asm.go

Documentation: cmd/link/internal/amd64

     1  // Inferno utils/6l/asm.c
     2  // https://bitbucket.org/inferno-os/inferno-os/src/master/utils/6l/asm.c
     3  //
     4  //	Copyright © 1994-1999 Lucent Technologies Inc.  All rights reserved.
     5  //	Portions Copyright © 1995-1997 C H Forsyth (forsyth@terzarima.net)
     6  //	Portions Copyright © 1997-1999 Vita Nuova Limited
     7  //	Portions Copyright © 2000-2007 Vita Nuova Holdings Limited (www.vitanuova.com)
     8  //	Portions Copyright © 2004,2006 Bruce Ellis
     9  //	Portions Copyright © 2005-2007 C H Forsyth (forsyth@terzarima.net)
    10  //	Revisions Copyright © 2000-2007 Lucent Technologies Inc. and others
    11  //	Portions Copyright © 2009 The Go Authors. All rights reserved.
    12  //
    13  // Permission is hereby granted, free of charge, to any person obtaining a copy
    14  // of this software and associated documentation files (the "Software"), to deal
    15  // in the Software without restriction, including without limitation the rights
    16  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    17  // copies of the Software, and to permit persons to whom the Software is
    18  // furnished to do so, subject to the following conditions:
    19  //
    20  // The above copyright notice and this permission notice shall be included in
    21  // all copies or substantial portions of the Software.
    22  //
    23  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    24  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    25  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
    26  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    27  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    28  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    29  // THE SOFTWARE.
    30  
    31  package amd64
    32  
    33  import (
    34  	"cmd/internal/objabi"
    35  	"cmd/internal/sys"
    36  	"cmd/link/internal/ld"
    37  	"cmd/link/internal/loader"
    38  	"cmd/link/internal/sym"
    39  	"debug/elf"
    40  	"log"
    41  )
    42  
    43  func PADDR(x uint32) uint32 {
    44  	return x &^ 0x80000000
    45  }
    46  
    47  func gentext(ctxt *ld.Link, ldr *loader.Loader) {
    48  	initfunc, addmoduledata := ld.PrepareAddmoduledata(ctxt)
    49  	if initfunc == nil {
    50  		return
    51  	}
    52  
    53  	o := func(op ...uint8) {
    54  		for _, op1 := range op {
    55  			initfunc.AddUint8(op1)
    56  		}
    57  	}
    58  
    59  	// 0000000000000000 <local.dso_init>:
    60  	//    0:	48 8d 3d 00 00 00 00 	lea    0x0(%rip),%rdi        # 7 <local.dso_init+0x7>
    61  	// 			3: R_X86_64_PC32	runtime.firstmoduledata-0x4
    62  	o(0x48, 0x8d, 0x3d)
    63  	initfunc.AddPCRelPlus(ctxt.Arch, ctxt.Moduledata, 0)
    64  	//    7:	e8 00 00 00 00       	callq  c <local.dso_init+0xc>
    65  	// 			8: R_X86_64_PLT32	runtime.addmoduledata-0x4
    66  	o(0xe8)
    67  	initfunc.AddSymRef(ctxt.Arch, addmoduledata, 0, objabi.R_CALL, 4)
    68  	//    c:	c3                   	retq
    69  	o(0xc3)
    70  }
    71  
    72  func adddynrel(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s loader.Sym, r loader.Reloc, rIdx int) bool {
    73  	targ := r.Sym()
    74  	var targType sym.SymKind
    75  	if targ != 0 {
    76  		targType = ldr.SymType(targ)
    77  	}
    78  
    79  	switch rt := r.Type(); rt {
    80  	default:
    81  		if rt >= objabi.ElfRelocOffset {
    82  			ldr.Errorf(s, "unexpected relocation type %d (%s)", r.Type(), sym.RelocName(target.Arch, r.Type()))
    83  			return false
    84  		}
    85  
    86  		// Handle relocations found in ELF object files.
