src/cmd/link/internal/loadpe/ldpe.go

   1 // Copyright 2010 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 loadpe implements a PE/COFF file reader.
   6 package loadpe
   7
   8 import (
   9         "cmd/internal/bio"
  10         "cmd/internal/objabi"
  11         "cmd/internal/sys"
  12         "cmd/link/internal/loader"
  13         "cmd/link/internal/sym"
  14         "debug/pe"
  15         "encoding/binary"
  16         "errors"
  17         "fmt"
  18         "io"
  19         "sort"
  20         "strings"
  21 )
  22
  23 const (
  24         // TODO: the Microsoft doco says IMAGE_SYM_DTYPE_ARRAY is 3 (same with IMAGE_SYM_DTYPE_POINTER and IMAGE_SYM_DTYPE_FUNCTION)
  25         IMAGE_SYM_UNDEFINED              = 0
  26         IMAGE_SYM_ABSOLUTE               = -1
  27         IMAGE_SYM_DEBUG                  = -2
  28         IMAGE_SYM_TYPE_NULL              = 0
  29         IMAGE_SYM_TYPE_VOID              = 1
  30         IMAGE_SYM_TYPE_CHAR              = 2
  31         IMAGE_SYM_TYPE_SHORT             = 3
  32         IMAGE_SYM_TYPE_INT               = 4
  33         IMAGE_SYM_TYPE_LONG              = 5
  34         IMAGE_SYM_TYPE_FLOAT             = 6
  35         IMAGE_SYM_TYPE_DOUBLE            = 7
  36         IMAGE_SYM_TYPE_STRUCT            = 8
  37         IMAGE_SYM_TYPE_UNION             = 9
  38         IMAGE_SYM_TYPE_ENUM              = 10
  39         IMAGE_SYM_TYPE_MOE               = 11
  40         IMAGE_SYM_TYPE_BYTE              = 12
  41         IMAGE_SYM_TYPE_WORD              = 13
  42         IMAGE_SYM_TYPE_UINT              = 14
  43         IMAGE_SYM_TYPE_DWORD             = 15
  44         IMAGE_SYM_TYPE_PCODE             = 32768
  45         IMAGE_SYM_DTYPE_NULL             = 0
  46         IMAGE_SYM_DTYPE_POINTER          = 0x10
  47         IMAGE_SYM_DTYPE_FUNCTION         = 0x20
  48         IMAGE_SYM_DTYPE_ARRAY            = 0x30
  49         IMAGE_SYM_CLASS_END_OF_FUNCTION  = -1
  50         IMAGE_SYM_CLASS_NULL             = 0
  51         IMAGE_SYM_CLASS_AUTOMATIC        = 1
  52         IMAGE_SYM_CLASS_EXTERNAL         = 2
  53         IMAGE_SYM_CLASS_STATIC           = 3
  54         IMAGE_SYM_CLASS_REGISTER         = 4
  55         IMAGE_SYM_CLASS_EXTERNAL_DEF     = 5
  56         IMAGE_SYM_CLASS_LABEL            = 6
  57         IMAGE_SYM_CLASS_UNDEFINED_LABEL  = 7
  58         IMAGE_SYM_CLASS_MEMBER_OF_STRUCT = 8
  59         IMAGE_SYM_CLASS_ARGUMENT         = 9
  60         IMAGE_SYM_CLASS_STRUCT_TAG       = 10
  61         IMAGE_SYM_CLASS_MEMBER_OF_UNION  = 11
  62         IMAGE_SYM_CLASS_UNION_TAG        = 12
  63         IMAGE_SYM_CLASS_TYPE_DEFINITION  = 13
  64         IMAGE_SYM_CLASS_UNDEFINED_STATIC = 14
  65         IMAGE_SYM_CLASS_ENUM_TAG         = 15
  66         IMAGE_SYM_CLASS_MEMBER_OF_ENUM   = 16
  67         IMAGE_SYM_CLASS_REGISTER_PARAM   = 17
  68         IMAGE_SYM_CLASS_BIT_FIELD        = 18
  69         IMAGE_SYM_CLASS_FAR_EXTERNAL     = 68 /* Not in PECOFF v8 spec */
  70         IMAGE_SYM_CLASS_BLOCK            = 100
  71         IMAGE_SYM_CLASS_FUNCTION         = 101
  72         IMAGE_SYM_CLASS_END_OF_STRUCT    = 102
