1 //===-- ReaderWriter/MachO/LayoutPass.cpp - Layout atoms ------------------===//
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 "LayoutPass.h"
10 #include "lld/Core/Instrumentation.h"
11 #include "lld/Core/PassManager.h"
12 #include "lld/ReaderWriter/MachOLinkingContext.h"
13 #include "llvm/ADT/STLExtras.h"
14 #include "llvm/ADT/Twine.h"
15 #include "llvm/Support/Debug.h"
16 #include "llvm/Support/Parallel.h"
23 #define DEBUG_TYPE "LayoutPass"
28 static bool compareAtoms(const LayoutPass::SortKey &,
29 const LayoutPass::SortKey &,
30 LayoutPass::SortOverride customSorter);
33 // Return "reason (leftval, rightval)"
34 static std::string formatReason(StringRef reason, int leftVal, int rightVal) {
35 return (Twine(reason) + " (" + Twine(leftVal) + ", " + Twine(rightVal) + ")")
39 // Less-than relationship of two atoms must be transitive, which is, if a < b
40 // and b < c, a < c must be true. This function checks the transitivity by
41 // checking the sort results.
42 static void checkTransitivity(std::vector<LayoutPass::SortKey> &vec,
43 LayoutPass::SortOverride customSorter) {
44 for (auto i = vec.begin(), e = vec.end(); (i + 1) != e; ++i) {
45 for (auto j = i + 1; j != e; ++j) {
46 assert(compareAtoms(*i, *j, customSorter));
47 assert(!compareAtoms(*j, *i, customSorter));
52 // Helper functions to check follow-on graph.
53 typedef llvm::DenseMap<const DefinedAtom *, const DefinedAtom *> AtomToAtomT;
55 static std::string atomToDebugString(const Atom *atom) {
56 const DefinedAtom *definedAtom = dyn_cast<DefinedAtom>(atom);
58 llvm::raw_string_ostream s(str);
59 if (definedAtom->name().empty())
60 s << "<anonymous " << definedAtom << ">";
62 s << definedAtom->name();
64 if (definedAtom->customSectionName().empty())
67 s << definedAtom->customSectionName();
72 static void showCycleDetectedError(const Registry ®istry,
73 AtomToAtomT &followOnNexts,
74 const DefinedAtom *atom) {
75 const DefinedAtom *start = atom;
76 llvm::dbgs() << "There's a cycle in a follow-on chain!\n";
78 llvm::dbgs() << " " << atomToDebugString(atom) << "\n";
79 for (const Reference *ref : *atom) {
81 if (!registry.referenceKindToString(ref->kindNamespace(), ref->kindArch(),
82 ref->kindValue(), kindValStr)) {
83 kindValStr = "<unknown>";
85 llvm::dbgs() << " " << kindValStr
86 << ": " << atomToDebugString(ref->target()) << "\n";
88 atom = followOnNexts[atom];
89 } while (atom != start);
90 llvm::report_fatal_error("Cycle detected");
93 /// Exit if there's a cycle in a followon chain reachable from the
94 /// given root atom. Uses the tortoise and hare algorithm to detect a
96 static void checkNoCycleInFollowonChain(const Registry ®istry,
97 AtomToAtomT &followOnNexts,
98 const DefinedAtom *root) {
99 const DefinedAtom *tortoise = root;
100 const DefinedAtom *hare = followOnNexts[root];
102 if (!tortoise || !hare)
104 if (tortoise == hare)
105 showCycleDetectedError(registry, followOnNexts, tortoise);
106 tortoise = followOnNexts[tortoise];
107 hare = followOnNexts[followOnNexts[hare]];
111 static void checkReachabilityFromRoot(AtomToAtomT &followOnRoots,
112 const DefinedAtom *atom) {
114 auto i = followOnRoots.find(atom);
115 if (i == followOnRoots.end()) {
116 llvm_unreachable(((Twine("Atom <") + atomToDebugString(atom) +
117 "> has no follow-on root!"))
121 const DefinedAtom *ap = i->second;
123 const DefinedAtom *next = followOnRoots[ap];
125 llvm_unreachable((Twine("Atom <" + atomToDebugString(atom) +
126 "> is not reachable from its root!"))
136 static void printDefinedAtoms(const File::AtomRange<DefinedAtom> &atomRange) {
137 for (const DefinedAtom *atom : atomRange) {
138 llvm::dbgs() << " file=" << atom->file().path()
139 << ", name=" << atom->name()
140 << ", size=" << atom->size()
141 << ", type=" << atom->contentType()
142 << ", ordinal=" << atom->ordinal()
147 /// Verify that the followon chain is sane. Should not be called in
149 void LayoutPass::checkFollowonChain(const File::AtomRange<DefinedAtom> &range) {
150 ScopedTask task(getDefaultDomain(), "LayoutPass::checkFollowonChain");
152 // Verify that there's no cycle in follow-on chain.
