r.Xsym = r.Sym
  				r.Xadd = r.Add
  				o = 0
  				if ctxt.Arch.Family != sys.AMD64 {
  					o = r.Add
  				}
  				break
  			}
  
  			if ctxt.IsELF && ctxt.Arch.Family == sys.ARM {
  				// On ELF ARM, the thread pointer is 8 bytes before
  				// the start of the thread-local data block, so add 8
  				// to the actual TLS offset (r->sym->value).
  				// This 8 seems to be a fundamental constant of
  				// ELF on ARM (or maybe Glibc on ARM); it is not
  				// related to the fact that our own TLS storage happens
  				// to take up 8 bytes.
  				o = 8 + r.Sym.Value
  			} else if ctxt.IsELF || ctxt.HeadType == objabi.Hplan9 || ctxt.HeadType == objabi.Hdarwin || isAndroidX86 {
  				o = int64(ctxt.Tlsoffset) + r.Add
  			} else if ctxt.HeadType == objabi.Hwindows {
  				o = r.Add
  			} else {
  				log.Fatalf("unexpected R_TLS_LE relocation for %v", ctxt.HeadType)
  			}
  		case objabi.R_TLS_IE:
  			isAndroidX86 := objabi.GOOS == "android" && (ctxt.Arch.InFamily(sys.AMD64, sys.I386))
  
  			if ctxt.LinkMode == LinkExternal && ctxt.IsELF && !isAndroidX86 {
  				r.Done = false
  				if r.Sym == nil {
  					r.Sym = ctxt.Tlsg
  				}
  				r.Xsym = r.Sym
  				r.Xadd = r.Add
  				o = 0
  				if ctxt.Arch.Family != sys.AMD64 {
  					o = r.Add
  				}
  				break
  			}
  			if ctxt.BuildMode == BuildModePIE && ctxt.IsELF {
  				// We are linking the final executable, so we
  				// can optimize any TLS IE relocation to LE.
  				if Thearch.TLSIEtoLE == nil {
  					log.Fatalf("internal linking of TLS IE not supported on %v", ctxt.Arch.Family)
  				}
  				Thearch.TLSIEtoLE(s, int(off), int(r.Siz))
  				o = int64(ctxt.Tlsoffset)
  				// TODO: o += r.Add when ctxt.Arch.Family != sys.AMD64?
  				// Why do we treat r.Add differently on AMD64?
  				// Is the external linker using Xadd at all?
  			} else {
  				log.Fatalf("cannot handle R_TLS_IE (sym %s) when linking internally", s.Name)
  			}
  		case objabi.R_ADDR:
  			if ctxt.LinkMode == LinkExternal && r.Sym.Type != sym.SCONST {
  				r.Done = false
  
  				// set up addend for eventual relocation via outer symbol.
  				rs := r.Sym
  
  				r.Xadd = r.Add
  				for rs.Outer != nil {
  					r.Xadd += Symaddr(rs) - Symaddr(rs.Outer)
  					rs = rs.Outer
  				}
  
  				if rs.Type != sym.SHOSTOBJ && rs.Type != sym.SDYNIMPORT && rs.Sect == nil {
  					Errorf(s, "missing section for relocation target %s", rs.Name)
  				}
  				r.Xsym = rs
  
  				o = r.Xadd
  				if ctxt.IsELF {
  					if ctxt.Arch.Family == sys.AMD64 {
  						o = 0
  					}
  				} else if ctxt.HeadType == objabi.Hdarwin {
  					// ld64 for arm64 has a bug where if the address pointed to by o exists in the
  					// symbol table (dynid >= 0), or is inside a symbol that exists in the symbol
  					// table, then it will add o twice into the relocated value.
  					// The workaround is that on arm64 don't ever add symaddr to o and always use
  					// extern relocation by requiring rs->dynid >= 0.
  					if rs.Type != sym.SHOSTOBJ {
  						if ctxt.Arch.Family == sys.ARM64 && rs.Dynid < 0 {
  							Errorf(s, "R_ADDR reloc to %s+%d is not supported on darwin/arm64", rs.Name, o)
  						}
  						if ctxt.Arch.Family != sys.ARM64 {
  							o += Symaddr(rs)
  						}
  					}
  				} else if ctxt.HeadType == objabi.Hwindows {
  					// nothing to do
  				} else {
  					Errorf(s, "unhandled pcrel relocation to %s on %v", rs.Name, ctxt.HeadType)
  				}
  
  				break
  			}
  
  			o = Symaddr(r.Sym) + r.Add
  
  			// On amd64, 4-byte offsets will be sign-extended, so it is impossible to
  			// access more than 2GB of static data; fail at link time is better than
  			// fail at runtime. See https://golang.org/issue/7980.
  			// Instead of special casing only amd64, we treat this as an error on all
  			// 64-bit architectures so as to be future-proof.
  			if int32(o) < 0 && ctxt.Arch.PtrSize > 4 && siz == 4 {
  				Errorf(s, "non-pc-relative relocation address for %s is too big: %#x (%#x + %#x)", r.Sym.Name, uint64(o), Symaddr(r.Sym), r.Add)
  				errorexit()
  			}
  		case objabi.R_DWARFSECREF:
  			if r.Sym.Sect == nil {
  				Errorf(s, "missing DWARF section for relocation target %s", r.Sym.Name)
  			}
  
  			if ctxt.LinkMode == LinkExternal {
  				r.Done = false
  
  				// On most platforms, the external linker needs to adjust DWARF references
  				// as it combines DWARF sections. However, on Darwin, dsymutil does the
  				// DWARF linking, and it understands how to follow section offsets.
  				// Leaving in the relocation records confuses it (see
  				// https://golang.org/issue/22068) so drop them for Darwin.
  				if ctxt.HeadType == objabi.Hdarwin {
  					r.Done = true
  				}
  
  				// PE code emits IMAGE_REL_I386_SECREL and IMAGE_REL_AMD64_SECREL
  				// for R_DWARFSECREF relocations, while R_ADDR is replaced with
  				// IMAGE_REL_I386_DIR32, IMAGE_REL_AMD64_ADDR64 and IMAGE_REL_AMD64_ADDR32.
  				// Do not replace R_DWARFSECREF with R_ADDR for windows -
  				// let PE code emit correct relocations.
  				if ctxt.HeadType != objabi.Hwindows {
  					r.Type = objabi.R_ADDR
  				}
  
  				r.Xsym = ctxt.Syms.ROLookup(r.Sym.Sect.Name, 0)
  				r.Xadd = r.Add + Symaddr(r.Sym) - int64(r.Sym.Sect.Vaddr)
  
  				o = r.Xadd
  				if ctxt.IsELF && ctxt.Arch.Family == sys.AMD64 {
  					o = 0
  				}
  				break
  			}
  			o = Symaddr(r.Sym) + r.Add - int64(r.Sym.Sect.Vaddr)
  		case objabi.R_WEAKADDROFF:
  			if !r.Sym.Attr.Reachable() {
  				continue
  			}
  			fallthrough
  		case objabi.R_ADDROFF:
  			// The method offset tables using this relocation expect the offset to be relative
  			// to the start of the first text section, even if there are multiple.
  
  			if r.Sym.Sect.Name == ".text" {
  				o = Symaddr(r.Sym) - int64(Segtext.Sections[0].Vaddr) + r.Add
  			} else {
  				o = Symaddr(r.Sym) - int64(r.Sym.Sect.Vaddr) + r.Add
  			}
  
  		case objabi.R_ADDRCUOFF:
  			// debug_range and debug_loc elements use this relocation type to get an
  			// offset from the start of the compile unit.
  			o = Symaddr(r.Sym) + r.Add - Symaddr(r.Sym.Lib.Textp[0])
  
  			// r->sym can be null when CALL $(constant) is transformed from absolute PC to relative PC call.
  		case objabi.R_GOTPCREL:
  			if ctxt.DynlinkingGo() && ctxt.HeadType == objabi.Hdarwin && r.Sym != nil && r.Sym.Type != sym.SCONST {
  				r.Done = false
  				r.Xadd = r.Add
  				r.Xadd -= int64(r.Siz) // relative to address after the relocated chunk
  				r.Xsym = r.Sym
  
  				o = r.Xadd
  				o += int64(r.Siz)
  				break
  			}
  			fallthrough
  		case objabi.R_CALL, objabi.R_PCREL:
  			if ctxt.LinkMode == LinkExternal && r.Sym != nil && r.Sym.Type != sym.SCONST && (r.Sym.Sect != s.Sect || r.Type == objabi.R_GOTPCREL) {
  				r.Done = false
  
