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Source file src/cmd/link/internal/amd64/asm.go

Documentation: cmd/link/internal/amd64

  // Inferno utils/6l/asm.c
  // https://bitbucket.org/inferno-os/inferno-os/src/default/utils/6l/asm.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 amd64
  
  import (
  	"cmd/internal/objabi"
  	"cmd/link/internal/ld"
  	"debug/elf"
  	"log"
  )
  
  func PADDR(x uint32) uint32 {
  	return x &^ 0x80000000
  }
  
  func Addcall(ctxt *ld.Link, s *ld.Symbol, t *ld.Symbol) int64 {
  	s.Attr |= ld.AttrReachable
  	i := s.Size
  	s.Size += 4
  	ld.Symgrow(s, s.Size)
  	r := ld.Addrel(s)
  	r.Sym = t
  	r.Off = int32(i)
  	r.Type = objabi.R_CALL
  	r.Siz = 4
  	return i + int64(r.Siz)
  }
  
  func gentext(ctxt *ld.Link) {
  	if !ctxt.DynlinkingGo() {
  		return
  	}
  	addmoduledata := ctxt.Syms.Lookup("runtime.addmoduledata", 0)
  	if addmoduledata.Type == ld.STEXT && ld.Buildmode != ld.BuildmodePlugin {
  		// we're linking a module containing the runtime -> no need for
  		// an init function
  		return
  	}
  	addmoduledata.Attr |= ld.AttrReachable
  	initfunc := ctxt.Syms.Lookup("go.link.addmoduledata", 0)
  	initfunc.Type = ld.STEXT
  	initfunc.Attr |= ld.AttrLocal
  	initfunc.Attr |= ld.AttrReachable
  	o := func(op ...uint8) {
  		for _, op1 := range op {
  			ld.Adduint8(ctxt, initfunc, op1)
  		}
  	}
  	// 0000000000000000 <local.dso_init>:
  	//    0:	48 8d 3d 00 00 00 00 	lea    0x0(%rip),%rdi        # 7 <local.dso_init+0x7>
  	// 			3: R_X86_64_PC32	runtime.firstmoduledata-0x4
  	o(0x48, 0x8d, 0x3d)
  	ld.Addpcrelplus(ctxt, initfunc, ctxt.Moduledata, 0)
  	//    7:	e8 00 00 00 00       	callq  c <local.dso_init+0xc>
  	// 			8: R_X86_64_PLT32	runtime.addmoduledata-0x4
  	o(0xe8)
  	Addcall(ctxt, initfunc, addmoduledata)
  	//    c:	c3                   	retq
  	o(0xc3)
  	if ld.Buildmode == ld.BuildmodePlugin {
  		ctxt.Textp = append(ctxt.Textp, addmoduledata)
  	}
  	ctxt.Textp = append(ctxt.Textp, initfunc)
  	initarray_entry := ctxt.Syms.Lookup("go.link.addmoduledatainit", 0)
  	initarray_entry.Attr |= ld.AttrReachable
  	initarray_entry.Attr |= ld.AttrLocal
  	initarray_entry.Type = ld.SINITARR
  	ld.Addaddr(ctxt, initarray_entry, initfunc)
  }
  
  func adddynrel(ctxt *ld.Link, s *ld.Symbol, r *ld.Reloc) bool {
  	targ := r.Sym
  
  	switch r.Type {
  	default:
  		if r.Type >= 256 {
  			ld.Errorf(s, "unexpected relocation type %d", r.Type)
  			return false
  		}
  
  		// Handle relocations found in ELF object files.
  	case 256 + ld.R_X86_64_PC32:
  		if targ.Type == ld.SDYNIMPORT {
  			ld.Errorf(s, "unexpected R_X86_64_PC32 relocation for dynamic symbol %s", targ.Name)
  		}
  		if targ.Type == 0 || targ.Type == ld.SXREF {
  			ld.Errorf(s, "unknown symbol %s in pcrel", targ.Name)
  		}
  		r.Type = objabi.R_PCREL
  		r.Add += 4
  		return true
  
  	case 256 + ld.R_X86_64_PLT32:
  		r.Type = objabi.R_PCREL
  		r.Add += 4
  		if targ.Type == ld.SDYNIMPORT {
  			addpltsym(ctxt, targ)
  			r.Sym = ctxt.Syms.Lookup(".plt", 0)
  			r.Add += int64(targ.Plt)
  		}
  
