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         IMAGE_SYM_UNDEFINED              = 0
  25         IMAGE_SYM_ABSOLUTE               = -1
  26         IMAGE_SYM_DEBUG                  = -2
  27         IMAGE_SYM_TYPE_NULL              = 0
  28         IMAGE_SYM_TYPE_VOID              = 1
  29         IMAGE_SYM_TYPE_CHAR              = 2
  30         IMAGE_SYM_TYPE_SHORT             = 3
  31         IMAGE_SYM_TYPE_INT               = 4
  32         IMAGE_SYM_TYPE_LONG              = 5
  33         IMAGE_SYM_TYPE_FLOAT             = 6
  34         IMAGE_SYM_TYPE_DOUBLE            = 7
  35         IMAGE_SYM_TYPE_STRUCT            = 8
  36         IMAGE_SYM_TYPE_UNION             = 9
  37         IMAGE_SYM_TYPE_ENUM              = 10
  38         IMAGE_SYM_TYPE_MOE               = 11
  39         IMAGE_SYM_TYPE_BYTE              = 12
  40         IMAGE_SYM_TYPE_WORD              = 13
  41         IMAGE_SYM_TYPE_UINT              = 14
  42         IMAGE_SYM_TYPE_DWORD             = 15
  43         IMAGE_SYM_TYPE_PCODE             = 32768
  44         IMAGE_SYM_DTYPE_NULL             = 0
  45         IMAGE_SYM_DTYPE_POINTER          = 1
  46         IMAGE_SYM_DTYPE_FUNCTION         = 2
  47         IMAGE_SYM_DTYPE_ARRAY            = 3
  48         IMAGE_SYM_CLASS_END_OF_FUNCTION  = -1
  49         IMAGE_SYM_CLASS_NULL             = 0
  50         IMAGE_SYM_CLASS_AUTOMATIC        = 1
  51         IMAGE_SYM_CLASS_EXTERNAL         = 2
  52         IMAGE_SYM_CLASS_STATIC           = 3
  53         IMAGE_SYM_CLASS_REGISTER         = 4
  54         IMAGE_SYM_CLASS_EXTERNAL_DEF     = 5
  55         IMAGE_SYM_CLASS_LABEL            = 6
  56         IMAGE_SYM_CLASS_UNDEFINED_LABEL  = 7
  57         IMAGE_SYM_CLASS_MEMBER_OF_STRUCT = 8
  58         IMAGE_SYM_CLASS_ARGUMENT         = 9
  59         IMAGE_SYM_CLASS_STRUCT_TAG       = 10
  60         IMAGE_SYM_CLASS_MEMBER_OF_UNION  = 11
  61         IMAGE_SYM_CLASS_UNION_TAG        = 12
  62         IMAGE_SYM_CLASS_TYPE_DEFINITION  = 13
  63         IMAGE_SYM_CLASS_UNDEFINED_STATIC = 14
  64         IMAGE_SYM_CLASS_ENUM_TAG         = 15
  65         IMAGE_SYM_CLASS_MEMBER_OF_ENUM   = 16
  66         IMAGE_SYM_CLASS_REGISTER_PARAM   = 17
  67         IMAGE_SYM_CLASS_BIT_FIELD        = 18
  68         IMAGE_SYM_CLASS_FAR_EXTERNAL     = 68 /* Not in PECOFF v8 spec */
  69         IMAGE_SYM_CLASS_BLOCK            = 100
  70         IMAGE_SYM_CLASS_FUNCTION         = 101
  71         IMAGE_SYM_CLASS_END_OF_STRUCT    = 102
  72         IMAGE_SYM_CLASS_FILE             = 103
  73         IMAGE_SYM_CLASS_SECTION          = 104
  74         IMAGE_SYM_CLASS_WEAK_EXTERNAL    = 105
  75         IMAGE_SYM_CLASS_CLR_TOKEN        = 107
  76         IMAGE_REL_I386_ABSOLUTE          = 0x0000
  77         IMAGE_REL_I386_DIR16             = 0x0001
  78         IMAGE_REL_I386_REL16             = 0x0002
  79         IMAGE_REL_I386_DIR32             = 0x0006
  80         IMAGE_REL_I386_DIR32NB           = 0x0007
  81         IMAGE_REL_I386_SEG12             = 0x0009
  82         IMAGE_REL_I386_SECTION           = 0x000A
  83         IMAGE_REL_I386_SECREL            = 0x000B
  84         IMAGE_REL_I386_TOKEN             = 0x000C
  85         IMAGE_REL_I386_SECREL7           = 0x000D
  86         IMAGE_REL_I386_REL32             = 0x0014
  87         IMAGE_REL_AMD64_ABSOLUTE         = 0x0000
  88         IMAGE_REL_AMD64_ADDR64           = 0x0001
  89         IMAGE_REL_AMD64_ADDR32           = 0x0002
  90         IMAGE_REL_AMD64_ADDR32NB         = 0x0003
  91         IMAGE_REL_AMD64_REL32            = 0x0004
  92         IMAGE_REL_AMD64_REL32_1          = 0x0005
  93         IMAGE_REL_AMD64_REL32_2          = 0x0006
  94         IMAGE_REL_AMD64_REL32_3          = 0x0007
  95         IMAGE_REL_AMD64_REL32_4          = 0x0008
  96         IMAGE_REL_AMD64_REL32_5          = 0x0009
  97         IMAGE_REL_AMD64_SECTION          = 0x000A
