blob: 1376e6c2c253a7fad3aba41e60e8e7ccee17ca3b [file] [log] [blame]
//===- Driver.cpp ---------------------------------------------------------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// The driver drives the entire linking process. It is responsible for
// parsing command line options and doing whatever it is instructed to do.
// One notable thing in the LLD's driver when compared to other linkers is
// that the LLD's driver is agnostic on the host operating system.
// Other linkers usually have implicit default values (such as a dynamic
// linker path or library paths) for each host OS.
// I don't think implicit default values are useful because they are
// usually explicitly specified by the compiler driver. They can even
// be harmful when you are doing cross-linking. Therefore, in LLD, we
// simply trust the compiler driver to pass all required options and
// don't try to make effort on our side.
#include "Driver.h"
#include "Config.h"
#include "ICF.h"
#include "InputFiles.h"
#include "InputSection.h"
#include "LinkerScript.h"
#include "MarkLive.h"
#include "OutputSections.h"
#include "ScriptParser.h"
#include "SymbolTable.h"
#include "Symbols.h"
#include "SyntheticSections.h"
#include "Target.h"
#include "Writer.h"
#include "lld/Common/Args.h"
#include "lld/Common/Driver.h"
#include "lld/Common/ErrorHandler.h"
#include "lld/Common/Filesystem.h"
#include "lld/Common/Memory.h"
#include "lld/Common/Strings.h"
#include "lld/Common/TargetOptionsCommandFlags.h"
#include "lld/Common/Version.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/StringSwitch.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/LTO/LTO.h"
#include "llvm/Remarks/HotnessThresholdParser.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compression.h"
#include "llvm/Support/GlobPattern.h"
#include "llvm/Support/LEB128.h"
#include "llvm/Support/Parallel.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/TarWriter.h"
#include "llvm/Support/TargetSelect.h"
#include "llvm/Support/TimeProfiler.h"
#include "llvm/Support/raw_ostream.h"
#include <cstdlib>
#include <utility>
using namespace llvm;
using namespace llvm::ELF;
using namespace llvm::object;
using namespace llvm::sys;
using namespace llvm::support;
using namespace lld;
using namespace lld::elf;
Configuration *elf::config;
LinkerDriver *elf::driver;
static void setConfigs(opt::InputArgList &args);
static void readConfigs(opt::InputArgList &args);
bool elf::link(ArrayRef<const char *> args, bool canExitEarly,
raw_ostream &stdoutOS, raw_ostream &stderrOS) {
lld::stdoutOS = &stdoutOS;
lld::stderrOS = &stderrOS;
errorHandler().cleanupCallback = []() {
tar = nullptr;
memset(&in, 0, sizeof(in));
partitions = {Partition()};
SharedFile::vernauxNum = 0;
errorHandler().logName = args::getFilenameWithoutExe(args[0]);
errorHandler().errorLimitExceededMsg =
"too many errors emitted, stopping now (use "
"-error-limit=0 to see all errors)";
errorHandler().exitEarly = canExitEarly;
config = make<Configuration>();
driver = make<LinkerDriver>();
script = make<LinkerScript>();
symtab = make<SymbolTable>();
partitions = {Partition()};
config->progName = args[0];
// Exit immediately if we don't need to return to the caller.
// This saves time because the overhead of calling destructors
// for all globally-allocated objects is not negligible.
if (canExitEarly)
exitLld(errorCount() ? 1 : 0);
bool ret = errorCount() == 0;
if (!canExitEarly)
return ret;
// Parses a linker -m option.