  		return true
  
  	case 256 + ld.R_X86_64_GOTPCREL, 256 + ld.R_X86_64_GOTPCRELX, 256 + ld.R_X86_64_REX_GOTPCRELX:
  		if targ.Type != ld.SDYNIMPORT {
  			// have symbol
  			if r.Off >= 2 && s.P[r.Off-2] == 0x8b {
  				// turn MOVQ of GOT entry into LEAQ of symbol itself
  				s.P[r.Off-2] = 0x8d
  
  				r.Type = objabi.R_PCREL
  				r.Add += 4
  				return true
  			}
  		}
  
  		// fall back to using GOT and hope for the best (CMOV*)
  		// TODO: just needs relocation, no need to put in .dynsym
  		addgotsym(ctxt, targ)
  
  		r.Type = objabi.R_PCREL
  		r.Sym = ctxt.Syms.Lookup(".got", 0)
  		r.Add += 4
  		r.Add += int64(targ.Got)
  		return true
  
  	case 256 + ld.R_X86_64_64:
  		if targ.Type == ld.SDYNIMPORT {
  			ld.Errorf(s, "unexpected R_X86_64_64 relocation for dynamic symbol %s", targ.Name)
  		}
  		r.Type = objabi.R_ADDR
  		return true
  
  	// Handle relocations found in Mach-O object files.
  	case 512 + ld.MACHO_X86_64_RELOC_UNSIGNED*2 + 0,
  		512 + ld.MACHO_X86_64_RELOC_SIGNED*2 + 0,
  		512 + ld.MACHO_X86_64_RELOC_BRANCH*2 + 0:
  		// TODO: What is the difference between all these?
  		r.Type = objabi.R_ADDR
  
  		if targ.Type == ld.SDYNIMPORT {
  			ld.Errorf(s, "unexpected reloc for dynamic symbol %s", targ.Name)
  		}
  		return true
  
  	case 512 + ld.MACHO_X86_64_RELOC_BRANCH*2 + 1:
  		if targ.Type == ld.SDYNIMPORT {
  			addpltsym(ctxt, targ)
  			r.Sym = ctxt.Syms.Lookup(".plt", 0)
  			r.Add = int64(targ.Plt)
  			r.Type = objabi.R_PCREL
  			return true
  		}
  		fallthrough
  
  		// fall through
  	case 512 + ld.MACHO_X86_64_RELOC_UNSIGNED*2 + 1,
  		512 + ld.MACHO_X86_64_RELOC_SIGNED*2 + 1,
  		512 + ld.MACHO_X86_64_RELOC_SIGNED_1*2 + 1,
  		512 + ld.MACHO_X86_64_RELOC_SIGNED_2*2 + 1,
  		512 + ld.MACHO_X86_64_RELOC_SIGNED_4*2 + 1:
  		r.Type = objabi.R_PCREL
  
  		if targ.Type == ld.SDYNIMPORT {
  			ld.Errorf(s, "unexpected pc-relative reloc for dynamic symbol %s", targ.Name)
  		}
  		return true
  
  	case 512 + ld.MACHO_X86_64_RELOC_GOT_LOAD*2 + 1:
  		if targ.Type != ld.SDYNIMPORT {
  			// have symbol
  			// turn MOVQ of GOT entry into LEAQ of symbol itself
  			if r.Off < 2 || s.P[r.Off-2] != 0x8b {
  				ld.Errorf(s, "unexpected GOT_LOAD reloc for non-dynamic symbol %s", targ.Name)
  				return false
  			}
  
  			s.P[r.Off-2] = 0x8d
  			r.Type = objabi.R_PCREL
  			return true
  		}
  		fallthrough
  
