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

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package ld
     6  
     7  import (
     8  	"bytes"
     9  	"cmd/internal/codesign"
    10  	"cmd/internal/objabi"
    11  	"cmd/internal/sys"
    12  	"cmd/link/internal/loader"
    13  	"cmd/link/internal/sym"
    14  	"debug/macho"
    15  	"encoding/binary"
    16  	"fmt"
    17  	"internal/buildcfg"
    18  	"io"
    19  	"os"
    20  	"sort"
    21  	"strings"
    22  	"unsafe"
    23  )
    24  
    25  type MachoHdr struct {
    26  	cpu    uint32
    27  	subcpu uint32
    28  }
    29  
    30  type MachoSect struct {
    31  	name    string
    32  	segname string
    33  	addr    uint64
    34  	size    uint64
    35  	off     uint32
    36  	align   uint32
    37  	reloc   uint32
    38  	nreloc  uint32
    39  	flag    uint32
    40  	res1    uint32
    41  	res2    uint32
    42  }
    43  
    44  type MachoSeg struct {
    45  	name       string
    46  	vsize      uint64
    47  	vaddr      uint64
    48  	fileoffset uint64
    49  	filesize   uint64
    50  	prot1      uint32
    51  	prot2      uint32
    52  	nsect      uint32
    53  	msect      uint32
    54  	sect       []MachoSect
    55  	flag       uint32
    56  }
    57  
    58  // MachoPlatformLoad represents a LC_VERSION_MIN_* or
    59  // LC_BUILD_VERSION load command.
    60  type MachoPlatformLoad struct {
    61  	platform MachoPlatform // One of PLATFORM_* constants.
    62  	cmd      MachoLoad
    63  }
    64  
    65  type MachoLoad struct {
    66  	type_ uint32
    67  	data  []uint32
    68  }
    69  
    70  type MachoPlatform int
    71  
    72  /*
    73   * Total amount of space to reserve at the start of the file
    74   * for Header, PHeaders, and SHeaders.
    75   * May waste some.
    76   */
    77  const (
    78  	INITIAL_MACHO_HEADR = 4 * 1024
    79  )
    80  
    81  const (
    82  	MACHO_CPU_AMD64                      = 1<<24 | 7
    83  	MACHO_CPU_386                        = 7
    84  	MACHO_SUBCPU_X86                     = 3
    85  	MACHO_CPU_ARM                        = 12
    86  	MACHO_SUBCPU_ARM                     = 0
    87  	MACHO_SUBCPU_ARMV7                   = 9
    88  	MACHO_CPU_ARM64                      = 1<<24 | 12
    89  	MACHO_SUBCPU_ARM64_ALL               = 0
    90  	MACHO_SUBCPU_ARM64_V8                = 1
    91  	MACHO_SUBCPU_ARM64E                  = 2
    92  	MACHO32SYMSIZE                       = 12
    93  	MACHO64SYMSIZE                       = 16
    94  	MACHO_X86_64_RELOC_UNSIGNED          = 0
    95  	MACHO_X86_64_RELOC_SIGNED            = 1
    96  	MACHO_X86_64_RELOC_BRANCH            = 2
    97  	MACHO_X86_64_RELOC_GOT_LOAD          = 3
    98  	MACHO_X86_64_RELOC_GOT               = 4
    99  	MACHO_X86_64_RELOC_SUBTRACTOR        = 5
   100  	MACHO_X86_64_RELOC_SIGNED_1          = 6
   101  	MACHO_X86_64_RELOC_SIGNED_2          = 7
   102  	MACHO_X86_64_RELOC_SIGNED_4          = 8
   103  	MACHO_ARM_RELOC_VANILLA              = 0
   104  	MACHO_ARM_RELOC_PAIR                 = 1
   105  	MACHO_ARM_RELOC_SECTDIFF             = 2
   106  	MACHO_ARM_RELOC_BR24                 = 5
   107  	MACHO_ARM64_RELOC_UNSIGNED           = 0
   108  	MACHO_ARM64_RELOC_BRANCH26           = 2
   109  	MACHO_ARM64_RELOC_PAGE21             = 3
   110  	MACHO_ARM64_RELOC_PAGEOFF12          = 4
   111  	MACHO_ARM64_RELOC_GOT_LOAD_PAGE21    = 5
   112  	MACHO_ARM64_RELOC_GOT_LOAD_PAGEOFF12 = 6
   113  	MACHO_ARM64_RELOC_ADDEND             = 10
   114  	MACHO_GENERIC_RELOC_VANILLA          = 0
   115  	MACHO_FAKE_GOTPCREL                  = 100
   116  )
   117  
   118  const (
   119  	MH_MAGIC    = 0xfeedface
   120  	MH_MAGIC_64 = 0xfeedfacf
   121  
   122  	MH_OBJECT  = 0x1
   123  	MH_EXECUTE = 0x2
   124  
   125  	MH_NOUNDEFS = 0x1
   126  	MH_DYLDLINK = 0x4
   127  	MH_PIE      = 0x200000
   128  )
   129  
   130  const (
   131  	LC_SEGMENT                  = 0x1
   132  	LC_SYMTAB                   = 0x2
   133  	LC_SYMSEG                   = 0x3
   134  	LC_THREAD                   = 0x4
   135  	LC_UNIXTHREAD               = 0x5
   136  	LC_LOADFVMLIB               = 0x6
   137  	LC_IDFVMLIB                 = 0x7
   138  	LC_IDENT                    = 0x8
   139  	LC_FVMFILE                  = 0x9
   140  	LC_PREPAGE                  = 0xa
   141  	LC_DYSYMTAB                 = 0xb
   142  	LC_LOAD_DYLIB               = 0xc
   143  	LC_ID_DYLIB                 = 0xd
   144  	LC_LOAD_DYLINKER            = 0xe
   145  	LC_ID_DYLINKER              = 0xf
   146  	LC_PREBOUND_DYLIB           = 0x10
   147  	LC_ROUTINES                 = 0x11
   148  	LC_SUB_FRAMEWORK            = 0x12
   149  	LC_SUB_UMBRELLA             = 0x13
   150  	LC_SUB_CLIENT               = 0x14
   151  	LC_SUB_LIBRARY              = 0x15
   152  	LC_TWOLEVEL_HINTS           = 0x16
   153  	LC_PREBIND_CKSUM            = 0x17
   154  	LC_LOAD_WEAK_DYLIB          = 0x80000018
   155  	LC_SEGMENT_64               = 0x19
   156  	LC_ROUTINES_64              = 0x1a
   157  	LC_UUID                     = 0x1b
   158  	LC_RPATH                    = 0x8000001c
   159  	LC_CODE_SIGNATURE           = 0x1d
   160  	LC_SEGMENT_SPLIT_INFO       = 0x1e
   161  	LC_REEXPORT_DYLIB           = 0x8000001f
   162  	LC_LAZY_LOAD_DYLIB          = 0x20
   163  	LC_ENCRYPTION_INFO          = 0x21
   164  	LC_DYLD_INFO                = 0x22
   165  	LC_DYLD_INFO_ONLY           = 0x80000022
   166  	LC_LOAD_UPWARD_DYLIB        = 0x80000023
   167  	LC_VERSION_MIN_MACOSX       = 0x24
   168  	LC_VERSION_MIN_IPHONEOS     = 0x25
   169  	LC_FUNCTION_STARTS          = 0x26
   170  	LC_DYLD_ENVIRONMENT         = 0x27
   171  	LC_MAIN                     = 0x80000028
   172  	LC_DATA_IN_CODE             = 0x29
   173  	LC_SOURCE_VERSION           = 0x2A
   174  	LC_DYLIB_CODE_SIGN_DRS      = 0x2B
   175  	LC_ENCRYPTION_INFO_64       = 0x2C
   176  	LC_LINKER_OPTION            = 0x2D
   177  	LC_LINKER_OPTIMIZATION_HINT = 0x2E
   178  	LC_VERSION_MIN_TVOS         = 0x2F
   179  	LC_VERSION_MIN_WATCHOS      = 0x30
   180  	LC_VERSION_NOTE             = 0x31
   181  	LC_BUILD_VERSION            = 0x32
   182  	LC_DYLD_EXPORTS_TRIE        = 0x80000033
   183  	LC_DYLD_CHAINED_FIXUPS      = 0x80000034
   184  )
   185  
   186  const (
   187  	S_REGULAR                  = 0x0
   188  	S_ZEROFILL                 = 0x1
   189  	S_NON_LAZY_SYMBOL_POINTERS = 0x6
   190  	S_SYMBOL_STUBS             = 0x8
   191  	S_MOD_INIT_FUNC_POINTERS   = 0x9
   192  	S_ATTR_PURE_INSTRUCTIONS   = 0x80000000
   193  	S_ATTR_DEBUG               = 0x02000000
   194  	S_ATTR_SOME_INSTRUCTIONS   = 0x00000400
   195  )
   196  
   197  const (
   198  	PLATFORM_MACOS    MachoPlatform = 1
   199  	PLATFORM_IOS      MachoPlatform = 2
   200  	PLATFORM_TVOS     MachoPlatform = 3
   201  	PLATFORM_WATCHOS  MachoPlatform = 4
   202  	PLATFORM_BRIDGEOS MachoPlatform = 5
   203  )
   204  
   205  // rebase table opcode
   206  const (
   207  	REBASE_TYPE_POINTER         = 1
   208  	REBASE_TYPE_TEXT_ABSOLUTE32 = 2
   209  	REBASE_TYPE_TEXT_PCREL32    = 3
   210  
   211  	REBASE_OPCODE_MASK                               = 0xF0
   212  	REBASE_IMMEDIATE_MASK                            = 0x0F
   213  	REBASE_OPCODE_DONE                               = 0x00
   214  	REBASE_OPCODE_SET_TYPE_IMM                       = 0x10
   215  	REBASE_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB        = 0x20
   216  	REBASE_OPCODE_ADD_ADDR_ULEB                      = 0x30
   217  	REBASE_OPCODE_ADD_ADDR_IMM_SCALED                = 0x40
   218  	REBASE_OPCODE_DO_REBASE_IMM_TIMES                = 0x50
   219  	REBASE_OPCODE_DO_REBASE_ULEB_TIMES               = 0x60
   220  	REBASE_OPCODE_DO_REBASE_ADD_ADDR_ULEB            = 0x70
   221  	REBASE_OPCODE_DO_REBASE_ULEB_TIMES_SKIPPING_ULEB = 0x80
