1//===- Writer.cpp ---------------------------------------------------------===//
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#include "Writer.h"
10#include "ConcatOutputSection.h"
11#include "Config.h"
12#include "InputFiles.h"
13#include "InputSection.h"
14#include "MapFile.h"
15#include "OutputSection.h"
16#include "OutputSegment.h"
17#include "SectionPriorities.h"
18#include "SymbolTable.h"
19#include "Symbols.h"
20#include "SyntheticSections.h"
21#include "Target.h"
22#include "UnwindInfoSection.h"
23
24#include "lld/Common/Arrays.h"
25#include "lld/Common/CommonLinkerContext.h"
26#include "llvm/BinaryFormat/MachO.h"
27#include "llvm/Config/llvm-config.h"
28#include "llvm/Support/LEB128.h"
29#include "llvm/Support/Parallel.h"
30#include "llvm/Support/Path.h"
31#include "llvm/Support/ThreadPool.h"
32#include "llvm/Support/TimeProfiler.h"
33#include "llvm/Support/xxhash.h"
34
35#include <algorithm>
36
37using namespace llvm;
38using namespace llvm::MachO;
39using namespace llvm::sys;
40using namespace lld;
41using namespace lld::macho;
42
43namespace {
44class LCUuid;
45
46class Writer {
47public:
48 Writer() : buffer(errorHandler().outputBuffer) {}
49
50 void treatSpecialUndefineds();
51 void scanRelocations();
52 void scanSymbols();
53 template <class LP> void createOutputSections();
54 template <class LP> void createLoadCommands();
55 void finalizeAddresses();
56 void finalizeLinkEditSegment();
57 void assignAddresses(OutputSegment *);
58
59 void openFile();
60 void writeSections();
61 void applyOptimizationHints();
62 void buildFixupChains();
63 void writeUuid();
64 void writeCodeSignature();
65 void writeOutputFile();
66
67 template <class LP> void run();
68
69 ThreadPool threadPool;
70 std::unique_ptr<FileOutputBuffer> &buffer;
71 uint64_t addr = 0;
72 uint64_t fileOff = 0;
73 MachHeaderSection *header = nullptr;
74 StringTableSection *stringTableSection = nullptr;
75 SymtabSection *symtabSection = nullptr;
76 IndirectSymtabSection *indirectSymtabSection = nullptr;
77 CodeSignatureSection *codeSignatureSection = nullptr;
78 DataInCodeSection *dataInCodeSection = nullptr;
79 FunctionStartsSection *functionStartsSection = nullptr;
80
81 LCUuid *uuidCommand = nullptr;
82 OutputSegment *linkEditSegment = nullptr;
83};
84
85// LC_DYLD_INFO_ONLY stores the offsets of symbol import/export information.
86class LCDyldInfo final : public LoadCommand {
87public:
88 LCDyldInfo(RebaseSection *rebaseSection, BindingSection *bindingSection,
89 WeakBindingSection *weakBindingSection,
90 LazyBindingSection *lazyBindingSection,
91 ExportSection *exportSection)
92 : rebaseSection(rebaseSection), bindingSection(bindingSection),
93 weakBindingSection(weakBindingSection),
94 lazyBindingSection(lazyBindingSection), exportSection(exportSection) {}
95
96 uint32_t getSize() const override { return sizeof(dyld_info_command); }
97
98 void writeTo(uint8_t *buf) const override {
99 auto *c = reinterpret_cast<dyld_info_command *>(buf);
100 c->cmd = LC_DYLD_INFO_ONLY;
101 c->cmdsize = getSize();
102 if (rebaseSection->isNeeded()) {
103 c->rebase_off = rebaseSection->fileOff;
104 c->rebase_size = rebaseSection->getFileSize();
105 }
106 if (bindingSection->isNeeded()) {
107 c->bind_off = bindingSection->fileOff;
108 c->bind_size = bindingSection->getFileSize();
109 }
110 if (weakBindingSection->isNeeded()) {
111 c->weak_bind_off = weakBindingSection->fileOff;
112 c->weak_bind_size = weakBindingSection->getFileSize();
113 }
114 if (lazyBindingSection->isNeeded()) {
115 c->lazy_bind_off = lazyBindingSection->fileOff;
116 c->lazy_bind_size = lazyBindingSection->getFileSize();
117 }
118 if (exportSection->isNeeded()) {
119 c->export_off = exportSection->fileOff;
120 c->export_size = exportSection->getFileSize();
121 }
122 }
123
124 RebaseSection *rebaseSection;
125 BindingSection *bindingSection;
126 WeakBindingSection *weakBindingSection;
127 LazyBindingSection *lazyBindingSection;
128 ExportSection *exportSection;
129};
130
131class LCSubFramework final : public LoadCommand {
132public:
133 LCSubFramework(StringRef umbrella) : umbrella(umbrella) {}
134
135 uint32_t getSize() const override {
136 return alignToPowerOf2(Value: sizeof(sub_framework_command) + umbrella.size() + 1,
137 Align: target->wordSize);
138 }
139
140 void writeTo(uint8_t *buf) const override {
141 auto *c = reinterpret_cast<sub_framework_command *>(buf);
142 buf += sizeof(sub_framework_command);
143
144 c->cmd = LC_SUB_FRAMEWORK;
145 c->cmdsize = getSize();
146 c->umbrella = sizeof(sub_framework_command);
147
148 memcpy(dest: buf, src: umbrella.data(), n: umbrella.size());
149 buf[umbrella.size()] = '\0';
150 }
151
152private:
153 const StringRef umbrella;
154};
155
156class LCFunctionStarts final : public LoadCommand {
157public:
158 explicit LCFunctionStarts(FunctionStartsSection *functionStartsSection)
159 : functionStartsSection(functionStartsSection) {}
160
161 uint32_t getSize() const override { return sizeof(linkedit_data_command); }
162
163 void writeTo(uint8_t *buf) const override {
164 auto *c = reinterpret_cast<linkedit_data_command *>(buf);
165 c->cmd = LC_FUNCTION_STARTS;
166 c->cmdsize = getSize();
167 c->dataoff = functionStartsSection->fileOff;
168 c->datasize = functionStartsSection->getFileSize();
169 }
170
171private:
172 FunctionStartsSection *functionStartsSection;
173};
174
175class LCDataInCode final : public LoadCommand {
176public:
177 explicit LCDataInCode(DataInCodeSection *dataInCodeSection)
178 : dataInCodeSection(dataInCodeSection) {}
179
180 uint32_t getSize() const override { return sizeof(linkedit_data_command); }
181
182 void writeTo(uint8_t *buf) const override {
183 auto *c = reinterpret_cast<linkedit_data_command *>(buf);
184 c->cmd = LC_DATA_IN_CODE;
185 c->cmdsize = getSize();
186 c->dataoff = dataInCodeSection->fileOff;
187 c->datasize = dataInCodeSection->getFileSize();
188 }
189
190private:
191 DataInCodeSection *dataInCodeSection;
192};
193
194class LCDysymtab final : public LoadCommand {