153 std::set<const DefinedAtom *> roots;
154 for (const auto &ai : _followOnRoots)
155 roots.insert(ai.second);
156 for (const DefinedAtom *root : roots)
157 checkNoCycleInFollowonChain(_registry, _followOnNexts, root);
159 // Verify that all the atoms in followOnNexts have references to
161 for (const auto &ai : _followOnNexts) {
162 checkReachabilityFromRoot(_followOnRoots, ai.first);
163 checkReachabilityFromRoot(_followOnRoots, ai.second);
166 #endif // #ifndef NDEBUG
168 /// The function compares atoms by sorting atoms in the following order
169 /// a) Sorts atoms by their ordinal overrides (layout-after/ingroup)
170 /// b) Sorts atoms by their permissions
171 /// c) Sorts atoms by their content
172 /// d) Sorts atoms by custom sorter
173 /// e) Sorts atoms on how they appear using File Ordinality
174 /// f) Sorts atoms on how they appear within the File
175 static bool compareAtomsSub(const LayoutPass::SortKey &lc,
176 const LayoutPass::SortKey &rc,
177 LayoutPass::SortOverride customSorter,
178 std::string &reason) {
179 const DefinedAtom *left = lc._atom.get();
180 const DefinedAtom *right = rc._atom.get();
186 // Find the root of the chain if it is a part of a follow-on chain.
187 const DefinedAtom *leftRoot = lc._root;
188 const DefinedAtom *rightRoot = rc._root;
190 // Sort atoms by their ordinal overrides only if they fall in the same
192 if (leftRoot == rightRoot) {
193 LLVM_DEBUG(reason = formatReason("override", lc._override, rc._override));
194 return lc._override < rc._override;
197 // Sort same permissions together.
198 DefinedAtom::ContentPermissions leftPerms = leftRoot->permissions();
199 DefinedAtom::ContentPermissions rightPerms = rightRoot->permissions();
201 if (leftPerms != rightPerms) {
203 reason = formatReason("contentPerms", (int)leftPerms, (int)rightPerms));
204 return leftPerms < rightPerms;
207 // Sort same content types together.
208 DefinedAtom::ContentType leftType = leftRoot->contentType();
209 DefinedAtom::ContentType rightType = rightRoot->contentType();
211 if (leftType != rightType) {
213 formatReason("contentType", (int)leftType, (int)rightType));
214 return leftType < rightType;
217 // Use custom sorter if supplied.
219 bool leftBeforeRight;
220 if (customSorter(leftRoot, rightRoot, leftBeforeRight))
221 return leftBeforeRight;
225 const File *leftFile = &leftRoot->file();
226 const File *rightFile = &rightRoot->file();
228 if (leftFile != rightFile) {
229 LLVM_DEBUG(reason = formatReason(".o order", (int)leftFile->ordinal(),
230 (int)rightFile->ordinal()));
231 return leftFile->ordinal() < rightFile->ordinal();
234 // Sort by atom order with .o file.
235 uint64_t leftOrdinal = leftRoot->ordinal();
236 uint64_t rightOrdinal = rightRoot->ordinal();
238 if (leftOrdinal != rightOrdinal) {
239 LLVM_DEBUG(reason = formatReason("ordinal", (int)leftRoot->ordinal(),
240 (int)rightRoot->ordinal()));
241 return leftOrdinal < rightOrdinal;
244 llvm::errs() << "Unordered: <" << left->name() << "> <"
245 << right->name() << ">\n";
246 llvm_unreachable("Atoms with Same Ordinal!");
249 static bool compareAtoms(const LayoutPass::SortKey &lc,
250 const LayoutPass::SortKey &rc,
251 LayoutPass::SortOverride customSorter) {
253 bool result = compareAtomsSub(lc, rc, customSorter, reason);
255 StringRef comp = result ? "<" : ">=";
256 llvm::dbgs() << "Layout: '" << lc._atom.get()->name()
257 << "' " << comp << " '"
258 << rc._atom.get()->name() << "' (" << reason << ")\n";
263 LayoutPass::LayoutPass(const Registry ®istry, SortOverride sorter)
264 : _registry(registry), _customSorter(std::move(sorter)) {}
266 // Returns the atom immediately followed by the given atom in the followon
268 const DefinedAtom *LayoutPass::findAtomFollowedBy(
269 const DefinedAtom *targetAtom) {
270 // Start from the beginning of the chain and follow the chain until
271 // we find the targetChain.
