lld/COFF/Chunks.h

   1 //===- Chunks.h -------------------------------------------------*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef LLD_COFF_CHUNKS_H
  10 #define LLD_COFF_CHUNKS_H
  11
  12 #include "Config.h"
  13 #include "InputFiles.h"
  14 #include "lld/Common/LLVM.h"
  15 #include "llvm/ADT/ArrayRef.h"
  16 #include "llvm/ADT/PointerIntPair.h"
  17 #include "llvm/ADT/iterator.h"
  18 #include "llvm/ADT/iterator_range.h"
  19 #include "llvm/MC/StringTableBuilder.h"
  20 #include "llvm/Object/COFF.h"
  21 #include <utility>
  22 #include <vector>
  23
  24 namespace lld {
  25 namespace coff {
  26
  27 using llvm::COFF::ImportDirectoryTableEntry;
  28 using llvm::object::COFFSymbolRef;
  29 using llvm::object::SectionRef;
  30 using llvm::object::coff_relocation;
  31 using llvm::object::coff_section;
  32
  33 class Baserel;
  34 class Defined;
  35 class DefinedImportData;
  36 class DefinedRegular;
  37 class ObjFile;
  38 class OutputSection;
  39 class RuntimePseudoReloc;
  40 class Symbol;
  41
  42 // Mask for permissions (discardable, writable, readable, executable, etc).
  43 const uint32_t permMask = 0xFE000000;
  44
  45 // Mask for section types (code, data, bss).
  46 const uint32_t typeMask = 0x000000E0;
  47
  48 // The log base 2 of the largest section alignment, which is log2(8192), or 13.
  49 enum : unsigned { Log2MaxSectionAlignment = 13 };
  50
  51 // A Chunk represents a chunk of data that will occupy space in the
  52 // output (if the resolver chose that). It may or may not be backed by
  53 // a section of an input file. It could be linker-created data, or
  54 // doesn't even have actual data (if common or bss).
  55 class Chunk {
  56 public:
  57   enum Kind : uint8_t { SectionKind, OtherKind, ImportThunkKind };
  58   Kind kind() const { return chunkKind; }
  59
  60   // Returns the size of this chunk (even if this is a common or BSS.)
  61   size_t getSize() const;
  62
  63   // Returns chunk alignment in power of two form. Value values are powers of
  64   // two from 1 to 8192.
  65   uint32_t getAlignment() const { return 1U << p2Align; }
  66
  67   // Update the chunk section alignment measured in bytes. Internally alignment
  68   // is stored in log2.
  69   void setAlignment(uint32_t align) {
  70     // Treat zero byte alignment as 1 byte alignment.
  71     align = align ? align : 1;
  72     assert(llvm::isPowerOf2_32(align) && "alignment is not a power of 2");
  73     p2Align = llvm::Log2_32(align);
  74     assert(p2Align <= Log2MaxSectionAlignment &&
  75            "impossible requested alignment");
  76   }
  77
  78   // Write this chunk to a mmap'ed file, assuming Buf is pointing to
  79   // beginning of the file. Because this function may use RVA values
  80   // of other chunks for relocations, you need to set them properly
  81   // before calling this function.
  82   void writeTo(uint8_t *buf) const;
  83
  84   // The writer sets and uses the addresses. In practice, PE images cannot be
  85   // larger than 2GB. Chunks are always laid as part of the image, so Chunk RVAs
  86   // can be stored with 32 bits.
  87   uint32_t getRVA() const { return rva; }
  88   void setRVA(uint64_t v) {
  89     rva = (uint32_t)v;
  90     assert(rva == v && "RVA truncated");
  91   }
  92
  93   // Returns readable/writable/executable bits.
  94   uint32_t getOutputCharacteristics() const;
  95
  96   // Returns the section name if this is a section chunk.
  97   // It is illegal to call this function on non-section chunks.
  98   StringRef getSectionName() const;
  99
 100   // An output section has pointers to chunks in the section, and each
 101   // chunk has a back pointer to an output section.
