1 //===- Writer.cpp ---------------------------------------------------------===//
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
7 //===----------------------------------------------------------------------===//
12 #include "InputFiles.h"
15 #include "SymbolTable.h"
17 #include "lld/Common/ErrorHandler.h"
18 #include "lld/Common/Memory.h"
19 #include "lld/Common/Threads.h"
20 #include "lld/Common/Timer.h"
21 #include "llvm/ADT/DenseMap.h"
22 #include "llvm/ADT/STLExtras.h"
23 #include "llvm/ADT/StringSwitch.h"
24 #include "llvm/Support/BinaryStreamReader.h"
25 #include "llvm/Support/Debug.h"
26 #include "llvm/Support/Endian.h"
27 #include "llvm/Support/FileOutputBuffer.h"
28 #include "llvm/Support/Parallel.h"
29 #include "llvm/Support/Path.h"
30 #include "llvm/Support/RandomNumberGenerator.h"
31 #include "llvm/Support/xxhash.h"
39 using namespace llvm::COFF;
40 using namespace llvm::object;
41 using namespace llvm::support;
42 using namespace llvm::support::endian;
47 /* To re-generate DOSProgram:
48 $ cat > /tmp/DOSProgram.asm
53 ; Point ds:dx at the $-terminated string.
55 ; Int 21/AH=09h: Write string to standard output.
58 ; Int 21/AH=4Ch: Exit with return code (in AL).
62 db 'This program cannot be run in DOS mode.$'
64 $ nasm -fbin /tmp/DOSProgram.asm -o /tmp/DOSProgram.bin
65 $ xxd -i /tmp/DOSProgram.bin
67 static unsigned char dosProgram[] = {
68 0x0e, 0x1f, 0xba, 0x0e, 0x00, 0xb4, 0x09, 0xcd, 0x21, 0xb8, 0x01, 0x4c,
69 0xcd, 0x21, 0x54, 0x68, 0x69, 0x73, 0x20, 0x70, 0x72, 0x6f, 0x67, 0x72,
70 0x61, 0x6d, 0x20, 0x63, 0x61, 0x6e, 0x6e, 0x6f, 0x74, 0x20, 0x62, 0x65,
71 0x20, 0x72, 0x75, 0x6e, 0x20, 0x69, 0x6e, 0x20, 0x44, 0x4f, 0x53, 0x20,
72 0x6d, 0x6f, 0x64, 0x65, 0x2e, 0x24, 0x00, 0x00
74 static_assert(sizeof(dosProgram) % 8 == 0,
75 "DOSProgram size must be multiple of 8");
77 static const int dosStubSize = sizeof(dos_header) + sizeof(dosProgram);
78 static_assert(dosStubSize % 8 == 0, "DOSStub size must be multiple of 8");
80 static const int numberOfDataDirectory = 16;
82 // Global vector of all output sections. After output sections are finalized,
83 // this can be indexed by Chunk::getOutputSection.
84 static std::vector<OutputSection *> outputSections;
86 OutputSection *Chunk::getOutputSection() const {
87 return osidx == 0 ? nullptr : outputSections[osidx - 1];
92 class DebugDirectoryChunk : public NonSectionChunk {
94 DebugDirectoryChunk(const std::vector<Chunk *> &r, bool writeRepro)
95 : records(r), writeRepro(writeRepro) {}
97 size_t getSize() const override {
98 return (records.size() + int(writeRepro)) * sizeof(debug_directory);
101 void writeTo(uint8_t *b) const override {
102 auto *d = reinterpret_cast<debug_directory *>(b);
104 for (const Chunk *record : records) {
105 OutputSection *os = record->getOutputSection();
106 uint64_t offs = os->getFileOff() + (record->getRVA() - os->getRVA());
107 fillEntry(d, COFF::IMAGE_DEBUG_TYPE_CODEVIEW, record->getSize(),
108 record->getRVA(), offs);
113 // FIXME: The COFF spec allows either a 0-sized entry to just say
114 // "the timestamp field is really a hash", or a 4-byte size field
115 // followed by that many bytes containing a longer hash (with the
116 // lowest 4 bytes usually being the timestamp in little-endian order).
117 // Consider storing the full 8 bytes computed by xxHash64 here.
118 fillEntry(d, COFF::IMAGE_DEBUG_TYPE_REPRO, 0, 0, 0);
122 void setTimeDateStamp(uint32_t timeDateStamp) {
123 for (support::ulittle32_t *tds : timeDateStamps)
124 *tds = timeDateStamp;
128 void fillEntry(debug_directory *d, COFF::DebugType debugType, size_t size,
129 uint64_t rva, uint64_t offs) const {
130 d->Characteristics = 0;
131 d->TimeDateStamp = 0;
135 d->SizeOfData = size;
136 d->AddressOfRawData = rva;
137 d->PointerToRawData = offs;
139 timeDateStamps.push_back(&d->TimeDateStamp);
142 mutable std::vector<support::ulittle32_t *> timeDateStamps;
143 const std::vector<Chunk *> &records;
147 class CVDebugRecordChunk : public NonSectionChunk {
149 size_t getSize() const override {
150 return sizeof(codeview::DebugInfo) + config->pdbAltPath.size() + 1;
153 void writeTo(uint8_t *b) const override {
154 // Save off the DebugInfo entry to backfill the file signature (build id)
155 // in Writer::writeBuildId
156 buildId = reinterpret_cast<codeview::DebugInfo *>(b);
158 // variable sized field (PDB Path)
159 char *p = reinterpret_cast<char *>(b + sizeof(*buildId));
160 if (!config->pdbAltPath.empty())
161 memcpy(p, config->pdbAltPath.data(), config->pdbAltPath.size());
162 p[config->pdbAltPath.size()] = '\0';
165 mutable codeview::DebugInfo *buildId = nullptr;
168 // PartialSection represents a group of chunks that contribute to an
169 // OutputSection. Collating a collection of PartialSections of same name and
170 // characteristics constitutes the OutputSection.
171 class PartialSectionKey {
174 unsigned characteristics;
176 bool operator<(const PartialSectionKey &other) const {
177 int c = name.compare(other.name);
181 return characteristics < other.characteristics;
186 // The writer writes a SymbolTable result to a file.
189 Writer() : buffer(errorHandler().outputBuffer) {}
193 void createSections();
194 void createMiscChunks();
195 void createImportTables();
196 void appendImportThunks();
197 void locateImportTables();
198 void createExportTable();
199 void mergeSections();
200 void removeUnusedSections();
201 void assignAddresses();
202 void finalizeAddresses();
203 void removeEmptySections();
204 void assignOutputSectionIndices();
205 void createSymbolAndStringTable();
206 void openFile(StringRef outputPath);
207 template <typename PEHeaderTy> void writeHeader();
208 void createSEHTable();
209 void createRuntimePseudoRelocs();
210 void insertCtorDtorSymbols();
211 void createGuardCFTables();
212 void markSymbolsForRVATable(ObjFile *file,
213 ArrayRef<SectionChunk *> symIdxChunks,
214 SymbolRVASet &tableSymbols);
215 void maybeAddRVATable(SymbolRVASet tableSymbols, StringRef tableSym,
217 void setSectionPermissions();
218 void writeSections();
220 void sortExceptionTable();
221 void sortCRTSectionChunks(std::vector<Chunk *> &chunks);
222 void addSyntheticIdata();
223 void fixPartialSectionChars(StringRef name, uint32_t chars);
224 bool fixGnuImportChunks();
225 PartialSection *createPartialSection(StringRef name, uint32_t outChars);
226 PartialSection *findPartialSection(StringRef name, uint32_t outChars);
228 llvm::Optional<coff_symbol16> createSymbol(Defined *d);
229 size_t addEntryToStringTable(StringRef str);
231 OutputSection *findSection(StringRef name);
233 void addBaserelBlocks(std::vector<Baserel> &v);
235 uint32_t getSizeOfInitializedData();
237 std::unique_ptr<FileOutputBuffer> &buffer;
238 std::map<PartialSectionKey, PartialSection *> partialSections;
239 std::vector<char> strtab;
240 std::vector<llvm::object::coff_symbol16> outputSymtab;
242 Chunk *importTableStart = nullptr;
243 uint64_t importTableSize = 0;
244 Chunk *edataStart = nullptr;
245 Chunk *edataEnd = nullptr;
246 Chunk *iatStart = nullptr;
247 uint64_t iatSize = 0;
248 DelayLoadContents delayIdata;
250 bool setNoSEHCharacteristic = false;
252 DebugDirectoryChunk *debugDirectory = nullptr;
253 std::vector<Chunk *> debugRecords;
254 CVDebugRecordChunk *buildId = nullptr;
255 ArrayRef<uint8_t> sectionTable;
258 uint32_t pointerToSymbolTable = 0;
259 uint64_t sizeOfImage;
260 uint64_t sizeOfHeaders;
262 OutputSection *textSec;
263 OutputSection *rdataSec;
264 OutputSection *buildidSec;
265 OutputSection *dataSec;
266 OutputSection *pdataSec;
267 OutputSection *idataSec;
268 OutputSection *edataSec;
269 OutputSection *didatSec;
270 OutputSection *rsrcSec;
271 OutputSection *relocSec;
272 OutputSection *ctorsSec;
273 OutputSection *dtorsSec;
275 // The first and last .pdata sections in the output file.