  98         IMAGE_REL_AMD64_SECREL           = 0x000B
  99         IMAGE_REL_AMD64_SECREL7          = 0x000C
 100         IMAGE_REL_AMD64_TOKEN            = 0x000D
 101         IMAGE_REL_AMD64_SREL32           = 0x000E
 102         IMAGE_REL_AMD64_PAIR             = 0x000F
 103         IMAGE_REL_AMD64_SSPAN32          = 0x0010
 104         IMAGE_REL_ARM_ABSOLUTE           = 0x0000
 105         IMAGE_REL_ARM_ADDR32             = 0x0001
 106         IMAGE_REL_ARM_ADDR32NB           = 0x0002
 107         IMAGE_REL_ARM_BRANCH24           = 0x0003
 108         IMAGE_REL_ARM_BRANCH11           = 0x0004
 109         IMAGE_REL_ARM_SECTION            = 0x000E
 110         IMAGE_REL_ARM_SECREL             = 0x000F
 111         IMAGE_REL_ARM_MOV32              = 0x0010
 112         IMAGE_REL_THUMB_MOV32            = 0x0011
 113         IMAGE_REL_THUMB_BRANCH20         = 0x0012
 114         IMAGE_REL_THUMB_BRANCH24         = 0x0014
 115         IMAGE_REL_THUMB_BLX23            = 0x0015
 116         IMAGE_REL_ARM_PAIR               = 0x0016
 117         IMAGE_REL_ARM64_ABSOLUTE         = 0x0000
 118         IMAGE_REL_ARM64_ADDR32           = 0x0001
 119         IMAGE_REL_ARM64_ADDR32NB         = 0x0002
 120         IMAGE_REL_ARM64_BRANCH26         = 0x0003
 121         IMAGE_REL_ARM64_PAGEBASE_REL21   = 0x0004
 122         IMAGE_REL_ARM64_REL21            = 0x0005
 123         IMAGE_REL_ARM64_PAGEOFFSET_12A   = 0x0006
 124         IMAGE_REL_ARM64_PAGEOFFSET_12L   = 0x0007
 125         IMAGE_REL_ARM64_SECREL           = 0x0008
 126         IMAGE_REL_ARM64_SECREL_LOW12A    = 0x0009
 127         IMAGE_REL_ARM64_SECREL_HIGH12A   = 0x000A
 128         IMAGE_REL_ARM64_SECREL_LOW12L    = 0x000B
 129         IMAGE_REL_ARM64_TOKEN            = 0x000C
 130         IMAGE_REL_ARM64_SECTION          = 0x000D
 131         IMAGE_REL_ARM64_ADDR64           = 0x000E
 132         IMAGE_REL_ARM64_BRANCH19         = 0x000F
 133         IMAGE_REL_ARM64_BRANCH14         = 0x0010
 134         IMAGE_REL_ARM64_REL32            = 0x0011
 135 )
 136
 137 const (
 138         // When stored into the PLT value for a symbol, this token tells
 139         // windynrelocsym to redirect direct references to this symbol to a stub
 140         // that loads from the corresponding import symbol and then does
 141         // a jump to the loaded value.
 142         CreateImportStubPltToken = -2
 143
 144         // When stored into the GOT value for an import symbol __imp_X this
 145         // token tells windynrelocsym to redirect references to the
 146         // underlying DYNIMPORT symbol X.
 147         RedirectToDynImportGotToken = -2
 148 )
 149
 150 // TODO(brainman): maybe just add ReadAt method to bio.Reader instead of creating peBiobuf
 151
 152 // peBiobuf makes bio.Reader look like io.ReaderAt.
 153 type peBiobuf bio.Reader
 154
 155 func (f *peBiobuf) ReadAt(p []byte, off int64) (int, error) {
 156         ret := ((*bio.Reader)(f)).MustSeek(off, 0)
 157         if ret < 0 {
 158                 return 0, errors.New("fail to seek")
 159         }
 160         n, err := f.Read(p)
 161         if err != nil {
 162                 return 0, err
 163         }
 164         return n, nil
 165 }
 166
 167 // makeUpdater creates a loader.SymbolBuilder if one hasn't been created previously.
 168 // 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.
 169 func makeUpdater(l *loader.Loader, bld *loader.SymbolBuilder, s loader.Sym) *loader.SymbolBuilder {
 170         if bld != nil {
 171                 return bld
 172         }
 173         bld = l.MakeSymbolUpdater(s)
 174         return bld
 175 }
 176
 177 // peImportSymsState tracks the set of DLL import symbols we've seen
 178 // while reading host objects. We create a singleton instance of this
 179 // type, which will persist across multiple host objects.
 180 type peImportSymsState struct {
 181
 182         // Text and non-text sections read in by the host object loader.