  				// set up addend for eventual relocation via outer symbol.
  				rs := r.Sym
  
  				r.Xadd = r.Add
  				for rs.Outer != nil {
  					r.Xadd += Symaddr(rs) - Symaddr(rs.Outer)
  					rs = rs.Outer
  				}
  
  				r.Xadd -= int64(r.Siz) // relative to address after the relocated chunk
  				if rs.Type != sym.SHOSTOBJ && rs.Type != sym.SDYNIMPORT && rs.Sect == nil {
  					Errorf(s, "missing section for relocation target %s", rs.Name)
  				}
  				r.Xsym = rs
  
  				o = r.Xadd
  				if ctxt.IsELF {
  					if ctxt.Arch.Family == sys.AMD64 {
  						o = 0
  					}
  				} else if ctxt.HeadType == objabi.Hdarwin {
  					if r.Type == objabi.R_CALL {
  						if rs.Type != sym.SHOSTOBJ {
  							o += int64(uint64(Symaddr(rs)) - rs.Sect.Vaddr)
  						}
  						o -= int64(r.Off) // relative to section offset, not symbol
  					} else if ctxt.Arch.Family == sys.ARM {
  						// see ../arm/asm.go:/machoreloc1
  						o += Symaddr(rs) - int64(s.Value) - int64(r.Off)
  					} else {
  						o += int64(r.Siz)
  					}
  				} else if ctxt.HeadType == objabi.Hwindows && ctxt.Arch.Family == sys.AMD64 { // only amd64 needs PCREL
  					// PE/COFF's PC32 relocation uses the address after the relocated
  					// bytes as the base. Compensate by skewing the addend.
  					o += int64(r.Siz)
  				} else {
  					Errorf(s, "unhandled pcrel relocation to %s on %v", rs.Name, ctxt.HeadType)
  				}
  
  				break
  			}
  
  			o = 0
  			if r.Sym != nil {
  				o += Symaddr(r.Sym)
  			}
  
  			o += r.Add - (s.Value + int64(r.Off) + int64(r.Siz))
  		case objabi.R_SIZE:
  			o = r.Sym.Size + r.Add
  		}
  
  		if r.Variant != sym.RV_NONE {
  			o = Thearch.Archrelocvariant(ctxt, r, s, o)
  		}
  
  		if false {
  			nam := "<nil>"
  			if r.Sym != nil {
  				nam = r.Sym.Name
  			}
  			fmt.Printf("relocate %s %#x (%#x+%#x, size %d) => %s %#x +%#x [type %d (%s)/%d, %x]\n", s.Name, s.Value+int64(off), s.Value, r.Off, r.Siz, nam, Symaddr(r.Sym), r.Add, r.Type, sym.RelocName(ctxt.Arch, r.Type), r.Variant, o)
  		}
  		switch siz {
  		default:
  			Errorf(s, "bad reloc size %#x for %s", uint32(siz), r.Sym.Name)
  			fallthrough
  
  			// TODO(rsc): Remove.
  		case 1:
  			s.P[off] = byte(int8(o))
  		case 2:
  			if o != int64(int16(o)) {
  				Errorf(s, "relocation address for %s is too big: %#x", r.Sym.Name, o)
  			}
  			i16 := int16(o)
  			ctxt.Arch.ByteOrder.PutUint16(s.P[off:], uint16(i16))
  		case 4:
  			if r.Type == objabi.R_PCREL || r.Type == objabi.R_CALL {
  				if o != int64(int32(o)) {
  					Errorf(s, "pc-relative relocation address for %s is too big: %#x", r.Sym.Name, o)
  				}
  			} else {
  				if o != int64(int32(o)) && o != int64(uint32(o)) {
  					Errorf(s, "non-pc-relative relocation address for %s is too big: %#x", r.Sym.Name, uint64(o))
  				}
  			}
  
  			fl := int32(o)
  			ctxt.Arch.ByteOrder.PutUint32(s.P[off:], uint32(fl))
  		case 8:
  			ctxt.Arch.ByteOrder.PutUint64(s.P[off:], uint64(o))
  		}
  	}
  }
  
  func (ctxt *Link) reloc() {
  	if ctxt.Debugvlog != 0 {
  		ctxt.Logf("%5.2f reloc\n", Cputime())
  	}
  
  	for _, s := range ctxt.Textp {
  		relocsym(ctxt, s)
  	}
  	for _, s := range datap {
  		relocsym(ctxt, s)
  	}
  	for _, s := range dwarfp {
  		relocsym(ctxt, s)
  	}
  }
  
  func windynrelocsym(ctxt *Link, s *sym.Symbol) {
  	rel := ctxt.Syms.Lookup(".rel", 0)
  	if s == rel {
  		return
  	}
  	for ri := 0; ri < len(s.R); ri++ {
  		r := &s.R[ri]
  		targ := r.Sym
  		if targ == nil {
  			continue
  		}
  		if !targ.Attr.Reachable() {
  			if r.Type == objabi.R_WEAKADDROFF {
  				continue
  			}
  			Errorf(s, "dynamic relocation to unreachable symbol %s", targ.Name)
  		}
  		if r.Sym.Plt == -2 && r.Sym.Got != -2 { // make dynimport JMP table for PE object files.
  			targ.Plt = int32(rel.Size)
  			r.Sym = rel
  			r.Add = int64(targ.Plt)
  
  			// jmp *addr
  			if ctxt.Arch.Family == sys.I386 {
  				rel.AddUint8(0xff)
  				rel.AddUint8(0x25)
  				rel.AddAddr(ctxt.Arch, targ)
  				rel.AddUint8(0x90)
  				rel.AddUint8(0x90)
  			} else {
  				rel.AddUint8(0xff)
  				rel.AddUint8(0x24)
  				rel.AddUint8(0x25)
  				rel.AddAddrPlus4(targ, 0)
  				rel.AddUint8(0x90)
  			}
  		} else if r.Sym.Plt >= 0 {
  			r.Sym = rel
  			r.Add = int64(targ.Plt)
  		}
  	}
  }
  
  func dynrelocsym(ctxt *Link, s *sym.Symbol) {
  	if ctxt.HeadType == objabi.Hwindows {
  		if ctxt.LinkMode == LinkInternal {
  			windynrelocsym(ctxt, s)
  		}
  		return
  	}
  
  	for ri := 0; ri < len(s.R); ri++ {
  		r := &s.R[ri]
  		if ctxt.BuildMode == BuildModePIE && ctxt.LinkMode == LinkInternal {
  			// It's expected that some relocations will be done
  			// later by relocsym (R_TLS_LE, R_ADDROFF), so
  			// don't worry if Adddynrel returns false.
  			Thearch.Adddynrel(ctxt, s, r)
  			continue
  		}
  		if r.Sym != nil && r.Sym.Type == sym.SDYNIMPORT || r.Type >= 256 {
  			if r.Sym != nil && !r.Sym.Attr.Reachable() {
  				Errorf(s, "dynamic relocation to unreachable symbol %s", r.Sym.Name)
  			}
  			if !Thearch.Adddynrel(ctxt, s, r) {
  				Errorf(s, "unsupported dynamic relocation for symbol %s (type=%d (%s) stype=%d (%s))", r.Sym.Name, r.Type, sym.RelocName(ctxt.Arch, r.Type), r.Sym.Type, r.Sym.Type)
  			}
  		}
  	}
  }
  
  func dynreloc(ctxt *Link, data *[sym.SXREF][]*sym.Symbol) {
  	// -d suppresses dynamic loader format, so we may as well not
  	// compute these sections or mark their symbols as reachable.
  	if *FlagD && ctxt.HeadType != objabi.Hwindows {
  		return
  	}
  	if ctxt.Debugvlog != 0 {
  		ctxt.Logf("%5.2f dynreloc\n", Cputime())
  	}
  
  	for _, s := range ctxt.Textp {
  		dynrelocsym(ctxt, s)
  	}
  	for _, syms := range data {
  		for _, s := range syms {
  			dynrelocsym(ctxt, s)
  		}
  	}
  	if ctxt.IsELF {
  		elfdynhash(ctxt)
  	}
  }
  
  func Codeblk(ctxt *Link, addr int64, size int64) {
  	CodeblkPad(ctxt, addr, size, zeros[:])
  }
  func CodeblkPad(ctxt *Link, addr int64, size int64, pad []byte) {
  	if *flagA {
  		ctxt.Logf("codeblk [%#x,%#x) at offset %#x\n", addr, addr+size, ctxt.Out.Offset())
  	}
  
  	blk(ctxt, ctxt.Textp, addr, size, pad)
  
  	/* again for printing */
  	if !*flagA {
  		return
  	}
  
  	syms := ctxt.Textp
  	for i, s := range syms {
  		if !s.Attr.Reachable() {
  			continue
  		}
  		if s.Value >= addr {
  			syms = syms[i:]
  			break
  		}
  	}
  
  	eaddr := addr + size
  	var q []byte
  	for _, s := range syms {
  		if !s.Attr.Reachable() {
  			continue
  		}
  		if s.Value >= eaddr {
  			break
  		}
  
  		if addr < s.Value {
  			ctxt.Logf("%-20s %.8x|", "_", uint64(addr))
  			for ; addr < s.Value; addr++ {
  				ctxt.Logf(" %.2x", 0)
  			}
  			ctxt.Logf("\n")
  		}
  
  		ctxt.Logf("%.6x\t%-20s\n", uint64(addr), s.Name)
  		q = s.P
  
  		for len(q) >= 16 {
  			ctxt.Logf("%.6x\t% x\n", uint64(addr), q[:16])
  			addr += 16
  			q = q[16:]
  		}
  
  		if len(q) > 0 {
  			ctxt.Logf("%.6x\t% x\n", uint64(addr), q)
  			addr += int64(len(q))
  		}
  	}
  
  	if addr < eaddr {
  		ctxt.Logf("%-20s %.8x|", "_", uint64(addr))
  		for ; addr < eaddr; addr++ {
  			ctxt.Logf(" %.2x", 0)
  		}
  	}
  }
  
  func blk(ctxt *Link, syms []*sym.Symbol, addr, size int64, pad []byte) {
  	for i, s := range syms {
  		if !s.Attr.SubSymbol() && s.Value >= addr {
  			syms = syms[i:]
  			break
  		}
  	}
  
  	eaddr := addr + size
  	for _, s := range syms {
  		if s.Attr.SubSymbol() {
  			continue
  		}
  		if s.Value >= eaddr {
  			break
  		}
  		if s.Value < addr {
  			Errorf(s, "phase error: addr=%#x but sym=%#x type=%d", addr, s.Value, s.Type)
  			errorexit()
  		}
  		if addr < s.Value {
  			ctxt.Out.WriteStringPad("", int(s.Value-addr), pad)
  			addr = s.Value
  		}
  		ctxt.Out.Write(s.P)
  		addr += int64(len(s.P))
  		if addr < s.Value+s.Size {
  			ctxt.Out.WriteStringPad("", int(s.Value+s.Size-addr), pad)
  			addr = s.Value + s.Size
  		}
  		if addr != s.Value+s.Size {
  			Errorf(s, "phase error: addr=%#x value+size=%#x", addr, s.Value+s.Size)
  			errorexit()
  		}
  		if s.Value+s.Size >= eaddr {
  			break
  		}
  	}
  
  	if addr < eaddr {
  		ctxt.Out.WriteStringPad("", int(eaddr-addr), pad)
  	}
  	ctxt.Out.Flush()
  }
  
  func Datblk(ctxt *Link, addr int64, size int64) {
  	if *flagA {
  		ctxt.Logf("datblk [%#x,%#x) at offset %#x\n", addr, addr+size, ctxt.Out.Offset())
  	}
  
  	blk(ctxt, datap, addr, size, zeros[:])
  
