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llvm-project/lld/MachO/Writer.cpp

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//===- Writer.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 "Writer.h"
#include "ConcatOutputSection.h"
#include "Config.h"
#include "InputFiles.h"
#include "InputSection.h"
#include "MapFile.h"
#include "OutputSection.h"
#include "OutputSegment.h"
#include "SectionPriorities.h"
#include "SymbolTable.h"
#include "Symbols.h"
#include "SyntheticSections.h"
#include "Target.h"
#include "UnwindInfoSection.h"
#include "lld/Common/Arrays.h"
#include "lld/Common/CommonLinkerContext.h"
#include "llvm/BinaryFormat/MachO.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/Support/LEB128.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/Parallel.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/ThreadPool.h"
#include "llvm/Support/TimeProfiler.h"
#include "llvm/Support/xxhash.h"
#include <algorithm>
using namespace llvm;
using namespace llvm::MachO;
using namespace llvm::sys;
using namespace lld;
using namespace lld::macho;
namespace {
class LCUuid;
class Writer {
public:
Writer() : buffer(errorHandler().outputBuffer) {}
void treatSpecialUndefineds();
void scanRelocations();
void scanSymbols();
template <class LP> void createOutputSections();
template <class LP> void createLoadCommands();
void finalizeAddresses();
void finalizeLinkEditSegment();
void assignAddresses(OutputSegment *);
void openFile();
void writeSections();
void writeUuid();
void writeCodeSignature();
void writeOutputFile();
template <class LP> void run();
ThreadPool threadPool;
std::unique_ptr<FileOutputBuffer> &buffer;
uint64_t addr = 0;
uint64_t fileOff = 0;
MachHeaderSection *header = nullptr;
StringTableSection *stringTableSection = nullptr;
SymtabSection *symtabSection = nullptr;
IndirectSymtabSection *indirectSymtabSection = nullptr;
CodeSignatureSection *codeSignatureSection = nullptr;
DataInCodeSection *dataInCodeSection = nullptr;
FunctionStartsSection *functionStartsSection = nullptr;
LCUuid *uuidCommand = nullptr;
OutputSegment *linkEditSegment = nullptr;
};
// LC_DYLD_INFO_ONLY stores the offsets of symbol import/export information.
class LCDyldInfo final : public LoadCommand {
public:
LCDyldInfo(RebaseSection *rebaseSection, BindingSection *bindingSection,
WeakBindingSection *weakBindingSection,
LazyBindingSection *lazyBindingSection,
ExportSection *exportSection)
: rebaseSection(rebaseSection), bindingSection(bindingSection),
weakBindingSection(weakBindingSection),
lazyBindingSection(lazyBindingSection), exportSection(exportSection) {}
uint32_t getSize() const override { return sizeof(dyld_info_command); }
void writeTo(uint8_t *buf) const override {
auto *c = reinterpret_cast<dyld_info_command *>(buf);
c->cmd = LC_DYLD_INFO_ONLY;
c->cmdsize = getSize();
if (rebaseSection->isNeeded()) {
c->rebase_off = rebaseSection->fileOff;
c->rebase_size = rebaseSection->getFileSize();
}
if (bindingSection->isNeeded()) {
c->bind_off = bindingSection->fileOff;
c->bind_size = bindingSection->getFileSize();
}
if (weakBindingSection->isNeeded()) {
c->weak_bind_off = weakBindingSection->fileOff;
c->weak_bind_size = weakBindingSection->getFileSize();
}
if (lazyBindingSection->isNeeded()) {
c->lazy_bind_off = lazyBindingSection->fileOff;
c->lazy_bind_size = lazyBindingSection->getFileSize();
}
if (exportSection->isNeeded()) {
c->export_off = exportSection->fileOff;
c->export_size = exportSection->getFileSize();
}
}
RebaseSection *rebaseSection;
BindingSection *bindingSection;
WeakBindingSection *weakBindingSection;
LazyBindingSection *lazyBindingSection;
ExportSection *exportSection;
};
class LCSubFramework final : public LoadCommand {
public:
LCSubFramework(StringRef umbrella) : umbrella(umbrella) {}
uint32_t getSize() const override {
return alignTo(sizeof(sub_framework_command) + umbrella.size() + 1,
target->wordSize);
}
void writeTo(uint8_t *buf) const override {
auto *c = reinterpret_cast<sub_framework_command *>(buf);
buf += sizeof(sub_framework_command);
c->cmd = LC_SUB_FRAMEWORK;
c->cmdsize = getSize();
c->umbrella = sizeof(sub_framework_command);
memcpy(buf, umbrella.data(), umbrella.size());
buf[umbrella.size()] = '\0';
}
private:
const StringRef umbrella;
};
class LCFunctionStarts final : public LoadCommand {
public:
explicit LCFunctionStarts(FunctionStartsSection *functionStartsSection)
: functionStartsSection(functionStartsSection) {}
uint32_t getSize() const override { return sizeof(linkedit_data_command); }
void writeTo(uint8_t *buf) const override {
auto *c = reinterpret_cast<linkedit_data_command *>(buf);
c->cmd = LC_FUNCTION_STARTS;
c->cmdsize = getSize();
c->dataoff = functionStartsSection->fileOff;
c->datasize = functionStartsSection->getFileSize();
}
private:
FunctionStartsSection *functionStartsSection;
};
class LCDataInCode final : public LoadCommand {
public:
explicit LCDataInCode(DataInCodeSection *dataInCodeSection)
: dataInCodeSection(dataInCodeSection) {}
uint32_t getSize() const override { return sizeof(linkedit_data_command); }
void writeTo(uint8_t *buf) const override {
auto *c = reinterpret_cast<linkedit_data_command *>(buf);
c->cmd = LC_DATA_IN_CODE;
c->cmdsize = getSize();
c->dataoff = dataInCodeSection->fileOff;