 183         secSyms []loader.Sym
 184
 185         // SDYNIMPORT symbols encountered along the way
 186         dynimports map[loader.Sym]struct{}
 187
 188         // Loader and arch, for use in postprocessing.
 189         l    *loader.Loader
 190         arch *sys.Arch
 191 }
 192
 193 var importSymsState *peImportSymsState
 194
 195 func createImportSymsState(l *loader.Loader, arch *sys.Arch) {
 196         if importSymsState != nil {
 197                 return
 198         }
 199         importSymsState = &peImportSymsState{
 200                 dynimports: make(map[loader.Sym]struct{}),
 201                 l:          l,
 202                 arch:       arch,
 203         }
 204 }
 205
 206 // peLoaderState holds various bits of useful state information needed
 207 // while loading a single PE object file.
 208 type peLoaderState struct {
 209         l               *loader.Loader
 210         arch            *sys.Arch
 211         f               *pe.File
 212         pn              string
 213         sectsyms        map[*pe.Section]loader.Sym
 214         comdats         map[uint16]int64 // key is section index, val is size
 215         sectdata        map[*pe.Section][]byte
 216         localSymVersion int
 217 }
 218
 219 // comdatDefinitions records the names of symbols for which we've
 220 // previously seen a definition in COMDAT. Key is symbol name, value
 221 // is symbol size (or -1 if we're using the "any" strategy).
 222 var comdatDefinitions map[string]int64
 223
 224 // Symbols contains the symbols that can be loaded from a PE file.
 225 type Symbols struct {
 226         Textp     []loader.Sym // text symbols
 227         Resources []loader.Sym // .rsrc section or set of .rsrc$xx sections
 228         PData     loader.Sym
 229         XData     loader.Sym
 230 }
 231
 232 // Load loads the PE file pn from input.
 233 // Symbols from the object file are created via the loader 'l'.
 234 func Load(l *loader.Loader, arch *sys.Arch, localSymVersion int, input *bio.Reader, pkg string, length int64, pn string) (*Symbols, error) {
 235         state := &peLoaderState{
 236                 l:               l,
 237                 arch:            arch,
 238                 sectsyms:        make(map[*pe.Section]loader.Sym),
 239                 sectdata:        make(map[*pe.Section][]byte),
 240                 localSymVersion: localSymVersion,
 241                 pn:              pn,
 242         }
 243         createImportSymsState(state.l, state.arch)
 244         if comdatDefinitions == nil {
 245                 comdatDefinitions = make(map[string]int64)
 246         }
 247
 248         // Some input files are archives containing multiple of
 249         // object files, and pe.NewFile seeks to the start of
 250         // input file and get confused. Create section reader
 251         // to stop pe.NewFile looking before current position.
 252         sr := io.NewSectionReader((*peBiobuf)(input), input.Offset(), 1<<63-1)
 253
 254         // TODO: replace pe.NewFile with pe.Load (grep for "add Load function" in debug/pe for details)
 255         f, err := pe.NewFile(sr)
 256         if err != nil {
 257                 return nil, err
 258         }
 259         defer f.Close()
 260         state.f = f
 261
 262         var ls Symbols
 263
 264         // TODO return error if found .cormeta
 265
 266         // create symbols for mapped sections
 267         for _, sect := range f.Sections {
 268                 if sect.Characteristics&pe.IMAGE_SCN_MEM_DISCARDABLE != 0 {
 269                         continue
 270                 }
 271
 272                 if sect.Characteristics&(pe.IMAGE_SCN_CNT_CODE|pe.IMAGE_SCN_CNT_INITIALIZED_DATA|pe.IMAGE_SCN_CNT_UNINITIALIZED_DATA) == 0 {
 273                         // This has been seen for .idata sections, which we
 274                         // want to ignore. See issues 5106 and 5273.