  	/* again for printing */
  	if !*flagA {
  		return
  	}
  
  	syms := datap
  	for i, sym := range syms {
  		if sym.Value >= addr {
  			syms = syms[i:]
  			break
  		}
  	}
  
  	eaddr := addr + size
  	for _, sym := range syms {
  		if sym.Value >= eaddr {
  			break
  		}
  		if addr < sym.Value {
  			ctxt.Logf("\t%.8x| 00 ...\n", uint64(addr))
  			addr = sym.Value
  		}
  
  		ctxt.Logf("%s\n\t%.8x|", sym.Name, uint64(addr))
  		for i, b := range sym.P {
  			if i > 0 && i%16 == 0 {
  				ctxt.Logf("\n\t%.8x|", uint64(addr)+uint64(i))
  			}
  			ctxt.Logf(" %.2x", b)
  		}
  
  		addr += int64(len(sym.P))
  		for ; addr < sym.Value+sym.Size; addr++ {
  			ctxt.Logf(" %.2x", 0)
  		}
  		ctxt.Logf("\n")
  
  		if ctxt.LinkMode != LinkExternal {
  			continue
  		}
  		for _, r := range sym.R {
  			rsname := ""
  			if r.Sym != nil {
  				rsname = r.Sym.Name
  			}
  			typ := "?"
  			switch r.Type {
  			case objabi.R_ADDR:
  				typ = "addr"
  			case objabi.R_PCREL:
  				typ = "pcrel"
  			case objabi.R_CALL:
  				typ = "call"
  			}
  			ctxt.Logf("\treloc %.8x/%d %s %s+%#x [%#x]\n", uint(sym.Value+int64(r.Off)), r.Siz, typ, rsname, r.Add, r.Sym.Value+r.Add)
  		}
  	}
  
  	if addr < eaddr {
  		ctxt.Logf("\t%.8x| 00 ...\n", uint(addr))
  	}
  	ctxt.Logf("\t%.8x|\n", uint(eaddr))
  }
  
  func Dwarfblk(ctxt *Link, addr int64, size int64) {
  	if *flagA {
  		ctxt.Logf("dwarfblk [%#x,%#x) at offset %#x\n", addr, addr+size, ctxt.Out.Offset())
  	}
  
  	blk(ctxt, dwarfp, addr, size, zeros[:])
  }
  
  var zeros [512]byte
  
  var (
  	strdata  = make(map[string]string)
  	strnames []string
  )
  
  func addstrdata1(ctxt *Link, arg string) {
  	eq := strings.Index(arg, "=")
  	dot := strings.LastIndex(arg[:eq+1], ".")
  	if eq < 0 || dot < 0 {
  		Exitf("-X flag requires argument of the form importpath.name=value")
  	}
  	pkg := arg[:dot]
  	if ctxt.BuildMode == BuildModePlugin && pkg == "main" {
  		pkg = *flagPluginPath
  	}
  	pkg = objabi.PathToPrefix(pkg)
  	name := pkg + arg[dot:eq]
  	value := arg[eq+1:]
  	if _, ok := strdata[name]; !ok {
  		strnames = append(strnames, name)
  	}
  	strdata[name] = value
  }
  
  func addstrdata(ctxt *Link, name, value string) {
  	s := ctxt.Syms.ROLookup(name, 0)
  	if s == nil || s.Gotype == nil {
  		// Not defined in the loaded packages.
  		return
  	}
  	if s.Gotype.Name != "type.string" {
  		Errorf(s, "cannot set with -X: not a var of type string (%s)", s.Gotype.Name)
  		return
  	}
  	if s.Type == sym.SBSS {
  		s.Type = sym.SDATA
  	}
  
  	p := fmt.Sprintf("%s.str", s.Name)
  	sp := ctxt.Syms.Lookup(p, 0)
  
  	Addstring(sp, value)
  	sp.Type = sym.SRODATA
  
  	s.Size = 0
  	s.P = s.P[:0]
  	s.R = s.R[:0]
  	reachable := s.Attr.Reachable()
  	s.AddAddr(ctxt.Arch, sp)
  	s.AddUint(ctxt.Arch, uint64(len(value)))
  
  	// addstring, addaddr, etc., mark the symbols as reachable.
  	// In this case that is not necessarily true, so stick to what
  	// we know before entering this function.
  	s.Attr.Set(sym.AttrReachable, reachable)
  
  	sp.Attr.Set(sym.AttrReachable, reachable)
  }
  
  func (ctxt *Link) dostrdata() {
  	for _, name := range strnames {
  		addstrdata(ctxt, name, strdata[name])
  	}
  }
  
  func Addstring(s *sym.Symbol, str string) int64 {
  	if s.Type == 0 {
  		s.Type = sym.SNOPTRDATA
  	}
  	s.Attr |= sym.AttrReachable
  	r := s.Size
  	if s.Name == ".shstrtab" {
  		elfsetstring(s, str, int(r))
  	}
  	s.P = append(s.P, str...)
  	s.P = append(s.P, 0)
  	s.Size = int64(len(s.P))
  	return r
  }
  
  // addgostring adds str, as a Go string value, to s. symname is the name of the
  // symbol used to define the string data and must be unique per linked object.
  func addgostring(ctxt *Link, s *sym.Symbol, symname, str string) {
  	sdata := ctxt.Syms.Lookup(symname, 0)
  	if sdata.Type != sym.Sxxx {
  		Errorf(s, "duplicate symname in addgostring: %s", symname)
  	}
  	sdata.Attr |= sym.AttrReachable
  	sdata.Attr |= sym.AttrLocal
  	sdata.Type = sym.SRODATA
  	sdata.Size = int64(len(str))
  	sdata.P = []byte(str)
  	s.AddAddr(ctxt.Arch, sdata)
  	s.AddUint(ctxt.Arch, uint64(len(str)))
  }
  
  func addinitarrdata(ctxt *Link, s *sym.Symbol) {
  	p := s.Name + ".ptr"
  	sp := ctxt.Syms.Lookup(p, 0)
  	sp.Type = sym.SINITARR
  	sp.Size = 0
  	sp.Attr |= sym.AttrDuplicateOK
  	sp.AddAddr(ctxt.Arch, s)
  }
  
  func dosymtype(ctxt *Link) {
  	switch ctxt.BuildMode {
  	case BuildModeCArchive, BuildModeCShared:
  		for _, s := range ctxt.Syms.Allsym {
  			// Create a new entry in the .init_array section that points to the
  			// library initializer function.
  			if s.Name == *flagEntrySymbol {
  				addinitarrdata(ctxt, s)
  			}
  		}
  	}
  }
  
  // symalign returns the required alignment for the given symbol s.
  func symalign(s *sym.Symbol) int32 {
  	min := int32(Thearch.Minalign)
  	if s.Align >= min {
  		return s.Align
  	} else if s.Align != 0 {
  		return min
  	}
  	if strings.HasPrefix(s.Name, "go.string.") || strings.HasPrefix(s.Name, "type..namedata.") {
  		// String data is just bytes.
  		// If we align it, we waste a lot of space to padding.
  		return min
  	}
  	align := int32(Thearch.Maxalign)
  	for int64(align) > s.Size && align > min {
  		align >>= 1
  	}
  	return align
  }
  
  func aligndatsize(datsize int64, s *sym.Symbol) int64 {
  	return Rnd(datsize, int64(symalign(s)))
  }
  
  const debugGCProg = false
  
  type GCProg struct {
  	ctxt *Link
  	sym  *sym.Symbol
  	w    gcprog.Writer
  }
  
  func (p *GCProg) Init(ctxt *Link, name string) {
  	p.ctxt = ctxt
  	p.sym = ctxt.Syms.Lookup(name, 0)
  	p.w.Init(p.writeByte(ctxt))
  	if debugGCProg {
  		fmt.Fprintf(os.Stderr, "ld: start GCProg %s\n", name)
  		p.w.Debug(os.Stderr)
  	}
  }
  
  func (p *GCProg) writeByte(ctxt *Link) func(x byte) {
  	return func(x byte) {
  		p.sym.AddUint8(x)
  	}
  }
  
  func (p *GCProg) End(size int64) {
  	p.w.ZeroUntil(size / int64(p.ctxt.Arch.PtrSize))
  	p.w.End()
  	if debugGCProg {
  		fmt.Fprintf(os.Stderr, "ld: end GCProg\n")
  	}
  }
  
