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llvm / llvm-project / lld / 7475af91c50d4030286271bbc5520dd51456b26b / . / MachO / UnwindInfoSection.cpp
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//===- UnwindInfoSection.cpp ----------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "UnwindInfoSection.h"
#include "ConcatOutputSection.h"
#include "Config.h"
#include "InputSection.h"
#include "OutputSection.h"
#include "OutputSegment.h"
#include "SymbolTable.h"
#include "Symbols.h"
#include "SyntheticSections.h"
#include "Target.h"
#include "lld/Common/ErrorHandler.h"
#include "lld/Common/Memory.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/BinaryFormat/MachO.h"
#include "llvm/Support/Parallel.h"
#include <numeric>
using namespace llvm;
using namespace llvm::MachO;
using namespace lld;
using namespace lld::macho;
#define COMMON_ENCODINGS_MAX 127
#define COMPACT_ENCODINGS_MAX 256
#define SECOND_LEVEL_PAGE_BYTES 4096
#define SECOND_LEVEL_PAGE_WORDS (SECOND_LEVEL_PAGE_BYTES / sizeof(uint32_t))
#define REGULAR_SECOND_LEVEL_ENTRIES_MAX \
((SECOND_LEVEL_PAGE_BYTES - \
sizeof(unwind_info_regular_second_level_page_header)) / \
sizeof(unwind_info_regular_second_level_entry))
#define COMPRESSED_SECOND_LEVEL_ENTRIES_MAX \
((SECOND_LEVEL_PAGE_BYTES - \
sizeof(unwind_info_compressed_second_level_page_header)) / \
sizeof(uint32_t))
#define COMPRESSED_ENTRY_FUNC_OFFSET_BITS 24
#define COMPRESSED_ENTRY_FUNC_OFFSET_MASK \
UNWIND_INFO_COMPRESSED_ENTRY_FUNC_OFFSET(~0)
// Compact Unwind format is a Mach-O evolution of DWARF Unwind that
// optimizes space and exception-time lookup. Most DWARF unwind
// entries can be replaced with Compact Unwind entries, but the ones
// that cannot are retained in DWARF form.
//
// This comment will address macro-level organization of the pre-link
// and post-link compact unwind tables. For micro-level organization
// pertaining to the bitfield layout of the 32-bit compact unwind
// entries, see libunwind/include/mach-o/compact_unwind_encoding.h
//
// Important clarifying factoids:
//
// * __LD,__compact_unwind is the compact unwind format for compiler
// output and linker input. It is never a final output. It could be
// an intermediate output with the `-r` option which retains relocs.
//
// * __TEXT,__unwind_info is the compact unwind format for final
// linker output. It is never an input.
//
// * __TEXT,__eh_frame is the DWARF format for both linker input and output.
//
// * __TEXT,__unwind_info entries are divided into 4 KiB pages (2nd
// level) by ascending address, and the pages are referenced by an
// index (1st level) in the section header.
//
// * Following the headers in __TEXT,__unwind_info, the bulk of the
// section contains a vector of compact unwind entries
// `{functionOffset, encoding}` sorted by ascending `functionOffset`.
// Adjacent entries with the same encoding can be folded to great
// advantage, achieving a 3-order-of-magnitude reduction in the
// number of entries.
//
// * The __TEXT,__unwind_info format can accommodate up to 127 unique
// encodings for the space-efficient compressed format. In practice,
// fewer than a dozen unique encodings are used by C++ programs of
// all sizes. Therefore, we don't even bother implementing the regular
// non-compressed format. Time will tell if anyone in the field ever
// overflows the 127-encodings limit.
//
// Refer to the definition of unwind_info_section_header in
// compact_unwind_encoding.h for an overview of the format we are encoding
// here.