c->datasize = dataInCodeSection->getFileSize();
}
private:
DataInCodeSection *dataInCodeSection;
};
class LCDysymtab final : public LoadCommand {
public:
LCDysymtab(SymtabSection *symtabSection,
IndirectSymtabSection *indirectSymtabSection)
: symtabSection(symtabSection),
indirectSymtabSection(indirectSymtabSection) {}
uint32_t getSize() const override { return sizeof(dysymtab_command); }
void writeTo(uint8_t *buf) const override {
auto *c = reinterpret_cast<dysymtab_command *>(buf);
c->cmd = LC_DYSYMTAB;
c->cmdsize = getSize();
c->ilocalsym = 0;
c->iextdefsym = c->nlocalsym = symtabSection->getNumLocalSymbols();
c->nextdefsym = symtabSection->getNumExternalSymbols();
c->iundefsym = c->iextdefsym + c->nextdefsym;
c->nundefsym = symtabSection->getNumUndefinedSymbols();
c->indirectsymoff = indirectSymtabSection->fileOff;
c->nindirectsyms = indirectSymtabSection->getNumSymbols();
}
SymtabSection *symtabSection;
IndirectSymtabSection *indirectSymtabSection;
};
template <class LP> class LCSegment final : public LoadCommand {
public:
LCSegment(StringRef name, OutputSegment *seg) : name(name), seg(seg) {}
uint32_t getSize() const override {
return sizeof(typename LP::segment_command) +
seg->numNonHiddenSections() * sizeof(typename LP::section);
}
void writeTo(uint8_t *buf) const override {
using SegmentCommand = typename LP::segment_command;
using SectionHeader = typename LP::section;
auto *c = reinterpret_cast<SegmentCommand *>(buf);
buf += sizeof(SegmentCommand);
c->cmd = LP::segmentLCType;
c->cmdsize = getSize();
memcpy(c->segname, name.data(), name.size());
c->fileoff = seg->fileOff;
c->maxprot = seg->maxProt;
c->initprot = seg->initProt;
c->vmaddr = seg->addr;
c->vmsize = seg->vmSize;
c->filesize = seg->fileSize;
c->nsects = seg->numNonHiddenSections();
for (const OutputSection *osec : seg->getSections()) {
if (osec->isHidden())
continue;
auto *sectHdr = reinterpret_cast<SectionHeader *>(buf);
buf += sizeof(SectionHeader);
memcpy(sectHdr->sectname, osec->name.data(), osec->name.size());
memcpy(sectHdr->segname, name.data(), name.size());
sectHdr->addr = osec->addr;
sectHdr->offset = osec->fileOff;
sectHdr->align = Log2_32(osec->align);
sectHdr->flags = osec->flags;
sectHdr->size = osec->getSize();
sectHdr->reserved1 = osec->reserved1;
sectHdr->reserved2 = osec->reserved2;
}
}
private:
StringRef name;
OutputSegment *seg;
};
class LCMain final : public LoadCommand {
uint32_t getSize() const override {
return sizeof(structs::entry_point_command);
}
void writeTo(uint8_t *buf) const override {
auto *c = reinterpret_cast<structs::entry_point_command *>(buf);
c->cmd = LC_MAIN;
c->cmdsize = getSize();
if (config->entry->isInStubs())
c->entryoff =
in.stubs->fileOff + config->entry->stubsIndex * target->stubSize;
else
c->entryoff = config->entry->getVA() - in.header->addr;
c->stacksize = 0;
}
};
class LCSymtab final : public LoadCommand {
public:
LCSymtab(SymtabSection *symtabSection, StringTableSection *stringTableSection)
: symtabSection(symtabSection), stringTableSection(stringTableSection) {}
uint32_t getSize() const override { return sizeof(symtab_command); }
void writeTo(uint8_t *buf) const override {
auto *c = reinterpret_cast<symtab_command *>(buf);
c->cmd = LC_SYMTAB;
c->cmdsize = getSize();
c->symoff = symtabSection->fileOff;
c->nsyms = symtabSection->getNumSymbols();
c->stroff = stringTableSection->fileOff;
c->strsize = stringTableSection->getFileSize();
}
SymtabSection *symtabSection = nullptr;
StringTableSection *stringTableSection = nullptr;
};
// There are several dylib load commands that share the same structure:
// * LC_LOAD_DYLIB
// * LC_ID_DYLIB
// * LC_REEXPORT_DYLIB
class LCDylib final : public LoadCommand {
public:
LCDylib(LoadCommandType type, StringRef path,
uint32_t compatibilityVersion = 0, uint32_t currentVersion = 0)
: type(type), path(path), compatibilityVersion(compatibilityVersion),
currentVersion(currentVersion) {
instanceCount++;
}
uint32_t getSize() const override {
return alignTo(sizeof(dylib_command) + path.size() + 1, 8);
}
void writeTo(uint8_t *buf) const override {
auto *c = reinterpret_cast<dylib_command *>(buf);
buf += sizeof(dylib_command);
c->cmd = type;
c->cmdsize = getSize();
c->dylib.name = sizeof(dylib_command);
c->dylib.timestamp = 0;
c->dylib.compatibility_version = compatibilityVersion;
c->dylib.current_version = currentVersion;
memcpy(buf, path.data(), path.size());
buf[path.size()] = '\0';
}
static uint32_t getInstanceCount() { return instanceCount; }
static void resetInstanceCount() { instanceCount = 0; }
private:
LoadCommandType type;
StringRef path;
uint32_t compatibilityVersion;
uint32_t currentVersion;
static uint32_t instanceCount;
};
uint32_t LCDylib::instanceCount = 0;
class LCLoadDylinker final : public LoadCommand {
public:
uint32_t getSize() const override {
return alignTo(sizeof(dylinker_command) + path.size() + 1, 8);
}
void writeTo(uint8_t *buf) const override {
auto *c = reinterpret_cast<dylinker_command *>(buf);
buf += sizeof(dylinker_command);
c->cmd = LC_LOAD_DYLINKER;
c->cmdsize = getSize();
c->name = sizeof(dylinker_command);
memcpy(buf, path.data(), path.size());
buf[path.size()] = '\0';
}
private:
// Recent versions of Darwin won't run any binary that has dyld at a
// different location.