   222  )
   223  
   224  // bind table opcode
   225  const (
   226  	BIND_TYPE_POINTER         = 1
   227  	BIND_TYPE_TEXT_ABSOLUTE32 = 2
   228  	BIND_TYPE_TEXT_PCREL32    = 3
   229  
   230  	BIND_SPECIAL_DYLIB_SELF            = 0
   231  	BIND_SPECIAL_DYLIB_MAIN_EXECUTABLE = -1
   232  	BIND_SPECIAL_DYLIB_FLAT_LOOKUP     = -2
   233  	BIND_SPECIAL_DYLIB_WEAK_LOOKUP     = -3
   234  
   235  	BIND_OPCODE_MASK                                         = 0xF0
   236  	BIND_IMMEDIATE_MASK                                      = 0x0F
   237  	BIND_OPCODE_DONE                                         = 0x00
   238  	BIND_OPCODE_SET_DYLIB_ORDINAL_IMM                        = 0x10
   239  	BIND_OPCODE_SET_DYLIB_ORDINAL_ULEB                       = 0x20
   240  	BIND_OPCODE_SET_DYLIB_SPECIAL_IMM                        = 0x30
   241  	BIND_OPCODE_SET_SYMBOL_TRAILING_FLAGS_IMM                = 0x40
   242  	BIND_OPCODE_SET_TYPE_IMM                                 = 0x50
   243  	BIND_OPCODE_SET_ADDEND_SLEB                              = 0x60
   244  	BIND_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB                  = 0x70
   245  	BIND_OPCODE_ADD_ADDR_ULEB                                = 0x80
   246  	BIND_OPCODE_DO_BIND                                      = 0x90
   247  	BIND_OPCODE_DO_BIND_ADD_ADDR_ULEB                        = 0xA0
   248  	BIND_OPCODE_DO_BIND_ADD_ADDR_IMM_SCALED                  = 0xB0
   249  	BIND_OPCODE_DO_BIND_ULEB_TIMES_SKIPPING_ULEB             = 0xC0
   250  	BIND_OPCODE_THREADED                                     = 0xD0
   251  	BIND_SUBOPCODE_THREADED_SET_BIND_ORDINAL_TABLE_SIZE_ULEB = 0x00
   252  	BIND_SUBOPCODE_THREADED_APPLY                            = 0x01
   253  )
   254  
   255  const machoHeaderSize64 = 8 * 4 // size of 64-bit Mach-O header
   256  
   257  // Mach-O file writing
   258  // https://developer.apple.com/mac/library/DOCUMENTATION/DeveloperTools/Conceptual/MachORuntime/Reference/reference.html
   259  
   260  var machohdr MachoHdr
   261  
   262  var load []MachoLoad
   263  
   264  var machoPlatform MachoPlatform
   265  
   266  var seg [16]MachoSeg
   267  
   268  var nseg int
   269  
   270  var ndebug int
   271  
   272  var nsect int
   273  
   274  const (
   275  	SymKindLocal = 0 + iota
   276  	SymKindExtdef
   277  	SymKindUndef
   278  	NumSymKind
   279  )
   280  
   281  var nkind [NumSymKind]int
   282  
   283  var sortsym []loader.Sym
   284  
   285  var nsortsym int
   286  
   287  // Amount of space left for adding load commands
   288  // that refer to dynamic libraries. Because these have
   289  // to go in the Mach-O header, we can't just pick a
   290  // "big enough" header size. The initial header is
   291  // one page, the non-dynamic library stuff takes
   292  // up about 1300 bytes; we overestimate that as 2k.
   293  var loadBudget = INITIAL_MACHO_HEADR - 2*1024
   294  
   295  func getMachoHdr() *MachoHdr {
   296  	return &machohdr
   297  }
   298  
   299  func newMachoLoad(arch *sys.Arch, type_ uint32, ndata uint32) *MachoLoad {
   300  	if arch.PtrSize == 8 && (ndata&1 != 0) {
   301  		ndata++
   302  	}
   303  
   304  	load = append(load, MachoLoad{})
   305  	l := &load[len(load)-1]
   306  	l.type_ = type_
   307  	l.data = make([]uint32, ndata)
   308  	return l
   309  }
   310  
   311  func newMachoSeg(name string, msect int) *MachoSeg {
   312  	if nseg >= len(seg) {
   313  		Exitf("too many segs")
   314  	}
   315  
   316  	s := &seg[nseg]
   317  	nseg++
   318  	s.name = name
   319  	s.msect = uint32(msect)
   320  	s.sect = make([]MachoSect, msect)
   321  	return s
   322  }
   323  
   324  func newMachoSect(seg *MachoSeg, name string, segname string) *MachoSect {
   325  	if seg.nsect >= seg.msect {
   326  		Exitf("too many sects in segment %s", seg.name)
   327  	}
   328  
   329  	s := &seg.sect[seg.nsect]
   330  	seg.nsect++
   331  	s.name = name
   332  	s.segname = segname
   333  	nsect++
   334  	return s
   335  }
   336  
   337  // Generic linking code.
   338  
   339  var dylib []string
   340  
   341  var linkoff int64
   342  
   343  func machowrite(ctxt *Link, arch *sys.Arch, out *OutBuf, linkmode LinkMode) int {
   344  	o1 := out.Offset()
   345  
   346  	loadsize := 4 * 4 * ndebug
   347  	for i := range load {
   348  		loadsize += 4 * (len(load[i].data) + 2)
   349  	}
   350  	if arch.PtrSize == 8 {
   351  		loadsize += 18 * 4 * nseg
   352  		loadsize += 20 * 4 * nsect
   353  	} else {
   354  		loadsize += 14 * 4 * nseg
   355  		loadsize += 17 * 4 * nsect
   356  	}
   357  
   358  	if arch.PtrSize == 8 {
   359  		out.Write32(MH_MAGIC_64)
   360  	} else {
   361  		out.Write32(MH_MAGIC)
   362  	}
   363  	out.Write32(machohdr.cpu)
   364  	out.Write32(machohdr.subcpu)
   365  	if linkmode == LinkExternal {
   366  		out.Write32(MH_OBJECT) /* file type - mach object */
   367  	} else {
   368  		out.Write32(MH_EXECUTE) /* file type - mach executable */
   369  	}
   370  	out.Write32(uint32(len(load)) + uint32(nseg) + uint32(ndebug))
   371  	out.Write32(uint32(loadsize))
   372  	flags := uint32(0)
   373  	if nkind[SymKindUndef] == 0 {
   374  		flags |= MH_NOUNDEFS
   375  	}
   376  	if ctxt.IsPIE() && linkmode == LinkInternal {
   377  		flags |= MH_PIE | MH_DYLDLINK
   378  	}
   379  	out.Write32(flags) /* flags */
   380  	if arch.PtrSize == 8 {
   381  		out.Write32(0) /* reserved */
   382  	}
   383  
   384  	for i := 0; i < nseg; i++ {
   385  		s := &seg[i]
   386  		if arch.PtrSize == 8 {
   387  			out.Write32(LC_SEGMENT_64)
   388  			out.Write32(72 + 80*s.nsect)
   389  			out.WriteStringN(s.name, 16)
   390  			out.Write64(s.vaddr)
   391  			out.Write64(s.vsize)
   392  			out.Write64(s.fileoffset)
   393  			out.Write64(s.filesize)
   394  			out.Write32(s.prot1)
   395  			out.Write32(s.prot2)
   396  			out.Write32(s.nsect)
   397  			out.Write32(s.flag)
   398  		} else {
   399  			out.Write32(LC_SEGMENT)
   400  			out.Write32(56 + 68*s.nsect)
   401  			out.WriteStringN(s.name, 16)
   402  			out.Write32(uint32(s.vaddr))
   403  			out.Write32(uint32(s.vsize))
   404  			out.Write32(uint32(s.fileoffset))
   405  			out.Write32(uint32(s.filesize))
   406  			out.Write32(s.prot1)
   407  			out.Write32(s.prot2)
   408  			out.Write32(s.nsect)
   409  			out.Write32(s.flag)
   410  		}
   411  
   412  		for j := uint32(0); j < s.nsect; j++ {
   413  			t := &s.sect[j]
   414  			if arch.PtrSize == 8 {
   415  				out.WriteStringN(t.name, 16)
   416  				out.WriteStringN(t.segname, 16)
   417  				out.Write64(t.addr)
   418  				out.Write64(t.size)
   419  				out.Write32(t.off)
   420  				out.Write32(t.align)
   421  				out.Write32(t.reloc)
   422  				out.Write32(t.nreloc)
   423  				out.Write32(t.flag)
   424  				out.Write32(t.res1) /* reserved */
   425  				out.Write32(t.res2) /* reserved */
   426  				out.Write32(0)      /* reserved */
   427  			} else {
   428  				out.WriteStringN(t.name, 16)
   429  				out.WriteStringN(t.segname, 16)
   430  				out.Write32(uint32(t.addr))
   431  				out.Write32(uint32(t.size))
   432  				out.Write32(t.off)
   433  				out.Write32(t.align)
   434  				out.Write32(t.reloc)
   435  				out.Write32(t.nreloc)
   436  				out.Write32(t.flag)
   437  				out.Write32(t.res1) /* reserved */
   438  				out.Write32(t.res2) /* reserved */
   439  			}
   440  		}
   441  	}
   442  
   443  	for i := range load {
   444  		l := &load[i]
   445  		out.Write32(l.type_)
   446  		out.Write32(4 * (uint32(len(l.data)) + 2))
   447  		for j := 0; j < len(l.data); j++ {
   448  			out.Write32(l.data[j])
   449  		}
   450  	}
   451  
   452  	return int(out.Offset() - o1)
   453  }
   454  
   455  func (ctxt *Link) domacho() {
   456  	if *FlagD {
   457  		return
   458  	}
   459  
   460  	// Copy platform load command.