// TODO(gkm): prune __eh_frame entries superseded by __unwind_info, PR50410
// TODO(gkm): how do we align the 2nd-level pages?
template <class Ptr> struct CompactUnwindEntry {
Ptr functionAddress;
uint32_t functionLength;
compact_unwind_encoding_t encoding;
Ptr personality;
Ptr lsda;
};
using EncodingMap = DenseMap<compact_unwind_encoding_t, size_t>;
struct SecondLevelPage {
uint32_t kind;
size_t entryIndex;
size_t entryCount;
size_t byteCount;
std::vector<compact_unwind_encoding_t> localEncodings;
EncodingMap localEncodingIndexes;
};
template <class Ptr>
class UnwindInfoSectionImpl final : public UnwindInfoSection {
public:
void prepareRelocations(ConcatInputSection *) override;
void relocateCompactUnwind(std::vector<CompactUnwindEntry<Ptr>> &);
Reloc *findLsdaReloc(ConcatInputSection *) const;
void encodePersonalities();
void finalize() override;
void writeTo(uint8_t *buf) const override;
private:
std::vector<std::pair<compact_unwind_encoding_t, size_t>> commonEncodings;
EncodingMap commonEncodingIndexes;
// The entries here will be in the same order as their originating symbols
// in symbolsVec.
std::vector<CompactUnwindEntry<Ptr>> cuEntries;
// Indices into the cuEntries vector.
std::vector<size_t> cuIndices;
// Indices of personality functions within the GOT.
std::vector<Ptr> personalities;
SmallDenseMap<std::pair<InputSection *, uint64_t /* addend */>, Symbol *>
personalityTable;
// Indices into cuEntries for CUEs with a non-null LSDA.
std::vector<size_t> entriesWithLsda;
// Map of cuEntries index to an index within the LSDA array.
DenseMap<size_t, uint32_t> lsdaIndex;
std::vector<SecondLevelPage> secondLevelPages;
uint64_t level2PagesOffset = 0;
};
UnwindInfoSection::UnwindInfoSection()
: SyntheticSection(segment_names::text, section_names::unwindInfo) {
align = 4;
}
void UnwindInfoSection::prepareRelocations() {
// This iteration needs to be deterministic, since prepareRelocations may add
// entries to the GOT. Hence the use of a MapVector for
// UnwindInfoSection::symbols.
for (const Defined *d : make_second_range(symbols))
if (d->unwindEntry)
prepareRelocations(d->unwindEntry);
}
// Record function symbols that may need entries emitted in __unwind_info, which
// stores unwind data for address ranges.
//
// Note that if several adjacent functions have the same unwind encoding, LSDA,
// and personality function, they share one unwind entry. For this to work,
// functions without unwind info need explicit "no unwind info" unwind entries
// -- else the unwinder would think they have the unwind info of the closest
// function with unwind info right before in the image. Thus, we add function
// symbols for each unique address regardless of whether they have associated
// unwind info.
void UnwindInfoSection::addSymbol(const Defined *d) {
if (d->unwindEntry)
allEntriesAreOmitted = false;
// We don't yet know the final output address of this symbol, but we know that
// they are uniquely determined by a combination of the isec and value, so
// we use that as the key here.
auto p = symbols.insert({{d->isec, d->value}, d});
// If we have multiple symbols at the same address, only one of them can have
// an associated CUE.
if (!p.second && d->unwindEntry) {
assert(!p.first->second->unwindEntry);
p.first->second = d;
}
}
// Compact unwind relocations have different semantics, so we handle them in a
// separate code path from regular relocations. First, we do not wish to add
// rebase opcodes for __LD,__compact_unwind, because that section doesn't
// actually end up in the final binary. Second, personality pointers always
// reside in the GOT and must be treated specially.
template <class Ptr>
void UnwindInfoSectionImpl<Ptr>::prepareRelocations(ConcatInputSection *isec) {
assert(!isec->shouldOmitFromOutput() &&
"__compact_unwind section should not be omitted");
// FIXME: Make this skip relocations for CompactUnwindEntries that
// point to dead-stripped functions. That might save some amount of
// work. But since there are usually just few personality functions
// that are referenced from many places, at least some of them likely
// live, it wouldn't reduce number of got entries.
for (size_t i = 0; i < isec->relocs.size(); ++i) {
Reloc &r = isec->relocs[i];
assert(target->hasAttr(r.type, RelocAttrBits::UNSIGNED));
// Functions and LSDA entries always reside in the same object file as the
// compact unwind entries that references them, and thus appear as section
// relocs. There is no need to prepare them. We only prepare relocs for
// personality functions.