static std::tuple<ELFKind, uint16_t, uint8_t> parseEmulation(StringRef emul) {
uint8_t osabi = 0;
StringRef s = emul;
if (s.endswith("_fbsd")) {
s = s.drop_back(5);
std::pair<ELFKind, uint16_t> ret =
StringSwitch<std::pair<ELFKind, uint16_t>>(s)
.Cases("aarch64elf", "aarch64linux", {ELF64LEKind, EM_AARCH64})
.Cases("aarch64elfb", "aarch64linuxb", {ELF64BEKind, EM_AARCH64})
.Cases("armelf", "armelf_linux_eabi", {ELF32LEKind, EM_ARM})
.Case("elf32_x86_64", {ELF32LEKind, EM_X86_64})
.Cases("elf32btsmip", "elf32btsmipn32", {ELF32BEKind, EM_MIPS})
.Cases("elf32ltsmip", "elf32ltsmipn32", {ELF32LEKind, EM_MIPS})
.Case("elf32lriscv", {ELF32LEKind, EM_RISCV})
.Cases("elf32ppc", "elf32ppclinux", {ELF32BEKind, EM_PPC})
.Cases("elf32lppc", "elf32lppclinux", {ELF32LEKind, EM_PPC})
.Case("elf64btsmip", {ELF64BEKind, EM_MIPS})
.Case("elf64ltsmip", {ELF64LEKind, EM_MIPS})
.Case("elf64lriscv", {ELF64LEKind, EM_RISCV})
.Case("elf64ppc", {ELF64BEKind, EM_PPC64})
.Case("elf64lppc", {ELF64LEKind, EM_PPC64})
.Cases("elf_amd64", "elf_x86_64", {ELF64LEKind, EM_X86_64})
.Case("elf_i386", {ELF32LEKind, EM_386})
.Case("elf_iamcu", {ELF32LEKind, EM_IAMCU})
.Case("elf64_sparc", {ELF64BEKind, EM_SPARCV9})
.Case("msp430elf", {ELF32LEKind, EM_MSP430})
.Default({ELFNoneKind, EM_NONE});
if (ret.first == ELFNoneKind)
error("unknown emulation: " + emul);
if (ret.second == EM_MSP430)
return std::make_tuple(ret.first, ret.second, osabi);
// Returns slices of MB by parsing MB as an archive file.
// Each slice consists of a member file in the archive.
std::vector<std::pair<MemoryBufferRef, uint64_t>> static getArchiveMembers(
MemoryBufferRef mb) {
std::unique_ptr<Archive> file =
mb.getBufferIdentifier() + ": failed to parse archive");
std::vector<std::pair<MemoryBufferRef, uint64_t>> v;
Error err = Error::success();
bool addToTar = file->isThin() && tar;
for (const Archive::Child &c : file->children(err)) {
MemoryBufferRef mbref =
mb.getBufferIdentifier() +
": could not get the buffer for a child of the archive");
if (addToTar)
tar->append(relativeToRoot(check(c.getFullName())), mbref.getBuffer());
v.push_back(std::make_pair(mbref, c.getChildOffset()));
if (err)
fatal(mb.getBufferIdentifier() + ": Archive::children failed: " +
// Take ownership of memory buffers created for members of thin archives.
for (std::unique_ptr<MemoryBuffer> &mb : file->takeThinBuffers())
return v;
// Opens a file and create a file object. Path has to be resolved already.
void LinkerDriver::addFile(StringRef path, bool withLOption) {
using namespace sys::fs;
Optional<MemoryBufferRef> buffer = readFile(path);
if (!buffer.hasValue())
MemoryBufferRef mbref = *buffer;
if (config->formatBinary) {
switch (identify_magic(mbref.getBuffer())) {
case file_magic::unknown:
case file_magic::archive: {
if (inWholeArchive) {
for (const auto &p : getArchiveMembers(mbref))
files.push_back(createObjectFile(p.first, path, p.second));
std::unique_ptr<Archive> file =
CHECK(Archive::create(mbref), path + ": failed to parse archive");
// If an archive file has no symbol table, it is likely that a user
// is attempting LTO and using a default ar command that doesn't
// understand the LLVM bitcode file. It is a pretty common error, so
// we'll handle it as if it had a symbol table.
if (!file->isEmpty() && !file->hasSymbolTable()) {
// Check if all members are bitcode files. If not, ignore, which is the
// default action without the LTO hack described above.
for (const std::pair<MemoryBufferRef, uint64_t> &p :
if (identify_magic(p.first.getBuffer()) != file_magic::bitcode) {
error(path + ": archive has no index; run ranlib to add one");
for (const std::pair<MemoryBufferRef, uint64_t> &p :
files.push_back(make<LazyObjFile>(p.first, path, p.second));
// Handle the regular case.
case file_magic::elf_shared_object:
if (config->isStatic || config->relocatable) {
error("attempted static link of dynamic object " + path);
// Shared objects are identified by soname. soname is (if specified)
// DT_SONAME and falls back to filename. If a file was specified by -lfoo,
// the directory part is ignored. Note that path may be a temporary and
// cannot be stored into SharedFile::soName.
path = mbref.getBufferIdentifier();
make<SharedFile>(mbref, withLOption ? path::filename(path) : path));
case file_magic::bitcode:
case file_magic::elf_relocatable:
if (inLib)
files.push_back(make<LazyObjFile>(mbref, "", 0));
error(path + ": unknown file type");
// Add a given library by searching it from input search paths.
void LinkerDriver::addLibrary(StringRef name) {
if (Optional<std::string> path = searchLibrary(name))
addFile(*path, /*withLOption=*/true);
error("unable to find library -l" + name, ErrorTag::LibNotFound, {name});
// This function is called on startup. We need this for LTO since
// LTO calls LLVM functions to compile bitcode files to native code.