    87  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_X86_64_PC32):
    88  		if targType == sym.SDYNIMPORT {
    89  			ldr.Errorf(s, "unexpected R_X86_64_PC32 relocation for dynamic symbol %s", ldr.SymName(targ))
    90  		}
    91  		if targType == 0 || targType == sym.SXREF {
    92  			ldr.Errorf(s, "unknown symbol %s in pcrel", ldr.SymName(targ))
    93  		}
    94  		su := ldr.MakeSymbolUpdater(s)
    95  		su.SetRelocType(rIdx, objabi.R_PCREL)
    96  		su.SetRelocAdd(rIdx, r.Add()+4)
    97  		return true
    98  
    99  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_X86_64_PC64):
   100  		if targType == sym.SDYNIMPORT {
   101  			ldr.Errorf(s, "unexpected R_X86_64_PC64 relocation for dynamic symbol %s", ldr.SymName(targ))
   102  		}
   103  		if targType == 0 || targType == sym.SXREF {
   104  			ldr.Errorf(s, "unknown symbol %s in pcrel", ldr.SymName(targ))
   105  		}
   106  		su := ldr.MakeSymbolUpdater(s)
   107  		su.SetRelocType(rIdx, objabi.R_PCREL)
   108  		su.SetRelocAdd(rIdx, r.Add()+8)
   109  		return true
   110  
   111  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_X86_64_PLT32):
   112  		su := ldr.MakeSymbolUpdater(s)
   113  		su.SetRelocType(rIdx, objabi.R_PCREL)
   114  		su.SetRelocAdd(rIdx, r.Add()+4)
   115  		if targType == sym.SDYNIMPORT {
   116  			addpltsym(target, ldr, syms, targ)
   117  			su.SetRelocSym(rIdx, syms.PLT)
   118  			su.SetRelocAdd(rIdx, r.Add()+int64(ldr.SymPlt(targ)))
   119  		}
   120  
   121  		return true
   122  
   123  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_X86_64_GOTPCREL),
   124  		objabi.ElfRelocOffset + objabi.RelocType(elf.R_X86_64_GOTPCRELX),
   125  		objabi.ElfRelocOffset + objabi.RelocType(elf.R_X86_64_REX_GOTPCRELX):
   126  		su := ldr.MakeSymbolUpdater(s)
   127  		if targType != sym.SDYNIMPORT {
   128  			// have symbol
   129  			sData := ldr.Data(s)
   130  			if r.Off() >= 2 && sData[r.Off()-2] == 0x8b {
   131  				su.MakeWritable()
   132  				// turn MOVQ of GOT entry into LEAQ of symbol itself
   133  				writeableData := su.Data()
   134  				writeableData[r.Off()-2] = 0x8d
   135  				su.SetRelocType(rIdx, objabi.R_PCREL)
   136  				su.SetRelocAdd(rIdx, r.Add()+4)
   137  				return true
   138  			}
   139  		}
   140  
   141  		// fall back to using GOT and hope for the best (CMOV*)
   142  		// TODO: just needs relocation, no need to put in .dynsym
   143  		ld.AddGotSym(target, ldr, syms, targ, uint32(elf.R_X86_64_GLOB_DAT))
   144  
   145  		su.SetRelocType(rIdx, objabi.R_PCREL)
   146  		su.SetRelocSym(rIdx, syms.GOT)
   147  		su.SetRelocAdd(rIdx, r.Add()+4+int64(ldr.SymGot(targ)))
   148  		return true
   149  
   150  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_X86_64_64):
   151  		if targType == sym.SDYNIMPORT {
   152  			ldr.Errorf(s, "unexpected R_X86_64_64 relocation for dynamic symbol %s", ldr.SymName(targ))
   153  		}
   154  		su := ldr.MakeSymbolUpdater(s)
   155  		su.SetRelocType(rIdx, objabi.R_ADDR)
   156  		if target.IsPIE() && target.IsInternal() {
   157  			// For internal linking PIE, this R_ADDR relocation cannot
   158  			// be resolved statically. We need to generate a dynamic
   159  			// relocation. Let the code below handle it.
   160  			break
   161  		}
   162  		return true
   163  
   164  	// Handle relocations found in Mach-O object files.