 275                         continue
 276                 }
 277
 278                 name := fmt.Sprintf("%s(%s)", pkg, sect.Name)
 279                 s := state.l.LookupOrCreateCgoExport(name, localSymVersion)
 280                 bld := l.MakeSymbolUpdater(s)
 281
 282                 switch sect.Characteristics & (pe.IMAGE_SCN_CNT_UNINITIALIZED_DATA | pe.IMAGE_SCN_CNT_INITIALIZED_DATA | pe.IMAGE_SCN_MEM_READ | pe.IMAGE_SCN_MEM_WRITE | pe.IMAGE_SCN_CNT_CODE | pe.IMAGE_SCN_MEM_EXECUTE) {
 283                 case pe.IMAGE_SCN_CNT_INITIALIZED_DATA | pe.IMAGE_SCN_MEM_READ: //.rdata
 284                         if issehsect(arch, sect) {
 285                                 bld.SetType(sym.SSEHSECT)
 286                                 bld.SetAlign(4)
 287                         } else {
 288                                 bld.SetType(sym.SRODATA)
 289                         }
 290
 291                 case pe.IMAGE_SCN_CNT_UNINITIALIZED_DATA | pe.IMAGE_SCN_MEM_READ | pe.IMAGE_SCN_MEM_WRITE: //.bss
 292                         bld.SetType(sym.SNOPTRBSS)
 293
 294                 case pe.IMAGE_SCN_CNT_INITIALIZED_DATA | pe.IMAGE_SCN_MEM_READ | pe.IMAGE_SCN_MEM_WRITE: //.data
 295                         bld.SetType(sym.SNOPTRDATA)
 296
 297                 case pe.IMAGE_SCN_CNT_CODE | pe.IMAGE_SCN_MEM_EXECUTE | pe.IMAGE_SCN_MEM_READ: //.text
 298                         bld.SetType(sym.STEXT)
 299
 300                 default:
 301                         return nil, fmt.Errorf("unexpected flags %#06x for PE section %s", sect.Characteristics, sect.Name)
 302                 }
 303
 304                 if bld.Type() != sym.SNOPTRBSS {
 305                         data, err := sect.Data()
 306                         if err != nil {
 307                                 return nil, err
 308                         }
 309                         state.sectdata[sect] = data
 310                         bld.SetData(data)
 311                 }
 312                 bld.SetSize(int64(sect.Size))
 313                 state.sectsyms[sect] = s
 314                 if sect.Name == ".rsrc" || strings.HasPrefix(sect.Name, ".rsrc$") {
 315                         ls.Resources = append(ls.Resources, s)
 316                 } else if bld.Type() == sym.SSEHSECT {
 317                         if sect.Name == ".pdata" {
 318                                 ls.PData = s
 319                         } else if sect.Name == ".xdata" {
 320                                 ls.XData = s
 321                         }
 322                 }
 323         }
 324
 325         // Make a prepass over the symbols to collect info about COMDAT symbols.
 326         if err := state.preprocessSymbols(); err != nil {
 327                 return nil, err
 328         }
 329
 330         // load relocations
 331         for _, rsect := range f.Sections {
 332                 if _, found := state.sectsyms[rsect]; !found {
 333                         continue
 334                 }
 335                 if rsect.NumberOfRelocations == 0 {
 336                         continue
 337                 }
 338                 if rsect.Characteristics&pe.IMAGE_SCN_MEM_DISCARDABLE != 0 {
 339                         continue
 340                 }
 341                 if rsect.Characteristics&(pe.IMAGE_SCN_CNT_CODE|pe.IMAGE_SCN_CNT_INITIALIZED_DATA|pe.IMAGE_SCN_CNT_UNINITIALIZED_DATA) == 0 {
 342                         // This has been seen for .idata sections, which we
 343                         // want to ignore. See issues 5106 and 5273.
 344                         continue
 345                 }
 346
 347                 splitResources := strings.HasPrefix(rsect.Name, ".rsrc$")
 348                 issehsect := issehsect(arch, rsect)
 349                 sb := l.MakeSymbolUpdater(state.sectsyms[rsect])
 350                 for j, r := range rsect.Relocs {
 351                         if int(r.SymbolTableIndex) >= len(f.COFFSymbols) {
 352                                 return nil, fmt.Errorf("relocation number %d symbol index idx=%d cannot be large then number of symbols %d", j, r.SymbolTableIndex, len(f.COFFSymbols))
 353                         }
 354                         pesym := &f.COFFSymbols[r.SymbolTableIndex]
 355                         _, gosym, err := state.readpesym(pesym)
 356                         if err != nil {
 357                                 return nil, err
 358                         }
 359                         if gosym == 0 {
 360                                 name, err := pesym.FullName(f.StringTable)
 361                                 if err != nil {
 362                                         name = string(pesym.Name[:])
 363                                 }
 364                                 return nil, fmt.Errorf("reloc of invalid sym %s idx=%d type=%d", name, r.SymbolTableIndex, pesym.Type)
 365                         }
 366
 367                         rSym := gosym
 368                         rSize := uint8(4)
 369                         rOff := int32(r.VirtualAddress)
 370                         var rAdd int64
 371                         var rType objabi.RelocType
 372                         switch arch.Family {
 373                         default:
 374                                 return nil, fmt.Errorf("%s: unsupported arch %v", pn, arch.Family)
 375                         case sys.I386, sys.AMD64:
 376                                 switch r.Type {
 377                                 default:
 378                                         return nil, fmt.Errorf("%s: %v: unknown relocation type %v", pn, state.sectsyms[rsect], r.Type)
 379
 380                                 case IMAGE_REL_I386_REL32, IMAGE_REL_AMD64_REL32,
 381                                         IMAGE_REL_AMD64_ADDR32, // R_X86_64_PC32
 382                                         IMAGE_REL_AMD64_ADDR32NB:
 383                                         if r.Type == IMAGE_REL_AMD64_ADDR32NB {
 384                                                 rType = objabi.R_PEIMAGEOFF
 385                                         } else {
 386                                                 rType = objabi.R_PCREL
 387                                         }
 388
 389                                         rAdd = int64(int32(binary.LittleEndian.Uint32(state.sectdata[rsect][rOff:])))
 390
 391                                 case IMAGE_REL_I386_DIR32NB, IMAGE_REL_I386_DIR32:
 392                                         if r.Type == IMAGE_REL_I386_DIR32NB {
 393                                                 rType = objabi.R_PEIMAGEOFF