// Technically this can be delayed until we read bitcode files, but
// we don't bother to do lazily because the initialization is fast.
static void initLLVM() {
// Some command line options or some combinations of them are not allowed.
// This function checks for such errors.
static void checkOptions() {
// The MIPS ABI as of 2016 does not support the GNU-style symbol lookup
// table which is a relatively new feature.
if (config->emachine == EM_MIPS && config->gnuHash)
error("the .gnu.hash section is not compatible with the MIPS target");
if (config->fixCortexA53Errata843419 && config->emachine != EM_AARCH64)
error("--fix-cortex-a53-843419 is only supported on AArch64 targets");
if (config->fixCortexA8 && config->emachine != EM_ARM)
error("--fix-cortex-a8 is only supported on ARM targets");
if (config->tocOptimize && config->emachine != EM_PPC64)
error("--toc-optimize is only supported on PowerPC64 targets");
if (config->pcRelOptimize && config->emachine != EM_PPC64)
error("--pcrel-optimize is only supported on PowerPC64 targets");
if (config->pie && config->shared)
error("-shared and -pie may not be used together");
if (!config->shared && !config->filterList.empty())
error("-F may not be used without -shared");
if (!config->shared && !config->auxiliaryList.empty())
error("-f may not be used without -shared");
if (!config->relocatable && !config->defineCommon)
error("-no-define-common not supported in non relocatable output");
if (config->strip == StripPolicy::All && config->emitRelocs)
error("--strip-all and --emit-relocs may not be used together");
if (config->zText && config->zIfuncNoplt)
error("-z text and -z ifunc-noplt may not be used together");
if (config->relocatable) {
if (config->shared)
error("-r and -shared may not be used together");
if (config->gdbIndex)
error("-r and --gdb-index may not be used together");
if (config->icf != ICFLevel::None)
error("-r and --icf may not be used together");
if (config->pie)
error("-r and -pie may not be used together");
if (config->exportDynamic)
error("-r and --export-dynamic may not be used together");
if (config->executeOnly) {
if (config->emachine != EM_AARCH64)
error("--execute-only is only supported on AArch64 targets");
if (config->singleRoRx && !script->hasSectionsCommand)
error("--execute-only and --no-rosegment cannot be used together");
if (config->zRetpolineplt && config->zForceIbt)
error("-z force-ibt may not be used with -z retpolineplt");
if (config->emachine != EM_AARCH64) {
if (config->zPacPlt)
error("-z pac-plt only supported on AArch64");
if (config->zForceBti)
error("-z force-bti only supported on AArch64");
static const char *getReproduceOption(opt::InputArgList &args) {
if (auto *arg = args.getLastArg(OPT_reproduce))
return arg->getValue();
return getenv("LLD_REPRODUCE");
static bool hasZOption(opt::InputArgList &args, StringRef key) {
for (auto *arg : args.filtered(OPT_z))
if (key == arg->getValue())
return true;
return false;
static bool getZFlag(opt::InputArgList &args, StringRef k1, StringRef k2,
bool Default) {
for (auto *arg : args.filtered_reverse(OPT_z)) {
if (k1 == arg->getValue())
return true;
if (k2 == arg->getValue())
return false;
return Default;
static SeparateSegmentKind getZSeparate(opt::InputArgList &args) {
for (auto *arg : args.filtered_reverse(OPT_z)) {
StringRef v = arg->getValue();
if (v == "noseparate-code")
return SeparateSegmentKind::None;
if (v == "separate-code")
return SeparateSegmentKind::Code;
if (v == "separate-loadable-segments")
return SeparateSegmentKind::Loadable;
return SeparateSegmentKind::None;
static GnuStackKind getZGnuStack(opt::InputArgList &args) {
for (auto *arg : args.filtered_reverse(OPT_z)) {
if (StringRef("execstack") == arg->getValue())
return GnuStackKind::Exec;
if (StringRef("noexecstack") == arg->getValue())
return GnuStackKind::NoExec;
if (StringRef("nognustack") == arg->getValue())
return GnuStackKind::None;
return GnuStackKind::NoExec;
static uint8_t getZStartStopVisibility(opt::InputArgList &args) {
for (auto *arg : args.filtered_reverse(OPT_z)) {