  func (p *GCProg) AddSym(s *sym.Symbol) {
  	typ := s.Gotype
  	// Things without pointers should be in sym.SNOPTRDATA or sym.SNOPTRBSS;
  	// everything we see should have pointers and should therefore have a type.
  	if typ == nil {
  		switch s.Name {
  		case "runtime.data", "runtime.edata", "runtime.bss", "runtime.ebss":
  			// Ignore special symbols that are sometimes laid out
  			// as real symbols. See comment about dyld on darwin in
  			// the address function.
  			return
  		}
  		Errorf(s, "missing Go type information for global symbol: size %d", s.Size)
  		return
  	}
  
  	ptrsize := int64(p.ctxt.Arch.PtrSize)
  	nptr := decodetypePtrdata(p.ctxt.Arch, typ) / ptrsize
  
  	if debugGCProg {
  		fmt.Fprintf(os.Stderr, "gcprog sym: %s at %d (ptr=%d+%d)\n", s.Name, s.Value, s.Value/ptrsize, nptr)
  	}
  
  	if decodetypeUsegcprog(p.ctxt.Arch, typ) == 0 {
  		// Copy pointers from mask into program.
  		mask := decodetypeGcmask(p.ctxt, typ)
  		for i := int64(0); i < nptr; i++ {
  			if (mask[i/8]>>uint(i%8))&1 != 0 {
  				p.w.Ptr(s.Value/ptrsize + i)
  			}
  		}
  		return
  	}
  
  	// Copy program.
  	prog := decodetypeGcprog(p.ctxt, typ)
  	p.w.ZeroUntil(s.Value / ptrsize)
  	p.w.Append(prog[4:], nptr)
  }
  
  // dataSortKey is used to sort a slice of data symbol *sym.Symbol pointers.
  // The sort keys are kept inline to improve cache behavior while sorting.
  type dataSortKey struct {
  	size int64
  	name string
  	sym  *sym.Symbol
  }
  
  type bySizeAndName []dataSortKey
  
  func (d bySizeAndName) Len() int      { return len(d) }
  func (d bySizeAndName) Swap(i, j int) { d[i], d[j] = d[j], d[i] }
  func (d bySizeAndName) Less(i, j int) bool {
  	s1, s2 := d[i], d[j]
  	if s1.size != s2.size {
  		return s1.size < s2.size
  	}
  	return s1.name < s2.name
  }
  
  // cutoff is the maximum data section size permitted by the linker
  // (see issue #9862).
  const cutoff = 2e9 // 2 GB (or so; looks better in errors than 2^31)
  
  func checkdatsize(ctxt *Link, datsize int64, symn sym.SymKind) {
  	if datsize > cutoff {
  		Errorf(nil, "too much data in section %v (over %v bytes)", symn, cutoff)
  	}
  }
  
  // datap is a collection of reachable data symbols in address order.
  // Generated by dodata.
  var datap []*sym.Symbol
  
  func (ctxt *Link) dodata() {
  	if ctxt.Debugvlog != 0 {
  		ctxt.Logf("%5.2f dodata\n", Cputime())
  	}
  
  	if ctxt.DynlinkingGo() && ctxt.HeadType == objabi.Hdarwin {
  		// The values in moduledata are filled out by relocations
  		// pointing to the addresses of these special symbols.
  		// Typically these symbols have no size and are not laid
  		// out with their matching section.
  		//
  		// However on darwin, dyld will find the special symbol
  		// in the first loaded module, even though it is local.
  		//
  		// (An hypothesis, formed without looking in the dyld sources:
  		// these special symbols have no size, so their address
  		// matches a real symbol. The dynamic linker assumes we
  		// want the normal symbol with the same address and finds
  		// it in the other module.)
  		//
  		// To work around this we lay out the symbls whose
  		// addresses are vital for multi-module programs to work
  		// as normal symbols, and give them a little size.
  		bss := ctxt.Syms.Lookup("runtime.bss", 0)
  		bss.Size = 8
  		bss.Attr.Set(sym.AttrSpecial, false)
  
  		ctxt.Syms.Lookup("runtime.ebss", 0).Attr.Set(sym.AttrSpecial, false)
  
  		data := ctxt.Syms.Lookup("runtime.data", 0)
  		data.Size = 8
  		data.Attr.Set(sym.AttrSpecial, false)
  
  		ctxt.Syms.Lookup("runtime.edata", 0).Attr.Set(sym.AttrSpecial, false)
  
  		types := ctxt.Syms.Lookup("runtime.types", 0)
  		types.Type = sym.STYPE
  		types.Size = 8
  		types.Attr.Set(sym.AttrSpecial, false)
  
  		etypes := ctxt.Syms.Lookup("runtime.etypes", 0)
  		etypes.Type = sym.SFUNCTAB
  		etypes.Attr.Set(sym.AttrSpecial, false)
  	}
  
  	// Collect data symbols by type into data.
  	var data [sym.SXREF][]*sym.Symbol
  	for _, s := range ctxt.Syms.Allsym {
  		if !s.Attr.Reachable() || s.Attr.Special() || s.Attr.SubSymbol() {
  			continue
  		}
  		if s.Type <= sym.STEXT || s.Type >= sym.SXREF {
  			continue
  		}
  		data[s.Type] = append(data[s.Type], s)
  	}
  
  	// Now that we have the data symbols, but before we start
  	// to assign addresses, record all the necessary
  	// dynamic relocations. These will grow the relocation
  	// symbol, which is itself data.
  	//
  	// On darwin, we need the symbol table numbers for dynreloc.
  	if ctxt.HeadType == objabi.Hdarwin {
  		machosymorder(ctxt)
  	}
  	dynreloc(ctxt, &data)
  
  	if ctxt.UseRelro() {
  		// "read only" data with relocations needs to go in its own section
  		// when building a shared library. We do this by boosting objects of
  		// type SXXX with relocations to type SXXXRELRO.
  		for _, symnro := range sym.ReadOnly {
  			symnrelro := sym.RelROMap[symnro]
  
  			ro := []*sym.Symbol{}
  			relro := data[symnrelro]
  
  			for _, s := range data[symnro] {
  				isRelro := len(s.R) > 0
  				switch s.Type {
  				case sym.STYPE, sym.STYPERELRO, sym.SGOFUNCRELRO:
  					// Symbols are not sorted yet, so it is possible
  					// that an Outer symbol has been changed to a
  					// relro Type before it reaches here.
  					isRelro = true
  				}
  				if isRelro {
  					s.Type = symnrelro
  					if s.Outer != nil {
  						s.Outer.Type = s.Type
  					}
  					relro = append(relro, s)
  				} else {
  					ro = append(ro, s)
  				}
  			}
  
  			// Check that we haven't made two symbols with the same .Outer into
  			// different types (because references two symbols with non-nil Outer
  			// become references to the outer symbol + offset it's vital that the
  			// symbol and the outer end up in the same section).
  			for _, s := range relro {
  				if s.Outer != nil && s.Outer.Type != s.Type {
  					Errorf(s, "inconsistent types for symbol and its Outer %s (%v != %v)",
  						s.Outer.Name, s.Type, s.Outer.Type)
  				}
  			}
  
  			data[symnro] = ro
  			data[symnrelro] = relro
  		}
  	}
  
  	// Sort symbols.
  	var dataMaxAlign [sym.SXREF]int32
  	var wg sync.WaitGroup
  	for symn := range data {
  		symn := sym.SymKind(symn)
  		wg.Add(1)
  		go func() {
  			data[symn], dataMaxAlign[symn] = dodataSect(ctxt, symn, data[symn])
  			wg.Done()
  		}()
  	}
  	wg.Wait()
  
  	// Allocate sections.
  	// Data is processed before segtext, because we need
  	// to see all symbols in the .data and .bss sections in order
  	// to generate garbage collection information.
  	datsize := int64(0)
  
  	// Writable data sections that do not need any specialized handling.
  	writable := []sym.SymKind{
  		sym.SELFSECT,
  		sym.SMACHO,
  		sym.SMACHOGOT,
  		sym.SWINDOWS,
  	}
  	for _, symn := range writable {
  		for _, s := range data[symn] {
  			sect := addsection(ctxt.Arch, &Segdata, s.Name, 06)
  			sect.Align = symalign(s)
  			datsize = Rnd(datsize, int64(sect.Align))
  			sect.Vaddr = uint64(datsize)
  			s.Sect = sect
  			s.Type = sym.SDATA
  			s.Value = int64(uint64(datsize) - sect.Vaddr)
  			datsize += s.Size
  			sect.Length = uint64(datsize) - sect.Vaddr
  		}
  		checkdatsize(ctxt, datsize, symn)
  	}
  
  	// .got (and .toc on ppc64)
  	if len(data[sym.SELFGOT]) > 0 {
  		sect := addsection(ctxt.Arch, &Segdata, ".got", 06)
  		sect.Align = dataMaxAlign[sym.SELFGOT]
  		datsize = Rnd(datsize, int64(sect.Align))
  		sect.Vaddr = uint64(datsize)
  		var toc *sym.Symbol
  		for _, s := range data[sym.SELFGOT] {
  			datsize = aligndatsize(datsize, s)
  			s.Sect = sect
  			s.Type = sym.SDATA
  			s.Value = int64(uint64(datsize) - sect.Vaddr)
  
  			// Resolve .TOC. symbol for this object file (ppc64)
  			toc = ctxt.Syms.ROLookup(".TOC.", int(s.Version))
  			if toc != nil {
  				toc.Sect = sect
  				toc.Outer = s
  				toc.Sub = s.Sub
  				s.Sub = toc
  
  				toc.Value = 0x8000
  			}
  
  			datsize += s.Size
  		}
  		checkdatsize(ctxt, datsize, sym.SELFGOT)
  		sect.Length = uint64(datsize) - sect.Vaddr
  	}
  