   165  	case objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_UNSIGNED*2 + 0,
   166  		objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_SIGNED*2 + 0,
   167  		objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_BRANCH*2 + 0:
   168  		su := ldr.MakeSymbolUpdater(s)
   169  		su.SetRelocType(rIdx, objabi.R_ADDR)
   170  
   171  		if targType == sym.SDYNIMPORT {
   172  			ldr.Errorf(s, "unexpected reloc for dynamic symbol %s", ldr.SymName(targ))
   173  		}
   174  		if target.IsPIE() && target.IsInternal() {
   175  			// For internal linking PIE, this R_ADDR relocation cannot
   176  			// be resolved statically. We need to generate a dynamic
   177  			// relocation. Let the code below handle it.
   178  			if rt == objabi.MachoRelocOffset+ld.MACHO_X86_64_RELOC_UNSIGNED*2 {
   179  				break
   180  			} else {
   181  				// MACHO_X86_64_RELOC_SIGNED or MACHO_X86_64_RELOC_BRANCH
   182  				// Can this happen? The object is expected to be PIC.
   183  				ldr.Errorf(s, "unsupported relocation for PIE: %v", rt)
   184  			}
   185  		}
   186  		return true
   187  
   188  	case objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_BRANCH*2 + 1:
   189  		if targType == sym.SDYNIMPORT {
   190  			addpltsym(target, ldr, syms, targ)
   191  			su := ldr.MakeSymbolUpdater(s)
   192  			su.SetRelocSym(rIdx, syms.PLT)
   193  			su.SetRelocType(rIdx, objabi.R_PCREL)
   194  			su.SetRelocAdd(rIdx, int64(ldr.SymPlt(targ)))
   195  			return true
   196  		}
   197  		fallthrough
   198  
   199  	case objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_UNSIGNED*2 + 1,
   200  		objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_SIGNED*2 + 1,
   201  		objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_SIGNED_1*2 + 1,
   202  		objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_SIGNED_2*2 + 1,
   203  		objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_SIGNED_4*2 + 1:
   204  		su := ldr.MakeSymbolUpdater(s)
   205  		su.SetRelocType(rIdx, objabi.R_PCREL)
   206  
   207  		if targType == sym.SDYNIMPORT {
   208  			ldr.Errorf(s, "unexpected pc-relative reloc for dynamic symbol %s", ldr.SymName(targ))
   209  		}
   210  		return true
   211  
   212  	case objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_GOT_LOAD*2 + 1:
   213  		if targType != sym.SDYNIMPORT {
   214  			// have symbol
   215  			// turn MOVQ of GOT entry into LEAQ of symbol itself
   216  			sdata := ldr.Data(s)
   217  			if r.Off() < 2 || sdata[r.Off()-2] != 0x8b {
   218  				ldr.Errorf(s, "unexpected GOT_LOAD reloc for non-dynamic symbol %s", ldr.SymName(targ))
   219  				return false
   220  			}
   221  
   222  			su := ldr.MakeSymbolUpdater(s)
   223  			su.MakeWritable()
   224  			sdata = su.Data()
   225  			sdata[r.Off()-2] = 0x8d
   226  			su.SetRelocType(rIdx, objabi.R_PCREL)
   227  			return true
   228  		}
   229  		fallthrough
   230  
   231  	case objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_GOT*2 + 1:
   232  		if targType != sym.SDYNIMPORT {
   233  			ldr.Errorf(s, "unexpected GOT reloc for non-dynamic symbol %s", ldr.SymName(targ))
   234  		}
   235  		ld.AddGotSym(target, ldr, syms, targ, 0)
   236  		su := ldr.MakeSymbolUpdater(s)
   237  		su.SetRelocType(rIdx, objabi.R_PCREL)
   238  		su.SetRelocSym(rIdx, syms.GOT)
   239  		su.SetRelocAdd(rIdx, r.Add()+int64(ldr.SymGot(targ)))
   240  		return true
   241  	}
   242  
   243  	// Reread the reloc to incorporate any changes in type above.