195public:
196 LCDysymtab(SymtabSection *symtabSection,
197 IndirectSymtabSection *indirectSymtabSection)
198 : symtabSection(symtabSection),
199 indirectSymtabSection(indirectSymtabSection) {}
200
201 uint32_t getSize() const override { return sizeof(dysymtab_command); }
202
203 void writeTo(uint8_t *buf) const override {
204 auto *c = reinterpret_cast<dysymtab_command *>(buf);
205 c->cmd = LC_DYSYMTAB;
206 c->cmdsize = getSize();
207
208 c->ilocalsym = 0;
209 c->iextdefsym = c->nlocalsym = symtabSection->getNumLocalSymbols();
210 c->nextdefsym = symtabSection->getNumExternalSymbols();
211 c->iundefsym = c->iextdefsym + c->nextdefsym;
212 c->nundefsym = symtabSection->getNumUndefinedSymbols();
213
214 c->indirectsymoff = indirectSymtabSection->fileOff;
215 c->nindirectsyms = indirectSymtabSection->getNumSymbols();
216 }
217
218 SymtabSection *symtabSection;
219 IndirectSymtabSection *indirectSymtabSection;
220};
221
222template <class LP> class LCSegment final : public LoadCommand {
223public:
224 LCSegment(StringRef name, OutputSegment *seg) : name(name), seg(seg) {}
225
226 uint32_t getSize() const override {
227 return sizeof(typename LP::segment_command) +
228 seg->numNonHiddenSections() * sizeof(typename LP::section);
229 }
230
231 void writeTo(uint8_t *buf) const override {
232 using SegmentCommand = typename LP::segment_command;
233 using SectionHeader = typename LP::section;
234
235 auto *c = reinterpret_cast<SegmentCommand *>(buf);
236 buf += sizeof(SegmentCommand);
237
238 c->cmd = LP::segmentLCType;
239 c->cmdsize = getSize();
240 memcpy(c->segname, name.data(), name.size());
241 c->fileoff = seg->fileOff;
242 c->maxprot = seg->maxProt;
243 c->initprot = seg->initProt;
244
245 c->vmaddr = seg->addr;
246 c->vmsize = seg->vmSize;
247 c->filesize = seg->fileSize;
248 c->nsects = seg->numNonHiddenSections();
249 c->flags = seg->flags;
250
251 for (const OutputSection *osec : seg->getSections()) {
252 if (osec->isHidden())
253 continue;
254
255 auto *sectHdr = reinterpret_cast<SectionHeader *>(buf);
256 buf += sizeof(SectionHeader);
257
258 memcpy(sectHdr->sectname, osec->name.data(), osec->name.size());
259 memcpy(sectHdr->segname, name.data(), name.size());
260
261 sectHdr->addr = osec->addr;
262 sectHdr->offset = osec->fileOff;
263 sectHdr->align = Log2_32(Value: osec->align);
264 sectHdr->flags = osec->flags;
265 sectHdr->size = osec->getSize();
266 sectHdr->reserved1 = osec->reserved1;
267 sectHdr->reserved2 = osec->reserved2;
268 }
269 }
270
271private:
272 StringRef name;
273 OutputSegment *seg;
274};
275
276class LCMain final : public LoadCommand {
277 uint32_t getSize() const override {
278 return sizeof(structs::entry_point_command);
279 }
280
281 void writeTo(uint8_t *buf) const override {
282 auto *c = reinterpret_cast<structs::entry_point_command *>(buf);
283 c->cmd = LC_MAIN;
284 c->cmdsize = getSize();
285
286 if (config->entry->isInStubs())
287 c->entryoff =
288 in.stubs->fileOff + config->entry->stubsIndex * target->stubSize;
289 else
290 c->entryoff = config->entry->getVA() - in.header->addr;
291
292 c->stacksize = 0;
293 }
294};
295
296class LCSymtab final : public LoadCommand {
297public:
298 LCSymtab(SymtabSection *symtabSection, StringTableSection *stringTableSection)
299 : symtabSection(symtabSection), stringTableSection(stringTableSection) {}
300
301 uint32_t getSize() const override { return sizeof(symtab_command); }
302
303 void writeTo(uint8_t *buf) const override {
304 auto *c = reinterpret_cast<symtab_command *>(buf);
305 c->cmd = LC_SYMTAB;
306 c->cmdsize = getSize();
307 c->symoff = symtabSection->fileOff;
308 c->nsyms = symtabSection->getNumSymbols();
309 c->stroff = stringTableSection->fileOff;
310 c->strsize = stringTableSection->getFileSize();
311 }
312
313 SymtabSection *symtabSection = nullptr;
314 StringTableSection *stringTableSection = nullptr;
315};
316
317// There are several dylib load commands that share the same structure:
318// * LC_LOAD_DYLIB
319// * LC_ID_DYLIB
320// * LC_REEXPORT_DYLIB
321class LCDylib final : public LoadCommand {
322public:
323 LCDylib(LoadCommandType type, StringRef path,
324 uint32_t compatibilityVersion = 0, uint32_t currentVersion = 0)
325 : type(type), path(path), compatibilityVersion(compatibilityVersion),
326 currentVersion(currentVersion) {
327 instanceCount++;
328 }
329
330 uint32_t getSize() const override {
331 return alignToPowerOf2(Value: sizeof(dylib_command) + path.size() + 1,
332 Align: target->wordSize);
333 }
334
335 void writeTo(uint8_t *buf) const override {
336 auto *c = reinterpret_cast<dylib_command *>(buf);
337 buf += sizeof(dylib_command);
338
339 c->cmd = type;
340 c->cmdsize = getSize();
341 c->dylib.name = sizeof(dylib_command);
342 c->dylib.timestamp = 0;
343 c->dylib.compatibility_version = compatibilityVersion;
344 c->dylib.current_version = currentVersion;
345
346 memcpy(dest: buf, src: path.data(), n: path.size());
347 buf[path.size()] = '\0';
348 }
349
350 static uint32_t getInstanceCount() { return instanceCount; }
351 static void resetInstanceCount() { instanceCount = 0; }
352
353private:
354 LoadCommandType type;
355 StringRef path;
356 uint32_t compatibilityVersion;
357 uint32_t currentVersion;
358 static uint32_t instanceCount;
359};
360
361uint32_t LCDylib::instanceCount = 0;
362
363class LCLoadDylinker final : public LoadCommand {
364public:
365 uint32_t getSize() const override {
366 return alignToPowerOf2(Value: sizeof(dylinker_command) + path.size() + 1,
367 Align: target->wordSize);
368 }
369
370 void writeTo(uint8_t *buf) const override {
371 auto *c = reinterpret_cast<dylinker_command *>(buf);
372 buf += sizeof(dylinker_command);
373
374 c->cmd = LC_LOAD_DYLINKER;
375 c->cmdsize = getSize();
376 c->name = sizeof(dylinker_command);
377
378 memcpy(dest: buf, src: path.data(), n: path.size());
379 buf[path.size()] = '\0';
380 }
381
382private:
383 // Recent versions of Darwin won't run any binary that has dyld at a
384 // different location.