std::pair<StringRef, StringRef> kv = StringRef(arg->getValue()).split('=');
if (kv.first == "start-stop-visibility") {
if (kv.second == "default")
else if (kv.second == "internal")
else if (kv.second == "hidden")
return STV_HIDDEN;
else if (kv.second == "protected")
error("unknown -z start-stop-visibility= value: " + StringRef(kv.second));
static bool isKnownZFlag(StringRef s) {
return s == "combreloc" || s == "copyreloc" || s == "defs" ||
s == "execstack" || s == "force-bti" || s == "force-ibt" ||
s == "global" || s == "hazardplt" || s == "ifunc-noplt" ||
s == "initfirst" || s == "interpose" ||
s == "keep-text-section-prefix" || s == "lazy" || s == "muldefs" ||
s == "separate-code" || s == "separate-loadable-segments" ||
s == "start-stop-gc" || s == "nocombreloc" || s == "nocopyreloc" ||
s == "nodefaultlib" || s == "nodelete" || s == "nodlopen" ||
s == "noexecstack" || s == "nognustack" ||
s == "nokeep-text-section-prefix" || s == "norelro" ||
s == "noseparate-code" || s == "nostart-stop-gc" || s == "notext" ||
s == "now" || s == "origin" || s == "pac-plt" || s == "rel" ||
s == "rela" || s == "relro" || s == "retpolineplt" ||
s == "rodynamic" || s == "shstk" || s == "text" || s == "undefs" ||
s == "wxneeded" || s.startswith("common-page-size=") ||
s.startswith("dead-reloc-in-nonalloc=") ||
s.startswith("max-page-size=") || s.startswith("stack-size=") ||
// Report a warning for an unknown -z option.
static void checkZOptions(opt::InputArgList &args) {
for (auto *arg : args.filtered(OPT_z))
if (!isKnownZFlag(arg->getValue()))
warn("unknown -z value: " + StringRef(arg->getValue()));
void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
ELFOptTable parser;
opt::InputArgList args = parser.parse(argsArr.slice(1));
// Interpret the flags early because error()/warn() depend on them.
errorHandler().errorLimit = args::getInteger(args, OPT_error_limit, 20);
errorHandler().fatalWarnings =
args.hasFlag(OPT_fatal_warnings, OPT_no_fatal_warnings, false);
// Handle -help
if (args.hasArg(OPT_help)) {
// Handle -v or -version.
// A note about "compatible with GNU linkers" message: this is a hack for
// scripts generated by GNU Libtool up to 2021-10 to recognize LLD as
// a GNU compatible linker. See
// <>.
// This is somewhat ugly hack, but in reality, we had no choice other
// than doing this. Considering the very long release cycle of Libtool,
// it is not easy to improve it to recognize LLD as a GNU compatible
// linker in a timely manner. Even if we can make it, there are still a
// lot of "configure" scripts out there that are generated by old version
// of Libtool. We cannot convince every software developer to migrate to
// the latest version and re-generate scripts. So we have this hack.
if (args.hasArg(OPT_v) || args.hasArg(OPT_version))
message(getLLDVersion() + " (compatible with GNU linkers)");
if (const char *path = getReproduceOption(args)) {
// Note that --reproduce is a debug option so you can ignore it
// if you are trying to understand the whole picture of the code.
Expected<std::unique_ptr<TarWriter>> errOrWriter =
TarWriter::create(path, path::stem(path));
if (errOrWriter) {
tar = std::move(*errOrWriter);
tar->append("response.txt", createResponseFile(args));
tar->append("version.txt", getLLDVersion() + "\n");
StringRef ltoSampleProfile = args.getLastArgValue(OPT_lto_sample_profile);
if (!ltoSampleProfile.empty())
} else {
error("--reproduce: " + toString(errOrWriter.takeError()));
// The behavior of -v or --version is a bit strange, but this is
// needed for compatibility with GNU linkers.
if (args.hasArg(OPT_v) && !args.hasArg(OPT_INPUT))
if (args.hasArg(OPT_version))
// Initialize time trace profiler.
if (config->timeTraceEnabled)
timeTraceProfilerInitialize(config->timeTraceGranularity, config->progName);
llvm::TimeTraceScope timeScope("ExecuteLinker");
if (errorCount())
if (errorCount())
// The Target instance handles target-specific stuff, such as applying
// relocations or writing a PLT section. It also contains target-dependent
// values such as a default image base address.