   244  	relocs := ldr.Relocs(s)
   245  	r = relocs.At(rIdx)
   246  
   247  	switch r.Type() {
   248  	case objabi.R_CALL:
   249  		if targType != sym.SDYNIMPORT {
   250  			// nothing to do, the relocation will be laid out in reloc
   251  			return true
   252  		}
   253  		if target.IsExternal() {
   254  			// External linker will do this relocation.
   255  			return true
   256  		}
   257  		// Internal linking, for both ELF and Mach-O.
   258  		// Build a PLT entry and change the relocation target to that entry.
   259  		addpltsym(target, ldr, syms, targ)
   260  		su := ldr.MakeSymbolUpdater(s)
   261  		su.SetRelocSym(rIdx, syms.PLT)
   262  		su.SetRelocAdd(rIdx, int64(ldr.SymPlt(targ)))
   263  		return true
   264  
   265  	case objabi.R_PCREL:
   266  		if targType == sym.SDYNIMPORT && ldr.SymType(s) == sym.STEXT && target.IsDarwin() {
   267  			// Loading the address of a dynamic symbol. Rewrite to use GOT.
   268  			// turn LEAQ symbol address to MOVQ of GOT entry
   269  			if r.Add() != 0 {
   270  				ldr.Errorf(s, "unexpected nonzero addend for dynamic symbol %s", ldr.SymName(targ))
   271  				return false
   272  			}
   273  			su := ldr.MakeSymbolUpdater(s)
   274  			if r.Off() >= 2 && su.Data()[r.Off()-2] == 0x8d {
   275  				su.MakeWritable()
   276  				su.Data()[r.Off()-2] = 0x8b
   277  				if target.IsInternal() {
   278  					ld.AddGotSym(target, ldr, syms, targ, 0)
   279  					su.SetRelocSym(rIdx, syms.GOT)
   280  					su.SetRelocAdd(rIdx, int64(ldr.SymGot(targ)))
   281  				} else {
   282  					su.SetRelocType(rIdx, objabi.R_GOTPCREL)
   283  				}
   284  				return true
   285  			}
   286  			ldr.Errorf(s, "unexpected R_PCREL reloc for dynamic symbol %s: not preceded by LEAQ instruction", ldr.SymName(targ))
   287  		}
   288  
   289  	case objabi.R_ADDR:
   290  		if ldr.SymType(s) == sym.STEXT && target.IsElf() {
   291  			su := ldr.MakeSymbolUpdater(s)
   292  			if target.IsSolaris() {
   293  				addpltsym(target, ldr, syms, targ)
   294  				su.SetRelocSym(rIdx, syms.PLT)
   295  				su.SetRelocAdd(rIdx, r.Add()+int64(ldr.SymPlt(targ)))
   296  				return true
   297  			}
   298  			// The code is asking for the address of an external
   299  			// function. We provide it with the address of the
   300  			// correspondent GOT symbol.
   301  			ld.AddGotSym(target, ldr, syms, targ, uint32(elf.R_X86_64_GLOB_DAT))
   302  
   303  			su.SetRelocSym(rIdx, syms.GOT)
   304  			su.SetRelocAdd(rIdx, r.Add()+int64(ldr.SymGot(targ)))
   305  			return true
   306  		}
   307  
   308  		// Process dynamic relocations for the data sections.
   309  		if target.IsPIE() && target.IsInternal() {
   310  			// When internally linking, generate dynamic relocations
   311  			// for all typical R_ADDR relocations. The exception
   312  			// are those R_ADDR that are created as part of generating
   313  			// the dynamic relocations and must be resolved statically.
   314  			//
   315  			// There are three phases relevant to understanding this:
   316  			//
   317  			//	dodata()  // we are here
   318  			//	address() // symbol address assignment
   319  			//	reloc()   // resolution of static R_ADDR relocs
   320  			//
   321  			// At this point symbol addresses have not been
   322  			// assigned yet (as the final size of the .rela section
   323  			// will affect the addresses), and so we cannot write
   324  			// the Elf64_Rela.r_offset now. Instead we delay it
   325  			// until after the 'address' phase of the linker is
   326  			// complete. We do this via Addaddrplus, which creates
   327  			// a new R_ADDR relocation which will be resolved in
   328  			// the 'reloc' phase.