385 const StringRef path = "/usr/lib/dyld";
386};
387
388class LCRPath final : public LoadCommand {
389public:
390 explicit LCRPath(StringRef path) : path(path) {}
391
392 uint32_t getSize() const override {
393 return alignToPowerOf2(Value: sizeof(rpath_command) + path.size() + 1,
394 Align: target->wordSize);
395 }
396
397 void writeTo(uint8_t *buf) const override {
398 auto *c = reinterpret_cast<rpath_command *>(buf);
399 buf += sizeof(rpath_command);
400
401 c->cmd = LC_RPATH;
402 c->cmdsize = getSize();
403 c->path = sizeof(rpath_command);
404
405 memcpy(dest: buf, src: path.data(), n: path.size());
406 buf[path.size()] = '\0';
407 }
408
409private:
410 StringRef path;
411};
412
413class LCDyldEnv final : public LoadCommand {
414public:
415 explicit LCDyldEnv(StringRef name) : name(name) {}
416
417 uint32_t getSize() const override {
418 return alignToPowerOf2(Value: sizeof(dyld_env_command) + name.size() + 1,
419 Align: target->wordSize);
420 }
421
422 void writeTo(uint8_t *buf) const override {
423 auto *c = reinterpret_cast<dyld_env_command *>(buf);
424 buf += sizeof(dyld_env_command);
425
426 c->cmd = LC_DYLD_ENVIRONMENT;
427 c->cmdsize = getSize();
428 c->name = sizeof(dyld_env_command);
429
430 memcpy(dest: buf, src: name.data(), n: name.size());
431 buf[name.size()] = '\0';
432 }
433
434private:
435 StringRef name;
436};
437
438class LCMinVersion final : public LoadCommand {
439public:
440 explicit LCMinVersion(const PlatformInfo &platformInfo)
441 : platformInfo(platformInfo) {}
442
443 uint32_t getSize() const override { return sizeof(version_min_command); }
444
445 void writeTo(uint8_t *buf) const override {
446 auto *c = reinterpret_cast<version_min_command *>(buf);
447 switch (platformInfo.target.Platform) {
448 case PLATFORM_MACOS:
449 c->cmd = LC_VERSION_MIN_MACOSX;
450 break;
451 case PLATFORM_IOS:
452 case PLATFORM_IOSSIMULATOR:
453 c->cmd = LC_VERSION_MIN_IPHONEOS;
454 break;
455 case PLATFORM_TVOS:
456 case PLATFORM_TVOSSIMULATOR:
457 c->cmd = LC_VERSION_MIN_TVOS;
458 break;
459 case PLATFORM_WATCHOS:
460 case PLATFORM_WATCHOSSIMULATOR:
461 c->cmd = LC_VERSION_MIN_WATCHOS;
462 break;
463 default:
464 llvm_unreachable("invalid platform");
465 break;
466 }
467 c->cmdsize = getSize();
468 c->version = encodeVersion(version: platformInfo.target.MinDeployment);
469 c->sdk = encodeVersion(version: platformInfo.sdk);
470 }
471
472private:
473 const PlatformInfo &platformInfo;
474};
475
476class LCBuildVersion final : public LoadCommand {
477public:
478 explicit LCBuildVersion(const PlatformInfo &platformInfo)
479 : platformInfo(platformInfo) {}
480
481 const int ntools = 1;
482
483 uint32_t getSize() const override {
484 return sizeof(build_version_command) + ntools * sizeof(build_tool_version);
485 }
486
487 void writeTo(uint8_t *buf) const override {
488 auto *c = reinterpret_cast<build_version_command *>(buf);
489 c->cmd = LC_BUILD_VERSION;
490 c->cmdsize = getSize();
491
492 c->platform = static_cast<uint32_t>(platformInfo.target.Platform);
493 c->minos = encodeVersion(version: platformInfo.target.MinDeployment);
494 c->sdk = encodeVersion(version: platformInfo.sdk);
495
496 c->ntools = ntools;
497 auto *t = reinterpret_cast<build_tool_version *>(&c[1]);
498 t->tool = TOOL_LLD;
499 t->version = encodeVersion(version: VersionTuple(
500 LLVM_VERSION_MAJOR, LLVM_VERSION_MINOR, LLVM_VERSION_PATCH));
501 }
502
503private:
504 const PlatformInfo &platformInfo;
505};
506
507// Stores a unique identifier for the output file based on an MD5 hash of its
508// contents. In order to hash the contents, we must first write them, but
509// LC_UUID itself must be part of the written contents in order for all the
510// offsets to be calculated correctly. We resolve this circular paradox by
511// first writing an LC_UUID with an all-zero UUID, then updating the UUID with
512// its real value later.
513class LCUuid final : public LoadCommand {
514public:
515 uint32_t getSize() const override { return sizeof(uuid_command); }
516
517 void writeTo(uint8_t *buf) const override {
518 auto *c = reinterpret_cast<uuid_command *>(buf);
519 c->cmd = LC_UUID;
520 c->cmdsize = getSize();
521 uuidBuf = c->uuid;
522 }
523
524 void writeUuid(uint64_t digest) const {
525 // xxhash only gives us 8 bytes, so put some fixed data in the other half.
526 static_assert(sizeof(uuid_command::uuid) == 16, "unexpected uuid size");
527 memcpy(dest: uuidBuf, src: "LLD\xa1UU1D", n: 8);
528 memcpy(dest: uuidBuf + 8, src: &digest, n: 8);
529
530 // RFC 4122 conformance. We need to fix 4 bits in byte 6 and 2 bits in
531 // byte 8. Byte 6 is already fine due to the fixed data we put in. We don't
532 // want to lose bits of the digest in byte 8, so swap that with a byte of
533 // fixed data that happens to have the right bits set.
534 std::swap(a&: uuidBuf[3], b&: uuidBuf[8]);
535
536 // Claim that this is an MD5-based hash. It isn't, but this signals that
537 // this is not a time-based and not a random hash. MD5 seems like the least
538 // bad lie we can put here.
539 assert((uuidBuf[6] & 0xf0) == 0x30 && "See RFC 4122 Sections 4.2.2, 4.1.3");
540 assert((uuidBuf[8] & 0xc0) == 0x80 && "See RFC 4122 Section 4.2.2");
541 }
542
543 mutable uint8_t *uuidBuf;
544};
545
546template <class LP> class LCEncryptionInfo final : public LoadCommand {
547public:
548 uint32_t getSize() const override {
549 return sizeof(typename LP::encryption_info_command);
550 }
551
552 void writeTo(uint8_t *buf) const override {
553 using EncryptionInfo = typename LP::encryption_info_command;
554 auto *c = reinterpret_cast<EncryptionInfo *>(buf);
555 buf += sizeof(EncryptionInfo);
556 c->cmd = LP::encryptionInfoLCType;
557 c->cmdsize = getSize();
558 c->cryptoff = in.header->getSize();
559 auto it = find_if(outputSegments, [](const OutputSegment *seg) {
560 return seg->name == segment_names::text;
561 });
562 assert(it != outputSegments.end());
563 c->cryptsize = (*it)->fileSize - c->cryptoff;
564 }
565};
566
567class LCCodeSignature final : public LoadCommand {
568public:
569 LCCodeSignature(CodeSignatureSection *section) : section(section) {}
570
571 uint32_t getSize() const override { return sizeof(linkedit_data_command); }
572
573 void writeTo(uint8_t *buf) const override {
574 auto *c = reinterpret_cast<linkedit_data_command *>(buf);
575 c->cmd = LC_CODE_SIGNATURE;
576 c->cmdsize = getSize();
577 c->dataoff = static_cast<uint32_t>(section->fileOff);
578 c->datasize = section->getSize();
579 }
580
581 CodeSignatureSection *section;
582};
583
584class LCExportsTrie final : public LoadCommand {
585public:
586 LCExportsTrie(ExportSection *section) : section(section) {}
587
588 uint32_t getSize() const override { return sizeof(linkedit_data_command); }
589
590 void writeTo(uint8_t *buf) const override {
591 auto *c = reinterpret_cast<linkedit_data_command *>(buf);
592 c->cmd = LC_DYLD_EXPORTS_TRIE;
593 c->cmdsize = getSize();
594 c->dataoff = section->fileOff;
595 c->datasize = section->getSize();
596 }
597
598 ExportSection *section;
599};
600
601class LCChainedFixups final : public LoadCommand {
602public:
603 LCChainedFixups(ChainedFixupsSection *section) : section(section) {}
604
605 uint32_t getSize() const override { return sizeof(linkedit_data_command); }
606
607 void writeTo(uint8_t *buf) const override {
608 auto *c = reinterpret_cast<linkedit_data_command *>(buf);
609 c->cmd = LC_DYLD_CHAINED_FIXUPS;
610 c->cmdsize = getSize();
611 c->dataoff = section->fileOff;
612 c->datasize = section->getSize();
613 }
614
615 ChainedFixupsSection *section;
616};
617
618} // namespace
619
620void Writer::treatSpecialUndefineds() {
621 if (config->entry)
622 if (auto *undefined = dyn_cast<Undefined>(Val: config->entry))
623 treatUndefinedSymbol(*undefined, source: "the entry point");
624
625 // FIXME: This prints symbols that are undefined both in input files and
626 // via -u flag twice.