target = getTarget();
switch (config->ekind) {
case ELF32LEKind:
case ELF32BEKind:
case ELF64LEKind:
case ELF64BEKind:
llvm_unreachable("unknown Config->EKind");
if (config->timeTraceEnabled) {
static std::string getRpath(opt::InputArgList &args) {
std::vector<StringRef> v = args::getStrings(args, OPT_rpath);
return llvm::join(v.begin(), v.end(), ":");
// Determines what we should do if there are remaining unresolved
// symbols after the name resolution.
static void setUnresolvedSymbolPolicy(opt::InputArgList &args) {
UnresolvedPolicy errorOrWarn = args.hasFlag(OPT_error_unresolved_symbols,
OPT_warn_unresolved_symbols, true)
? UnresolvedPolicy::ReportError
: UnresolvedPolicy::Warn;
// -shared implies --unresolved-symbols=ignore-all because missing
// symbols are likely to be resolved at runtime.
bool diagRegular = !config->shared, diagShlib = !config->shared;
for (const opt::Arg *arg : args) {
switch (arg->getOption().getID()) {
case OPT_unresolved_symbols: {
StringRef s = arg->getValue();
if (s == "ignore-all") {
diagRegular = false;
diagShlib = false;
} else if (s == "ignore-in-object-files") {
diagRegular = false;
diagShlib = true;
} else if (s == "ignore-in-shared-libs") {
diagRegular = true;
diagShlib = false;
} else if (s == "report-all") {
diagRegular = true;
diagShlib = true;
} else {
error("unknown --unresolved-symbols value: " + s);
case OPT_no_undefined:
diagRegular = true;
case OPT_z:
if (StringRef(arg->getValue()) == "defs")
diagRegular = true;
else if (StringRef(arg->getValue()) == "undefs")
diagRegular = false;
case OPT_allow_shlib_undefined:
diagShlib = false;
case OPT_no_allow_shlib_undefined:
diagShlib = true;
config->unresolvedSymbols =
diagRegular ? errorOrWarn : UnresolvedPolicy::Ignore;
config->unresolvedSymbolsInShlib =
diagShlib ? errorOrWarn : UnresolvedPolicy::Ignore;
static Target2Policy getTarget2(opt::InputArgList &args) {
StringRef s = args.getLastArgValue(OPT_target2, "got-rel");
if (s == "rel")
return Target2Policy::Rel;
if (s == "abs")
return Target2Policy::Abs;
if (s == "got-rel")
return Target2Policy::GotRel;
error("unknown --target2 option: " + s);
return Target2Policy::GotRel;
static bool isOutputFormatBinary(opt::InputArgList &args) {
StringRef s = args.getLastArgValue(OPT_oformat, "elf");
if (s == "binary")
return true;
if (!s.startswith("elf"))
error("unknown --oformat value: " + s);
return false;
static DiscardPolicy getDiscard(opt::InputArgList &args) {
auto *arg =
args.getLastArg(OPT_discard_all, OPT_discard_locals, OPT_discard_none);
if (!arg)
return DiscardPolicy::Default;
if (arg->getOption().getID() == OPT_discard_all)
return DiscardPolicy::All;
if (arg->getOption().getID() == OPT_discard_locals)
return DiscardPolicy::Locals;
return DiscardPolicy::None;
static StringRef getDynamicLinker(opt::InputArgList &args) {
auto *arg = args.getLastArg(OPT_dynamic_linker, OPT_no_dynamic_linker);
if (!arg)
return "";
if (arg->getOption().getID() == OPT_no_dynamic_linker) {
// --no-dynamic-linker suppresses undefined weak symbols in .dynsym
config->noDynamicLinker = true;
return "";
return arg->getValue();
static ICFLevel getICF(opt::InputArgList &args) {
auto *arg = args.getLastArg(OPT_icf_none, OPT_icf_safe, OPT_icf_all);
if (!arg || arg->getOption().getID() == OPT_icf_none)
return ICFLevel::None;
if (arg->getOption().getID() == OPT_icf_safe)
return ICFLevel::Safe;
return ICFLevel::All;
static StripPolicy getStrip(opt::InputArgList &args) {
if (args.hasArg(OPT_relocatable))
return StripPolicy::None;
auto *arg = args.getLastArg(OPT_strip_all, OPT_strip_debug);
if (!arg)
return StripPolicy::None;
if (arg->getOption().getID() == OPT_strip_all)
return StripPolicy::All;
return StripPolicy::Debug;
static uint64_t parseSectionAddress(StringRef s, opt::InputArgList &args,
const opt::Arg &arg) {