const StringRef path = "/usr/lib/dyld";
};
class LCRPath final : public LoadCommand {
public:
explicit LCRPath(StringRef path) : path(path) {}
uint32_t getSize() const override {
return alignTo(sizeof(rpath_command) + path.size() + 1, target->wordSize);
}
void writeTo(uint8_t *buf) const override {
auto *c = reinterpret_cast<rpath_command *>(buf);
buf += sizeof(rpath_command);
c->cmd = LC_RPATH;
c->cmdsize = getSize();
c->path = sizeof(rpath_command);
memcpy(buf, path.data(), path.size());
buf[path.size()] = '\0';
}
private:
StringRef path;
};
class LCMinVersion final : public LoadCommand {
public:
explicit LCMinVersion(const PlatformInfo &platformInfo)
: platformInfo(platformInfo) {}
uint32_t getSize() const override { return sizeof(version_min_command); }
void writeTo(uint8_t *buf) const override {
auto *c = reinterpret_cast<version_min_command *>(buf);
switch (platformInfo.target.Platform) {
case PLATFORM_MACOS:
c->cmd = LC_VERSION_MIN_MACOSX;
break;
case PLATFORM_IOS:
case PLATFORM_IOSSIMULATOR:
c->cmd = LC_VERSION_MIN_IPHONEOS;
break;
case PLATFORM_TVOS:
case PLATFORM_TVOSSIMULATOR:
c->cmd = LC_VERSION_MIN_TVOS;
break;
case PLATFORM_WATCHOS:
case PLATFORM_WATCHOSSIMULATOR:
c->cmd = LC_VERSION_MIN_WATCHOS;
break;
default:
llvm_unreachable("invalid platform");
break;
}
c->cmdsize = getSize();
c->version = encodeVersion(platformInfo.minimum);
c->sdk = encodeVersion(platformInfo.sdk);
}
private:
const PlatformInfo &platformInfo;
};
class LCBuildVersion final : public LoadCommand {
public:
explicit LCBuildVersion(const PlatformInfo &platformInfo)
: platformInfo(platformInfo) {}
const int ntools = 1;
uint32_t getSize() const override {
return sizeof(build_version_command) + ntools * sizeof(build_tool_version);
}
void writeTo(uint8_t *buf) const override {
auto *c = reinterpret_cast<build_version_command *>(buf);
c->cmd = LC_BUILD_VERSION;
c->cmdsize = getSize();
c->platform = static_cast<uint32_t>(platformInfo.target.Platform);
c->minos = encodeVersion(platformInfo.minimum);
c->sdk = encodeVersion(platformInfo.sdk);
c->ntools = ntools;
auto *t = reinterpret_cast<build_tool_version *>(&c[1]);
t->tool = TOOL_LD;
t->version = encodeVersion(VersionTuple(
LLVM_VERSION_MAJOR, LLVM_VERSION_MINOR, LLVM_VERSION_PATCH));
}
private:
const PlatformInfo &platformInfo;
};
// Stores a unique identifier for the output file based on an MD5 hash of its
// contents. In order to hash the contents, we must first write them, but
// LC_UUID itself must be part of the written contents in order for all the
// offsets to be calculated correctly. We resolve this circular paradox by
// first writing an LC_UUID with an all-zero UUID, then updating the UUID with
// its real value later.
class LCUuid final : public LoadCommand {
public:
uint32_t getSize() const override { return sizeof(uuid_command); }
void writeTo(uint8_t *buf) const override {
auto *c = reinterpret_cast<uuid_command *>(buf);
c->cmd = LC_UUID;
c->cmdsize = getSize();
uuidBuf = c->uuid;
}
void writeUuid(uint64_t digest) const {
// xxhash only gives us 8 bytes, so put some fixed data in the other half.
