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diff --git a/lib/ReaderWriter/MachO/LayoutPass.cpp b/lib/ReaderWriter/MachO/LayoutPass.cpp
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+//===-- ReaderWriter/MachO/LayoutPass.cpp - Layout atoms ------------------===//
+//
+// The LLVM Linker
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "LayoutPass.h"
+#include "lld/Core/Instrumentation.h"
+#include "lld/Core/Parallel.h"
+#include "lld/Core/PassManager.h"
+#include "lld/ReaderWriter/MachOLinkingContext.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/Twine.h"
+#include "llvm/Support/Debug.h"
+#include <algorithm>
+#include <set>
+
+using namespace lld;
+
+#define DEBUG_TYPE "LayoutPass"
+
+namespace lld {
+namespace mach_o {
+
+static bool compareAtoms(const LayoutPass::SortKey &,
+ const LayoutPass::SortKey &,
+ LayoutPass::SortOverride customSorter);
+
+#ifndef NDEBUG
+// Return "reason (leftval, rightval)"
+static std::string formatReason(StringRef reason, int leftVal, int rightVal) {
+ return (Twine(reason) + " (" + Twine(leftVal) + ", " + Twine(rightVal) + ")")
+ .str();
+}
+
+// Less-than relationship of two atoms must be transitive, which is, if a < b
+// and b < c, a < c must be true. This function checks the transitivity by
+// checking the sort results.
+static void checkTransitivity(std::vector<LayoutPass::SortKey> &vec,
+ LayoutPass::SortOverride customSorter) {
+ for (auto i = vec.begin(), e = vec.end(); (i + 1) != e; ++i) {
+ for (auto j = i + 1; j != e; ++j) {
+ assert(compareAtoms(*i, *j, customSorter));
+ assert(!compareAtoms(*j, *i, customSorter));
+ }
+ }
+}
+
+// Helper functions to check follow-on graph.
+typedef llvm::DenseMap<const DefinedAtom *, const DefinedAtom *> AtomToAtomT;
+
+static std::string atomToDebugString(const Atom *atom) {
+ const DefinedAtom *definedAtom = dyn_cast<DefinedAtom>(atom);
+ std::string str;
+ llvm::raw_string_ostream s(str);
+ if (definedAtom->name().empty())
+ s << "<anonymous " << definedAtom << ">";
+ else
+ s << definedAtom->name();
+ s << " in ";
+ if (definedAtom->customSectionName().empty())
+ s << "<anonymous>";
+ else
+ s << definedAtom->customSectionName();
+ s.flush();
+ return str;
+}
+
+static void showCycleDetectedError(const Registry &registry,
+ AtomToAtomT &followOnNexts,
+ const DefinedAtom *atom) {
+ const DefinedAtom *start = atom;
+ llvm::dbgs() << "There's a cycle in a follow-on chain!\n";
+ do {
+ llvm::dbgs() << " " << atomToDebugString(atom) << "\n";
+ for (const Reference *ref : *atom) {
+ StringRef kindValStr;
+ if (!registry.referenceKindToString(ref->kindNamespace(), ref->kindArch(),
+ ref->kindValue(), kindValStr)) {
+ kindValStr = "<unknown>";
+ }
+ llvm::dbgs() << " " << kindValStr
+ << ": " << atomToDebugString(ref->target()) << "\n";
+ }
+ atom = followOnNexts[atom];
+ } while (atom != start);
+ llvm::report_fatal_error("Cycle detected");
+}
+
+/// Exit if there's a cycle in a followon chain reachable from the
+/// given root atom. Uses the tortoise and hare algorithm to detect a
+/// cycle.
