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/TimeProfiler.h"
32#include "llvm/Support/thread.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 std::unique_ptr<FileOutputBuffer> &buffer;
70 uint64_t addr = 0;
71 uint64_t fileOff = 0;
72 MachHeaderSection *header = nullptr;
73 StringTableSection *stringTableSection = nullptr;
74 SymtabSection *symtabSection = nullptr;
75 IndirectSymtabSection *indirectSymtabSection = nullptr;
76 CodeSignatureSection *codeSignatureSection = nullptr;
77 DataInCodeSection *dataInCodeSection = nullptr;
78 FunctionStartsSection *functionStartsSection = nullptr;
79
80 LCUuid *uuidCommand = nullptr;
81 OutputSegment *linkEditSegment = nullptr;
82};
83
84// LC_DYLD_INFO_ONLY stores the offsets of symbol import/export information.
85class LCDyldInfo final : public LoadCommand {
86public:
87 LCDyldInfo(RebaseSection *rebaseSection, BindingSection *bindingSection,
88 WeakBindingSection *weakBindingSection,
89 LazyBindingSection *lazyBindingSection,
90 ExportSection *exportSection)
91 : rebaseSection(rebaseSection), bindingSection(bindingSection),
92 weakBindingSection(weakBindingSection),
93 lazyBindingSection(lazyBindingSection), exportSection(exportSection) {}
94
95 uint32_t getSize() const override { return sizeof(dyld_info_command); }
96
97 void writeTo(uint8_t *buf) const override {
98 auto *c = reinterpret_cast<dyld_info_command *>(buf);
99 c->cmd = LC_DYLD_INFO_ONLY;
100 c->cmdsize = getSize();
101 if (rebaseSection->isNeeded()) {
102 c->rebase_off = rebaseSection->fileOff;
103 c->rebase_size = rebaseSection->getFileSize();
104 }
105 if (bindingSection->isNeeded()) {
106 c->bind_off = bindingSection->fileOff;
107 c->bind_size = bindingSection->getFileSize();
108 }
109 if (weakBindingSection->isNeeded()) {
110 c->weak_bind_off = weakBindingSection->fileOff;
111 c->weak_bind_size = weakBindingSection->getFileSize();
112 }
113 if (lazyBindingSection->isNeeded()) {
114 c->lazy_bind_off = lazyBindingSection->fileOff;
115 c->lazy_bind_size = lazyBindingSection->getFileSize();
116 }
117 if (exportSection->isNeeded()) {
118 c->export_off = exportSection->fileOff;
119 c->export_size = exportSection->getFileSize();
120 }
121 }
122
123 RebaseSection *rebaseSection;
124 BindingSection *bindingSection;
125 WeakBindingSection *weakBindingSection;
126 LazyBindingSection *lazyBindingSection;
127 ExportSection *exportSection;
128};
129
130class LCSubFramework final : public LoadCommand {
131public:
132 LCSubFramework(StringRef umbrella) : umbrella(umbrella) {}
133
134 uint32_t getSize() const override {
135 return alignToPowerOf2(Value: sizeof(sub_framework_command) + umbrella.size() + 1,
136 Align: target->wordSize);
137 }
138
139 void writeTo(uint8_t *buf) const override {
140 auto *c = reinterpret_cast<sub_framework_command *>(buf);
141 buf += sizeof(sub_framework_command);
142
143 c->cmd = LC_SUB_FRAMEWORK;
144 c->cmdsize = getSize();
145 c->umbrella = sizeof(sub_framework_command);
146
147 memcpy(dest: buf, src: umbrella.data(), n: umbrella.size());
148 buf[umbrella.size()] = '\0';
149 }
150
151private:
152 const StringRef umbrella;
153};
154
155class LCFunctionStarts final : public LoadCommand {
156public:
157 explicit LCFunctionStarts(FunctionStartsSection *functionStartsSection)
158 : functionStartsSection(functionStartsSection) {}
159
160 uint32_t getSize() const override { return sizeof(linkedit_data_command); }
161
162 void writeTo(uint8_t *buf) const override {
163 auto *c = reinterpret_cast<linkedit_data_command *>(buf);
164 c->cmd = LC_FUNCTION_STARTS;
165 c->cmdsize = getSize();
166 c->dataoff = functionStartsSection->fileOff;
167 c->datasize = functionStartsSection->getFileSize();
168 }
169
170private:
171 FunctionStartsSection *functionStartsSection;
172};
173
174class LCDataInCode final : public LoadCommand {
175public:
176 explicit LCDataInCode(DataInCodeSection *dataInCodeSection)
177 : dataInCodeSection(dataInCodeSection) {}
178
179 uint32_t getSize() const override { return sizeof(linkedit_data_command); }
180
181 void writeTo(uint8_t *buf) const override {
182 auto *c = reinterpret_cast<linkedit_data_command *>(buf);
183 c->cmd = LC_DATA_IN_CODE;
184 c->cmdsize = getSize();
185 c->dataoff = dataInCodeSection->fileOff;
186 c->datasize = dataInCodeSection->getFileSize();
187 }
188
189private:
190 DataInCodeSection *dataInCodeSection;
191};
192
193class LCDysymtab final : public LoadCommand {
194public:
195 LCDysymtab(SymtabSection *symtabSection,
196 IndirectSymtabSection *indirectSymtabSection)
197 : symtabSection(symtabSection),
198 indirectSymtabSection(indirectSymtabSection) {}
199
200 uint32_t getSize() const override { return sizeof(dysymtab_command); }
201
202 void writeTo(uint8_t *buf) const override {
203 auto *c = reinterpret_cast<dysymtab_command *>(buf);
204 c->cmd = LC_DYSYMTAB;
205 c->cmdsize = getSize();
206
207 c->ilocalsym = 0;
208 c->iextdefsym = c->nlocalsym = symtabSection->getNumLocalSymbols();
209 c->nextdefsym = symtabSection->getNumExternalSymbols();
210 c->iundefsym = c->iextdefsym + c->nextdefsym;
211 c->nundefsym = symtabSection->getNumUndefinedSymbols();
212
213 c->indirectsymoff = indirectSymtabSection->fileOff;