   461  	for _, h := range hostobj {
   462  		load, err := hostobjMachoPlatform(&h)
   463  		if err != nil {
   464  			Exitf("%v", err)
   465  		}
   466  		if load != nil {
   467  			machoPlatform = load.platform
   468  			ml := newMachoLoad(ctxt.Arch, load.cmd.type_, uint32(len(load.cmd.data)))
   469  			copy(ml.data, load.cmd.data)
   470  			break
   471  		}
   472  	}
   473  	if machoPlatform == 0 {
   474  		machoPlatform = PLATFORM_MACOS
   475  		if buildcfg.GOOS == "ios" {
   476  			machoPlatform = PLATFORM_IOS
   477  		}
   478  		if ctxt.LinkMode == LinkInternal && machoPlatform == PLATFORM_MACOS {
   479  			var version uint32
   480  			switch ctxt.Arch.Family {
   481  			case sys.AMD64:
   482  				// This must be fairly recent for Apple signing (go.dev/issue/30488).
   483  				// Having too old a version here was also implicated in some problems
   484  				// calling into macOS libraries (go.dev/issue/56784).
   485  				// In general this can be the most recent supported macOS version.
   486  				version = 10<<16 | 13<<8 | 0<<0 // 10.13.0
   487  			case sys.ARM64:
   488  				version = 11<<16 | 0<<8 | 0<<0 // 11.0.0
   489  			}
   490  			ml := newMachoLoad(ctxt.Arch, LC_BUILD_VERSION, 4)
   491  			ml.data[0] = uint32(machoPlatform)
   492  			ml.data[1] = version // OS version
   493  			ml.data[2] = version // SDK version
   494  			ml.data[3] = 0       // ntools
   495  		}
   496  	}
   497  
   498  	// empirically, string table must begin with " \x00".
   499  	s := ctxt.loader.LookupOrCreateSym(".machosymstr", 0)
   500  	sb := ctxt.loader.MakeSymbolUpdater(s)
   501  
   502  	sb.SetType(sym.SMACHOSYMSTR)
   503  	sb.SetReachable(true)
   504  	sb.AddUint8(' ')
   505  	sb.AddUint8('\x00')
   506  
   507  	s = ctxt.loader.LookupOrCreateSym(".machosymtab", 0)
   508  	sb = ctxt.loader.MakeSymbolUpdater(s)
   509  	sb.SetType(sym.SMACHOSYMTAB)
   510  	sb.SetReachable(true)
   511  
   512  	if ctxt.IsInternal() {
   513  		s = ctxt.loader.LookupOrCreateSym(".plt", 0) // will be __symbol_stub
   514  		sb = ctxt.loader.MakeSymbolUpdater(s)
   515  		sb.SetType(sym.SMACHOPLT)
   516  		sb.SetReachable(true)
   517  
   518  		s = ctxt.loader.LookupOrCreateSym(".got", 0) // will be __nl_symbol_ptr
   519  		sb = ctxt.loader.MakeSymbolUpdater(s)
   520  		sb.SetType(sym.SMACHOGOT)
   521  		sb.SetReachable(true)
   522  		sb.SetAlign(4)
   523  
   524  		s = ctxt.loader.LookupOrCreateSym(".linkedit.plt", 0) // indirect table for .plt
   525  		sb = ctxt.loader.MakeSymbolUpdater(s)
   526  		sb.SetType(sym.SMACHOINDIRECTPLT)
   527  		sb.SetReachable(true)
   528  
   529  		s = ctxt.loader.LookupOrCreateSym(".linkedit.got", 0) // indirect table for .got
   530  		sb = ctxt.loader.MakeSymbolUpdater(s)
   531  		sb.SetType(sym.SMACHOINDIRECTGOT)
   532  		sb.SetReachable(true)
   533  	}
   534  
   535  	// Add a dummy symbol that will become the __asm marker section.
   536  	if ctxt.IsExternal() {
   537  		s = ctxt.loader.LookupOrCreateSym(".llvmasm", 0)
   538  		sb = ctxt.loader.MakeSymbolUpdater(s)
   539  		sb.SetType(sym.SMACHO)
   540  		sb.SetReachable(true)
   541  		sb.AddUint8(0)
   542  	}
   543  
   544  	// Un-export runtime symbols from plugins. Since the runtime
   545  	// is included in both the main binary and each plugin, these
   546  	// symbols appear in both images. If we leave them exported in
   547  	// the plugin, then the dynamic linker will resolve
   548  	// relocations to these functions in the plugin's functab to
   549  	// point to the main image, causing the runtime to think the
   550  	// plugin's functab is corrupted. By unexporting them, these
   551  	// become static references, which are resolved to the
   552  	// plugin's text.
   553  	//
   554  	// It would be better to omit the runtime from plugins. (Using
   555  	// relative PCs in the functab instead of relocations would
   556  	// also address this.)
   557  	//
   558  	// See issue #18190.
   559  	if ctxt.BuildMode == BuildModePlugin {
   560  		for _, name := range []string{"_cgo_topofstack", "__cgo_topofstack", "_cgo_panic", "crosscall2"} {
   561  			// Most of these are data symbols or C
   562  			// symbols, so they have symbol version 0.
   563  			ver := 0
   564  			// _cgo_panic is a Go function, so it uses ABIInternal.
   565  			if name == "_cgo_panic" {
   566  				ver = abiInternalVer
   567  			}
   568  			s := ctxt.loader.Lookup(name, ver)
   569  			if s != 0 {
   570  				ctxt.loader.SetAttrCgoExportDynamic(s, false)
   571  			}
   572  		}
   573  	}
   574  }
   575  
   576  func machoadddynlib(lib string, linkmode LinkMode) {
   577  	if seenlib[lib] || linkmode == LinkExternal {
   578  		return
   579  	}
   580  	seenlib[lib] = true
   581  
   582  	// Will need to store the library name rounded up
   583  	// and 24 bytes of header metadata. If not enough
   584  	// space, grab another page of initial space at the
   585  	// beginning of the output file.