static_assert(sizeof(uuid_command::uuid) == 16, "unexpected uuid size");
memcpy(uuidBuf, "LLD\xa1UU1D", 8);
memcpy(uuidBuf + 8, &digest, 8);
// RFC 4122 conformance. We need to fix 4 bits in byte 6 and 2 bits in
// byte 8. Byte 6 is already fine due to the fixed data we put in. We don't
// want to lose bits of the digest in byte 8, so swap that with a byte of
// fixed data that happens to have the right bits set.
std::swap(uuidBuf[3], uuidBuf[8]);
// Claim that this is an MD5-based hash. It isn't, but this signals that
// this is not a time-based and not a random hash. MD5 seems like the least
// bad lie we can put here.
assert((uuidBuf[6] & 0xf0) == 0x30 && "See RFC 4122 Sections 4.2.2, 4.1.3");
assert((uuidBuf[8] & 0xc0) == 0x80 && "See RFC 4122 Section 4.2.2");
}
mutable uint8_t *uuidBuf;
};
template <class LP> class LCEncryptionInfo final : public LoadCommand {
public:
uint32_t getSize() const override {
return sizeof(typename LP::encryption_info_command);
}
void writeTo(uint8_t *buf) const override {
using EncryptionInfo = typename LP::encryption_info_command;
auto *c = reinterpret_cast<EncryptionInfo *>(buf);
buf += sizeof(EncryptionInfo);
c->cmd = LP::encryptionInfoLCType;
c->cmdsize = getSize();
c->cryptoff = in.header->getSize();
auto it = find_if(outputSegments, [](const OutputSegment *seg) {
return seg->name == segment_names::text;
});
assert(it != outputSegments.end());
c->cryptsize = (*it)->fileSize - c->cryptoff;
}
};
class LCCodeSignature final : public LoadCommand {
public:
LCCodeSignature(CodeSignatureSection *section) : section(section) {}
uint32_t getSize() const override { return sizeof(linkedit_data_command); }
void writeTo(uint8_t *buf) const override {
auto *c = reinterpret_cast<linkedit_data_command *>(buf);
c->cmd = LC_CODE_SIGNATURE;
c->cmdsize = getSize();
c->dataoff = static_cast<uint32_t>(section->fileOff);
c->datasize = section->getSize();
}
CodeSignatureSection *section;
};
} // namespace
void Writer::treatSpecialUndefineds() {
if (config->entry)
if (auto *undefined = dyn_cast<Undefined>(config->entry))
treatUndefinedSymbol(*undefined, "the entry point");
// FIXME: This prints symbols that are undefined both in input files and
// via -u flag twice.
for (const Symbol *sym : config->explicitUndefineds) {
if (const auto *undefined = dyn_cast<Undefined>(sym))
treatUndefinedSymbol(*undefined, "-u");
}
// Literal exported-symbol names must be defined, but glob
// patterns need not match.
for (const CachedHashStringRef &cachedName :
config->exportedSymbols.literals) {
if (const Symbol *sym = symtab->find(cachedName))
if (const auto *undefined = dyn_cast<Undefined>(sym))
treatUndefinedSymbol(*undefined, "-exported_symbol(s_list)");
}
}
// Add stubs and bindings where necessary (e.g. if the symbol is a
// DylibSymbol.)
static void prepareBranchTarget(Symbol *sym) {
if (auto *dysym = dyn_cast<DylibSymbol>(sym)) {
if (in.stubs->addEntry(dysym)) {
if (sym->isWeakDef()) {
in.binding->addEntry(dysym, in.lazyPointers->isec,
sym->stubsIndex * target->wordSize);
in.weakBinding->addEntry(sym, in.lazyPointers->isec,
sym->stubsIndex * target->wordSize);
} else {
in.lazyBinding->addEntry(dysym);
}
}
} else if (auto *defined = dyn_cast<Defined>(sym)) {
if (defined->isExternalWeakDef()) {
if (in.stubs->addEntry(sym)) {
in.rebase->addEntry(in.lazyPointers->isec,
sym->stubsIndex * target->wordSize);
in.weakBinding->addEntry(sym, in.lazyPointers->isec,
sym->stubsIndex * target->wordSize);
}
}
} else {
llvm_unreachable("invalid branch target symbol type");
}
}
// Can a symbol's address can only be resolved at runtime?
static bool needsBinding(const Symbol *sym) {
if (isa<DylibSymbol>(sym))
return true;
if (const auto *defined = dyn_cast<Defined>(sym))
return defined->isExternalWeakDef();
return false;
}
static void prepareSymbolRelocation(Symbol *sym, const InputSection *isec,
const lld::macho::Reloc &r) {
assert(sym->isLive());
const RelocAttrs &relocAttrs = target->getRelocAttrs(r.type);
if (relocAttrs.hasAttr(RelocAttrBits::BRANCH)) {
prepareBranchTarget(sym);
} else if (relocAttrs.hasAttr(RelocAttrBits::GOT)) {
if (relocAttrs.hasAttr(RelocAttrBits::POINTER) || needsBinding(sym))
in.got->addEntry(sym);
} else if (relocAttrs.hasAttr(RelocAttrBits::TLV)) {
if (needsBinding(sym))
in.tlvPointers->addEntry(sym);
} else if (relocAttrs.hasAttr(RelocAttrBits::UNSIGNED)) {
// References from thread-local variable sections are treated as offsets
// relative to the start of the referent section, and therefore have no
// need of rebase opcodes.