+static void checkNoCycleInFollowonChain(const Registry &registry,
+ AtomToAtomT &followOnNexts,
+ const DefinedAtom *root) {
+ const DefinedAtom *tortoise = root;
+ const DefinedAtom *hare = followOnNexts[root];
+ while (true) {
+ if (!tortoise || !hare)
+ return;
+ if (tortoise == hare)
+ showCycleDetectedError(registry, followOnNexts, tortoise);
+ tortoise = followOnNexts[tortoise];
+ hare = followOnNexts[followOnNexts[hare]];
+ }
+}
+
+static void checkReachabilityFromRoot(AtomToAtomT &followOnRoots,
+ const DefinedAtom *atom) {
+ if (!atom) return;
+ auto i = followOnRoots.find(atom);
+ if (i == followOnRoots.end()) {
+ llvm_unreachable(((Twine("Atom <") + atomToDebugString(atom) +
+ "> has no follow-on root!"))
+ .str()
+ .c_str());
+ }
+ const DefinedAtom *ap = i->second;
+ while (true) {
+ const DefinedAtom *next = followOnRoots[ap];
+ if (!next) {
+ llvm_unreachable((Twine("Atom <" + atomToDebugString(atom) +
+ "> is not reachable from its root!"))
+ .str()
+ .c_str());
+ }
+ if (next == ap)
+ return;
+ ap = next;
+ }
+}
+
+static void printDefinedAtoms(const MutableFile::DefinedAtomRange &atomRange) {
+ for (const DefinedAtom *atom : atomRange) {
+ llvm::dbgs() << " file=" << atom->file().path()
+ << ", name=" << atom->name()
+ << ", size=" << atom->size()
+ << ", type=" << atom->contentType()
+ << ", ordinal=" << atom->ordinal()
+ << "\n";
+ }
+}
+
+/// Verify that the followon chain is sane. Should not be called in
+/// release binary.
+void LayoutPass::checkFollowonChain(MutableFile::DefinedAtomRange &range) {
+ ScopedTask task(getDefaultDomain(), "LayoutPass::checkFollowonChain");
+
+ // Verify that there's no cycle in follow-on chain.
+ std::set<const DefinedAtom *> roots;
+ for (const auto &ai : _followOnRoots)
+ roots.insert(ai.second);
+ for (const DefinedAtom *root : roots)
+ checkNoCycleInFollowonChain(_registry, _followOnNexts, root);
+
+ // Verify that all the atoms in followOnNexts have references to
+ // their roots.
+ for (const auto &ai : _followOnNexts) {
+ checkReachabilityFromRoot(_followOnRoots, ai.first);
+ checkReachabilityFromRoot(_followOnRoots, ai.second);
+ }
+}
+#endif // #ifndef NDEBUG
+
+/// The function compares atoms by sorting atoms in the following order
+/// a) Sorts atoms by their ordinal overrides (layout-after/ingroup)
+/// b) Sorts atoms by their permissions
+/// c) Sorts atoms by their content
+/// d) Sorts atoms by custom sorter
+/// e) Sorts atoms on how they appear using File Ordinality
+/// f) Sorts atoms on how they appear within the File
+static bool compareAtomsSub(const LayoutPass::SortKey &lc,
+ const LayoutPass::SortKey &rc,
+ LayoutPass::SortOverride customSorter,
+ std::string &reason) {
+ const DefinedAtom *left = lc._atom;
+ const DefinedAtom *right = rc._atom;
+ if (left == right) {
+ reason = "same";
+ return false;
+ }
+
+ // Find the root of the chain if it is a part of a follow-on chain.
+ const DefinedAtom *leftRoot = lc._root;
+ const DefinedAtom *rightRoot = rc._root;
+
+ // Sort atoms by their ordinal overrides only if they fall in the same
+ // chain.
+ if (leftRoot == rightRoot) {
+ DEBUG(reason = formatReason("override", lc._override, rc._override));
+ return lc._override < rc._override;
+ }
+
+ // Sort same permissions together.
+ DefinedAtom::ContentPermissions leftPerms = leftRoot->permissions();
+ DefinedAtom::ContentPermissions rightPerms = rightRoot->permissions();
+
+ if (leftPerms != rightPerms) {
+ DEBUG(reason =
+ formatReason("contentPerms", (int)leftPerms, (int)rightPerms));
+ return leftPerms < rightPerms;
+ }
+
+ // Sort same content types together.
