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llvm-project/lld/lib/ReaderWriter/MachO/CompactUnwindPass.cpp

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//===- lib/ReaderWriter/MachO/CompactUnwindPass.cpp -------------*- C++ -*-===//
//
// The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
///
/// \file A pass to convert MachO's __compact_unwind sections into the final
/// __unwind_info format used during runtime. See
/// mach-o/compact_unwind_encoding.h for more details on the formats involved.
///
//===----------------------------------------------------------------------===//
#include "ArchHandler.h"
#include "File.h"
#include "MachONormalizedFileBinaryUtils.h"
#include "MachOPasses.h"
#include "lld/Core/DefinedAtom.h"
#include "lld/Core/File.h"
#include "lld/Core/LLVM.h"
#include "lld/Core/Reference.h"
#include "lld/Core/Simple.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Format.h"
#define DEBUG_TYPE "macho-compact-unwind"
namespace lld {
namespace mach_o {
namespace {
struct CompactUnwindEntry {
const Atom *rangeStart;
const Atom *personalityFunction;
const Atom *lsdaLocation;
const Atom *ehFrame;
uint32_t rangeLength;
// There are 3 types of compact unwind entry, distinguished by the encoding
// value: 0 indicates a function with no unwind info;
// _archHandler.dwarfCompactUnwindType() indicates that the entry defers to
// __eh_frame, and that the ehFrame entry will be valid; any other value is a
// real compact unwind entry -- personalityFunction will be set and
// lsdaLocation may be.
uint32_t encoding;
CompactUnwindEntry(const DefinedAtom *function)
: rangeStart(function), personalityFunction(nullptr),
lsdaLocation(nullptr), ehFrame(nullptr), rangeLength(function->size()),
encoding(0) {}
CompactUnwindEntry()
: rangeStart(nullptr), personalityFunction(nullptr),
lsdaLocation(nullptr), ehFrame(nullptr), rangeLength(0), encoding(0) {}
};
struct UnwindInfoPage {
ArrayRef<CompactUnwindEntry> entries;
};
}
class UnwindInfoAtom : public SimpleDefinedAtom {
public:
UnwindInfoAtom(ArchHandler &archHandler, const File &file, bool isBig,
std::vector<const Atom *> &personalities,
std::vector<uint32_t> &commonEncodings,
std::vector<UnwindInfoPage> &pages, uint32_t numLSDAs)
: SimpleDefinedAtom(file), _archHandler(archHandler),
_commonEncodingsOffset(7 * sizeof(uint32_t)),
_personalityArrayOffset(_commonEncodingsOffset +
commonEncodings.size() * sizeof(uint32_t)),
_topLevelIndexOffset(_personalityArrayOffset +
personalities.size() * sizeof(uint32_t)),
_lsdaIndexOffset(_topLevelIndexOffset +
3 * (pages.size() + 1) * sizeof(uint32_t)),
_firstPageOffset(_lsdaIndexOffset + 2 * numLSDAs * sizeof(uint32_t)),
_isBig(isBig) {
addHeader(commonEncodings.size(), personalities.size(), pages.size());
addCommonEncodings(commonEncodings);
addPersonalityFunctions(personalities);
addTopLevelIndexes(pages);
addLSDAIndexes(pages, numLSDAs);
addSecondLevelPages(pages);
}
~UnwindInfoAtom() override = default;
ContentType contentType() const override {
return DefinedAtom::typeProcessedUnwindInfo;
}
Alignment alignment() const override { return 4; }
uint64_t size() const override { return _contents.size(); }
ContentPermissions permissions() const override {
return DefinedAtom::permR__;
}
ArrayRef<uint8_t> rawContent() const override { return _contents; }
void addHeader(uint32_t numCommon, uint32_t numPersonalities,
uint32_t numPages) {
using normalized::write32;
uint32_t headerSize = 7 * sizeof(uint32_t);
_contents.resize(headerSize);
uint8_t *headerEntries = _contents.data();
// version
write32(headerEntries, 1, _isBig);
// commonEncodingsArraySectionOffset
write32(headerEntries + sizeof(uint32_t), _commonEncodingsOffset, _isBig);
// commonEncodingsArrayCount
write32(headerEntries + 2 * sizeof(uint32_t), numCommon, _isBig);
// personalityArraySectionOffset
write32(headerEntries + 3 * sizeof(uint32_t), _personalityArrayOffset,
_isBig);
// personalityArrayCount
write32(headerEntries + 4 * sizeof(uint32_t), numPersonalities, _isBig);
// indexSectionOffset
write32(headerEntries + 5 * sizeof(uint32_t), _topLevelIndexOffset, _isBig);
// indexCount
write32(headerEntries + 6 * sizeof(uint32_t), numPages + 1, _isBig);
}
/// Add the list of common encodings to the section; this is simply an array
/// of uint32_t compact values. Size has already been specified in the header.