  73         IMAGE_SYM_CLASS_FILE             = 103
  74         IMAGE_SYM_CLASS_SECTION          = 104
  75         IMAGE_SYM_CLASS_WEAK_EXTERNAL    = 105
  76         IMAGE_SYM_CLASS_CLR_TOKEN        = 107
  77         IMAGE_REL_I386_ABSOLUTE          = 0x0000
  78         IMAGE_REL_I386_DIR16             = 0x0001
  79         IMAGE_REL_I386_REL16             = 0x0002
  80         IMAGE_REL_I386_DIR32             = 0x0006
  81         IMAGE_REL_I386_DIR32NB           = 0x0007
  82         IMAGE_REL_I386_SEG12             = 0x0009
  83         IMAGE_REL_I386_SECTION           = 0x000A
  84         IMAGE_REL_I386_SECREL            = 0x000B
  85         IMAGE_REL_I386_TOKEN             = 0x000C
  86         IMAGE_REL_I386_SECREL7           = 0x000D
  87         IMAGE_REL_I386_REL32             = 0x0014
  88         IMAGE_REL_AMD64_ABSOLUTE         = 0x0000
  89         IMAGE_REL_AMD64_ADDR64           = 0x0001
  90         IMAGE_REL_AMD64_ADDR32           = 0x0002
  91         IMAGE_REL_AMD64_ADDR32NB         = 0x0003
  92         IMAGE_REL_AMD64_REL32            = 0x0004
  93         IMAGE_REL_AMD64_REL32_1          = 0x0005
  94         IMAGE_REL_AMD64_REL32_2          = 0x0006
  95         IMAGE_REL_AMD64_REL32_3          = 0x0007
  96         IMAGE_REL_AMD64_REL32_4          = 0x0008
  97         IMAGE_REL_AMD64_REL32_5          = 0x0009
  98         IMAGE_REL_AMD64_SECTION          = 0x000A
  99         IMAGE_REL_AMD64_SECREL           = 0x000B
 100         IMAGE_REL_AMD64_SECREL7          = 0x000C
 101         IMAGE_REL_AMD64_TOKEN            = 0x000D
 102         IMAGE_REL_AMD64_SREL32           = 0x000E
 103         IMAGE_REL_AMD64_PAIR             = 0x000F
 104         IMAGE_REL_AMD64_SSPAN32          = 0x0010
 105         IMAGE_REL_ARM_ABSOLUTE           = 0x0000
 106         IMAGE_REL_ARM_ADDR32             = 0x0001
 107         IMAGE_REL_ARM_ADDR32NB           = 0x0002
 108         IMAGE_REL_ARM_BRANCH24           = 0x0003
 109         IMAGE_REL_ARM_BRANCH11           = 0x0004
 110         IMAGE_REL_ARM_SECTION            = 0x000E
 111         IMAGE_REL_ARM_SECREL             = 0x000F
 112         IMAGE_REL_ARM_MOV32              = 0x0010
 113         IMAGE_REL_THUMB_MOV32            = 0x0011
 114         IMAGE_REL_THUMB_BRANCH20         = 0x0012
 115         IMAGE_REL_THUMB_BRANCH24         = 0x0014
 116         IMAGE_REL_THUMB_BLX23            = 0x0015
 117         IMAGE_REL_ARM_PAIR               = 0x0016
 118 )
 119
 120 // TODO(crawshaw): de-duplicate these symbols with cmd/internal/ld, ideally in debug/pe.
 121 const (
 122         IMAGE_SCN_CNT_CODE               = 0x00000020
 123         IMAGE_SCN_CNT_INITIALIZED_DATA   = 0x00000040
 124         IMAGE_SCN_CNT_UNINITIALIZED_DATA = 0x00000080
 125         IMAGE_SCN_MEM_DISCARDABLE        = 0x02000000
 126         IMAGE_SCN_MEM_EXECUTE            = 0x20000000
 127         IMAGE_SCN_MEM_READ               = 0x40000000
 128         IMAGE_SCN_MEM_WRITE              = 0x80000000
 129 )
 130
 131 // TODO(brainman): maybe just add ReadAt method to bio.Reader instead of creating peBiobuf
 132
 133 // peBiobuf makes bio.Reader look like io.ReaderAt.