214 c->nindirectsyms = indirectSymtabSection->getNumSymbols();
215 }
216
217 SymtabSection *symtabSection;
218 IndirectSymtabSection *indirectSymtabSection;
219};
220
221template <class LP> class LCSegment final : public LoadCommand {
222public:
223 LCSegment(StringRef name, OutputSegment *seg) : name(name), seg(seg) {}
224
225 uint32_t getSize() const override {
226 return sizeof(typename LP::segment_command) +
227 seg->numNonHiddenSections() * sizeof(typename LP::section);
228 }
229
230 void writeTo(uint8_t *buf) const override {
231 using SegmentCommand = typename LP::segment_command;
232 using SectionHeader = typename LP::section;
233
234 auto *c = reinterpret_cast<SegmentCommand *>(buf);
235 buf += sizeof(SegmentCommand);
236
237 c->cmd = LP::segmentLCType;
238 c->cmdsize = getSize();
239 memcpy(c->segname, name.data(), name.size());
240 c->fileoff = seg->fileOff;
241 c->maxprot = seg->maxProt;
242 c->initprot = seg->initProt;
243
244 c->vmaddr = seg->addr;
245 c->vmsize = seg->vmSize;
246 c->filesize = seg->fileSize;
247 c->nsects = seg->numNonHiddenSections();
248 c->flags = seg->flags;
249
250 for (const OutputSection *osec : seg->getSections()) {
251 if (osec->isHidden())
252 continue;
253
254 auto *sectHdr = reinterpret_cast<SectionHeader *>(buf);
255 buf += sizeof(SectionHeader);
256
257 memcpy(sectHdr->sectname, osec->name.data(), osec->name.size());
258 memcpy(sectHdr->segname, name.data(), name.size());
259
260 sectHdr->addr = osec->addr;
261 sectHdr->offset = osec->fileOff;
262 sectHdr->align = Log2_32(Value: osec->align);
263 sectHdr->flags = osec->flags;
264 sectHdr->size = osec->getSize();
265 sectHdr->reserved1 = osec->reserved1;
266 sectHdr->reserved2 = osec->reserved2;
267 }
268 }
269
270private:
271 StringRef name;
272 OutputSegment *seg;
273};
274
275class LCMain final : public LoadCommand {
276 uint32_t getSize() const override {
277 return sizeof(structs::entry_point_command);
278 }
279
280 void writeTo(uint8_t *buf) const override {
281 auto *c = reinterpret_cast<structs::entry_point_command *>(buf);
282 c->cmd = LC_MAIN;
283 c->cmdsize = getSize();
284
285 if (config->entry->isInStubs())
286 c->entryoff =
287 in.stubs->fileOff + config->entry->stubsIndex * target->stubSize;
288 else
289 c->entryoff = config->entry->getVA() - in.header->addr;
290
291 c->stacksize = 0;
292 }
293};
294
295class LCSymtab final : public LoadCommand {
296public:
297 LCSymtab(SymtabSection *symtabSection, StringTableSection *stringTableSection)
298 : symtabSection(symtabSection), stringTableSection(stringTableSection) {}
299
300 uint32_t getSize() const override { return sizeof(symtab_command); }
301
302 void writeTo(uint8_t *buf) const override {
303 auto *c = reinterpret_cast<symtab_command *>(buf);
304 c->cmd = LC_SYMTAB;
305 c->cmdsize = getSize();
306 c->symoff = symtabSection->fileOff;
307 c->nsyms = symtabSection->getNumSymbols();
308 c->stroff = stringTableSection->fileOff;
309 c->strsize = stringTableSection->getFileSize();
310 }
311
312 SymtabSection *symtabSection = nullptr;
313 StringTableSection *stringTableSection = nullptr;
314};
315
316// There are several dylib load commands that share the same structure:
317// * LC_LOAD_DYLIB
318// * LC_ID_DYLIB
319// * LC_REEXPORT_DYLIB
320class LCDylib final : public LoadCommand {
321public:
322 LCDylib(LoadCommandType type, StringRef path,
323 uint32_t compatibilityVersion = 0, uint32_t currentVersion = 0)
324 : type(type), path(path), compatibilityVersion(compatibilityVersion),
325 currentVersion(currentVersion) {
326 instanceCount++;
327 }
328
329 uint32_t getSize() const override {
330 return alignToPowerOf2(Value: sizeof(dylib_command) + path.size() + 1,
331 Align: target->wordSize);
332 }
333
334 void writeTo(uint8_t *buf) const override {
335 auto *c = reinterpret_cast<dylib_command *>(buf);
336 buf += sizeof(dylib_command);
337
338 c->cmd = type;
339 c->cmdsize = getSize();
340 c->dylib.name = sizeof(dylib_command);
341 c->dylib.timestamp = 0;
342 c->dylib.compatibility_version = compatibilityVersion;
343 c->dylib.current_version = currentVersion;
344
345 memcpy(dest: buf, src: path.data(), n: path.size());
346 buf[path.size()] = '\0';
347 }
348
349 static uint32_t getInstanceCount() { return instanceCount; }
350 static void resetInstanceCount() { instanceCount = 0; }
351
352private:
353 LoadCommandType type;
354 StringRef path;
355 uint32_t compatibilityVersion;
356 uint32_t currentVersion;
357 static uint32_t instanceCount;
358};
359
360uint32_t LCDylib::instanceCount = 0;
361
362class LCLoadDylinker final : public LoadCommand {
363public:
364 uint32_t getSize() const override {
365 return alignToPowerOf2(Value: sizeof(dylinker_command) + path.size() + 1,
366 Align: target->wordSize);
367 }
368
369 void writeTo(uint8_t *buf) const override {
370 auto *c = reinterpret_cast<dylinker_command *>(buf);
371 buf += sizeof(dylinker_command);
372
373 c->cmd = LC_LOAD_DYLINKER;
374 c->cmdsize = getSize();
375 c->name = sizeof(dylinker_command);
376
377 memcpy(dest: buf, src: path.data(), n: path.size());
378 buf[path.size()] = '\0';
379 }
380
381private:
382 // Recent versions of Darwin won't run any binary that has dyld at a
383 // different location.
