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llvm-project/lld/MachO/SyntheticSections.cpp

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//===- SyntheticSections.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 "SyntheticSections.h"
#include "Config.h"
#include "ExportTrie.h"
#include "InputFiles.h"
#include "MachOStructs.h"
#include "MergedOutputSection.h"
#include "OutputSegment.h"
#include "SymbolTable.h"
#include "Symbols.h"
#include "Writer.h"
#include "lld/Common/ErrorHandler.h"
#include "lld/Common/Memory.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Support/EndianStream.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/LEB128.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/SHA256.h"
#if defined(__APPLE__)
#include <sys/mman.h>
#endif
using namespace llvm;
using namespace llvm::MachO;
using namespace llvm::support;
using namespace llvm::support::endian;
using namespace lld;
using namespace lld::macho;
InStruct macho::in;
std::vector<SyntheticSection *> macho::syntheticSections;
SyntheticSection::SyntheticSection(const char *segname, const char *name)
: OutputSection(SyntheticKind, name), segname(segname) {
isec = make<InputSection>();
isec->segname = segname;
isec->name = name;
isec->parent = this;
isec->outSecOff = 0;
syntheticSections.push_back(this);
}
// dyld3's MachOLoaded::getSlide() assumes that the __TEXT segment starts
// from the beginning of the file (i.e. the header).
MachHeaderSection::MachHeaderSection()
: SyntheticSection(segment_names::text, section_names::header) {
// XXX: This is a hack. (See D97007)
// Setting the index to 1 to pretend that this section is the text
// section.
index = 1;
}
void MachHeaderSection::addLoadCommand(LoadCommand *lc) {
loadCommands.push_back(lc);
sizeOfCmds += lc->getSize();
}
// This serves to hide (type-erase) the template parameter from
// MachHeaderSection.
template <class LP> class MachHeaderSectionImpl : public MachHeaderSection {
public:
MachHeaderSectionImpl() = default;
uint64_t getSize() const override;
void writeTo(uint8_t *buf) const override;
};
template <class LP> MachHeaderSection *macho::makeMachHeaderSection() {
return make<MachHeaderSectionImpl<LP>>();
}
template <class LP> uint64_t MachHeaderSectionImpl<LP>::getSize() const {
return sizeof(typename LP::mach_header) + sizeOfCmds + config->headerPad;
}
static uint32_t cpuSubtype() {
uint32_t subtype = target->cpuSubtype;
if (config->outputType == MH_EXECUTE && !config->staticLink &&
target->cpuSubtype == CPU_SUBTYPE_X86_64_ALL &&
config->target.Platform == PlatformKind::macOS &&
config->platformInfo.minimum >= VersionTuple(10, 5))
subtype |= CPU_SUBTYPE_LIB64;
return subtype;
}
template <class LP>
void MachHeaderSectionImpl<LP>::writeTo(uint8_t *buf) const {
auto *hdr = reinterpret_cast<typename LP::mach_header *>(buf);
hdr->magic = LP::magic;
hdr->cputype = target->cpuType;
hdr->cpusubtype = cpuSubtype();
hdr->filetype = config->outputType;
hdr->ncmds = loadCommands.size();
hdr->sizeofcmds = sizeOfCmds;
hdr->flags = MH_DYLDLINK;
if (config->namespaceKind == NamespaceKind::twolevel)
hdr->flags |= MH_NOUNDEFS | MH_TWOLEVEL;
if (config->outputType == MH_DYLIB && !config->hasReexports)
hdr->flags |= MH_NO_REEXPORTED_DYLIBS;
if (config->markDeadStrippableDylib)
hdr->flags |= MH_DEAD_STRIPPABLE_DYLIB;
if (config->outputType == MH_EXECUTE && config->isPic)
hdr->flags |= MH_PIE;
if (in.exports->hasWeakSymbol || in.weakBinding->hasNonWeakDefinition())
hdr->flags |= MH_WEAK_DEFINES;
if (in.exports->hasWeakSymbol || in.weakBinding->hasEntry())
hdr->flags |= MH_BINDS_TO_WEAK;
for (const OutputSegment *seg : outputSegments) {
for (const OutputSection *osec : seg->getSections()) {
if (isThreadLocalVariables(osec->flags)) {
hdr->flags |= MH_HAS_TLV_DESCRIPTORS;
break;
}
}
}
uint8_t *p = reinterpret_cast<uint8_t *>(hdr + 1);
for (const LoadCommand *lc : loadCommands) {
lc->writeTo(p);
p += lc->getSize();
}
}
PageZeroSection::PageZeroSection()
: SyntheticSection(segment_names::pageZero, section_names::pageZero) {}
RebaseSection::RebaseSection()
: LinkEditSection(segment_names::linkEdit, section_names::rebase) {}
namespace {
struct Rebase {
OutputSegment *segment = nullptr;
uint64_t offset = 0;
uint64_t consecutiveCount = 0;
};
} // namespace
// Rebase opcodes allow us to describe a contiguous sequence of rebase location
// using a single DO_REBASE opcode. To take advantage of it, we delay emitting
// `DO_REBASE` until we have reached the end of a contiguous sequence.