 134 type peBiobuf bio.Reader
 135
 136 func (f *peBiobuf) ReadAt(p []byte, off int64) (int, error) {
 137         ret := ((*bio.Reader)(f)).MustSeek(off, 0)
 138         if ret < 0 {
 139                 return 0, errors.New("fail to seek")
 140         }
 141         n, err := f.Read(p)
 142         if err != nil {
 143                 return 0, err
 144         }
 145         return n, nil
 146 }
 147
 148 func Load(l *loader.Loader, arch *sys.Arch, syms *sym.Symbols, input *bio.Reader, pkg string, length int64, pn string) (textp []*sym.Symbol, rsrc *sym.Symbol, err error) {
 149         lookup := func(name string, version int) *sym.Symbol {
 150                 return l.LookupOrCreate(name, version, syms)
 151         }
 152         return load(arch, lookup, syms.IncVersion(), input, pkg, length, pn)
 153 }
 154
 155 func LoadOld(arch *sys.Arch, syms *sym.Symbols, input *bio.Reader, pkg string, length int64, pn string) (textp []*sym.Symbol, rsrc *sym.Symbol, err error) {
 156         return load(arch, syms.Lookup, syms.IncVersion(), input, pkg, length, pn)
 157 }
 158
 159 // load loads the PE file pn from input.
 160 // Symbols are written into syms, and a slice of the text symbols is returned.
 161 // If an .rsrc section is found, its symbol is returned as rsrc.
 162 func load(arch *sys.Arch, lookup func(string, int) *sym.Symbol, localSymVersion int, input *bio.Reader, pkg string, length int64, pn string) (textp []*sym.Symbol, rsrc *sym.Symbol, err error) {
 163         sectsyms := make(map[*pe.Section]*sym.Symbol)
 164         sectdata := make(map[*pe.Section][]byte)
 165
 166         // Some input files are archives containing multiple of
 167         // object files, and pe.NewFile seeks to the start of
 168         // input file and get confused. Create section reader
 169         // to stop pe.NewFile looking before current position.
 170         sr := io.NewSectionReader((*peBiobuf)(input), input.Offset(), 1<<63-1)
 171
 172         // TODO: replace pe.NewFile with pe.Load (grep for "add Load function" in debug/pe for details)
 173         f, err := pe.NewFile(sr)
 174         if err != nil {
 175                 return nil, nil, err
 176         }
 177         defer f.Close()
 178
 179         // TODO return error if found .cormeta
 180
 181         // create symbols for mapped sections
 182         for _, sect := range f.Sections {
 183                 if sect.Characteristics&IMAGE_SCN_MEM_DISCARDABLE != 0 {
 184                         continue
 185                 }
 186
 187                 if sect.Characteristics&(IMAGE_SCN_CNT_CODE|IMAGE_SCN_CNT_INITIALIZED_DATA|IMAGE_SCN_CNT_UNINITIALIZED_DATA) == 0 {
 188                         // This has been seen for .idata sections, which we
 189                         // want to ignore. See issues 5106 and 5273.
 190                         continue
 191                 }
 192
 193                 name := fmt.Sprintf("%s(%s)", pkg, sect.Name)
 194                 s := lookup(name, localSymVersion)
 195
 196                 switch sect.Characteristics & (IMAGE_SCN_CNT_UNINITIALIZED_DATA | IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_WRITE | IMAGE_SCN_CNT_CODE | IMAGE_SCN_MEM_EXECUTE) {
 197                 case IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ: //.rdata
 198                         s.Type = sym.SRODATA
 199
 200                 case IMAGE_SCN_CNT_UNINITIALIZED_DATA | IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_WRITE: //.bss
 201                         s.Type = sym.SNOPTRBSS
 202
 203                 case IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_WRITE: //.data
 204                         s.Type = sym.SNOPTRDATA
 205
 206                 case IMAGE_SCN_CNT_CODE | IMAGE_SCN_MEM_EXECUTE | IMAGE_SCN_MEM_READ: //.text
 207                         s.Type = sym.STEXT
 208
 209                 default:
 210                         return nil, nil, fmt.Errorf("unexpected flags %#06x for PE section %s", sect.Characteristics, sect.Name)
 211                 }
 212
 213                 if s.Type != sym.SNOPTRBSS {
 214                         data, err := sect.Data()
 215                         if err != nil {
 216                                 return nil, nil, err
 217                         }
 218                         sectdata[sect] = data
 219                         s.P = data
 220                 }
 221                 s.Size = int64(sect.Size)
 222                 sectsyms[sect] = s
 223                 if sect.Name == ".rsrc" {
 224                         rsrc = s
 225                 }
 226         }
 227
 228         // load relocations
 229         for _, rsect := range f.Sections {
 230                 if _, found := sectsyms[rsect]; !found {
 231                         continue
 232                 }
 233                 if rsect.NumberOfRelocations == 0 {
 234                         continue
 235                 }
 236                 if rsect.Characteristics&IMAGE_SCN_MEM_DISCARDABLE != 0 {
 237                         continue
 238                 }
 239                 if rsect.Characteristics&(IMAGE_SCN_CNT_CODE|IMAGE_SCN_CNT_INITIALIZED_DATA|IMAGE_SCN_CNT_UNINITIALIZED_DATA) == 0 {
 240                         // This has been seen for .idata sections, which we
 241                         // want to ignore. See issues 5106 and 5273.