384 const StringRef path = "/usr/lib/dyld";
385};
386
387class LCRPath final : public LoadCommand {
388public:
389 explicit LCRPath(StringRef path) : path(path) {}
390
391 uint32_t getSize() const override {
392 return alignToPowerOf2(Value: sizeof(rpath_command) + path.size() + 1,
393 Align: target->wordSize);
394 }
395
396 void writeTo(uint8_t *buf) const override {
397 auto *c = reinterpret_cast<rpath_command *>(buf);
398 buf += sizeof(rpath_command);
399
400 c->cmd = LC_RPATH;
401 c->cmdsize = getSize();
402 c->path = sizeof(rpath_command);
403
404 memcpy(dest: buf, src: path.data(), n: path.size());
405 buf[path.size()] = '\0';
406 }
407
408private:
409 StringRef path;
410};
411
412class LCDyldEnv final : public LoadCommand {
413public:
414 explicit LCDyldEnv(StringRef name) : name(name) {}
415
416 uint32_t getSize() const override {
417 return alignToPowerOf2(Value: sizeof(dyld_env_command) + name.size() + 1,
418 Align: target->wordSize);
419 }
420
421 void writeTo(uint8_t *buf) const override {
422 auto *c = reinterpret_cast<dyld_env_command *>(buf);
423 buf += sizeof(dyld_env_command);
424
425 c->cmd = LC_DYLD_ENVIRONMENT;
426 c->cmdsize = getSize();
427 c->name = sizeof(dyld_env_command);
428
429 memcpy(dest: buf, src: name.data(), n: name.size());
430 buf[name.size()] = '\0';
431 }
432
433private:
434 StringRef name;
435};
436
437class LCMinVersion final : public LoadCommand {
438public:
439 explicit LCMinVersion(const PlatformInfo &platformInfo)
440 : platformInfo(platformInfo) {}
441
442 uint32_t getSize() const override { return sizeof(version_min_command); }
443
444 void writeTo(uint8_t *buf) const override {
445 auto *c = reinterpret_cast<version_min_command *>(buf);
446 switch (platformInfo.target.Platform) {
447 case PLATFORM_MACOS:
448 c->cmd = LC_VERSION_MIN_MACOSX;
449 break;
450 case PLATFORM_IOS:
451 case PLATFORM_IOSSIMULATOR:
452 c->cmd = LC_VERSION_MIN_IPHONEOS;
453 break;
454 case PLATFORM_TVOS:
455 case PLATFORM_TVOSSIMULATOR:
456 c->cmd = LC_VERSION_MIN_TVOS;
457 break;
458 case PLATFORM_WATCHOS:
459 case PLATFORM_WATCHOSSIMULATOR:
460 c->cmd = LC_VERSION_MIN_WATCHOS;
461 break;
462 default:
463 llvm_unreachable("invalid platform");
464 break;
465 }
466 c->cmdsize = getSize();
467 c->version = encodeVersion(version: platformInfo.target.MinDeployment);
468 c->sdk = encodeVersion(version: platformInfo.sdk);
469 }
470
471private:
472 const PlatformInfo &platformInfo;
473};
474
475class LCBuildVersion final : public LoadCommand {
476public:
477 explicit LCBuildVersion(const PlatformInfo &platformInfo)
478 : platformInfo(platformInfo) {}
479
480 const int ntools = 1;
481
482 uint32_t getSize() const override {
483 return sizeof(build_version_command) + ntools * sizeof(build_tool_version);
484 }
485
486 void writeTo(uint8_t *buf) const override {
487 auto *c = reinterpret_cast<build_version_command *>(buf);
488 c->cmd = LC_BUILD_VERSION;
489 c->cmdsize = getSize();
490
491 c->platform = static_cast<uint32_t>(platformInfo.target.Platform);
492 c->minos = encodeVersion(version: platformInfo.target.MinDeployment);
493 c->sdk = encodeVersion(version: platformInfo.sdk);
494
495 c->ntools = ntools;
496 auto *t = reinterpret_cast<build_tool_version *>(&c[1]);
497 t->tool = TOOL_LLD;
498 t->version = encodeVersion(version: VersionTuple(
499 LLVM_VERSION_MAJOR, LLVM_VERSION_MINOR, LLVM_VERSION_PATCH));
500 }
501
502private:
503 const PlatformInfo &platformInfo;
504};
505
506// Stores a unique identifier for the output file based on an MD5 hash of its
507// contents. In order to hash the contents, we must first write them, but
508// LC_UUID itself must be part of the written contents in order for all the
509// offsets to be calculated correctly. We resolve this circular paradox by
510// first writing an LC_UUID with an all-zero UUID, then updating the UUID with
511// its real value later.
512class LCUuid final : public LoadCommand {
513public:
514 uint32_t getSize() const override { return sizeof(uuid_command); }
515
516 void writeTo(uint8_t *buf) const override {
517 auto *c = reinterpret_cast<uuid_command *>(buf);
518 c->cmd = LC_UUID;
519 c->cmdsize = getSize();
520 uuidBuf = c->uuid;
521 }
522
523 void writeUuid(uint64_t digest) const {
524 // xxhash only gives us 8 bytes, so put some fixed data in the other half.
525 static_assert(sizeof(uuid_command::uuid) == 16, "unexpected uuid size");
526 memcpy(dest: uuidBuf, src: "LLD\xa1UU1D", n: 8);
527 memcpy(dest: uuidBuf + 8, src: &digest, n: 8);
528
529 // RFC 4122 conformance. We need to fix 4 bits in byte 6 and 2 bits in
530 // byte 8. Byte 6 is already fine due to the fixed data we put in. We don't
531 // want to lose bits of the digest in byte 8, so swap that with a byte of
532 // fixed data that happens to have the right bits set.
533 std::swap(a&: uuidBuf[3], b&: uuidBuf[8]);
534
535 // Claim that this is an MD5-based hash. It isn't, but this signals that
536 // this is not a time-based and not a random hash. MD5 seems like the least
537 // bad lie we can put here.
538 assert((uuidBuf[6] & 0xf0) == 0x30 && "See RFC 4122 Sections 4.2.2, 4.1.3");
539 assert((uuidBuf[8] & 0xc0) == 0x80 && "See RFC 4122 Section 4.2.2");
540 }
541
542 mutable uint8_t *uuidBuf;
543};
544
545template <class LP> class LCEncryptionInfo final : public LoadCommand {
546public:
547 uint32_t getSize() const override {
548 return sizeof(typename LP::encryption_info_command);
549 }
550
551 void writeTo(uint8_t *buf) const override {
552 using EncryptionInfo = typename LP::encryption_info_command;
553 auto *c = reinterpret_cast<EncryptionInfo *>(buf);
554 buf += sizeof(EncryptionInfo);
555 c->cmd = LP::encryptionInfoLCType;
556 c->cmdsize = getSize();
557 c->cryptoff = in.header->getSize();
558 auto it = find_if(outputSegments, [](const OutputSegment *seg) {
559 return seg->name == segment_names::text;
560 });
561 assert(it != outputSegments.end());
562 c->cryptsize = (*it)->fileSize - c->cryptoff;
563 }
564};
565
566class LCCodeSignature final : public LoadCommand {
567public:
568 LCCodeSignature(CodeSignatureSection *section) : section(section) {}
569
570 uint32_t getSize() const override { return sizeof(linkedit_data_command); }
571
572 void writeTo(uint8_t *buf) const override {
573 auto *c = reinterpret_cast<linkedit_data_command *>(buf);
574 c->cmd = LC_CODE_SIGNATURE;
575 c->cmdsize = getSize();
576 c->dataoff = static_cast<uint32_t>(section->fileOff);
577 c->datasize = section->getSize();
578 }
579
580 CodeSignatureSection *section;
581};
582
583class LCExportsTrie final : public LoadCommand {
584public:
585 LCExportsTrie(ExportSection *section) : section(section) {}
586
587 uint32_t getSize() const override { return sizeof(linkedit_data_command); }
588
589 void writeTo(uint8_t *buf) const override {
590 auto *c = reinterpret_cast<linkedit_data_command *>(buf);
591 c->cmd = LC_DYLD_EXPORTS_TRIE;
592 c->cmdsize = getSize();
593 c->dataoff = section->fileOff;
594 c->datasize = section->getSize();
595 }
596
597 ExportSection *section;
598};
599
600class LCChainedFixups final : public LoadCommand {
601public:
602 LCChainedFixups(ChainedFixupsSection *section) : section(section) {}
603
604 uint32_t getSize() const override { return sizeof(linkedit_data_command); }
605
606 void writeTo(uint8_t *buf) const override {
607 auto *c = reinterpret_cast<linkedit_data_command *>(buf);
608 c->cmd = LC_DYLD_CHAINED_FIXUPS;
609 c->cmdsize = getSize();
610 c->dataoff = section->fileOff;
611 c->datasize = section->getSize();
612 }
613
614 ChainedFixupsSection *section;
615};
616
617} // namespace
618
619void Writer::treatSpecialUndefineds() {
620 if (config->entry)
621 if (auto *undefined = dyn_cast<Undefined>(Val: config->entry))
622 treatUndefinedSymbol(*undefined, source: "the entry point");
623
624 // FIXME: This prints symbols that are undefined both in input files and
625 // via -u flag twice.