  		// fall through
  	case 512 + ld.MACHO_X86_64_RELOC_GOT*2 + 1:
  		if targ.Type != ld.SDYNIMPORT {
  			ld.Errorf(s, "unexpected GOT reloc for non-dynamic symbol %s", targ.Name)
  		}
  		addgotsym(ctxt, targ)
  		r.Type = objabi.R_PCREL
  		r.Sym = ctxt.Syms.Lookup(".got", 0)
  		r.Add += int64(targ.Got)
  		return true
  	}
  
  	switch r.Type {
  	case objabi.R_CALL,
  		objabi.R_PCREL:
  		if targ.Type != ld.SDYNIMPORT {
  			// nothing to do, the relocation will be laid out in reloc
  			return true
  		}
  		if ld.Headtype == objabi.Hwindows {
  			// nothing to do, the relocation will be laid out in pereloc1
  			return true
  		} else {
  			// for both ELF and Mach-O
  			addpltsym(ctxt, targ)
  			r.Sym = ctxt.Syms.Lookup(".plt", 0)
  			r.Add = int64(targ.Plt)
  			return true
  		}
  
  	case objabi.R_ADDR:
  		if s.Type == ld.STEXT && ld.Iself {
  			if ld.Headtype == objabi.Hsolaris {
  				addpltsym(ctxt, targ)
  				r.Sym = ctxt.Syms.Lookup(".plt", 0)
  				r.Add += int64(targ.Plt)
  				return true
  			}
  			// The code is asking for the address of an external
  			// function. We provide it with the address of the
  			// correspondent GOT symbol.
  			addgotsym(ctxt, targ)
  
  			r.Sym = ctxt.Syms.Lookup(".got", 0)
  			r.Add += int64(targ.Got)
  			return true
  		}
  
  		// Process dynamic relocations for the data sections.
  		if ld.Buildmode == ld.BuildmodePIE && ld.Linkmode == ld.LinkInternal {
  			// When internally linking, generate dynamic relocations
  			// for all typical R_ADDR relocations. The exception
  			// are those R_ADDR that are created as part of generating
  			// the dynamic relocations and must be resolved statically.
  			//
  			// There are three phases relevant to understanding this:
  			//
  			//	dodata()  // we are here
  			//	address() // symbol address assignment
  			//	reloc()   // resolution of static R_ADDR relocs
  			//
  			// At this point symbol addresses have not been
  			// assigned yet (as the final size of the .rela section
  			// will affect the addresses), and so we cannot write
  			// the Elf64_Rela.r_offset now. Instead we delay it
  			// until after the 'address' phase of the linker is
  			// complete. We do this via Addaddrplus, which creates
  			// a new R_ADDR relocation which will be resolved in
  			// the 'reloc' phase.
  			//
  			// These synthetic static R_ADDR relocs must be skipped
  			// now, or else we will be caught in an infinite loop
  			// of generating synthetic relocs for our synthetic
  			// relocs.
  			//
  			// Furthermore, the rela sections contain dynamic
  			// relocations with R_ADDR relocations on
  			// Elf64_Rela.r_offset. This field should contain the
  			// symbol offset as determined by reloc(), not the
  			// final dynamically linked address as a dynamic
  			// relocation would provide.
  			switch s.Name {
  			case ".dynsym", ".rela", ".rela.plt", ".got.plt", ".dynamic":
  				return false
  			}
  		} else {
  			// Either internally linking a static executable,
  			// in which case we can resolve these relocations
  			// statically in the 'reloc' phase, or externally
  			// linking, in which case the relocation will be
  			// prepared in the 'reloc' phase and passed to the
  			// external linker in the 'asmb' phase.
  			if s.Type != ld.SDATA && s.Type != ld.SRODATA {
  				break
  			}
  		}
  
  		if ld.Iself {
  			// TODO: We generate a R_X86_64_64 relocation for every R_ADDR, even
  			// though it would be more efficient (for the dynamic linker) if we
  			// generated R_X86_RELATIVE instead.
  			ld.Adddynsym(ctxt, targ)
  			rela := ctxt.Syms.Lookup(".rela", 0)
  			ld.Addaddrplus(ctxt, rela, s, int64(r.Off))
  			if r.Siz == 8 {
  				ld.Adduint64(ctxt, rela, ld.ELF64_R_INFO(uint32(targ.Dynid), ld.R_X86_64_64))
  			} else {
  				// TODO: never happens, remove.
  				ld.Adduint64(ctxt, rela, ld.ELF64_R_INFO(uint32(targ.Dynid), ld.R_X86_64_32))
  			}
  			ld.Adduint64(ctxt, rela, uint64(r.Add))
  			r.Type = 256 // ignore during relocsym
  			return true
  		}
  