 242                         continue
 243                 }
 244
 245                 rs := make([]sym.Reloc, rsect.NumberOfRelocations)
 246                 for j, r := range rsect.Relocs {
 247                         rp := &rs[j]
 248                         if int(r.SymbolTableIndex) >= len(f.COFFSymbols) {
 249                                 return nil, nil, fmt.Errorf("relocation number %d symbol index idx=%d cannot be large then number of symbols %d", j, r.SymbolTableIndex, len(f.COFFSymbols))
 250                         }
 251                         pesym := &f.COFFSymbols[r.SymbolTableIndex]
 252                         gosym, err := readpesym(arch, lookup, f, pesym, sectsyms, localSymVersion)
 253                         if err != nil {
 254                                 return nil, nil, err
 255                         }
 256                         if gosym == nil {
 257                                 name, err := pesym.FullName(f.StringTable)
 258                                 if err != nil {
 259                                         name = string(pesym.Name[:])
 260                                 }
 261                                 return nil, nil, fmt.Errorf("reloc of invalid sym %s idx=%d type=%d", name, r.SymbolTableIndex, pesym.Type)
 262                         }
 263
 264                         rp.Sym = gosym
 265                         rp.Siz = 4
 266                         rp.Off = int32(r.VirtualAddress)
 267                         switch arch.Family {
 268                         default:
 269                                 return nil, nil, fmt.Errorf("%s: unsupported arch %v", pn, arch.Family)
 270                         case sys.I386, sys.AMD64:
 271                                 switch r.Type {
 272                                 default:
 273                                         return nil, nil, fmt.Errorf("%s: %v: unknown relocation type %v", pn, sectsyms[rsect], r.Type)
 274
 275                                 case IMAGE_REL_I386_REL32, IMAGE_REL_AMD64_REL32,
 276                                         IMAGE_REL_AMD64_ADDR32, // R_X86_64_PC32
 277                                         IMAGE_REL_AMD64_ADDR32NB:
 278                                         rp.Type = objabi.R_PCREL
 279
 280                                         rp.Add = int64(int32(binary.LittleEndian.Uint32(sectdata[rsect][rp.Off:])))
 281
 282                                 case IMAGE_REL_I386_DIR32NB, IMAGE_REL_I386_DIR32:
 283                                         rp.Type = objabi.R_ADDR
 284
 285                                         // load addend from image
 286                                         rp.Add = int64(int32(binary.LittleEndian.Uint32(sectdata[rsect][rp.Off:])))
 287
 288                                 case IMAGE_REL_AMD64_ADDR64: // R_X86_64_64
 289                                         rp.Siz = 8
 290
 291                                         rp.Type = objabi.R_ADDR
 292
 293                                         // load addend from image
 294                                         rp.Add = int64(binary.LittleEndian.Uint64(sectdata[rsect][rp.Off:]))
 295                                 }
 296
 297                         case sys.ARM:
 298                                 switch r.Type {
 299                                 default:
 300                                         return nil, nil, fmt.Errorf("%s: %v: unknown ARM relocation type %v", pn, sectsyms[rsect], r.Type)
 301
 302                                 case IMAGE_REL_ARM_SECREL:
 303                                         rp.Type = objabi.R_PCREL
 304
 305                                         rp.Add = int64(int32(binary.LittleEndian.Uint32(sectdata[rsect][rp.Off:])))
 306
 307                                 case IMAGE_REL_ARM_ADDR32:
 308                                         rp.Type = objabi.R_ADDR
 309
 310                                         rp.Add = int64(int32(binary.LittleEndian.Uint32(sectdata[rsect][rp.Off:])))
 311
 312                                 case IMAGE_REL_ARM_BRANCH24:
 313                                         rp.Type = objabi.R_CALLARM
 314
 315                                         rp.Add = int64(int32(binary.LittleEndian.Uint32(sectdata[rsect][rp.Off:])))
 316                                 }
 317                         }
 318
 319                         // ld -r could generate multiple section symbols for the
 320                         // same section but with different values, we have to take
 321                         // that into account
 322                         if issect(pesym) {
 323                                 rp.Add += int64(pesym.Value)
 324                         }
 325                 }
 326
 327                 sort.Sort(sym.RelocByOff(rs[:rsect.NumberOfRelocations]))
 328
 329                 s := sectsyms[rsect]
 330                 s.R = rs
 331                 s.R = s.R[:rsect.NumberOfRelocations]
 332         }
 333
 334         // enter sub-symbols into symbol table.