void addCommonEncodings(std::vector<uint32_t> &commonEncodings) {
using normalized::write32;
_contents.resize(_commonEncodingsOffset +
commonEncodings.size() * sizeof(uint32_t));
uint8_t *commonEncodingsArea =
reinterpret_cast<uint8_t *>(_contents.data() + _commonEncodingsOffset);
for (uint32_t encoding : commonEncodings) {
write32(commonEncodingsArea, encoding, _isBig);
commonEncodingsArea += sizeof(uint32_t);
}
}
void addPersonalityFunctions(std::vector<const Atom *> personalities) {
_contents.resize(_personalityArrayOffset +
personalities.size() * sizeof(uint32_t));
for (unsigned i = 0; i < personalities.size(); ++i)
addImageReferenceIndirect(_personalityArrayOffset + i * sizeof(uint32_t),
personalities[i]);
}
void addTopLevelIndexes(std::vector<UnwindInfoPage> &pages) {
using normalized::write32;
uint32_t numIndexes = pages.size() + 1;
_contents.resize(_topLevelIndexOffset + numIndexes * 3 * sizeof(uint32_t));
uint32_t pageLoc = _firstPageOffset;
// The most difficult job here is calculating the LSDAs; everything else
// follows fairly naturally, but we can't state where the first
uint8_t *indexData = &_contents[_topLevelIndexOffset];
uint32_t numLSDAs = 0;
for (unsigned i = 0; i < pages.size(); ++i) {
// functionOffset
addImageReference(_topLevelIndexOffset + 3 * i * sizeof(uint32_t),
pages[i].entries[0].rangeStart);
// secondLevelPagesSectionOffset
write32(indexData + (3 * i + 1) * sizeof(uint32_t), pageLoc, _isBig);
write32(indexData + (3 * i + 2) * sizeof(uint32_t),
_lsdaIndexOffset + numLSDAs * 2 * sizeof(uint32_t), _isBig);
for (auto &entry : pages[i].entries)
if (entry.lsdaLocation)
++numLSDAs;
}
// Finally, write out the final sentinel index
auto &finalEntry = pages[pages.size() - 1].entries.back();
addImageReference(_topLevelIndexOffset +
3 * pages.size() * sizeof(uint32_t),
finalEntry.rangeStart, finalEntry.rangeLength);
// secondLevelPagesSectionOffset => 0
write32(indexData + (3 * pages.size() + 2) * sizeof(uint32_t),
_lsdaIndexOffset + numLSDAs * 2 * sizeof(uint32_t), _isBig);
}
void addLSDAIndexes(std::vector<UnwindInfoPage> &pages, uint32_t numLSDAs) {
_contents.resize(_lsdaIndexOffset + numLSDAs * 2 * sizeof(uint32_t));
uint32_t curOffset = _lsdaIndexOffset;
for (auto &page : pages) {
for (auto &entry : page.entries) {
if (!entry.lsdaLocation)
continue;
addImageReference(curOffset, entry.rangeStart);
addImageReference(curOffset + sizeof(uint32_t), entry.lsdaLocation);
curOffset += 2 * sizeof(uint32_t);
}
}
}
void addSecondLevelPages(std::vector<UnwindInfoPage> &pages) {
for (auto &page : pages) {
addRegularSecondLevelPage(page);
}
}
void addRegularSecondLevelPage(const UnwindInfoPage &page) {
uint32_t curPageOffset = _contents.size();
const int16_t headerSize = sizeof(uint32_t) + 2 * sizeof(uint16_t);
uint32_t curPageSize =
headerSize + 2 * page.entries.size() * sizeof(uint32_t);
_contents.resize(curPageOffset + curPageSize);
using normalized::write32;
using normalized::write16;
// 2 => regular page
write32(&_contents[curPageOffset], 2, _isBig);
// offset of 1st entry
write16(&_contents[curPageOffset + 4], headerSize, _isBig);
write16(&_contents[curPageOffset + 6], page.entries.size(), _isBig);
uint32_t pagePos = curPageOffset + headerSize;
for (auto &entry : page.entries) {
addImageReference(pagePos, entry.rangeStart);