  		if ld.Headtype == objabi.Hdarwin && s.Size == int64(ld.SysArch.PtrSize) && r.Off == 0 {
  			// Mach-O relocations are a royal pain to lay out.
  			// They use a compact stateful bytecode representation
  			// that is too much bother to deal with.
  			// Instead, interpret the C declaration
  			//	void *_Cvar_stderr = &stderr;
  			// as making _Cvar_stderr the name of a GOT entry
  			// for stderr. This is separate from the usual GOT entry,
  			// just in case the C code assigns to the variable,
  			// and of course it only works for single pointers,
  			// but we only need to support cgo and that's all it needs.
  			ld.Adddynsym(ctxt, targ)
  
  			got := ctxt.Syms.Lookup(".got", 0)
  			s.Type = got.Type | ld.SSUB
  			s.Outer = got
  			s.Sub = got.Sub
  			got.Sub = s
  			s.Value = got.Size
  			ld.Adduint64(ctxt, got, 0)
  			ld.Adduint32(ctxt, ctxt.Syms.Lookup(".linkedit.got", 0), uint32(targ.Dynid))
  			r.Type = 256 // ignore during relocsym
  			return true
  		}
  
  		if ld.Headtype == objabi.Hwindows {
  			// nothing to do, the relocation will be laid out in pereloc1
  			return true
  		}
  	}
  
  	return false
  }
  
  func elfreloc1(ctxt *ld.Link, r *ld.Reloc, sectoff int64) int {
  	ld.Thearch.Vput(uint64(sectoff))
  
  	elfsym := r.Xsym.ElfsymForReloc()
  	switch r.Type {
  	default:
  		return -1
  
  	case objabi.R_ADDR:
  		if r.Siz == 4 {
  			ld.Thearch.Vput(ld.R_X86_64_32 | uint64(elfsym)<<32)
  		} else if r.Siz == 8 {
  			ld.Thearch.Vput(ld.R_X86_64_64 | uint64(elfsym)<<32)
  		} else {
  			return -1
  		}
  
  	case objabi.R_TLS_LE:
  		if r.Siz == 4 {
  			ld.Thearch.Vput(ld.R_X86_64_TPOFF32 | uint64(elfsym)<<32)
  		} else {
  			return -1
  		}
  
  	case objabi.R_TLS_IE:
  		if r.Siz == 4 {
  			ld.Thearch.Vput(ld.R_X86_64_GOTTPOFF | uint64(elfsym)<<32)
  		} else {
  			return -1
  		}
  
  	case objabi.R_CALL:
  		if r.Siz == 4 {
  			if r.Xsym.Type == ld.SDYNIMPORT {
  				if ctxt.DynlinkingGo() {
  					ld.Thearch.Vput(ld.R_X86_64_PLT32 | uint64(elfsym)<<32)
  				} else {
  					ld.Thearch.Vput(ld.R_X86_64_GOTPCREL | uint64(elfsym)<<32)
  				}
  			} else {
  				ld.Thearch.Vput(ld.R_X86_64_PC32 | uint64(elfsym)<<32)
  			}
  		} else {
  			return -1
  		}
  
  	case objabi.R_PCREL:
  		if r.Siz == 4 {
  			if r.Xsym.Type == ld.SDYNIMPORT && r.Xsym.ElfType == elf.STT_FUNC {
  				ld.Thearch.Vput(ld.R_X86_64_PLT32 | uint64(elfsym)<<32)
  			} else {
  				ld.Thearch.Vput(ld.R_X86_64_PC32 | uint64(elfsym)<<32)
  			}
  		} else {
  			return -1
  		}
  
  	case objabi.R_GOTPCREL:
  		if r.Siz == 4 {
  			ld.Thearch.Vput(ld.R_X86_64_GOTPCREL | uint64(elfsym)<<32)
  		} else {
  			return -1
  		}
  	}
  
  	ld.Thearch.Vput(uint64(r.Xadd))
  	return 0
  }
  
  func machoreloc1(s *ld.Symbol, r *ld.Reloc, sectoff int64) int {
  	var v uint32
  
  	rs := r.Xsym
  
  	if rs.Type == ld.SHOSTOBJ || r.Type == objabi.R_PCREL || r.Type == objabi.R_GOTPCREL {
  		if rs.Dynid < 0 {
  			ld.Errorf(s, "reloc %d to non-macho symbol %s type=%d", r.Type, rs.Name, rs.Type)
  			return -1
  		}
  