   329  			//
   330  			// These synthetic static R_ADDR relocs must be skipped
   331  			// now, or else we will be caught in an infinite loop
   332  			// of generating synthetic relocs for our synthetic
   333  			// relocs.
   334  			//
   335  			// Furthermore, the rela sections contain dynamic
   336  			// relocations with R_ADDR relocations on
   337  			// Elf64_Rela.r_offset. This field should contain the
   338  			// symbol offset as determined by reloc(), not the
   339  			// final dynamically linked address as a dynamic
   340  			// relocation would provide.
   341  			switch ldr.SymName(s) {
   342  			case ".dynsym", ".rela", ".rela.plt", ".got.plt", ".dynamic":
   343  				return false
   344  			}
   345  		} else {
   346  			// Either internally linking a static executable,
   347  			// in which case we can resolve these relocations
   348  			// statically in the 'reloc' phase, or externally
   349  			// linking, in which case the relocation will be
   350  			// prepared in the 'reloc' phase and passed to the
   351  			// external linker in the 'asmb' phase.
   352  			if ldr.SymType(s) != sym.SDATA && ldr.SymType(s) != sym.SRODATA {
   353  				break
   354  			}
   355  		}
   356  
   357  		if target.IsElf() {
   358  			// Generate R_X86_64_RELATIVE relocations for best
   359  			// efficiency in the dynamic linker.
   360  			//
   361  			// As noted above, symbol addresses have not been
   362  			// assigned yet, so we can't generate the final reloc
   363  			// entry yet. We ultimately want:
   364  			//
   365  			// r_offset = s + r.Off
   366  			// r_info = R_X86_64_RELATIVE
   367  			// r_addend = targ + r.Add
   368  			//
   369  			// The dynamic linker will set *offset = base address +
   370  			// addend.
   371  			//
   372  			// AddAddrPlus is used for r_offset and r_addend to
   373  			// generate new R_ADDR relocations that will update
   374  			// these fields in the 'reloc' phase.
   375  			rela := ldr.MakeSymbolUpdater(syms.Rela)
   376  			rela.AddAddrPlus(target.Arch, s, int64(r.Off()))
   377  			if r.Siz() == 8 {
   378  				rela.AddUint64(target.Arch, elf.R_INFO(0, uint32(elf.R_X86_64_RELATIVE)))
   379  			} else {
   380  				ldr.Errorf(s, "unexpected relocation for dynamic symbol %s", ldr.SymName(targ))
   381  			}
   382  			rela.AddAddrPlus(target.Arch, targ, int64(r.Add()))
   383  			// Not mark r done here. So we still apply it statically,
   384  			// so in the file content we'll also have the right offset
   385  			// to the relocation target. So it can be examined statically
   386  			// (e.g. go version).
   387  			return true
   388  		}
   389  
   390  		if target.IsDarwin() {
   391  			// Mach-O relocations are a royal pain to lay out.
   392  			// They use a compact stateful bytecode representation.
   393  			// Here we record what are needed and encode them later.
   394  			ld.MachoAddRebase(s, int64(r.Off()))
   395  			// Not mark r done here. So we still apply it statically,
   396  			// so in the file content we'll also have the right offset
   397  			// to the relocation target. So it can be examined statically
   398  			// (e.g. go version).