write32(_contents.data() + pagePos + sizeof(uint32_t), entry.encoding,
_isBig);
if ((entry.encoding & 0x0f000000U) ==
_archHandler.dwarfCompactUnwindType())
addEhFrameReference(pagePos + sizeof(uint32_t), entry.ehFrame);
pagePos += 2 * sizeof(uint32_t);
}
}
void addEhFrameReference(uint32_t offset, const Atom *dest,
Reference::Addend addend = 0) {
addReference(Reference::KindNamespace::mach_o, _archHandler.kindArch(),
_archHandler.unwindRefToEhFrameKind(), offset, dest, addend);
}
void addImageReference(uint32_t offset, const Atom *dest,
Reference::Addend addend = 0) {
addReference(Reference::KindNamespace::mach_o, _archHandler.kindArch(),
_archHandler.imageOffsetKind(), offset, dest, addend);
}
void addImageReferenceIndirect(uint32_t offset, const Atom *dest) {
addReference(Reference::KindNamespace::mach_o, _archHandler.kindArch(),
_archHandler.imageOffsetKindIndirect(), offset, dest, 0);
}
private:
mach_o::ArchHandler &_archHandler;
std::vector<uint8_t> _contents;
uint32_t _commonEncodingsOffset;
uint32_t _personalityArrayOffset;
uint32_t _topLevelIndexOffset;
uint32_t _lsdaIndexOffset;
uint32_t _firstPageOffset;
bool _isBig;
};
/// Pass for instantiating and optimizing GOT slots.
///
class CompactUnwindPass : public Pass {
public:
CompactUnwindPass(const MachOLinkingContext &context)
: _ctx(context), _archHandler(_ctx.archHandler()),
_file(*_ctx.make_file<MachOFile>("<mach-o Compact Unwind Pass>")),
_isBig(MachOLinkingContext::isBigEndian(_ctx.arch())) {
_file.setOrdinal(_ctx.getNextOrdinalAndIncrement());
}
private:
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();
// 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();
}
void collectCompactUnwindEntries(
const SimpleFile &mergedFile,
std::map<const Atom *, CompactUnwindEntry> &unwindLocs,
std::vector<const Atom *> &personalities, uint32_t &numLSDAs) {
DEBUG(llvm::dbgs() << " Collecting __compact_unwind entries\n");
for (const DefinedAtom *atom : mergedFile.defined()) {
if (atom->contentType() != DefinedAtom::typeCompactUnwindInfo)
continue;
auto unwindEntry = extractCompactUnwindEntry(atom);
unwindLocs.insert(std::make_pair(unwindEntry.rangeStart, unwindEntry));
DEBUG(llvm::dbgs() << " Entry for " << unwindEntry.rangeStart->name()
<< ", encoding="
<< llvm::format("0x%08x", unwindEntry.encoding));
if (unwindEntry.personalityFunction)
DEBUG(llvm::dbgs() << ", personality="
<< unwindEntry.personalityFunction->name()
<< ", lsdaLoc=" << unwindEntry.lsdaLocation->name());
DEBUG(llvm::dbgs() << '\n');
// Count number of LSDAs we see, since we need to know how big the index
// will be while laying out the section.
if (unwindEntry.lsdaLocation)
++numLSDAs;
// Gather the personality functions now, so that they're in deterministic
// order (derived from the DefinedAtom order).
if (unwindEntry.personalityFunction) {
auto pFunc = std::find(personalities.begin(), personalities.end(),
unwindEntry.personalityFunction);
if (pFunc == personalities.end())
personalities.push_back(unwindEntry.personalityFunction);
}
}
}
CompactUnwindEntry extractCompactUnwindEntry(const DefinedAtom *atom) {
CompactUnwindEntry entry;
for (const Reference *ref : *atom) {
switch (ref->offsetInAtom()) {
case 0:
// FIXME: there could legitimately be functions with multiple encoding
// entries. However, nothing produces them at the moment.