  		v = uint32(rs.Dynid)
  		v |= 1 << 27 // external relocation
  	} else {
  		v = uint32(rs.Sect.Extnum)
  		if v == 0 {
  			ld.Errorf(s, "reloc %d to symbol %s in non-macho section %s type=%d", r.Type, rs.Name, rs.Sect.Name, rs.Type)
  			return -1
  		}
  	}
  
  	switch r.Type {
  	default:
  		return -1
  
  	case objabi.R_ADDR:
  		v |= ld.MACHO_X86_64_RELOC_UNSIGNED << 28
  
  	case objabi.R_CALL:
  		v |= 1 << 24 // pc-relative bit
  		v |= ld.MACHO_X86_64_RELOC_BRANCH << 28
  
  		// NOTE: Only works with 'external' relocation. Forced above.
  	case objabi.R_PCREL:
  		v |= 1 << 24 // pc-relative bit
  		v |= ld.MACHO_X86_64_RELOC_SIGNED << 28
  	case objabi.R_GOTPCREL:
  		v |= 1 << 24 // pc-relative bit
  		v |= ld.MACHO_X86_64_RELOC_GOT_LOAD << 28
  	}
  
  	switch r.Siz {
  	default:
  		return -1
  
  	case 1:
  		v |= 0 << 25
  
  	case 2:
  		v |= 1 << 25
  
  	case 4:
  		v |= 2 << 25
  
  	case 8:
  		v |= 3 << 25
  	}
  
  	ld.Thearch.Lput(uint32(sectoff))
  	ld.Thearch.Lput(v)
  	return 0
  }
  
  func pereloc1(s *ld.Symbol, r *ld.Reloc, sectoff int64) bool {
  	var v uint32
  
  	rs := r.Xsym
  
  	if rs.Dynid < 0 {
  		ld.Errorf(s, "reloc %d to non-coff symbol %s type=%d", r.Type, rs.Name, rs.Type)
  		return false
  	}
  
  	ld.Thearch.Lput(uint32(sectoff))
  	ld.Thearch.Lput(uint32(rs.Dynid))
  
  	switch r.Type {
  	default:
  		return false
  
  	case objabi.R_DWARFREF:
  		v = ld.IMAGE_REL_AMD64_SECREL
  
  	case objabi.R_ADDR:
  		if r.Siz == 8 {
  			v = ld.IMAGE_REL_AMD64_ADDR64
  		} else {
  			v = ld.IMAGE_REL_AMD64_ADDR32
  		}
  
  	case objabi.R_CALL,
  		objabi.R_PCREL:
  		v = ld.IMAGE_REL_AMD64_REL32
  	}
  
  	ld.Thearch.Wput(uint16(v))
  
  	return true
  }
  
  func archreloc(ctxt *ld.Link, r *ld.Reloc, s *ld.Symbol, val *int64) int {
  	return -1
  }
  
  func archrelocvariant(ctxt *ld.Link, r *ld.Reloc, s *ld.Symbol, t int64) int64 {
  	log.Fatalf("unexpected relocation variant")
  	return t
  }
  
  func elfsetupplt(ctxt *ld.Link) {
  	plt := ctxt.Syms.Lookup(".plt", 0)
  	got := ctxt.Syms.Lookup(".got.plt", 0)
  	if plt.Size == 0 {
  		// pushq got+8(IP)
  		ld.Adduint8(ctxt, plt, 0xff)
  
  		ld.Adduint8(ctxt, plt, 0x35)
  		ld.Addpcrelplus(ctxt, plt, got, 8)
  
  		// jmpq got+16(IP)
  		ld.Adduint8(ctxt, plt, 0xff)
  
  		ld.Adduint8(ctxt, plt, 0x25)
  		ld.Addpcrelplus(ctxt, plt, got, 16)
  
  		// nopl 0(AX)
  		ld.Adduint32(ctxt, plt, 0x00401f0f)
  
  		// assume got->size == 0 too
  		ld.Addaddrplus(ctxt, got, ctxt.Syms.Lookup(".dynamic", 0), 0)
  
  		ld.Adduint64(ctxt, got, 0)
  		ld.Adduint64(ctxt, got, 0)
  	}
  }
  
  func addpltsym(ctxt *ld.Link, s *ld.Symbol) {
  	if s.Plt >= 0 {
  		return
  	}
  
  	ld.Adddynsym(ctxt, s)
  
  	if ld.Iself {
  		plt := ctxt.Syms.Lookup(".plt", 0)
  		got := ctxt.Syms.Lookup(".got.plt", 0)
  		rela := ctxt.Syms.Lookup(".rela.plt", 0)
  		if plt.Size == 0 {
  			elfsetupplt(ctxt)
  		}
  