272 const DefinedAtom *atom = _followOnRoots[targetAtom];
274 const DefinedAtom *prevAtom = atom;
275 AtomToAtomT::iterator targetFollowOnAtomsIter = _followOnNexts.find(atom);
276 // The target atom must be in the chain of its root.
277 assert(targetFollowOnAtomsIter != _followOnNexts.end());
278 atom = targetFollowOnAtomsIter->second;
279 if (atom == targetAtom)
284 // Check if all the atoms followed by the given target atom are of size zero.
285 // When this method is called, an atom being added is not of size zero and
286 // will be added to the head of the followon chain. All the atoms between the
287 // atom and the targetAtom (specified by layout-after) need to be of size zero
288 // in this case. Otherwise the desired layout is impossible.
289 bool LayoutPass::checkAllPrevAtomsZeroSize(const DefinedAtom *targetAtom) {
290 const DefinedAtom *atom = _followOnRoots[targetAtom];
292 if (atom == targetAtom)
294 if (atom->size() != 0)
295 // TODO: print warning that an impossible layout is being desired by the
298 AtomToAtomT::iterator targetFollowOnAtomsIter = _followOnNexts.find(atom);
299 // The target atom must be in the chain of its root.
300 assert(targetFollowOnAtomsIter != _followOnNexts.end());
301 atom = targetFollowOnAtomsIter->second;
305 // Set the root of all atoms in targetAtom's chain to the given root.
306 void LayoutPass::setChainRoot(const DefinedAtom *targetAtom,
307 const DefinedAtom *root) {
308 // Walk through the followon chain and override each node's root.
310 _followOnRoots[targetAtom] = root;
311 AtomToAtomT::iterator targetFollowOnAtomsIter =
312 _followOnNexts.find(targetAtom);
313 if (targetFollowOnAtomsIter == _followOnNexts.end())
315 targetAtom = targetFollowOnAtomsIter->second;
319 /// This pass builds the followon tables described by two DenseMaps
320 /// followOnRoots and followonNexts.
321 /// The followOnRoots map contains a mapping of a DefinedAtom to its root
322 /// The followOnNexts map contains a mapping of what DefinedAtom follows the
324 /// The algorithm follows a very simple approach
325 /// a) If the atom is first seen, then make that as the root atom
326 /// b) The targetAtom which this Atom contains, has the root thats set to the
327 /// root of the current atom
328 /// c) If the targetAtom is part of a different tree and the root of the
329 /// targetAtom is itself, Chain all the atoms that are contained in the tree
330 /// to the current Tree
331 /// d) If the targetAtom is part of a different chain and the root of the
332 /// targetAtom until the targetAtom has all atoms of size 0, then chain the
333 /// targetAtoms and its tree to the current chain
334 void LayoutPass::buildFollowOnTable(const File::AtomRange<DefinedAtom> &range) {
335 ScopedTask task(getDefaultDomain(), "LayoutPass::buildFollowOnTable");
336 // Set the initial size of the followon and the followonNext hash to the
337 // number of atoms that we have.
338 _followOnRoots.reserve(range.size());
339 _followOnNexts.reserve(range.size());
340 for (const DefinedAtom *ai : range) {
341 for (const Reference *r : *ai) {
342 if (r->kindNamespace() != lld::Reference::KindNamespace::all ||
343 r->kindValue() != lld::Reference::kindLayoutAfter)
345 const DefinedAtom *targetAtom = dyn_cast<DefinedAtom>(r->target());
346 _followOnNexts[ai] = targetAtom;
348 // If we find a followon for the first time, let's make that atom as the
350 if (_followOnRoots.count(ai) == 0)
351 _followOnRoots[ai] = ai;
353 auto iter = _followOnRoots.find(targetAtom);
354 if (iter == _followOnRoots.end()) {
355 // If the targetAtom is not a root of any chain, let's make the root of
356 // the targetAtom to the root of the current chain.
358 // The expression m[i] = m[j] where m is a DenseMap and i != j is not
359 // safe. m[j] returns a reference, which would be invalidated when a
360 // rehashing occurs. If rehashing occurs to make room for m[i], m[j]
361 // becomes invalid, and that invalid reference would be used as the RHS
362 // value of the expression.
363 // Copy the value to workaround.