   586  	loadBudget -= (len(lib)+7)/8*8 + 24
   587  
   588  	if loadBudget < 0 {
   589  		HEADR += 4096
   590  		*FlagTextAddr += 4096
   591  		loadBudget += 4096
   592  	}
   593  
   594  	dylib = append(dylib, lib)
   595  }
   596  
   597  func machoshbits(ctxt *Link, mseg *MachoSeg, sect *sym.Section, segname string) {
   598  	buf := "__" + strings.Replace(sect.Name[1:], ".", "_", -1)
   599  
   600  	msect := newMachoSect(mseg, buf, segname)
   601  
   602  	if sect.Rellen > 0 {
   603  		msect.reloc = uint32(sect.Reloff)
   604  		msect.nreloc = uint32(sect.Rellen / 8)
   605  	}
   606  
   607  	for 1<<msect.align < sect.Align {
   608  		msect.align++
   609  	}
   610  	msect.addr = sect.Vaddr
   611  	msect.size = sect.Length
   612  
   613  	if sect.Vaddr < sect.Seg.Vaddr+sect.Seg.Filelen {
   614  		// data in file
   615  		if sect.Length > sect.Seg.Vaddr+sect.Seg.Filelen-sect.Vaddr {
   616  			Errorf(nil, "macho cannot represent section %s crossing data and bss", sect.Name)
   617  		}
   618  		msect.off = uint32(sect.Seg.Fileoff + sect.Vaddr - sect.Seg.Vaddr)
   619  	} else {
   620  		msect.off = 0
   621  		msect.flag |= S_ZEROFILL
   622  	}
   623  
   624  	if sect.Rwx&1 != 0 {
   625  		msect.flag |= S_ATTR_SOME_INSTRUCTIONS
   626  	}
   627  
   628  	if sect.Name == ".text" {
   629  		msect.flag |= S_ATTR_PURE_INSTRUCTIONS
   630  	}
   631  
   632  	if sect.Name == ".plt" {
   633  		msect.name = "__symbol_stub1"
   634  		msect.flag = S_ATTR_PURE_INSTRUCTIONS | S_ATTR_SOME_INSTRUCTIONS | S_SYMBOL_STUBS
   635  		msect.res1 = 0 //nkind[SymKindLocal];
   636  		msect.res2 = 6
   637  	}
   638  
   639  	if sect.Name == ".got" {
   640  		msect.name = "__nl_symbol_ptr"
   641  		msect.flag = S_NON_LAZY_SYMBOL_POINTERS
   642  		msect.res1 = uint32(ctxt.loader.SymSize(ctxt.ArchSyms.LinkEditPLT) / 4) /* offset into indirect symbol table */
   643  	}
   644  
   645  	if sect.Name == ".init_array" {
   646  		msect.name = "__mod_init_func"
   647  		msect.flag = S_MOD_INIT_FUNC_POINTERS
   648  	}
   649  
   650  	// Some platforms such as watchOS and tvOS require binaries with
   651  	// bitcode enabled. The Go toolchain can't output bitcode, so use
   652  	// a marker section in the __LLVM segment, "__asm", to tell the Apple
   653  	// toolchain that the Go text came from assembler and thus has no
   654  	// bitcode. This is not true, but Kotlin/Native, Rust and Flutter
   655  	// are also using this trick.
   656  	if sect.Name == ".llvmasm" {
   657  		msect.name = "__asm"
   658  		msect.segname = "__LLVM"
   659  	}
   660  
   661  	if segname == "__DWARF" {
   662  		msect.flag |= S_ATTR_DEBUG
   663  	}
   664  }
   665  
   666  func asmbMacho(ctxt *Link) {
   667  	machlink := doMachoLink(ctxt)
   668  	if ctxt.IsExternal() {
   669  		symo := int64(Segdwarf.Fileoff + uint64(Rnd(int64(Segdwarf.Filelen), *FlagRound)) + uint64(machlink))
   670  		ctxt.Out.SeekSet(symo)
   671  		machoEmitReloc(ctxt)
   672  	}
   673  	ctxt.Out.SeekSet(0)
   674  
   675  	ldr := ctxt.loader
   676  
   677  	/* apple MACH */
   678  	va := *FlagTextAddr - int64(HEADR)
   679  
   680  	mh := getMachoHdr()
   681  	switch ctxt.Arch.Family {
   682  	default:
   683  		Exitf("unknown macho architecture: %v", ctxt.Arch.Family)
   684  
   685  	case sys.AMD64:
   686  		mh.cpu = MACHO_CPU_AMD64
   687  		mh.subcpu = MACHO_SUBCPU_X86
   688  
   689  	case sys.ARM64:
   690  		mh.cpu = MACHO_CPU_ARM64
   691  		mh.subcpu = MACHO_SUBCPU_ARM64_ALL
   692  	}
   693  
   694  	var ms *MachoSeg
   695  	if ctxt.LinkMode == LinkExternal {
   696  		/* segment for entire file */
   697  		ms = newMachoSeg("", 40)
   698  
   699  		ms.fileoffset = Segtext.Fileoff
   700  		ms.filesize = Segdwarf.Fileoff + Segdwarf.Filelen - Segtext.Fileoff
   701  		ms.vsize = Segdwarf.Vaddr + Segdwarf.Length - Segtext.Vaddr
   702  	}
   703  
   704  	/* segment for zero page */
   705  	if ctxt.LinkMode != LinkExternal {
   706  		ms = newMachoSeg("__PAGEZERO", 0)
   707  		ms.vsize = uint64(va)
   708  	}
   709  
   710  	/* text */
   711  	v := Rnd(int64(uint64(HEADR)+Segtext.Length), *FlagRound)
   712  
   713  	var mstext *MachoSeg
   714  	if ctxt.LinkMode != LinkExternal {
   715  		ms = newMachoSeg("__TEXT", 20)
   716  		ms.vaddr = uint64(va)
   717  		ms.vsize = uint64(v)
   718  		ms.fileoffset = 0
   719  		ms.filesize = uint64(v)
   720  		ms.prot1 = 7
   721  		ms.prot2 = 5
   722  		mstext = ms
   723  	}
   724  
   725  	for _, sect := range Segtext.Sections {
   726  		machoshbits(ctxt, ms, sect, "__TEXT")
   727  	}
   728  
   729  	/* rodata */
   730  	if ctxt.LinkMode != LinkExternal && Segrelrodata.Length > 0 {
   731  		ms = newMachoSeg("__DATA_CONST", 20)
   732  		ms.vaddr = Segrelrodata.Vaddr
   733  		ms.vsize = Segrelrodata.Length
   734  		ms.fileoffset = Segrelrodata.Fileoff
   735  		ms.filesize = Segrelrodata.Filelen
   736  		ms.prot1 = 3
   737  		ms.prot2 = 3
   738  		ms.flag = 0x10 // SG_READ_ONLY
   739  	}
   740  
   741  	for _, sect := range Segrelrodata.Sections {
   742  		machoshbits(ctxt, ms, sect, "__DATA_CONST")
   743  	}
   744  
   745  	/* data */
   746  	if ctxt.LinkMode != LinkExternal {
   747  		ms = newMachoSeg("__DATA", 20)
   748  		ms.vaddr = Segdata.Vaddr
   749  		ms.vsize = Segdata.Length
   750  		ms.fileoffset = Segdata.Fileoff
   751  		ms.filesize = Segdata.Filelen
   752  		ms.prot1 = 3
   753  		ms.prot2 = 3
   754  	}
   755  
   756  	for _, sect := range Segdata.Sections {
   757  		machoshbits(ctxt, ms, sect, "__DATA")
   758  	}
   759  
   760  	/* dwarf */
   761  	if !*FlagW {
   762  		if ctxt.LinkMode != LinkExternal {
   763  			ms = newMachoSeg("__DWARF", 20)
   764  			ms.vaddr = Segdwarf.Vaddr
   765  			ms.vsize = 0
   766  			ms.fileoffset = Segdwarf.Fileoff
   767  			ms.filesize = Segdwarf.Filelen
   768  		}
   769  		for _, sect := range Segdwarf.Sections {
   770  			machoshbits(ctxt, ms, sect, "__DWARF")
   771  		}
   772  	}
   773  
   774  	if ctxt.LinkMode != LinkExternal {
   775  		switch ctxt.Arch.Family {
   776  		default:
   777  			Exitf("unknown macho architecture: %v", ctxt.Arch.Family)
   778  
   779  		case sys.AMD64:
   780  			ml := newMachoLoad(ctxt.Arch, LC_UNIXTHREAD, 42+2)
   781  			ml.data[0] = 4                           /* thread type */
   782  			ml.data[1] = 42                          /* word count */
   783  			ml.data[2+32] = uint32(Entryvalue(ctxt)) /* start pc */
   784  			ml.data[2+32+1] = uint32(Entryvalue(ctxt) >> 32)
   785  
   786  		case sys.ARM64:
   787  			ml := newMachoLoad(ctxt.Arch, LC_MAIN, 4)
   788  			ml.data[0] = uint32(uint64(Entryvalue(ctxt)) - (Segtext.Vaddr - uint64(HEADR)))
   789  			ml.data[1] = uint32((uint64(Entryvalue(ctxt)) - (Segtext.Vaddr - uint64(HEADR))) >> 32)
   790  		}
   791  	}
   792  
   793  	var codesigOff int64
   794  	if !*FlagD {
   795  		// must match doMachoLink below
   796  		s1 := ldr.SymSize(ldr.Lookup(".machorebase", 0))
   797  		s2 := ldr.SymSize(ldr.Lookup(".machobind", 0))
   798  		s3 := ldr.SymSize(ldr.Lookup(".machosymtab", 0))
   799  		s4 := ldr.SymSize(ctxt.ArchSyms.LinkEditPLT)
   800  		s5 := ldr.SymSize(ctxt.ArchSyms.LinkEditGOT)
   801  		s6 := ldr.SymSize(ldr.Lookup(".machosymstr", 0))
   802  		s7 := ldr.SymSize(ldr.Lookup(".machocodesig", 0))
   803  
   804  		if ctxt.LinkMode != LinkExternal {
   805  			ms := newMachoSeg("__LINKEDIT", 0)
   806  			ms.vaddr = uint64(Rnd(int64(Segdata.Vaddr+Segdata.Length), *FlagRound))
   807  			ms.vsize = uint64(s1 + s2 + s3 + s4 + s5 + s6 + s7)
   808  			ms.fileoffset = uint64(linkoff)
