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         "bytes"
  10         "cmd/internal/bio"
  11         "cmd/internal/objabi"
  12         "cmd/internal/sys"
  13         "cmd/link/internal/loader"
  14         "cmd/link/internal/sym"
  15         "debug/pe"
  16         "encoding/binary"
  17         "errors"
  18         "fmt"
  19         "io"
  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 // makeUpdater creates a loader.SymbolBuilder if one hasn't been created previously.
 149 // We use this to lazily make SymbolBuilders as we don't always need a builder, and creating them for all symbols might be an error.
 150 func makeUpdater(l *loader.Loader, bld *loader.SymbolBuilder, s loader.Sym) *loader.SymbolBuilder {
 151         if bld != nil {
 152                 return bld
 153         }
 154         bld = l.MakeSymbolUpdater(s)
 155         return bld
 156 }
 157
 158 // Load loads the PE file pn from input.
 159 // Symbols are written into syms, and a slice of the text symbols is returned.
 160 // If an .rsrc section is found, its symbol is returned as rsrc.
 161 func Load(l *loader.Loader, arch *sys.Arch, localSymVersion int, input *bio.Reader, pkg string, length int64, pn string) (textp []loader.Sym, rsrc loader.Sym, err error) {
 162         lookup := func(name string, version int) (*loader.SymbolBuilder, loader.Sym) {
 163                 s := l.LookupOrCreateSym(name, version)
 164                 sb := l.MakeSymbolUpdater(s)
 165                 return sb, s
 166         }
 167         sectsyms := make(map[*pe.Section]loader.Sym)
 168         sectdata := make(map[*pe.Section][]byte)
 169
 170         // Some input files are archives containing multiple of
 171         // object files, and pe.NewFile seeks to the start of
 172         // input file and get confused. Create section reader
 173         // to stop pe.NewFile looking before current position.
 174         sr := io.NewSectionReader((*peBiobuf)(input), input.Offset(), 1<<63-1)
 175
 176         // TODO: replace pe.NewFile with pe.Load (grep for "add Load function" in debug/pe for details)
 177         f, err := pe.NewFile(sr)
 178         if err != nil {
 179                 return nil, 0, err
 180         }
 181         defer f.Close()
 182
 183         // TODO return error if found .cormeta
 184
 185         // create symbols for mapped sections
 186         for _, sect := range f.Sections {
 187                 if sect.Characteristics&IMAGE_SCN_MEM_DISCARDABLE != 0 {
 188                         continue
 189                 }
 190
 191                 if sect.Characteristics&(IMAGE_SCN_CNT_CODE|IMAGE_SCN_CNT_INITIALIZED_DATA|IMAGE_SCN_CNT_UNINITIALIZED_DATA) == 0 {
 192                         // This has been seen for .idata sections, which we
 193                         // want to ignore. See issues 5106 and 5273.
 194                         continue
 195                 }
 196
 197                 name := fmt.Sprintf("%s(%s)", pkg, sect.Name)
 198                 bld, s := lookup(name, localSymVersion)
 199
 200                 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) {
 201                 case IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ: //.rdata
 202                         bld.SetType(sym.SRODATA)
 203
 204                 case IMAGE_SCN_CNT_UNINITIALIZED_DATA | IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_WRITE: //.bss
 205                         bld.SetType(sym.SNOPTRBSS)
 206
 207                 case IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_WRITE: //.data
 208                         bld.SetType(sym.SNOPTRDATA)
 209
 210                 case IMAGE_SCN_CNT_CODE | IMAGE_SCN_MEM_EXECUTE | IMAGE_SCN_MEM_READ: //.text
 211                         bld.SetType(sym.STEXT)
 212
 213                 default:
 214                         return nil, 0, fmt.Errorf("unexpected flags %#06x for PE section %s", sect.Characteristics, sect.Name)
 215                 }
 216
 217                 if bld.Type() != sym.SNOPTRBSS {
 218                         data, err := sect.Data()
 219                         if err != nil {
 220                                 return nil, 0, err
 221                         }
 222                         sectdata[sect] = data
 223                         bld.SetData(data)
 224                 }
 225                 bld.SetSize(int64(sect.Size))
 226                 sectsyms[sect] = s
 227                 if sect.Name == ".rsrc" {
 228                         rsrc = s
 229                 }
 230         }
 231
 232         // load relocations
 233         for _, rsect := range f.Sections {
 234                 if _, found := sectsyms[rsect]; !found {
 235                         continue
 236                 }
 237                 if rsect.NumberOfRelocations == 0 {
 238                         continue
 239                 }
 240                 if rsect.Characteristics&IMAGE_SCN_MEM_DISCARDABLE != 0 {
 241                         continue
 242                 }
 243                 if rsect.Characteristics&(IMAGE_SCN_CNT_CODE|IMAGE_SCN_CNT_INITIALIZED_DATA|IMAGE_SCN_CNT_UNINITIALIZED_DATA) == 0 {
 244                         // This has been seen for .idata sections, which we
 245                         // want to ignore. See issues 5106 and 5273.