364 const DefinedAtom *tmp = _followOnRoots[ai];
365 _followOnRoots[targetAtom] = tmp;
368 if (iter->second == targetAtom) {
369 // If the targetAtom is the root of a chain, the chain becomes part of
370 // the current chain. Rewrite the subchain's root to the current
372 setChainRoot(targetAtom, _followOnRoots[ai]);
375 // The targetAtom is already a part of a chain. If the current atom is
376 // of size zero, we can insert it in the middle of the chain just
377 // before the target atom, while not breaking other atom's followon
378 // relationships. If it's not, we can only insert the current atom at
379 // the beginning of the chain. All the atoms followed by the target
380 // atom must be of size zero in that case to satisfy the followon
382 size_t currentAtomSize = ai->size();
383 if (currentAtomSize == 0) {
384 const DefinedAtom *targetPrevAtom = findAtomFollowedBy(targetAtom);
385 _followOnNexts[targetPrevAtom] = ai;
386 const DefinedAtom *tmp = _followOnRoots[targetPrevAtom];
387 _followOnRoots[ai] = tmp;
390 if (!checkAllPrevAtomsZeroSize(targetAtom))
392 _followOnNexts[ai] = _followOnRoots[targetAtom];
393 setChainRoot(_followOnRoots[targetAtom], _followOnRoots[ai]);
398 /// Build an ordinal override map by traversing the followon chain, and
399 /// assigning ordinals to each atom, if the atoms have their ordinals
400 /// already assigned skip the atom and move to the next. This is the
401 /// main map thats used to sort the atoms while comparing two atoms together
403 LayoutPass::buildOrdinalOverrideMap(const File::AtomRange<DefinedAtom> &range) {
404 ScopedTask task(getDefaultDomain(), "LayoutPass::buildOrdinalOverrideMap");
406 for (const DefinedAtom *ai : range) {
407 const DefinedAtom *atom = ai;
408 if (_ordinalOverrideMap.find(atom) != _ordinalOverrideMap.end())
410 AtomToAtomT::iterator start = _followOnRoots.find(atom);
411 if (start == _followOnRoots.end())
413 for (const DefinedAtom *nextAtom = start->second; nextAtom;
414 nextAtom = _followOnNexts[nextAtom]) {
415 AtomToOrdinalT::iterator pos = _ordinalOverrideMap.find(nextAtom);
416 if (pos == _ordinalOverrideMap.end())
417 _ordinalOverrideMap[nextAtom] = index++;
422 std::vector<LayoutPass::SortKey>
423 LayoutPass::decorate(File::AtomRange<DefinedAtom> &atomRange) const {
424 std::vector<SortKey> ret;
425 for (OwningAtomPtr<DefinedAtom> &atom : atomRange.owning_ptrs()) {
426 auto ri = _followOnRoots.find(atom.get());
427 auto oi = _ordinalOverrideMap.find(atom.get());
428 const auto *root = (ri == _followOnRoots.end()) ? atom.get() : ri->second;
429 uint64_t override = (oi == _ordinalOverrideMap.end()) ? 0 : oi->second;
430 ret.push_back(SortKey(std::move(atom), root, override));
435 void LayoutPass::undecorate(File::AtomRange<DefinedAtom> &atomRange,
436 std::vector<SortKey> &keys) const {
438 for (SortKey &k : keys)
439 atomRange[i++] = std::move(k._atom);
442 /// Perform the actual pass
443 llvm::Error LayoutPass::perform(SimpleFile &mergedFile) {
444 LLVM_DEBUG(llvm::dbgs() << "******** Laying out atoms:\n");
446 ScopedTask task(getDefaultDomain(), "LayoutPass");
447 File::AtomRange<DefinedAtom> atomRange = mergedFile.defined();
449 // Build follow on tables
450 buildFollowOnTable(atomRange);
452 // Check the structure of followon graph if running in debug mode.
453 LLVM_DEBUG(checkFollowonChain(atomRange));
455 // Build override maps
456 buildOrdinalOverrideMap(atomRange);
459 llvm::dbgs() << "unsorted atoms:\n";
460 printDefinedAtoms(atomRange);
463 std::vector<LayoutPass::SortKey> vec = decorate(atomRange);
464 sort(llvm::parallel::par, vec.begin(), vec.end(),
465 [&](const LayoutPass::SortKey &l, const LayoutPass::SortKey &r) -> bool {
466 return compareAtoms(l, r, _customSorter);
468 LLVM_DEBUG(checkTransitivity(vec, _customSorter));
469 undecorate(atomRange, vec);
472 llvm::dbgs() << "sorted atoms:\n";
473 printDefinedAtoms(atomRange);
476 LLVM_DEBUG(llvm::dbgs() << "******** Finished laying out atoms\n");
477 return llvm::Error::success();
480 void addLayoutPass(PassManager &pm, const MachOLinkingContext &ctx) {
481 pm.add(llvm::make_unique<LayoutPass>(
482 ctx.registry(), [&](const DefinedAtom * left, const DefinedAtom * right,
483 bool & leftBeforeRight) ->bool {
484 return ctx.customAtomOrderer(left, right, leftBeforeRight);
488 } // namespace mach_o