if (!(isThreadLocalVariables(isec->getFlags()) && isa<Defined>(sym)))
addNonLazyBindingEntries(sym, isec, r.offset, r.addend);
}
}
void Writer::scanRelocations() {
TimeTraceScope timeScope("Scan relocations");
// This can't use a for-each loop: It calls treatUndefinedSymbol(), which can
// add to inputSections, which invalidates inputSections's iterators.
for (size_t i = 0; i < inputSections.size(); ++i) {
ConcatInputSection *isec = inputSections[i];
if (isec->shouldOmitFromOutput())
continue;
for (auto it = isec->relocs.begin(); it != isec->relocs.end(); ++it) {
lld::macho::Reloc &r = *it;
if (target->hasAttr(r.type, RelocAttrBits::SUBTRAHEND)) {
// Skip over the following UNSIGNED relocation -- it's just there as the
// minuend, and doesn't have the usual UNSIGNED semantics. We don't want
// to emit rebase opcodes for it.
it++;
continue;
}
if (auto *sym = r.referent.dyn_cast<Symbol *>()) {
if (auto *undefined = dyn_cast<Undefined>(sym))
treatUndefinedSymbol(*undefined);
// treatUndefinedSymbol() can replace sym with a DylibSymbol; re-check.
if (!isa<Undefined>(sym) && validateSymbolRelocation(sym, isec, r))
prepareSymbolRelocation(sym, isec, r);
} else {
// Canonicalize the referent so that later accesses in Writer won't
// have to worry about it. Perhaps we should do this for Defined::isec
// too...
auto *referentIsec = r.referent.get<InputSection *>();
r.referent = referentIsec->canonical();
if (!r.pcrel)
in.rebase->addEntry(isec, r.offset);
}
}
}
in.unwindInfo->prepareRelocations();
}
void Writer::scanSymbols() {
TimeTraceScope timeScope("Scan symbols");
for (Symbol *sym : symtab->getSymbols()) {
if (auto *defined = dyn_cast<Defined>(sym)) {
if (!defined->isLive())
continue;
defined->canonicalize();
if (defined->overridesWeakDef)
in.weakBinding->addNonWeakDefinition(defined);
if (!defined->isAbsolute() && isCodeSection(defined->isec))
in.unwindInfo->addSymbol(defined);
} else if (const auto *dysym = dyn_cast<DylibSymbol>(sym)) {
// This branch intentionally doesn't check isLive().
if (dysym->isDynamicLookup())
continue;
dysym->getFile()->refState =
std::max(dysym->getFile()->refState, dysym->getRefState());
}
}
for (const InputFile *file : inputFiles) {
if (auto *objFile = dyn_cast<ObjFile>(file))
for (Symbol *sym : objFile->symbols) {
if (auto *defined = dyn_cast_or_null<Defined>(sym)) {
if (!defined->isLive())
continue;
defined->canonicalize();
if (!defined->isExternal() && !defined->isAbsolute() &&
isCodeSection(defined->isec))
in.unwindInfo->addSymbol(defined);
}
}
}
}
// TODO: ld64 enforces the old load commands in a few other cases.
static bool useLCBuildVersion(const PlatformInfo &platformInfo) {
static const std::vector<std::pair<PlatformType, VersionTuple>> minVersion = {
{PLATFORM_MACOS, VersionTuple(10, 14)},
{PLATFORM_IOS, VersionTuple(12, 0)},
{PLATFORM_IOSSIMULATOR, VersionTuple(13, 0)},
{PLATFORM_TVOS, VersionTuple(12, 0)},
{PLATFORM_TVOSSIMULATOR, VersionTuple(13, 0)},
{PLATFORM_WATCHOS, VersionTuple(5, 0)},
{PLATFORM_WATCHOSSIMULATOR, VersionTuple(6, 0)}};
auto it = llvm::find_if(minVersion, [&](const auto &p) {
return p.first == platformInfo.target.Platform;
});
return it == minVersion.end() ? true : platformInfo.minimum >= it->second;
}
template <class LP> void Writer::createLoadCommands() {
uint8_t segIndex = 0;
for (OutputSegment *seg : outputSegments) {
in.header->addLoadCommand(make<LCSegment<LP>>(seg->name, seg));
seg->index = segIndex++;
}
in.header->addLoadCommand(make<LCDyldInfo>(
in.rebase, in.binding, in.weakBinding, in.lazyBinding, in.exports));
in.header->addLoadCommand(make<LCSymtab>(symtabSection, stringTableSection));
in.header->addLoadCommand(
make<LCDysymtab>(symtabSection, indirectSymtabSection));
if (!config->umbrella.empty())
in.header->addLoadCommand(make<LCSubFramework>(config->umbrella));
if (config->emitEncryptionInfo)
in.header->addLoadCommand(make<LCEncryptionInfo<LP>>());
for (StringRef path : config->runtimePaths)
in.header->addLoadCommand(make<LCRPath>(path));
switch (config->outputType) {
case MH_EXECUTE:
in.header->addLoadCommand(make<LCLoadDylinker>());
break;
case MH_DYLIB:
in.header->addLoadCommand(make<LCDylib>(LC_ID_DYLIB, config->installName,
config->dylibCompatibilityVersion,
config->dylibCurrentVersion));
break;
case MH_BUNDLE:
break;
default:
llvm_unreachable("unhandled output file type");
}
uuidCommand = make<LCUuid>();
in.header->addLoadCommand(uuidCommand);
if (useLCBuildVersion(config->platformInfo))
in.header->addLoadCommand(make<LCBuildVersion>(config->platformInfo));
else
in.header->addLoadCommand(make<LCMinVersion>(config->platformInfo));
// This is down here to match ld64's load command order.