  		// jmpq *got+size(IP)
  		ld.Adduint8(ctxt, plt, 0xff)
  
  		ld.Adduint8(ctxt, plt, 0x25)
  		ld.Addpcrelplus(ctxt, plt, got, got.Size)
  
  		// add to got: pointer to current pos in plt
  		ld.Addaddrplus(ctxt, got, plt, plt.Size)
  
  		// pushq $x
  		ld.Adduint8(ctxt, plt, 0x68)
  
  		ld.Adduint32(ctxt, plt, uint32((got.Size-24-8)/8))
  
  		// jmpq .plt
  		ld.Adduint8(ctxt, plt, 0xe9)
  
  		ld.Adduint32(ctxt, plt, uint32(-(plt.Size + 4)))
  
  		// rela
  		ld.Addaddrplus(ctxt, rela, got, got.Size-8)
  
  		ld.Adduint64(ctxt, rela, ld.ELF64_R_INFO(uint32(s.Dynid), ld.R_X86_64_JMP_SLOT))
  		ld.Adduint64(ctxt, rela, 0)
  
  		s.Plt = int32(plt.Size - 16)
  	} else if ld.Headtype == objabi.Hdarwin {
  		// To do lazy symbol lookup right, we're supposed
  		// to tell the dynamic loader which library each
  		// symbol comes from and format the link info
  		// section just so. I'm too lazy (ha!) to do that
  		// so for now we'll just use non-lazy pointers,
  		// which don't need to be told which library to use.
  		//
  		// http://networkpx.blogspot.com/2009/09/about-lcdyldinfoonly-command.html
  		// has details about what we're avoiding.
  
  		addgotsym(ctxt, s)
  		plt := ctxt.Syms.Lookup(".plt", 0)
  
  		ld.Adduint32(ctxt, ctxt.Syms.Lookup(".linkedit.plt", 0), uint32(s.Dynid))
  
  		// jmpq *got+size(IP)
  		s.Plt = int32(plt.Size)
  
  		ld.Adduint8(ctxt, plt, 0xff)
  		ld.Adduint8(ctxt, plt, 0x25)
  		ld.Addpcrelplus(ctxt, plt, ctxt.Syms.Lookup(".got", 0), int64(s.Got))
  	} else {
  		ld.Errorf(s, "addpltsym: unsupported binary format")
  	}
  }
  
  func addgotsym(ctxt *ld.Link, s *ld.Symbol) {
  	if s.Got >= 0 {
  		return
  	}
  
  	ld.Adddynsym(ctxt, s)
  	got := ctxt.Syms.Lookup(".got", 0)
  	s.Got = int32(got.Size)
  	ld.Adduint64(ctxt, got, 0)
  
  	if ld.Iself {
  		rela := ctxt.Syms.Lookup(".rela", 0)
  		ld.Addaddrplus(ctxt, rela, got, int64(s.Got))
  		ld.Adduint64(ctxt, rela, ld.ELF64_R_INFO(uint32(s.Dynid), ld.R_X86_64_GLOB_DAT))
  		ld.Adduint64(ctxt, rela, 0)
  	} else if ld.Headtype == objabi.Hdarwin {
  		ld.Adduint32(ctxt, ctxt.Syms.Lookup(".linkedit.got", 0), uint32(s.Dynid))
  	} else {
  		ld.Errorf(s, "addgotsym: unsupported binary format")
  	}
  }
  
  func asmb(ctxt *ld.Link) {
  	if ctxt.Debugvlog != 0 {
  		ctxt.Logf("%5.2f asmb\n", ld.Cputime())
  	}
  