626 for (const Symbol *sym : config->explicitUndefineds) {
627 if (const auto *undefined = dyn_cast<Undefined>(Val: sym))
628 treatUndefinedSymbol(*undefined, source: "-u");
629 }
630 // Literal exported-symbol names must be defined, but glob
631 // patterns need not match.
632 for (const CachedHashStringRef &cachedName :
633 config->exportedSymbols.literals) {
634 if (const Symbol *sym = symtab->find(name: cachedName))
635 if (const auto *undefined = dyn_cast<Undefined>(Val: sym))
636 treatUndefinedSymbol(*undefined, source: "-exported_symbol(s_list)");
637 }
638}
639
640static void prepareSymbolRelocation(Symbol *sym, const InputSection *isec,
641 const lld::macho::Reloc &r) {
642 if (!sym->isLive()) {
643 if (Defined *defined = dyn_cast<Defined>(Val: sym)) {
644 if (config->emitInitOffsets &&
645 defined->isec()->getName() == section_names::moduleInitFunc)
646 fatal(msg: isec->getLocation(off: r.offset) + ": cannot reference " +
647 sym->getName() +
648 " defined in __mod_init_func when -init_offsets is used");
649 }
650 assert(false && "referenced symbol must be live");
651 }
652
653 const RelocAttrs &relocAttrs = target->getRelocAttrs(type: r.type);
654
655 if (relocAttrs.hasAttr(b: RelocAttrBits::BRANCH)) {
656 if (needsBinding(sym))
657 in.stubs->addEntry(sym);
658 } else if (relocAttrs.hasAttr(b: RelocAttrBits::GOT)) {
659 if (relocAttrs.hasAttr(b: RelocAttrBits::POINTER) || needsBinding(sym))
660 in.got->addEntry(sym);
661 } else if (relocAttrs.hasAttr(b: RelocAttrBits::TLV)) {
662 if (needsBinding(sym))
663 in.tlvPointers->addEntry(sym);
664 } else if (relocAttrs.hasAttr(b: RelocAttrBits::UNSIGNED)) {
665 // References from thread-local variable sections are treated as offsets
666 // relative to the start of the referent section, and therefore have no
667 // need of rebase opcodes.
668 if (!(isThreadLocalVariables(flags: isec->getFlags()) && isa<Defined>(Val: sym)))
669 addNonLazyBindingEntries(sym, isec, offset: r.offset, addend: r.addend);
670 }
671}
672
673void Writer::scanRelocations() {
674 TimeTraceScope timeScope("Scan relocations");
675
676 // This can't use a for-each loop: It calls treatUndefinedSymbol(), which can
677 // add to inputSections, which invalidates inputSections's iterators.
678 for (size_t i = 0; i < inputSections.size(); ++i) {
679 ConcatInputSection *isec = inputSections[i];
680
681 if (isec->shouldOmitFromOutput())
682 continue;
683
684 for (auto it = isec->relocs.begin(); it != isec->relocs.end(); ++it) {
685 lld::macho::Reloc &r = *it;
686
687 // Canonicalize the referent so that later accesses in Writer won't
688 // have to worry about it.
689 if (auto *referentIsec = r.referent.dyn_cast<InputSection *>())
690 r.referent = referentIsec->canonical();
691
692 if (target->hasAttr(type: r.type, bit: RelocAttrBits::SUBTRAHEND)) {
693 // Skip over the following UNSIGNED relocation -- it's just there as the
694 // minuend, and doesn't have the usual UNSIGNED semantics. We don't want
695 // to emit rebase opcodes for it.
696 ++it;
697 // Canonicalize the referent so that later accesses in Writer won't
698 // have to worry about it.
699 if (auto *referentIsec = it->referent.dyn_cast<InputSection *>())
700 it->referent = referentIsec->canonical();
701 continue;
702 }
703 if (auto *sym = r.referent.dyn_cast<Symbol *>()) {
704 if (auto *undefined = dyn_cast<Undefined>(Val: sym))
705 treatUndefinedSymbol(*undefined, isec, offset: r.offset);
706 // treatUndefinedSymbol() can replace sym with a DylibSymbol; re-check.
707 if (!isa<Undefined>(Val: sym) && validateSymbolRelocation(sym, isec, r))
708 prepareSymbolRelocation(sym, isec, r);
709 } else {
710 if (!r.pcrel) {
711 if (config->emitChainedFixups)
712 in.chainedFixups->addRebase(isec, offset: r.offset);
713 else
714 in.rebase->addEntry(isec, offset: r.offset);
715 }
716 }
717 }
718 }
719
720 in.unwindInfo->prepare();
721}
722
723static void addNonWeakDefinition(const Defined *defined) {
724 if (config->emitChainedFixups)
725 in.chainedFixups->setHasNonWeakDefinition();
726 else
727 in.weakBinding->addNonWeakDefinition(defined);
728}
729
730void Writer::scanSymbols() {
731 TimeTraceScope timeScope("Scan symbols");
732 ObjCSelRefsHelper::initialize();
733 for (Symbol *sym : symtab->getSymbols()) {
734 if (auto *defined = dyn_cast<Defined>(Val: sym)) {
735 if (!defined->isLive())
736 continue;
737 if (defined->overridesWeakDef)
738 addNonWeakDefinition(defined);
739 if (!defined->isAbsolute() && isCodeSection(defined->isec()))
740 in.unwindInfo->addSymbol(defined);
741 } else if (const auto *dysym = dyn_cast<DylibSymbol>(Val: sym)) {
742 // This branch intentionally doesn't check isLive().
743 if (dysym->isDynamicLookup())
744 continue;
745 dysym->getFile()->refState =
746 std::max(a: dysym->getFile()->refState, b: dysym->getRefState());
747 } else if (isa<Undefined>(Val: sym)) {
748 if (ObjCStubsSection::isObjCStubSymbol(sym)) {
749 // When -dead_strip is enabled, we don't want to emit any dead stubs.
750 // Although this stub symbol is yet undefined, addSym() was called
751 // during MarkLive.
752 if (config->deadStrip) {
753 if (!sym->isLive())
754 continue;
755 }
756 in.objcStubs->addEntry(sym);
757 }
758 }
759 }
760
761 for (const InputFile *file : inputFiles) {
762 if (auto *objFile = dyn_cast<ObjFile>(Val: file))
763 for (Symbol *sym : objFile->symbols) {
764 if (auto *defined = dyn_cast_or_null<Defined>(Val: sym)) {
765 if (!defined->isLive())
766 continue;
767 if (!defined->isExternal() && !defined->isAbsolute() &&
768 isCodeSection(defined->isec()))
769 in.unwindInfo->addSymbol(defined);
770 }
771 }
772 }
773}
774
775// TODO: ld64 enforces the old load commands in a few other cases.