 102   void setOutputSectionIdx(uint16_t o) { osidx = o; }
 103   uint16_t getOutputSectionIdx() const { return osidx; }
 104   OutputSection *getOutputSection() const;
 105
 106   // Windows-specific.
 107   // Collect all locations that contain absolute addresses for base relocations.
 108   void getBaserels(std::vector<Baserel> *res);
 109
 110   // Returns a human-readable name of this chunk. Chunks are unnamed chunks of
 111   // bytes, so this is used only for logging or debugging.
 112   StringRef getDebugName() const;
 113
 114   // Return true if this file has the hotpatch flag set to true in the
 115   // S_COMPILE3 record in codeview debug info. Also returns true for some thunks
 116   // synthesized by the linker.
 117   bool isHotPatchable() const;
 118
 119 protected:
 120   Chunk(Kind k = OtherKind) : chunkKind(k), hasData(true), p2Align(0) {}
 121
 122   const Kind chunkKind;
 123
 124 public:
 125   // Returns true if this has non-zero data. BSS chunks return
 126   // false. If false is returned, the space occupied by this chunk
 127   // will be filled with zeros. Corresponds to the
 128   // IMAGE_SCN_CNT_UNINITIALIZED_DATA section characteristic bit.
 129   uint8_t hasData : 1;
 130
 131 public:
 132   // The alignment of this chunk, stored in log2 form. The writer uses the
 133   // value.
 134   uint8_t p2Align : 7;
 135
 136   // The output section index for this chunk. The first valid section number is
 137   // one.
 138   uint16_t osidx = 0;
 139
 140   // The RVA of this chunk in the output. The writer sets a value.
 141   uint32_t rva = 0;
 142 };
 143
 144 class NonSectionChunk : public Chunk {
 145 public:
 146   virtual ~NonSectionChunk() = default;
 147
 148   // Returns the size of this chunk (even if this is a common or BSS.)
 149   virtual size_t getSize() const = 0;
 150
 151   virtual uint32_t getOutputCharacteristics() const { return 0; }
 152
 153   // Write this chunk to a mmap'ed file, assuming Buf is pointing to
 154   // beginning of the file. Because this function may use RVA values
 155   // of other chunks for relocations, you need to set them properly
 156   // before calling this function.
 157   virtual void writeTo(uint8_t *buf) const {}
 158
 159   // Returns the section name if this is a section chunk.
 160   // It is illegal to call this function on non-section chunks.
 161   virtual StringRef getSectionName() const {
 162     llvm_unreachable("unimplemented getSectionName");
 163   }
 164
 165   // Windows-specific.
 166   // Collect all locations that contain absolute addresses for base relocations.
 167   virtual void getBaserels(std::vector<Baserel> *res) {}
 168
 169   // Returns a human-readable name of this chunk. Chunks are unnamed chunks of
 170   // bytes, so this is used only for logging or debugging.
 171   virtual StringRef getDebugName() const { return ""; }
 172
 173   static bool classof(const Chunk *c) { return c->kind() != SectionKind; }
 174
 175 protected:
 176   NonSectionChunk(Kind k = OtherKind) : Chunk(k) {}
 177 };
 178
 179 // A chunk corresponding a section of an input file.
 180 class SectionChunk final : public Chunk {
 181   // Identical COMDAT Folding feature accesses section internal data.