277 // We need to keep track of the location of .pdata in whichever section it
278 // gets merged into so that we can sort its contents and emit a correct data
279 // directory entry for the exception table. This is also the case for some
280 // other sections (such as .edata) but because the contents of those sections
281 // are entirely linker-generated we can keep track of their locations using
282 // the chunks that the linker creates. All .pdata chunks come from input
283 // files, so we need to keep track of them separately.
284 Chunk *firstPdata = nullptr;
287 } // anonymous namespace
289 static Timer codeLayoutTimer("Code Layout", Timer::root());
290 static Timer diskCommitTimer("Commit Output File", Timer::root());
292 void writeResult() { Writer().run(); }
294 void OutputSection::addChunk(Chunk *c) {
298 void OutputSection::insertChunkAtStart(Chunk *c) {
299 chunks.insert(chunks.begin(), c);
302 void OutputSection::setPermissions(uint32_t c) {
303 header.Characteristics &= ~permMask;
304 header.Characteristics |= c;
307 void OutputSection::merge(OutputSection *other) {
308 chunks.insert(chunks.end(), other->chunks.begin(), other->chunks.end());
309 other->chunks.clear();
310 contribSections.insert(contribSections.end(), other->contribSections.begin(),
311 other->contribSections.end());
312 other->contribSections.clear();
315 // Write the section header to a given buffer.
316 void OutputSection::writeHeaderTo(uint8_t *buf) {
317 auto *hdr = reinterpret_cast<coff_section *>(buf);
319 if (stringTableOff) {
320 // If name is too long, write offset into the string table as a name.
321 sprintf(hdr->Name, "/%d", stringTableOff);
323 assert(!config->debug || name.size() <= COFF::NameSize ||
324 (hdr->Characteristics & IMAGE_SCN_MEM_DISCARDABLE) == 0);
325 strncpy(hdr->Name, name.data(),
326 std::min(name.size(), (size_t)COFF::NameSize));
330 void OutputSection::addContributingPartialSection(PartialSection *sec) {
331 contribSections.push_back(sec);
334 // Check whether the target address S is in range from a relocation
335 // of type relType at address P.
336 static bool isInRange(uint16_t relType, uint64_t s, uint64_t p, int margin) {
337 if (config->machine == ARMNT) {
338 int64_t diff = AbsoluteDifference(s, p + 4) + margin;
340 case IMAGE_REL_ARM_BRANCH20T:
341 return isInt<21>(diff);
342 case IMAGE_REL_ARM_BRANCH24T:
343 case IMAGE_REL_ARM_BLX23T:
344 return isInt<25>(diff);
348 } else if (config->machine == ARM64) {
349 int64_t diff = AbsoluteDifference(s, p) + margin;
351 case IMAGE_REL_ARM64_BRANCH26:
352 return isInt<28>(diff);
353 case IMAGE_REL_ARM64_BRANCH19:
354 return isInt<21>(diff);
355 case IMAGE_REL_ARM64_BRANCH14:
356 return isInt<16>(diff);
361 llvm_unreachable("Unexpected architecture");
365 // Return the last thunk for the given target if it is in range,
366 // or create a new one.
367 static std::pair<Defined *, bool>
368 getThunk(DenseMap<uint64_t, Defined *> &lastThunks, Defined *target, uint64_t p,
369 uint16_t type, int margin) {
370 Defined *&lastThunk = lastThunks[target->getRVA()];
371 if (lastThunk && isInRange(type, lastThunk->getRVA(), p, margin))
372 return {lastThunk, false};
374 switch (config->machine) {
376 c = make<RangeExtensionThunkARM>(target);
379 c = make<RangeExtensionThunkARM64>(target);
382 llvm_unreachable("Unexpected architecture");
384 Defined *d = make<DefinedSynthetic>("", c);
389 // This checks all relocations, and for any relocation which isn't in range
390 // it adds a thunk after the section chunk that contains the relocation.
391 // If the latest thunk for the specific target is in range, that is used
392 // instead of creating a new thunk. All range checks are done with the
393 // specified margin, to make sure that relocations that originally are in
394 // range, but only barely, also get thunks - in case other added thunks makes
395 // the target go out of range.
397 // After adding thunks, we verify that all relocations are in range (with
398 // no extra margin requirements). If this failed, we restart (throwing away
399 // the previously created thunks) and retry with a wider margin.
400 static bool createThunks(OutputSection *os, int margin) {
401 bool addressesChanged = false;
402 DenseMap<uint64_t, Defined *> lastThunks;
403 DenseMap<std::pair<ObjFile *, Defined *>, uint32_t> thunkSymtabIndices;
404 size_t thunksSize = 0;
405 // Recheck Chunks.size() each iteration, since we can insert more
407 for (size_t i = 0; i != os->chunks.size(); ++i) {
408 SectionChunk *sc = dyn_cast_or_null<SectionChunk>(os->chunks[i]);
411 size_t thunkInsertionSpot = i + 1;
413 // Try to get a good enough estimate of where new thunks will be placed.
414 // Offset this by the size of the new thunks added so far, to make the
415 // estimate slightly better.
416 size_t thunkInsertionRVA = sc->getRVA() + sc->getSize() + thunksSize;
417 ObjFile *file = sc->file;
418 std::vector<std::pair<uint32_t, uint32_t>> relocReplacements;
419 ArrayRef<coff_relocation> originalRelocs =
420 file->getCOFFObj()->getRelocations(sc->header);
421 for (size_t j = 0, e = originalRelocs.size(); j < e; ++j) {
422 const coff_relocation &rel = originalRelocs[j];
423 Symbol *relocTarget = file->getSymbol(rel.SymbolTableIndex);
425 // The estimate of the source address P should be pretty accurate,
426 // but we don't know whether the target Symbol address should be
427 // offset by thunksSize or not (or by some of thunksSize but not all of
428 // it), giving us some uncertainty once we have added one thunk.
429 uint64_t p = sc->getRVA() + rel.VirtualAddress + thunksSize;
431 Defined *sym = dyn_cast_or_null<Defined>(relocTarget);
435 uint64_t s = sym->getRVA();
437 if (isInRange(rel.Type, s, p, margin))
440 // If the target isn't in range, hook it up to an existing or new
444 std::tie(thunk, wasNew) = getThunk(lastThunks, sym, p, rel.Type, margin);
446 Chunk *thunkChunk = thunk->getChunk();
448 thunkInsertionRVA); // Estimate of where it will be located.
449 os->chunks.insert(os->chunks.begin() + thunkInsertionSpot, thunkChunk);
450 thunkInsertionSpot++;
451 thunksSize += thunkChunk->getSize();
452 thunkInsertionRVA += thunkChunk->getSize();
453 addressesChanged = true;
456 // To redirect the relocation, add a symbol to the parent object file's
457 // symbol table, and replace the relocation symbol table index with the
459 auto insertion = thunkSymtabIndices.insert({{file, thunk}, ~0U});
460 uint32_t &thunkSymbolIndex = insertion.first->second;
461 if (insertion.second)
462 thunkSymbolIndex = file->addRangeThunkSymbol(thunk);
463 relocReplacements.push_back({j, thunkSymbolIndex});
466 // Get a writable copy of this section's relocations so they can be
467 // modified. If the relocations point into the object file, allocate new
468 // memory. Otherwise, this must be previously allocated memory that can be
469 // modified in place.
470 ArrayRef<coff_relocation> curRelocs = sc->getRelocs();
471 MutableArrayRef<coff_relocation> newRelocs;
472 if (originalRelocs.data() == curRelocs.data()) {
473 newRelocs = makeMutableArrayRef(
474 bAlloc.Allocate<coff_relocation>(originalRelocs.size()),
475 originalRelocs.size());
477 newRelocs = makeMutableArrayRef(
478 const_cast<coff_relocation *>(curRelocs.data()), curRelocs.size());
481 // Copy each relocation, but replace the symbol table indices which need
483 auto nextReplacement = relocReplacements.begin();
484 auto endReplacement = relocReplacements.end();
485 for (size_t i = 0, e = originalRelocs.size(); i != e; ++i) {
486 newRelocs[i] = originalRelocs[i];
487 if (nextReplacement != endReplacement && nextReplacement->first == i) {
488 newRelocs[i].SymbolTableIndex = nextReplacement->second;
493 sc->setRelocs(newRelocs);
495 return addressesChanged;
498 // Verify that all relocations are in range, with no extra margin requirements.
499 static bool verifyRanges(const std::vector<Chunk *> chunks) {
500 for (Chunk *c : chunks) {
501 SectionChunk *sc = dyn_cast_or_null<SectionChunk>(c);
505 ArrayRef<coff_relocation> relocs = sc->getRelocs();
506 for (size_t j = 0, e = relocs.size(); j < e; ++j) {
507 const coff_relocation &rel = relocs[j];
508 Symbol *relocTarget = sc->file->getSymbol(rel.SymbolTableIndex);
510 Defined *sym = dyn_cast_or_null<Defined>(relocTarget);
514 uint64_t p = sc->getRVA() + rel.VirtualAddress;
515 uint64_t s = sym->getRVA();
517 if (!isInRange(rel.Type, s, p, 0))
524 // Assign addresses and add thunks if necessary.