   399  			return true
   400  		}
   401  	}
   402  
   403  	return false
   404  }
   405  
   406  func elfreloc1(ctxt *ld.Link, out *ld.OutBuf, ldr *loader.Loader, s loader.Sym, r loader.ExtReloc, ri int, sectoff int64) bool {
   407  	out.Write64(uint64(sectoff))
   408  
   409  	elfsym := ld.ElfSymForReloc(ctxt, r.Xsym)
   410  	siz := r.Size
   411  	switch r.Type {
   412  	default:
   413  		return false
   414  	case objabi.R_ADDR, objabi.R_DWARFSECREF:
   415  		if siz == 4 {
   416  			out.Write64(uint64(elf.R_X86_64_32) | uint64(elfsym)<<32)
   417  		} else if siz == 8 {
   418  			out.Write64(uint64(elf.R_X86_64_64) | uint64(elfsym)<<32)
   419  		} else {
   420  			return false
   421  		}
   422  	case objabi.R_TLS_LE:
   423  		if siz == 4 {
   424  			out.Write64(uint64(elf.R_X86_64_TPOFF32) | uint64(elfsym)<<32)
   425  		} else {
   426  			return false
   427  		}
   428  	case objabi.R_TLS_IE:
   429  		if siz == 4 {
   430  			out.Write64(uint64(elf.R_X86_64_GOTTPOFF) | uint64(elfsym)<<32)
   431  		} else {
   432  			return false
   433  		}
   434  	case objabi.R_CALL:
   435  		if siz == 4 {
   436  			if ldr.SymType(r.Xsym) == sym.SDYNIMPORT {
   437  				out.Write64(uint64(elf.R_X86_64_PLT32) | uint64(elfsym)<<32)
   438  			} else {
   439  				out.Write64(uint64(elf.R_X86_64_PC32) | uint64(elfsym)<<32)
   440  			}
   441  		} else {
   442  			return false
   443  		}
   444  	case objabi.R_PCREL:
   445  		if siz == 4 {
   446  			if ldr.SymType(r.Xsym) == sym.SDYNIMPORT && ldr.SymElfType(r.Xsym) == elf.STT_FUNC {
   447  				out.Write64(uint64(elf.R_X86_64_PLT32) | uint64(elfsym)<<32)
   448  			} else {
   449  				out.Write64(uint64(elf.R_X86_64_PC32) | uint64(elfsym)<<32)
   450  			}
   451  		} else {
   452  			return false
   453  		}
   454  	case objabi.R_GOTPCREL:
   455  		if siz == 4 {
   456  			out.Write64(uint64(elf.R_X86_64_GOTPCREL) | uint64(elfsym)<<32)
   457  		} else {
   458  			return false
   459  		}
   460  	}
   461  
   462  	out.Write64(uint64(r.Xadd))
   463  	return true
   464  }
   465  
   466  func machoreloc1(arch *sys.Arch, out *ld.OutBuf, ldr *loader.Loader, s loader.Sym, r loader.ExtReloc, sectoff int64) bool {
   467  	var v uint32
   468  
   469  	rs := r.Xsym
   470  	rt := r.Type
   471  
   472  	if !ldr.SymType(s).IsDWARF() {
   473  		if ldr.SymDynid(rs) < 0 {
   474  			ldr.Errorf(s, "reloc %d (%s) to non-macho symbol %s type=%d (%s)", rt, sym.RelocName(arch, rt), ldr.SymName(rs), ldr.SymType(rs), ldr.SymType(rs))
   475  			return false
   476  		}
   477  
   478  		v = uint32(ldr.SymDynid(rs))
   479  		v |= 1 << 27 // external relocation
   480  	} else {
   481  		v = uint32(ldr.SymSect(rs).Extnum)
   482  		if v == 0 {
   483  			ldr.Errorf(s, "reloc %d (%s) to symbol %s in non-macho section %s type=%d (%s)", rt, sym.RelocName(arch, rt), ldr.SymName(rs), ldr.SymSect(rs).Name, ldr.SymType(rs), ldr.SymType(rs))
   484  			return false
   485  		}
   486  	}
   487  
   488  	switch rt {
   489  	default:
   490  		return false
   491  
   492  	case objabi.R_ADDR:
   493  		v |= ld.MACHO_X86_64_RELOC_UNSIGNED << 28
   494  
   495  	case objabi.R_CALL:
   496  		v |= 1 << 24 // pc-relative bit
   497  		v |= ld.MACHO_X86_64_RELOC_BRANCH << 28
   498  
   499  		// NOTE: Only works with 'external' relocation. Forced above.
