/// Remove unused EH frames.
///
/// An EH frame is considered unused if there is a corresponding compact
/// unwind atom that doesn't require the EH frame.
void pruneUnusedEHFrames(
SimpleFile &mergedFile,
const std::vector<CompactUnwindEntry> &unwindInfos,
const std::map<const Atom *, CompactUnwindEntry> &unwindLocs,
const std::map<const Atom *, const Atom *> &dwarfFrames) {
// Worklist of all 'used' FDEs.
std::vector<const DefinedAtom *> usedDwarfWorklist;
// We have to check two conditions when building the worklist:
// (1) EH frames used by compact unwind entries.
for (auto &entry : unwindInfos)
if (entry.ehFrame)
usedDwarfWorklist.push_back(cast<DefinedAtom>(entry.ehFrame));
// (2) EH frames that reference functions with no corresponding compact
// unwind info.
for (auto &entry : dwarfFrames)
if (!unwindLocs.count(entry.first))
usedDwarfWorklist.push_back(cast<DefinedAtom>(entry.second));
// Add all transitively referenced CFI atoms by processing the worklist.
std::set<const Atom *> usedDwarfFrames;
while (!usedDwarfWorklist.empty()) {
const DefinedAtom *cfiAtom = usedDwarfWorklist.back();
usedDwarfWorklist.pop_back();
usedDwarfFrames.insert(cfiAtom);
for (const auto *ref : *cfiAtom) {
const DefinedAtom *cfiTarget = dyn_cast<DefinedAtom>(ref->target());
if (cfiTarget->contentType() == DefinedAtom::typeCFI)
usedDwarfWorklist.push_back(cfiTarget);
}
}
// Finally, delete all unreferenced CFI atoms.
mergedFile.removeDefinedAtomsIf([&](const DefinedAtom *atom) {
if ((atom->contentType() == DefinedAtom::typeCFI) &&
!usedDwarfFrames.count(atom))
return true;
return false;
});
}
llvm::Error perform(SimpleFile &mergedFile) override {
DEBUG(llvm::dbgs() << "MachO Compact Unwind pass\n");
std::map<const Atom *, CompactUnwindEntry> unwindLocs;
std::map<const Atom *, const Atom *> dwarfFrames;
std::vector<const Atom *> personalities;
uint32_t numLSDAs = 0;
// First collect all __compact_unwind and __eh_frame entries, addressable by
// the function referred to.
collectCompactUnwindEntries(mergedFile, unwindLocs, personalities,
numLSDAs);
collectDwarfFrameEntries(mergedFile, dwarfFrames);
// Skip rest of pass if no unwind info.
if (unwindLocs.empty() && dwarfFrames.empty())
return llvm::Error::success();
// FIXME: if there are more than 4 personality functions then we need to
// defer to DWARF info for the ones we don't put in the list. They should
// also probably be sorted by frequency.
assert(personalities.size() <= 4);
// TODO: Find commmon encodings for use by compressed pages.
std::vector<uint32_t> commonEncodings;
// Now sort the entries by final address and fixup the compact encoding to
// its final form (i.e. set personality function bits & create DWARF
// references where needed).
std::vector<CompactUnwindEntry> unwindInfos = createUnwindInfoEntries(
mergedFile, unwindLocs, personalities, dwarfFrames);
// Remove any unused eh-frame atoms.
pruneUnusedEHFrames(mergedFile, unwindInfos, unwindLocs, dwarfFrames);
// Finally, we can start creating pages based on these entries.
DEBUG(llvm::dbgs() << " Splitting entries into pages\n");
// FIXME: we split the entries into pages naively: lots of 4k pages followed
// by a small one. ld64 tried to minimize space and align them to real 4k
// boundaries. That might be worth doing, or perhaps we could perform some
// minor balancing for expected number of lookups.
std::vector<UnwindInfoPage> pages;
auto remainingInfos = llvm::makeArrayRef(unwindInfos);
do {
pages.push_back(UnwindInfoPage());
// FIXME: we only create regular pages at the moment. These can hold up to
// 1021 entries according to the documentation.
unsigned entriesInPage = std::min(1021U, (unsigned)remainingInfos.size());
pages.back().entries = remainingInfos.slice(0, entriesInPage);
remainingInfos = remainingInfos.slice(entriesInPage);
DEBUG(llvm::dbgs()
<< " Page from " << pages.back().entries[0].rangeStart->name()
<< " to " << pages.back().entries.back().rangeStart->name() << " + "
<< llvm::format("0x%x", pages.back().entries.back().rangeLength)
<< " has " << entriesInPage << " entries\n");
} while (!remainingInfos.empty());
auto *unwind = new (_file.allocator())
UnwindInfoAtom(_archHandler, _file, _isBig, personalities,
commonEncodings, pages, numLSDAs);
mergedFile.addAtom(*unwind);
// Finally, remove all __compact_unwind atoms now that we've processed them.
mergedFile.removeDefinedAtomsIf([](const DefinedAtom *atom) {
return atom->contentType() == DefinedAtom::typeCompactUnwindInfo;
});
return llvm::Error::success();
}