  	/* pointer-free data */
  	sect := addsection(ctxt.Arch, &Segdata, ".noptrdata", 06)
  	sect.Align = dataMaxAlign[sym.SNOPTRDATA]
  	datsize = Rnd(datsize, int64(sect.Align))
  	sect.Vaddr = uint64(datsize)
  	ctxt.Syms.Lookup("runtime.noptrdata", 0).Sect = sect
  	ctxt.Syms.Lookup("runtime.enoptrdata", 0).Sect = sect
  	for _, s := range data[sym.SNOPTRDATA] {
  		datsize = aligndatsize(datsize, s)
  		s.Sect = sect
  		s.Type = sym.SDATA
  		s.Value = int64(uint64(datsize) - sect.Vaddr)
  		datsize += s.Size
  	}
  	checkdatsize(ctxt, datsize, sym.SNOPTRDATA)
  	sect.Length = uint64(datsize) - sect.Vaddr
  
  	hasinitarr := ctxt.linkShared
  
  	/* shared library initializer */
  	switch ctxt.BuildMode {
  	case BuildModeCArchive, BuildModeCShared, BuildModeShared, BuildModePlugin:
  		hasinitarr = true
  	}
  	if hasinitarr {
  		sect := addsection(ctxt.Arch, &Segdata, ".init_array", 06)
  		sect.Align = dataMaxAlign[sym.SINITARR]
  		datsize = Rnd(datsize, int64(sect.Align))
  		sect.Vaddr = uint64(datsize)
  		for _, s := range data[sym.SINITARR] {
  			datsize = aligndatsize(datsize, s)
  			s.Sect = sect
  			s.Value = int64(uint64(datsize) - sect.Vaddr)
  			datsize += s.Size
  		}
  		sect.Length = uint64(datsize) - sect.Vaddr
  		checkdatsize(ctxt, datsize, sym.SINITARR)
  	}
  
  	/* data */
  	sect = addsection(ctxt.Arch, &Segdata, ".data", 06)
  	sect.Align = dataMaxAlign[sym.SDATA]
  	datsize = Rnd(datsize, int64(sect.Align))
  	sect.Vaddr = uint64(datsize)
  	ctxt.Syms.Lookup("runtime.data", 0).Sect = sect
  	ctxt.Syms.Lookup("runtime.edata", 0).Sect = sect
  	var gc GCProg
  	gc.Init(ctxt, "runtime.gcdata")
  	for _, s := range data[sym.SDATA] {
  		s.Sect = sect
  		s.Type = sym.SDATA
  		datsize = aligndatsize(datsize, s)
  		s.Value = int64(uint64(datsize) - sect.Vaddr)
  		gc.AddSym(s)
  		datsize += s.Size
  	}
  	checkdatsize(ctxt, datsize, sym.SDATA)
  	sect.Length = uint64(datsize) - sect.Vaddr
  	gc.End(int64(sect.Length))
  
  	/* bss */
  	sect = addsection(ctxt.Arch, &Segdata, ".bss", 06)
  	sect.Align = dataMaxAlign[sym.SBSS]
  	datsize = Rnd(datsize, int64(sect.Align))
  	sect.Vaddr = uint64(datsize)
  	ctxt.Syms.Lookup("runtime.bss", 0).Sect = sect
  	ctxt.Syms.Lookup("runtime.ebss", 0).Sect = sect
  	gc = GCProg{}
  	gc.Init(ctxt, "runtime.gcbss")
  	for _, s := range data[sym.SBSS] {
  		s.Sect = sect
  		datsize = aligndatsize(datsize, s)
  		s.Value = int64(uint64(datsize) - sect.Vaddr)
  		gc.AddSym(s)
  		datsize += s.Size
  	}
  	checkdatsize(ctxt, datsize, sym.SBSS)
  	sect.Length = uint64(datsize) - sect.Vaddr
  	gc.End(int64(sect.Length))
  
  	/* pointer-free bss */
  	sect = addsection(ctxt.Arch, &Segdata, ".noptrbss", 06)
  	sect.Align = dataMaxAlign[sym.SNOPTRBSS]
  	datsize = Rnd(datsize, int64(sect.Align))
  	sect.Vaddr = uint64(datsize)
  	ctxt.Syms.Lookup("runtime.noptrbss", 0).Sect = sect
  	ctxt.Syms.Lookup("runtime.enoptrbss", 0).Sect = sect
  	for _, s := range data[sym.SNOPTRBSS] {
  		datsize = aligndatsize(datsize, s)
  		s.Sect = sect
  		s.Value = int64(uint64(datsize) - sect.Vaddr)
  		datsize += s.Size
  	}
  
  	sect.Length = uint64(datsize) - sect.Vaddr
  	ctxt.Syms.Lookup("runtime.end", 0).Sect = sect
  	checkdatsize(ctxt, datsize, sym.SNOPTRBSS)
  
  	if len(data[sym.STLSBSS]) > 0 {
  		var sect *sym.Section
  		if ctxt.IsELF && (ctxt.LinkMode == LinkExternal || !*FlagD) {
  			sect = addsection(ctxt.Arch, &Segdata, ".tbss", 06)
  			sect.Align = int32(ctxt.Arch.PtrSize)
  			sect.Vaddr = 0
  		}
  		datsize = 0
  
  		for _, s := range data[sym.STLSBSS] {
  			datsize = aligndatsize(datsize, s)
  			s.Sect = sect
  			s.Value = datsize
  			datsize += s.Size
  		}
  		checkdatsize(ctxt, datsize, sym.STLSBSS)
  
  		if sect != nil {
  			sect.Length = uint64(datsize)
  		}
  	}
  
  	/*
  	 * We finished data, begin read-only data.
  	 * Not all systems support a separate read-only non-executable data section.
  	 * ELF systems do.
  	 * OS X and Plan 9 do not.
  	 * Windows PE may, but if so we have not implemented it.
  	 * And if we're using external linking mode, the point is moot,
  	 * since it's not our decision; that code expects the sections in
  	 * segtext.
  	 */
  	var segro *sym.Segment
  	if ctxt.IsELF && ctxt.LinkMode == LinkInternal {
  		segro = &Segrodata
  	} else {
  		segro = &Segtext
  	}
  
  	datsize = 0
  
  	/* read-only executable ELF, Mach-O sections */
  	if len(data[sym.STEXT]) != 0 {
  		Errorf(nil, "dodata found an sym.STEXT symbol: %s", data[sym.STEXT][0].Name)
  	}
  	for _, s := range data[sym.SELFRXSECT] {
  		sect := addsection(ctxt.Arch, &Segtext, s.Name, 04)
  		sect.Align = symalign(s)
  		datsize = Rnd(datsize, int64(sect.Align))
  		sect.Vaddr = uint64(datsize)
  		s.Sect = sect
  		s.Type = sym.SRODATA
  		s.Value = int64(uint64(datsize) - sect.Vaddr)
  		datsize += s.Size
  		sect.Length = uint64(datsize) - sect.Vaddr
  		checkdatsize(ctxt, datsize, sym.SELFRXSECT)
  	}
  
  	/* read-only data */
  	sect = addsection(ctxt.Arch, segro, ".rodata", 04)
  
  	sect.Vaddr = 0
  	ctxt.Syms.Lookup("runtime.rodata", 0).Sect = sect
  	ctxt.Syms.Lookup("runtime.erodata", 0).Sect = sect
  	if !ctxt.UseRelro() {
  		ctxt.Syms.Lookup("runtime.types", 0).Sect = sect
  		ctxt.Syms.Lookup("runtime.etypes", 0).Sect = sect
  	}
  	for _, symn := range sym.ReadOnly {
  		align := dataMaxAlign[symn]
  		if sect.Align < align {
  			sect.Align = align
  		}
  	}
  	datsize = Rnd(datsize, int64(sect.Align))
  	for _, symn := range sym.ReadOnly {
  		for _, s := range data[symn] {
  			datsize = aligndatsize(datsize, s)
  			s.Sect = sect
  			s.Type = sym.SRODATA
  			s.Value = int64(uint64(datsize) - sect.Vaddr)
  			datsize += s.Size
  		}
  		checkdatsize(ctxt, datsize, symn)
  	}
  	sect.Length = uint64(datsize) - sect.Vaddr
  
  	/* read-only ELF, Mach-O sections */
  	for _, s := range data[sym.SELFROSECT] {
  		sect = addsection(ctxt.Arch, segro, s.Name, 04)
  		sect.Align = symalign(s)
  		datsize = Rnd(datsize, int64(sect.Align))
  		sect.Vaddr = uint64(datsize)
  		s.Sect = sect
  		s.Type = sym.SRODATA
  		s.Value = int64(uint64(datsize) - sect.Vaddr)
  		datsize += s.Size
  		sect.Length = uint64(datsize) - sect.Vaddr
  	}
  	checkdatsize(ctxt, datsize, sym.SELFROSECT)
  
  	for _, s := range data[sym.SMACHOPLT] {
  		sect = addsection(ctxt.Arch, segro, s.Name, 04)
  		sect.Align = symalign(s)
  		datsize = Rnd(datsize, int64(sect.Align))
  		sect.Vaddr = uint64(datsize)
  		s.Sect = sect
  		s.Type = sym.SRODATA
  		s.Value = int64(uint64(datsize) - sect.Vaddr)
  		datsize += s.Size
  		sect.Length = uint64(datsize) - sect.Vaddr
  	}
  	checkdatsize(ctxt, datsize, sym.SMACHOPLT)
  