 394                                         } else {
 395                                                 rType = objabi.R_ADDR
 396                                         }
 397
 398                                         // load addend from image
 399                                         rAdd = int64(int32(binary.LittleEndian.Uint32(state.sectdata[rsect][rOff:])))
 400
 401                                 case IMAGE_REL_AMD64_ADDR64: // R_X86_64_64
 402                                         rSize = 8
 403
 404                                         rType = objabi.R_ADDR
 405
 406                                         // load addend from image
 407                                         rAdd = int64(binary.LittleEndian.Uint64(state.sectdata[rsect][rOff:]))
 408                                 }
 409
 410                         case sys.ARM:
 411                                 switch r.Type {
 412                                 default:
 413                                         return nil, fmt.Errorf("%s: %v: unknown ARM relocation type %v", pn, state.sectsyms[rsect], r.Type)
 414
 415                                 case IMAGE_REL_ARM_SECREL:
 416                                         rType = objabi.R_PCREL
 417
 418                                         rAdd = int64(int32(binary.LittleEndian.Uint32(state.sectdata[rsect][rOff:])))
 419
 420                                 case IMAGE_REL_ARM_ADDR32, IMAGE_REL_ARM_ADDR32NB:
 421                                         if r.Type == IMAGE_REL_ARM_ADDR32NB {
 422                                                 rType = objabi.R_PEIMAGEOFF
 423                                         } else {
 424                                                 rType = objabi.R_ADDR
 425                                         }
 426
 427                                         rAdd = int64(int32(binary.LittleEndian.Uint32(state.sectdata[rsect][rOff:])))
 428
 429                                 case IMAGE_REL_ARM_BRANCH24:
 430                                         rType = objabi.R_CALLARM
 431
 432                                         rAdd = int64(int32(binary.LittleEndian.Uint32(state.sectdata[rsect][rOff:])))
 433                                 }
 434
 435                         case sys.ARM64:
 436                                 switch r.Type {
 437                                 default:
 438                                         return nil, fmt.Errorf("%s: %v: unknown ARM64 relocation type %v", pn, state.sectsyms[rsect], r.Type)
 439
 440                                 case IMAGE_REL_ARM64_ADDR32, IMAGE_REL_ARM64_ADDR32NB:
 441                                         if r.Type == IMAGE_REL_ARM64_ADDR32NB {
 442                                                 rType = objabi.R_PEIMAGEOFF
 443                                         } else {
 444                                                 rType = objabi.R_ADDR
 445                                         }
 446
 447                                         rAdd = int64(int32(binary.LittleEndian.Uint32(state.sectdata[rsect][rOff:])))
 448                                 }
 449                         }
 450
 451                         // ld -r could generate multiple section symbols for the
 452                         // same section but with different values, we have to take
 453                         // that into account, or in the case of split resources,
 454                         // the section and its symbols are split into two sections.
 455                         if issect(pesym) || splitResources {
 456                                 rAdd += int64(pesym.Value)
 457                         }
 458                         if issehsect {
 459                                 // .pdata and .xdata sections can contain records
 460                                 // associated to functions that won't be used in
 461                                 // the final binary, in which case the relocation
 462                                 // target symbol won't be reachable.
 463                                 rType |= objabi.R_WEAK
 464                         }
 465
 466                         rel, _ := sb.AddRel(rType)
 467                         rel.SetOff(rOff)
 468                         rel.SetSiz(rSize)
 469                         rel.SetSym(rSym)
 470                         rel.SetAdd(rAdd)
 471
 472                 }
 473
 474                 sb.SortRelocs()
 475         }
 476
 477         // enter sub-symbols into symbol table.
 478         for i, numaux := 0, 0; i < len(f.COFFSymbols); i += numaux + 1 {
 479                 pesym := &f.COFFSymbols[i]
 480
 481                 numaux = int(pesym.NumberOfAuxSymbols)
 482
 483                 name, err := pesym.FullName(f.StringTable)
 484                 if err != nil {
 485                         return nil, err
 486                 }
 487                 if name == "" {
 488                         continue
 489                 }
 490                 if issect(pesym) {
 491                         continue
 492                 }
 493                 if int(pesym.SectionNumber) > len(f.Sections) {
 494                         continue
 495                 }
 496                 if pesym.SectionNumber == IMAGE_SYM_DEBUG {
 497                         continue
 498                 }
 499                 if pesym.SectionNumber == IMAGE_SYM_ABSOLUTE && bytes.Equal(pesym.Name[:], []byte("@feat.00")) {
 500                         // Microsoft's linker looks at whether all input objects have an empty
 501                         // section called @feat.00. If all of them do, then it enables SEH;
 502                         // otherwise it doesn't enable that feature. So, since around the Windows
 503                         // XP SP2 era, most tools that make PE objects just tack on that section,
 504                         // so that it won't gimp Microsoft's linker logic. Go doesn't support SEH,
 505                         // so in theory, none of this really matters to us. But actually, if the
 506                         // linker tries to ingest an object with @feat.00 -- which are produced by
 507                         // LLVM's resource compiler, for example -- it chokes because of the
 508                         // IMAGE_SYM_ABSOLUTE section that it doesn't know how to deal with. Since
 509                         // @feat.00 is just a marking anyway, skip IMAGE_SYM_ABSOLUTE sections that
 510                         // are called @feat.00.