+ DefinedAtom::ContentType leftType = leftRoot->contentType();
+ DefinedAtom::ContentType rightType = rightRoot->contentType();
+
+ if (leftType != rightType) {
+ DEBUG(reason = formatReason("contentType", (int)leftType, (int)rightType));
+ return leftType < rightType;
+ }
+
+ // Use custom sorter if supplied.
+ if (customSorter) {
+ bool leftBeforeRight;
+ if (customSorter(leftRoot, rightRoot, leftBeforeRight))
+ return leftBeforeRight;
+ }
+
+ // Sort by .o order.
+ const File *leftFile = &leftRoot->file();
+ const File *rightFile = &rightRoot->file();
+
+ if (leftFile != rightFile) {
+ DEBUG(reason = formatReason(".o order", (int)leftFile->ordinal(),
+ (int)rightFile->ordinal()));
+ return leftFile->ordinal() < rightFile->ordinal();
+ }
+
+ // Sort by atom order with .o file.
+ uint64_t leftOrdinal = leftRoot->ordinal();
+ uint64_t rightOrdinal = rightRoot->ordinal();
+
+ if (leftOrdinal != rightOrdinal) {
+ DEBUG(reason = formatReason("ordinal", (int)leftRoot->ordinal(),
+ (int)rightRoot->ordinal()));
+ return leftOrdinal < rightOrdinal;
+ }
+
+ llvm::errs() << "Unordered: <" << left->name() << "> <"
+ << right->name() << ">\n";
+ llvm_unreachable("Atoms with Same Ordinal!");
+}
+
+static bool compareAtoms(const LayoutPass::SortKey &lc,
+ const LayoutPass::SortKey &rc,
+ LayoutPass::SortOverride customSorter) {
+ std::string reason;
+ bool result = compareAtomsSub(lc, rc, customSorter, reason);
+ DEBUG({
+ StringRef comp = result ? "<" : ">=";
+ llvm::dbgs() << "Layout: '" << lc._atom->name() << "' " << comp << " '"
+ << rc._atom->name() << "' (" << reason << ")\n";
+ });
+ return result;
+}
+
+LayoutPass::LayoutPass(const Registry &registry, SortOverride sorter)
+ : _registry(registry), _customSorter(sorter) {}
+
+// Returns the atom immediately followed by the given atom in the followon
+// chain.
+const DefinedAtom *LayoutPass::findAtomFollowedBy(
+ const DefinedAtom *targetAtom) {
+ // Start from the beginning of the chain and follow the chain until
+ // we find the targetChain.
+ const DefinedAtom *atom = _followOnRoots[targetAtom];
+ while (true) {
+ const DefinedAtom *prevAtom = atom;
+ AtomToAtomT::iterator targetFollowOnAtomsIter = _followOnNexts.find(atom);
+ // The target atom must be in the chain of its root.
+ assert(targetFollowOnAtomsIter != _followOnNexts.end());
+ atom = targetFollowOnAtomsIter->second;
+ if (atom == targetAtom)
+ return prevAtom;
+ }
+}
+
+// Check if all the atoms followed by the given target atom are of size zero.
+// When this method is called, an atom being added is not of size zero and
+// will be added to the head of the followon chain. All the atoms between the
+// atom and the targetAtom (specified by layout-after) need to be of size zero
+// in this case. Otherwise the desired layout is impossible.
+bool LayoutPass::checkAllPrevAtomsZeroSize(const DefinedAtom *targetAtom) {
+ const DefinedAtom *atom = _followOnRoots[targetAtom];
+ while (true) {
+ if (atom == targetAtom)
+ return true;
+ if (atom->size() != 0)
+ // TODO: print warning that an impossible layout is being desired by the
+ // user.
+ return false;
+ AtomToAtomT::iterator targetFollowOnAtomsIter = _followOnNexts.find(atom);
+ // The target atom must be in the chain of its root.
+ assert(targetFollowOnAtomsIter != _followOnNexts.end());
+ atom = targetFollowOnAtomsIter->second;
+ }
+}
+
+// Set the root of all atoms in targetAtom's chain to the given root.
+void LayoutPass::setChainRoot(const DefinedAtom *targetAtom,
+ const DefinedAtom *root) {
+ // Walk through the followon chain and override each node's root.