 246                         continue
 247                 }
 248
 249                 sb := l.MakeSymbolUpdater(sectsyms[rsect])
 250                 for j, r := range rsect.Relocs {
 251                         if int(r.SymbolTableIndex) >= len(f.COFFSymbols) {
 252                                 return nil, 0, fmt.Errorf("relocation number %d symbol index idx=%d cannot be large then number of symbols %d", j, r.SymbolTableIndex, len(f.COFFSymbols))
 253                         }
 254                         pesym := &f.COFFSymbols[r.SymbolTableIndex]
 255                         _, gosym, err := readpesym(l, arch, l.LookupOrCreateSym, f, pesym, sectsyms, localSymVersion)
 256                         if err != nil {
 257                                 return nil, 0, err
 258                         }
 259                         if gosym == 0 {
 260                                 name, err := pesym.FullName(f.StringTable)
 261                                 if err != nil {
 262                                         name = string(pesym.Name[:])
 263                                 }
 264                                 return nil, 0, fmt.Errorf("reloc of invalid sym %s idx=%d type=%d", name, r.SymbolTableIndex, pesym.Type)
 265                         }
 266
 267                         rSym := gosym
 268                         rSize := uint8(4)
 269                         rOff := int32(r.VirtualAddress)
 270                         var rAdd int64
 271                         var rType objabi.RelocType
 272                         switch arch.Family {
 273                         default:
 274                                 return nil, 0, fmt.Errorf("%s: unsupported arch %v", pn, arch.Family)
 275                         case sys.I386, sys.AMD64:
 276                                 switch r.Type {
 277                                 default:
 278                                         return nil, 0, fmt.Errorf("%s: %v: unknown relocation type %v", pn, sectsyms[rsect], r.Type)
 279
 280                                 case IMAGE_REL_I386_REL32, IMAGE_REL_AMD64_REL32,
 281                                         IMAGE_REL_AMD64_ADDR32, // R_X86_64_PC32
 282                                         IMAGE_REL_AMD64_ADDR32NB:
 283                                         rType = objabi.R_PCREL
 284
 285                                         rAdd = int64(int32(binary.LittleEndian.Uint32(sectdata[rsect][rOff:])))
 286
 287                                 case IMAGE_REL_I386_DIR32NB, IMAGE_REL_I386_DIR32:
 288                                         rType = objabi.R_ADDR
 289
 290                                         // load addend from image
 291                                         rAdd = int64(int32(binary.LittleEndian.Uint32(sectdata[rsect][rOff:])))
 292
 293                                 case IMAGE_REL_AMD64_ADDR64: // R_X86_64_64
 294                                         rSize = 8
 295
 296                                         rType = objabi.R_ADDR
 297
 298                                         // load addend from image
 299                                         rAdd = int64(binary.LittleEndian.Uint64(sectdata[rsect][rOff:]))
 300                                 }
 301
 302                         case sys.ARM:
 303                                 switch r.Type {
 304                                 default:
 305                                         return nil, 0, fmt.Errorf("%s: %v: unknown ARM relocation type %v", pn, sectsyms[rsect], r.Type)
 306
 307                                 case IMAGE_REL_ARM_SECREL:
 308                                         rType = objabi.R_PCREL
 309
 310                                         rAdd = int64(int32(binary.LittleEndian.Uint32(sectdata[rsect][rOff:])))
 311
 312                                 case IMAGE_REL_ARM_ADDR32, IMAGE_REL_ARM_ADDR32NB:
 313                                         rType = objabi.R_ADDR
 314
 315                                         rAdd = int64(int32(binary.LittleEndian.Uint32(sectdata[rsect][rOff:])))
 316
 317                                 case IMAGE_REL_ARM_BRANCH24:
 318                                         rType = objabi.R_CALLARM
 319
 320                                         rAdd = int64(int32(binary.LittleEndian.Uint32(sectdata[rsect][rOff:])))
 321                                 }
 322                         }
 323
 324                         // ld -r could generate multiple section symbols for the
 325                         // same section but with different values, we have to take
 326                         // that into account
 327                         if issect(pesym) {
 328                                 rAdd += int64(pesym.Value)
 329                         }
 330
 331                         rel, _ := sb.AddRel(rType)
 332                         rel.SetOff(rOff)
 333                         rel.SetSiz(rSize)
 334                         rel.SetSym(rSym)
 335                         rel.SetAdd(rAdd)
 336                 }
 337
 338                 sb.SortRelocs()
 339         }
 340
 341         // enter sub-symbols into symbol table.