776static bool useLCBuildVersion(const PlatformInfo &platformInfo) {
777 static const std::array<std::pair<PlatformType, VersionTuple>, 7> minVersion =
778 {._M_elems: {{PLATFORM_MACOS, VersionTuple(10, 14)},
779 {PLATFORM_IOS, VersionTuple(12, 0)},
780 {PLATFORM_IOSSIMULATOR, VersionTuple(13, 0)},
781 {PLATFORM_TVOS, VersionTuple(12, 0)},
782 {PLATFORM_TVOSSIMULATOR, VersionTuple(13, 0)},
783 {PLATFORM_WATCHOS, VersionTuple(5, 0)},
784 {PLATFORM_WATCHOSSIMULATOR, VersionTuple(6, 0)}}};
785 auto it = llvm::find_if(Range: minVersion, P: [&](const auto &p) {
786 return p.first == platformInfo.target.Platform;
787 });
788 return it == minVersion.end()
789 ? true
790 : platformInfo.target.MinDeployment >= it->second;
791}
792
793template <class LP> void Writer::createLoadCommands() {
794 uint8_t segIndex = 0;
795 for (OutputSegment *seg : outputSegments) {
796 in.header->addLoadCommand(make<LCSegment<LP>>(seg->name, seg));
797 seg->index = segIndex++;
798 }
799
800 if (config->emitChainedFixups) {
801 in.header->addLoadCommand(make<LCChainedFixups>(args&: in.chainedFixups));
802 in.header->addLoadCommand(make<LCExportsTrie>(args&: in.exports));
803 } else {
804 in.header->addLoadCommand(make<LCDyldInfo>(
805 args&: in.rebase, args&: in.binding, args&: in.weakBinding, args&: in.lazyBinding, args&: in.exports));
806 }
807 in.header->addLoadCommand(make<LCSymtab>(args&: symtabSection, args&: stringTableSection));
808 in.header->addLoadCommand(
809 make<LCDysymtab>(args&: symtabSection, args&: indirectSymtabSection));
810 if (!config->umbrella.empty())
811 in.header->addLoadCommand(make<LCSubFramework>(args&: config->umbrella));
812 if (config->emitEncryptionInfo)
813 in.header->addLoadCommand(make<LCEncryptionInfo<LP>>());
814 for (StringRef path : config->runtimePaths)
815 in.header->addLoadCommand(make<LCRPath>(args&: path));
816
817 switch (config->outputType) {
818 case MH_EXECUTE:
819 in.header->addLoadCommand(make<LCLoadDylinker>());
820 break;
821 case MH_DYLIB:
822 in.header->addLoadCommand(make<LCDylib>(args: LC_ID_DYLIB, args&: config->installName,
823 args&: config->dylibCompatibilityVersion,
824 args&: config->dylibCurrentVersion));
825 break;
826 case MH_BUNDLE:
827 break;
828 default:
829 llvm_unreachable("unhandled output file type");
830 }
831
832 if (config->generateUuid) {
833 uuidCommand = make<LCUuid>();
834 in.header->addLoadCommand(uuidCommand);
835 }
836
837 if (useLCBuildVersion(platformInfo: config->platformInfo))
838 in.header->addLoadCommand(make<LCBuildVersion>(args&: config->platformInfo));
839 else
840 in.header->addLoadCommand(make<LCMinVersion>(args&: config->platformInfo));
841
842 if (config->secondaryPlatformInfo) {
843 in.header->addLoadCommand(
844 make<LCBuildVersion>(args&: *config->secondaryPlatformInfo));
845 }
846
847 // This is down here to match ld64's load command order.
848 if (config->outputType == MH_EXECUTE)
849 in.header->addLoadCommand(make<LCMain>());
850
851 // See ld64's OutputFile::buildDylibOrdinalMapping for the corresponding
852 // library ordinal computation code in ld64.
853 int64_t dylibOrdinal = 1;
854 DenseMap<StringRef, int64_t> ordinalForInstallName;
855
856 std::vector<DylibFile *> dylibFiles;
857 for (InputFile *file : inputFiles) {
858 if (auto *dylibFile = dyn_cast<DylibFile>(Val: file))
859 dylibFiles.push_back(x: dylibFile);
860 }
861 for (size_t i = 0; i < dylibFiles.size(); ++i)
862 dylibFiles.insert(position: dylibFiles.end(), first: dylibFiles[i]->extraDylibs.begin(),
863 last: dylibFiles[i]->extraDylibs.end());
864
865 for (DylibFile *dylibFile : dylibFiles) {
866 if (dylibFile->isBundleLoader) {
867 dylibFile->ordinal = BIND_SPECIAL_DYLIB_MAIN_EXECUTABLE;
868 // Shortcut since bundle-loader does not re-export the symbols.
869
870 dylibFile->reexport = false;
871 continue;
872 }
873
874 // Don't emit load commands for a dylib that is not referenced if:
875 // - it was added implicitly (via a reexport, an LC_LOAD_DYLINKER --
876 // if it's on the linker command line, it's explicit)
877 // - or it's marked MH_DEAD_STRIPPABLE_DYLIB
878 // - or the flag -dead_strip_dylibs is used
879 // FIXME: `isReferenced()` is currently computed before dead code
880 // stripping, so references from dead code keep a dylib alive. This
881 // matches ld64, but it's something we should do better.
882 if (!dylibFile->isReferenced() && !dylibFile->forceNeeded &&
883 (!dylibFile->isExplicitlyLinked() || dylibFile->deadStrippable ||
884 config->deadStripDylibs))
885 continue;
886
887 // Several DylibFiles can have the same installName. Only emit a single
888 // load command for that installName and give all these DylibFiles the
889 // same ordinal.
890 // This can happen in several cases:
891 // - a new framework could change its installName to an older
892 // framework name via an $ld$ symbol depending on platform_version
893 // - symlinks (for example, libpthread.tbd is a symlink to libSystem.tbd;
894 // Foo.framework/Foo.tbd is usually a symlink to
895 // Foo.framework/Versions/Current/Foo.tbd, where
896 // Foo.framework/Versions/Current is usually a symlink to
897 // Foo.framework/Versions/A)
898 // - a framework can be linked both explicitly on the linker
899 // command line and implicitly as a reexport from a different
900 // framework. The re-export will usually point to the tbd file
901 // in Foo.framework/Versions/A/Foo.tbd, while the explicit link will
902 // usually find Foo.framework/Foo.tbd. These are usually symlinks,
903 // but in a --reproduce archive they will be identical but distinct
904 // files.
905 // In the first case, *semantically distinct* DylibFiles will have the
906 // same installName.