   809  			ms.filesize = ms.vsize
   810  			ms.prot1 = 1
   811  			ms.prot2 = 1
   812  
   813  			codesigOff = linkoff + s1 + s2 + s3 + s4 + s5 + s6
   814  		}
   815  
   816  		if ctxt.LinkMode != LinkExternal && ctxt.IsPIE() {
   817  			ml := newMachoLoad(ctxt.Arch, LC_DYLD_INFO_ONLY, 10)
   818  			ml.data[0] = uint32(linkoff)      // rebase off
   819  			ml.data[1] = uint32(s1)           // rebase size
   820  			ml.data[2] = uint32(linkoff + s1) // bind off
   821  			ml.data[3] = uint32(s2)           // bind size
   822  			ml.data[4] = 0                    // weak bind off
   823  			ml.data[5] = 0                    // weak bind size
   824  			ml.data[6] = 0                    // lazy bind off
   825  			ml.data[7] = 0                    // lazy bind size
   826  			ml.data[8] = 0                    // export
   827  			ml.data[9] = 0                    // export size
   828  		}
   829  
   830  		ml := newMachoLoad(ctxt.Arch, LC_SYMTAB, 4)
   831  		ml.data[0] = uint32(linkoff + s1 + s2)                /* symoff */
   832  		ml.data[1] = uint32(nsortsym)                         /* nsyms */
   833  		ml.data[2] = uint32(linkoff + s1 + s2 + s3 + s4 + s5) /* stroff */
   834  		ml.data[3] = uint32(s6)                               /* strsize */
   835  
   836  		if ctxt.LinkMode != LinkExternal {
   837  			machodysymtab(ctxt, linkoff+s1+s2)
   838  
   839  			ml := newMachoLoad(ctxt.Arch, LC_LOAD_DYLINKER, 6)
   840  			ml.data[0] = 12 /* offset to string */
   841  			stringtouint32(ml.data[1:], "/usr/lib/dyld")
   842  
   843  			for _, lib := range dylib {
   844  				ml = newMachoLoad(ctxt.Arch, LC_LOAD_DYLIB, 4+(uint32(len(lib))+1+7)/8*2)
   845  				ml.data[0] = 24 /* offset of string from beginning of load */
   846  				ml.data[1] = 0  /* time stamp */
   847  				ml.data[2] = 0  /* version */
   848  				ml.data[3] = 0  /* compatibility version */
   849  				stringtouint32(ml.data[4:], lib)
   850  			}
   851  		}
   852  
   853  		if ctxt.IsInternal() && ctxt.NeedCodeSign() {
   854  			ml := newMachoLoad(ctxt.Arch, LC_CODE_SIGNATURE, 2)
   855  			ml.data[0] = uint32(codesigOff)
   856  			ml.data[1] = uint32(s7)
   857  		}
   858  	}
   859  
   860  	a := machowrite(ctxt, ctxt.Arch, ctxt.Out, ctxt.LinkMode)
   861  	if int32(a) > HEADR {
   862  		Exitf("HEADR too small: %d > %d", a, HEADR)
   863  	}
   864  
   865  	// Now we have written everything. Compute the code signature (which
   866  	// is a hash of the file content, so it must be done at last.)
   867  	if ctxt.IsInternal() && ctxt.NeedCodeSign() {
   868  		cs := ldr.Lookup(".machocodesig", 0)
   869  		data := ctxt.Out.Data()
   870  		if int64(len(data)) != codesigOff {
   871  			panic("wrong size")
   872  		}
   873  		codesign.Sign(ldr.Data(cs), bytes.NewReader(data), "a.out", codesigOff, int64(mstext.fileoffset), int64(mstext.filesize), ctxt.IsExe() || ctxt.IsPIE())
   874  		ctxt.Out.SeekSet(codesigOff)
   875  		ctxt.Out.Write(ldr.Data(cs))
   876  	}
   877  }
   878  
   879  func symkind(ldr *loader.Loader, s loader.Sym) int {
   880  	if t := ldr.SymType(s); t == sym.SDYNIMPORT || t == sym.SHOSTOBJ || t == sym.SUNDEFEXT {
   881  		return SymKindUndef
   882  	}
   883  	if ldr.AttrCgoExport(s) {
   884  		return SymKindExtdef
   885  	}
   886  	return SymKindLocal
   887  }
   888  
   889  func collectmachosyms(ctxt *Link) {
   890  	ldr := ctxt.loader
   891  
   892  	addsym := func(s loader.Sym) {
   893  		sortsym = append(sortsym, s)
   894  		nkind[symkind(ldr, s)]++
   895  	}
   896  
   897  	// On Mach-O, even with -s, we still need to keep dynamically exported and
   898  	// referenced symbols. We can strip defined local text and data symbols.
   899  	// So *FlagS is applied based on symbol type.
   900  
   901  	// Add special runtime.text and runtime.etext symbols (which are local).
   902  	// We've already included this symbol in Textp on darwin if ctxt.DynlinkingGo().
   903  	// See data.go:/textaddress
   904  	if !*FlagS {
   905  		if !ctxt.DynlinkingGo() {
   906  			s := ldr.Lookup("runtime.text", 0)
   907  			if ldr.SymType(s) == sym.STEXT {
   908  				addsym(s)
   909  			}
   910  			for n := range Segtext.Sections[1:] {
   911  				s := ldr.Lookup(fmt.Sprintf("runtime.text.%d", n+1), 0)
   912  				if s != 0 {
   913  					addsym(s)
   914  				} else {
   915  					break
   916  				}
   917  			}
   918  			s = ldr.Lookup("runtime.etext", 0)
   919  			if ldr.SymType(s) == sym.STEXT {
   920  				addsym(s)
   921  			}
   922  		}
   923  	}
   924  
   925  	// Add text symbols.
   926  	for _, s := range ctxt.Textp {
   927  		if *FlagS && !ldr.AttrCgoExportDynamic(s) {
   928  			continue
   929  		}
   930  		addsym(s)
   931  	}
   932  
   933  	shouldBeInSymbolTable := func(s loader.Sym) bool {
   934  		if ldr.AttrNotInSymbolTable(s) {
   935  			return false
   936  		}
   937  		name := ldr.SymName(s) // TODO: try not to read the name
   938  		if name == "" || name[0] == '.' {
   939  			return false
   940  		}
   941  		return true
   942  	}
   943  
   944  	// Add data symbols and external references.
   945  	for s := loader.Sym(1); s < loader.Sym(ldr.NSym()); s++ {
   946  		if !ldr.AttrReachable(s) {
   947  			continue
   948  		}
   949  		t := ldr.SymType(s)
   950  		if t >= sym.SELFRXSECT && t < sym.SXREF { // data sections handled in dodata
   951  			if t == sym.STLSBSS {
   952  				// TLSBSS is not used on darwin. See data.go:allocateDataSections
   953  				continue
   954  			}
   955  			if !shouldBeInSymbolTable(s) {
   956  				continue
   957  			}
   958  			if *FlagS && !ldr.AttrCgoExportDynamic(s) {
   959  				continue
   960  			}
   961  			addsym(s)
   962  			continue
   963  		}
   964  
   965  		switch t {
   966  		case sym.SDYNIMPORT, sym.SHOSTOBJ, sym.SUNDEFEXT:
   967  			// Keep dynamic symbol references even if *FlagS.
   968  			addsym(s)
   969  		}
   970  
   971  		// Some 64-bit functions have a "$INODE64" or "$INODE64$UNIX2003" suffix.
   972  		if t == sym.SDYNIMPORT && ldr.SymDynimplib(s) == "/usr/lib/libSystem.B.dylib" {
   973  			// But only on macOS.
   974  			if machoPlatform == PLATFORM_MACOS {
   975  				switch n := ldr.SymExtname(s); n {
   976  				case "fdopendir":
   977  					switch buildcfg.GOARCH {
   978  					case "amd64":
   979  						ldr.SetSymExtname(s, n+"$INODE64")
   980  					}
   981  				case "readdir_r", "getfsstat":
   982  					switch buildcfg.GOARCH {
   983  					case "amd64":
   984  						ldr.SetSymExtname(s, n+"$INODE64")
   985  					}
   986  				}
   987  			}
   988  		}
   989  	}
   990  
   991  	nsortsym = len(sortsym)
   992  }
   993  
   994  func machosymorder(ctxt *Link) {
   995  	ldr := ctxt.loader
   996  
   997  	// On Mac OS X Mountain Lion, we must sort exported symbols
   998  	// So we sort them here and pre-allocate dynid for them
   999  	// See https://golang.org/issue/4029
  1000  	for _, s := range ctxt.dynexp {
  1001  		if !ldr.AttrReachable(s) {
  1002  			panic("dynexp symbol is not reachable")
  1003  		}
  1004  	}
  1005  	collectmachosyms(ctxt)
  1006  	sort.Slice(sortsym[:nsortsym], func(i, j int) bool {
  1007  		s1 := sortsym[i]
  1008  		s2 := sortsym[j]
  1009  		k1 := symkind(ldr, s1)
  1010  		k2 := symkind(ldr, s2)
  1011  		if k1 != k2 {
  1012  			return k1 < k2
  1013  		}
  1014  		return ldr.SymExtname(s1) < ldr.SymExtname(s2) // Note: unnamed symbols are not added in collectmachosyms
  1015  	})
  1016  	for i, s := range sortsym {
  1017  		ldr.SetSymDynid(s, int32(i))
  1018  	}
  1019  }
  1020  
  1021  // AddMachoSym adds s to Mach-O symbol table, used in GenSymLate.