 182   friend class ICF;
 183
 184 public:
 185   class symbol_iterator : public llvm::iterator_adaptor_base<
 186                               symbol_iterator, const coff_relocation *,
 187                               std::random_access_iterator_tag, Symbol *> {
 188     friend SectionChunk;
 189
 190     ObjFile *file;
 191
 192     symbol_iterator(ObjFile *file, const coff_relocation *i)
 193         : symbol_iterator::iterator_adaptor_base(i), file(file) {}
 194
 195   public:
 196     symbol_iterator() = default;
 197
 198     Symbol *operator*() const { return file->getSymbol(I->SymbolTableIndex); }
 199   };
 200
 201   SectionChunk(ObjFile *file, const coff_section *header);
 202   static bool classof(const Chunk *c) { return c->kind() == SectionKind; }
 203   size_t getSize() const { return header->SizeOfRawData; }
 204   ArrayRef<uint8_t> getContents() const;
 205   void writeTo(uint8_t *buf) const;
 206
 207   uint32_t getOutputCharacteristics() const {
 208     return header->Characteristics & (permMask | typeMask);
 209   }
 210   StringRef getSectionName() const {
 211     return StringRef(sectionNameData, sectionNameSize);
 212   }
 213   void getBaserels(std::vector<Baserel> *res);
 214   bool isCOMDAT() const;
 215   void applyRelX64(uint8_t *off, uint16_t type, OutputSection *os, uint64_t s,
 216                    uint64_t p) const;
 217   void applyRelX86(uint8_t *off, uint16_t type, OutputSection *os, uint64_t s,
 218                    uint64_t p) const;
 219   void applyRelARM(uint8_t *off, uint16_t type, OutputSection *os, uint64_t s,
 220                    uint64_t p) const;
 221   void applyRelARM64(uint8_t *off, uint16_t type, OutputSection *os, uint64_t s,
 222                      uint64_t p) const;
 223
 224   void getRuntimePseudoRelocs(std::vector<RuntimePseudoReloc> &res);
 225
 226   // Called if the garbage collector decides to not include this chunk
 227   // in a final output. It's supposed to print out a log message to stdout.
 228   void printDiscardedMessage() const;
 229
 230   // Adds COMDAT associative sections to this COMDAT section. A chunk
 231   // and its children are treated as a group by the garbage collector.
 232   void addAssociative(SectionChunk *child);
 233
 234   StringRef getDebugName() const;
 235
 236   // True if this is a codeview debug info chunk. These will not be laid out in
 237   // the image. Instead they will end up in the PDB, if one is requested.
 238   bool isCodeView() const {
 239     return getSectionName() == ".debug" || getSectionName().startswith(".debug$");
 240   }
 241
 242   // True if this is a DWARF debug info or exception handling chunk.
 243   bool isDWARF() const {
 244     return getSectionName().startswith(".debug_") || getSectionName() == ".eh_frame";
 245   }
 246
 247   // Allow iteration over the bodies of this chunk's relocated symbols.
 248   llvm::iterator_range<symbol_iterator> symbols() const {
 249     return llvm::make_range(symbol_iterator(file, relocsData),
 250                             symbol_iterator(file, relocsData + relocsSize));
 251   }
 252
 253   ArrayRef<coff_relocation> getRelocs() const {
 254     return llvm::makeArrayRef(relocsData, relocsSize);
 255   }
 256
 257   // Reloc setter used by ARM range extension thunk insertion.
 258   void setRelocs(ArrayRef<coff_relocation> newRelocs) {
 259     relocsData = newRelocs.data();
 260     relocsSize = newRelocs.size();
 261     assert(relocsSize == newRelocs.size() && "reloc size truncation");
 262   }
 263
 264   // Single linked list iterator for associated comdat children.
 265   class AssociatedIterator
 266       : public llvm::iterator_facade_base<
 267             AssociatedIterator, std::forward_iterator_tag, SectionChunk> {
 268   public:
 269     AssociatedIterator() = default;
 270     AssociatedIterator(SectionChunk *head) : cur(head) {}
 271     bool operator==(const AssociatedIterator &r) const { return cur == r.cur; }
 272     const SectionChunk &operator*() const { return *cur; }
 273     SectionChunk &operator*() { return *cur; }
 274     AssociatedIterator &operator++() {
 275       cur = cur->assocChildren;
 276       return *this;
 277     }
 278
 279   private:
 280     SectionChunk *cur = nullptr;
 281   };
 282
 283   // Allow iteration over the associated child chunks for this section.
 284   llvm::iterator_range<AssociatedIterator> children() const {
 285     return llvm::make_range(AssociatedIterator(assocChildren),
 286                             AssociatedIterator(nullptr));
 287   }
 288
 289   // The section ID this chunk belongs to in its Obj.