525 void Writer::finalizeAddresses() {
527 if (config->machine != ARMNT && config->machine != ARM64)
530 size_t origNumChunks = 0;
531 for (OutputSection *sec : outputSections) {
532 sec->origChunks = sec->chunks;
533 origNumChunks += sec->chunks.size();
537 int margin = 1024 * 100;
539 // First check whether we need thunks at all, or if the previous pass of
540 // adding them turned out ok.
541 bool rangesOk = true;
542 size_t numChunks = 0;
543 for (OutputSection *sec : outputSections) {
544 if (!verifyRanges(sec->chunks)) {
548 numChunks += sec->chunks.size();
552 log("Added " + Twine(numChunks - origNumChunks) + " thunks with " +
553 "margin " + Twine(margin) + " in " + Twine(pass) + " passes");
558 fatal("adding thunks hasn't converged after " + Twine(pass) + " passes");
561 // If the previous pass didn't work out, reset everything back to the
562 // original conditions before retrying with a wider margin. This should
563 // ideally never happen under real circumstances.
564 for (OutputSection *sec : outputSections)
565 sec->chunks = sec->origChunks;
569 // Try adding thunks everywhere where it is needed, with a margin
570 // to avoid things going out of range due to the added thunks.
571 bool addressesChanged = false;
572 for (OutputSection *sec : outputSections)
573 addressesChanged |= createThunks(sec, margin);
574 // If the verification above thought we needed thunks, we should have
576 assert(addressesChanged);
578 // Recalculate the layout for the whole image (and verify the ranges at
579 // the start of the next round).
586 // The main function of the writer.
588 ScopedTimer t1(codeLayoutTimer);
590 createImportTables();
593 appendImportThunks();
596 removeUnusedSections();
598 removeEmptySections();
599 assignOutputSectionIndices();
600 setSectionPermissions();
601 createSymbolAndStringTable();
603 if (fileSize > UINT32_MAX)
604 fatal("image size (" + Twine(fileSize) + ") " +
605 "exceeds maximum allowable size (" + Twine(UINT32_MAX) + ")");
607 openFile(config->outputFile);
608 if (config->is64()) {
609 writeHeader<pe32plus_header>();
611 writeHeader<pe32_header>();
614 sortExceptionTable();
618 if (!config->pdbPath.empty() && config->debug) {
620 createPDB(symtab, outputSections, sectionTable, buildId->buildId);
624 writeMapFile(outputSections);
629 ScopedTimer t2(diskCommitTimer);
630 if (auto e = buffer->commit())
631 fatal("failed to write the output file: " + toString(std::move(e)));
634 static StringRef getOutputSectionName(StringRef name) {
635 StringRef s = name.split('$').first;
637 // Treat a later period as a separator for MinGW, for sections like
639 return s.substr(0, s.find('.', 1));
643 static void sortBySectionOrder(std::vector<Chunk *> &chunks) {
644 auto getPriority = [](const Chunk *c) {
645 if (auto *sec = dyn_cast<SectionChunk>(c))
647 return config->order.lookup(sec->sym->getName());
651 llvm::stable_sort(chunks, [=](const Chunk *a, const Chunk *b) {
652 return getPriority(a) < getPriority(b);
656 // Change the characteristics of existing PartialSections that belong to the
657 // section Name to Chars.
658 void Writer::fixPartialSectionChars(StringRef name, uint32_t chars) {
659 for (auto it : partialSections) {
660 PartialSection *pSec = it.second;
661 StringRef curName = pSec->name;
662 if (!curName.consume_front(name) ||
663 (!curName.empty() && !curName.startswith("$")))
665 if (pSec->characteristics == chars)
667 PartialSection *destSec = createPartialSection(pSec->name, chars);
668 destSec->chunks.insert(destSec->chunks.end(), pSec->chunks.begin(),
670 pSec->chunks.clear();
674 // Sort concrete section chunks from GNU import libraries.
676 // GNU binutils doesn't use short import files, but instead produces import
677 // libraries that consist of object files, with section chunks for the .idata$*
678 // sections. These are linked just as regular static libraries. Each import
679 // library consists of one header object, one object file for every imported
680 // symbol, and one trailer object. In order for the .idata tables/lists to
681 // be formed correctly, the section chunks within each .idata$* section need
682 // to be grouped by library, and sorted alphabetically within each library
683 // (which makes sure the header comes first and the trailer last).
684 bool Writer::fixGnuImportChunks() {
685 uint32_t rdata = IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ;
687 // Make sure all .idata$* section chunks are mapped as RDATA in order to
688 // be sorted into the same sections as our own synthesized .idata chunks.
689 fixPartialSectionChars(".idata", rdata);
691 bool hasIdata = false;
692 // Sort all .idata$* chunks, grouping chunks from the same library,
693 // with alphabetical ordering of the object fils within a library.
694 for (auto it : partialSections) {
695 PartialSection *pSec = it.second;
696 if (!pSec->name.startswith(".idata"))
699 if (!pSec->chunks.empty())
701 llvm::stable_sort(pSec->chunks, [&](Chunk *s, Chunk *t) {
702 SectionChunk *sc1 = dyn_cast_or_null<SectionChunk>(s);
703 SectionChunk *sc2 = dyn_cast_or_null<SectionChunk>(t);
705 // if SC1, order them ascending. If SC2 or both null,
706 // S is not less than T.
707 return sc1 != nullptr;
709 // Make a string with "libraryname/objectfile" for sorting, achieving
710 // both grouping by library and sorting of objects within a library,
713 (sc1->file->parentName + "/" + sc1->file->getName()).str();
715 (sc2->file->parentName + "/" + sc2->file->getName()).str();
722 // Add generated idata chunks, for imported symbols and DLLs, and a
723 // terminator in .idata$2.
724 void Writer::addSyntheticIdata() {
725 uint32_t rdata = IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ;
728 // Add the .idata content in the right section groups, to allow
729 // chunks from other linked in object files to be grouped together.
730 // See Microsoft PE/COFF spec 5.4 for details.
731 auto add = [&](StringRef n, std::vector<Chunk *> &v) {
732 PartialSection *pSec = createPartialSection(n, rdata);
733 pSec->chunks.insert(pSec->chunks.end(), v.begin(), v.end());
736 // The loader assumes a specific order of data.
737 // Add each type in the correct order.
738 add(".idata$2", idata.dirs);
739 add(".idata$4", idata.lookups);
740 add(".idata$5", idata.addresses);
741 if (!idata.hints.empty())
742 add(".idata$6", idata.hints);
743 add(".idata$7", idata.dllNames);
746 // Locate the first Chunk and size of the import directory list and the
748 void Writer::locateImportTables() {
749 uint32_t rdata = IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ;
751 if (PartialSection *importDirs = findPartialSection(".idata$2", rdata)) {
752 if (!importDirs->chunks.empty())
753 importTableStart = importDirs->chunks.front();
754 for (Chunk *c : importDirs->chunks)
755 importTableSize += c->getSize();
758 if (PartialSection *importAddresses = findPartialSection(".idata$5", rdata)) {
759 if (!importAddresses->chunks.empty())
760 iatStart = importAddresses->chunks.front();
761 for (Chunk *c : importAddresses->chunks)
762 iatSize += c->getSize();
766 // Return whether a SectionChunk's suffix (the dollar and any trailing
767 // suffix) should be removed and sorted into the main suffixless
769 static bool shouldStripSectionSuffix(SectionChunk *sc, StringRef name) {
770 // On MinGW, comdat groups are formed by putting the comdat group name
771 // after the '$' in the section name. For .eh_frame$<symbol>, that must
772 // still be sorted before the .eh_frame trailer from crtend.o, thus just
773 // strip the section name trailer. For other sections, such as
774 // .tls$$<symbol> (where non-comdat .tls symbols are otherwise stored in
775 // ".tls$"), they must be strictly sorted after .tls. And for the
776 // hypothetical case of comdat .CRT$XCU, we definitely need to keep the
777 // suffix for sorting. Thus, to play it safe, only strip the suffix for
778 // the standard sections.
781 if (!sc || !sc->isCOMDAT())
783 return name.startswith(".text$") || name.startswith(".data$") ||
784 name.startswith(".rdata$") || name.startswith(".pdata$") ||
785 name.startswith(".xdata$") || name.startswith(".eh_frame$");
788 // Create output section objects and add them to OutputSections.
789 void Writer::createSections() {
790 // First, create the builtin sections.
791 const uint32_t data = IMAGE_SCN_CNT_INITIALIZED_DATA;
792 const uint32_t bss = IMAGE_SCN_CNT_UNINITIALIZED_DATA;
793 const uint32_t code = IMAGE_SCN_CNT_CODE;
794 const uint32_t discardable = IMAGE_SCN_MEM_DISCARDABLE;
795 const uint32_t r = IMAGE_SCN_MEM_READ;
796 const uint32_t w = IMAGE_SCN_MEM_WRITE;
797 const uint32_t x = IMAGE_SCN_MEM_EXECUTE;
799 SmallDenseMap<std::pair<StringRef, uint32_t>, OutputSection *> sections;
800 auto createSection = [&](StringRef name, uint32_t outChars) {
801 OutputSection *&sec = sections[{name, outChars}];
803 sec = make<OutputSection>(name, outChars);
804 outputSections.push_back(sec);
809 // Try to match the section order used by link.exe.