if (r.offset % sizeof(CompactUnwindEntry<Ptr>) !=
offsetof(CompactUnwindEntry<Ptr>, personality))
continue;
if (auto *s = r.referent.dyn_cast<Symbol *>()) {
// Personality functions are nearly always system-defined (e.g.,
// ___gxx_personality_v0 for C++) and relocated as dylib symbols. When an
// application provides its own personality function, it might be
// referenced by an extern Defined symbol reloc, or a local section reloc.
if (auto *defined = dyn_cast<Defined>(s)) {
// XXX(vyng) This is a a special case for handling duplicate personality
// symbols. Note that LD64's behavior is a bit different and it is
// inconsistent with how symbol resolution usually work
//
// So we've decided not to follow it. Instead, simply pick the symbol
// with the same name from the symbol table to replace the local one.
//
// (See discussions/alternatives already considered on D107533)
if (!defined->isExternal())
if (Symbol *sym = symtab->find(defined->getName()))
if (sym->kind() != Symbol::LazyKind)
r.referent = s = sym;
}
if (auto *undefined = dyn_cast<Undefined>(s)) {
treatUndefinedSymbol(*undefined);
// treatUndefinedSymbol() can replace s with a DylibSymbol; re-check.
if (isa<Undefined>(s))
continue;
}
if (auto *defined = dyn_cast<Defined>(s)) {
// Check if we have created a synthetic symbol at the same address.
Symbol *&personality =
personalityTable[{defined->isec, defined->value}];
if (personality == nullptr) {
personality = defined;
in.got->addEntry(defined);
} else if (personality != defined) {
r.referent = personality;
}
continue;
}
assert(isa<DylibSymbol>(s));
in.got->addEntry(s);
continue;
}
if (auto *referentIsec = r.referent.dyn_cast<InputSection *>()) {
assert(!isCoalescedWeak(referentIsec));
// Personality functions can be referenced via section relocations
// if they live in the same object file. Create placeholder synthetic
// symbols for them in the GOT.
Symbol *&s = personalityTable[{referentIsec, r.addend}];
if (s == nullptr) {
// This runs after dead stripping, so the noDeadStrip argument does not
// matter.
s = make<Defined>("<internal>", /*file=*/nullptr, referentIsec,
r.addend, /*size=*/0, /*isWeakDef=*/false,
/*isExternal=*/false, /*isPrivateExtern=*/false,
/*isThumb=*/false, /*isReferencedDynamically=*/false,
/*noDeadStrip=*/false);
in.got->addEntry(s);
}
r.referent = s;
r.addend = 0;
}
}
}
// Unwind info lives in __DATA, and finalization of __TEXT will occur before
// finalization of __DATA. Moreover, the finalization of unwind info depends on
// the exact addresses that it references. So it is safe for compact unwind to
// reference addresses in __TEXT, but not addresses in any other segment.
static ConcatInputSection *checkTextSegment(InputSection *isec) {
if (isec->getSegName() != segment_names::text)
error("compact unwind references address in " + toString(isec) +
" which is not in segment __TEXT");
// __text should always be a ConcatInputSection.
return cast<ConcatInputSection>(isec);
}
// We need to apply the relocations to the pre-link compact unwind section
// before converting it to post-link form. There should only be absolute
// relocations here: since we are not emitting the pre-link CU section, there
// is no source address to make a relative location meaningful.
template <class Ptr>
void UnwindInfoSectionImpl<Ptr>::relocateCompactUnwind(
std::vector<CompactUnwindEntry<Ptr>> &cuEntries) {
parallelForEachN(0, symbolsVec.size(), [&](size_t i) {
uint8_t *buf = reinterpret_cast<uint8_t *>(cuEntries.data()) +
i * sizeof(CompactUnwindEntry<Ptr>);
const Defined *d = symbolsVec[i].second;
// Write the functionAddress.
writeAddress(buf, d->getVA(), sizeof(Ptr) == 8 ? 3 : 2);
if (!d->unwindEntry)
return;
// Write the rest of the CUE.
memcpy(buf + sizeof(Ptr), d->unwindEntry->data.data(),
d->unwindEntry->data.size());
for (const Reloc &r : d->unwindEntry->relocs) {
uint64_t referentVA = 0;
if (auto *referentSym = r.referent.dyn_cast<Symbol *>()) {
if (!isa<Undefined>(referentSym)) {
if (auto *defined = dyn_cast<Defined>(referentSym))
checkTextSegment(defined->isec);
// At this point in the link, we may not yet know the final address of
// the GOT, so we just encode the index. We make it a 1-based index so
// that we can distinguish the null pointer case.