  	// There is some data that are conceptually read-only but are written to by
  	// relocations. On GNU systems, we can arrange for the dynamic linker to
  	// mprotect sections after relocations are applied by giving them write
  	// permissions in the object file and calling them ".data.rel.ro.FOO". We
  	// divide the .rodata section between actual .rodata and .data.rel.ro.rodata,
  	// but for the other sections that this applies to, we just write a read-only
  	// .FOO section or a read-write .data.rel.ro.FOO section depending on the
  	// situation.
  	// TODO(mwhudson): It would make sense to do this more widely, but it makes
  	// the system linker segfault on darwin.
  	addrelrosection := func(suffix string) *sym.Section {
  		return addsection(ctxt.Arch, segro, suffix, 04)
  	}
  
  	if ctxt.UseRelro() {
  		addrelrosection = func(suffix string) *sym.Section {
  			seg := &Segrelrodata
  			if ctxt.LinkMode == LinkExternal {
  				// Using a separate segment with an external
  				// linker results in some programs moving
  				// their data sections unexpectedly, which
  				// corrupts the moduledata. So we use the
  				// rodata segment and let the external linker
  				// sort out a rel.ro segment.
  				seg = &Segrodata
  			}
  			return addsection(ctxt.Arch, seg, ".data.rel.ro"+suffix, 06)
  		}
  		/* data only written by relocations */
  		sect = addrelrosection("")
  
  		sect.Vaddr = 0
  		ctxt.Syms.Lookup("runtime.types", 0).Sect = sect
  		ctxt.Syms.Lookup("runtime.etypes", 0).Sect = sect
  		for _, symnro := range sym.ReadOnly {
  			symn := sym.RelROMap[symnro]
  			align := dataMaxAlign[symn]
  			if sect.Align < align {
  				sect.Align = align
  			}
  		}
  		datsize = Rnd(datsize, int64(sect.Align))
  		for _, symnro := range sym.ReadOnly {
  			symn := sym.RelROMap[symnro]
  			for _, s := range data[symn] {
  				datsize = aligndatsize(datsize, s)
  				if s.Outer != nil && s.Outer.Sect != nil && s.Outer.Sect != sect {
  					Errorf(s, "s.Outer (%s) in different section from s, %s != %s", s.Outer.Name, s.Outer.Sect.Name, sect.Name)
  				}
  				s.Sect = sect
  				s.Type = sym.SRODATA
  				s.Value = int64(uint64(datsize) - sect.Vaddr)
  				datsize += s.Size
  			}
  			checkdatsize(ctxt, datsize, symn)
  		}
  
  		sect.Length = uint64(datsize) - sect.Vaddr
  	}
  
  	/* typelink */
  	sect = addrelrosection(".typelink")
  	sect.Align = dataMaxAlign[sym.STYPELINK]
  	datsize = Rnd(datsize, int64(sect.Align))
  	sect.Vaddr = uint64(datsize)
  	typelink := ctxt.Syms.Lookup("runtime.typelink", 0)
  	typelink.Sect = sect
  	typelink.Type = sym.SRODATA
  	datsize += typelink.Size
  	checkdatsize(ctxt, datsize, sym.STYPELINK)
  	sect.Length = uint64(datsize) - sect.Vaddr
  
  	/* itablink */
  	sect = addrelrosection(".itablink")
  	sect.Align = dataMaxAlign[sym.SITABLINK]
  	datsize = Rnd(datsize, int64(sect.Align))
  	sect.Vaddr = uint64(datsize)
  	ctxt.Syms.Lookup("runtime.itablink", 0).Sect = sect
  	ctxt.Syms.Lookup("runtime.eitablink", 0).Sect = sect
  	for _, s := range data[sym.SITABLINK] {
  		datsize = aligndatsize(datsize, s)
  		s.Sect = sect
  		s.Type = sym.SRODATA
  		s.Value = int64(uint64(datsize) - sect.Vaddr)
  		datsize += s.Size
  	}
  	checkdatsize(ctxt, datsize, sym.SITABLINK)
  	sect.Length = uint64(datsize) - sect.Vaddr
  
  	/* gosymtab */
  	sect = addrelrosection(".gosymtab")
  	sect.Align = dataMaxAlign[sym.SSYMTAB]
  	datsize = Rnd(datsize, int64(sect.Align))
  	sect.Vaddr = uint64(datsize)
  	ctxt.Syms.Lookup("runtime.symtab", 0).Sect = sect
  	ctxt.Syms.Lookup("runtime.esymtab", 0).Sect = sect
  	for _, s := range data[sym.SSYMTAB] {
  		datsize = aligndatsize(datsize, s)
  		s.Sect = sect
  		s.Type = sym.SRODATA
  		s.Value = int64(uint64(datsize) - sect.Vaddr)
  		datsize += s.Size
  	}
  	checkdatsize(ctxt, datsize, sym.SSYMTAB)
  	sect.Length = uint64(datsize) - sect.Vaddr
  
  	/* gopclntab */
  	sect = addrelrosection(".gopclntab")
  	sect.Align = dataMaxAlign[sym.SPCLNTAB]
  	datsize = Rnd(datsize, int64(sect.Align))
  	sect.Vaddr = uint64(datsize)
  	ctxt.Syms.Lookup("runtime.pclntab", 0).Sect = sect
  	ctxt.Syms.Lookup("runtime.epclntab", 0).Sect = sect
  	for _, s := range data[sym.SPCLNTAB] {
  		datsize = aligndatsize(datsize, s)
  		s.Sect = sect
  		s.Type = sym.SRODATA
  		s.Value = int64(uint64(datsize) - sect.Vaddr)
  		datsize += s.Size
  	}
  	checkdatsize(ctxt, datsize, sym.SRODATA)
  	sect.Length = uint64(datsize) - sect.Vaddr
  
  	// 6g uses 4-byte relocation offsets, so the entire segment must fit in 32 bits.
  	if datsize != int64(uint32(datsize)) {
  		Errorf(nil, "read-only data segment too large: %d", datsize)
  	}
  
  	for symn := sym.SELFRXSECT; symn < sym.SXREF; symn++ {
  		datap = append(datap, data[symn]...)
  	}
  
  	dwarfgeneratedebugsyms(ctxt)
  
  	var i int
  	for ; i < len(dwarfp); i++ {
  		s := dwarfp[i]
  		if s.Type != sym.SDWARFSECT {
  			break
  		}
  
  		sect = addsection(ctxt.Arch, &Segdwarf, s.Name, 04)
  		sect.Align = 1
  		datsize = Rnd(datsize, int64(sect.Align))
  		sect.Vaddr = uint64(datsize)
  		s.Sect = sect
  		s.Type = sym.SRODATA
  		s.Value = int64(uint64(datsize) - sect.Vaddr)
  		datsize += s.Size
  		sect.Length = uint64(datsize) - sect.Vaddr
  	}
  	checkdatsize(ctxt, datsize, sym.SDWARFSECT)
  
  	for i < len(dwarfp) {
  		curType := dwarfp[i].Type
  		var sect *sym.Section
  		switch curType {
  		case sym.SDWARFINFO:
  			sect = addsection(ctxt.Arch, &Segdwarf, ".debug_info", 04)
  		case sym.SDWARFRANGE:
  			sect = addsection(ctxt.Arch, &Segdwarf, ".debug_ranges", 04)
  		case sym.SDWARFLOC:
  			sect = addsection(ctxt.Arch, &Segdwarf, ".debug_loc", 04)
  		default:
  			Errorf(dwarfp[i], "unknown DWARF section %v", curType)
  		}
  
  		sect.Align = 1
  		datsize = Rnd(datsize, int64(sect.Align))
  		sect.Vaddr = uint64(datsize)
  		for ; i < len(dwarfp); i++ {
  			s := dwarfp[i]
  			if s.Type != curType {
  				break
  			}
  			s.Sect = sect
  			s.Type = sym.SRODATA
  			s.Value = int64(uint64(datsize) - sect.Vaddr)
  			s.Attr |= sym.AttrLocal
  			datsize += s.Size
  		}
  		sect.Length = uint64(datsize) - sect.Vaddr
  		checkdatsize(ctxt, datsize, curType)
  	}
  
  	/* number the sections */
  	n := int32(1)
  
  	for _, sect := range Segtext.Sections {
  		sect.Extnum = int16(n)
  		n++
  	}
  	for _, sect := range Segrodata.Sections {
  		sect.Extnum = int16(n)
  		n++
  	}
  	for _, sect := range Segrelrodata.Sections {
  		sect.Extnum = int16(n)
  		n++
  	}
  	for _, sect := range Segdata.Sections {
  		sect.Extnum = int16(n)
  		n++
  	}
  	for _, sect := range Segdwarf.Sections {
  		sect.Extnum = int16(n)
  		n++
  	}
  }
  
  func dodataSect(ctxt *Link, symn sym.SymKind, syms []*sym.Symbol) (result []*sym.Symbol, maxAlign int32) {
  	if ctxt.HeadType == objabi.Hdarwin {
  		// Some symbols may no longer belong in syms
  		// due to movement in machosymorder.
  		newSyms := make([]*sym.Symbol, 0, len(syms))
  		for _, s := range syms {
  			if s.Type == symn {
  				newSyms = append(newSyms, s)
  			}
  		}
  		syms = newSyms
  	}
  
  	var head, tail *sym.Symbol
  	symsSort := make([]dataSortKey, 0, len(syms))
  	for _, s := range syms {
  		if s.Attr.OnList() {
  			log.Fatalf("symbol %s listed multiple times", s.Name)
  		}
  		s.Attr |= sym.AttrOnList
  		switch {
  		case s.Size < int64(len(s.P)):
  			Errorf(s, "initialize bounds (%d < %d)", s.Size, len(s.P))
  		case s.Size < 0:
  			Errorf(s, "negative size (%d bytes)", s.Size)
  		case s.Size > cutoff:
  			Errorf(s, "symbol too large (%d bytes)", s.Size)
  		}
  