810 textSec = createSection(".text", code | r | x);
811 createSection(".bss", bss | r | w);
812 rdataSec = createSection(".rdata", data | r);
813 buildidSec = createSection(".buildid", data | r);
814 dataSec = createSection(".data", data | r | w);
815 pdataSec = createSection(".pdata", data | r);
816 idataSec = createSection(".idata", data | r);
817 edataSec = createSection(".edata", data | r);
818 didatSec = createSection(".didat", data | r);
819 rsrcSec = createSection(".rsrc", data | r);
820 relocSec = createSection(".reloc", data | discardable | r);
821 ctorsSec = createSection(".ctors", data | r | w);
822 dtorsSec = createSection(".dtors", data | r | w);
824 // Then bin chunks by name and output characteristics.
825 for (Chunk *c : symtab->getChunks()) {
826 auto *sc = dyn_cast<SectionChunk>(c);
827 if (sc && !sc->live) {
829 sc->printDiscardedMessage();
832 StringRef name = c->getSectionName();
833 if (shouldStripSectionSuffix(sc, name))
834 name = name.split('$').first;
835 PartialSection *pSec = createPartialSection(name,
836 c->getOutputCharacteristics());
837 pSec->chunks.push_back(c);
840 fixPartialSectionChars(".rsrc", data | r);
841 fixPartialSectionChars(".edata", data | r);
842 // Even in non MinGW cases, we might need to link against GNU import
844 bool hasIdata = fixGnuImportChunks();
851 // Process an /order option.
852 if (!config->order.empty())
853 for (auto it : partialSections)
854 sortBySectionOrder(it.second->chunks);
857 locateImportTables();
859 // Then create an OutputSection for each section.
860 // '$' and all following characters in input section names are
861 // discarded when determining output section. So, .text$foo
862 // contributes to .text, for example. See PE/COFF spec 3.2.
863 for (auto it : partialSections) {
864 PartialSection *pSec = it.second;
865 StringRef name = getOutputSectionName(pSec->name);
866 uint32_t outChars = pSec->characteristics;
868 if (name == ".CRT") {
869 // In link.exe, there is a special case for the I386 target where .CRT
870 // sections are treated as if they have output characteristics DATA | R if
871 // their characteristics are DATA | R | W. This implements the same
872 // special case for all architectures.
875 log("Processing section " + pSec->name + " -> " + name);
877 sortCRTSectionChunks(pSec->chunks);
880 OutputSection *sec = createSection(name, outChars);
881 for (Chunk *c : pSec->chunks)
884 sec->addContributingPartialSection(pSec);
887 // Finally, move some output sections to the end.
888 auto sectionOrder = [&](const OutputSection *s) {
889 // Move DISCARDABLE (or non-memory-mapped) sections to the end of file
890 // because the loader cannot handle holes. Stripping can remove other
891 // discardable ones than .reloc, which is first of them (created early).
892 if (s->header.Characteristics & IMAGE_SCN_MEM_DISCARDABLE)
894 // .rsrc should come at the end of the non-discardable sections because its
895 // size may change by the Win32 UpdateResources() function, causing
896 // subsequent sections to move (see https://crbug.com/827082).
901 llvm::stable_sort(outputSections,
902 [&](const OutputSection *s, const OutputSection *t) {
903 return sectionOrder(s) < sectionOrder(t);
907 void Writer::createMiscChunks() {
908 for (MergeChunk *p : MergeChunk::instances) {
910 p->finalizeContents();
911 rdataSec->addChunk(p);
915 // Create thunks for locally-dllimported symbols.
916 if (!symtab->localImportChunks.empty()) {
917 for (Chunk *c : symtab->localImportChunks)
918 rdataSec->addChunk(c);
921 // Create Debug Information Chunks
922 OutputSection *debugInfoSec = config->mingw ? buildidSec : rdataSec;
923 if (config->debug || config->repro) {
924 debugDirectory = make<DebugDirectoryChunk>(debugRecords, config->repro);
925 debugInfoSec->addChunk(debugDirectory);
929 // Make a CVDebugRecordChunk even when /DEBUG:CV is not specified. We
930 // output a PDB no matter what, and this chunk provides the only means of
931 // allowing a debugger to match a PDB and an executable. So we need it even
932 // if we're ultimately not going to write CodeView data to the PDB.
933 buildId = make<CVDebugRecordChunk>();
934 debugRecords.push_back(buildId);
936 for (Chunk *c : debugRecords)
937 debugInfoSec->addChunk(c);
940 // Create SEH table. x86-only.
944 // Create /guard:cf tables if requested.
945 if (config->guardCF != GuardCFLevel::Off)
946 createGuardCFTables();
949 createRuntimePseudoRelocs();
951 insertCtorDtorSymbols();
955 // Create .idata section for the DLL-imported symbol table.
956 // The format of this section is inherently Windows-specific.
957 // IdataContents class abstracted away the details for us,
958 // so we just let it create chunks and add them to the section.
959 void Writer::createImportTables() {
960 // Initialize DLLOrder so that import entries are ordered in
961 // the same order as in the command line. (That affects DLL
962 // initialization order, and this ordering is MSVC-compatible.)
963 for (ImportFile *file : ImportFile::instances) {
967 std::string dll = StringRef(file->dllName).lower();
968 if (config->dllOrder.count(dll) == 0)
969 config->dllOrder[dll] = config->dllOrder.size();
971 if (file->impSym && !isa<DefinedImportData>(file->impSym))
972 fatal(toString(*file->impSym) + " was replaced");
973 DefinedImportData *impSym = cast_or_null<DefinedImportData>(file->impSym);
974 if (config->delayLoads.count(StringRef(file->dllName).lower())) {
976 fatal("cannot delay-load " + toString(file) +
977 " due to import of data: " + toString(*impSym));
978 delayIdata.add(impSym);
985 void Writer::appendImportThunks() {
986 if (ImportFile::instances.empty())
989 for (ImportFile *file : ImportFile::instances) {
996 if (!isa<DefinedImportThunk>(file->thunkSym))
997 fatal(toString(*file->thunkSym) + " was replaced");
998 DefinedImportThunk *thunk = cast<DefinedImportThunk>(file->thunkSym);
1000 textSec->addChunk(thunk->getChunk());
1003 if (!delayIdata.empty()) {
1004 Defined *helper = cast<Defined>(config->delayLoadHelper);
1005 delayIdata.create(helper);
1006 for (Chunk *c : delayIdata.getChunks())
1007 didatSec->addChunk(c);
1008 for (Chunk *c : delayIdata.getDataChunks())
1009 dataSec->addChunk(c);
1010 for (Chunk *c : delayIdata.getCodeChunks())
1011 textSec->addChunk(c);
1015 void Writer::createExportTable() {
1016 if (!edataSec->chunks.empty()) {
1017 // Allow using a custom built export table from input object files, instead
1018 // of having the linker synthesize the tables.
1019 if (config->hadExplicitExports)
1020 warn("literal .edata sections override exports");
1021 } else if (!config->exports.empty()) {
1022 for (Chunk *c : edata.chunks)
1023 edataSec->addChunk(c);
1025 if (!edataSec->chunks.empty()) {
1026 edataStart = edataSec->chunks.front();
1027 edataEnd = edataSec->chunks.back();
1031 void Writer::removeUnusedSections() {
1032 // Remove sections that we can be sure won't get content, to avoid
1033 // allocating space for their section headers.
1034 auto isUnused = [this](OutputSection *s) {
1036 return false; // This section is populated later.
1037 // MergeChunks have zero size at this point, as their size is finalized
1038 // later. Only remove sections that have no Chunks at all.
1039 return s->chunks.empty();
1041 outputSections.erase(
1042 std::remove_if(outputSections.begin(), outputSections.end(), isUnused),
1043 outputSections.end());
1046 // The Windows loader doesn't seem to like empty sections,
1047 // so we remove them if any.
1048 void Writer::removeEmptySections() {
1049 auto isEmpty = [](OutputSection *s) { return s->getVirtualSize() == 0; };
1050 outputSections.erase(
1051 std::remove_if(outputSections.begin(), outputSections.end(), isEmpty),
1052 outputSections.end());
1055 void Writer::assignOutputSectionIndices() {
1056 // Assign final output section indices, and assign each chunk to its output
1059 for (OutputSection *os : outputSections) {
1060 os->sectionIndex = idx;
1061 for (Chunk *c : os->chunks)
1062 c->setOutputSectionIdx(idx);
1066 // Merge chunks are containers of chunks, so assign those an output section
1068 for (MergeChunk *mc : MergeChunk::instances)
1070 for (SectionChunk *sc : mc->sections)
1072 sc->setOutputSectionIdx(mc->getOutputSectionIdx());
1075 size_t Writer::addEntryToStringTable(StringRef str) {
1076 assert(str.size() > COFF::NameSize);
1077 size_t offsetOfEntry = strtab.size() + 4; // +4 for the size field
1078 strtab.insert(strtab.end(), str.begin(), str.end());
1079 strtab.push_back('\0');
1080 return offsetOfEntry;
1083 Optional<coff_symbol16> Writer::createSymbol(Defined *def) {
1085 switch (def->kind()) {
1086 case Symbol::DefinedAbsoluteKind:
1087 sym.Value = def->getRVA();
1088 sym.SectionNumber = IMAGE_SYM_ABSOLUTE;
1090 case Symbol::DefinedSyntheticKind:
1091 // Relative symbols are unrepresentable in a COFF symbol table.