 342         for i, numaux := 0, 0; i < len(f.COFFSymbols); i += numaux + 1 {
 343                 pesym := &f.COFFSymbols[i]
 344
 345                 numaux = int(pesym.NumberOfAuxSymbols)
 346
 347                 name, err := pesym.FullName(f.StringTable)
 348                 if err != nil {
 349                         return nil, 0, err
 350                 }
 351                 if name == "" {
 352                         continue
 353                 }
 354                 if issect(pesym) {
 355                         continue
 356                 }
 357                 if int(pesym.SectionNumber) > len(f.Sections) {
 358                         continue
 359                 }
 360                 if pesym.SectionNumber == IMAGE_SYM_DEBUG {
 361                         continue
 362                 }
 363                 if pesym.SectionNumber == IMAGE_SYM_ABSOLUTE && bytes.Equal(pesym.Name[:], []byte("@feat.00")) {
 364                         // Microsoft's linker looks at whether all input objects have an empty
 365                         // section called @feat.00. If all of them do, then it enables SEH;
 366                         // otherwise it doesn't enable that feature. So, since around the Windows
 367                         // XP SP2 era, most tools that make PE objects just tack on that section,
 368                         // so that it won't gimp Microsoft's linker logic. Go doesn't support SEH,
 369                         // so in theory, none of this really matters to us. But actually, if the
 370                         // linker tries to ingest an object with @feat.00 -- which are produced by
 371                         // LLVM's resource compiler, for example -- it chokes because of the
 372                         // IMAGE_SYM_ABSOLUTE section that it doesn't know how to deal with. Since
 373                         // @feat.00 is just a marking anyway, skip IMAGE_SYM_ABSOLUTE sections that
 374                         // are called @feat.00.
 375                         continue
 376                 }
 377                 var sect *pe.Section
 378                 if pesym.SectionNumber > 0 {
 379                         sect = f.Sections[pesym.SectionNumber-1]
 380                         if _, found := sectsyms[sect]; !found {
 381                                 continue
 382                         }
 383                 }
 384
 385                 bld, s, err := readpesym(l, arch, l.LookupOrCreateSym, f, pesym, sectsyms, localSymVersion)
 386                 if err != nil {
 387                         return nil, 0, err
 388                 }
 389
 390                 if pesym.SectionNumber == 0 { // extern
 391                         if l.SymType(s) == sym.SDYNIMPORT {
 392                                 bld = makeUpdater(l, bld, s)
 393                                 bld.SetPlt(-2) // flag for dynimport in PE object files.
 394                         }
 395                         if l.SymType(s) == sym.SXREF && pesym.Value > 0 { // global data
 396                                 bld = makeUpdater(l, bld, s)
 397                                 bld.SetType(sym.SNOPTRDATA)
 398                                 bld.SetSize(int64(pesym.Value))
 399                         }
 400
 401                         continue
 402                 } else if pesym.SectionNumber > 0 && int(pesym.SectionNumber) <= len(f.Sections) {
 403                         sect = f.Sections[pesym.SectionNumber-1]
 404                         if _, found := sectsyms[sect]; !found {
 405                                 return nil, 0, fmt.Errorf("%s: %v: missing sect.sym", pn, s)
 406                         }
 407                 } else {
 408                         return nil, 0, fmt.Errorf("%s: %v: sectnum < 0!", pn, s)
 409                 }
 410
 411                 if sect == nil {
 412                         return nil, 0, nil
 413                 }
 414
 415                 if l.OuterSym(s) != 0 {
 416                         if l.AttrDuplicateOK(s) {
 417                                 continue
 418                         }
 419                         outerName := l.SymName(l.OuterSym(s))
 420                         sectName := l.SymName(sectsyms[sect])
 421                         return nil, 0, fmt.Errorf("%s: duplicate symbol reference: %s in both %s and %s", pn, l.SymName(s), outerName, sectName)
 422                 }
 423
 424                 bld = makeUpdater(l, bld, s)
 425                 sectsym := sectsyms[sect]
 426                 bld.SetType(l.SymType(sectsym))
 427                 l.AddInteriorSym(sectsym, s)
 428                 bld.SetValue(int64(pesym.Value))
 429                 bld.SetSize(4)
 430                 if l.SymType(sectsym) == sym.STEXT {
 431                         if bld.External() && !bld.DuplicateOK() {
 432                                 return nil, 0, fmt.Errorf("%s: duplicate symbol definition", l.SymName(s))
 433                         }
 434                         bld.SetExternal(true)
 435                 }
 436         }
 437
 438         // Sort outer lists by address, adding to textp.