static void encodeDoRebase(Rebase &rebase, raw_svector_ostream &os) {
assert(rebase.consecutiveCount != 0);
if (rebase.consecutiveCount <= REBASE_IMMEDIATE_MASK) {
os << static_cast<uint8_t>(REBASE_OPCODE_DO_REBASE_IMM_TIMES |
rebase.consecutiveCount);
} else {
os << static_cast<uint8_t>(REBASE_OPCODE_DO_REBASE_ULEB_TIMES);
encodeULEB128(rebase.consecutiveCount, os);
}
rebase.consecutiveCount = 0;
}
static void encodeRebase(const OutputSection *osec, uint64_t outSecOff,
Rebase &lastRebase, raw_svector_ostream &os) {
OutputSegment *seg = osec->parent;
uint64_t offset = osec->getSegmentOffset() + outSecOff;
if (lastRebase.segment != seg || lastRebase.offset != offset) {
if (lastRebase.consecutiveCount != 0)
encodeDoRebase(lastRebase, os);
if (lastRebase.segment != seg) {
os << static_cast<uint8_t>(REBASE_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB |
seg->index);
encodeULEB128(offset, os);
lastRebase.segment = seg;
lastRebase.offset = offset;
} else {
assert(lastRebase.offset != offset);
os << static_cast<uint8_t>(REBASE_OPCODE_ADD_ADDR_ULEB);
encodeULEB128(offset - lastRebase.offset, os);
lastRebase.offset = offset;
}
}
++lastRebase.consecutiveCount;
// DO_REBASE causes dyld to both perform the binding and increment the offset
lastRebase.offset += target->wordSize;
}
void RebaseSection::finalizeContents() {
if (locations.empty())
return;
raw_svector_ostream os{contents};
Rebase lastRebase;
os << static_cast<uint8_t>(REBASE_OPCODE_SET_TYPE_IMM | REBASE_TYPE_POINTER);
llvm::sort(locations, [](const Location &a, const Location &b) {
return a.isec->getVA() < b.isec->getVA();
});
for (const Location &loc : locations)
encodeRebase(loc.isec->parent, loc.isec->outSecOff + loc.offset, lastRebase,
os);
if (lastRebase.consecutiveCount != 0)
encodeDoRebase(lastRebase, os);
os << static_cast<uint8_t>(REBASE_OPCODE_DONE);
}
void RebaseSection::writeTo(uint8_t *buf) const {
memcpy(buf, contents.data(), contents.size());
}
NonLazyPointerSectionBase::NonLazyPointerSectionBase(const char *segname,
const char *name)
: SyntheticSection(segname, name) {
align = target->wordSize;
flags = S_NON_LAZY_SYMBOL_POINTERS;
}
void macho::addNonLazyBindingEntries(const Symbol *sym,
const InputSection *isec, uint64_t offset,
int64_t addend) {
if (const auto *dysym = dyn_cast<DylibSymbol>(sym)) {
in.binding->addEntry(dysym, isec, offset, addend);
if (dysym->isWeakDef())
in.weakBinding->addEntry(sym, isec, offset, addend);
} else if (const auto *defined = dyn_cast<Defined>(sym)) {
in.rebase->addEntry(isec, offset);
if (defined->isExternalWeakDef())
in.weakBinding->addEntry(sym, isec, offset, addend);
} else {
// Undefined symbols are filtered out in scanRelocations(); we should never
// get here
llvm_unreachable("cannot bind to an undefined symbol");
}
}
void NonLazyPointerSectionBase::addEntry(Symbol *sym) {
if (entries.insert(sym)) {
assert(!sym->isInGot());
sym->gotIndex = entries.size() - 1;
addNonLazyBindingEntries(sym, isec, sym->gotIndex * target->wordSize);
}
}
void NonLazyPointerSectionBase::writeTo(uint8_t *buf) const {
for (size_t i = 0, n = entries.size(); i < n; ++i)
if (auto *defined = dyn_cast<Defined>(entries[i]))
write64le(&buf[i * target->wordSize], defined->getVA());
}
BindingSection::BindingSection()
: LinkEditSection(segment_names::linkEdit, section_names::binding) {}
namespace {
struct Binding {
OutputSegment *segment = nullptr;
uint64_t offset = 0;
int64_t addend = 0;
int16_t ordinal = 0;
};
} // namespace
// Encode a sequence of opcodes that tell dyld to write the address of symbol +
// addend at osec->addr + outSecOff.
//
// The bind opcode "interpreter" remembers the values of each binding field, so
// we only need to encode the differences between bindings. Hence the use of
// lastBinding.