907 int64_t &ordinal = ordinalForInstallName[dylibFile->installName];
908 if (ordinal) {
909 dylibFile->ordinal = ordinal;
910 continue;
911 }
912
913 ordinal = dylibFile->ordinal = dylibOrdinal++;
914 LoadCommandType lcType =
915 dylibFile->forceWeakImport || dylibFile->refState == RefState::Weak
916 ? LC_LOAD_WEAK_DYLIB
917 : LC_LOAD_DYLIB;
918 in.header->addLoadCommand(make<LCDylib>(args&: lcType, args&: dylibFile->installName,
919 args&: dylibFile->compatibilityVersion,
920 args&: dylibFile->currentVersion));
921
922 if (dylibFile->reexport)
923 in.header->addLoadCommand(
924 make<LCDylib>(args: LC_REEXPORT_DYLIB, args&: dylibFile->installName));
925 }
926
927 for (const auto &dyldEnv : config->dyldEnvs)
928 in.header->addLoadCommand(make<LCDyldEnv>(args: dyldEnv));
929
930 if (functionStartsSection)
931 in.header->addLoadCommand(make<LCFunctionStarts>(args&: functionStartsSection));
932 if (dataInCodeSection)
933 in.header->addLoadCommand(make<LCDataInCode>(args&: dataInCodeSection));
934 if (codeSignatureSection)
935 in.header->addLoadCommand(make<LCCodeSignature>(args&: codeSignatureSection));
936
937 const uint32_t MACOS_MAXPATHLEN = 1024;
938 config->headerPad = std::max(
939 a: config->headerPad, b: (config->headerPadMaxInstallNames
940 ? LCDylib::getInstanceCount() * MACOS_MAXPATHLEN
941 : 0));
942}
943
944// Sorting only can happen once all outputs have been collected. Here we sort
945// segments, output sections within each segment, and input sections within each
946// output segment.
947static void sortSegmentsAndSections() {
948 TimeTraceScope timeScope("Sort segments and sections");
949 sortOutputSegments();
950
951 DenseMap<const InputSection *, size_t> isecPriorities =
952 priorityBuilder.buildInputSectionPriorities();
953
954 uint32_t sectionIndex = 0;
955 for (OutputSegment *seg : outputSegments) {
956 seg->sortOutputSections();
957 // References from thread-local variable sections are treated as offsets
958 // relative to the start of the thread-local data memory area, which
959 // is initialized via copying all the TLV data sections (which are all
960 // contiguous). If later data sections require a greater alignment than
961 // earlier ones, the offsets of data within those sections won't be
962 // guaranteed to aligned unless we normalize alignments. We therefore use
963 // the largest alignment for all TLV data sections.
964 uint32_t tlvAlign = 0;
965 for (const OutputSection *osec : seg->getSections())
966 if (isThreadLocalData(flags: osec->flags) && osec->align > tlvAlign)
967 tlvAlign = osec->align;
968
969 for (OutputSection *osec : seg->getSections()) {
970 // Now that the output sections are sorted, assign the final
971 // output section indices.
972 if (!osec->isHidden())
973 osec->index = ++sectionIndex;
974 if (isThreadLocalData(flags: osec->flags)) {
975 if (!firstTLVDataSection)
976 firstTLVDataSection = osec;
977 osec->align = tlvAlign;
978 }
979
980 if (!isecPriorities.empty()) {
981 if (auto *merged = dyn_cast<ConcatOutputSection>(Val: osec)) {
982 llvm::stable_sort(
983 Range&: merged->inputs, C: [&](InputSection *a, InputSection *b) {
984 return isecPriorities.lookup(Val: a) > isecPriorities.lookup(Val: b);
985 });
986 }
987 }
988 }
989 }
990}
991
992template <class LP> void Writer::createOutputSections() {
993 TimeTraceScope timeScope("Create output sections");
994 // First, create hidden sections
995 stringTableSection = make<StringTableSection>();
996 symtabSection = makeSymtabSection<LP>(*stringTableSection);
997 indirectSymtabSection = make<IndirectSymtabSection>();
998 if (config->adhocCodesign)
999 codeSignatureSection = make<CodeSignatureSection>();
1000 if (config->emitDataInCodeInfo)
1001 dataInCodeSection = make<DataInCodeSection>();
1002 if (config->emitFunctionStarts)
1003 functionStartsSection = make<FunctionStartsSection>();
1004
1005 switch (config->outputType) {
1006 case MH_EXECUTE:
1007 make<PageZeroSection>();
1008 break;
1009 case MH_DYLIB:
1010 case MH_BUNDLE:
1011 break;
1012 default:
1013 llvm_unreachable("unhandled output file type");
1014 }
1015
1016 // Then add input sections to output sections.
1017 for (ConcatInputSection *isec : inputSections) {
1018 if (isec->shouldOmitFromOutput())
1019 continue;
1020 ConcatOutputSection *osec = cast<ConcatOutputSection>(Val: isec->parent);
1021 osec->addInput(input: isec);
1022 osec->inputOrder =
1023 std::min(a: osec->inputOrder, b: static_cast<int>(isec->outSecOff));
1024 }
1025
1026 // Once all the inputs are added, we can finalize the output section
1027 // properties and create the corresponding output segments.
1028 for (const auto &it : concatOutputSections) {
1029 StringRef segname = it.first.first;
1030 ConcatOutputSection *osec = it.second;
1031 assert(segname != segment_names::ld);
1032 if (osec->isNeeded()) {
1033 // See comment in ObjFile::splitEhFrames()
1034 if (osec->name == section_names::ehFrame &&
1035 segname == segment_names::text)
1036 osec->align = target->wordSize;
1037
1038 // MC keeps the default 1-byte alignment for __thread_vars, even though it
1039 // contains pointers that are fixed up by dyld, which requires proper
1040 // alignment.
1041 if (isThreadLocalVariables(flags: osec->flags))
1042 osec->align = std::max<uint32_t>(a: osec->align, b: target->wordSize);
1043
1044 getOrCreateOutputSegment(name: segname)->addOutputSection(os: osec);
1045 }
1046 }
1047
1048 for (SyntheticSection *ssec : syntheticSections) {
1049 auto it = concatOutputSections.find(Key: {ssec->segname, ssec->name});
1050 // We add all LinkEdit sections here because we don't know if they are
1051 // needed until their finalizeContents() methods get called later. While
1052 // this means that we add some redundant sections to __LINKEDIT, there is
1053 // is no redundancy in the output, as we do not emit section headers for
1054 // any LinkEdit sections.
1055 if (ssec->isNeeded() || ssec->segname == segment_names::linkEdit) {
1056 if (it == concatOutputSections.end()) {
1057 getOrCreateOutputSegment(name: ssec->segname)->addOutputSection(os: ssec);
1058 } else {
1059 fatal(msg: "section from " +
1060 toString(file: it->second->firstSection()->getFile()) +
1061 " conflicts with synthetic section " + ssec->segname + "," +
1062 ssec->name);
1063 }
1064 }
1065 }
1066
1067 // dyld requires __LINKEDIT segment to always exist (even if empty).
1068 linkEditSegment = getOrCreateOutputSegment(name: segment_names::linkEdit);
1069}
1070
1071void Writer::finalizeAddresses() {
1072 TimeTraceScope timeScope("Finalize addresses");
1073 uint64_t pageSize = target->getPageSize();
1074
1075 // We could parallelize this loop, but local benchmarking indicates it is
1076 // faster to do it all in the main thread.