1094 // Don't write symbols that won't be written to the output to the symbol
1096 Chunk *c = def->getChunk();
1099 OutputSection *os = c->getOutputSection();
1103 sym.Value = def->getRVA() - os->getRVA();
1104 sym.SectionNumber = os->sectionIndex;
1109 // Symbols that are runtime pseudo relocations don't point to the actual
1110 // symbol data itself (as they are imported), but points to the IAT entry
1111 // instead. Avoid emitting them to the symbol table, as they can confuse
1113 if (def->isRuntimePseudoReloc)
1116 StringRef name = def->getName();
1117 if (name.size() > COFF::NameSize) {
1118 sym.Name.Offset.Zeroes = 0;
1119 sym.Name.Offset.Offset = addEntryToStringTable(name);
1121 memset(sym.Name.ShortName, 0, COFF::NameSize);
1122 memcpy(sym.Name.ShortName, name.data(), name.size());
1125 if (auto *d = dyn_cast<DefinedCOFF>(def)) {
1126 COFFSymbolRef ref = d->getCOFFSymbol();
1127 sym.Type = ref.getType();
1128 sym.StorageClass = ref.getStorageClass();
1130 sym.Type = IMAGE_SYM_TYPE_NULL;
1131 sym.StorageClass = IMAGE_SYM_CLASS_EXTERNAL;
1133 sym.NumberOfAuxSymbols = 0;
1137 void Writer::createSymbolAndStringTable() {
1138 // PE/COFF images are limited to 8 byte section names. Longer names can be
1139 // supported by writing a non-standard string table, but this string table is
1140 // not mapped at runtime and the long names will therefore be inaccessible.
1141 // link.exe always truncates section names to 8 bytes, whereas binutils always
1142 // preserves long section names via the string table. LLD adopts a hybrid
1143 // solution where discardable sections have long names preserved and
1144 // non-discardable sections have their names truncated, to ensure that any
1145 // section which is mapped at runtime also has its name mapped at runtime.
1146 for (OutputSection *sec : outputSections) {
1147 if (sec->name.size() <= COFF::NameSize)
1149 if ((sec->header.Characteristics & IMAGE_SCN_MEM_DISCARDABLE) == 0)
1151 sec->setStringTableOff(addEntryToStringTable(sec->name));
1154 if (config->debugDwarf || config->debugSymtab) {
1155 for (ObjFile *file : ObjFile::instances) {
1156 for (Symbol *b : file->getSymbols()) {
1157 auto *d = dyn_cast_or_null<Defined>(b);
1158 if (!d || d->writtenToSymtab)
1160 d->writtenToSymtab = true;
1162 if (Optional<coff_symbol16> sym = createSymbol(d))
1163 outputSymtab.push_back(*sym);
1168 if (outputSymtab.empty() && strtab.empty())
1171 // We position the symbol table to be adjacent to the end of the last section.
1172 uint64_t fileOff = fileSize;
1173 pointerToSymbolTable = fileOff;
1174 fileOff += outputSymtab.size() * sizeof(coff_symbol16);
1175 fileOff += 4 + strtab.size();
1176 fileSize = alignTo(fileOff, config->fileAlign);
1179 void Writer::mergeSections() {
1180 if (!pdataSec->chunks.empty()) {
1181 firstPdata = pdataSec->chunks.front();
1182 lastPdata = pdataSec->chunks.back();
1185 for (auto &p : config->merge) {
1186 StringRef toName = p.second;
1187 if (p.first == toName)
1191 if (!names.insert(toName).second)
1192 fatal("/merge: cycle found for section '" + p.first + "'");
1193 auto i = config->merge.find(toName);
1194 if (i == config->merge.end())
1198 OutputSection *from = findSection(p.first);
1199 OutputSection *to = findSection(toName);
1203 from->name = toName;
1210 // Visits all sections to assign incremental, non-overlapping RVAs and
1212 void Writer::assignAddresses() {
1213 sizeOfHeaders = dosStubSize + sizeof(PEMagic) + sizeof(coff_file_header) +
1214 sizeof(data_directory) * numberOfDataDirectory +
1215 sizeof(coff_section) * outputSections.size();
1217 config->is64() ? sizeof(pe32plus_header) : sizeof(pe32_header);
1218 sizeOfHeaders = alignTo(sizeOfHeaders, config->fileAlign);
1219 fileSize = sizeOfHeaders;
1221 // The first page is kept unmapped.
1222 uint64_t rva = alignTo(sizeOfHeaders, config->align);
1224 for (OutputSection *sec : outputSections) {
1225 if (sec == relocSec)
1227 uint64_t rawSize = 0, virtualSize = 0;
1228 sec->header.VirtualAddress = rva;
1230 // If /FUNCTIONPADMIN is used, functions are padded in order to create a
1231 // hotpatchable image.
1232 const bool isCodeSection =
1233 (sec->header.Characteristics & IMAGE_SCN_CNT_CODE) &&
1234 (sec->header.Characteristics & IMAGE_SCN_MEM_READ) &&
1235 (sec->header.Characteristics & IMAGE_SCN_MEM_EXECUTE);
1236 uint32_t padding = isCodeSection ? config->functionPadMin : 0;
1238 for (Chunk *c : sec->chunks) {
1239 if (padding && c->isHotPatchable())
1240 virtualSize += padding;
1241 virtualSize = alignTo(virtualSize, c->getAlignment());
1242 c->setRVA(rva + virtualSize);
1243 virtualSize += c->getSize();
1245 rawSize = alignTo(virtualSize, config->fileAlign);
1247 if (virtualSize > UINT32_MAX)
1248 error("section larger than 4 GiB: " + sec->name);
1249 sec->header.VirtualSize = virtualSize;
1250 sec->header.SizeOfRawData = rawSize;
1252 sec->header.PointerToRawData = fileSize;
1253 rva += alignTo(virtualSize, config->align);
1254 fileSize += alignTo(rawSize, config->fileAlign);
1256 sizeOfImage = alignTo(rva, config->align);
1258 // Assign addresses to sections in MergeChunks.
1259 for (MergeChunk *mc : MergeChunk::instances)
1261 mc->assignSubsectionRVAs();
1264 template <typename PEHeaderTy> void Writer::writeHeader() {
1265 // Write DOS header. For backwards compatibility, the first part of a PE/COFF
1266 // executable consists of an MS-DOS MZ executable. If the executable is run
1267 // under DOS, that program gets run (usually to just print an error message).
1268 // When run under Windows, the loader looks at AddressOfNewExeHeader and uses
1269 // the PE header instead.
1270 uint8_t *buf = buffer->getBufferStart();
1271 auto *dos = reinterpret_cast<dos_header *>(buf);
1272 buf += sizeof(dos_header);
1273 dos->Magic[0] = 'M';
1274 dos->Magic[1] = 'Z';
1275 dos->UsedBytesInTheLastPage = dosStubSize % 512;
1276 dos->FileSizeInPages = divideCeil(dosStubSize, 512);
1277 dos->HeaderSizeInParagraphs = sizeof(dos_header) / 16;
1279 dos->AddressOfRelocationTable = sizeof(dos_header);
1280 dos->AddressOfNewExeHeader = dosStubSize;
1282 // Write DOS program.
1283 memcpy(buf, dosProgram, sizeof(dosProgram));
1284 buf += sizeof(dosProgram);
1287 memcpy(buf, PEMagic, sizeof(PEMagic));
1288 buf += sizeof(PEMagic);
1290 // Write COFF header
1291 auto *coff = reinterpret_cast<coff_file_header *>(buf);
1292 buf += sizeof(*coff);
1293 coff->Machine = config->machine;
1294 coff->NumberOfSections = outputSections.size();
1295 coff->Characteristics = IMAGE_FILE_EXECUTABLE_IMAGE;
1296 if (config->largeAddressAware)
1297 coff->Characteristics |= IMAGE_FILE_LARGE_ADDRESS_AWARE;
1298 if (!config->is64())
1299 coff->Characteristics |= IMAGE_FILE_32BIT_MACHINE;
1301 coff->Characteristics |= IMAGE_FILE_DLL;
1302 if (!config->relocatable)
1303 coff->Characteristics |= IMAGE_FILE_RELOCS_STRIPPED;
1304 if (config->swaprunCD)
1305 coff->Characteristics |= IMAGE_FILE_REMOVABLE_RUN_FROM_SWAP;
1306 if (config->swaprunNet)
1307 coff->Characteristics |= IMAGE_FILE_NET_RUN_FROM_SWAP;
1308 coff->SizeOfOptionalHeader =
1309 sizeof(PEHeaderTy) + sizeof(data_directory) * numberOfDataDirectory;
1312 auto *pe = reinterpret_cast<PEHeaderTy *>(buf);
1314 pe->Magic = config->is64() ? PE32Header::PE32_PLUS : PE32Header::PE32;
1316 // If {Major,Minor}LinkerVersion is left at 0.0, then for some
1317 // reason signing the resulting PE file with Authenticode produces a
1318 // signature that fails to validate on Windows 7 (but is OK on 10).