static void encodeBinding(const Symbol *sym, const OutputSection *osec,
uint64_t outSecOff, int64_t addend,
bool isWeakBinding, Binding &lastBinding,
raw_svector_ostream &os) {
OutputSegment *seg = osec->parent;
uint64_t offset = osec->getSegmentOffset() + outSecOff;
if (lastBinding.segment != seg) {
os << static_cast<uint8_t>(BIND_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB |
seg->index);
encodeULEB128(offset, os);
lastBinding.segment = seg;
lastBinding.offset = offset;
} else if (lastBinding.offset != offset) {
os << static_cast<uint8_t>(BIND_OPCODE_ADD_ADDR_ULEB);
encodeULEB128(offset - lastBinding.offset, os);
lastBinding.offset = offset;
}
if (lastBinding.addend != addend) {
os << static_cast<uint8_t>(BIND_OPCODE_SET_ADDEND_SLEB);
encodeSLEB128(addend, os);
lastBinding.addend = addend;
}
uint8_t flags = BIND_OPCODE_SET_SYMBOL_TRAILING_FLAGS_IMM;
if (!isWeakBinding && sym->isWeakRef())
flags |= BIND_SYMBOL_FLAGS_WEAK_IMPORT;
os << flags << sym->getName() << '\0'
<< static_cast<uint8_t>(BIND_OPCODE_SET_TYPE_IMM | BIND_TYPE_POINTER)
<< static_cast<uint8_t>(BIND_OPCODE_DO_BIND);
// DO_BIND causes dyld to both perform the binding and increment the offset
lastBinding.offset += target->wordSize;
}
// Non-weak bindings need to have their dylib ordinal encoded as well.
static int16_t ordinalForDylibSymbol(const DylibSymbol &dysym) {
return config->namespaceKind == NamespaceKind::flat || dysym.isDynamicLookup()
? static_cast<int16_t>(BIND_SPECIAL_DYLIB_FLAT_LOOKUP)
: dysym.getFile()->ordinal;
}
static void encodeDylibOrdinal(int16_t ordinal, raw_svector_ostream &os) {
if (ordinal <= 0) {
os << static_cast<uint8_t>(BIND_OPCODE_SET_DYLIB_SPECIAL_IMM |
(ordinal & BIND_IMMEDIATE_MASK));
} else if (ordinal <= BIND_IMMEDIATE_MASK) {
os << static_cast<uint8_t>(BIND_OPCODE_SET_DYLIB_ORDINAL_IMM | ordinal);
} else {
os << static_cast<uint8_t>(BIND_OPCODE_SET_DYLIB_ORDINAL_ULEB);
encodeULEB128(ordinal, os);
}
}
static void encodeWeakOverride(const Defined *defined,
raw_svector_ostream &os) {
os << static_cast<uint8_t>(BIND_OPCODE_SET_SYMBOL_TRAILING_FLAGS_IMM |
BIND_SYMBOL_FLAGS_NON_WEAK_DEFINITION)
<< defined->getName() << '\0';
}
// Emit bind opcodes, which are a stream of byte-sized opcodes that dyld
// interprets to update a record with the following fields:
// * segment index (of the segment to write the symbol addresses to, typically
// the __DATA_CONST segment which contains the GOT)
// * offset within the segment, indicating the next location to write a binding
// * symbol type
// * symbol library ordinal (the index of its library's LC_LOAD_DYLIB command)
// * symbol name
// * addend
// When dyld sees BIND_OPCODE_DO_BIND, it uses the current record state to bind
// a symbol in the GOT, and increments the segment offset to point to the next
// entry. It does *not* clear the record state after doing the bind, so
// subsequent opcodes only need to encode the differences between bindings.
void BindingSection::finalizeContents() {
raw_svector_ostream os{contents};
Binding lastBinding;
// Since bindings are delta-encoded, sorting them allows for a more compact
// result. Note that sorting by address alone ensures that bindings for the
// same segment / section are located together.
llvm::sort(bindings, [](const BindingEntry &a, const BindingEntry &b) {
return a.target.getVA() < b.target.getVA();
});
for (const BindingEntry &b : bindings) {
int16_t ordinal = ordinalForDylibSymbol(*b.dysym);
if (ordinal != lastBinding.ordinal) {
encodeDylibOrdinal(ordinal, os);
lastBinding.ordinal = ordinal;
}
encodeBinding(b.dysym, b.target.isec->parent,
b.target.isec->outSecOff + b.target.offset, b.addend,
/*isWeakBinding=*/false, lastBinding, os);
}
if (!bindings.empty())
os << static_cast<uint8_t>(BIND_OPCODE_DONE);
}
void BindingSection::writeTo(uint8_t *buf) const {
memcpy(buf, contents.data(), contents.size());
}
WeakBindingSection::WeakBindingSection()
: LinkEditSection(segment_names::linkEdit, section_names::weakBinding) {}
void WeakBindingSection::finalizeContents() {
raw_svector_ostream os{contents};
Binding lastBinding;
for (const Defined *defined : definitions)
encodeWeakOverride(defined, os);
// Since bindings are delta-encoded, sorting them allows for a more compact
// result.
llvm::sort(bindings,
[](const WeakBindingEntry &a, const WeakBindingEntry &b) {
return a.target.getVA() < b.target.getVA();
});
for (const WeakBindingEntry &b : bindings)
encodeBinding(b.symbol, b.target.isec->parent,
b.target.isec->outSecOff + b.target.offset, b.addend,
/*isWeakBinding=*/true, lastBinding, os);
if (!bindings.empty() || !definitions.empty())
os << static_cast<uint8_t>(BIND_OPCODE_DONE);
}
void WeakBindingSection::writeTo(uint8_t *buf) const {
memcpy(buf, contents.data(), contents.size());
}
StubsSection::StubsSection()
: SyntheticSection(segment_names::text, "__stubs") {
flags = S_SYMBOL_STUBS | S_ATTR_SOME_INSTRUCTIONS | S_ATTR_PURE_INSTRUCTIONS;
// The stubs section comprises machine instructions, which are aligned to
// 4 bytes on the archs we care about.