 511                         continue
 512                 }
 513                 var sect *pe.Section
 514                 if pesym.SectionNumber > 0 {
 515                         sect = f.Sections[pesym.SectionNumber-1]
 516                         if _, found := state.sectsyms[sect]; !found {
 517                                 continue
 518                         }
 519                 }
 520
 521                 bld, s, err := state.readpesym(pesym)
 522                 if err != nil {
 523                         return nil, err
 524                 }
 525
 526                 if pesym.SectionNumber == 0 { // extern
 527                         if l.SymType(s) == sym.SXREF && pesym.Value > 0 { // global data
 528                                 bld = makeUpdater(l, bld, s)
 529                                 bld.SetType(sym.SNOPTRDATA)
 530                                 bld.SetSize(int64(pesym.Value))
 531                         }
 532
 533                         continue
 534                 } else if pesym.SectionNumber > 0 && int(pesym.SectionNumber) <= len(f.Sections) {
 535                         sect = f.Sections[pesym.SectionNumber-1]
 536                         if _, found := state.sectsyms[sect]; !found {
 537                                 return nil, fmt.Errorf("%s: %v: missing sect.sym", pn, s)
 538                         }
 539                 } else {
 540                         return nil, fmt.Errorf("%s: %v: sectnum < 0!", pn, s)
 541                 }
 542
 543                 if sect == nil {
 544                         return nil, nil
 545                 }
 546
 547                 // Check for COMDAT symbol.
 548                 if sz, ok1 := state.comdats[uint16(pesym.SectionNumber-1)]; ok1 {
 549                         if psz, ok2 := comdatDefinitions[l.SymName(s)]; ok2 {
 550                                 if sz == psz {
 551                                         //  OK to discard, we've seen an instance
 552                                         // already.
 553                                         continue
 554                                 }
 555                         }
 556                 }
 557                 if l.OuterSym(s) != 0 {
 558                         if l.AttrDuplicateOK(s) {
 559                                 continue
 560                         }
 561                         outerName := l.SymName(l.OuterSym(s))
 562                         sectName := l.SymName(state.sectsyms[sect])
 563                         return nil, fmt.Errorf("%s: duplicate symbol reference: %s in both %s and %s", pn, l.SymName(s), outerName, sectName)
 564                 }
 565
 566                 bld = makeUpdater(l, bld, s)
 567                 sectsym := state.sectsyms[sect]
 568                 bld.SetType(l.SymType(sectsym))
 569                 l.AddInteriorSym(sectsym, s)
 570                 bld.SetValue(int64(pesym.Value))
 571                 bld.SetSize(4)
 572                 if l.SymType(sectsym) == sym.STEXT {
 573                         if bld.External() && !bld.DuplicateOK() {
 574                                 return nil, fmt.Errorf("%s: duplicate symbol definition", l.SymName(s))
 575                         }
 576                         bld.SetExternal(true)
 577                 }
 578                 if sz, ok := state.comdats[uint16(pesym.SectionNumber-1)]; ok {
 579                         // This is a COMDAT definition. Record that we're picking
 580                         // this instance so that we can ignore future defs.
 581                         if _, ok := comdatDefinitions[l.SymName(s)]; ok {
 582                                 return nil, fmt.Errorf("internal error: preexisting COMDAT definition for %q", name)
 583                         }
 584                         comdatDefinitions[l.SymName(s)] = sz
 585                 }
 586         }
 587
 588         // Sort outer lists by address, adding to textp.
 589         // This keeps textp in increasing address order.
 590         for _, sect := range f.Sections {
 591                 s := state.sectsyms[sect]
 592                 if s == 0 {
 593                         continue
 594                 }
 595                 l.SortSub(s)
 596                 importSymsState.secSyms = append(importSymsState.secSyms, s)
 597                 if l.SymType(s) == sym.STEXT {
 598                         for ; s != 0; s = l.SubSym(s) {
 599                                 if l.AttrOnList(s) {
 600                                         return nil, fmt.Errorf("symbol %s listed multiple times", l.SymName(s))
 601                                 }
 602                                 l.SetAttrOnList(s, true)
 603                                 ls.Textp = append(ls.Textp, s)
 604                         }
 605                 }
 606         }
 607
 608         if ls.PData != 0 {
 609                 processSEH(l, arch, ls.PData, ls.XData)
 610         }
 611
 612         return &ls, nil
 613 }
 614
 615 // PostProcessImports works to resolve inconsistencies with DLL import
 616 // symbols; it is needed when building with more "modern" C compilers
 617 // with internal linkage.
 618 //
 619 // Background: DLL import symbols are data (SNOPTRDATA) symbols whose
 620 // name is of the form "__imp_XXX", which contain a pointer/reference
 621 // to symbol XXX. It's possible to have import symbols for both data
 622 // symbols ("__imp__fmode") and text symbols ("__imp_CreateEventA").
 623 // In some case import symbols are just references to some external
 624 // thing, and in other cases we see actual definitions of import
 625 // symbols when reading host objects.