  1022  // Currently only used on ARM64 when external linking.
  1023  func AddMachoSym(ldr *loader.Loader, s loader.Sym) {
  1024  	ldr.SetSymDynid(s, int32(nsortsym))
  1025  	sortsym = append(sortsym, s)
  1026  	nsortsym++
  1027  	nkind[symkind(ldr, s)]++
  1028  }
  1029  
  1030  // machoShouldExport reports whether a symbol needs to be exported.
  1031  //
  1032  // When dynamically linking, all non-local variables and plugin-exported
  1033  // symbols need to be exported.
  1034  func machoShouldExport(ctxt *Link, ldr *loader.Loader, s loader.Sym) bool {
  1035  	if !ctxt.DynlinkingGo() || ldr.AttrLocal(s) {
  1036  		return false
  1037  	}
  1038  	if ctxt.BuildMode == BuildModePlugin && strings.HasPrefix(ldr.SymExtname(s), objabi.PathToPrefix(*flagPluginPath)) {
  1039  		return true
  1040  	}
  1041  	name := ldr.SymName(s)
  1042  	if strings.HasPrefix(name, "go:itab.") {
  1043  		return true
  1044  	}
  1045  	if strings.HasPrefix(name, "type:") && !strings.HasPrefix(name, "type:.") {
  1046  		// reduce runtime typemap pressure, but do not
  1047  		// export alg functions (type:.*), as these
  1048  		// appear in pclntable.
  1049  		return true
  1050  	}
  1051  	if strings.HasPrefix(name, "go:link.pkghash") {
  1052  		return true
  1053  	}
  1054  	return ldr.SymType(s) >= sym.SFirstWritable // only writable sections
  1055  }
  1056  
  1057  func machosymtab(ctxt *Link) {
  1058  	ldr := ctxt.loader
  1059  	symtab := ldr.CreateSymForUpdate(".machosymtab", 0)
  1060  	symstr := ldr.CreateSymForUpdate(".machosymstr", 0)
  1061  
  1062  	for _, s := range sortsym[:nsortsym] {
  1063  		symtab.AddUint32(ctxt.Arch, uint32(symstr.Size()))
  1064  
  1065  		export := machoShouldExport(ctxt, ldr, s)
  1066  
  1067  		// Prefix symbol names with "_" to match the system toolchain.
  1068  		// (We used to only prefix C symbols, which is all required for the build.
  1069  		// But some tools don't recognize Go symbols as symbols, so we prefix them
  1070  		// as well.)
  1071  		symstr.AddUint8('_')
  1072  
  1073  		// replace "·" as ".", because DTrace cannot handle it.
  1074  		name := strings.Replace(ldr.SymExtname(s), "·", ".", -1)
  1075  
  1076  		name = mangleABIName(ctxt, ldr, s, name)
  1077  		symstr.Addstring(name)
  1078  
  1079  		if t := ldr.SymType(s); t == sym.SDYNIMPORT || t == sym.SHOSTOBJ || t == sym.SUNDEFEXT {
  1080  			symtab.AddUint8(0x01)                             // type N_EXT, external symbol
  1081  			symtab.AddUint8(0)                                // no section
  1082  			symtab.AddUint16(ctxt.Arch, 0)                    // desc
  1083  			symtab.AddUintXX(ctxt.Arch, 0, ctxt.Arch.PtrSize) // no value
  1084  		} else {
  1085  			if export || ldr.AttrCgoExportDynamic(s) {
  1086  				symtab.AddUint8(0x0f) // N_SECT | N_EXT
  1087  			} else if ldr.AttrCgoExportStatic(s) {
  1088  				// Only export statically, not dynamically. (N_PEXT is like hidden visibility)
  1089  				symtab.AddUint8(0x1f) // N_SECT | N_EXT | N_PEXT
  1090  			} else {
  1091  				symtab.AddUint8(0x0e) // N_SECT
  1092  			}
  1093  			o := s
  1094  			if outer := ldr.OuterSym(o); outer != 0 {
  1095  				o = outer
  1096  			}
  1097  			if ldr.SymSect(o) == nil {
  1098  				ldr.Errorf(s, "missing section for symbol")
  1099  				symtab.AddUint8(0)
  1100  			} else {
  1101  				symtab.AddUint8(uint8(ldr.SymSect(o).Extnum))
  1102  			}
  1103  			symtab.AddUint16(ctxt.Arch, 0) // desc
  1104  			symtab.AddUintXX(ctxt.Arch, uint64(ldr.SymAddr(s)), ctxt.Arch.PtrSize)
  1105  		}
  1106  	}
  1107  }
  1108  
  1109  func machodysymtab(ctxt *Link, base int64) {
  1110  	ml := newMachoLoad(ctxt.Arch, LC_DYSYMTAB, 18)
  1111  
  1112  	n := 0
  1113  	ml.data[0] = uint32(n)                   /* ilocalsym */
  1114  	ml.data[1] = uint32(nkind[SymKindLocal]) /* nlocalsym */
  1115  	n += nkind[SymKindLocal]
  1116  
  1117  	ml.data[2] = uint32(n)                    /* iextdefsym */
  1118  	ml.data[3] = uint32(nkind[SymKindExtdef]) /* nextdefsym */
  1119  	n += nkind[SymKindExtdef]
  1120  
  1121  	ml.data[4] = uint32(n)                   /* iundefsym */
  1122  	ml.data[5] = uint32(nkind[SymKindUndef]) /* nundefsym */
  1123  
  1124  	ml.data[6] = 0  /* tocoffset */
  1125  	ml.data[7] = 0  /* ntoc */
  1126  	ml.data[8] = 0  /* modtaboff */
  1127  	ml.data[9] = 0  /* nmodtab */
  1128  	ml.data[10] = 0 /* extrefsymoff */
  1129  	ml.data[11] = 0 /* nextrefsyms */
  1130  
  1131  	ldr := ctxt.loader
  1132  
  1133  	// must match domacholink below
  1134  	s1 := ldr.SymSize(ldr.Lookup(".machosymtab", 0))
  1135  	s2 := ldr.SymSize(ctxt.ArchSyms.LinkEditPLT)
  1136  	s3 := ldr.SymSize(ctxt.ArchSyms.LinkEditGOT)
  1137  	ml.data[12] = uint32(base + s1)     /* indirectsymoff */
  1138  	ml.data[13] = uint32((s2 + s3) / 4) /* nindirectsyms */
  1139  
  1140  	ml.data[14] = 0 /* extreloff */
  1141  	ml.data[15] = 0 /* nextrel */
  1142  	ml.data[16] = 0 /* locreloff */
  1143  	ml.data[17] = 0 /* nlocrel */
  1144  }
  1145  
  1146  func doMachoLink(ctxt *Link) int64 {
  1147  	machosymtab(ctxt)
  1148  	machoDyldInfo(ctxt)
  1149  
  1150  	ldr := ctxt.loader
  1151  
  1152  	// write data that will be linkedit section
  1153  	s1 := ldr.Lookup(".machorebase", 0)
  1154  	s2 := ldr.Lookup(".machobind", 0)
  1155  	s3 := ldr.Lookup(".machosymtab", 0)
  1156  	s4 := ctxt.ArchSyms.LinkEditPLT
  1157  	s5 := ctxt.ArchSyms.LinkEditGOT
  1158  	s6 := ldr.Lookup(".machosymstr", 0)
  1159  
  1160  	size := ldr.SymSize(s1) + ldr.SymSize(s2) + ldr.SymSize(s3) + ldr.SymSize(s4) + ldr.SymSize(s5) + ldr.SymSize(s6)
  1161  
  1162  	// Force the linkedit section to end on a 16-byte
  1163  	// boundary. This allows pure (non-cgo) Go binaries
  1164  	// to be code signed correctly.
  1165  	//
  1166  	// Apple's codesign_allocate (a helper utility for
  1167  	// the codesign utility) can do this fine itself if
  1168  	// it is run on a dynamic Mach-O binary. However,
  1169  	// when it is run on a pure (non-cgo) Go binary, where
  1170  	// the linkedit section is mostly empty, it fails to
  1171  	// account for the extra padding that it itself adds
  1172  	// when adding the LC_CODE_SIGNATURE load command
  1173  	// (which must be aligned on a 16-byte boundary).
  1174  	//
  1175  	// By forcing the linkedit section to end on a 16-byte
  1176  	// boundary, codesign_allocate will not need to apply
  1177  	// any alignment padding itself, working around the
  1178  	// issue.
  1179  	if size%16 != 0 {
  1180  		n := 16 - size%16
  1181  		s6b := ldr.MakeSymbolUpdater(s6)
  1182  		s6b.Grow(s6b.Size() + n)
  1183  		s6b.SetSize(s6b.Size() + n)
  1184  		size += n
  1185  	}
  1186  
  1187  	if size > 0 {
  1188  		linkoff = Rnd(int64(uint64(HEADR)+Segtext.Length), *FlagRound) + Rnd(int64(Segrelrodata.Filelen), *FlagRound) + Rnd(int64(Segdata.Filelen), *FlagRound) + Rnd(int64(Segdwarf.Filelen), *FlagRound)
  1189  		ctxt.Out.SeekSet(linkoff)
  1190  
  1191  		ctxt.Out.Write(ldr.Data(s1))
  1192  		ctxt.Out.Write(ldr.Data(s2))
  1193  		ctxt.Out.Write(ldr.Data(s3))
  1194  		ctxt.Out.Write(ldr.Data(s4))
  1195  		ctxt.Out.Write(ldr.Data(s5))
  1196  		ctxt.Out.Write(ldr.Data(s6))
  1197  
  1198  		// Add code signature if necessary. This must be the last.