align = 4;
reserved2 = target->stubSize;
}
uint64_t StubsSection::getSize() const {
return entries.size() * target->stubSize;
}
void StubsSection::writeTo(uint8_t *buf) const {
size_t off = 0;
for (const Symbol *sym : entries) {
target->writeStub(buf + off, *sym);
off += target->stubSize;
}
}
bool StubsSection::addEntry(Symbol *sym) {
bool inserted = entries.insert(sym);
if (inserted)
sym->stubsIndex = entries.size() - 1;
return inserted;
}
StubHelperSection::StubHelperSection()
: SyntheticSection(segment_names::text, "__stub_helper") {
flags = S_ATTR_SOME_INSTRUCTIONS | S_ATTR_PURE_INSTRUCTIONS;
align = 4; // This section comprises machine instructions
}
uint64_t StubHelperSection::getSize() const {
return target->stubHelperHeaderSize +
in.lazyBinding->getEntries().size() * target->stubHelperEntrySize;
}
bool StubHelperSection::isNeeded() const { return in.lazyBinding->isNeeded(); }
void StubHelperSection::writeTo(uint8_t *buf) const {
target->writeStubHelperHeader(buf);
size_t off = target->stubHelperHeaderSize;
for (const DylibSymbol *sym : in.lazyBinding->getEntries()) {
target->writeStubHelperEntry(buf + off, *sym, addr + off);
off += target->stubHelperEntrySize;
}
}
void StubHelperSection::setup() {
stubBinder = dyn_cast_or_null<DylibSymbol>(symtab->find("dyld_stub_binder"));
if (stubBinder == nullptr) {
error("symbol dyld_stub_binder not found (normally in libSystem.dylib). "
"Needed to perform lazy binding.");
return;
}
stubBinder->refState = RefState::Strong;
in.got->addEntry(stubBinder);
inputSections.push_back(in.imageLoaderCache);
dyldPrivate =
make<Defined>("__dyld_private", nullptr, in.imageLoaderCache, 0, 0,
/*isWeakDef=*/false,
/*isExternal=*/false, /*isPrivateExtern=*/false);
}
ImageLoaderCacheSection::ImageLoaderCacheSection() {
segname = segment_names::data;
name = "__data";
uint8_t *arr = bAlloc.Allocate<uint8_t>(target->wordSize);
memset(arr, 0, target->wordSize);
data = {arr, target->wordSize};
align = target->wordSize;
}
LazyPointerSection::LazyPointerSection()
: SyntheticSection(segment_names::data, "__la_symbol_ptr") {
align = target->wordSize;
flags = S_LAZY_SYMBOL_POINTERS;
}
uint64_t LazyPointerSection::getSize() const {
return in.stubs->getEntries().size() * target->wordSize;
}
bool LazyPointerSection::isNeeded() const {
return !in.stubs->getEntries().empty();
}
void LazyPointerSection::writeTo(uint8_t *buf) const {
size_t off = 0;
for (const Symbol *sym : in.stubs->getEntries()) {
if (const auto *dysym = dyn_cast<DylibSymbol>(sym)) {
if (dysym->hasStubsHelper()) {
uint64_t stubHelperOffset =
target->stubHelperHeaderSize +
dysym->stubsHelperIndex * target->stubHelperEntrySize;
write64le(buf + off, in.stubHelper->addr + stubHelperOffset);
}
} else {
write64le(buf + off, sym->getVA());
}
off += target->wordSize;
}
}
LazyBindingSection::LazyBindingSection()
: LinkEditSection(segment_names::linkEdit, section_names::lazyBinding) {}
void LazyBindingSection::finalizeContents() {
// TODO: Just precompute output size here instead of writing to a temporary
// buffer
for (DylibSymbol *sym : entries)
sym->lazyBindOffset = encode(*sym);
}
void LazyBindingSection::writeTo(uint8_t *buf) const {
memcpy(buf, contents.data(), contents.size());
}
void LazyBindingSection::addEntry(DylibSymbol *dysym) {
if (entries.insert(dysym)) {
dysym->stubsHelperIndex = entries.size() - 1;
in.rebase->addEntry(in.lazyPointers->isec,
dysym->stubsIndex * target->wordSize);
}
}
// Unlike the non-lazy binding section, the bind opcodes in this section aren't
// interpreted all at once. Rather, dyld will start interpreting opcodes at a
// given offset, typically only binding a single symbol before it finds a
// BIND_OPCODE_DONE terminator. As such, unlike in the non-lazy-binding case,
// we cannot encode just the differences between symbols; we have to emit the
// complete bind information for each symbol.