 290   uint32_t getSectionNumber() const;
 291
 292   ArrayRef<uint8_t> consumeDebugMagic();
 293
 294   static ArrayRef<uint8_t> consumeDebugMagic(ArrayRef<uint8_t> data,
 295                                              StringRef sectionName);
 296
 297   static SectionChunk *findByName(ArrayRef<SectionChunk *> sections,
 298                                   StringRef name);
 299
 300   // The file that this chunk was created from.
 301   ObjFile *file;
 302
 303   // Pointer to the COFF section header in the input file.
 304   const coff_section *header;
 305
 306   // The COMDAT leader symbol if this is a COMDAT chunk.
 307   DefinedRegular *sym = nullptr;
 308
 309   // The CRC of the contents as described in the COFF spec 4.5.5.
 310   // Auxiliary Format 5: Section Definitions. Used for ICF.
 311   uint32_t checksum = 0;
 312
 313   // Used by the garbage collector.
 314   bool live;
 315
 316   // Whether this section needs to be kept distinct from other sections during
 317   // ICF. This is set by the driver using address-significance tables.
 318   bool keepUnique = false;
 319
 320   // The COMDAT selection if this is a COMDAT chunk.
 321   llvm::COFF::COMDATType selection = (llvm::COFF::COMDATType)0;
 322
 323   // A pointer pointing to a replacement for this chunk.
 324   // Initially it points to "this" object. If this chunk is merged
 325   // with other chunk by ICF, it points to another chunk,
 326   // and this chunk is considered as dead.
 327   SectionChunk *repl;
 328
 329 private:
 330   SectionChunk *assocChildren = nullptr;
 331
 332   // Used for ICF (Identical COMDAT Folding)
 333   void replace(SectionChunk *other);
 334   uint32_t eqClass[2] = {0, 0};
 335
 336   // Relocations for this section. Size is stored below.
 337   const coff_relocation *relocsData;
 338
 339   // Section name string. Size is stored below.
 340   const char *sectionNameData;
 341
 342   uint32_t relocsSize = 0;
 343   uint32_t sectionNameSize = 0;
 344 };
 345
 346 // Inline methods to implement faux-virtual dispatch for SectionChunk.
 347
 348 inline size_t Chunk::getSize() const {
 349   if (isa<SectionChunk>(this))
 350     return static_cast<const SectionChunk *>(this)->getSize();
 351   else
 352     return static_cast<const NonSectionChunk *>(this)->getSize();
 353 }
 354
 355 inline uint32_t Chunk::getOutputCharacteristics() const {
 356   if (isa<SectionChunk>(this))
 357     return static_cast<const SectionChunk *>(this)->getOutputCharacteristics();
 358   else
 359     return static_cast<const NonSectionChunk *>(this)
 360         ->getOutputCharacteristics();
 361 }
 362
 363 inline void Chunk::writeTo(uint8_t *buf) const {
 364   if (isa<SectionChunk>(this))
 365     static_cast<const SectionChunk *>(this)->writeTo(buf);
 366   else
 367     static_cast<const NonSectionChunk *>(this)->writeTo(buf);
 368 }
 369
 370 inline StringRef Chunk::getSectionName() const {
 371   if (isa<SectionChunk>(this))
 372     return static_cast<const SectionChunk *>(this)->getSectionName();
 373   else
 374     return static_cast<const NonSectionChunk *>(this)->getSectionName();
 375 }
 376
 377 inline void Chunk::getBaserels(std::vector<Baserel> *res) {
 378   if (isa<SectionChunk>(this))
 379     static_cast<SectionChunk *>(this)->getBaserels(res);
 380   else
 381     static_cast<NonSectionChunk *>(this)->getBaserels(res);
 382 }
 383
 384 inline StringRef Chunk::getDebugName() const {
 385   if (isa<SectionChunk>(this))
 386     return static_cast<const SectionChunk *>(this)->getDebugName();
 387   else
 388     return static_cast<const NonSectionChunk *>(this)->getDebugName();
 389 }
 390
 391 // This class is used to implement an lld-specific feature (not implemented in
 392 // MSVC) that minimizes the output size by finding string literals sharing tail
 393 // parts and merging them.