uint64_t va = 0;
if (s.startswith("0x"))
s = s.drop_front(2);
if (!to_integer(s, va, 16))
error("invalid argument: " + arg.getAsString(args));
return va;
static StringMap<uint64_t> getSectionStartMap(opt::InputArgList &args) {
StringMap<uint64_t> ret;
for (auto *arg : args.filtered(OPT_section_start)) {
StringRef name;
StringRef addr;
std::tie(name, addr) = StringRef(arg->getValue()).split('=');
ret[name] = parseSectionAddress(addr, args, *arg);
if (auto *arg = args.getLastArg(OPT_Ttext))
ret[".text"] = parseSectionAddress(arg->getValue(), args, *arg);
if (auto *arg = args.getLastArg(OPT_Tdata))
ret[".data"] = parseSectionAddress(arg->getValue(), args, *arg);
if (auto *arg = args.getLastArg(OPT_Tbss))
ret[".bss"] = parseSectionAddress(arg->getValue(), args, *arg);
return ret;
static SortSectionPolicy getSortSection(opt::InputArgList &args) {
StringRef s = args.getLastArgValue(OPT_sort_section);
if (s == "alignment")
return SortSectionPolicy::Alignment;
if (s == "name")
return SortSectionPolicy::Name;
if (!s.empty())
error("unknown --sort-section rule: " + s);
return SortSectionPolicy::Default;
static OrphanHandlingPolicy getOrphanHandling(opt::InputArgList &args) {
StringRef s = args.getLastArgValue(OPT_orphan_handling, "place");
if (s == "warn")
return OrphanHandlingPolicy::Warn;
if (s == "error")
return OrphanHandlingPolicy::Error;
if (s != "place")
error("unknown --orphan-handling mode: " + s);
return OrphanHandlingPolicy::Place;
// Parse --build-id or --build-id=<style>. We handle "tree" as a
// synonym for "sha1" because all our hash functions including
// --build-id=sha1 are actually tree hashes for performance reasons.
static std::pair<BuildIdKind, std::vector<uint8_t>>
getBuildId(opt::InputArgList &args) {
auto *arg = args.getLastArg(OPT_build_id, OPT_build_id_eq);
if (!arg)
return {BuildIdKind::None, {}};
if (arg->getOption().getID() == OPT_build_id)
return {BuildIdKind::Fast, {}};
StringRef s = arg->getValue();
if (s == "fast")
return {BuildIdKind::Fast, {}};
if (s == "md5")
return {BuildIdKind::Md5, {}};
if (s == "sha1" || s == "tree")
return {BuildIdKind::Sha1, {}};
if (s == "uuid")
return {BuildIdKind::Uuid, {}};
if (s.startswith("0x"))
return {BuildIdKind::Hexstring, parseHex(s.substr(2))};
if (s != "none")
error("unknown --build-id style: " + s);
return {BuildIdKind::None, {}};
static std::pair<bool, bool> getPackDynRelocs(opt::InputArgList &args) {
StringRef s = args.getLastArgValue(OPT_pack_dyn_relocs, "none");
if (s == "android")
return {true, false};
if (s == "relr")
return {false, true};
if (s == "android+relr")
return {true, true};
if (s != "none")
error("unknown --pack-dyn-relocs format: " + s);
return {false, false};
static void readCallGraph(MemoryBufferRef mb) {
// Build a map from symbol name to section
DenseMap<StringRef, Symbol *> map;
for (InputFile *file : objectFiles)
for (Symbol *sym : file->getSymbols())
map[sym->getName()] = sym;
auto findSection = [&](StringRef name) -> InputSectionBase * {
Symbol *sym = map.lookup(name);
if (!sym) {
if (config->warnSymbolOrdering)
warn(mb.getBufferIdentifier() + ": no such symbol: " + name);
return nullptr;
if (Defined *dr = dyn_cast_or_null<Defined>(sym))
return dyn_cast_or_null<InputSectionBase>(dr->section);
return nullptr;
for (StringRef line : args::getLines(mb)) {
SmallVector<StringRef, 3> fields;
line.split(fields, ' ');
uint64_t count;
if (fields.size() != 3 || !to_integer(fields[2], count)) {
error(mb.getBufferIdentifier() + ": parse error");
if (InputSectionBase *from = findSection(fields[0]))
if (InputSectionBase *to = findSection(fields[1]))
config->callGraphProfile[std::make_pair(from, to)] += count;
// If SHT_LLVM_CALL_GRAPH_PROFILE and its relocation section exist, returns
// true and populates cgProfile and symbolIndices.