uint32_t LazyBindingSection::encode(const DylibSymbol &sym) {
uint32_t opstreamOffset = contents.size();
OutputSegment *dataSeg = in.lazyPointers->parent;
os << static_cast<uint8_t>(BIND_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB |
dataSeg->index);
uint64_t offset = in.lazyPointers->addr - dataSeg->firstSection()->addr +
sym.stubsIndex * target->wordSize;
encodeULEB128(offset, os);
encodeDylibOrdinal(ordinalForDylibSymbol(sym), os);
uint8_t flags = BIND_OPCODE_SET_SYMBOL_TRAILING_FLAGS_IMM;
if (sym.isWeakRef())
flags |= BIND_SYMBOL_FLAGS_WEAK_IMPORT;
os << flags << sym.getName() << '\0'
<< static_cast<uint8_t>(BIND_OPCODE_DO_BIND)
<< static_cast<uint8_t>(BIND_OPCODE_DONE);
return opstreamOffset;
}
ExportSection::ExportSection()
: LinkEditSection(segment_names::linkEdit, section_names::export_) {}
static void validateExportSymbol(const Defined *defined) {
StringRef symbolName = defined->getName();
if (defined->privateExtern && config->exportedSymbols.match(symbolName))
error("cannot export hidden symbol " + symbolName + "\n>>> defined in " +
toString(defined->getFile()));
}
static bool shouldExportSymbol(const Defined *defined) {
if (defined->privateExtern)
return false;
// TODO: Is this a performance bottleneck? If a build has mostly
// global symbols in the input but uses -exported_symbols to filter
// out most of them, then it would be better to set the value of
// privateExtern at parse time instead of calling
// exportedSymbols.match() more than once.
//
// Measurements show that symbol ordering (which again looks up
// every symbol in a hashmap) is the biggest bottleneck when linking
// chromium_framework, so this will likely be worth optimizing.
return config->exportedSymbols.empty()
? !config->unexportedSymbols.match(defined->getName())
: config->exportedSymbols.match(defined->getName());
}
void ExportSection::finalizeContents() {
trieBuilder.setImageBase(in.header->addr);
for (const Symbol *sym : symtab->getSymbols()) {
if (const auto *defined = dyn_cast<Defined>(sym)) {
validateExportSymbol(defined);
if (!shouldExportSymbol(defined))
continue;
trieBuilder.addSymbol(*defined);
hasWeakSymbol = hasWeakSymbol || sym->isWeakDef();
}
}
size = trieBuilder.build();
}
void ExportSection::writeTo(uint8_t *buf) const { trieBuilder.writeTo(buf); }
FunctionStartsSection::FunctionStartsSection()
: LinkEditSection(segment_names::linkEdit, section_names::functionStarts) {}
void FunctionStartsSection::finalizeContents() {
raw_svector_ostream os{contents};
uint64_t addr = in.header->addr;
for (const Symbol *sym : symtab->getSymbols()) {
if (const auto *defined = dyn_cast<Defined>(sym)) {
if (!defined->isec || !isCodeSection(defined->isec))
continue;
// TODO: Add support for thumbs, in that case
// the lowest bit of nextAddr needs to be set to 1.
uint64_t nextAddr = defined->getVA();
uint64_t delta = nextAddr - addr;
if (delta == 0)
continue;
encodeULEB128(delta, os);
addr = nextAddr;
}
}
os << '\0';
}
void FunctionStartsSection::writeTo(uint8_t *buf) const {
memcpy(buf, contents.data(), contents.size());
}
SymtabSection::SymtabSection(StringTableSection &stringTableSection)
: LinkEditSection(segment_names::linkEdit, section_names::symbolTable),
stringTableSection(stringTableSection) {}
void SymtabSection::emitBeginSourceStab(DWARFUnit *compileUnit) {
StabsEntry stab(N_SO);
SmallString<261> dir(compileUnit->getCompilationDir());
StringRef sep = sys::path::get_separator();
// We don't use `path::append` here because we want an empty `dir` to result
// in an absolute path. `append` would give us a relative path for that case.
if (!dir.endswith(sep))
dir += sep;
stab.strx = stringTableSection.addString(
saver.save(dir + compileUnit->getUnitDIE().getShortName()));
stabs.emplace_back(std::move(stab));
}
void SymtabSection::emitEndSourceStab() {
StabsEntry stab(N_SO);
stab.sect = 1;
stabs.emplace_back(std::move(stab));
}
void SymtabSection::emitObjectFileStab(ObjFile *file) {
StabsEntry stab(N_OSO);
stab.sect = target->cpuSubtype;
SmallString<261> path(!file->archiveName.empty() ? file->archiveName
: file->getName());
std::error_code ec = sys::fs::make_absolute(path);
if (ec)
fatal("failed to get absolute path for " + path);
if (!file->archiveName.empty())
path.append({"(", file->getName(), ")"});
stab.strx = stringTableSection.addString(saver.save(path.str()));
stab.desc = 1;
stab.value = file->modTime;
stabs.emplace_back(std::move(stab));
}
void SymtabSection::emitEndFunStab(Defined *defined) {
StabsEntry stab(N_FUN);
stab.value = defined->size;
stabs.emplace_back(std::move(stab));
}
void SymtabSection::emitStabs() {
for (const std::string &s : config->astPaths) {
StabsEntry astStab(N_AST);
astStab.strx = stringTableSection.addString(s);
stabs.emplace_back(std::move(astStab));
}
std::vector<Defined *> symbolsNeedingStabs;
for (const SymtabEntry &entry :
concat<SymtabEntry>(localSymbols, externalSymbols)) {
Symbol *sym = entry.sym;
if (auto *defined = dyn_cast<Defined>(sym)) {
if (defined->isAbsolute())
continue;
InputSection *isec = defined->isec;
ObjFile *file = dyn_cast_or_null<ObjFile>(isec->file);
if (!file || !file->compileUnit)
continue;
symbolsNeedingStabs.push_back(defined);
}
}
llvm::stable_sort(symbolsNeedingStabs, [&](Defined *a, Defined *b) {
return a->isec->file->id < b->isec->file->id;
});
// Emit STABS symbols so that dsymutil and/or the debugger can map address
// regions in the final binary to the source and object files from which they
// originated.