  	if ctxt.Debugvlog != 0 {
  		ctxt.Logf("%5.2f codeblk\n", ld.Cputime())
  	}
  
  	if ld.Iself {
  		ld.Asmbelfsetup()
  	}
  
  	sect := ld.Segtext.Sections[0]
  	ld.Cseek(int64(sect.Vaddr - ld.Segtext.Vaddr + ld.Segtext.Fileoff))
  	// 0xCC is INT $3 - breakpoint instruction
  	ld.CodeblkPad(ctxt, int64(sect.Vaddr), int64(sect.Length), []byte{0xCC})
  	for _, sect = range ld.Segtext.Sections[1:] {
  		ld.Cseek(int64(sect.Vaddr - ld.Segtext.Vaddr + ld.Segtext.Fileoff))
  		ld.Datblk(ctxt, int64(sect.Vaddr), int64(sect.Length))
  	}
  
  	if ld.Segrodata.Filelen > 0 {
  		if ctxt.Debugvlog != 0 {
  			ctxt.Logf("%5.2f rodatblk\n", ld.Cputime())
  		}
  		ld.Cseek(int64(ld.Segrodata.Fileoff))
  		ld.Datblk(ctxt, int64(ld.Segrodata.Vaddr), int64(ld.Segrodata.Filelen))
  	}
  	if ld.Segrelrodata.Filelen > 0 {
  		if ctxt.Debugvlog != 0 {
  			ctxt.Logf("%5.2f relrodatblk\n", ld.Cputime())
  		}
  		ld.Cseek(int64(ld.Segrelrodata.Fileoff))
  		ld.Datblk(ctxt, int64(ld.Segrelrodata.Vaddr), int64(ld.Segrelrodata.Filelen))
  	}
  
  	if ctxt.Debugvlog != 0 {
  		ctxt.Logf("%5.2f datblk\n", ld.Cputime())
  	}
  
  	ld.Cseek(int64(ld.Segdata.Fileoff))
  	ld.Datblk(ctxt, int64(ld.Segdata.Vaddr), int64(ld.Segdata.Filelen))
  
  	ld.Cseek(int64(ld.Segdwarf.Fileoff))
  	ld.Dwarfblk(ctxt, int64(ld.Segdwarf.Vaddr), int64(ld.Segdwarf.Filelen))
  
  	machlink := int64(0)
  	if ld.Headtype == objabi.Hdarwin {
  		machlink = ld.Domacholink(ctxt)
  	}
  
  	switch ld.Headtype {
  	default:
  		ld.Errorf(nil, "unknown header type %v", ld.Headtype)
  		fallthrough
  
  	case objabi.Hplan9:
  		break
  
  	case objabi.Hdarwin:
  		ld.Flag8 = true /* 64-bit addresses */
  
  	case objabi.Hlinux,
  		objabi.Hfreebsd,
  		objabi.Hnetbsd,
  		objabi.Hopenbsd,
  		objabi.Hdragonfly,
  		objabi.Hsolaris:
  		ld.Flag8 = true /* 64-bit addresses */
  
  	case objabi.Hnacl,
  		objabi.Hwindows:
  		break
  	}
  
  	ld.Symsize = 0
  	ld.Spsize = 0
  	ld.Lcsize = 0
  	symo := int64(0)
  	if !*ld.FlagS {
  		if ctxt.Debugvlog != 0 {
  			ctxt.Logf("%5.2f sym\n", ld.Cputime())
  		}
  		switch ld.Headtype {
  		default:
  		case objabi.Hplan9:
  			*ld.FlagS = true
  			symo = int64(ld.Segdata.Fileoff + ld.Segdata.Filelen)
  
  		case objabi.Hdarwin:
  			symo = int64(ld.Segdwarf.Fileoff + uint64(ld.Rnd(int64(ld.Segdwarf.Filelen), int64(*ld.FlagRound))) + uint64(machlink))
  
  		case objabi.Hlinux,
  			objabi.Hfreebsd,
  			objabi.Hnetbsd,
  			objabi.Hopenbsd,
  			objabi.Hdragonfly,
  			objabi.Hsolaris,
  			objabi.Hnacl:
  			symo = int64(ld.Segdwarf.Fileoff + ld.Segdwarf.Filelen)
  			symo = ld.Rnd(symo, int64(*ld.FlagRound))
  
  		case objabi.Hwindows:
  			symo = int64(ld.Segdwarf.Fileoff + ld.Segdwarf.Filelen)
  			symo = ld.Rnd(symo, ld.PEFILEALIGN)
  		}
  