 335         for i, numaux := 0, 0; i < len(f.COFFSymbols); i += numaux + 1 {
 336                 pesym := &f.COFFSymbols[i]
 337
 338                 numaux = int(pesym.NumberOfAuxSymbols)
 339
 340                 name, err := pesym.FullName(f.StringTable)
 341                 if err != nil {
 342                         return nil, nil, err
 343                 }
 344                 if name == "" {
 345                         continue
 346                 }
 347                 if issect(pesym) {
 348                         continue
 349                 }
 350                 if int(pesym.SectionNumber) > len(f.Sections) {
 351                         continue
 352                 }
 353                 if pesym.SectionNumber == IMAGE_SYM_DEBUG {
 354                         continue
 355                 }
 356                 var sect *pe.Section
 357                 if pesym.SectionNumber > 0 {
 358                         sect = f.Sections[pesym.SectionNumber-1]
 359                         if _, found := sectsyms[sect]; !found {
 360                                 continue
 361                         }
 362                 }
 363
 364                 s, err := readpesym(arch, lookup, f, pesym, sectsyms, localSymVersion)
 365                 if err != nil {
 366                         return nil, nil, err
 367                 }
 368
 369                 if pesym.SectionNumber == 0 { // extern
 370                         if s.Type == sym.SDYNIMPORT {
 371                                 s.SetPlt(-2) // flag for dynimport in PE object files.
 372                         }
 373                         if s.Type == sym.SXREF && pesym.Value > 0 { // global data
 374                                 s.Type = sym.SNOPTRDATA
 375                                 s.Size = int64(pesym.Value)
 376                         }
 377
 378                         continue
 379                 } else if pesym.SectionNumber > 0 && int(pesym.SectionNumber) <= len(f.Sections) {
 380                         sect = f.Sections[pesym.SectionNumber-1]
 381                         if _, found := sectsyms[sect]; !found {
 382                                 return nil, nil, fmt.Errorf("%s: %v: missing sect.sym", pn, s)
 383                         }
 384                 } else {
 385                         return nil, nil, fmt.Errorf("%s: %v: sectnum < 0!", pn, s)
 386                 }
 387
 388                 if sect == nil {
 389                         return nil, rsrc, nil
 390                 }
 391
 392                 if s.Outer != nil {
 393                         if s.Attr.DuplicateOK() {
 394                                 continue
 395                         }
 396                         return nil, nil, fmt.Errorf("%s: duplicate symbol reference: %s in both %s and %s", pn, s.Name, s.Outer.Name, sectsyms[sect].Name)
 397                 }
 398
 399                 sectsym := sectsyms[sect]
 400                 s.Sub = sectsym.Sub
 401                 sectsym.Sub = s
 402                 s.Type = sectsym.Type
 403                 s.Attr |= sym.AttrSubSymbol
 404                 s.Value = int64(pesym.Value)
 405                 s.Size = 4
 406                 s.Outer = sectsym
 407                 if sectsym.Type == sym.STEXT {
 408                         if s.Attr.External() && !s.Attr.DuplicateOK() {
 409                                 return nil, nil, fmt.Errorf("%s: duplicate symbol definition", s.Name)
 410                         }
 411                         s.Attr |= sym.AttrExternal
 412                 }
 413         }
 414
 415         // Sort outer lists by address, adding to textp.
 416         // This keeps textp in increasing address order.