assert(ref->addend() == 0 && "unexpected offset into function");
entry.rangeStart = ref->target();
break;
case 0x10:
assert(ref->addend() == 0 && "unexpected offset into personality fn");
entry.personalityFunction = ref->target();
break;
case 0x18:
assert(ref->addend() == 0 && "unexpected offset into LSDA atom");
entry.lsdaLocation = ref->target();
break;
}
}
if (atom->rawContent().size() < 4 * sizeof(uint32_t))
return entry;
using normalized::read32;
entry.rangeLength =
read32(atom->rawContent().data() + 2 * sizeof(uint32_t), _isBig);
entry.encoding =
read32(atom->rawContent().data() + 3 * sizeof(uint32_t), _isBig);
return entry;
}
void
collectDwarfFrameEntries(const SimpleFile &mergedFile,
std::map<const Atom *, const Atom *> &dwarfFrames) {
for (const DefinedAtom *ehFrameAtom : mergedFile.defined()) {
if (ehFrameAtom->contentType() != DefinedAtom::typeCFI)
continue;
if (ArchHandler::isDwarfCIE(_isBig, ehFrameAtom))
continue;
if (const Atom *function = _archHandler.fdeTargetFunction(ehFrameAtom))
dwarfFrames[function] = ehFrameAtom;
}
}
/// Every atom defined in __TEXT,__text needs an entry in the final
/// __unwind_info section (in order). These comes from two sources:
/// + Input __compact_unwind sections where possible (after adding the
/// personality function offset which is only known now).
/// + A synthesised reference to __eh_frame if there's no __compact_unwind
/// or too many personality functions to be accommodated.
std::vector<CompactUnwindEntry> createUnwindInfoEntries(
const SimpleFile &mergedFile,
const std::map<const Atom *, CompactUnwindEntry> &unwindLocs,
const std::vector<const Atom *> &personalities,
const std::map<const Atom *, const Atom *> &dwarfFrames) {
std::vector<CompactUnwindEntry> unwindInfos;
DEBUG(llvm::dbgs() << " Creating __unwind_info entries\n");
// The final order in the __unwind_info section must be derived from the
// order of typeCode atoms, since that's how they'll be put into the object
// file eventually (yuck!).
for (const DefinedAtom *atom : mergedFile.defined()) {
if (atom->contentType() != DefinedAtom::typeCode)
continue;
unwindInfos.push_back(finalizeUnwindInfoEntryForAtom(
atom, unwindLocs, personalities, dwarfFrames));
DEBUG(llvm::dbgs() << " Entry for " << atom->name()
<< ", final encoding="
<< llvm::format("0x%08x", unwindInfos.back().encoding)
<< '\n');
}
return unwindInfos;
}
/// 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;
});
}
CompactUnwindEntry finalizeUnwindInfoEntryForAtom(
const DefinedAtom *function,
const std::map<const Atom *, CompactUnwindEntry> &unwindLocs,
const std::vector<const Atom *> &personalities,
const std::map<const Atom *, const Atom *> &dwarfFrames) {
auto unwindLoc = unwindLocs.find(function);
CompactUnwindEntry entry;
if (unwindLoc == unwindLocs.end()) {
// Default entry has correct encoding (0 => no unwind), but we need to
// synthesise the function.
entry.rangeStart = function;
entry.rangeLength = function->size();
} else
entry = unwindLoc->second;
// If there's no __compact_unwind entry, or it explicitly says to use
// __eh_frame, we need to try and fill in the correct DWARF atom.
if (entry.encoding == _archHandler.dwarfCompactUnwindType() ||
entry.encoding == 0) {
auto dwarfFrame = dwarfFrames.find(function);
if (dwarfFrame != dwarfFrames.end()) {
entry.encoding = _archHandler.dwarfCompactUnwindType();
entry.ehFrame = dwarfFrame->second;
}
}
auto personality = std::find(personalities.begin(), personalities.end(),
entry.personalityFunction);
uint32_t personalityIdx = personality == personalities.end()
? 0
: personality - personalities.begin() + 1;
// FIXME: We should also use DWARF when there isn't enough room for the
// personality function in the compact encoding.
assert(personalityIdx < 4 && "too many personality functions");
entry.encoding |= personalityIdx << 28;
if (entry.lsdaLocation)
entry.encoding |= 1U << 30;
return entry;
}
const MachOLinkingContext &_ctx;
mach_o::ArchHandler &_archHandler;
MachOFile &_file;
bool _isBig;
};
void addCompactUnwindPass(PassManager &pm, const MachOLinkingContext &ctx) {
assert(ctx.needsCompactUnwindPass());
pm.add(llvm::make_unique<CompactUnwindPass>(ctx));
}
} // end namesapce mach_o
} // end namesapce lld
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