referentVA = referentSym->gotIndex + 1;
}
} else {
auto *referentIsec = r.referent.get<InputSection *>();
checkTextSegment(referentIsec);
referentVA = referentIsec->getVA(r.addend);
}
writeAddress(buf + r.offset, referentVA, r.length);
}
});
}
// There should only be a handful of unique personality pointers, so we can
// encode them as 2-bit indices into a small array.
template <class Ptr> void UnwindInfoSectionImpl<Ptr>::encodePersonalities() {
for (size_t idx : cuIndices) {
CompactUnwindEntry<Ptr> &cu = cuEntries[idx];
if (cu.personality == 0)
continue;
// Linear search is fast enough for a small array.
auto it = find(personalities, cu.personality);
uint32_t personalityIndex; // 1-based index
if (it != personalities.end()) {
personalityIndex = std::distance(personalities.begin(), it) + 1;
} else {
personalities.push_back(cu.personality);
personalityIndex = personalities.size();
}
cu.encoding |=
personalityIndex << countTrailingZeros(
static_cast<compact_unwind_encoding_t>(UNWIND_PERSONALITY_MASK));
}
if (personalities.size() > 3)
error("too many personalities (" + std::to_string(personalities.size()) +
") for compact unwind to encode");
}
static bool canFoldEncoding(compact_unwind_encoding_t encoding) {
// From compact_unwind_encoding.h:
// UNWIND_X86_64_MODE_STACK_IND:
// A "frameless" (RBP not used as frame pointer) function large constant
// stack size. This case is like the previous, except the stack size is too
// large to encode in the compact unwind encoding. Instead it requires that
// the function contains "subq $nnnnnnnn,RSP" in its prolog. The compact
// encoding contains the offset to the nnnnnnnn value in the function in
// UNWIND_X86_64_FRAMELESS_STACK_SIZE.
// Since this means the unwinder has to look at the `subq` in the function
// of the unwind info's unwind address, two functions that have identical
// unwind info can't be folded if it's using this encoding since both
// entries need unique addresses.
static_assert(UNWIND_X86_64_MODE_MASK == UNWIND_X86_MODE_MASK, "");
static_assert(UNWIND_X86_64_MODE_STACK_IND == UNWIND_X86_MODE_STACK_IND, "");
if ((target->cpuType == CPU_TYPE_X86_64 || target->cpuType == CPU_TYPE_X86) &&
(encoding & UNWIND_X86_64_MODE_MASK) == UNWIND_X86_64_MODE_STACK_IND) {
// FIXME: Consider passing in the two function addresses and getting
// their two stack sizes off the `subq` and only returning false if they're
// actually different.
return false;
}
return true;
}
template <class Ptr>
Reloc *
UnwindInfoSectionImpl<Ptr>::findLsdaReloc(ConcatInputSection *isec) const {
if (isec == nullptr)
return nullptr;
auto it = llvm::find_if(isec->relocs, [](const Reloc &r) {
return r.offset % sizeof(CompactUnwindEntry<Ptr>) ==
offsetof(CompactUnwindEntry<Ptr>, lsda);
});
if (it == isec->relocs.end())
return nullptr;
return &*it;
}
// Scan the __LD,__compact_unwind entries and compute the space needs of
// __TEXT,__unwind_info and __TEXT,__eh_frame
template <class Ptr> void UnwindInfoSectionImpl<Ptr>::finalize() {
if (symbols.empty())
return;
// At this point, the address space for __TEXT,__text has been
// assigned, so we can relocate the __LD,__compact_unwind entries
// into a temporary buffer. Relocation is necessary in order to sort
// the CU entries by function address. Sorting is necessary so that
// we can fold adjacent CU entries with identical
// encoding+personality+lsda. Folding is necessary because it reduces
// the number of CU entries by as much as 3 orders of magnitude!
cuEntries.resize(symbols.size());
// The "map" part of the symbols MapVector was only needed for deduplication
// in addSymbol(). Now that we are done adding, move the contents to a plain
// std::vector for indexed access.