 417         for _, sect := range f.Sections {
 418                 s := sectsyms[sect]
 419                 if s == nil {
 420                         continue
 421                 }
 422                 if s.Sub != nil {
 423                         s.Sub = sym.SortSub(s.Sub)
 424                 }
 425                 if s.Type == sym.STEXT {
 426                         if s.Attr.OnList() {
 427                                 return nil, nil, fmt.Errorf("symbol %s listed multiple times", s.Name)
 428                         }
 429                         s.Attr |= sym.AttrOnList
 430                         textp = append(textp, s)
 431                         for s = s.Sub; s != nil; s = s.Sub {
 432                                 if s.Attr.OnList() {
 433                                         return nil, nil, fmt.Errorf("symbol %s listed multiple times", s.Name)
 434                                 }
 435                                 s.Attr |= sym.AttrOnList
 436                                 textp = append(textp, s)
 437                         }
 438                 }
 439         }
 440
 441         return textp, rsrc, nil
 442 }
 443
 444 func issect(s *pe.COFFSymbol) bool {
 445         return s.StorageClass == IMAGE_SYM_CLASS_STATIC && s.Type == 0 && s.Name[0] == '.'
 446 }
 447
 448 func readpesym(arch *sys.Arch, lookup func(string, int) *sym.Symbol, f *pe.File, pesym *pe.COFFSymbol, sectsyms map[*pe.Section]*sym.Symbol, localSymVersion int) (*sym.Symbol, error) {
 449         symname, err := pesym.FullName(f.StringTable)
 450         if err != nil {
 451                 return nil, err
 452         }
 453         var name string
 454         if issect(pesym) {
 455                 name = sectsyms[f.Sections[pesym.SectionNumber-1]].Name
 456         } else {
 457                 name = symname
 458                 switch arch.Family {
 459                 case sys.AMD64:
 460                         if name == "__imp___acrt_iob_func" {
 461                                 // Do not rename __imp___acrt_iob_func into __acrt_iob_func,
 462                                 // because __imp___acrt_iob_func symbol is real
 463                                 // (see commit b295099 from git://git.code.sf.net/p/mingw-w64/mingw-w64 for details).
 464                         } else {
 465                                 name = strings.TrimPrefix(name, "__imp_") // __imp_Name => Name
 466                         }
 467                 case sys.I386:
 468                         if name == "__imp____acrt_iob_func" {
 469                                 // Do not rename __imp____acrt_iob_func into ___acrt_iob_func,
 470                                 // because __imp____acrt_iob_func symbol is real
 471                                 // (see commit b295099 from git://git.code.sf.net/p/mingw-w64/mingw-w64 for details).
 472                         } else {
 473                                 name = strings.TrimPrefix(name, "__imp_") // __imp_Name => Name
 474                         }
 475                         if name[0] == '_' {
 476                                 name = name[1:] // _Name => Name
 477                         }
 478                 }
 479         }
 480
 481         // remove last @XXX
 482         if i := strings.LastIndex(name, "@"); i >= 0 {
 483                 name = name[:i]
 484         }
 485
 486         var s *sym.Symbol
 487         switch pesym.Type {
 488         default:
 489                 return nil, fmt.Errorf("%s: invalid symbol type %d", symname, pesym.Type)
 490
 491         case IMAGE_SYM_DTYPE_FUNCTION, IMAGE_SYM_DTYPE_NULL:
 492                 switch pesym.StorageClass {
 493                 case IMAGE_SYM_CLASS_EXTERNAL: //global
 494                         s = lookup(name, 0)
 495
 496                 case IMAGE_SYM_CLASS_NULL, IMAGE_SYM_CLASS_STATIC, IMAGE_SYM_CLASS_LABEL:
 497                         s = lookup(name, localSymVersion)
 498                         s.Attr |= sym.AttrDuplicateOK
 499
 500                 default:
 501                         return nil, fmt.Errorf("%s: invalid symbol binding %d", symname, pesym.StorageClass)
 502                 }
 503         }
 504
 505         if s != nil && s.Type == 0 && (pesym.StorageClass != IMAGE_SYM_CLASS_STATIC || pesym.Value != 0) {
 506                 s.Type = sym.SXREF
 507         }
 508         if strings.HasPrefix(symname, "__imp_") {
 509                 s.SetGot(-2) // flag for __imp_
 510         }
 511
 512         return s, nil
 513 }