627 for (const Symbol *sym : config->explicitUndefineds) {
628 if (const auto *undefined = dyn_cast<Undefined>(Val: sym))
629 treatUndefinedSymbol(*undefined, source: "-u");
630 }
631 // Literal exported-symbol names must be defined, but glob
632 // patterns need not match.
633 for (const CachedHashStringRef &cachedName :
634 config->exportedSymbols.literals) {
635 if (const Symbol *sym = symtab->find(name: cachedName))
636 if (const auto *undefined = dyn_cast<Undefined>(Val: sym))
637 treatUndefinedSymbol(*undefined, source: "-exported_symbol(s_list)");
638 }
639}
640
641static void prepareSymbolRelocation(Symbol *sym, const InputSection *isec,
642 const lld::macho::Reloc &r) {
643 assert(sym->isLive());
644 const RelocAttrs &relocAttrs = target->getRelocAttrs(type: r.type);
645
646 if (relocAttrs.hasAttr(b: RelocAttrBits::BRANCH)) {
647 if (needsBinding(sym))
648 in.stubs->addEntry(sym);
649 } else if (relocAttrs.hasAttr(b: RelocAttrBits::GOT)) {
650 if (relocAttrs.hasAttr(b: RelocAttrBits::POINTER) || needsBinding(sym))
651 in.got->addEntry(sym);
652 } else if (relocAttrs.hasAttr(b: RelocAttrBits::TLV)) {
653 if (needsBinding(sym))
654 in.tlvPointers->addEntry(sym);
655 } else if (relocAttrs.hasAttr(b: RelocAttrBits::UNSIGNED)) {
656 // References from thread-local variable sections are treated as offsets
657 // relative to the start of the referent section, and therefore have no
658 // need of rebase opcodes.
659 if (!(isThreadLocalVariables(flags: isec->getFlags()) && isa<Defined>(Val: sym)))
660 addNonLazyBindingEntries(sym, isec, offset: r.offset, addend: r.addend);
661 }
662}
663
664void Writer::scanRelocations() {
665 TimeTraceScope timeScope("Scan relocations");
666
667 // This can't use a for-each loop: It calls treatUndefinedSymbol(), which can
668 // add to inputSections, which invalidates inputSections's iterators.
669 for (size_t i = 0; i < inputSections.size(); ++i) {
670 ConcatInputSection *isec = inputSections[i];
671
672 if (isec->shouldOmitFromOutput())
673 continue;
674
675 for (auto it = isec->relocs.begin(); it != isec->relocs.end(); ++it) {
676 lld::macho::Reloc &r = *it;
677
678 // Canonicalize the referent so that later accesses in Writer won't
679 // have to worry about it.
680 if (auto *referentIsec = r.referent.dyn_cast<InputSection *>())
681 r.referent = referentIsec->canonical();
682
683 if (target->hasAttr(type: r.type, bit: RelocAttrBits::SUBTRAHEND)) {
684 // Skip over the following UNSIGNED relocation -- it's just there as the
685 // minuend, and doesn't have the usual UNSIGNED semantics. We don't want
686 // to emit rebase opcodes for it.
687 ++it;
688 // Canonicalize the referent so that later accesses in Writer won't
689 // have to worry about it.
690 if (auto *referentIsec = it->referent.dyn_cast<InputSection *>())
691 it->referent = referentIsec->canonical();
692 continue;
693 }
694 if (auto *sym = r.referent.dyn_cast<Symbol *>()) {
695 if (auto *undefined = dyn_cast<Undefined>(Val: sym))
696 treatUndefinedSymbol(*undefined, isec, offset: r.offset);
697 // treatUndefinedSymbol() can replace sym with a DylibSymbol; re-check.
698 if (!isa<Undefined>(Val: sym) && validateSymbolRelocation(sym, isec, r))
699 prepareSymbolRelocation(sym, isec, r);
700 } else {
701 if (!r.pcrel) {
702 if (config->emitChainedFixups)
703 in.chainedFixups->addRebase(isec, offset: r.offset);
704 else
705 in.rebase->addEntry(isec, offset: r.offset);
706 }
707 }
708 }
709 }
710
711 in.unwindInfo->prepare();
712}
713
714static void addNonWeakDefinition(const Defined *defined) {
715 if (config->emitChainedFixups)
716 in.chainedFixups->setHasNonWeakDefinition();
717 else
718 in.weakBinding->addNonWeakDefinition(defined);
719}
720
721void Writer::scanSymbols() {
722 TimeTraceScope timeScope("Scan symbols");
723 in.objcStubs->initialize();
724 for (Symbol *sym : symtab->getSymbols()) {
725 if (auto *defined = dyn_cast<Defined>(Val: sym)) {
726 if (!defined->isLive())
727 continue;
728 defined->canonicalize();
729 if (defined->overridesWeakDef)
730 addNonWeakDefinition(defined);
731 if (!defined->isAbsolute() && isCodeSection(defined->isec))
732 in.unwindInfo->addSymbol(defined);
733 } else if (const auto *dysym = dyn_cast<DylibSymbol>(Val: sym)) {
734 // This branch intentionally doesn't check isLive().
735 if (dysym->isDynamicLookup())
736 continue;
737 dysym->getFile()->refState =
738 std::max(a: dysym->getFile()->refState, b: dysym->getRefState());
739 } else if (isa<Undefined>(Val: sym)) {
740 if (ObjCStubsSection::isObjCStubSymbol(sym)) {
741 // When -dead_strip is enabled, we don't want to emit any dead stubs.
742 // Although this stub symbol is yet undefined, addSym() was called
743 // during MarkLive.