 439         // This keeps textp in increasing address order.
 440         for _, sect := range f.Sections {
 441                 s := sectsyms[sect]
 442                 if s == 0 {
 443                         continue
 444                 }
 445                 l.SortSub(s)
 446                 if l.SymType(s) == sym.STEXT {
 447                         for ; s != 0; s = l.SubSym(s) {
 448                                 if l.AttrOnList(s) {
 449                                         return nil, 0, fmt.Errorf("symbol %s listed multiple times", l.SymName(s))
 450                                 }
 451                                 l.SetAttrOnList(s, true)
 452                                 textp = append(textp, s)
 453                         }
 454                 }
 455         }
 456
 457         return textp, rsrc, nil
 458 }
 459
 460 func issect(s *pe.COFFSymbol) bool {
 461         return s.StorageClass == IMAGE_SYM_CLASS_STATIC && s.Type == 0 && s.Name[0] == '.'
 462 }
 463
 464 func readpesym(l *loader.Loader, arch *sys.Arch, lookup func(string, int) loader.Sym, f *pe.File, pesym *pe.COFFSymbol, sectsyms map[*pe.Section]loader.Sym, localSymVersion int) (*loader.SymbolBuilder, loader.Sym, error) {
 465         symname, err := pesym.FullName(f.StringTable)
 466         if err != nil {
 467                 return nil, 0, err
 468         }
 469         var name string
 470         if issect(pesym) {
 471                 name = l.SymName(sectsyms[f.Sections[pesym.SectionNumber-1]])
 472         } else {
 473                 name = symname
 474                 switch arch.Family {
 475                 case sys.AMD64:
 476                         if name == "__imp___acrt_iob_func" {
 477                                 // Do not rename __imp___acrt_iob_func into __acrt_iob_func,
 478                                 // because __imp___acrt_iob_func symbol is real
 479                                 // (see commit b295099 from git://git.code.sf.net/p/mingw-w64/mingw-w64 for details).
 480                         } else {
 481                                 name = strings.TrimPrefix(name, "__imp_") // __imp_Name => Name
 482                         }
 483                 case sys.I386:
 484                         if name == "__imp____acrt_iob_func" {
 485                                 // Do not rename __imp____acrt_iob_func into ___acrt_iob_func,
 486                                 // because __imp____acrt_iob_func symbol is real
 487                                 // (see commit b295099 from git://git.code.sf.net/p/mingw-w64/mingw-w64 for details).
 488                         } else {
 489                                 name = strings.TrimPrefix(name, "__imp_") // __imp_Name => Name
 490                         }
 491                         if name[0] == '_' {
 492                                 name = name[1:] // _Name => Name
 493                         }
 494                 }
 495         }
 496
 497         // remove last @XXX
 498         if i := strings.LastIndex(name, "@"); i >= 0 {
 499                 name = name[:i]
 500         }
 501
 502         var s loader.Sym
 503         var bld *loader.SymbolBuilder
 504         switch pesym.Type {
 505         default:
 506                 return nil, 0, fmt.Errorf("%s: invalid symbol type %d", symname, pesym.Type)
 507
 508         case IMAGE_SYM_DTYPE_FUNCTION, IMAGE_SYM_DTYPE_NULL:
 509                 switch pesym.StorageClass {
 510                 case IMAGE_SYM_CLASS_EXTERNAL: //global
 511                         s = lookup(name, 0)
 512
 513                 case IMAGE_SYM_CLASS_NULL, IMAGE_SYM_CLASS_STATIC, IMAGE_SYM_CLASS_LABEL:
 514                         s = lookup(name, localSymVersion)
 515                         bld = makeUpdater(l, bld, s)
 516                         bld.SetDuplicateOK(true)
 517
 518                 default:
 519                         return nil, 0, fmt.Errorf("%s: invalid symbol binding %d", symname, pesym.StorageClass)
 520                 }
 521         }
 522
 523         if s != 0 && l.SymType(s) == 0 && (pesym.StorageClass != IMAGE_SYM_CLASS_STATIC || pesym.Value != 0) {
 524                 bld = makeUpdater(l, bld, s)
 525                 bld.SetType(sym.SXREF)
 526         }
 527         if strings.HasPrefix(symname, "__imp_") {
 528                 bld = makeUpdater(l, bld, s)
 529                 bld.SetGot(-2) // flag for __imp_
 530         }
 531
 532         return bld, s, nil
 533 }