template <class ELFT>
static bool
processCallGraphRelocations(SmallVector<uint32_t, 32> &symbolIndices,
ArrayRef<typename ELFT::CGProfile> &cgProfile,
ObjFile<ELFT> *inputObj) {
const ELFFile<ELFT> &obj = inputObj->getObj();
ArrayRef<Elf_Shdr_Impl<ELFT>> objSections =
CHECK(obj.sections(), "could not retrieve object sections");
if (inputObj->cgProfileSectionIndex == SHN_UNDEF)
return false;
cgProfile =
check(obj.template getSectionContentsAsArray<typename ELFT::CGProfile>(
for (size_t i = 0, e = objSections.size(); i < e; ++i) {
const Elf_Shdr_Impl<ELFT> &sec = objSections[i];
if (sec.sh_info == inputObj->cgProfileSectionIndex) {
if (sec.sh_type == SHT_RELA) {
ArrayRef<typename ELFT::Rela> relas =
CHECK(obj.relas(sec), "could not retrieve cg profile rela section");
for (const typename ELFT::Rela &rel : relas)
if (sec.sh_type == SHT_REL) {
ArrayRef<typename ELFT::Rel> rels =
CHECK(obj.rels(sec), "could not retrieve cg profile rel section");
for (const typename ELFT::Rel &rel : rels)
if (symbolIndices.empty())
warn("SHT_LLVM_CALL_GRAPH_PROFILE exists, but relocation section doesn't");
return !symbolIndices.empty();
template <class ELFT> static void readCallGraphsFromObjectFiles() {
SmallVector<uint32_t, 32> symbolIndices;
ArrayRef<typename ELFT::CGProfile> cgProfile;
for (auto file : objectFiles) {
auto *obj = cast<ObjFile<ELFT>>(file);
if (!processCallGraphRelocations(symbolIndices, cgProfile, obj))
if (symbolIndices.size() != cgProfile.size() * 2)
fatal("number of relocations doesn't match Weights");
for (uint32_t i = 0, size = cgProfile.size(); i < size; ++i) {
const Elf_CGProfile_Impl<ELFT> &cgpe = cgProfile[i];
uint32_t fromIndex = symbolIndices[i * 2];
uint32_t toIndex = symbolIndices[i * 2 + 1];
auto *fromSym = dyn_cast<Defined>(&obj->getSymbol(fromIndex));
auto *toSym = dyn_cast<Defined>(&obj->getSymbol(toIndex));
if (!fromSym || !toSym)
auto *from = dyn_cast_or_null<InputSectionBase>(fromSym->section);
auto *to = dyn_cast_or_null<InputSectionBase>(toSym->section);
if (from && to)
config->callGraphProfile[{from, to}] += cgpe.cgp_weight;
static bool getCompressDebugSections(opt::InputArgList &args) {
StringRef s = args.getLastArgValue(OPT_compress_debug_sections, "none");
if (s == "none")
return false;
if (s != "zlib")
error("unknown --compress-debug-sections value: " + s);
if (!zlib::isAvailable())
error("--compress-debug-sections: zlib is not available");
return true;
static StringRef getAliasSpelling(opt::Arg *arg) {
if (const opt::Arg *alias = arg->getAlias())
return alias->getSpelling();
return arg->getSpelling();
static std::pair<StringRef, StringRef> getOldNewOptions(opt::InputArgList &args,
unsigned id) {
auto *arg = args.getLastArg(id);
if (!arg)
return {"", ""};
StringRef s = arg->getValue();
std::pair<StringRef, StringRef> ret = s.split(';');
if (ret.second.empty())
error(getAliasSpelling(arg) + " expects 'old;new' format, but got " + s);
return ret;
// Parse the symbol ordering file and warn for any duplicate entries.
static std::vector<StringRef> getSymbolOrderingFile(MemoryBufferRef mb) {
SetVector<StringRef> names;
for (StringRef s : args::getLines(mb))
if (!names.insert(s) && config->warnSymbolOrdering)
warn(mb.getBufferIdentifier() + ": duplicate ordered symbol: " + s);
return names.takeVector();
static bool getIsRela(opt::InputArgList &args) {
// If -z rel or -z rela is specified, use the last option.
for (auto *arg : args.filtered_reverse(OPT_z)) {
StringRef s(arg->getValue());
if (s == "rel")
return false;
if (s == "rela")
return true;
// Otherwise use the psABI defined relocation entry format.
uint16_t m = config->emachine;
return m == EM_AARCH64 || m == EM_AMDGPU || m == EM_HEXAGON || m == EM_PPC ||
m == EM_PPC64 || m == EM_RISCV || m == EM_X86_64;
static void parseClangOption(StringRef opt, const Twine &msg) {
std::string err;
raw_string_ostream os(err);
const char *argv[] = {config->,};
if (cl::ParseCommandLineOptions(2, argv, "", &os))
error(msg + ": " + StringRef(err).trim());
// Initializes Config members by the command line options.