  		// If the usually-special section-marker symbols are being laid
  		// out as regular symbols, put them either at the beginning or
  		// end of their section.
  		if ctxt.DynlinkingGo() && ctxt.HeadType == objabi.Hdarwin {
  			switch s.Name {
  			case "runtime.text", "runtime.bss", "runtime.data", "runtime.types":
  				head = s
  				continue
  			case "runtime.etext", "runtime.ebss", "runtime.edata", "runtime.etypes":
  				tail = s
  				continue
  			}
  		}
  
  		key := dataSortKey{
  			size: s.Size,
  			name: s.Name,
  			sym:  s,
  		}
  
  		switch s.Type {
  		case sym.SELFGOT:
  			// For ppc64, we want to interleave the .got and .toc sections
  			// from input files. Both are type sym.SELFGOT, so in that case
  			// we skip size comparison and fall through to the name
  			// comparison (conveniently, .got sorts before .toc).
  			key.size = 0
  		}
  
  		symsSort = append(symsSort, key)
  	}
  
  	sort.Sort(bySizeAndName(symsSort))
  
  	off := 0
  	if head != nil {
  		syms[0] = head
  		off++
  	}
  	for i, symSort := range symsSort {
  		syms[i+off] = symSort.sym
  		align := symalign(symSort.sym)
  		if maxAlign < align {
  			maxAlign = align
  		}
  	}
  	if tail != nil {
  		syms[len(syms)-1] = tail
  	}
  
  	if ctxt.IsELF && symn == sym.SELFROSECT {
  		// Make .rela and .rela.plt contiguous, the ELF ABI requires this
  		// and Solaris actually cares.
  		reli, plti := -1, -1
  		for i, s := range syms {
  			switch s.Name {
  			case ".rel.plt", ".rela.plt":
  				plti = i
  			case ".rel", ".rela":
  				reli = i
  			}
  		}
  		if reli >= 0 && plti >= 0 && plti != reli+1 {
  			var first, second int
  			if plti > reli {
  				first, second = reli, plti
  			} else {
  				first, second = plti, reli
  			}
  			rel, plt := syms[reli], syms[plti]
  			copy(syms[first+2:], syms[first+1:second])
  			syms[first+0] = rel
  			syms[first+1] = plt
  
  			// Make sure alignment doesn't introduce a gap.
  			// Setting the alignment explicitly prevents
  			// symalign from basing it on the size and
  			// getting it wrong.
  			rel.Align = int32(ctxt.Arch.RegSize)
  			plt.Align = int32(ctxt.Arch.RegSize)
  		}
  	}
  
  	return syms, maxAlign
  }
  
  // Add buildid to beginning of text segment, on non-ELF systems.
  // Non-ELF binary formats are not always flexible enough to
  // give us a place to put the Go build ID. On those systems, we put it
  // at the very beginning of the text segment.
  // This ``header'' is read by cmd/go.
  func (ctxt *Link) textbuildid() {
  	if ctxt.IsELF || ctxt.BuildMode == BuildModePlugin || *flagBuildid == "" {
  		return
  	}
  
  	s := ctxt.Syms.Lookup("go.buildid", 0)
  	s.Attr |= sym.AttrReachable
  	// The \xff is invalid UTF-8, meant to make it less likely
  	// to find one of these accidentally.
  	data := "\xff Go build ID: " + strconv.Quote(*flagBuildid) + "\n \xff"
  	s.Type = sym.STEXT
  	s.P = []byte(data)
  	s.Size = int64(len(s.P))
  
  	ctxt.Textp = append(ctxt.Textp, nil)
  	copy(ctxt.Textp[1:], ctxt.Textp)
  	ctxt.Textp[0] = s
  }
  
  // assign addresses to text
  func (ctxt *Link) textaddress() {
  	addsection(ctxt.Arch, &Segtext, ".text", 05)
  
  	// Assign PCs in text segment.
  	// Could parallelize, by assigning to text
  	// and then letting threads copy down, but probably not worth it.
  	sect := Segtext.Sections[0]
  
  	sect.Align = int32(Funcalign)
  
  	text := ctxt.Syms.Lookup("runtime.text", 0)
  	text.Sect = sect
  
  	if ctxt.DynlinkingGo() && ctxt.HeadType == objabi.Hdarwin {
  		etext := ctxt.Syms.Lookup("runtime.etext", 0)
  		etext.Sect = sect
  
  		ctxt.Textp = append(ctxt.Textp, etext, nil)
  		copy(ctxt.Textp[1:], ctxt.Textp)
  		ctxt.Textp[0] = text
  	}
  
  	va := uint64(*FlagTextAddr)
  	n := 1
  	sect.Vaddr = va
  	ntramps := 0
  	for _, s := range ctxt.Textp {
  		sect, n, va = assignAddress(ctxt, sect, n, s, va, false)
  
  		trampoline(ctxt, s) // resolve jumps, may add trampolines if jump too far
  
  		// lay down trampolines after each function
  		for ; ntramps < len(ctxt.tramps); ntramps++ {
  			tramp := ctxt.tramps[ntramps]
  			sect, n, va = assignAddress(ctxt, sect, n, tramp, va, true)
  		}
  	}
  
  	sect.Length = va - sect.Vaddr
  	ctxt.Syms.Lookup("runtime.etext", 0).Sect = sect
  
  	// merge tramps into Textp, keeping Textp in address order
  	if ntramps != 0 {
  		newtextp := make([]*sym.Symbol, 0, len(ctxt.Textp)+ntramps)
  		i := 0
  		for _, s := range ctxt.Textp {
  			for ; i < ntramps && ctxt.tramps[i].Value < s.Value; i++ {
  				newtextp = append(newtextp, ctxt.tramps[i])
  			}
  			newtextp = append(newtextp, s)
  		}
  		newtextp = append(newtextp, ctxt.tramps[i:ntramps]...)
  
  		ctxt.Textp = newtextp
  	}
  }
  
  // assigns address for a text symbol, returns (possibly new) section, its number, and the address
  // Note: once we have trampoline insertion support for external linking, this function
  // will not need to create new text sections, and so no need to return sect and n.
  func assignAddress(ctxt *Link, sect *sym.Section, n int, s *sym.Symbol, va uint64, isTramp bool) (*sym.Section, int, uint64) {
  	s.Sect = sect
  	if s.Attr.SubSymbol() {
  		return sect, n, va
  	}
  	if s.Align != 0 {
  		va = uint64(Rnd(int64(va), int64(s.Align)))
  	} else {
  		va = uint64(Rnd(int64(va), int64(Funcalign)))
  	}
  	s.Value = 0
  	for sub := s; sub != nil; sub = sub.Sub {
  		sub.Value += int64(va)
  	}
  
  	funcsize := uint64(MINFUNC) // spacing required for findfunctab
  	if s.Size > MINFUNC {
  		funcsize = uint64(s.Size)
  	}
  
  	// On ppc64x a text section should not be larger than 2^26 bytes due to the size of
  	// call target offset field in the bl instruction.  Splitting into smaller text
  	// sections smaller than this limit allows the GNU linker to modify the long calls
  	// appropriately.  The limit allows for the space needed for tables inserted by the linker.
  
  	// If this function doesn't fit in the current text section, then create a new one.
  
  	// Only break at outermost syms.
  
  	if ctxt.Arch.InFamily(sys.PPC64) && s.Outer == nil && ctxt.IsELF && ctxt.LinkMode == LinkExternal && va-sect.Vaddr+funcsize+maxSizeTrampolinesPPC64(s, isTramp) > 0x1c00000 {
  
  		// Set the length for the previous text section
  		sect.Length = va - sect.Vaddr
  
  		// Create new section, set the starting Vaddr
  		sect = addsection(ctxt.Arch, &Segtext, ".text", 05)
  		sect.Vaddr = va
  		s.Sect = sect
  
  		// Create a symbol for the start of the secondary text sections
  		ctxt.Syms.Lookup(fmt.Sprintf("runtime.text.%d", n), 0).Sect = sect
  		n++
  	}
  	va += funcsize
  
  	return sect, n, va
  }
  
  // assign addresses
  func (ctxt *Link) address() {
  	va := uint64(*FlagTextAddr)
  	Segtext.Rwx = 05
  	Segtext.Vaddr = va
  	Segtext.Fileoff = uint64(HEADR)
  	for _, s := range Segtext.Sections {
  		va = uint64(Rnd(int64(va), int64(s.Align)))
  		s.Vaddr = va
  		va += s.Length
  	}
  
  	Segtext.Length = va - uint64(*FlagTextAddr)
  	Segtext.Filelen = Segtext.Length
  	if ctxt.HeadType == objabi.Hnacl {
  		va += 32 // room for the "halt sled"
  	}
  
  	if len(Segrodata.Sections) > 0 {
  		// align to page boundary so as not to mix
  		// rodata and executable text.
  		//
  		// Note: gold or GNU ld will reduce the size of the executable
  		// file by arranging for the relro segment to end at a page
  		// boundary, and overlap the end of the text segment with the
  		// start of the relro segment in the file.  The PT_LOAD segments
  		// will be such that the last page of the text segment will be
  		// mapped twice, once r-x and once starting out rw- and, after
  		// relocation processing, changed to r--.
  		//
  		// Ideally the last page of the text segment would not be
  		// writable even for this short period.
  		va = uint64(Rnd(int64(va), int64(*FlagRound)))
  