  		ld.Cseek(symo)
  		switch ld.Headtype {
  		default:
  			if ld.Iself {
  				ld.Cseek(symo)
  				ld.Asmelfsym(ctxt)
  				ld.Cflush()
  				ld.Cwrite(ld.Elfstrdat)
  
  				if ctxt.Debugvlog != 0 {
  					ctxt.Logf("%5.2f dwarf\n", ld.Cputime())
  				}
  
  				if ld.Linkmode == ld.LinkExternal {
  					ld.Elfemitreloc(ctxt)
  				}
  			}
  
  		case objabi.Hplan9:
  			ld.Asmplan9sym(ctxt)
  			ld.Cflush()
  
  			sym := ctxt.Syms.Lookup("pclntab", 0)
  			if sym != nil {
  				ld.Lcsize = int32(len(sym.P))
  				for i := 0; int32(i) < ld.Lcsize; i++ {
  					ld.Cput(sym.P[i])
  				}
  
  				ld.Cflush()
  			}
  
  		case objabi.Hwindows:
  			if ctxt.Debugvlog != 0 {
  				ctxt.Logf("%5.2f dwarf\n", ld.Cputime())
  			}
  
  		case objabi.Hdarwin:
  			if ld.Linkmode == ld.LinkExternal {
  				ld.Machoemitreloc(ctxt)
  			}
  		}
  	}
  
  	if ctxt.Debugvlog != 0 {
  		ctxt.Logf("%5.2f headr\n", ld.Cputime())
  	}
  	ld.Cseek(0)
  	switch ld.Headtype {
  	default:
  	case objabi.Hplan9: /* plan9 */
  		magic := int32(4*26*26 + 7)
  
  		magic |= 0x00008000                  /* fat header */
  		ld.Lputb(uint32(magic))              /* magic */
  		ld.Lputb(uint32(ld.Segtext.Filelen)) /* sizes */
  		ld.Lputb(uint32(ld.Segdata.Filelen))
  		ld.Lputb(uint32(ld.Segdata.Length - ld.Segdata.Filelen))
  		ld.Lputb(uint32(ld.Symsize)) /* nsyms */
  		vl := ld.Entryvalue(ctxt)
  		ld.Lputb(PADDR(uint32(vl))) /* va of entry */
  		ld.Lputb(uint32(ld.Spsize)) /* sp offsets */
  		ld.Lputb(uint32(ld.Lcsize)) /* line offsets */
  		ld.Vputb(uint64(vl))        /* va of entry */
  
  	case objabi.Hdarwin:
  		ld.Asmbmacho(ctxt)
  
  	case objabi.Hlinux,
  		objabi.Hfreebsd,
  		objabi.Hnetbsd,
  		objabi.Hopenbsd,
  		objabi.Hdragonfly,
  		objabi.Hsolaris,
  		objabi.Hnacl:
  		ld.Asmbelf(ctxt, symo)
  
  	case objabi.Hwindows:
  		ld.Asmbpe(ctxt)
  	}
  
  	ld.Cflush()
  }
  
  func tlsIEtoLE(s *ld.Symbol, off, size int) {
  	// Transform the PC-relative instruction into a constant load.
  	// That is,
  	//
  	//	MOVQ X(IP), REG  ->  MOVQ $Y, REG
  	//
  	// To determine the instruction and register, we study the op codes.
  	// Consult an AMD64 instruction encoding guide to decipher this.
  	if off < 3 {
  		log.Fatal("R_X86_64_GOTTPOFF reloc not preceded by MOVQ or ADDQ instruction")
  	}
  	op := s.P[off-3 : off]
  	reg := op[2] >> 3
  
  	if op[1] == 0x8b || reg == 4 {
  		// MOVQ
  		if op[0] == 0x4c {
  			op[0] = 0x49
  		} else if size == 4 && op[0] == 0x44 {
  			op[0] = 0x41
  		}
  		if op[1] == 0x8b {
  			op[1] = 0xc7
  		} else {
  			op[1] = 0x81 // special case for SP
  		}
  		op[2] = 0xc0 | reg
  	} else {
  		// An alternate op is ADDQ. This is handled by GNU gold,
  		// but right now is not generated by the Go compiler:
  		//	ADDQ X(IP), REG  ->  ADDQ $Y, REG
  		// Consider adding support for it here.
  		log.Fatalf("expected TLS IE op to be MOVQ, got %v", op)
  	}
  }
  

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