 394 //
 395 // If string tail merging is enabled and a section is identified as containing a
 396 // string literal, it is added to a MergeChunk with an appropriate alignment.
 397 // The MergeChunk then tail merges the strings using the StringTableBuilder
 398 // class and assigns RVAs and section offsets to each of the member chunks based
 399 // on the offsets assigned by the StringTableBuilder.
 400 class MergeChunk : public NonSectionChunk {
 401 public:
 402   MergeChunk(uint32_t alignment);
 403   static void addSection(SectionChunk *c);
 404   void finalizeContents();
 405   void assignSubsectionRVAs();
 406
 407   uint32_t getOutputCharacteristics() const override;
 408   StringRef getSectionName() const override { return ".rdata"; }
 409   size_t getSize() const override;
 410   void writeTo(uint8_t *buf) const override;
 411
 412   static MergeChunk *instances[Log2MaxSectionAlignment + 1];
 413   std::vector<SectionChunk *> sections;
 414
 415 private:
 416   llvm::StringTableBuilder builder;
 417   bool finalized = false;
 418 };
 419
 420 // A chunk for common symbols. Common chunks don't have actual data.
 421 class CommonChunk : public NonSectionChunk {
 422 public:
 423   CommonChunk(const COFFSymbolRef sym);
 424   size_t getSize() const override { return sym.getValue(); }
 425   uint32_t getOutputCharacteristics() const override;
 426   StringRef getSectionName() const override { return ".bss"; }
 427
 428 private:
 429   const COFFSymbolRef sym;
 430 };
 431
 432 // A chunk for linker-created strings.
 433 class StringChunk : public NonSectionChunk {
 434 public:
 435   explicit StringChunk(StringRef s) : str(s) {}
 436   size_t getSize() const override { return str.size() + 1; }
 437   void writeTo(uint8_t *buf) const override;
 438
 439 private:
 440   StringRef str;
 441 };
 442
 443 static const uint8_t importThunkX86[] = {
 444     0xff, 0x25, 0x00, 0x00, 0x00, 0x00, // JMP *0x0
 445 };
 446
 447 static const uint8_t importThunkARM[] = {
 448     0x40, 0xf2, 0x00, 0x0c, // mov.w ip, #0
 449     0xc0, 0xf2, 0x00, 0x0c, // mov.t ip, #0
 450     0xdc, 0xf8, 0x00, 0xf0, // ldr.w pc, [ip]
 451 };
 452
 453 static const uint8_t importThunkARM64[] = {
 454     0x10, 0x00, 0x00, 0x90, // adrp x16, #0
 455     0x10, 0x02, 0x40, 0xf9, // ldr  x16, [x16]
 456     0x00, 0x02, 0x1f, 0xd6, // br   x16
 457 };
 458
 459 // Windows-specific.
 460 // A chunk for DLL import jump table entry. In a final output, its
 461 // contents will be a JMP instruction to some __imp_ symbol.