   500  	case objabi.R_PCREL:
   501  		v |= 1 << 24 // pc-relative bit
   502  		v |= ld.MACHO_X86_64_RELOC_SIGNED << 28
   503  	case objabi.R_GOTPCREL:
   504  		v |= 1 << 24 // pc-relative bit
   505  		v |= ld.MACHO_X86_64_RELOC_GOT_LOAD << 28
   506  	}
   507  
   508  	switch r.Size {
   509  	default:
   510  		return false
   511  
   512  	case 1:
   513  		v |= 0 << 25
   514  
   515  	case 2:
   516  		v |= 1 << 25
   517  
   518  	case 4:
   519  		v |= 2 << 25
   520  
   521  	case 8:
   522  		v |= 3 << 25
   523  	}
   524  
   525  	out.Write32(uint32(sectoff))
   526  	out.Write32(v)
   527  	return true
   528  }
   529  
   530  func pereloc1(arch *sys.Arch, out *ld.OutBuf, ldr *loader.Loader, s loader.Sym, r loader.ExtReloc, sectoff int64) bool {
   531  	var v uint32
   532  
   533  	rs := r.Xsym
   534  	rt := r.Type
   535  
   536  	if ldr.SymDynid(rs) < 0 {
   537  		ldr.Errorf(s, "reloc %d (%s) to non-coff symbol %s type=%d (%s)", rt, sym.RelocName(arch, rt), ldr.SymName(rs), ldr.SymType(rs), ldr.SymType(rs))
   538  		return false
   539  	}
   540  
   541  	out.Write32(uint32(sectoff))
   542  	out.Write32(uint32(ldr.SymDynid(rs)))
   543  
   544  	switch rt {
   545  	default:
   546  		return false
   547  
   548  	case objabi.R_DWARFSECREF:
   549  		v = ld.IMAGE_REL_AMD64_SECREL
   550  
   551  	case objabi.R_ADDR:
   552  		if r.Size == 8 {
   553  			v = ld.IMAGE_REL_AMD64_ADDR64
   554  		} else {
   555  			v = ld.IMAGE_REL_AMD64_ADDR32
   556  		}
   557  
   558  	case objabi.R_PEIMAGEOFF:
   559  		v = ld.IMAGE_REL_AMD64_ADDR32NB
   560  
   561  	case objabi.R_CALL,
   562  		objabi.R_PCREL:
   563  		v = ld.IMAGE_REL_AMD64_REL32
   564  	}
   565  
   566  	out.Write16(uint16(v))
   567  
   568  	return true
   569  }
   570  
   571  func archreloc(*ld.Target, *loader.Loader, *ld.ArchSyms, loader.Reloc, loader.Sym, int64) (int64, int, bool) {
   572  	return -1, 0, false
   573  }
   574  
   575  func archrelocvariant(*ld.Target, *loader.Loader, loader.Reloc, sym.RelocVariant, loader.Sym, int64, []byte) int64 {
   576  	log.Fatalf("unexpected relocation variant")
   577  	return -1
   578  }
   579  
   580  func elfsetupplt(ctxt *ld.Link, ldr *loader.Loader, plt, got *loader.SymbolBuilder, dynamic loader.Sym) {
   581  	if plt.Size() == 0 {
   582  		// pushq got+8(IP)
   583  		plt.AddUint8(0xff)
   584  
   585  		plt.AddUint8(0x35)
   586  		plt.AddPCRelPlus(ctxt.Arch, got.Sym(), 8)
   587  
   588  		// jmpq got+16(IP)
   589  		plt.AddUint8(0xff)
   590  
   591  		plt.AddUint8(0x25)
   592  		plt.AddPCRelPlus(ctxt.Arch, got.Sym(), 16)
   593  
   594  		// nopl 0(AX)
   595  		plt.AddUint32(ctxt.Arch, 0x00401f0f)
   596  
   597  		// assume got->size == 0 too
   598  		got.AddAddrPlus(ctxt.Arch, dynamic, 0)
   599  
   600  		got.AddUint64(ctxt.Arch, 0)
   601  		got.AddUint64(ctxt.Arch, 0)
   602  	}
   603  }
   604  
   605  func addpltsym(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s loader.Sym) {
   606  	if ldr.SymPlt(s) >= 0 {
   607  		return
   608  	}
   609  
   610  	ld.Adddynsym(ldr, target, syms, s)