InputFile *lastFile = nullptr;
for (Defined *defined : symbolsNeedingStabs) {
InputSection *isec = defined->isec;
ObjFile *file = cast<ObjFile>(isec->file);
if (lastFile == nullptr || lastFile != file) {
if (lastFile != nullptr)
emitEndSourceStab();
lastFile = file;
emitBeginSourceStab(file->compileUnit);
emitObjectFileStab(file);
}
StabsEntry symStab;
symStab.sect = defined->isec->parent->index;
symStab.strx = stringTableSection.addString(defined->getName());
symStab.value = defined->getVA();
if (isCodeSection(isec)) {
symStab.type = N_FUN;
stabs.emplace_back(std::move(symStab));
emitEndFunStab(defined);
} else {
symStab.type = defined->isExternal() ? N_GSYM : N_STSYM;
stabs.emplace_back(std::move(symStab));
}
}
if (!stabs.empty())
emitEndSourceStab();
}
void SymtabSection::finalizeContents() {
auto addSymbol = [&](std::vector<SymtabEntry> &symbols, Symbol *sym) {
uint32_t strx = stringTableSection.addString(sym->getName());
symbols.push_back({sym, strx});
};
// Local symbols aren't in the SymbolTable, so we walk the list of object
// files to gather them.
for (const InputFile *file : inputFiles) {
if (auto *objFile = dyn_cast<ObjFile>(file)) {
for (Symbol *sym : objFile->symbols) {
if (sym == nullptr)
continue;
// TODO: when we implement -dead_strip, we should filter out symbols
// that belong to dead sections.
if (auto *defined = dyn_cast<Defined>(sym)) {
if (!defined->isExternal()) {
StringRef name = defined->getName();
if (!name.startswith("l") && !name.startswith("L"))
addSymbol(localSymbols, sym);
}
}
}
}
}
// __dyld_private is a local symbol too. It's linker-created and doesn't
// exist in any object file.
if (Defined *dyldPrivate = in.stubHelper->dyldPrivate)
addSymbol(localSymbols, dyldPrivate);
for (Symbol *sym : symtab->getSymbols()) {
if (auto *defined = dyn_cast<Defined>(sym)) {
if (!defined->includeInSymtab)
continue;
assert(defined->isExternal());
addSymbol(externalSymbols, defined);
} else if (auto *dysym = dyn_cast<DylibSymbol>(sym)) {
if (dysym->isReferenced())
addSymbol(undefinedSymbols, sym);
}
}
emitStabs();
uint32_t symtabIndex = stabs.size();
for (const SymtabEntry &entry :
concat<SymtabEntry>(localSymbols, externalSymbols, undefinedSymbols)) {
entry.sym->symtabIndex = symtabIndex++;
}
}
uint32_t SymtabSection::getNumSymbols() const {
return stabs.size() + localSymbols.size() + externalSymbols.size() +
undefinedSymbols.size();
}
// This serves to hide (type-erase) the template parameter from SymtabSection.
template <class LP> class SymtabSectionImpl : public SymtabSection {
public:
SymtabSectionImpl(StringTableSection &stringTableSection)
: SymtabSection(stringTableSection) {}
uint64_t getRawSize() const override;
void writeTo(uint8_t *buf) const override;
};
template <class LP> uint64_t SymtabSectionImpl<LP>::getRawSize() const {
return getNumSymbols() * sizeof(typename LP::nlist);
}
template <class LP> void SymtabSectionImpl<LP>::writeTo(uint8_t *buf) const {
auto *nList = reinterpret_cast<typename LP::nlist *>(buf);
// Emit the stabs entries before the "real" symbols. We cannot emit them
// after as that would render Symbol::symtabIndex inaccurate.
for (const StabsEntry &entry : stabs) {
nList->n_strx = entry.strx;
nList->n_type = entry.type;
nList->n_sect = entry.sect;
nList->n_desc = entry.desc;
nList->n_value = entry.value;
++nList;
}
for (const SymtabEntry &entry : concat<const SymtabEntry>(
localSymbols, externalSymbols, undefinedSymbols)) {
nList->n_strx = entry.strx;
// TODO populate n_desc with more flags
if (auto *defined = dyn_cast<Defined>(entry.sym)) {
uint8_t scope = 0;
if (!shouldExportSymbol(defined)) {
// Private external -- dylib scoped symbol.