 626 //
 627 // Previous versions of the linker would in most cases immediately
 628 // "forward" import symbol references, e.g. treat a references to
 629 // "__imp_XXX" a references to "XXX", however this doesn't work well
 630 // with more modern compilers, where you can sometimes see import
 631 // symbols that are defs (as opposed to external refs).
 632 //
 633 // The main actions taken below are to search for references to
 634 // SDYNIMPORT symbols in host object text/data sections and flag the
 635 // symbols for later fixup. When we see a reference to an import
 636 // symbol __imp_XYZ where XYZ corresponds to some SDYNIMPORT symbol,
 637 // we flag the symbol (via GOT setting) so that it can be redirected
 638 // to XYZ later in windynrelocsym. When we see a direct reference to
 639 // an SDYNIMPORT symbol XYZ, we also flag the symbol (via PLT setting)
 640 // to indicated that the reference will need to be redirected to a
 641 // stub.
 642 func PostProcessImports() error {
 643         ldr := importSymsState.l
 644         arch := importSymsState.arch
 645         keeprelocneeded := make(map[loader.Sym]loader.Sym)
 646         for _, s := range importSymsState.secSyms {
 647                 isText := ldr.SymType(s) == sym.STEXT
 648                 relocs := ldr.Relocs(s)
 649                 for i := 0; i < relocs.Count(); i++ {
 650                         r := relocs.At(i)
 651                         rs := r.Sym()
 652                         if ldr.SymType(rs) == sym.SDYNIMPORT {
 653                                 // Tag the symbol for later stub generation.
 654                                 ldr.SetPlt(rs, CreateImportStubPltToken)
 655                                 continue
 656                         }
 657                         isym, err := LookupBaseFromImport(rs, ldr, arch)
 658                         if err != nil {
 659                                 return err
 660                         }
 661                         if isym == 0 {
 662                                 continue
 663                         }
 664                         if ldr.SymType(isym) != sym.SDYNIMPORT {
 665                                 continue
 666                         }
 667                         // For non-text symbols, forward the reference from __imp_X to
 668                         // X immediately.
 669                         if !isText {
 670                                 r.SetSym(isym)
 671                                 continue
 672                         }
 673                         // Flag this imp symbol to be processed later in windynrelocsym.
 674                         ldr.SetGot(rs, RedirectToDynImportGotToken)
 675                         // Consistency check: should be no PLT token here.
 676                         splt := ldr.SymPlt(rs)
 677                         if splt != -1 {
 678                                 return fmt.Errorf("internal error: import symbol %q has invalid PLT setting %d", ldr.SymName(rs), splt)
 679                         }
 680                         // Flag for dummy relocation.
 681                         keeprelocneeded[rs] = isym
 682                 }
 683         }
 684         for k, v := range keeprelocneeded {
 685                 sb := ldr.MakeSymbolUpdater(k)
 686                 r, _ := sb.AddRel(objabi.R_KEEP)
 687                 r.SetSym(v)
 688         }
 689         importSymsState = nil
 690         return nil
 691 }
 692
 693 func issehsect(arch *sys.Arch, s *pe.Section) bool {
 694         return arch.Family == sys.AMD64 && (s.Name == ".pdata" || s.Name == ".xdata")
 695 }
 696
 697 func issect(s *pe.COFFSymbol) bool {
 698         return s.StorageClass == IMAGE_SYM_CLASS_STATIC && s.Type == 0 && s.Name[0] == '.'
 699 }
 700
 701 func (state *peLoaderState) readpesym(pesym *pe.COFFSymbol) (*loader.SymbolBuilder, loader.Sym, error) {
 702         symname, err := pesym.FullName(state.f.StringTable)
 703         if err != nil {
 704                 return nil, 0, err
 705         }
 706         var name string
 707         if issect(pesym) {
 708                 name = state.l.SymName(state.sectsyms[state.f.Sections[pesym.SectionNumber-1]])
 709         } else {
 710                 name = symname
 711                 // A note on the "_main" exclusion below: the main routine
 712                 // defined by the Go runtime is named "_main", not "main", so
 713                 // when reading references to _main from a host object we want
 714                 // to avoid rewriting "_main" to "main" in this specific
 715                 // instance. See #issuecomment-1143698749 on #35006 for more
 716                 // details on this problem.
 717                 if state.arch.Family == sys.I386 && name[0] == '_' && name != "_main" && !strings.HasPrefix(name, "__imp_") {
 718                         name = name[1:] // _Name => Name
 719                 }
 720         }
 721
 722         // remove last @XXX
 723         if i := strings.LastIndex(name, "@"); i >= 0 {
 724                 name = name[:i]
 725         }
 726
 727         var s loader.Sym
 728         var bld *loader.SymbolBuilder
 729         // Microsoft's PE documentation is contradictory. It says that the symbol's complex type
 730         // is stored in the pesym.Type most significant byte, but MSVC, LLVM, and mingw store it
 731         // in the 4 high bits of the less significant byte.