if (config->outputType == MH_EXECUTE)
in.header->addLoadCommand(make<LCMain>());
int64_t dylibOrdinal = 1;
DenseMap<StringRef, int64_t> ordinalForInstallName;
for (InputFile *file : inputFiles) {
if (auto *dylibFile = dyn_cast<DylibFile>(file)) {
if (dylibFile->isBundleLoader) {
dylibFile->ordinal = BIND_SPECIAL_DYLIB_MAIN_EXECUTABLE;
// Shortcut since bundle-loader does not re-export the symbols.
dylibFile->reexport = false;
continue;
}
// Don't emit load commands for a dylib that is not referenced if:
// - it was added implicitly (via a reexport, an LC_LOAD_DYLINKER --
// if it's on the linker command line, it's explicit)
// - or it's marked MH_DEAD_STRIPPABLE_DYLIB
// - or the flag -dead_strip_dylibs is used
// FIXME: `isReferenced()` is currently computed before dead code
// stripping, so references from dead code keep a dylib alive. This
// matches ld64, but it's something we should do better.
if (!dylibFile->isReferenced() && !dylibFile->forceNeeded &&
(!dylibFile->explicitlyLinked || dylibFile->deadStrippable ||
config->deadStripDylibs))
continue;
// Several DylibFiles can have the same installName. Only emit a single
// load command for that installName and give all these DylibFiles the
// same ordinal.
// This can happen in several cases:
// - a new framework could change its installName to an older
// framework name via an $ld$ symbol depending on platform_version
// - symlinks (for example, libpthread.tbd is a symlink to libSystem.tbd;
// Foo.framework/Foo.tbd is usually a symlink to
// Foo.framework/Versions/Current/Foo.tbd, where
// Foo.framework/Versions/Current is usually a symlink to
// Foo.framework/Versions/A)
// - a framework can be linked both explicitly on the linker
// command line and implicitly as a reexport from a different
// framework. The re-export will usually point to the tbd file
// in Foo.framework/Versions/A/Foo.tbd, while the explicit link will
// usually find Foo.framework/Foo.tbd. These are usually symlinks,
// but in a --reproduce archive they will be identical but distinct
// files.
// In the first case, *semantically distinct* DylibFiles will have the
// same installName.
int64_t &ordinal = ordinalForInstallName[dylibFile->installName];
if (ordinal) {
dylibFile->ordinal = ordinal;
continue;
}
ordinal = dylibFile->ordinal = dylibOrdinal++;
LoadCommandType lcType =
dylibFile->forceWeakImport || dylibFile->refState == RefState::Weak
? LC_LOAD_WEAK_DYLIB
: LC_LOAD_DYLIB;
in.header->addLoadCommand(make<LCDylib>(lcType, dylibFile->installName,
dylibFile->compatibilityVersion,
dylibFile->currentVersion));
if (dylibFile->reexport)
in.header->addLoadCommand(
make<LCDylib>(LC_REEXPORT_DYLIB, dylibFile->installName));
}
}
if (functionStartsSection)
in.header->addLoadCommand(make<LCFunctionStarts>(functionStartsSection));
if (dataInCodeSection)
in.header->addLoadCommand(make<LCDataInCode>(dataInCodeSection));
if (codeSignatureSection)
in.header->addLoadCommand(make<LCCodeSignature>(codeSignatureSection));
const uint32_t MACOS_MAXPATHLEN = 1024;
config->headerPad = std::max(
config->headerPad, (config->headerPadMaxInstallNames
? LCDylib::getInstanceCount() * MACOS_MAXPATHLEN
: 0));
}
// Sorting only can happen once all outputs have been collected. Here we sort
// segments, output sections within each segment, and input sections within each
// output segment.
static void sortSegmentsAndSections() {
TimeTraceScope timeScope("Sort segments and sections");
sortOutputSegments();
DenseMap<const InputSection *, size_t> isecPriorities =
buildInputSectionPriorities();
uint32_t sectionIndex = 0;
for (OutputSegment *seg : outputSegments) {
seg->sortOutputSections();
// References from thread-local variable sections are treated as offsets
// relative to the start of the thread-local data memory area, which
// is initialized via copying all the TLV data sections (which are all
// contiguous). If later data sections require a greater alignment than
// earlier ones, the offsets of data within those sections won't be
// guaranteed to aligned unless we normalize alignments. We therefore use
// the largest alignment for all TLV data sections.
uint32_t tlvAlign = 0;
for (const OutputSection *osec : seg->getSections())
if (isThreadLocalData(osec->flags) && osec->align > tlvAlign)
tlvAlign = osec->align;
for (OutputSection *osec : seg->getSections()) {
// Now that the output sections are sorted, assign the final
// output section indices.