// Promote to non-external at link time.
assert(defined->isExternal() && "invalid input file");
scope = N_PEXT;
} else if (defined->isExternal()) {
// Normal global symbol.
scope = N_EXT;
} else {
// TU-local symbol from localSymbols.
scope = 0;
}
if (defined->isAbsolute()) {
nList->n_type = scope | N_ABS;
nList->n_sect = NO_SECT;
nList->n_value = defined->value;
} else {
nList->n_type = scope | N_SECT;
nList->n_sect = defined->isec->parent->index;
// For the N_SECT symbol type, n_value is the address of the symbol
nList->n_value = defined->getVA();
}
nList->n_desc |= defined->isExternalWeakDef() ? N_WEAK_DEF : 0;
} else if (auto *dysym = dyn_cast<DylibSymbol>(entry.sym)) {
uint16_t n_desc = nList->n_desc;
int16_t ordinal = ordinalForDylibSymbol(*dysym);
if (ordinal == BIND_SPECIAL_DYLIB_FLAT_LOOKUP)
SET_LIBRARY_ORDINAL(n_desc, DYNAMIC_LOOKUP_ORDINAL);
else if (ordinal == BIND_SPECIAL_DYLIB_MAIN_EXECUTABLE)
SET_LIBRARY_ORDINAL(n_desc, EXECUTABLE_ORDINAL);
else {
assert(ordinal > 0);
SET_LIBRARY_ORDINAL(n_desc, static_cast<uint8_t>(ordinal));
}
nList->n_type = N_EXT;
n_desc |= dysym->isWeakDef() ? N_WEAK_DEF : 0;
n_desc |= dysym->isWeakRef() ? N_WEAK_REF : 0;
nList->n_desc = n_desc;
}
++nList;
}
}
template <class LP>
SymtabSection *
macho::makeSymtabSection(StringTableSection &stringTableSection) {
return make<SymtabSectionImpl<LP>>(stringTableSection);
}
IndirectSymtabSection::IndirectSymtabSection()
: LinkEditSection(segment_names::linkEdit,
section_names::indirectSymbolTable) {}
uint32_t IndirectSymtabSection::getNumSymbols() const {
return in.got->getEntries().size() + in.tlvPointers->getEntries().size() +
in.stubs->getEntries().size();
}
bool IndirectSymtabSection::isNeeded() const {
return in.got->isNeeded() || in.tlvPointers->isNeeded() ||
in.stubs->isNeeded();
}
void IndirectSymtabSection::finalizeContents() {
uint32_t off = 0;
in.got->reserved1 = off;
off += in.got->getEntries().size();
in.tlvPointers->reserved1 = off;
off += in.tlvPointers->getEntries().size();
// There is a 1:1 correspondence between stubs and LazyPointerSection
// entries, so they can share the same sub-array in the table.
in.stubs->reserved1 = in.lazyPointers->reserved1 = off;
}
static uint32_t indirectValue(const Symbol *sym) {
return sym->symtabIndex != UINT32_MAX ? sym->symtabIndex
: INDIRECT_SYMBOL_LOCAL;
}
void IndirectSymtabSection::writeTo(uint8_t *buf) const {
uint32_t off = 0;
for (const Symbol *sym : in.got->getEntries()) {
write32le(buf + off * sizeof(uint32_t), indirectValue(sym));
++off;
}
for (const Symbol *sym : in.tlvPointers->getEntries()) {
write32le(buf + off * sizeof(uint32_t), indirectValue(sym));
++off;
}
for (const Symbol *sym : in.stubs->getEntries()) {
write32le(buf + off * sizeof(uint32_t), indirectValue(sym));
++off;
}
}
StringTableSection::StringTableSection()
: LinkEditSection(segment_names::linkEdit, section_names::stringTable) {}
uint32_t StringTableSection::addString(StringRef str) {
uint32_t strx = size;
strings.push_back(str); // TODO: consider deduplicating strings
size += str.size() + 1; // account for null terminator
return strx;
}
void StringTableSection::writeTo(uint8_t *buf) const {
uint32_t off = 0;
for (StringRef str : strings) {
memcpy(buf + off, str.data(), str.size());
off += str.size() + 1; // account for null terminator
}
}
CodeSignatureSection::CodeSignatureSection()
: LinkEditSection(segment_names::linkEdit, section_names::codeSignature) {
align = 16; // required by libstuff
fileName = config->outputFile;
size_t slashIndex = fileName.rfind("/");
if (slashIndex != std::string::npos)
fileName = fileName.drop_front(slashIndex + 1);
allHeadersSize = alignTo<16>(fixedHeadersSize + fileName.size() + 1);
fileNamePad = allHeadersSize - fixedHeadersSize - fileName.size();
}
uint32_t CodeSignatureSection::getBlockCount() const {
return (fileOff + blockSize - 1) / blockSize;
}
uint64_t CodeSignatureSection::getRawSize() const {
return allHeadersSize + getBlockCount() * hashSize;
}
void CodeSignatureSection::writeHashes(uint8_t *buf) const {
uint8_t *code = buf;
uint8_t *codeEnd = buf + fileOff;
uint8_t *hashes = codeEnd + allHeadersSize;
while (code < codeEnd) {
StringRef block(reinterpret_cast<char *>(code),
std::min(codeEnd - code, static_cast<ssize_t>(blockSize)));
SHA256 hasher;
hasher.update(block);
StringRef hash = hasher.final();
assert(hash.size() == hashSize);
memcpy(hashes, hash.data(), hashSize);
code += blockSize;
hashes += hashSize;
}
#if defined(__APPLE__)
// This is macOS-specific work-around and makes no sense for any
// other host OS. See https://openradar.appspot.com/FB8914231
//
// The macOS kernel maintains a signature-verification cache to
// quickly validate applications at time of execve(2). The trouble
// is that for the kernel creates the cache entry at the time of the
// mmap(2) call, before we have a chance to write either the code to
// sign or the signature header+hashes. The fix is to invalidate
// all cached data associated with the output file, thus discarding
// the bogus prematurely-cached signature.