  		Segrodata.Rwx = 04
  		Segrodata.Vaddr = va
  		Segrodata.Fileoff = va - Segtext.Vaddr + Segtext.Fileoff
  		Segrodata.Filelen = 0
  		for _, s := range Segrodata.Sections {
  			va = uint64(Rnd(int64(va), int64(s.Align)))
  			s.Vaddr = va
  			va += s.Length
  		}
  
  		Segrodata.Length = va - Segrodata.Vaddr
  		Segrodata.Filelen = Segrodata.Length
  	}
  	if len(Segrelrodata.Sections) > 0 {
  		// align to page boundary so as not to mix
  		// rodata, rel-ro data, and executable text.
  		va = uint64(Rnd(int64(va), int64(*FlagRound)))
  
  		Segrelrodata.Rwx = 06
  		Segrelrodata.Vaddr = va
  		Segrelrodata.Fileoff = va - Segrodata.Vaddr + Segrodata.Fileoff
  		Segrelrodata.Filelen = 0
  		for _, s := range Segrelrodata.Sections {
  			va = uint64(Rnd(int64(va), int64(s.Align)))
  			s.Vaddr = va
  			va += s.Length
  		}
  
  		Segrelrodata.Length = va - Segrelrodata.Vaddr
  		Segrelrodata.Filelen = Segrelrodata.Length
  	}
  
  	va = uint64(Rnd(int64(va), int64(*FlagRound)))
  	Segdata.Rwx = 06
  	Segdata.Vaddr = va
  	Segdata.Fileoff = va - Segtext.Vaddr + Segtext.Fileoff
  	Segdata.Filelen = 0
  	if ctxt.HeadType == objabi.Hwindows {
  		Segdata.Fileoff = Segtext.Fileoff + uint64(Rnd(int64(Segtext.Length), PEFILEALIGN))
  	}
  	if ctxt.HeadType == objabi.Hplan9 {
  		Segdata.Fileoff = Segtext.Fileoff + Segtext.Filelen
  	}
  	var data *sym.Section
  	var noptr *sym.Section
  	var bss *sym.Section
  	var noptrbss *sym.Section
  	for i, s := range Segdata.Sections {
  		if ctxt.IsELF && s.Name == ".tbss" {
  			continue
  		}
  		vlen := int64(s.Length)
  		if i+1 < len(Segdata.Sections) && !(ctxt.IsELF && Segdata.Sections[i+1].Name == ".tbss") {
  			vlen = int64(Segdata.Sections[i+1].Vaddr - s.Vaddr)
  		}
  		s.Vaddr = va
  		va += uint64(vlen)
  		Segdata.Length = va - Segdata.Vaddr
  		if s.Name == ".data" {
  			data = s
  		}
  		if s.Name == ".noptrdata" {
  			noptr = s
  		}
  		if s.Name == ".bss" {
  			bss = s
  		}
  		if s.Name == ".noptrbss" {
  			noptrbss = s
  		}
  	}
  
  	Segdata.Filelen = bss.Vaddr - Segdata.Vaddr
  
  	va = uint64(Rnd(int64(va), int64(*FlagRound)))
  	Segdwarf.Rwx = 06
  	Segdwarf.Vaddr = va
  	Segdwarf.Fileoff = Segdata.Fileoff + uint64(Rnd(int64(Segdata.Filelen), int64(*FlagRound)))
  	Segdwarf.Filelen = 0
  	if ctxt.HeadType == objabi.Hwindows {
  		Segdwarf.Fileoff = Segdata.Fileoff + uint64(Rnd(int64(Segdata.Filelen), int64(PEFILEALIGN)))
  	}
  	for i, s := range Segdwarf.Sections {
  		vlen := int64(s.Length)
  		if i+1 < len(Segdwarf.Sections) {
  			vlen = int64(Segdwarf.Sections[i+1].Vaddr - s.Vaddr)
  		}
  		s.Vaddr = va
  		va += uint64(vlen)
  		if ctxt.HeadType == objabi.Hwindows {
  			va = uint64(Rnd(int64(va), PEFILEALIGN))
  		}
  		Segdwarf.Length = va - Segdwarf.Vaddr
  	}
  
  	Segdwarf.Filelen = va - Segdwarf.Vaddr
  
  	var (
  		text     = Segtext.Sections[0]
  		rodata   = ctxt.Syms.Lookup("runtime.rodata", 0).Sect
  		itablink = ctxt.Syms.Lookup("runtime.itablink", 0).Sect
  		symtab   = ctxt.Syms.Lookup("runtime.symtab", 0).Sect
  		pclntab  = ctxt.Syms.Lookup("runtime.pclntab", 0).Sect
  		types    = ctxt.Syms.Lookup("runtime.types", 0).Sect
  	)
  	lasttext := text
  	// Could be multiple .text sections
  	for _, sect := range Segtext.Sections {
  		if sect.Name == ".text" {
  			lasttext = sect
  		}
  	}
  
  	for _, s := range datap {
  		if s.Sect != nil {
  			s.Value += int64(s.Sect.Vaddr)
  		}
  		for sub := s.Sub; sub != nil; sub = sub.Sub {
  			sub.Value += s.Value
  		}
  	}
  
  	for _, s := range dwarfp {
  		if s.Sect != nil {
  			s.Value += int64(s.Sect.Vaddr)
  		}
  		for sub := s.Sub; sub != nil; sub = sub.Sub {
  			sub.Value += s.Value
  		}
  	}
  
  	if ctxt.BuildMode == BuildModeShared {
  		s := ctxt.Syms.Lookup("go.link.abihashbytes", 0)
  		sectSym := ctxt.Syms.Lookup(".note.go.abihash", 0)
  		s.Sect = sectSym.Sect
  		s.Value = int64(sectSym.Sect.Vaddr + 16)
  	}
  
  	ctxt.xdefine("runtime.text", sym.STEXT, int64(text.Vaddr))
  	ctxt.xdefine("runtime.etext", sym.STEXT, int64(lasttext.Vaddr+lasttext.Length))
  
  	// If there are multiple text sections, create runtime.text.n for
  	// their section Vaddr, using n for index
  	n := 1
  	for _, sect := range Segtext.Sections[1:] {
  		if sect.Name != ".text" {
  			break
  		}
  		symname := fmt.Sprintf("runtime.text.%d", n)
  		ctxt.xdefine(symname, sym.STEXT, int64(sect.Vaddr))
  		n++
  	}
  
  	ctxt.xdefine("runtime.rodata", sym.SRODATA, int64(rodata.Vaddr))
  	ctxt.xdefine("runtime.erodata", sym.SRODATA, int64(rodata.Vaddr+rodata.Length))
  	ctxt.xdefine("runtime.types", sym.SRODATA, int64(types.Vaddr))
  	ctxt.xdefine("runtime.etypes", sym.SRODATA, int64(types.Vaddr+types.Length))
  	ctxt.xdefine("runtime.itablink", sym.SRODATA, int64(itablink.Vaddr))
  	ctxt.xdefine("runtime.eitablink", sym.SRODATA, int64(itablink.Vaddr+itablink.Length))
  
  	s := ctxt.Syms.Lookup("runtime.gcdata", 0)
  	s.Attr |= sym.AttrLocal
  	ctxt.xdefine("runtime.egcdata", sym.SRODATA, Symaddr(s)+s.Size)
  	ctxt.Syms.Lookup("runtime.egcdata", 0).Sect = s.Sect
  
  	s = ctxt.Syms.Lookup("runtime.gcbss", 0)
  	s.Attr |= sym.AttrLocal
  	ctxt.xdefine("runtime.egcbss", sym.SRODATA, Symaddr(s)+s.Size)
  	ctxt.Syms.Lookup("runtime.egcbss", 0).Sect = s.Sect
  
  	ctxt.xdefine("runtime.symtab", sym.SRODATA, int64(symtab.Vaddr))
  	ctxt.xdefine("runtime.esymtab", sym.SRODATA, int64(symtab.Vaddr+symtab.Length))
  	ctxt.xdefine("runtime.pclntab", sym.SRODATA, int64(pclntab.Vaddr))
  	ctxt.xdefine("runtime.epclntab", sym.SRODATA, int64(pclntab.Vaddr+pclntab.Length))
  	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))
  	ctxt.xdefine("runtime.edata", sym.SDATA, int64(data.Vaddr+data.Length))
  	ctxt.xdefine("runtime.noptrbss", sym.SNOPTRBSS, int64(noptrbss.Vaddr))
  	ctxt.xdefine("runtime.enoptrbss", sym.SNOPTRBSS, int64(noptrbss.Vaddr+noptrbss.Length))
  	ctxt.xdefine("runtime.end", sym.SBSS, int64(Segdata.Vaddr+Segdata.Length))
  }
  
  // add a trampoline with symbol s (to be laid down after the current function)
  func (ctxt *Link) AddTramp(s *sym.Symbol) {
  	s.Type = sym.STEXT
  	s.Attr |= sym.AttrReachable
  	s.Attr |= sym.AttrOnList
  	ctxt.tramps = append(ctxt.tramps, s)
  	if *FlagDebugTramp > 0 && ctxt.Debugvlog > 0 {
  		ctxt.Logf("trampoline %s inserted\n", s)
  	}
  }
  

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