+ while (true) {
+ _followOnRoots[targetAtom] = root;
+ AtomToAtomT::iterator targetFollowOnAtomsIter =
+ _followOnNexts.find(targetAtom);
+ if (targetFollowOnAtomsIter == _followOnNexts.end())
+ return;
+ targetAtom = targetFollowOnAtomsIter->second;
+ }
+}
+
+/// This pass builds the followon tables described by two DenseMaps
+/// followOnRoots and followonNexts.
+/// The followOnRoots map contains a mapping of a DefinedAtom to its root
+/// The followOnNexts map contains a mapping of what DefinedAtom follows the
+/// current Atom
+/// The algorithm follows a very simple approach
+/// a) If the atom is first seen, then make that as the root atom
+/// b) The targetAtom which this Atom contains, has the root thats set to the
+/// root of the current atom
+/// c) If the targetAtom is part of a different tree and the root of the
+/// targetAtom is itself, Chain all the atoms that are contained in the tree
+/// to the current Tree
+/// d) If the targetAtom is part of a different chain and the root of the
+/// targetAtom until the targetAtom has all atoms of size 0, then chain the
+/// targetAtoms and its tree to the current chain
+void LayoutPass::buildFollowOnTable(MutableFile::DefinedAtomRange &range) {
+ ScopedTask task(getDefaultDomain(), "LayoutPass::buildFollowOnTable");
+ // Set the initial size of the followon and the followonNext hash to the
+ // number of atoms that we have.
+ _followOnRoots.resize(range.size());
+ _followOnNexts.resize(range.size());
+ for (const DefinedAtom *ai : range) {
+ for (const Reference *r : *ai) {
+ if (r->kindNamespace() != lld::Reference::KindNamespace::all ||
+ r->kindValue() != lld::Reference::kindLayoutAfter)
+ continue;
+ const DefinedAtom *targetAtom = dyn_cast<DefinedAtom>(r->target());
+ _followOnNexts[ai] = targetAtom;
+
+ // If we find a followon for the first time, let's make that atom as the
+ // root atom.
+ if (_followOnRoots.count(ai) == 0)
+ _followOnRoots[ai] = ai;
+
+ auto iter = _followOnRoots.find(targetAtom);
+ if (iter == _followOnRoots.end()) {
+ // If the targetAtom is not a root of any chain, let's make the root of
+ // the targetAtom to the root of the current chain.
+
+ // The expression m[i] = m[j] where m is a DenseMap and i != j is not
+ // safe. m[j] returns a reference, which would be invalidated when a
+ // rehashing occurs. If rehashing occurs to make room for m[i], m[j]
+ // becomes invalid, and that invalid reference would be used as the RHS
+ // value of the expression.
+ // Copy the value to workaround.
+ const DefinedAtom *tmp = _followOnRoots[ai];
+ _followOnRoots[targetAtom] = tmp;
+ continue;
+ }
+ if (iter->second == targetAtom) {
+ // If the targetAtom is the root of a chain, the chain becomes part of
+ // the current chain. Rewrite the subchain's root to the current
+ // chain's root.
+ setChainRoot(targetAtom, _followOnRoots[ai]);
+ continue;
+ }
+ // The targetAtom is already a part of a chain. If the current atom is
+ // of size zero, we can insert it in the middle of the chain just
+ // before the target atom, while not breaking other atom's followon
+ // relationships. If it's not, we can only insert the current atom at
+ // the beginning of the chain. All the atoms followed by the target
+ // atom must be of size zero in that case to satisfy the followon
+ // relationships.