msync(buf, fileOff + getSize(), MS_INVALIDATE);
#endif
}
void CodeSignatureSection::writeTo(uint8_t *buf) const {
uint32_t signatureSize = static_cast<uint32_t>(getSize());
auto *superBlob = reinterpret_cast<CS_SuperBlob *>(buf);
write32be(&superBlob->magic, CSMAGIC_EMBEDDED_SIGNATURE);
write32be(&superBlob->length, signatureSize);
write32be(&superBlob->count, 1);
auto *blobIndex = reinterpret_cast<CS_BlobIndex *>(&superBlob[1]);
write32be(&blobIndex->type, CSSLOT_CODEDIRECTORY);
write32be(&blobIndex->offset, blobHeadersSize);
auto *codeDirectory =
reinterpret_cast<CS_CodeDirectory *>(buf + blobHeadersSize);
write32be(&codeDirectory->magic, CSMAGIC_CODEDIRECTORY);
write32be(&codeDirectory->length, signatureSize - blobHeadersSize);
write32be(&codeDirectory->version, CS_SUPPORTSEXECSEG);
write32be(&codeDirectory->flags, CS_ADHOC | CS_LINKER_SIGNED);
write32be(&codeDirectory->hashOffset,
sizeof(CS_CodeDirectory) + fileName.size() + fileNamePad);
write32be(&codeDirectory->identOffset, sizeof(CS_CodeDirectory));
codeDirectory->nSpecialSlots = 0;
write32be(&codeDirectory->nCodeSlots, getBlockCount());
write32be(&codeDirectory->codeLimit, fileOff);
codeDirectory->hashSize = static_cast<uint8_t>(hashSize);
codeDirectory->hashType = kSecCodeSignatureHashSHA256;
codeDirectory->platform = 0;
codeDirectory->pageSize = blockSizeShift;
codeDirectory->spare2 = 0;
codeDirectory->scatterOffset = 0;
codeDirectory->teamOffset = 0;
codeDirectory->spare3 = 0;
codeDirectory->codeLimit64 = 0;
OutputSegment *textSeg = getOrCreateOutputSegment(segment_names::text);
write64be(&codeDirectory->execSegBase, textSeg->fileOff);
write64be(&codeDirectory->execSegLimit, textSeg->fileSize);
write64be(&codeDirectory->execSegFlags,
config->outputType == MH_EXECUTE ? CS_EXECSEG_MAIN_BINARY : 0);
auto *id = reinterpret_cast<char *>(&codeDirectory[1]);
memcpy(id, fileName.begin(), fileName.size());
memset(id + fileName.size(), 0, fileNamePad);
}
void macho::createSyntheticSymbols() {
auto addHeaderSymbol = [](const char *name) {
symtab->addSynthetic(name, in.header->isec, 0,
/*privateExtern=*/true,
/*includeInSymtab*/ false);
};
switch (config->outputType) {
// FIXME: Assign the right address value for these symbols
// (rather than 0). But we need to do that after assignAddresses().
case MH_EXECUTE:
// If linking PIE, __mh_execute_header is a defined symbol in
// __TEXT, __text)
// Otherwise, it's an absolute symbol.
if (config->isPic)
symtab->addSynthetic("__mh_execute_header", in.header->isec, 0,
/*privateExtern*/ false,
/*includeInSymbtab*/ true);
else
symtab->addSynthetic("__mh_execute_header",
/*isec*/ nullptr, 0,
/*privateExtern*/ false,
/*includeInSymbtab*/ true);
break;
// The following symbols are N_SECT symbols, even though the header is not
// part of any section and that they are private to the bundle/dylib/object
// they are part of.
case MH_BUNDLE:
addHeaderSymbol("__mh_bundle_header");
break;
case MH_DYLIB:
addHeaderSymbol("__mh_dylib_header");
break;
case MH_DYLINKER:
addHeaderSymbol("__mh_dylinker_header");
break;
case MH_OBJECT:
addHeaderSymbol("__mh_object_header");
break;
default:
llvm_unreachable("unexpected outputType");
break;
}
// The Itanium C++ ABI requires dylibs to pass a pointer to __cxa_atexit
// which does e.g. cleanup of static global variables. The ABI document
// says that the pointer can point to any address in one of the dylib's
// segments, but in practice ld64 seems to set it to point to the header,
// so that's what's implemented here.
addHeaderSymbol("___dso_handle");
}
template MachHeaderSection *macho::makeMachHeaderSection<LP64>();
template MachHeaderSection *macho::makeMachHeaderSection<ILP32>();
template SymtabSection *macho::makeSymtabSection<LP64>(StringTableSection &);
template SymtabSection *macho::makeSymtabSection<ILP32>(StringTableSection &);
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