symbolsVec = symbols.takeVector();
relocateCompactUnwind(cuEntries);
// Rather than sort & fold the 32-byte entries directly, we create a
// vector of indices to entries and sort & fold that instead.
cuIndices.resize(cuEntries.size());
std::iota(cuIndices.begin(), cuIndices.end(), 0);
llvm::sort(cuIndices, [&](size_t a, size_t b) {
return cuEntries[a].functionAddress < cuEntries[b].functionAddress;
});
// Fold adjacent entries with matching encoding+personality+lsda
// We use three iterators on the same cuIndices to fold in-situ:
// (1) `foldBegin` is the first of a potential sequence of matching entries
// (2) `foldEnd` is the first non-matching entry after `foldBegin`.
// The semi-open interval [ foldBegin .. foldEnd ) contains a range
// entries that can be folded into a single entry and written to ...
// (3) `foldWrite`
auto foldWrite = cuIndices.begin();
for (auto foldBegin = cuIndices.begin(); foldBegin < cuIndices.end();) {
auto foldEnd = foldBegin;
while (++foldEnd < cuIndices.end() &&
cuEntries[*foldBegin].encoding == cuEntries[*foldEnd].encoding &&
cuEntries[*foldBegin].personality ==
cuEntries[*foldEnd].personality &&
canFoldEncoding(cuEntries[*foldEnd].encoding)) {
// In most cases, we can just compare the values of cuEntries[*].lsda.
// However, it is possible for -rename_section to cause the LSDA section
// (__gcc_except_tab) to be finalized after the unwind info section. In
// that case, we don't yet have unique addresses for the LSDA entries.
// So we check their relocations instead.
// FIXME: should we account for an LSDA at an absolute address? ld64 seems
// to support it, but it seems unlikely to be used in practice.
Reloc *lsda1 = findLsdaReloc(symbolsVec[*foldBegin].second->unwindEntry);
Reloc *lsda2 = findLsdaReloc(symbolsVec[*foldEnd].second->unwindEntry);
if (lsda1 == nullptr && lsda2 == nullptr)
continue;
if (lsda1 == nullptr || lsda2 == nullptr)
break;
if (lsda1->referent != lsda2->referent)
break;
if (lsda1->addend != lsda2->addend)
break;
}
*foldWrite++ = *foldBegin;
foldBegin = foldEnd;
}
cuIndices.erase(foldWrite, cuIndices.end());
encodePersonalities();
// Count frequencies of the folded encodings
EncodingMap encodingFrequencies;
for (size_t idx : cuIndices)
encodingFrequencies[cuEntries[idx].encoding]++;
// Make a vector of encodings, sorted by descending frequency
for (const auto &frequency : encodingFrequencies)
commonEncodings.emplace_back(frequency);
llvm::sort(commonEncodings,
[](const std::pair<compact_unwind_encoding_t, size_t> &a,
const std::pair<compact_unwind_encoding_t, size_t> &b) {
if (a.second == b.second)
// When frequencies match, secondarily sort on encoding
// to maintain parity with validate-unwind-info.py
return a.first > b.first;
return a.second > b.second;
});
// Truncate the vector to 127 elements.
// Common encoding indexes are limited to 0..126, while encoding
// indexes 127..255 are local to each second-level page
if (commonEncodings.size() > COMMON_ENCODINGS_MAX)
commonEncodings.resize(COMMON_ENCODINGS_MAX);
// Create a map from encoding to common-encoding-table index
for (size_t i = 0; i < commonEncodings.size(); i++)
commonEncodingIndexes[commonEncodings[i].first] = i;
// Split folded encodings into pages, where each page is limited by ...
// (a) 4 KiB capacity
// (b) 24-bit difference between first & final function address
// (c) 8-bit compact-encoding-table index,
// for which 0..126 references the global common-encodings table,
// and 127..255 references a local per-second-level-page table.
// First we try the compact format and determine how many entries fit.