  1199  		s7 := machoCodeSigSym(ctxt, linkoff+size)
  1200  		size += ldr.SymSize(s7)
  1201  	}
  1202  
  1203  	return Rnd(size, *FlagRound)
  1204  }
  1205  
  1206  func machorelocsect(ctxt *Link, out *OutBuf, sect *sym.Section, syms []loader.Sym) {
  1207  	// If main section has no bits, nothing to relocate.
  1208  	if sect.Vaddr >= sect.Seg.Vaddr+sect.Seg.Filelen {
  1209  		return
  1210  	}
  1211  	ldr := ctxt.loader
  1212  
  1213  	for i, s := range syms {
  1214  		if !ldr.AttrReachable(s) {
  1215  			continue
  1216  		}
  1217  		if uint64(ldr.SymValue(s)) >= sect.Vaddr {
  1218  			syms = syms[i:]
  1219  			break
  1220  		}
  1221  	}
  1222  
  1223  	eaddr := sect.Vaddr + sect.Length
  1224  	for _, s := range syms {
  1225  		if !ldr.AttrReachable(s) {
  1226  			continue
  1227  		}
  1228  		if ldr.SymValue(s) >= int64(eaddr) {
  1229  			break
  1230  		}
  1231  
  1232  		// Compute external relocations on the go, and pass to Machoreloc1
  1233  		// to stream out.
  1234  		relocs := ldr.Relocs(s)
  1235  		for ri := 0; ri < relocs.Count(); ri++ {
  1236  			r := relocs.At(ri)
  1237  			rr, ok := extreloc(ctxt, ldr, s, r)
  1238  			if !ok {
  1239  				continue
  1240  			}
  1241  			if rr.Xsym == 0 {
  1242  				ldr.Errorf(s, "missing xsym in relocation")
  1243  				continue
  1244  			}
  1245  			if !ldr.AttrReachable(rr.Xsym) {
  1246  				ldr.Errorf(s, "unreachable reloc %d (%s) target %v", r.Type(), sym.RelocName(ctxt.Arch, r.Type()), ldr.SymName(rr.Xsym))
  1247  			}
  1248  			if !thearch.Machoreloc1(ctxt.Arch, out, ldr, s, rr, int64(uint64(ldr.SymValue(s)+int64(r.Off()))-sect.Vaddr)) {
  1249  				ldr.Errorf(s, "unsupported obj reloc %d (%s)/%d to %s", r.Type(), sym.RelocName(ctxt.Arch, r.Type()), r.Siz(), ldr.SymName(r.Sym()))
  1250  			}
  1251  		}
  1252  	}
  1253  
  1254  	// sanity check
  1255  	if uint64(out.Offset()) != sect.Reloff+sect.Rellen {
  1256  		panic("machorelocsect: size mismatch")
  1257  	}
  1258  }
  1259  
  1260  func machoEmitReloc(ctxt *Link) {
  1261  	for ctxt.Out.Offset()&7 != 0 {
  1262  		ctxt.Out.Write8(0)
  1263  	}
  1264  
  1265  	sizeExtRelocs(ctxt, thearch.MachorelocSize)
  1266  	relocSect, wg := relocSectFn(ctxt, machorelocsect)
  1267  
  1268  	relocSect(ctxt, Segtext.Sections[0], ctxt.Textp)
  1269  	for _, sect := range Segtext.Sections[1:] {
  1270  		if sect.Name == ".text" {
  1271  			relocSect(ctxt, sect, ctxt.Textp)
  1272  		} else {
  1273  			relocSect(ctxt, sect, ctxt.datap)
  1274  		}
  1275  	}
  1276  	for _, sect := range Segrelrodata.Sections {
  1277  		relocSect(ctxt, sect, ctxt.datap)
  1278  	}
  1279  	for _, sect := range Segdata.Sections {
  1280  		relocSect(ctxt, sect, ctxt.datap)
  1281  	}
  1282  	for i := 0; i < len(Segdwarf.Sections); i++ {
  1283  		sect := Segdwarf.Sections[i]
  1284  		si := dwarfp[i]
  1285  		if si.secSym() != loader.Sym(sect.Sym) ||
  1286  			ctxt.loader.SymSect(si.secSym()) != sect {
  1287  			panic("inconsistency between dwarfp and Segdwarf")
  1288  		}
  1289  		relocSect(ctxt, sect, si.syms)
  1290  	}
  1291  	wg.Wait()
  1292  }
  1293  
  1294  // hostobjMachoPlatform returns the first platform load command found
  1295  // in the host object, if any.
  1296  func hostobjMachoPlatform(h *Hostobj) (*MachoPlatformLoad, error) {
  1297  	f, err := os.Open(h.file)
  1298  	if err != nil {
  1299  		return nil, fmt.Errorf("%s: failed to open host object: %v\n", h.file, err)
  1300  	}
  1301  	defer f.Close()
  1302  	sr := io.NewSectionReader(f, h.off, h.length)
  1303  	m, err := macho.NewFile(sr)
  1304  	if err != nil {
  1305  		// Not a valid Mach-O file.
  1306  		return nil, nil
  1307  	}
  1308  	return peekMachoPlatform(m)
  1309  }
  1310  
  1311  // peekMachoPlatform returns the first LC_VERSION_MIN_* or LC_BUILD_VERSION
  1312  // load command found in the Mach-O file, if any.
  1313  func peekMachoPlatform(m *macho.File) (*MachoPlatformLoad, error) {
  1314  	for _, cmd := range m.Loads {
  1315  		raw := cmd.Raw()
  1316  		ml := MachoLoad{
  1317  			type_: m.ByteOrder.Uint32(raw),
  1318  		}
  1319  		// Skip the type and command length.
  1320  		data := raw[8:]
  1321  		var p MachoPlatform
  1322  		switch ml.type_ {
  1323  		case LC_VERSION_MIN_IPHONEOS:
  1324  			p = PLATFORM_IOS
  1325  		case LC_VERSION_MIN_MACOSX:
  1326  			p = PLATFORM_MACOS
  1327  		case LC_VERSION_MIN_WATCHOS:
  1328  			p = PLATFORM_WATCHOS
  1329  		case LC_VERSION_MIN_TVOS:
  1330  			p = PLATFORM_TVOS
  1331  		case LC_BUILD_VERSION:
  1332  			p = MachoPlatform(m.ByteOrder.Uint32(data))
  1333  		default:
  1334  			continue
  1335  		}
  1336  		ml.data = make([]uint32, len(data)/4)
  1337  		r := bytes.NewReader(data)
  1338  		if err := binary.Read(r, m.ByteOrder, &ml.data); err != nil {
  1339  			return nil, err
  1340  		}
  1341  		return &MachoPlatformLoad{
  1342  			platform: p,
  1343  			cmd:      ml,
  1344  		}, nil
  1345  	}
  1346  	return nil, nil
  1347  }
  1348  
  1349  // A rebase entry tells the dynamic linker the data at sym+off needs to be
  1350  // relocated when the in-memory image moves. (This is somewhat like, say,
  1351  // ELF R_X86_64_RELATIVE).
  1352  // For now, the only kind of entry we support is that the data is an absolute
  1353  // address. That seems all we need.
  1354  // In the binary it uses a compact stateful bytecode encoding. So we record
  1355  // entries as we go and build the table at the end.
  1356  type machoRebaseRecord struct {
  1357  	sym loader.Sym
  1358  	off int64
  1359  }
  1360  
  1361  var machorebase []machoRebaseRecord
  1362  
  1363  func MachoAddRebase(s loader.Sym, off int64) {
  1364  	machorebase = append(machorebase, machoRebaseRecord{s, off})
  1365  }
  1366  
  1367  // A bind entry tells the dynamic linker the data at GOT+off should be bound
  1368  // to the address of the target symbol, which is a dynamic import.
  1369  // For now, the only kind of entry we support is that the data is an absolute
  1370  // address, and the source symbol is always the GOT. That seems all we need.
  1371  // In the binary it uses a compact stateful bytecode encoding. So we record
  1372  // entries as we go and build the table at the end.
  1373  type machoBindRecord struct {
  1374  	off  int64
  1375  	targ loader.Sym
  1376  }
  1377  
  1378  var machobind []machoBindRecord
  1379  
  1380  func MachoAddBind(off int64, targ loader.Sym) {
  1381  	machobind = append(machobind, machoBindRecord{off, targ})
  1382  }
  1383  
  1384  // Generate data for the dynamic linker, used in LC_DYLD_INFO_ONLY load command.
  1385  // See mach-o/loader.h, struct dyld_info_command, for the encoding.