744 if (config->deadStrip) {
745 if (!sym->isLive())
746 continue;
747 }
748 in.objcStubs->addEntry(sym);
749 }
750 }
751 }
752
753 for (const InputFile *file : inputFiles) {
754 if (auto *objFile = dyn_cast<ObjFile>(Val: file))
755 for (Symbol *sym : objFile->symbols) {
756 if (auto *defined = dyn_cast_or_null<Defined>(Val: sym)) {
757 if (!defined->isLive())
758 continue;
759 defined->canonicalize();
760 if (!defined->isExternal() && !defined->isAbsolute() &&
761 isCodeSection(defined->isec))
762 in.unwindInfo->addSymbol(defined);
763 }
764 }
765 }
766}
767
768// TODO: ld64 enforces the old load commands in a few other cases.
769static bool useLCBuildVersion(const PlatformInfo &platformInfo) {
770 static const std::array<std::pair<PlatformType, VersionTuple>, 7> minVersion =
771 {._M_elems: {{PLATFORM_MACOS, VersionTuple(10, 14)},
772 {PLATFORM_IOS, VersionTuple(12, 0)},
773 {PLATFORM_IOSSIMULATOR, VersionTuple(13, 0)},
774 {PLATFORM_TVOS, VersionTuple(12, 0)},
775 {PLATFORM_TVOSSIMULATOR, VersionTuple(13, 0)},
776 {PLATFORM_WATCHOS, VersionTuple(5, 0)},
777 {PLATFORM_WATCHOSSIMULATOR, VersionTuple(6, 0)}}};
778 auto it = llvm::find_if(Range: minVersion, P: [&](const auto &p) {
779 return p.first == platformInfo.target.Platform;
780 });
781 return it == minVersion.end()
782 ? true
783 : platformInfo.target.MinDeployment >= it->second;
784}
785
786template <class LP> void Writer::createLoadCommands() {
787 uint8_t segIndex = 0;
788 for (OutputSegment *seg : outputSegments) {
789 in.header->addLoadCommand(make<LCSegment<LP>>(seg->name, seg));
790 seg->index = segIndex++;
791 }
792
793 if (config->emitChainedFixups) {
794 in.header->addLoadCommand(make<LCChainedFixups>(args&: in.chainedFixups));
795 in.header->addLoadCommand(make<LCExportsTrie>(args&: in.exports));
796 } else {
797 in.header->addLoadCommand(make<LCDyldInfo>(
798 args&: in.rebase, args&: in.binding, args&: in.weakBinding, args&: in.lazyBinding, args&: in.exports));
799 }
800 in.header->addLoadCommand(make<LCSymtab>(args&: symtabSection, args&: stringTableSection));
801 in.header->addLoadCommand(
802 make<LCDysymtab>(args&: symtabSection, args&: indirectSymtabSection));
803 if (!config->umbrella.empty())
804 in.header->addLoadCommand(make<LCSubFramework>(args&: config->umbrella));
805 if (config->emitEncryptionInfo)
806 in.header->addLoadCommand(make<LCEncryptionInfo<LP>>());
807 for (StringRef path : config->runtimePaths)
808 in.header->addLoadCommand(make<LCRPath>(args&: path));
809
810 switch (config->outputType) {
811 case MH_EXECUTE:
812 in.header->addLoadCommand(make<LCLoadDylinker>());
813 break;
814 case MH_DYLIB:
815 in.header->addLoadCommand(make<LCDylib>(args: LC_ID_DYLIB, args&: config->installName,
816 args&: config->dylibCompatibilityVersion,
817 args&: config->dylibCurrentVersion));
818 break;
819 case MH_BUNDLE:
820 break;
821 default:
822 llvm_unreachable("unhandled output file type");
823 }
824
825 if (config->generateUuid) {
826 uuidCommand = make<LCUuid>();
827 in.header->addLoadCommand(uuidCommand);
828 }
829
830 if (useLCBuildVersion(platformInfo: config->platformInfo))
831 in.header->addLoadCommand(make<LCBuildVersion>(args&: config->platformInfo));
832 else
833 in.header->addLoadCommand(make<LCMinVersion>(args&: config->platformInfo));
834
835 if (config->secondaryPlatformInfo) {
836 in.header->addLoadCommand(
837 make<LCBuildVersion>(args&: *config->secondaryPlatformInfo));
838 }
839
840 // This is down here to match ld64's load command order.
841 if (config->outputType == MH_EXECUTE)
842 in.header->addLoadCommand(make<LCMain>());
843
844 // See ld64's OutputFile::buildDylibOrdinalMapping for the corresponding
845 // library ordinal computation code in ld64.
846 int64_t dylibOrdinal = 1;
847 DenseMap<StringRef, int64_t> ordinalForInstallName;
848
849 std::vector<DylibFile *> dylibFiles;
850 for (InputFile *file : inputFiles) {
851 if (auto *dylibFile = dyn_cast<DylibFile>(Val: file))
852 dylibFiles.push_back(x: dylibFile);
853 }
854 for (size_t i = 0; i < dylibFiles.size(); ++i)
855 dylibFiles.insert(position: dylibFiles.end(), first: dylibFiles[i]->extraDylibs.begin(),
856 last: dylibFiles[i]->extraDylibs.end());
857
858 for (DylibFile *dylibFile : dylibFiles) {
859 if (dylibFile->isBundleLoader) {
860 dylibFile->ordinal = BIND_SPECIAL_DYLIB_MAIN_EXECUTABLE;
861 // Shortcut since bundle-loader does not re-export the symbols.
862
863 dylibFile->reexport = false;
864 continue;
865 }
866
867 // Don't emit load commands for a dylib that is not referenced if:
868 // - it was added implicitly (via a reexport, an LC_LOAD_DYLINKER --
869 // if it's on the linker command line, it's explicit)
870 // - or it's marked MH_DEAD_STRIPPABLE_DYLIB
871 // - or the flag -dead_strip_dylibs is used
872 // FIXME: `isReferenced()` is currently computed before dead code
873 // stripping, so references from dead code keep a dylib alive. This
874 // matches ld64, but it's something we should do better.
875 if (!dylibFile->isReferenced() && !dylibFile->forceNeeded &&
876 (!dylibFile->isExplicitlyLinked() || dylibFile->deadStrippable ||
877 config->deadStripDylibs))
878 continue;
879
880 // Several DylibFiles can have the same installName. Only emit a single
881 // load command for that installName and give all these DylibFiles the
882 // same ordinal.
883 // This can happen in several cases:
884 // - a new framework could change its installName to an older
885 // framework name via an $ld$ symbol depending on platform_version
886 // - symlinks (for example, libpthread.tbd is a symlink to libSystem.tbd;
887 // Foo.framework/Foo.tbd is usually a symlink to
888 // Foo.framework/Versions/Current/Foo.tbd, where
889 // Foo.framework/Versions/Current is usually a symlink to
890 // Foo.framework/Versions/A)
891 // - a framework can be linked both explicitly on the linker
892 // command line and implicitly as a reexport from a different
893 // framework. The re-export will usually point to the tbd file
894 // in Foo.framework/Versions/A/Foo.tbd, while the explicit link will
895 // usually find Foo.framework/Foo.tbd. These are usually symlinks,
896 // but in a --reproduce archive they will be identical but distinct
897 // files.
898 // In the first case, *semantically distinct* DylibFiles will have the
899 // same installName.