if (!osec->isHidden())
osec->index = ++sectionIndex;
if (isThreadLocalData(osec->flags)) {
if (!firstTLVDataSection)
firstTLVDataSection = osec;
osec->align = tlvAlign;
}
if (!isecPriorities.empty()) {
if (auto *merged = dyn_cast<ConcatOutputSection>(osec)) {
llvm::stable_sort(merged->inputs,
[&](InputSection *a, InputSection *b) {
return isecPriorities[a] > isecPriorities[b];
});
}
}
}
}
}
template <class LP> void Writer::createOutputSections() {
TimeTraceScope timeScope("Create output sections");
// First, create hidden sections
stringTableSection = make<StringTableSection>();
symtabSection = makeSymtabSection<LP>(*stringTableSection);
indirectSymtabSection = make<IndirectSymtabSection>();
if (config->adhocCodesign)
codeSignatureSection = make<CodeSignatureSection>();
if (config->emitDataInCodeInfo)
dataInCodeSection = make<DataInCodeSection>();
if (config->emitFunctionStarts)
functionStartsSection = make<FunctionStartsSection>();
if (config->emitBitcodeBundle)
make<BitcodeBundleSection>();
switch (config->outputType) {
case MH_EXECUTE:
make<PageZeroSection>();
break;
case MH_DYLIB:
case MH_BUNDLE:
break;
default:
llvm_unreachable("unhandled output file type");
}
// Then add input sections to output sections.
for (ConcatInputSection *isec : inputSections) {
if (isec->shouldOmitFromOutput())
continue;
ConcatOutputSection *osec = cast<ConcatOutputSection>(isec->parent);
osec->addInput(isec);
osec->inputOrder =
std::min(osec->inputOrder, static_cast<int>(isec->outSecOff));
}
// Once all the inputs are added, we can finalize the output section
// properties and create the corresponding output segments.
for (const auto &it : concatOutputSections) {
StringRef segname = it.first.first;
ConcatOutputSection *osec = it.second;
assert(segname != segment_names::ld);
if (osec->isNeeded())
getOrCreateOutputSegment(segname)->addOutputSection(osec);
}
for (SyntheticSection *ssec : syntheticSections) {
auto it = concatOutputSections.find({ssec->segname, ssec->name});
// We add all LinkEdit sections here because we don't know if they are
// needed until their finalizeContents() methods get called later. While
// this means that we add some redundant sections to __LINKEDIT, there is
// is no redundancy in the output, as we do not emit section headers for
// any LinkEdit sections.
if (ssec->isNeeded() || ssec->segname == segment_names::linkEdit) {
if (it == concatOutputSections.end()) {
getOrCreateOutputSegment(ssec->segname)->addOutputSection(ssec);
} else {
fatal("section from " +
toString(it->second->firstSection()->getFile()) +
" conflicts with synthetic section " + ssec->segname + "," +
ssec->name);
}
}
}
// dyld requires __LINKEDIT segment to always exist (even if empty).
linkEditSegment = getOrCreateOutputSegment(segment_names::linkEdit);
}
void Writer::finalizeAddresses() {
TimeTraceScope timeScope("Finalize addresses");
uint64_t pageSize = target->getPageSize();
// Ensure that segments (and the sections they contain) are allocated
// addresses in ascending order, which dyld requires.
//
// Note that at this point, __LINKEDIT sections are empty, but we need to
// determine addresses of other segments/sections before generating its
// contents.
for (OutputSegment *seg : outputSegments) {
if (seg == linkEditSegment)
continue;
seg->addr = addr;
assignAddresses(seg);
// codesign / libstuff checks for segment ordering by verifying that
// `fileOff + fileSize == next segment fileOff`. So we call alignTo() before
// (instead of after) computing fileSize to ensure that the segments are
// contiguous. We handle addr / vmSize similarly for the same reason.
fileOff = alignTo(fileOff, pageSize);
addr = alignTo(addr, pageSize);
seg->vmSize = addr - seg->addr;
seg->fileSize = fileOff - seg->fileOff;
seg->assignAddressesToStartEndSymbols();
}
}
void Writer::finalizeLinkEditSegment() {
TimeTraceScope timeScope("Finalize __LINKEDIT segment");
// Fill __LINKEDIT contents.
std::vector<LinkEditSection *> linkEditSections{
in.rebase,
in.binding,
in.weakBinding,
in.lazyBinding,
in.exports,
symtabSection,
indirectSymtabSection,
dataInCodeSection,
functionStartsSection,
};
SmallVector<std::shared_future<void>> threadFutures;
threadFutures.reserve(linkEditSections.size());
for (LinkEditSection *osec : linkEditSections)
if (osec)
threadFutures.emplace_back(threadPool.async(
[](LinkEditSection *osec) { osec->finalizeContents(); }, osec));
for (std::shared_future<void> &future : threadFutures)
future.wait();
// Now that __LINKEDIT is filled out, do a proper calculation of its
// addresses and offsets.
linkEditSegment->addr = addr;
assignAddresses(linkEditSegment);
// No need to page-align fileOff / addr here since this is the last segment.