  1386  // e.g. https://opensource.apple.com/source/xnu/xnu-6153.81.5/EXTERNAL_HEADERS/mach-o/loader.h
  1387  func machoDyldInfo(ctxt *Link) {
  1388  	ldr := ctxt.loader
  1389  	rebase := ldr.CreateSymForUpdate(".machorebase", 0)
  1390  	bind := ldr.CreateSymForUpdate(".machobind", 0)
  1391  
  1392  	if !(ctxt.IsPIE() && ctxt.IsInternal()) {
  1393  		return
  1394  	}
  1395  
  1396  	segId := func(seg *sym.Segment) uint8 {
  1397  		switch seg {
  1398  		case &Segtext:
  1399  			return 1
  1400  		case &Segrelrodata:
  1401  			return 2
  1402  		case &Segdata:
  1403  			if Segrelrodata.Length > 0 {
  1404  				return 3
  1405  			}
  1406  			return 2
  1407  		}
  1408  		panic("unknown segment")
  1409  	}
  1410  
  1411  	dylibId := func(s loader.Sym) int {
  1412  		slib := ldr.SymDynimplib(s)
  1413  		for i, lib := range dylib {
  1414  			if lib == slib {
  1415  				return i + 1
  1416  			}
  1417  		}
  1418  		return BIND_SPECIAL_DYLIB_FLAT_LOOKUP // don't know where it is from
  1419  	}
  1420  
  1421  	// Rebase table.
  1422  	// TODO: use more compact encoding. The encoding is stateful, and
  1423  	// we can use delta encoding.
  1424  	rebase.AddUint8(REBASE_OPCODE_SET_TYPE_IMM | REBASE_TYPE_POINTER)
  1425  	for _, r := range machorebase {
  1426  		seg := ldr.SymSect(r.sym).Seg
  1427  		off := uint64(ldr.SymValue(r.sym)+r.off) - seg.Vaddr
  1428  		rebase.AddUint8(REBASE_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB | segId(seg))
  1429  		rebase.AddUleb(off)
  1430  
  1431  		rebase.AddUint8(REBASE_OPCODE_DO_REBASE_IMM_TIMES | 1)
  1432  	}
  1433  	rebase.AddUint8(REBASE_OPCODE_DONE)
  1434  	sz := Rnd(rebase.Size(), 8)
  1435  	rebase.Grow(sz)
  1436  	rebase.SetSize(sz)
  1437  
  1438  	// Bind table.
  1439  	// TODO: compact encoding, as above.
  1440  	// TODO: lazy binding?
  1441  	got := ctxt.GOT
  1442  	seg := ldr.SymSect(got).Seg
  1443  	gotAddr := ldr.SymValue(got)
  1444  	bind.AddUint8(BIND_OPCODE_SET_TYPE_IMM | BIND_TYPE_POINTER)
  1445  	for _, r := range machobind {
  1446  		off := uint64(gotAddr+r.off) - seg.Vaddr
  1447  		bind.AddUint8(BIND_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB | segId(seg))
  1448  		bind.AddUleb(off)
  1449  
  1450  		d := dylibId(r.targ)
  1451  		if d > 0 && d < 128 {
  1452  			bind.AddUint8(BIND_OPCODE_SET_DYLIB_ORDINAL_IMM | uint8(d)&0xf)
  1453  		} else if d >= 128 {
  1454  			bind.AddUint8(BIND_OPCODE_SET_DYLIB_ORDINAL_ULEB)
  1455  			bind.AddUleb(uint64(d))
  1456  		} else { // d <= 0
  1457  			bind.AddUint8(BIND_OPCODE_SET_DYLIB_SPECIAL_IMM | uint8(d)&0xf)
  1458  		}
  1459  
  1460  		bind.AddUint8(BIND_OPCODE_SET_SYMBOL_TRAILING_FLAGS_IMM)
  1461  		// target symbol name as a C string, with _ prefix
  1462  		bind.AddUint8('_')
  1463  		bind.Addstring(ldr.SymExtname(r.targ))
  1464  
  1465  		bind.AddUint8(BIND_OPCODE_DO_BIND)
  1466  	}
  1467  	bind.AddUint8(BIND_OPCODE_DONE)
  1468  	sz = Rnd(bind.Size(), 16) // make it 16-byte aligned, see the comment in doMachoLink
  1469  	bind.Grow(sz)
  1470  	bind.SetSize(sz)
  1471  
  1472  	// TODO: export table.
  1473  	// The symbols names are encoded as a trie. I'm really too lazy to do that
  1474  	// for now.
  1475  	// Without it, the symbols are not dynamically exported, so they cannot be
  1476  	// e.g. dlsym'd. But internal linking is not the default in that case, so
  1477  	// it is fine.
  1478  }
  1479  
  1480  // machoCodeSigSym creates and returns a symbol for code signature.
  1481  // The symbol context is left as zeros, which will be generated at the end
  1482  // (as it depends on the rest of the file).
  1483  func machoCodeSigSym(ctxt *Link, codeSize int64) loader.Sym {
  1484  	ldr := ctxt.loader
  1485  	cs := ldr.CreateSymForUpdate(".machocodesig", 0)
  1486  	if !ctxt.NeedCodeSign() || ctxt.IsExternal() {
  1487  		return cs.Sym()
  1488  	}
  1489  	sz := codesign.Size(codeSize, "a.out")
  1490  	cs.Grow(sz)
  1491  	cs.SetSize(sz)
  1492  	return cs.Sym()
  1493  }
  1494  
  1495  // machoCodeSign code-signs Mach-O file fname with an ad-hoc signature.
  1496  // This is used for updating an external linker generated binary.
  1497  func machoCodeSign(ctxt *Link, fname string) error {
  1498  	f, err := os.OpenFile(fname, os.O_RDWR, 0)
  1499  	if err != nil {
  1500  		return err
  1501  	}
  1502  	defer f.Close()
  1503  
  1504  	mf, err := macho.NewFile(f)
  1505  	if err != nil {
  1506  		return err
  1507  	}
  1508  	if mf.Magic != macho.Magic64 {
  1509  		Exitf("not 64-bit Mach-O file: %s", fname)
  1510  	}
  1511  
  1512  	// Find existing LC_CODE_SIGNATURE and __LINKEDIT segment
  1513  	var sigOff, sigSz, csCmdOff, linkeditOff int64
  1514  	var linkeditSeg, textSeg *macho.Segment
  1515  	loadOff := int64(machoHeaderSize64)
  1516  	get32 := mf.ByteOrder.Uint32
  1517  	for _, l := range mf.Loads {
  1518  		data := l.Raw()
  1519  		cmd, sz := get32(data), get32(data[4:])
  1520  		if cmd == LC_CODE_SIGNATURE {
  1521  			sigOff = int64(get32(data[8:]))
  1522  			sigSz = int64(get32(data[12:]))
  1523  			csCmdOff = loadOff
  1524  		}
  1525  		if seg, ok := l.(*macho.Segment); ok {
  1526  			switch seg.Name {
  1527  			case "__LINKEDIT":
  1528  				linkeditSeg = seg
  1529  				linkeditOff = loadOff
  1530  			case "__TEXT":
  1531  				textSeg = seg
  1532  			}
  1533  		}
  1534  		loadOff += int64(sz)
  1535  	}
  1536  
  1537  	if sigOff == 0 {
  1538  		// The C linker doesn't generate a signed binary, for some reason.
  1539  		// Skip.
  1540  		return nil
  1541  	}
  1542  
  1543  	fi, err := f.Stat()
  1544  	if err != nil {
  1545  		return err
  1546  	}
  1547  	if sigOff+sigSz != fi.Size() {
  1548  		// We don't expect anything after the signature (this will invalidate
  1549  		// the signature anyway.)
  1550  		return fmt.Errorf("unexpected content after code signature")
  1551  	}
  1552  
  1553  	sz := codesign.Size(sigOff, "a.out")
  1554  	if sz != sigSz {
  1555  		// Update the load command,
  1556  		var tmp [8]byte
  1557  		mf.ByteOrder.PutUint32(tmp[:4], uint32(sz))
  1558  		_, err = f.WriteAt(tmp[:4], csCmdOff+12)
  1559  		if err != nil {
  1560  			return err
  1561  		}
  1562  
  1563  		// Uodate the __LINKEDIT segment.
  1564  		segSz := sigOff + sz - int64(linkeditSeg.Offset)
  1565  		mf.ByteOrder.PutUint64(tmp[:8], uint64(segSz))
  1566  		_, err = f.WriteAt(tmp[:8], int64(linkeditOff)+int64(unsafe.Offsetof(macho.Segment64{}.Memsz)))
  1567  		if err != nil {
  1568  			return err
  1569  		}
  1570  		_, err = f.WriteAt(tmp[:8], int64(linkeditOff)+int64(unsafe.Offsetof(macho.Segment64{}.Filesz)))
  1571  		if err != nil {
  1572  			return err
  1573  		}
  1574  	}
  1575  
  1576  	cs := make([]byte, sz)
  1577  	codesign.Sign(cs, f, "a.out", sigOff, int64(textSeg.Offset), int64(textSeg.Filesz), ctxt.IsExe() || ctxt.IsPIE())
  1578  	_, err = f.WriteAt(cs, sigOff)
  1579  	if err != nil {
  1580  		return err
  1581  	}
  1582  	err = f.Truncate(sigOff + sz)
  1583  	return err
  1584  }
  1585  

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