900 int64_t &ordinal = ordinalForInstallName[dylibFile->installName];
901 if (ordinal) {
902 dylibFile->ordinal = ordinal;
903 continue;
904 }
905
906 ordinal = dylibFile->ordinal = dylibOrdinal++;
907 LoadCommandType lcType =
908 dylibFile->forceWeakImport || dylibFile->refState == RefState::Weak
909 ? LC_LOAD_WEAK_DYLIB
910 : LC_LOAD_DYLIB;
911 in.header->addLoadCommand(make<LCDylib>(args&: lcType, args&: dylibFile->installName,
912 args&: dylibFile->compatibilityVersion,
913 args&: dylibFile->currentVersion));
914
915 if (dylibFile->reexport)
916 in.header->addLoadCommand(
917 make<LCDylib>(args: LC_REEXPORT_DYLIB, args&: dylibFile->installName));
918 }
919
920 for (const auto &dyldEnv : config->dyldEnvs)
921 in.header->addLoadCommand(make<LCDyldEnv>(args: dyldEnv));
922
923 if (functionStartsSection)
924 in.header->addLoadCommand(make<LCFunctionStarts>(args&: functionStartsSection));
925 if (dataInCodeSection)
926 in.header->addLoadCommand(make<LCDataInCode>(args&: dataInCodeSection));
927 if (codeSignatureSection)
928 in.header->addLoadCommand(make<LCCodeSignature>(args&: codeSignatureSection));
929
930 const uint32_t MACOS_MAXPATHLEN = 1024;
931 config->headerPad = std::max(
932 a: config->headerPad, b: (config->headerPadMaxInstallNames
933 ? LCDylib::getInstanceCount() * MACOS_MAXPATHLEN
934 : 0));
935}
936
937// Sorting only can happen once all outputs have been collected. Here we sort
938// segments, output sections within each segment, and input sections within each
939// output segment.
940static void sortSegmentsAndSections() {
941 TimeTraceScope timeScope("Sort segments and sections");
942 sortOutputSegments();
943
944 DenseMap<const InputSection *, size_t> isecPriorities =
945 priorityBuilder.buildInputSectionPriorities();
946
947 uint32_t sectionIndex = 0;
948 for (OutputSegment *seg : outputSegments) {
949 seg->sortOutputSections();
950 // References from thread-local variable sections are treated as offsets
951 // relative to the start of the thread-local data memory area, which
952 // is initialized via copying all the TLV data sections (which are all
953 // contiguous). If later data sections require a greater alignment than
954 // earlier ones, the offsets of data within those sections won't be
955 // guaranteed to aligned unless we normalize alignments. We therefore use
956 // the largest alignment for all TLV data sections.
957 uint32_t tlvAlign = 0;
958 for (const OutputSection *osec : seg->getSections())
959 if (isThreadLocalData(flags: osec->flags) && osec->align > tlvAlign)
960 tlvAlign = osec->align;
961
962 for (OutputSection *osec : seg->getSections()) {
963 // Now that the output sections are sorted, assign the final
964 // output section indices.
965 if (!osec->isHidden())
966 osec->index = ++sectionIndex;
967 if (isThreadLocalData(flags: osec->flags)) {
968 if (!firstTLVDataSection)
969 firstTLVDataSection = osec;
970 osec->align = tlvAlign;
971 }
972
973 if (!isecPriorities.empty()) {
974 if (auto *merged = dyn_cast<ConcatOutputSection>(Val: osec)) {
975 llvm::stable_sort(
976 Range&: merged->inputs, C: [&](InputSection *a, InputSection *b) {
977 return isecPriorities.lookup(Val: a) > isecPriorities.lookup(Val: b);
978 });
979 }
980 }
981 }
982 }
983}
984
985template <class LP> void Writer::createOutputSections() {
986 TimeTraceScope timeScope("Create output sections");
987 // First, create hidden sections
988 stringTableSection = make<StringTableSection>();
989 symtabSection = makeSymtabSection<LP>(*stringTableSection);
990 indirectSymtabSection = make<IndirectSymtabSection>();
991 if (config->adhocCodesign)
992 codeSignatureSection = make<CodeSignatureSection>();
993 if (config->emitDataInCodeInfo)
994 dataInCodeSection = make<DataInCodeSection>();
995 if (config->emitFunctionStarts)
996 functionStartsSection = make<FunctionStartsSection>();
997
998 switch (config->outputType) {
999 case MH_EXECUTE:
1000 make<PageZeroSection>();
1001 break;
1002 case MH_DYLIB:
1003 case MH_BUNDLE:
1004 break;
1005 default:
1006 llvm_unreachable("unhandled output file type");
1007 }
1008
1009 // Then add input sections to output sections.
1010 for (ConcatInputSection *isec : inputSections) {
1011 if (isec->shouldOmitFromOutput())
1012 continue;
1013 ConcatOutputSection *osec = cast<ConcatOutputSection>(Val: isec->parent);
1014 osec->addInput(input: isec);
1015 osec->inputOrder =
1016 std::min(a: osec->inputOrder, b: static_cast<int>(isec->outSecOff));
1017 }
1018
1019 // Once all the inputs are added, we can finalize the output section
1020 // properties and create the corresponding output segments.
1021 for (const auto &it : concatOutputSections) {
1022 StringRef segname = it.first.first;
1023 ConcatOutputSection *osec = it.second;
1024 assert(segname != segment_names::ld);
1025 if (osec->isNeeded()) {
1026 // See comment in ObjFile::splitEhFrames()
1027 if (osec->name == section_names::ehFrame &&
1028 segname == segment_names::text)
1029 osec->align = target->wordSize;
1030
1031 // MC keeps the default 1-byte alignment for __thread_vars, even though it
1032 // contains pointers that are fixed up by dyld, which requires proper
1033 // alignment.
1034 if (isThreadLocalVariables(flags: osec->flags))
1035 osec->align = std::max<uint32_t>(a: osec->align, b: target->wordSize);
1036
1037 getOrCreateOutputSegment(name: segname)->addOutputSection(os: osec);
1038 }
1039 }
1040
1041 for (SyntheticSection *ssec : syntheticSections) {
1042 auto it = concatOutputSections.find(Key: {ssec->segname, ssec->name});
1043 // We add all LinkEdit sections here because we don't know if they are
1044 // needed until their finalizeContents() methods get called later. While
1045 // this means that we add some redundant sections to __LINKEDIT, there is
1046 // is no redundancy in the output, as we do not emit section headers for
1047 // any LinkEdit sections.
1048 if (ssec->isNeeded() || ssec->segname == segment_names::linkEdit) {
1049 if (it == concatOutputSections.end()) {
1050 getOrCreateOutputSegment(name: ssec->segname)->addOutputSection(os: ssec);
1051 } else {
1052 fatal(msg: "section from " +
1053 toString(file: it->second->firstSection()->getFile()) +
1054 " conflicts with synthetic section " + ssec->segname + "," +
1055 ssec->name);
1056 }
1057 }
1058 }
1059
1060 // dyld requires __LINKEDIT segment to always exist (even if empty).