1077 for (OutputSegment *seg : outputSegments) {
1078 if (seg == linkEditSegment)
1079 continue;
1080 for (OutputSection *osec : seg->getSections()) {
1081 if (!osec->isNeeded())
1082 continue;
1083 // Other kinds of OutputSections have already been finalized.
1084 if (auto *concatOsec = dyn_cast<ConcatOutputSection>(Val: osec))
1085 concatOsec->finalizeContents();
1086 }
1087 }
1088
1089 // Ensure that segments (and the sections they contain) are allocated
1090 // addresses in ascending order, which dyld requires.
1091 //
1092 // Note that at this point, __LINKEDIT sections are empty, but we need to
1093 // determine addresses of other segments/sections before generating its
1094 // contents.
1095 for (OutputSegment *seg : outputSegments) {
1096 if (seg == linkEditSegment)
1097 continue;
1098 seg->addr = addr;
1099 assignAddresses(seg);
1100 // codesign / libstuff checks for segment ordering by verifying that
1101 // `fileOff + fileSize == next segment fileOff`. So we call
1102 // alignToPowerOf2() before (instead of after) computing fileSize to ensure
1103 // that the segments are contiguous. We handle addr / vmSize similarly for
1104 // the same reason.
1105 fileOff = alignToPowerOf2(Value: fileOff, Align: pageSize);
1106 addr = alignToPowerOf2(Value: addr, Align: pageSize);
1107 seg->vmSize = addr - seg->addr;
1108 seg->fileSize = fileOff - seg->fileOff;
1109 seg->assignAddressesToStartEndSymbols();
1110 }
1111}
1112
1113void Writer::finalizeLinkEditSegment() {
1114 TimeTraceScope timeScope("Finalize __LINKEDIT segment");
1115 // Fill __LINKEDIT contents.
1116 std::array<LinkEditSection *, 10> linkEditSections{
1117 in.rebase, in.binding,
1118 in.weakBinding, in.lazyBinding,
1119 in.exports, in.chainedFixups,
1120 symtabSection, indirectSymtabSection,
1121 dataInCodeSection, functionStartsSection,
1122 };
1123
1124 parallelForEach(Begin: linkEditSections.begin(), End: linkEditSections.end(),
1125 Fn: [](LinkEditSection *osec) {
1126 if (osec)
1127 osec->finalizeContents();
1128 });
1129
1130 // Now that __LINKEDIT is filled out, do a proper calculation of its
1131 // addresses and offsets.
1132 linkEditSegment->addr = addr;
1133 assignAddresses(linkEditSegment);
1134 // No need to page-align fileOff / addr here since this is the last segment.
1135 linkEditSegment->vmSize = addr - linkEditSegment->addr;
1136 linkEditSegment->fileSize = fileOff - linkEditSegment->fileOff;
1137}
1138
1139void Writer::assignAddresses(OutputSegment *seg) {
1140 seg->fileOff = fileOff;
1141
1142 for (OutputSection *osec : seg->getSections()) {
1143 if (!osec->isNeeded())
1144 continue;
1145 addr = alignToPowerOf2(Value: addr, Align: osec->align);
1146 fileOff = alignToPowerOf2(Value: fileOff, Align: osec->align);
1147 osec->addr = addr;
1148 osec->fileOff = isZeroFill(flags: osec->flags) ? 0 : fileOff;
1149 osec->finalize();
1150 osec->assignAddressesToStartEndSymbols();
1151
1152 addr += osec->getSize();
1153 fileOff += osec->getFileSize();
1154 }
1155}
1156
1157void Writer::openFile() {
1158 Expected<std::unique_ptr<FileOutputBuffer>> bufferOrErr =
1159 FileOutputBuffer::create(FilePath: config->outputFile, Size: fileOff,
1160 Flags: FileOutputBuffer::F_executable);
1161
1162 if (!bufferOrErr)
1163 fatal(msg: "failed to open " + config->outputFile + ": " +
1164 llvm::toString(E: bufferOrErr.takeError()));
1165 buffer = std::move(*bufferOrErr);
1166 in.bufferStart = buffer->getBufferStart();
1167}
1168
1169void Writer::writeSections() {
1170 TimeTraceScope timeScope("Write output sections");
1171
1172 uint8_t *buf = buffer->getBufferStart();
1173 std::vector<const OutputSection *> osecs;
1174 for (const OutputSegment *seg : outputSegments)
1175 append_range(C&: osecs, R: seg->getSections());
1176
1177 parallelForEach(Begin: osecs.begin(), End: osecs.end(), Fn: [&](const OutputSection *osec) {
1178 osec->writeTo(buf: buf + osec->fileOff);
1179 });
1180}
1181
1182void Writer::applyOptimizationHints() {
1183 if (config->arch() != AK_arm64 || config->ignoreOptimizationHints)
1184 return;
1185
1186 uint8_t *buf = buffer->getBufferStart();
1187 TimeTraceScope timeScope("Apply linker optimization hints");
1188 parallelForEach(R&: inputFiles, Fn: [buf](const InputFile *file) {
1189 if (const auto *objFile = dyn_cast<ObjFile>(Val: file))
1190 target->applyOptimizationHints(buf, *objFile);
1191 });
1192}
1193
1194// In order to utilize multiple cores, we first split the buffer into chunks,
1195// compute a hash for each chunk, and then compute a hash value of the hash
1196// values.
1197void Writer::writeUuid() {
1198 TimeTraceScope timeScope("Computing UUID");
1199
1200 ArrayRef<uint8_t> data{buffer->getBufferStart(), buffer->getBufferEnd()};
1201 std::vector<ArrayRef<uint8_t>> chunks = split(arr: data, chunkSize: 1024 * 1024);
1202
1203 // Leave one slot for filename
1204 std::vector<uint64_t> hashes(chunks.size() + 1);
1205 parallelFor(Begin: 0, End: chunks.size(),
1206 Fn: [&](size_t i) { hashes[i] = xxh3_64bits(data: chunks[i]); });
1207 // Append the output filename so that identical binaries with different names
1208 // don't get the same UUID.
1209 hashes[chunks.size()] = xxh3_64bits(data: sys::path::filename(path: config->finalOutput));
1210
1211 uint64_t digest = xxh3_64bits(data: {reinterpret_cast<uint8_t *>(hashes.data()),
1212 hashes.size() * sizeof(uint64_t)});
1213 uuidCommand->writeUuid(digest);
1214}
1215
1216// This is step 5 of the algorithm described in the class comment of
1217// ChainedFixupsSection.
