1 //===- Core/Resolver.cpp - Resolves Atom References -----------------------===//
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //===----------------------------------------------------------------------===//
9 #include "lld/Core/Resolver.h"
10 #include "lld/Common/LLVM.h"
11 #include "lld/Core/ArchiveLibraryFile.h"
12 #include "lld/Core/Atom.h"
13 #include "lld/Core/File.h"
14 #include "lld/Core/Instrumentation.h"
15 #include "lld/Core/LinkingContext.h"
16 #include "lld/Core/SharedLibraryFile.h"
17 #include "lld/Core/SymbolTable.h"
18 #include "lld/Core/UndefinedAtom.h"
19 #include "llvm/ADT/iterator_range.h"
20 #include "llvm/Support/Debug.h"
21 #include "llvm/Support/Error.h"
22 #include "llvm/Support/ErrorHandling.h"
23 #include "llvm/Support/Format.h"
24 #include "llvm/Support/raw_ostream.h"
32 llvm::Expected<bool> Resolver::handleFile(File &file) {
33 if (auto ec = _ctx.handleLoadedFile(file))
35 bool undefAdded = false;
36 for (auto &atom : file.defined().owning_ptrs())
37 doDefinedAtom(std::move(atom));
38 for (auto &atom : file.undefined().owning_ptrs()) {
39 if (doUndefinedAtom(std::move(atom)))
42 for (auto &atom : file.sharedLibrary().owning_ptrs())
43 doSharedLibraryAtom(std::move(atom));
44 for (auto &atom : file.absolute().owning_ptrs())
45 doAbsoluteAtom(std::move(atom));
49 llvm::Expected<bool> Resolver::forEachUndefines(File &file,
50 UndefCallback callback) {
51 size_t i = _undefineIndex[&file];
52 bool undefAdded = false;
54 for (; i < _undefines.size(); ++i) {
55 StringRef undefName = _undefines[i];
56 if (undefName.empty())
58 const Atom *atom = _symbolTable.findByName(undefName);
59 if (!isa<UndefinedAtom>(atom) || _symbolTable.isCoalescedAway(atom)) {
60 // The symbol was resolved by some other file. Cache the result.
64 auto undefAddedOrError = callback(undefName);
65 if (auto ec = undefAddedOrError.takeError())
67 undefAdded |= undefAddedOrError.get();
69 } while (i < _undefines.size());
70 _undefineIndex[&file] = i;
74 llvm::Expected<bool> Resolver::handleArchiveFile(File &file) {
75 ArchiveLibraryFile *archiveFile = cast<ArchiveLibraryFile>(&file);
76 return forEachUndefines(file,
77 [&](StringRef undefName) -> llvm::Expected<bool> {
78 if (File *member = archiveFile->find(undefName)) {
79 member->setOrdinal(_ctx.getNextOrdinalAndIncrement());
80 return handleFile(*member);
86 llvm::Error Resolver::handleSharedLibrary(File &file) {
87 // Add all the atoms from the shared library
88 SharedLibraryFile *sharedLibrary = cast<SharedLibraryFile>(&file);
89 auto undefAddedOrError = handleFile(*sharedLibrary);
90 if (auto ec = undefAddedOrError.takeError())
93 forEachUndefines(file, [&](StringRef undefName) -> llvm::Expected<bool> {
94 auto atom = sharedLibrary->exports(undefName);
96 doSharedLibraryAtom(std::move(atom));
100 if (auto ec = undefAddedOrError.takeError())
102 return llvm::Error::success();
105 bool Resolver::doUndefinedAtom(OwningAtomPtr<UndefinedAtom> atom) {
106 DEBUG_WITH_TYPE("resolver", llvm::dbgs()
107 << " UndefinedAtom: "
108 << llvm::format("0x%09lX", atom.get())
109 << ", name=" << atom.get()->name() << "\n");
112 bool newUndefAdded = _symbolTable.add(*atom.get());
114 _undefines.push_back(atom.get()->name());
116 // add to list of known atoms
117 _atoms.push_back(OwningAtomPtr<Atom>(atom.release()));
119 return newUndefAdded;
122 // Called on each atom when a file is added. Returns true if a given
123 // atom is added to the symbol table.
124 void Resolver::doDefinedAtom(OwningAtomPtr<DefinedAtom> atom) {
125 DEBUG_WITH_TYPE("resolver", llvm::dbgs()
127 << llvm::format("0x%09lX", atom.get())
129 << atom.get()->file().ordinal()
131 << atom.get()->ordinal()
133 << atom.get()->name()
135 << atom.get()->contentType()
138 // An atom that should never be dead-stripped is a dead-strip root.