// If more entries fit in the regular format, we use that.
for (size_t i = 0; i < cuIndices.size();) {
size_t idx = cuIndices[i];
secondLevelPages.emplace_back();
SecondLevelPage &page = secondLevelPages.back();
page.entryIndex = i;
uintptr_t functionAddressMax =
cuEntries[idx].functionAddress + COMPRESSED_ENTRY_FUNC_OFFSET_MASK;
size_t n = commonEncodings.size();
size_t wordsRemaining =
SECOND_LEVEL_PAGE_WORDS -
sizeof(unwind_info_compressed_second_level_page_header) /
sizeof(uint32_t);
while (wordsRemaining >= 1 && i < cuIndices.size()) {
idx = cuIndices[i];
const CompactUnwindEntry<Ptr> *cuPtr = &cuEntries[idx];
if (cuPtr->functionAddress >= functionAddressMax) {
break;
} else if (commonEncodingIndexes.count(cuPtr->encoding) ||
page.localEncodingIndexes.count(cuPtr->encoding)) {
i++;
wordsRemaining--;
} else if (wordsRemaining >= 2 && n < COMPACT_ENCODINGS_MAX) {
page.localEncodings.emplace_back(cuPtr->encoding);
page.localEncodingIndexes[cuPtr->encoding] = n++;
i++;
wordsRemaining -= 2;
} else {
break;
}
}
page.entryCount = i - page.entryIndex;
// If this is not the final page, see if it's possible to fit more
// entries by using the regular format. This can happen when there
// are many unique encodings, and we we saturated the local
// encoding table early.
if (i < cuIndices.size() &&
page.entryCount < REGULAR_SECOND_LEVEL_ENTRIES_MAX) {
page.kind = UNWIND_SECOND_LEVEL_REGULAR;
page.entryCount = std::min(REGULAR_SECOND_LEVEL_ENTRIES_MAX,
cuIndices.size() - page.entryIndex);
i = page.entryIndex + page.entryCount;
} else {
page.kind = UNWIND_SECOND_LEVEL_COMPRESSED;
}
}
for (size_t idx : cuIndices) {
lsdaIndex[idx] = entriesWithLsda.size();
const Defined *d = symbolsVec[idx].second;
if (findLsdaReloc(d->unwindEntry))
entriesWithLsda.push_back(idx);
}
// compute size of __TEXT,__unwind_info section
level2PagesOffset = sizeof(unwind_info_section_header) +
commonEncodings.size() * sizeof(uint32_t) +
personalities.size() * sizeof(uint32_t) +
// The extra second-level-page entry is for the sentinel
(secondLevelPages.size() + 1) *
sizeof(unwind_info_section_header_index_entry) +
entriesWithLsda.size() *
sizeof(unwind_info_section_header_lsda_index_entry);
unwindInfoSize =
level2PagesOffset + secondLevelPages.size() * SECOND_LEVEL_PAGE_BYTES;
}
// All inputs are relocated and output addresses are known, so write!
template <class Ptr>
void UnwindInfoSectionImpl<Ptr>::writeTo(uint8_t *buf) const {
assert(!cuIndices.empty() && "call only if there is unwind info");
// section header
auto *uip = reinterpret_cast<unwind_info_section_header *>(buf);
uip->version = 1;
uip->commonEncodingsArraySectionOffset = sizeof(unwind_info_section_header);
uip->commonEncodingsArrayCount = commonEncodings.size();
uip->personalityArraySectionOffset =
uip->commonEncodingsArraySectionOffset +
(uip->commonEncodingsArrayCount * sizeof(uint32_t));
uip->personalityArrayCount = personalities.size();
uip->indexSectionOffset = uip->personalityArraySectionOffset +
(uip->personalityArrayCount * sizeof(uint32_t));
uip->indexCount = secondLevelPages.size() + 1;
// Common encodings
auto *i32p = reinterpret_cast<uint32_t *>(&uip[1]);
for (const auto &encoding : commonEncodings)
*i32p++ = encoding.first;
// Personalities
for (Ptr personality : personalities)
*i32p++ =
in.got->addr + (personality - 1) * target->wordSize - in.header->addr;
// Level-1 index