1218void Writer::buildFixupChains() {
1219 if (!config->emitChainedFixups)
1220 return;
1221
1222 const std::vector<Location> &loc = in.chainedFixups->getLocations();
1223 if (loc.empty())
1224 return;
1225
1226 TimeTraceScope timeScope("Build fixup chains");
1227
1228 const uint64_t pageSize = target->getPageSize();
1229 constexpr uint32_t stride = 4; // for DYLD_CHAINED_PTR_64
1230
1231 for (size_t i = 0, count = loc.size(); i < count;) {
1232 const OutputSegment *oseg = loc[i].isec->parent->parent;
1233 uint8_t *buf = buffer->getBufferStart() + oseg->fileOff;
1234 uint64_t pageIdx = loc[i].offset / pageSize;
1235 ++i;
1236
1237 while (i < count && loc[i].isec->parent->parent == oseg &&
1238 (loc[i].offset / pageSize) == pageIdx) {
1239 uint64_t offset = loc[i].offset - loc[i - 1].offset;
1240
1241 auto fail = [&](Twine message) {
1242 error(msg: loc[i].isec->getSegName() + "," + loc[i].isec->getName() +
1243 ", offset " +
1244 Twine(loc[i].offset - loc[i].isec->parent->getSegmentOffset()) +
1245 ": " + message);
1246 };
1247
1248 if (offset < target->wordSize)
1249 return fail("fixups overlap");
1250 if (offset % stride != 0)
1251 return fail(
1252 "fixups are unaligned (offset " + Twine(offset) +
1253 " is not a multiple of the stride). Re-link with -no_fixup_chains");
1254
1255 // The "next" field is in the same location for bind and rebase entries.
1256 reinterpret_cast<dyld_chained_ptr_64_bind *>(buf + loc[i - 1].offset)
1257 ->next = offset / stride;
1258 ++i;
1259 }
1260 }
1261}
1262
1263void Writer::writeCodeSignature() {
1264 if (codeSignatureSection) {
1265 TimeTraceScope timeScope("Write code signature");
1266 codeSignatureSection->writeHashes(buf: buffer->getBufferStart());
1267 }
1268}
1269
1270void Writer::writeOutputFile() {
1271 TimeTraceScope timeScope("Write output file");
1272 openFile();
1273 reportPendingUndefinedSymbols();
1274 if (errorCount())
1275 return;
1276 writeSections();
1277 applyOptimizationHints();
1278 buildFixupChains();
1279 if (config->generateUuid)
1280 writeUuid();
1281 writeCodeSignature();
1282
1283 if (auto e = buffer->commit())
1284 fatal(msg: "failed to write output '" + buffer->getPath() +
1285 "': " + toString(E: std::move(e)));
1286}
1287
1288template <class LP> void Writer::run() {
1289 treatSpecialUndefineds();
1290 if (config->entry && needsBinding(sym: config->entry))
1291 in.stubs->addEntry(config->entry);
1292
1293 // Canonicalization of all pointers to InputSections should be handled by
1294 // these two scan* methods. I.e. from this point onward, for all live
1295 // InputSections, we should have `isec->canonical() == isec`.
1296 scanSymbols();
1297 if (in.objcStubs->isNeeded())
1298 in.objcStubs->setUp();
1299 if (in.objcMethList->isNeeded())
1300 in.objcMethList->setUp();
1301 scanRelocations();
1302 if (in.initOffsets->isNeeded())
1303 in.initOffsets->setUp();
1304
1305 // Do not proceed if there were undefined or duplicate symbols.
1306 reportPendingUndefinedSymbols();
1307 reportPendingDuplicateSymbols();
1308 if (errorCount())
1309 return;
1310
1311 if (in.stubHelper && in.stubHelper->isNeeded())
1312 in.stubHelper->setUp();
1313
1314 if (in.objCImageInfo->isNeeded())
1315 in.objCImageInfo->finalizeContents();
1316
1317 // At this point, we should know exactly which output sections are needed,
1318 // courtesy of scanSymbols() and scanRelocations().
1319 createOutputSections<LP>();
1320
1321 // After this point, we create no new segments; HOWEVER, we might
1322 // yet create branch-range extension thunks for architectures whose
1323 // hardware call instructions have limited range, e.g., ARM(64).
1324 // The thunks are created as InputSections interspersed among
1325 // the ordinary __TEXT,_text InputSections.
1326 sortSegmentsAndSections();
1327 createLoadCommands<LP>();
1328 finalizeAddresses();
1329
1330 llvm::thread mapFileWriter([&] {
1331 if (LLVM_ENABLE_THREADS && config->timeTraceEnabled)
1332 timeTraceProfilerInitialize(TimeTraceGranularity: config->timeTraceGranularity, ProcName: "writeMapFile");
1333 writeMapFile();
1334 if (LLVM_ENABLE_THREADS && config->timeTraceEnabled)
1335 timeTraceProfilerFinishThread();
1336 });
1337
1338 finalizeLinkEditSegment();
1339 writeOutputFile();
1340 mapFileWriter.join();
1341}
1342
1343template <class LP> void macho::writeResult() { Writer().run<LP>(); }
1344
1345void macho::resetWriter() { LCDylib::resetInstanceCount(); }
1346
1347void macho::createSyntheticSections() {
1348 in.header = make<MachHeaderSection>();
1349 if (config->dedupStrings)
1350 in.cStringSection =
1351 make<DeduplicatedCStringSection>(args: section_names::cString);
1352 else
1353 in.cStringSection = make<CStringSection>(args: section_names::cString);
1354 in.objcMethnameSection =
1355 make<DeduplicatedCStringSection>(args: section_names::objcMethname);
1356 in.wordLiteralSection = make<WordLiteralSection>();
1357 if (config->emitChainedFixups) {
1358 in.chainedFixups = make<ChainedFixupsSection>();
1359 } else {
1360 in.rebase = make<RebaseSection>();
1361 in.binding = make<BindingSection>();
1362 in.weakBinding = make<WeakBindingSection>();
1363 in.lazyBinding = make<LazyBindingSection>();
1364 in.lazyPointers = make<LazyPointerSection>();
1365 in.stubHelper = make<StubHelperSection>();
1366 }
1367 in.exports = make<ExportSection>();
1368 in.got = make<GotSection>();
1369 in.tlvPointers = make<TlvPointerSection>();
1370 in.stubs = make<StubsSection>();
1371 in.objcStubs = make<ObjCStubsSection>();
1372 in.unwindInfo = makeUnwindInfoSection();
1373 in.objCImageInfo = make<ObjCImageInfoSection>();
1374 in.initOffsets = make<InitOffsetsSection>();
1375 in.objcMethList = make<ObjCMethListSection>();
1376
1377 // This section contains space for just a single word, and will be used by
1378 // dyld to cache an address to the image loader it uses.
1379 uint8_t *arr = bAlloc().Allocate<uint8_t>(Num: target->wordSize);
1380 memset(s: arr, c: 0, n: target->wordSize);
1381 in.imageLoaderCache = makeSyntheticInputSection(
1382 segName: segment_names::data, sectName: section_names::data, flags: S_REGULAR,
1383 data: ArrayRef<uint8_t>{arr, target->wordSize},
1384 /*align=*/target->wordSize);
1385 assert(in.imageLoaderCache->live);
1386}
1387
1388OutputSection *macho::firstTLVDataSection = nullptr;
1389
1390template void macho::writeResult<LP64>();
1391template void macho::writeResult<ILP32>();
1392