1319 // Set it to 14.0, which is what VS2015 outputs, and which avoids
1321 pe->MajorLinkerVersion = 14;
1322 pe->MinorLinkerVersion = 0;
1324 pe->ImageBase = config->imageBase;
1325 pe->SectionAlignment = config->align;
1326 pe->FileAlignment = config->fileAlign;
1327 pe->MajorImageVersion = config->majorImageVersion;
1328 pe->MinorImageVersion = config->minorImageVersion;
1329 pe->MajorOperatingSystemVersion = config->majorOSVersion;
1330 pe->MinorOperatingSystemVersion = config->minorOSVersion;
1331 pe->MajorSubsystemVersion = config->majorOSVersion;
1332 pe->MinorSubsystemVersion = config->minorOSVersion;
1333 pe->Subsystem = config->subsystem;
1334 pe->SizeOfImage = sizeOfImage;
1335 pe->SizeOfHeaders = sizeOfHeaders;
1336 if (!config->noEntry) {
1337 Defined *entry = cast<Defined>(config->entry);
1338 pe->AddressOfEntryPoint = entry->getRVA();
1339 // Pointer to thumb code must have the LSB set, so adjust it.
1340 if (config->machine == ARMNT)
1341 pe->AddressOfEntryPoint |= 1;
1343 pe->SizeOfStackReserve = config->stackReserve;
1344 pe->SizeOfStackCommit = config->stackCommit;
1345 pe->SizeOfHeapReserve = config->heapReserve;
1346 pe->SizeOfHeapCommit = config->heapCommit;
1347 if (config->appContainer)
1348 pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_APPCONTAINER;
1349 if (config->dynamicBase)
1350 pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_DYNAMIC_BASE;
1351 if (config->highEntropyVA)
1352 pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_HIGH_ENTROPY_VA;
1353 if (!config->allowBind)
1354 pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_NO_BIND;
1355 if (config->nxCompat)
1356 pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_NX_COMPAT;
1357 if (!config->allowIsolation)
1358 pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_NO_ISOLATION;
1359 if (config->guardCF != GuardCFLevel::Off)
1360 pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_GUARD_CF;
1361 if (config->integrityCheck)
1362 pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_FORCE_INTEGRITY;
1363 if (setNoSEHCharacteristic)
1364 pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_NO_SEH;
1365 if (config->terminalServerAware)
1366 pe->DLLCharacteristics |= IMAGE_DLL_CHARACTERISTICS_TERMINAL_SERVER_AWARE;
1367 pe->NumberOfRvaAndSize = numberOfDataDirectory;
1368 if (textSec->getVirtualSize()) {
1369 pe->BaseOfCode = textSec->getRVA();
1370 pe->SizeOfCode = textSec->getRawSize();
1372 pe->SizeOfInitializedData = getSizeOfInitializedData();
1374 // Write data directory
1375 auto *dir = reinterpret_cast<data_directory *>(buf);
1376 buf += sizeof(*dir) * numberOfDataDirectory;
1378 dir[EXPORT_TABLE].RelativeVirtualAddress = edataStart->getRVA();
1379 dir[EXPORT_TABLE].Size =
1380 edataEnd->getRVA() + edataEnd->getSize() - edataStart->getRVA();
1382 if (importTableStart) {
1383 dir[IMPORT_TABLE].RelativeVirtualAddress = importTableStart->getRVA();
1384 dir[IMPORT_TABLE].Size = importTableSize;
1387 dir[IAT].RelativeVirtualAddress = iatStart->getRVA();
1388 dir[IAT].Size = iatSize;
1390 if (rsrcSec->getVirtualSize()) {
1391 dir[RESOURCE_TABLE].RelativeVirtualAddress = rsrcSec->getRVA();
1392 dir[RESOURCE_TABLE].Size = rsrcSec->getVirtualSize();
1395 dir[EXCEPTION_TABLE].RelativeVirtualAddress = firstPdata->getRVA();
1396 dir[EXCEPTION_TABLE].Size =
1397 lastPdata->getRVA() + lastPdata->getSize() - firstPdata->getRVA();
1399 if (relocSec->getVirtualSize()) {
1400 dir[BASE_RELOCATION_TABLE].RelativeVirtualAddress = relocSec->getRVA();
1401 dir[BASE_RELOCATION_TABLE].Size = relocSec->getVirtualSize();
1403 if (Symbol *sym = symtab->findUnderscore("_tls_used")) {
1404 if (Defined *b = dyn_cast<Defined>(sym)) {
1405 dir[TLS_TABLE].RelativeVirtualAddress = b->getRVA();
1406 dir[TLS_TABLE].Size = config->is64()
1407 ? sizeof(object::coff_tls_directory64)
1408 : sizeof(object::coff_tls_directory32);
1411 if (debugDirectory) {
1412 dir[DEBUG_DIRECTORY].RelativeVirtualAddress = debugDirectory->getRVA();
1413 dir[DEBUG_DIRECTORY].Size = debugDirectory->getSize();
1415 if (Symbol *sym = symtab->findUnderscore("_load_config_used")) {
1416 if (auto *b = dyn_cast<DefinedRegular>(sym)) {
1417 SectionChunk *sc = b->getChunk();
1418 assert(b->getRVA() >= sc->getRVA());
1419 uint64_t offsetInChunk = b->getRVA() - sc->getRVA();
1420 if (!sc->hasData || offsetInChunk + 4 > sc->getSize())
1421 fatal("_load_config_used is malformed");
1423 ArrayRef<uint8_t> secContents = sc->getContents();
1424 uint32_t loadConfigSize =
1425 *reinterpret_cast<const ulittle32_t *>(&secContents[offsetInChunk]);
1426 if (offsetInChunk + loadConfigSize > sc->getSize())
1427 fatal("_load_config_used is too large");
1428 dir[LOAD_CONFIG_TABLE].RelativeVirtualAddress = b->getRVA();
1429 dir[LOAD_CONFIG_TABLE].Size = loadConfigSize;
1432 if (!delayIdata.empty()) {
1433 dir[DELAY_IMPORT_DESCRIPTOR].RelativeVirtualAddress =
1434 delayIdata.getDirRVA();
1435 dir[DELAY_IMPORT_DESCRIPTOR].Size = delayIdata.getDirSize();
1438 // Write section table
1439 for (OutputSection *sec : outputSections) {
1440 sec->writeHeaderTo(buf);
1441 buf += sizeof(coff_section);
1443 sectionTable = ArrayRef<uint8_t>(
1444 buf - outputSections.size() * sizeof(coff_section), buf);
1446 if (outputSymtab.empty() && strtab.empty())
1449 coff->PointerToSymbolTable = pointerToSymbolTable;
1450 uint32_t numberOfSymbols = outputSymtab.size();
1451 coff->NumberOfSymbols = numberOfSymbols;
1452 auto *symbolTable = reinterpret_cast<coff_symbol16 *>(
1453 buffer->getBufferStart() + coff->PointerToSymbolTable);
1454 for (size_t i = 0; i != numberOfSymbols; ++i)
1455 symbolTable[i] = outputSymtab[i];
1456 // Create the string table, it follows immediately after the symbol table.
1457 // The first 4 bytes is length including itself.
1458 buf = reinterpret_cast<uint8_t *>(&symbolTable[numberOfSymbols]);
1459 write32le(buf, strtab.size() + 4);
1460 if (!strtab.empty())
1461 memcpy(buf + 4, strtab.data(), strtab.size());
1464 void Writer::openFile(StringRef path) {
1466 FileOutputBuffer::create(path, fileSize, FileOutputBuffer::F_executable),
1467 "failed to open " + path);
1470 void Writer::createSEHTable() {
1471 SymbolRVASet handlers;
1472 for (ObjFile *file : ObjFile::instances) {
1473 if (!file->hasSafeSEH())
1474 error("/safeseh: " + file->getName() + " is not compatible with SEH");
1475 markSymbolsForRVATable(file, file->getSXDataChunks(), handlers);
1478 // Set the "no SEH" characteristic if there really were no handlers, or if
1479 // there is no load config object to point to the table of handlers.
1480 setNoSEHCharacteristic =
1481 handlers.empty() || !symtab->findUnderscore("_load_config_used");
1483 maybeAddRVATable(std::move(handlers), "__safe_se_handler_table",
1484 "__safe_se_handler_count");
1487 // Add a symbol to an RVA set. Two symbols may have the same RVA, but an RVA set
1488 // cannot contain duplicates. Therefore, the set is uniqued by Chunk and the
1489 // symbol's offset into that Chunk.
1490 static void addSymbolToRVASet(SymbolRVASet &rvaSet, Defined *s) {
1491 Chunk *c = s->getChunk();
1492 if (auto *sc = dyn_cast<SectionChunk>(c))
1493 c = sc->repl; // Look through ICF replacement.
1494 uint32_t off = s->getRVA() - (c ? c->getRVA() : 0);
1495 rvaSet.insert({c, off});
1498 // Given a symbol, add it to the GFIDs table if it is a live, defined, function
1499 // symbol in an executable section.