139 if (_ctx.deadStrip() &&
140 atom.get()->deadStrip() == DefinedAtom::deadStripNever) {
141 _deadStripRoots.insert(atom.get());
144 // add to list of known atoms
145 _symbolTable.add(*atom.get());
146 _atoms.push_back(OwningAtomPtr<Atom>(atom.release()));
149 void Resolver::doSharedLibraryAtom(OwningAtomPtr<SharedLibraryAtom> atom) {
150 DEBUG_WITH_TYPE("resolver", llvm::dbgs()
151 << " SharedLibraryAtom: "
152 << llvm::format("0x%09lX", atom.get())
154 << atom.get()->name()
158 _symbolTable.add(*atom.get());
160 // add to list of known atoms
161 _atoms.push_back(OwningAtomPtr<Atom>(atom.release()));
164 void Resolver::doAbsoluteAtom(OwningAtomPtr<AbsoluteAtom> atom) {
165 DEBUG_WITH_TYPE("resolver", llvm::dbgs()
167 << llvm::format("0x%09lX", atom.get())
169 << atom.get()->name()
173 if (atom.get()->scope() != Atom::scopeTranslationUnit)
174 _symbolTable.add(*atom.get());
176 // add to list of known atoms
177 _atoms.push_back(OwningAtomPtr<Atom>(atom.release()));
180 // Returns true if at least one of N previous files has created an
182 bool Resolver::undefinesAdded(int begin, int end) {
183 std::vector<std::unique_ptr<Node>> &inputs = _ctx.getNodes();
184 for (int i = begin; i < end; ++i)
185 if (FileNode *node = dyn_cast<FileNode>(inputs[i].get()))
186 if (_newUndefinesAdded[node->getFile()])
191 File *Resolver::getFile(int &index) {
192 std::vector<std::unique_ptr<Node>> &inputs = _ctx.getNodes();
193 if ((size_t)index >= inputs.size())
195 if (GroupEnd *group = dyn_cast<GroupEnd>(inputs[index].get())) {
196 // We are at the end of the current group. If one or more new
197 // undefined atom has been added in the last groupSize files, we
198 // reiterate over the files.
199 int size = group->getSize();
200 if (undefinesAdded(index - size, index)) {
202 return getFile(index);
205 return getFile(index);
207 return cast<FileNode>(inputs[index++].get())->getFile();
210 // Keep adding atoms until _ctx.getNextFile() returns an error. This
211 // function is where undefined atoms are resolved.
212 bool Resolver::resolveUndefines() {
213 DEBUG_WITH_TYPE("resolver",
214 llvm::dbgs() << "******** Resolving undefines:\n");
215 ScopedTask task(getDefaultDomain(), "resolveUndefines");
217 std::set<File *> seen;
219 bool undefAdded = false;
220 DEBUG_WITH_TYPE("resolver",
221 llvm::dbgs() << "Loading file #" << index << "\n");
222 File *file = getFile(index);
225 if (std::error_code ec = file->parse()) {
226 llvm::errs() << "Cannot open " + file->path()
227 << ": " << ec.message() << "\n";
230 DEBUG_WITH_TYPE("resolver",
231 llvm::dbgs() << "Loaded file: " << file->path() << "\n");
232 switch (file->kind()) {
233 case File::kindErrorObject:
234 case File::kindNormalizedObject:
235 case File::kindMachObject:
236 case File::kindCEntryObject:
237 case File::kindHeaderObject:
238 case File::kindEntryObject:
239 case File::kindUndefinedSymsObject:
240 case File::kindStubHelperObject:
241 case File::kindResolverMergedObject:
242 case File::kindSectCreateObject: {
243 // The same file may be visited more than once if the file is
244 // in --start-group and --end-group. Only library files should
245 // be processed more than once.
246 if (seen.count(file))
249 assert(!file->hasOrdinal());
250 file->setOrdinal(_ctx.getNextOrdinalAndIncrement());
251 auto undefAddedOrError = handleFile(*file);
252 if (auto EC = undefAddedOrError.takeError()) {
253 // FIXME: This should be passed to logAllUnhandledErrors but it needs
254 // to be passed a Twine instead of a string.
255 llvm::errs() << "Error in " + file->path() << ": ";
256 logAllUnhandledErrors(std::move(EC), llvm::errs(), std::string());
259 undefAdded = undefAddedOrError.get();
262 case File::kindArchiveLibrary: {
263 if (!file->hasOrdinal())
264 file->setOrdinal(_ctx.getNextOrdinalAndIncrement());
265 auto undefAddedOrError = handleArchiveFile(*file);
266 if (auto EC = undefAddedOrError.takeError()) {
267 // FIXME: This should be passed to logAllUnhandledErrors but it needs
268 // to be passed a Twine instead of a string.