+ size_t currentAtomSize = ai->size();
+ if (currentAtomSize == 0) {
+ const DefinedAtom *targetPrevAtom = findAtomFollowedBy(targetAtom);
+ _followOnNexts[targetPrevAtom] = ai;
+ const DefinedAtom *tmp = _followOnRoots[targetPrevAtom];
+ _followOnRoots[ai] = tmp;
+ continue;
+ }
+ if (!checkAllPrevAtomsZeroSize(targetAtom))
+ break;
+ _followOnNexts[ai] = _followOnRoots[targetAtom];
+ setChainRoot(_followOnRoots[targetAtom], _followOnRoots[ai]);
+ }
+ }
+}
+
+/// Build an ordinal override map by traversing the followon chain, and
+/// assigning ordinals to each atom, if the atoms have their ordinals
+/// already assigned skip the atom and move to the next. This is the
+/// main map thats used to sort the atoms while comparing two atoms together
+void LayoutPass::buildOrdinalOverrideMap(MutableFile::DefinedAtomRange &range) {
+ ScopedTask task(getDefaultDomain(), "LayoutPass::buildOrdinalOverrideMap");
+ uint64_t index = 0;
+ for (const DefinedAtom *ai : range) {
+ const DefinedAtom *atom = ai;
+ if (_ordinalOverrideMap.find(atom) != _ordinalOverrideMap.end())
+ continue;
+ AtomToAtomT::iterator start = _followOnRoots.find(atom);
+ if (start == _followOnRoots.end())
+ continue;
+ for (const DefinedAtom *nextAtom = start->second; nextAtom != NULL;
+ nextAtom = _followOnNexts[nextAtom]) {
+ AtomToOrdinalT::iterator pos = _ordinalOverrideMap.find(nextAtom);
+ if (pos == _ordinalOverrideMap.end())
+ _ordinalOverrideMap[nextAtom] = index++;
+ }
+ }
+}
+
+std::vector<LayoutPass::SortKey>
+LayoutPass::decorate(MutableFile::DefinedAtomRange &atomRange) const {
+ std::vector<SortKey> ret;
+ for (const DefinedAtom *atom : atomRange) {
+ auto ri = _followOnRoots.find(atom);
+ auto oi = _ordinalOverrideMap.find(atom);
+ const DefinedAtom *root = (ri == _followOnRoots.end()) ? atom : ri->second;
+ uint64_t override = (oi == _ordinalOverrideMap.end()) ? 0 : oi->second;
+ ret.push_back(SortKey(atom, root, override));
+ }
+ return ret;
+}
+
+void LayoutPass::undecorate(MutableFile::DefinedAtomRange &atomRange,
+ std::vector<SortKey> &keys) const {
+ size_t i = 0;
+ for (SortKey &k : keys)
+ atomRange[i++] = k._atom;
+}
+
+/// Perform the actual pass
+void LayoutPass::perform(std::unique_ptr<MutableFile> &mergedFile) {
+ // sort the atoms
+ ScopedTask task(getDefaultDomain(), "LayoutPass");
+ MutableFile::DefinedAtomRange atomRange = mergedFile->definedAtoms();
+
+ // Build follow on tables
+ buildFollowOnTable(atomRange);
+
+ // Check the structure of followon graph if running in debug mode.
+ DEBUG(checkFollowonChain(atomRange));
+
+ // Build override maps
+ buildOrdinalOverrideMap(atomRange);
+
+ DEBUG({
+ llvm::dbgs() << "unsorted atoms:\n";
+ printDefinedAtoms(atomRange);
+ });
+
+ std::vector<LayoutPass::SortKey> vec = decorate(atomRange);
+ parallel_sort(vec.begin(), vec.end(),
+ [&](const LayoutPass::SortKey &l, const LayoutPass::SortKey &r) -> bool {
+ return compareAtoms(l, r, _customSorter);
+ });
+ DEBUG(checkTransitivity(vec, _customSorter));
+ undecorate(atomRange, vec);
+
+ DEBUG({
+ llvm::dbgs() << "sorted atoms:\n";
+ printDefinedAtoms(atomRange);
+ });
+}
+
+void addLayoutPass(PassManager &pm, const MachOLinkingContext &ctx) {
+ pm.add(llvm::make_unique<LayoutPass>(
+ ctx.registry(), [&](const DefinedAtom * left, const DefinedAtom * right,
+ bool & leftBeforeRight) ->bool {
+ return ctx.customAtomOrderer(left, right, leftBeforeRight);
+ }));
+}
+
+} // namespace mach_o
+} // namespace lld
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