1500 static void maybeAddAddressTakenFunction(SymbolRVASet &addressTakenSyms,
1505 switch (s->kind()) {
1506 case Symbol::DefinedLocalImportKind:
1507 case Symbol::DefinedImportDataKind:
1508 // Defines an __imp_ pointer, so it is data, so it is ignored.
1510 case Symbol::DefinedCommonKind:
1511 // Common is always data, so it is ignored.
1513 case Symbol::DefinedAbsoluteKind:
1514 case Symbol::DefinedSyntheticKind:
1515 // Absolute is never code, synthetic generally isn't and usually isn't
1518 case Symbol::LazyArchiveKind:
1519 case Symbol::LazyObjectKind:
1520 case Symbol::UndefinedKind:
1521 // Undefined symbols resolve to zero, so they don't have an RVA. Lazy
1522 // symbols shouldn't have relocations.
1525 case Symbol::DefinedImportThunkKind:
1526 // Thunks are always code, include them.
1527 addSymbolToRVASet(addressTakenSyms, cast<Defined>(s));
1530 case Symbol::DefinedRegularKind: {
1531 // This is a regular, defined, symbol from a COFF file. Mark the symbol as
1532 // address taken if the symbol type is function and it's in an executable
1534 auto *d = cast<DefinedRegular>(s);
1535 if (d->getCOFFSymbol().getComplexType() == COFF::IMAGE_SYM_DTYPE_FUNCTION) {
1536 SectionChunk *sc = dyn_cast<SectionChunk>(d->getChunk());
1537 if (sc && sc->live &&
1538 sc->getOutputCharacteristics() & IMAGE_SCN_MEM_EXECUTE)
1539 addSymbolToRVASet(addressTakenSyms, d);
1546 // Visit all relocations from all section contributions of this object file and
1547 // mark the relocation target as address-taken.
1548 static void markSymbolsWithRelocations(ObjFile *file,
1549 SymbolRVASet &usedSymbols) {
1550 for (Chunk *c : file->getChunks()) {
1551 // We only care about live section chunks. Common chunks and other chunks
1552 // don't generally contain relocations.
1553 SectionChunk *sc = dyn_cast<SectionChunk>(c);
1554 if (!sc || !sc->live)
1557 for (const coff_relocation &reloc : sc->getRelocs()) {
1558 if (config->machine == I386 && reloc.Type == COFF::IMAGE_REL_I386_REL32)
1559 // Ignore relative relocations on x86. On x86_64 they can't be ignored
1560 // since they're also used to compute absolute addresses.
1563 Symbol *ref = sc->file->getSymbol(reloc.SymbolTableIndex);
1564 maybeAddAddressTakenFunction(usedSymbols, ref);
1569 // Create the guard function id table. This is a table of RVAs of all
1570 // address-taken functions. It is sorted and uniqued, just like the safe SEH
1572 void Writer::createGuardCFTables() {
1573 SymbolRVASet addressTakenSyms;
1574 SymbolRVASet longJmpTargets;
1575 for (ObjFile *file : ObjFile::instances) {
1576 // If the object was compiled with /guard:cf, the address taken symbols
1577 // are in .gfids$y sections, and the longjmp targets are in .gljmp$y
1578 // sections. If the object was not compiled with /guard:cf, we assume there
1579 // were no setjmp targets, and that all code symbols with relocations are
1580 // possibly address-taken.
1581 if (file->hasGuardCF()) {
1582 markSymbolsForRVATable(file, file->getGuardFidChunks(), addressTakenSyms);
1583 markSymbolsForRVATable(file, file->getGuardLJmpChunks(), longJmpTargets);
1585 markSymbolsWithRelocations(file, addressTakenSyms);
1589 // Mark the image entry as address-taken.
1591 maybeAddAddressTakenFunction(addressTakenSyms, config->entry);
1593 // Mark exported symbols in executable sections as address-taken.
1594 for (Export &e : config->exports)
1595 maybeAddAddressTakenFunction(addressTakenSyms, e.sym);
1597 // Ensure sections referenced in the gfid table are 16-byte aligned.
1598 for (const ChunkAndOffset &c : addressTakenSyms)
1599 if (c.inputChunk->getAlignment() < 16)
1600 c.inputChunk->setAlignment(16);
1602 maybeAddRVATable(std::move(addressTakenSyms), "__guard_fids_table",
1603 "__guard_fids_count");
1605 // Add the longjmp target table unless the user told us not to.
1606 if (config->guardCF == GuardCFLevel::Full)
1607 maybeAddRVATable(std::move(longJmpTargets), "__guard_longjmp_table",
1608 "__guard_longjmp_count");
1610 // Set __guard_flags, which will be used in the load config to indicate that
1611 // /guard:cf was enabled.
1612 uint32_t guardFlags = uint32_t(coff_guard_flags::CFInstrumented) |
1613 uint32_t(coff_guard_flags::HasFidTable);
1614 if (config->guardCF == GuardCFLevel::Full)
1615 guardFlags |= uint32_t(coff_guard_flags::HasLongJmpTable);
1616 Symbol *flagSym = symtab->findUnderscore("__guard_flags");
1617 cast<DefinedAbsolute>(flagSym)->setVA(guardFlags);
1620 // Take a list of input sections containing symbol table indices and add those
1621 // symbols to an RVA table. The challenge is that symbol RVAs are not known and
1622 // depend on the table size, so we can't directly build a set of integers.
1623 void Writer::markSymbolsForRVATable(ObjFile *file,
1624 ArrayRef<SectionChunk *> symIdxChunks,
1625 SymbolRVASet &tableSymbols) {
1626 for (SectionChunk *c : symIdxChunks) {
1627 // Skip sections discarded by linker GC. This comes up when a .gfids section
1628 // is associated with something like a vtable and the vtable is discarded.
1629 // In this case, the associated gfids section is discarded, and we don't
1630 // mark the virtual member functions as address-taken by the vtable.
1634 // Validate that the contents look like symbol table indices.
1635 ArrayRef<uint8_t> data = c->getContents();
1636 if (data.size() % 4 != 0) {
1637 warn("ignoring " + c->getSectionName() +
1638 " symbol table index section in object " + toString(file));
1642 // Read each symbol table index and check if that symbol was included in the
1643 // final link. If so, add it to the table symbol set.
1644 ArrayRef<ulittle32_t> symIndices(
1645 reinterpret_cast<const ulittle32_t *>(data.data()), data.size() / 4);
1646 ArrayRef<Symbol *> objSymbols = file->getSymbols();
1647 for (uint32_t symIndex : symIndices) {
1648 if (symIndex >= objSymbols.size()) {
1649 warn("ignoring invalid symbol table index in section " +
1650 c->getSectionName() + " in object " + toString(file));
1653 if (Symbol *s = objSymbols[symIndex]) {
1655 addSymbolToRVASet(tableSymbols, cast<Defined>(s));
1661 // Replace the absolute table symbol with a synthetic symbol pointing to
1662 // tableChunk so that we can emit base relocations for it and resolve section
1663 // relative relocations.
1664 void Writer::maybeAddRVATable(SymbolRVASet tableSymbols, StringRef tableSym,
1665 StringRef countSym) {
1666 if (tableSymbols.empty())
1669 RVATableChunk *tableChunk = make<RVATableChunk>(std::move(tableSymbols));
1670 rdataSec->addChunk(tableChunk);
1672 Symbol *t = symtab->findUnderscore(tableSym);
1673 Symbol *c = symtab->findUnderscore(countSym);
1674 replaceSymbol<DefinedSynthetic>(t, t->getName(), tableChunk);
1675 cast<DefinedAbsolute>(c)->setVA(tableChunk->getSize() / 4);
1678 // MinGW specific. Gather all relocations that are imported from a DLL even
1679 // though the code didn't expect it to, produce the table that the runtime
1680 // uses for fixing them up, and provide the synthetic symbols that the
1681 // runtime uses for finding the table.
1682 void Writer::createRuntimePseudoRelocs() {
1683 std::vector<RuntimePseudoReloc> rels;
1685 for (Chunk *c : symtab->getChunks()) {
1686 auto *sc = dyn_cast<SectionChunk>(c);
1687 if (!sc || !sc->live)
1689 sc->getRuntimePseudoRelocs(rels);
1693 log("Writing " + Twine(rels.size()) + " runtime pseudo relocations");
1694 PseudoRelocTableChunk *table = make<PseudoRelocTableChunk>(rels);
1695 rdataSec->addChunk(table);
1696 EmptyChunk *endOfList = make<EmptyChunk>();
1697 rdataSec->addChunk(endOfList);
1699 Symbol *headSym = symtab->findUnderscore("__RUNTIME_PSEUDO_RELOC_LIST__");
1700 Symbol *endSym = symtab->findUnderscore("__RUNTIME_PSEUDO_RELOC_LIST_END__");
1701 replaceSymbol<DefinedSynthetic>(headSym, headSym->getName(), table);
1702 replaceSymbol<DefinedSynthetic>(endSym, endSym->getName(), endOfList);
1706 // The MinGW .ctors and .dtors lists have sentinels at each end;
1707 // a (uintptr_t)-1 at the start and a (uintptr_t)0 at the end.