269 llvm::errs() << "Error in " + file->path() << ": ";
270 logAllUnhandledErrors(std::move(EC), llvm::errs(), std::string());
273 undefAdded = undefAddedOrError.get();
276 case File::kindSharedLibrary:
277 if (!file->hasOrdinal())
278 file->setOrdinal(_ctx.getNextOrdinalAndIncrement());
279 if (auto EC = handleSharedLibrary(*file)) {
280 // FIXME: This should be passed to logAllUnhandledErrors but it needs
281 // to be passed a Twine instead of a string.
282 llvm::errs() << "Error in " + file->path() << ": ";
283 logAllUnhandledErrors(std::move(EC), llvm::errs(), std::string());
288 _newUndefinesAdded[file] = undefAdded;
292 // switch all references to undefined or coalesced away atoms
293 // to the new defined atom
294 void Resolver::updateReferences() {
295 DEBUG_WITH_TYPE("resolver",
296 llvm::dbgs() << "******** Updating references:\n");
297 ScopedTask task(getDefaultDomain(), "updateReferences");
298 for (const OwningAtomPtr<Atom> &atom : _atoms) {
299 if (const DefinedAtom *defAtom = dyn_cast<DefinedAtom>(atom.get())) {
300 for (const Reference *ref : *defAtom) {
301 // A reference of type kindAssociate should't be updated.
302 // Instead, an atom having such reference will be removed
303 // if the target atom is coalesced away, so that they will
304 // go away as a group.
305 if (ref->kindNamespace() == lld::Reference::KindNamespace::all &&
306 ref->kindValue() == lld::Reference::kindAssociate) {
307 if (_symbolTable.isCoalescedAway(atom.get()))
308 _deadAtoms.insert(ref->target());
311 const Atom *newTarget = _symbolTable.replacement(ref->target());
312 const_cast<Reference *>(ref)->setTarget(newTarget);
318 // For dead code stripping, recursively mark atoms "live"
319 void Resolver::markLive(const Atom *atom) {
320 // Mark the atom is live. If it's already marked live, then stop recursion.
321 auto exists = _liveAtoms.insert(atom);
325 // Mark all atoms it references as live
326 if (const DefinedAtom *defAtom = dyn_cast<DefinedAtom>(atom)) {
327 for (const Reference *ref : *defAtom)
328 markLive(ref->target());
329 for (auto &p : llvm::make_range(_reverseRef.equal_range(defAtom))) {
330 const Atom *target = p.second;
336 static bool isBackref(const Reference *ref) {
337 if (ref->kindNamespace() != lld::Reference::KindNamespace::all)
339 return (ref->kindValue() == lld::Reference::kindLayoutAfter);
342 // remove all atoms not actually used
343 void Resolver::deadStripOptimize() {
344 DEBUG_WITH_TYPE("resolver",
345 llvm::dbgs() << "******** Dead stripping unused atoms:\n");
346 ScopedTask task(getDefaultDomain(), "deadStripOptimize");
347 // only do this optimization with -dead_strip
348 if (!_ctx.deadStrip())
351 // Some type of references prevent referring atoms to be dead-striped.
352 // Make a reverse map of such references before traversing the graph.
353 // While traversing the list of atoms, mark AbsoluteAtoms as live
354 // in order to avoid reclaim.
355 for (const OwningAtomPtr<Atom> &atom : _atoms) {
356 if (const DefinedAtom *defAtom = dyn_cast<DefinedAtom>(atom.get()))
357 for (const Reference *ref : *defAtom)
359 _reverseRef.insert(std::make_pair(ref->target(), atom.get()));
360 if (const AbsoluteAtom *absAtom = dyn_cast<AbsoluteAtom>(atom.get()))
364 // By default, shared libraries are built with all globals as dead strip roots
365 if (_ctx.globalsAreDeadStripRoots())
366 for (const OwningAtomPtr<Atom> &atom : _atoms)
367 if (const DefinedAtom *defAtom = dyn_cast<DefinedAtom>(atom.get()))
368 if (defAtom->scope() == DefinedAtom::scopeGlobal)
369 _deadStripRoots.insert(defAtom);
371 // Or, use list of names that are dead strip roots.