uint32_t lsdaOffset =
uip->indexSectionOffset +
uip->indexCount * sizeof(unwind_info_section_header_index_entry);
uint64_t l2PagesOffset = level2PagesOffset;
auto *iep = reinterpret_cast<unwind_info_section_header_index_entry *>(i32p);
for (const SecondLevelPage &page : secondLevelPages) {
size_t idx = cuIndices[page.entryIndex];
iep->functionOffset = cuEntries[idx].functionAddress - in.header->addr;
iep->secondLevelPagesSectionOffset = l2PagesOffset;
iep->lsdaIndexArraySectionOffset =
lsdaOffset + lsdaIndex.lookup(idx) *
sizeof(unwind_info_section_header_lsda_index_entry);
iep++;
l2PagesOffset += SECOND_LEVEL_PAGE_BYTES;
}
// Level-1 sentinel
const CompactUnwindEntry<Ptr> &cuEnd = cuEntries[cuIndices.back()];
iep->functionOffset =
cuEnd.functionAddress - in.header->addr + cuEnd.functionLength;
iep->secondLevelPagesSectionOffset = 0;
iep->lsdaIndexArraySectionOffset =
lsdaOffset + entriesWithLsda.size() *
sizeof(unwind_info_section_header_lsda_index_entry);
iep++;
// LSDAs
auto *lep =
reinterpret_cast<unwind_info_section_header_lsda_index_entry *>(iep);
for (size_t idx : entriesWithLsda) {
const CompactUnwindEntry<Ptr> &cu = cuEntries[idx];
const Defined *d = symbolsVec[idx].second;
if (Reloc *r = findLsdaReloc(d->unwindEntry)) {
uint64_t va;
if (auto *isec = r->referent.dyn_cast<InputSection *>()) {
va = isec->getVA(r->addend);
} else {
auto *sym = r->referent.get<Symbol *>();
va = sym->getVA() + r->addend;
}
lep->lsdaOffset = va - in.header->addr;
}
lep->functionOffset = cu.functionAddress - in.header->addr;
lep++;
}
// Level-2 pages
auto *pp = reinterpret_cast<uint32_t *>(lep);
for (const SecondLevelPage &page : secondLevelPages) {
if (page.kind == UNWIND_SECOND_LEVEL_COMPRESSED) {
uintptr_t functionAddressBase =
cuEntries[cuIndices[page.entryIndex]].functionAddress;
auto *p2p =
reinterpret_cast<unwind_info_compressed_second_level_page_header *>(
pp);
p2p->kind = page.kind;
p2p->entryPageOffset =
sizeof(unwind_info_compressed_second_level_page_header);
p2p->entryCount = page.entryCount;
p2p->encodingsPageOffset =
p2p->entryPageOffset + p2p->entryCount * sizeof(uint32_t);
p2p->encodingsCount = page.localEncodings.size();
auto *ep = reinterpret_cast<uint32_t *>(&p2p[1]);
for (size_t i = 0; i < page.entryCount; i++) {
const CompactUnwindEntry<Ptr> &cue =
cuEntries[cuIndices[page.entryIndex + i]];
auto it = commonEncodingIndexes.find(cue.encoding);
if (it == commonEncodingIndexes.end())
it = page.localEncodingIndexes.find(cue.encoding);
*ep++ = (it->second << COMPRESSED_ENTRY_FUNC_OFFSET_BITS) |
(cue.functionAddress - functionAddressBase);
}
if (!page.localEncodings.empty())
memcpy(ep, page.localEncodings.data(),
page.localEncodings.size() * sizeof(uint32_t));
} else {
auto *p2p =
reinterpret_cast<unwind_info_regular_second_level_page_header *>(pp);
p2p->kind = page.kind;
p2p->entryPageOffset =
sizeof(unwind_info_regular_second_level_page_header);
p2p->entryCount = page.entryCount;
auto *ep = reinterpret_cast<uint32_t *>(&p2p[1]);
for (size_t i = 0; i < page.entryCount; i++) {
const CompactUnwindEntry<Ptr> &cue =
cuEntries[cuIndices[page.entryIndex + i]];
*ep++ = cue.functionAddress;
*ep++ = cue.encoding;
}
}
pp += SECOND_LEVEL_PAGE_WORDS;
}
}
UnwindInfoSection *macho::makeUnwindInfoSection() {
if (target->wordSize == 8)
return make<UnwindInfoSectionImpl<uint64_t>>();
else
return make<UnwindInfoSectionImpl<uint32_t>>();
}