linkEditSegment->vmSize = addr - linkEditSegment->addr;
linkEditSegment->fileSize = fileOff - linkEditSegment->fileOff;
}
void Writer::assignAddresses(OutputSegment *seg) {
seg->fileOff = fileOff;
for (OutputSection *osec : seg->getSections()) {
if (!osec->isNeeded())
continue;
addr = alignTo(addr, osec->align);
fileOff = alignTo(fileOff, osec->align);
osec->addr = addr;
osec->fileOff = isZeroFill(osec->flags) ? 0 : fileOff;
osec->finalize();
osec->assignAddressesToStartEndSymbols();
addr += osec->getSize();
fileOff += osec->getFileSize();
}
}
void Writer::openFile() {
Expected<std::unique_ptr<FileOutputBuffer>> bufferOrErr =
FileOutputBuffer::create(config->outputFile, fileOff,
FileOutputBuffer::F_executable);
if (!bufferOrErr)
fatal("failed to open " + config->outputFile + ": " +
llvm::toString(bufferOrErr.takeError()));
buffer = std::move(*bufferOrErr);
in.bufferStart = buffer->getBufferStart();
}
void Writer::writeSections() {
uint8_t *buf = buffer->getBufferStart();
for (const OutputSegment *seg : outputSegments)
for (const OutputSection *osec : seg->getSections())
osec->writeTo(buf + osec->fileOff);
}
// In order to utilize multiple cores, we first split the buffer into chunks,
// compute a hash for each chunk, and then compute a hash value of the hash
// values.
void Writer::writeUuid() {
TimeTraceScope timeScope("Computing UUID");
ArrayRef<uint8_t> data{buffer->getBufferStart(), buffer->getBufferEnd()};
unsigned chunkCount = parallel::strategy.compute_thread_count() * 10;
// Round-up integer division
size_t chunkSize = (data.size() + chunkCount - 1) / chunkCount;
std::vector<ArrayRef<uint8_t>> chunks = split(data, chunkSize);
std::vector<uint64_t> hashes(chunks.size());
SmallVector<std::shared_future<void>> threadFutures;
threadFutures.reserve(chunks.size());
for (size_t i = 0; i < chunks.size(); ++i)
threadFutures.emplace_back(threadPool.async(
[&](size_t j) { hashes[j] = xxHash64(chunks[j]); }, i));
for (std::shared_future<void> &future : threadFutures)
future.wait();
uint64_t digest = xxHash64({reinterpret_cast<uint8_t *>(hashes.data()),
hashes.size() * sizeof(uint64_t)});
uuidCommand->writeUuid(digest);
}
void Writer::writeCodeSignature() {
if (codeSignatureSection)
codeSignatureSection->writeHashes(buffer->getBufferStart());
}
void Writer::writeOutputFile() {
TimeTraceScope timeScope("Write output file");
openFile();
if (errorCount())
return;
writeSections();
writeUuid();
writeCodeSignature();
if (auto e = buffer->commit())
error("failed to write to the output file: " + toString(std::move(e)));
}
template <class LP> void Writer::run() {
treatSpecialUndefineds();
if (config->entry && !isa<Undefined>(config->entry))
prepareBranchTarget(config->entry);
// Canonicalization of all pointers to InputSections should be handled by
// these two scan* methods. I.e. from this point onward, for all live
// InputSections, we should have `isec->canonical() == isec`.
scanSymbols();
scanRelocations();
// Do not proceed if there was an undefined symbol.
if (errorCount())
return;
if (in.stubHelper->isNeeded())
in.stubHelper->setup();
// At this point, we should know exactly which output sections are needed,
// courtesy of scanSymbols() and scanRelocations().
createOutputSections<LP>();
// After this point, we create no new segments; HOWEVER, we might
// yet create branch-range extension thunks for architectures whose
// hardware call instructions have limited range, e.g., ARM(64).
// The thunks are created as InputSections interspersed among
// the ordinary __TEXT,_text InputSections.
sortSegmentsAndSections();
createLoadCommands<LP>();
finalizeAddresses();
threadPool.async([&] {
if (LLVM_ENABLE_THREADS && config->timeTraceEnabled)
timeTraceProfilerInitialize(config->timeTraceGranularity, "writeMapFile");
writeMapFile();
if (LLVM_ENABLE_THREADS && config->timeTraceEnabled)
timeTraceProfilerFinishThread();
});
finalizeLinkEditSegment();
writeOutputFile();
}
template <class LP> void macho::writeResult() { Writer().run<LP>(); }
void macho::resetWriter() { LCDylib::resetInstanceCount(); }
void macho::createSyntheticSections() {
in.header = make<MachHeaderSection>();
if (config->dedupLiterals)
in.cStringSection = make<DeduplicatedCStringSection>();
else
in.cStringSection = make<CStringSection>();
in.wordLiteralSection =
config->dedupLiterals ? make<WordLiteralSection>() : nullptr;
in.rebase = make<RebaseSection>();
in.binding = make<BindingSection>();
in.weakBinding = make<WeakBindingSection>();
in.lazyBinding = make<LazyBindingSection>();
in.exports = make<ExportSection>();
in.got = make<GotSection>();
in.tlvPointers = make<TlvPointerSection>();
in.lazyPointers = make<LazyPointerSection>();
in.stubs = make<StubsSection>();
in.stubHelper = make<StubHelperSection>();
in.unwindInfo = makeUnwindInfoSection();
// This section contains space for just a single word, and will be used by
// dyld to cache an address to the image loader it uses.
uint8_t *arr = bAlloc().Allocate<uint8_t>(target->wordSize);
memset(arr, 0, target->wordSize);
in.imageLoaderCache = makeSyntheticInputSection(
segment_names::data, section_names::data, S_REGULAR,
ArrayRef<uint8_t>{arr, target->wordSize},
/*align=*/target->wordSize);
// References from dyld are not visible to us, so ensure this section is
// always treated as live.
in.imageLoaderCache->live = true;
}
OutputSection *macho::firstTLVDataSection = nullptr;
template void macho::writeResult<LP64>();
template void macho::writeResult<ILP32>();
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