 462 class ImportThunkChunk : public NonSectionChunk {
 463 public:
 464   ImportThunkChunk(Defined *s)
 465       : NonSectionChunk(ImportThunkKind), impSymbol(s) {}
 466   static bool classof(const Chunk *c) { return c->kind() == ImportThunkKind; }
 467
 468 protected:
 469   Defined *impSymbol;
 470 };
 471
 472 class ImportThunkChunkX64 : public ImportThunkChunk {
 473 public:
 474   explicit ImportThunkChunkX64(Defined *s);
 475   size_t getSize() const override { return sizeof(importThunkX86); }
 476   void writeTo(uint8_t *buf) const override;
 477 };
 478
 479 class ImportThunkChunkX86 : public ImportThunkChunk {
 480 public:
 481   explicit ImportThunkChunkX86(Defined *s) : ImportThunkChunk(s) {}
 482   size_t getSize() const override { return sizeof(importThunkX86); }
 483   void getBaserels(std::vector<Baserel> *res) override;
 484   void writeTo(uint8_t *buf) const override;
 485 };
 486
 487 class ImportThunkChunkARM : public ImportThunkChunk {
 488 public:
 489   explicit ImportThunkChunkARM(Defined *s) : ImportThunkChunk(s) {
 490     setAlignment(2);
 491   }
 492   size_t getSize() const override { return sizeof(importThunkARM); }
 493   void getBaserels(std::vector<Baserel> *res) override;
 494   void writeTo(uint8_t *buf) const override;
 495 };
 496
 497 class ImportThunkChunkARM64 : public ImportThunkChunk {
 498 public:
 499   explicit ImportThunkChunkARM64(Defined *s) : ImportThunkChunk(s) {
 500     setAlignment(4);
 501   }
 502   size_t getSize() const override { return sizeof(importThunkARM64); }
 503   void writeTo(uint8_t *buf) const override;
 504 };
 505
 506 class RangeExtensionThunkARM : public NonSectionChunk {
 507 public:
 508   explicit RangeExtensionThunkARM(Defined *t) : target(t) { setAlignment(2); }
 509   size_t getSize() const override;
 510   void writeTo(uint8_t *buf) const override;
 511
 512   Defined *target;
 513 };
 514
 515 class RangeExtensionThunkARM64 : public NonSectionChunk {
 516 public:
 517   explicit RangeExtensionThunkARM64(Defined *t) : target(t) { setAlignment(4); }
 518   size_t getSize() const override;
 519   void writeTo(uint8_t *buf) const override;
 520
 521   Defined *target;
 522 };
 523
 524 // Windows-specific.
 525 // See comments for DefinedLocalImport class.
 526 class LocalImportChunk : public NonSectionChunk {
 527 public:
 528   explicit LocalImportChunk(Defined *s) : sym(s) {
 529     setAlignment(config->wordsize);
 530   }
 531   size_t getSize() const override;
 532   void getBaserels(std::vector<Baserel> *res) override;
 533   void writeTo(uint8_t *buf) const override;
 534
 535 private:
 536   Defined *sym;
 537 };
 538
 539 // Duplicate RVAs are not allowed in RVA tables, so unique symbols by chunk and
 540 // offset into the chunk. Order does not matter as the RVA table will be sorted
 541 // later.
 542 struct ChunkAndOffset {
 543   Chunk *inputChunk;
 544   uint32_t offset;
 545
 546   struct DenseMapInfo {
 547     static ChunkAndOffset getEmptyKey() {
 548       return {llvm::DenseMapInfo<Chunk *>::getEmptyKey(), 0};
 549     }
 550     static ChunkAndOffset getTombstoneKey() {
 551       return {llvm::DenseMapInfo<Chunk *>::getTombstoneKey(), 0};
 552     }
 553     static unsigned getHashValue(const ChunkAndOffset &co) {
 554       return llvm::DenseMapInfo<std::pair<Chunk *, uint32_t>>::getHashValue(
 555           {co.inputChunk, co.offset});
 556     }
 557     static bool isEqual(const ChunkAndOffset &lhs, const ChunkAndOffset &rhs) {
 558       return lhs.inputChunk == rhs.inputChunk && lhs.offset == rhs.offset;
 559     }
 560   };
 561 };
 562
 563 using SymbolRVASet = llvm::DenseSet<ChunkAndOffset>;
 564
 565 // Table which contains symbol RVAs. Used for /safeseh and /guard:cf.
 566 class RVATableChunk : public NonSectionChunk {
 567 public:
 568   explicit RVATableChunk(SymbolRVASet s) : syms(std::move(s)) {}
 569   size_t getSize() const override { return syms.size() * 4; }
 570   void writeTo(uint8_t *buf) const override;
 571
 572 private:
 573   SymbolRVASet syms;
 574 };
 575
 576 // Windows-specific.
 577 // This class represents a block in .reloc section.
 578 // See the PE/COFF spec 5.6 for details.