1708 // There's a symbol pointing to the start sentinel pointer, __CTOR_LIST__
1709 // and __DTOR_LIST__ respectively.
1710 void Writer::insertCtorDtorSymbols() {
1711 AbsolutePointerChunk *ctorListHead = make<AbsolutePointerChunk>(-1);
1712 AbsolutePointerChunk *ctorListEnd = make<AbsolutePointerChunk>(0);
1713 AbsolutePointerChunk *dtorListHead = make<AbsolutePointerChunk>(-1);
1714 AbsolutePointerChunk *dtorListEnd = make<AbsolutePointerChunk>(0);
1715 ctorsSec->insertChunkAtStart(ctorListHead);
1716 ctorsSec->addChunk(ctorListEnd);
1717 dtorsSec->insertChunkAtStart(dtorListHead);
1718 dtorsSec->addChunk(dtorListEnd);
1720 Symbol *ctorListSym = symtab->findUnderscore("__CTOR_LIST__");
1721 Symbol *dtorListSym = symtab->findUnderscore("__DTOR_LIST__");
1722 replaceSymbol<DefinedSynthetic>(ctorListSym, ctorListSym->getName(),
1724 replaceSymbol<DefinedSynthetic>(dtorListSym, dtorListSym->getName(),
1728 // Handles /section options to allow users to overwrite
1729 // section attributes.
1730 void Writer::setSectionPermissions() {
1731 for (auto &p : config->section) {
1732 StringRef name = p.first;
1733 uint32_t perm = p.second;
1734 for (OutputSection *sec : outputSections)
1735 if (sec->name == name)
1736 sec->setPermissions(perm);
1740 // Write section contents to a mmap'ed file.
1741 void Writer::writeSections() {
1742 // Record the number of sections to apply section index relocations
1743 // against absolute symbols. See applySecIdx in Chunks.cpp..
1744 DefinedAbsolute::numOutputSections = outputSections.size();
1746 uint8_t *buf = buffer->getBufferStart();
1747 for (OutputSection *sec : outputSections) {
1748 uint8_t *secBuf = buf + sec->getFileOff();
1749 // Fill gaps between functions in .text with INT3 instructions
1750 // instead of leaving as NUL bytes (which can be interpreted as
1751 // ADD instructions).
1752 if (sec->header.Characteristics & IMAGE_SCN_CNT_CODE)
1753 memset(secBuf, 0xCC, sec->getRawSize());
1754 parallelForEach(sec->chunks, [&](Chunk *c) {
1755 c->writeTo(secBuf + c->getRVA() - sec->getRVA());
1760 void Writer::writeBuildId() {
1761 // There are two important parts to the build ID.
1762 // 1) If building with debug info, the COFF debug directory contains a
1763 // timestamp as well as a Guid and Age of the PDB.
1764 // 2) In all cases, the PE COFF file header also contains a timestamp.
1765 // For reproducibility, instead of a timestamp we want to use a hash of the
1767 if (config->debug) {
1768 assert(buildId && "BuildId is not set!");
1769 // BuildId->BuildId was filled in when the PDB was written.
1772 // At this point the only fields in the COFF file which remain unset are the
1773 // "timestamp" in the COFF file header, and the ones in the coff debug
1774 // directory. Now we can hash the file and write that hash to the various
1775 // timestamp fields in the file.
1776 StringRef outputFileData(
1777 reinterpret_cast<const char *>(buffer->getBufferStart()),
1778 buffer->getBufferSize());
1780 uint32_t timestamp = config->timestamp;
1782 bool generateSyntheticBuildId =
1783 config->mingw && config->debug && config->pdbPath.empty();
1785 if (config->repro || generateSyntheticBuildId)
1786 hash = xxHash64(outputFileData);
1789 timestamp = static_cast<uint32_t>(hash);
1791 if (generateSyntheticBuildId) {
1792 // For MinGW builds without a PDB file, we still generate a build id
1793 // to allow associating a crash dump to the executable.
1794 buildId->buildId->PDB70.CVSignature = OMF::Signature::PDB70;
1795 buildId->buildId->PDB70.Age = 1;
1796 memcpy(buildId->buildId->PDB70.Signature, &hash, 8);
1797 // xxhash only gives us 8 bytes, so put some fixed data in the other half.
1798 memcpy(&buildId->buildId->PDB70.Signature[8], "LLD PDB.", 8);
1802 debugDirectory->setTimeDateStamp(timestamp);
1804 uint8_t *buf = buffer->getBufferStart();
1805 buf += dosStubSize + sizeof(PEMagic);
1806 object::coff_file_header *coffHeader =
1807 reinterpret_cast<coff_file_header *>(buf);
1808 coffHeader->TimeDateStamp = timestamp;
1811 // Sort .pdata section contents according to PE/COFF spec 5.5.
1812 void Writer::sortExceptionTable() {
1815 // We assume .pdata contains function table entries only.
1816 auto bufAddr = [&](Chunk *c) {
1817 OutputSection *os = c->getOutputSection();
1818 return buffer->getBufferStart() + os->getFileOff() + c->getRVA() -
1821 uint8_t *begin = bufAddr(firstPdata);
1822 uint8_t *end = bufAddr(lastPdata) + lastPdata->getSize();
1823 if (config->machine == AMD64) {
1824 struct Entry { ulittle32_t begin, end, unwind; };
1826 MutableArrayRef<Entry>((Entry *)begin, (Entry *)end),
1827 [](const Entry &a, const Entry &b) { return a.begin < b.begin; });
1830 if (config->machine == ARMNT || config->machine == ARM64) {
1831 struct Entry { ulittle32_t begin, unwind; };
1833 MutableArrayRef<Entry>((Entry *)begin, (Entry *)end),
1834 [](const Entry &a, const Entry &b) { return a.begin < b.begin; });
1837 errs() << "warning: don't know how to handle .pdata.\n";
1840 // The CRT section contains, among other things, the array of function
1841 // pointers that initialize every global variable that is not trivially
1842 // constructed. The CRT calls them one after the other prior to invoking
1845 // As per C++ spec, 3.6.2/2.3,
1846 // "Variables with ordered initialization defined within a single
1847 // translation unit shall be initialized in the order of their definitions
1848 // in the translation unit"
1850 // It is therefore critical to sort the chunks containing the function
1851 // pointers in the order that they are listed in the object file (top to
1852 // bottom), otherwise global objects might not be initialized in the
1854 void Writer::sortCRTSectionChunks(std::vector<Chunk *> &chunks) {
1855 auto sectionChunkOrder = [](const Chunk *a, const Chunk *b) {
1856 auto sa = dyn_cast<SectionChunk>(a);
1857 auto sb = dyn_cast<SectionChunk>(b);
1858 assert(sa && sb && "Non-section chunks in CRT section!");
1860 StringRef sAObj = sa->file->mb.getBufferIdentifier();
1861 StringRef sBObj = sb->file->mb.getBufferIdentifier();
1863 return sAObj == sBObj && sa->getSectionNumber() < sb->getSectionNumber();
1865 llvm::stable_sort(chunks, sectionChunkOrder);
1867 if (config->verbose) {
1868 for (auto &c : chunks) {
1869 auto sc = dyn_cast<SectionChunk>(c);
1870 log(" " + sc->file->mb.getBufferIdentifier().str() +
1871 ", SectionID: " + Twine(sc->getSectionNumber()));
1876 OutputSection *Writer::findSection(StringRef name) {
1877 for (OutputSection *sec : outputSections)
1878 if (sec->name == name)
1883 uint32_t Writer::getSizeOfInitializedData() {
1885 for (OutputSection *s : outputSections)
1886 if (s->header.Characteristics & IMAGE_SCN_CNT_INITIALIZED_DATA)
1887 res += s->getRawSize();
1891 // Add base relocations to .reloc section.
1892 void Writer::addBaserels() {
1893 if (!config->relocatable)
1895 relocSec->chunks.clear();
1896 std::vector<Baserel> v;
1897 for (OutputSection *sec : outputSections) {
1898 if (sec->header.Characteristics & IMAGE_SCN_MEM_DISCARDABLE)
1900 // Collect all locations for base relocations.
1901 for (Chunk *c : sec->chunks)
1903 // Add the addresses to .reloc section.
1905 addBaserelBlocks(v);
1910 // Add addresses to .reloc section. Note that addresses are grouped by page.
1911 void Writer::addBaserelBlocks(std::vector<Baserel> &v) {
1912 const uint32_t mask = ~uint32_t(pageSize - 1);
1913 uint32_t page = v[0].rva & mask;
1914 size_t i = 0, j = 1;
1915 for (size_t e = v.size(); j < e; ++j) {
1916 uint32_t p = v[j].rva & mask;
1919 relocSec->addChunk(make<BaserelChunk>(page, &v[i], &v[0] + j));
1925 relocSec->addChunk(make<BaserelChunk>(page, &v[i], &v[0] + j));
1928 PartialSection *Writer::createPartialSection(StringRef name,
1929 uint32_t outChars) {
1930 PartialSection *&pSec = partialSections[{name, outChars}];
1933 pSec = make<PartialSection>(name, outChars);
1937 PartialSection *Writer::findPartialSection(StringRef name, uint32_t outChars) {
1938 auto it = partialSections.find({name, outChars});
1939 if (it != partialSections.end())