 732         switch uint8(pesym.Type&0xf0) >> 4 {
 733         default:
 734                 return nil, 0, fmt.Errorf("%s: invalid symbol type %d", symname, pesym.Type)
 735
 736         case IMAGE_SYM_DTYPE_FUNCTION, IMAGE_SYM_DTYPE_NULL:
 737                 switch pesym.StorageClass {
 738                 case IMAGE_SYM_CLASS_EXTERNAL: //global
 739                         s = state.l.LookupOrCreateCgoExport(name, 0)
 740
 741                 case IMAGE_SYM_CLASS_NULL, IMAGE_SYM_CLASS_STATIC, IMAGE_SYM_CLASS_LABEL:
 742                         s = state.l.LookupOrCreateCgoExport(name, state.localSymVersion)
 743                         bld = makeUpdater(state.l, bld, s)
 744                         bld.SetDuplicateOK(true)
 745
 746                 default:
 747                         return nil, 0, fmt.Errorf("%s: invalid symbol binding %d", symname, pesym.StorageClass)
 748                 }
 749         }
 750
 751         if s != 0 && state.l.SymType(s) == 0 && (pesym.StorageClass != IMAGE_SYM_CLASS_STATIC || pesym.Value != 0) {
 752                 bld = makeUpdater(state.l, bld, s)
 753                 bld.SetType(sym.SXREF)
 754         }
 755
 756         return bld, s, nil
 757 }
 758
 759 // preprocessSymbols walks the COFF symbols for the PE file we're
 760 // reading and looks for cases where we have both a symbol definition
 761 // for "XXX" and an "__imp_XXX" symbol, recording these cases in a map
 762 // in the state struct. This information will be used in readpesym()
 763 // above to give such symbols special treatment. This function also
 764 // gathers information about COMDAT sections/symbols for later use
 765 // in readpesym().
 766 func (state *peLoaderState) preprocessSymbols() error {
 767
 768         // Locate comdat sections.
 769         state.comdats = make(map[uint16]int64)
 770         for i, s := range state.f.Sections {
 771                 if s.Characteristics&uint32(pe.IMAGE_SCN_LNK_COMDAT) != 0 {
 772                         state.comdats[uint16(i)] = int64(s.Size)
 773                 }
 774         }
 775
 776         // Examine symbol defs.
 777         for i, numaux := 0, 0; i < len(state.f.COFFSymbols); i += numaux + 1 {
 778                 pesym := &state.f.COFFSymbols[i]
 779                 numaux = int(pesym.NumberOfAuxSymbols)
 780                 if pesym.SectionNumber == 0 { // extern
 781                         continue
 782                 }
 783                 symname, err := pesym.FullName(state.f.StringTable)
 784                 if err != nil {
 785                         return err
 786                 }
 787                 if _, isc := state.comdats[uint16(pesym.SectionNumber-1)]; !isc {
 788                         continue
 789                 }
 790                 if pesym.StorageClass != uint8(IMAGE_SYM_CLASS_STATIC) {
 791                         continue
 792                 }
 793                 // This symbol corresponds to a COMDAT section. Read the
 794                 // aux data for it.
 795                 auxsymp, err := state.f.COFFSymbolReadSectionDefAux(i)
 796                 if err != nil {
 797                         return fmt.Errorf("unable to read aux info for section def symbol %d %s: pe.COFFSymbolReadComdatInfo returns %v", i, symname, err)
 798                 }
 799                 if auxsymp.Selection == pe.IMAGE_COMDAT_SELECT_SAME_SIZE {
 800                         // This is supported.
 801                 } else if auxsymp.Selection == pe.IMAGE_COMDAT_SELECT_ANY {
 802                         // Also supported.
 803                         state.comdats[uint16(pesym.SectionNumber-1)] = int64(-1)
 804                 } else {
 805                         // We don't support any of the other strategies at the
 806                         // moment. I suspect that we may need to also support
 807                         // "associative", we'll see.
 808                         return fmt.Errorf("internal error: unsupported COMDAT selection strategy found in path=%s sec=%d strategy=%d idx=%d, please file a bug", state.pn, auxsymp.SecNum, auxsymp.Selection, i)
 809                 }
 810         }
 811         return nil
 812 }
 813
 814 // LookupBaseFromImport examines the symbol "s" to see if it
 815 // corresponds to an import symbol (name of the form "__imp_XYZ") and
 816 // if so, it looks up the underlying target of the import symbol and
 817 // returns it. An error is returned if the symbol is of the form
 818 // "__imp_XYZ" but no XYZ can be found.
 819 func LookupBaseFromImport(s loader.Sym, ldr *loader.Loader, arch *sys.Arch) (loader.Sym, error) {
 820         sname := ldr.SymName(s)
 821         if !strings.HasPrefix(sname, "__imp_") {
 822                 return 0, nil
 823         }
 824         basename := sname[len("__imp_"):]
 825         if arch.Family == sys.I386 && basename[0] == '_' {
 826                 basename = basename[1:] // _Name => Name
 827         }
 828         isym := ldr.Lookup(basename, 0)
 829         if isym == 0 {
 830                 return 0, fmt.Errorf("internal error: import symbol %q with no underlying sym", sname)
 831         }
 832         return isym, nil
 833 }