372 for (const StringRef &name : _ctx.deadStripRoots()) {
373 const Atom *symAtom = _symbolTable.findByName(name);
375 _deadStripRoots.insert(symAtom);
378 // mark all roots as live, and recursively all atoms they reference
379 for (const Atom *dsrAtom : _deadStripRoots)
382 // now remove all non-live atoms from _atoms
383 _atoms.erase(std::remove_if(_atoms.begin(), _atoms.end(),
384 [&](OwningAtomPtr<Atom> &a) {
385 return _liveAtoms.count(a.get()) == 0;
390 // error out if some undefines remain
391 bool Resolver::checkUndefines() {
392 DEBUG_WITH_TYPE("resolver",
393 llvm::dbgs() << "******** Checking for undefines:\n");
395 // build vector of remaining undefined symbols
396 std::vector<const UndefinedAtom *> undefinedAtoms = _symbolTable.undefines();
397 if (_ctx.deadStrip()) {
398 // When dead code stripping, we don't care if dead atoms are undefined.
399 undefinedAtoms.erase(
400 std::remove_if(undefinedAtoms.begin(), undefinedAtoms.end(),
401 [&](const Atom *a) { return _liveAtoms.count(a) == 0; }),
402 undefinedAtoms.end());
405 if (undefinedAtoms.empty())
408 // Warn about unresolved symbols.
409 bool foundUndefines = false;
410 for (const UndefinedAtom *undef : undefinedAtoms) {
411 // Skip over a weak symbol.
412 if (undef->canBeNull() != UndefinedAtom::canBeNullNever)
415 // If this is a library and undefined symbols are allowed on the
416 // target platform, skip over it.
417 if (isa<SharedLibraryFile>(undef->file()) && _ctx.allowShlibUndefines())
420 // If the undefine is coalesced away, skip over it.
421 if (_symbolTable.isCoalescedAway(undef))
424 // Seems like this symbol is undefined. Warn that.
425 foundUndefines = true;
426 if (_ctx.printRemainingUndefines()) {
427 llvm::errs() << "Undefined symbol: " << undef->file().path()
428 << ": " << _ctx.demangle(undef->name())
434 if (_ctx.printRemainingUndefines())
435 llvm::errs() << "symbol(s) not found\n";
439 // remove from _atoms all coaleseced away atoms
440 void Resolver::removeCoalescedAwayAtoms() {
441 DEBUG_WITH_TYPE("resolver",
442 llvm::dbgs() << "******** Removing coalesced away atoms:\n");
443 ScopedTask task(getDefaultDomain(), "removeCoalescedAwayAtoms");
444 _atoms.erase(std::remove_if(_atoms.begin(), _atoms.end(),
445 [&](OwningAtomPtr<Atom> &a) {
446 return _symbolTable.isCoalescedAway(a.get()) ||
447 _deadAtoms.count(a.get());
452 bool Resolver::resolve() {
453 DEBUG_WITH_TYPE("resolver",
454 llvm::dbgs() << "******** Resolving atom references:\n");
455 if (!resolveUndefines())
459 if (checkUndefines()) {
460 DEBUG_WITH_TYPE("resolver", llvm::dbgs() << "Found undefines... ");
461 if (!_ctx.allowRemainingUndefines()) {
462 DEBUG_WITH_TYPE("resolver", llvm::dbgs() << "which we don't allow\n");
465 DEBUG_WITH_TYPE("resolver", llvm::dbgs() << "which we are ok with\n");
467 removeCoalescedAwayAtoms();
468 _result->addAtoms(_atoms);
469 DEBUG_WITH_TYPE("resolver", llvm::dbgs() << "******** Finished resolver\n");
473 void Resolver::MergedFile::addAtoms(
474 llvm::MutableArrayRef<OwningAtomPtr<Atom>> all) {
475 ScopedTask task(getDefaultDomain(), "addAtoms");
476 DEBUG_WITH_TYPE("resolver", llvm::dbgs() << "Resolver final atom list:\n");
478 for (OwningAtomPtr<Atom> &atom : all) {
480 if (auto *definedAtom = dyn_cast<DefinedAtom>(atom.get())) {
481 DEBUG_WITH_TYPE("resolver", llvm::dbgs()
482 << llvm::format(" 0x%09lX", definedAtom)
484 << definedAtom->file().ordinal()
486 << definedAtom->ordinal()
488 << definedAtom->name()
490 << definedAtom->contentType()
493 DEBUG_WITH_TYPE("resolver", llvm::dbgs()
494 << llvm::format(" 0x%09lX", atom.get())
496 << atom.get()->name()
500 addAtom(*atom.release());