1061 linkEditSegment = getOrCreateOutputSegment(name: segment_names::linkEdit);
1062}
1063
1064void Writer::finalizeAddresses() {
1065 TimeTraceScope timeScope("Finalize addresses");
1066 uint64_t pageSize = target->getPageSize();
1067
1068 // We could parallelize this loop, but local benchmarking indicates it is
1069 // faster to do it all in the main thread.
1070 for (OutputSegment *seg : outputSegments) {
1071 if (seg == linkEditSegment)
1072 continue;
1073 for (OutputSection *osec : seg->getSections()) {
1074 if (!osec->isNeeded())
1075 continue;
1076 // Other kinds of OutputSections have already been finalized.
1077 if (auto *concatOsec = dyn_cast<ConcatOutputSection>(Val: osec))
1078 concatOsec->finalizeContents();
1079 }
1080 }
1081
1082 // Ensure that segments (and the sections they contain) are allocated
1083 // addresses in ascending order, which dyld requires.
1084 //
1085 // Note that at this point, __LINKEDIT sections are empty, but we need to
1086 // determine addresses of other segments/sections before generating its
1087 // contents.
1088 for (OutputSegment *seg : outputSegments) {
1089 if (seg == linkEditSegment)
1090 continue;
1091 seg->addr = addr;
1092 assignAddresses(seg);
1093 // codesign / libstuff checks for segment ordering by verifying that
1094 // `fileOff + fileSize == next segment fileOff`. So we call
1095 // alignToPowerOf2() before (instead of after) computing fileSize to ensure
1096 // that the segments are contiguous. We handle addr / vmSize similarly for
1097 // the same reason.
1098 fileOff = alignToPowerOf2(Value: fileOff, Align: pageSize);
1099 addr = alignToPowerOf2(Value: addr, Align: pageSize);
1100 seg->vmSize = addr - seg->addr;
1101 seg->fileSize = fileOff - seg->fileOff;
1102 seg->assignAddressesToStartEndSymbols();
1103 }
1104}
1105
1106void Writer::finalizeLinkEditSegment() {
1107 TimeTraceScope timeScope("Finalize __LINKEDIT segment");
1108 // Fill __LINKEDIT contents.
1109 std::array<LinkEditSection *, 10> linkEditSections{
1110 in.rebase, in.binding,
1111 in.weakBinding, in.lazyBinding,
1112 in.exports, in.chainedFixups,
1113 symtabSection, indirectSymtabSection,
1114 dataInCodeSection, functionStartsSection,
1115 };
1116 SmallVector<std::shared_future<void>> threadFutures;
1117 threadFutures.reserve(N: linkEditSections.size());
1118 for (LinkEditSection *osec : linkEditSections)
1119 if (osec)
1120 threadFutures.emplace_back(Args: threadPool.async(
1121 F: [](LinkEditSection *osec) { osec->finalizeContents(); }, ArgList&: osec));
1122 for (std::shared_future<void> &future : threadFutures)
1123 future.wait();
1124
1125 // Now that __LINKEDIT is filled out, do a proper calculation of its
1126 // addresses and offsets.
1127 linkEditSegment->addr = addr;
1128 assignAddresses(linkEditSegment);
1129 // No need to page-align fileOff / addr here since this is the last segment.
1130 linkEditSegment->vmSize = addr - linkEditSegment->addr;
1131 linkEditSegment->fileSize = fileOff - linkEditSegment->fileOff;
1132}
1133
1134void Writer::assignAddresses(OutputSegment *seg) {
1135 seg->fileOff = fileOff;
1136
1137 for (OutputSection *osec : seg->getSections()) {
1138 if (!osec->isNeeded())
1139 continue;
1140 addr = alignToPowerOf2(Value: addr, Align: osec->align);
1141 fileOff = alignToPowerOf2(Value: fileOff, Align: osec->align);
1142 osec->addr = addr;
1143 osec->fileOff = isZeroFill(flags: osec->flags) ? 0 : fileOff;
1144 osec->finalize();
1145 osec->assignAddressesToStartEndSymbols();
1146
1147 addr += osec->getSize();
1148 fileOff += osec->getFileSize();
1149 }
1150}
1151
1152void Writer::openFile() {
1153 Expected<std::unique_ptr<FileOutputBuffer>> bufferOrErr =
1154 FileOutputBuffer::create(FilePath: config->outputFile, Size: fileOff,
1155 Flags: FileOutputBuffer::F_executable);
1156
1157 if (!bufferOrErr)
1158 fatal(msg: "failed to open " + config->outputFile + ": " +
1159 llvm::toString(E: bufferOrErr.takeError()));
1160 buffer = std::move(*bufferOrErr);
1161 in.bufferStart = buffer->getBufferStart();
1162}
1163
1164void Writer::writeSections() {
1165 uint8_t *buf = buffer->getBufferStart();
1166 std::vector<const OutputSection *> osecs;
1167 for (const OutputSegment *seg : outputSegments)
1168 append_range(C&: osecs, R: seg->getSections());
1169
1170 parallelForEach(Begin: osecs.begin(), End: osecs.end(), Fn: [&](const OutputSection *osec) {
1171 osec->writeTo(buf: buf + osec->fileOff);
1172 });
1173}
1174
1175void Writer::applyOptimizationHints() {
1176 if (config->arch() != AK_arm64 || config->ignoreOptimizationHints)
1177 return;
1178
1179 uint8_t *buf = buffer->getBufferStart();
1180 TimeTraceScope timeScope("Apply linker optimization hints");
1181 parallelForEach(R&: inputFiles, Fn: [buf](const InputFile *file) {
1182 if (const auto *objFile = dyn_cast<ObjFile>(Val: file))
1183 target->applyOptimizationHints(buf, *objFile);
1184 });
1185}
1186
1187// In order to utilize multiple cores, we first split the buffer into chunks,
1188// compute a hash for each chunk, and then compute a hash value of the hash
1189// values.
1190void Writer::writeUuid() {
1191 TimeTraceScope timeScope("Computing UUID");
1192
1193 ArrayRef<uint8_t> data{buffer->getBufferStart(), buffer->getBufferEnd()};
1194 std::vector<ArrayRef<uint8_t>> chunks = split(arr: data, chunkSize: 1024 * 1024);
1195 // Leave one slot for filename
1196 std::vector<uint64_t> hashes(chunks.size() + 1);
1197 SmallVector<std::shared_future<void>> threadFutures;
1198 threadFutures.reserve(N: chunks.size());
1199 for (size_t i = 0; i < chunks.size(); ++i)
1200 threadFutures.emplace_back(Args: threadPool.async(
1201 F: [&](size_t j) { hashes[j] = xxh3_64bits(data: chunks[j]); }, ArgList&: i));
1202 for (std::shared_future<void> &future : threadFutures)
1203 future.wait();
1204 // Append the output filename so that identical binaries with different names
1205 // don't get the same UUID.
1206 hashes[chunks.size()] = xxh3_64bits(data: sys::path::filename(path: config->finalOutput));
1207 uint64_t digest = xxh3_64bits(data: {reinterpret_cast<uint8_t *>(hashes.data()),
1208 hashes.size() * sizeof(uint64_t)});
1209 uuidCommand->writeUuid(digest);
1210}
1211
1212// This is step 5 of the algorithm described in the class comment of
1213// ChainedFixupsSection.