   611  
   612  	if target.IsElf() {
   613  		plt := ldr.MakeSymbolUpdater(syms.PLT)
   614  		got := ldr.MakeSymbolUpdater(syms.GOTPLT)
   615  		rela := ldr.MakeSymbolUpdater(syms.RelaPLT)
   616  		if plt.Size() == 0 {
   617  			panic("plt is not set up")
   618  		}
   619  
   620  		// jmpq *got+size(IP)
   621  		plt.AddUint8(0xff)
   622  
   623  		plt.AddUint8(0x25)
   624  		plt.AddPCRelPlus(target.Arch, got.Sym(), got.Size())
   625  
   626  		// add to got: pointer to current pos in plt
   627  		got.AddAddrPlus(target.Arch, plt.Sym(), plt.Size())
   628  
   629  		// pushq $x
   630  		plt.AddUint8(0x68)
   631  
   632  		plt.AddUint32(target.Arch, uint32((got.Size()-24-8)/8))
   633  
   634  		// jmpq .plt
   635  		plt.AddUint8(0xe9)
   636  
   637  		plt.AddUint32(target.Arch, uint32(-(plt.Size() + 4)))
   638  
   639  		// rela
   640  		rela.AddAddrPlus(target.Arch, got.Sym(), got.Size()-8)
   641  
   642  		sDynid := ldr.SymDynid(s)
   643  		rela.AddUint64(target.Arch, elf.R_INFO(uint32(sDynid), uint32(elf.R_X86_64_JMP_SLOT)))
   644  		rela.AddUint64(target.Arch, 0)
   645  
   646  		ldr.SetPlt(s, int32(plt.Size()-16))
   647  	} else if target.IsDarwin() {
   648  		ld.AddGotSym(target, ldr, syms, s, 0)
   649  
   650  		sDynid := ldr.SymDynid(s)
   651  		lep := ldr.MakeSymbolUpdater(syms.LinkEditPLT)
   652  		lep.AddUint32(target.Arch, uint32(sDynid))
   653  
   654  		plt := ldr.MakeSymbolUpdater(syms.PLT)
   655  		ldr.SetPlt(s, int32(plt.Size()))
   656  
   657  		// jmpq *got+size(IP)
   658  		plt.AddUint8(0xff)
   659  		plt.AddUint8(0x25)
   660  		plt.AddPCRelPlus(target.Arch, syms.GOT, int64(ldr.SymGot(s)))
   661  	} else {
   662  		ldr.Errorf(s, "addpltsym: unsupported binary format")
   663  	}
   664  }
   665  
   666  func tlsIEtoLE(P []byte, off, size int) {
   667  	// Transform the PC-relative instruction into a constant load.
   668  	// That is,
   669  	//
   670  	//	MOVQ X(IP), REG  ->  MOVQ $Y, REG
   671  	//
   672  	// To determine the instruction and register, we study the op codes.
   673  	// Consult an AMD64 instruction encoding guide to decipher this.
   674  	if off < 3 {
   675  		log.Fatal("R_X86_64_GOTTPOFF reloc not preceded by MOVQ or ADDQ instruction")
   676  	}
   677  	op := P[off-3 : off]
   678  	reg := op[2] >> 3
   679  
   680  	if op[1] == 0x8b || reg == 4 {
   681  		// MOVQ
   682  		if op[0] == 0x4c {
   683  			op[0] = 0x49
   684  		} else if size == 4 && op[0] == 0x44 {
   685  			op[0] = 0x41
   686  		}
   687  		if op[1] == 0x8b {
   688  			op[1] = 0xc7
   689  		} else {
   690  			op[1] = 0x81 // special case for SP
   691  		}
   692  		op[2] = 0xc0 | reg
   693  	} else {
   694  		// An alternate op is ADDQ. This is handled by GNU gold,
   695  		// but right now is not generated by the Go compiler:
   696  		//	ADDQ X(IP), REG  ->  ADDQ $Y, REG
   697  		// Consider adding support for it here.
   698  		log.Fatalf("expected TLS IE op to be MOVQ, got %v", op)
   699  	}
   700  }
   701
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