 579 class BaserelChunk : public NonSectionChunk {
 580 public:
 581   BaserelChunk(uint32_t page, Baserel *begin, Baserel *end);
 582   size_t getSize() const override { return data.size(); }
 583   void writeTo(uint8_t *buf) const override;
 584
 585 private:
 586   std::vector<uint8_t> data;
 587 };
 588
 589 class Baserel {
 590 public:
 591   Baserel(uint32_t v, uint8_t ty) : rva(v), type(ty) {}
 592   explicit Baserel(uint32_t v) : Baserel(v, getDefaultType()) {}
 593   uint8_t getDefaultType();
 594
 595   uint32_t rva;
 596   uint8_t type;
 597 };
 598
 599 // This is a placeholder Chunk, to allow attaching a DefinedSynthetic to a
 600 // specific place in a section, without any data. This is used for the MinGW
 601 // specific symbol __RUNTIME_PSEUDO_RELOC_LIST_END__, even though the concept
 602 // of an empty chunk isn't MinGW specific.
 603 class EmptyChunk : public NonSectionChunk {
 604 public:
 605   EmptyChunk() {}
 606   size_t getSize() const override { return 0; }
 607   void writeTo(uint8_t *buf) const override {}
 608 };
 609
 610 // MinGW specific, for the "automatic import of variables from DLLs" feature.
 611 // This provides the table of runtime pseudo relocations, for variable
 612 // references that turned out to need to be imported from a DLL even though
 613 // the reference didn't use the dllimport attribute. The MinGW runtime will
 614 // process this table after loading, before handling control over to user
 615 // code.
 616 class PseudoRelocTableChunk : public NonSectionChunk {
 617 public:
 618   PseudoRelocTableChunk(std::vector<RuntimePseudoReloc> &relocs)
 619       : relocs(std::move(relocs)) {
 620     setAlignment(4);
 621   }
 622   size_t getSize() const override;
 623   void writeTo(uint8_t *buf) const override;
 624
 625 private:
 626   std::vector<RuntimePseudoReloc> relocs;
 627 };
 628
 629 // MinGW specific; information about one individual location in the image
 630 // that needs to be fixed up at runtime after loading. This represents
 631 // one individual element in the PseudoRelocTableChunk table.
 632 class RuntimePseudoReloc {
 633 public:
 634   RuntimePseudoReloc(Defined *sym, SectionChunk *target, uint32_t targetOffset,
 635                      int flags)
 636       : sym(sym), target(target), targetOffset(targetOffset), flags(flags) {}
 637
 638   Defined *sym;
 639   SectionChunk *target;
 640   uint32_t targetOffset;
 641   // The Flags field contains the size of the relocation, in bits. No other
 642   // flags are currently defined.
 643   int flags;
 644 };
 645
 646 // MinGW specific. A Chunk that contains one pointer-sized absolute value.
 647 class AbsolutePointerChunk : public NonSectionChunk {
 648 public:
 649   AbsolutePointerChunk(uint64_t value) : value(value) {
 650     setAlignment(getSize());
 651   }
 652   size_t getSize() const override;
 653   void writeTo(uint8_t *buf) const override;
 654
 655 private:
 656   uint64_t value;
 657 };
 658
 659 // Return true if this file has the hotpatch flag set to true in the S_COMPILE3
 660 // record in codeview debug info. Also returns true for some thunks synthesized
 661 // by the linker.
 662 inline bool Chunk::isHotPatchable() const {
 663   if (auto *sc = dyn_cast<SectionChunk>(this))
 664     return sc->file->hotPatchable;
 665   else if (isa<ImportThunkChunk>(this))
 666     return true;
 667   return false;
 668 }
 669
 670 void applyMOV32T(uint8_t *off, uint32_t v);
 671 void applyBranch24T(uint8_t *off, int32_t v);
 672
 673 void applyArm64Addr(uint8_t *off, uint64_t s, uint64_t p, int shift);
 674 void applyArm64Imm(uint8_t *off, uint64_t imm, uint32_t rangeLimit);
 675 void applyArm64Branch26(uint8_t *off, int64_t v);
 676
 677 } // namespace coff
 678 } // namespace lld
 679
 680 namespace llvm {
 681 template <>
 682 struct DenseMapInfo<lld::coff::ChunkAndOffset>
 683     : lld::coff::ChunkAndOffset::DenseMapInfo {};
 684 }
 685
 686 #endif