1214void Writer::buildFixupChains() {
1215 if (!config->emitChainedFixups)
1216 return;
1217
1218 const std::vector<Location> &loc = in.chainedFixups->getLocations();
1219 if (loc.empty())
1220 return;
1221
1222 TimeTraceScope timeScope("Build fixup chains");
1223
1224 const uint64_t pageSize = target->getPageSize();
1225 constexpr uint32_t stride = 4; // for DYLD_CHAINED_PTR_64
1226
1227 for (size_t i = 0, count = loc.size(); i < count;) {
1228 const OutputSegment *oseg = loc[i].isec->parent->parent;
1229 uint8_t *buf = buffer->getBufferStart() + oseg->fileOff;
1230 uint64_t pageIdx = loc[i].offset / pageSize;
1231 ++i;
1232
1233 while (i < count && loc[i].isec->parent->parent == oseg &&
1234 (loc[i].offset / pageSize) == pageIdx) {
1235 uint64_t offset = loc[i].offset - loc[i - 1].offset;
1236
1237 auto fail = [&](Twine message) {
1238 error(msg: loc[i].isec->getSegName() + "," + loc[i].isec->getName() +
1239 ", offset " +
1240 Twine(loc[i].offset - loc[i].isec->parent->getSegmentOffset()) +
1241 ": " + message);
1242 };
1243
1244 if (offset < target->wordSize)
1245 return fail("fixups overlap");
1246 if (offset % stride != 0)
1247 return fail(
1248 "fixups are unaligned (offset " + Twine(offset) +
1249 " is not a multiple of the stride). Re-link with -no_fixup_chains");
1250
1251 // The "next" field is in the same location for bind and rebase entries.
1252 reinterpret_cast<dyld_chained_ptr_64_bind *>(buf + loc[i - 1].offset)
1253 ->next = offset / stride;
1254 ++i;
1255 }
1256 }
1257}
1258
1259void Writer::writeCodeSignature() {
1260 if (codeSignatureSection) {
1261 TimeTraceScope timeScope("Write code signature");
1262 codeSignatureSection->writeHashes(buf: buffer->getBufferStart());
1263 }
1264}
1265
1266void Writer::writeOutputFile() {
1267 TimeTraceScope timeScope("Write output file");
1268 openFile();
1269 reportPendingUndefinedSymbols();
1270 if (errorCount())
1271 return;
1272 writeSections();
1273 applyOptimizationHints();
1274 buildFixupChains();
1275 if (config->generateUuid)
1276 writeUuid();
1277 writeCodeSignature();
1278
1279 if (auto e = buffer->commit())
1280 fatal(msg: "failed to write output '" + buffer->getPath() +
1281 "': " + toString(E: std::move(e)));
1282}
1283
1284template <class LP> void Writer::run() {
1285 treatSpecialUndefineds();
1286 if (config->entry && needsBinding(sym: config->entry))
1287 in.stubs->addEntry(config->entry);
1288
1289 // Canonicalization of all pointers to InputSections should be handled by
1290 // these two scan* methods. I.e. from this point onward, for all live
1291 // InputSections, we should have `isec->canonical() == isec`.
1292 scanSymbols();
1293 if (in.objcStubs->isNeeded())
1294 in.objcStubs->setUp();
1295 scanRelocations();
1296 if (in.initOffsets->isNeeded())
1297 in.initOffsets->setUp();
1298
1299 // Do not proceed if there were undefined or duplicate symbols.
1300 reportPendingUndefinedSymbols();
1301 reportPendingDuplicateSymbols();
1302 if (errorCount())
1303 return;
1304
1305 if (in.stubHelper && in.stubHelper->isNeeded())
1306 in.stubHelper->setUp();
1307
1308 if (in.objCImageInfo->isNeeded())
1309 in.objCImageInfo->finalizeContents();
1310
1311 // At this point, we should know exactly which output sections are needed,
1312 // courtesy of scanSymbols() and scanRelocations().
1313 createOutputSections<LP>();
1314
1315 // After this point, we create no new segments; HOWEVER, we might
1316 // yet create branch-range extension thunks for architectures whose
1317 // hardware call instructions have limited range, e.g., ARM(64).
1318 // The thunks are created as InputSections interspersed among
1319 // the ordinary __TEXT,_text InputSections.
1320 sortSegmentsAndSections();
1321 createLoadCommands<LP>();
1322 finalizeAddresses();
1323 threadPool.async([&] {
1324 if (LLVM_ENABLE_THREADS && config->timeTraceEnabled)
1325 timeTraceProfilerInitialize(TimeTraceGranularity: config->timeTraceGranularity, ProcName: "writeMapFile");
1326 writeMapFile();
1327 if (LLVM_ENABLE_THREADS && config->timeTraceEnabled)
1328 timeTraceProfilerFinishThread();
1329 });
1330 finalizeLinkEditSegment();
1331 writeOutputFile();
1332}
1333
1334template <class LP> void macho::writeResult() { Writer().run<LP>(); }
1335
1336void macho::resetWriter() { LCDylib::resetInstanceCount(); }
1337
1338void macho::createSyntheticSections() {
1339 in.header = make<MachHeaderSection>();
1340 if (config->dedupStrings)
1341 in.cStringSection =
1342 make<DeduplicatedCStringSection>(args: section_names::cString);
1343 else
1344 in.cStringSection = make<CStringSection>(args: section_names::cString);
1345 in.objcMethnameSection =
1346 make<DeduplicatedCStringSection>(args: section_names::objcMethname);
1347 in.wordLiteralSection = make<WordLiteralSection>();
1348 if (config->emitChainedFixups) {
1349 in.chainedFixups = make<ChainedFixupsSection>();
1350 } else {
1351 in.rebase = make<RebaseSection>();
1352 in.binding = make<BindingSection>();
1353 in.weakBinding = make<WeakBindingSection>();
1354 in.lazyBinding = make<LazyBindingSection>();
1355 in.lazyPointers = make<LazyPointerSection>();
1356 in.stubHelper = make<StubHelperSection>();
1357 }
1358 in.exports = make<ExportSection>();
1359 in.got = make<GotSection>();
1360 in.tlvPointers = make<TlvPointerSection>();
1361 in.stubs = make<StubsSection>();
1362 in.objcStubs = make<ObjCStubsSection>();
1363 in.unwindInfo = makeUnwindInfoSection();
1364 in.objCImageInfo = make<ObjCImageInfoSection>();
1365 in.initOffsets = make<InitOffsetsSection>();
1366
1367 // This section contains space for just a single word, and will be used by
1368 // dyld to cache an address to the image loader it uses.
1369 uint8_t *arr = bAlloc().Allocate<uint8_t>(Num: target->wordSize);
1370 memset(s: arr, c: 0, n: target->wordSize);
1371 in.imageLoaderCache = makeSyntheticInputSection(
1372 segName: segment_names::data, sectName: section_names::data, flags: S_REGULAR,
1373 data: ArrayRef<uint8_t>{arr, target->wordSize},
1374 /*align=*/target->wordSize);
1375 // References from dyld are not visible to us, so ensure this section is
1376 // always treated as live.
1377 in.imageLoaderCache->live = true;
1378}
1379
1380OutputSection *macho::firstTLVDataSection = nullptr;
1381
1382template void macho::writeResult<LP64>();
1383template void macho::writeResult<ILP32>();
1384

source code of lld/MachO/Writer.cpp