static void readConfigs(opt::InputArgList &args) {
errorHandler().verbose = args.hasArg(OPT_verbose);
errorHandler().vsDiagnostics =
args.hasArg(OPT_visual_studio_diagnostics_format, false);
config->allowMultipleDefinition =
OPT_no_allow_multiple_definition, false) ||
hasZOption(args, "muldefs");
config->auxiliaryList = args::getStrings(args, OPT_auxiliary);
if (opt::Arg *arg =
args.getLastArg(OPT_Bno_symbolic, OPT_Bsymbolic_non_weak_functions,
OPT_Bsymbolic_functions, OPT_Bsymbolic)) {
if (arg->getOption().matches(OPT_Bsymbolic_non_weak_functions))
config->bsymbolic = BsymbolicKind::NonWeakFunctions;
else if (arg->getOption().matches(OPT_Bsymbolic_functions))
config->bsymbolic = BsymbolicKind::Functions;
else if (arg->getOption().matches(OPT_Bsymbolic))
config->bsymbolic = BsymbolicKind::All;
config->checkSections =
args.hasFlag(OPT_check_sections, OPT_no_check_sections, true);
config->chroot = args.getLastArgValue(OPT_chroot);
config->compressDebugSections = getCompressDebugSections(args);
config->cref = args.hasArg(OPT_cref);
config->defineCommon = args.hasFlag(OPT_define_common, OPT_no_define_common,
config->optimizeBBJumps =
args.hasFlag(OPT_optimize_bb_jumps, OPT_no_optimize_bb_jumps, false);
config->demangle = args.hasFlag(OPT_demangle, OPT_no_demangle, true);
config->dependencyFile = args.getLastArgValue(OPT_dependency_file);
config->dependentLibraries = args.hasFlag(OPT_dependent_libraries, OPT_no_dependent_libraries, true);
config->disableVerify = args.hasArg(OPT_disable_verify);
config->discard = getDiscard(args);
config->dwoDir = args.getLastArgValue(OPT_plugin_opt_dwo_dir_eq);
config->dynamicLinker = getDynamicLinker(args);
config->ehFrameHdr =
args.hasFlag(OPT_eh_frame_hdr, OPT_no_eh_frame_hdr, false);
config->emitLLVM = args.hasArg(OPT_plugin_opt_emit_llvm, false);
config->emitRelocs = args.hasArg(OPT_emit_relocs);
config->callGraphProfileSort = args.hasFlag(
OPT_call_graph_profile_sort, OPT_no_call_graph_profile_sort, true);
config->enableNewDtags =
args.hasFlag(OPT_enable_new_dtags, OPT_disable_new_dtags, true);
config->entry = args.getLastArgValue(OPT_entry);
errorHandler().errorHandlingScript =
config->executeOnly =
args.hasFlag(OPT_execute_only, OPT_no_execute_only, false);
config->exportDynamic =
args.hasFlag(OPT_export_dynamic, OPT_no_export_dynamic, false);
config->filterList = args::getStrings(args, OPT_filter);
config->fini = args.getLastArgValue(OPT_fini, "_fini");
config->fixCortexA53Errata843419 = args.hasArg(OPT_fix_cortex_a53_843419) &&
config->fixCortexA8 =
args.hasArg(OPT_fix_cortex_a8) && !args.hasArg(OPT_relocatable);
config->fortranCommon =
args.hasFlag(OPT_fortran_common, OPT_no_fortran_common, true);
config->gcSections = args.hasFlag(OPT_gc_sections, OPT_no_gc_sections, false);
config->gnuUnique = args.hasFlag(OPT_gnu_unique, OPT_no_gnu_unique, true);
config->gdbIndex = args.hasFlag(OPT_gdb_index, OPT_no_gdb_index, false);
config->icf = getICF(args);
config->ignoreDataAddressEquality =
config->ignoreFunctionAddressEquality =
config->init = args.getLastArgValue(OPT_init, "_init");
config->ltoAAPipeline = args.getLastArgValue(OPT_lto_aa_pipeline);
config->ltoCSProfileGenerate = args.hasArg(OPT_lto_cs_profile_generate);
config->ltoCSProfileFile = args.getLastArgValue(OPT_lto_cs_profile_file);
config->ltoPGOWarnMismatch = args.hasFlag(OPT_lto_pgo_warn_mismatch,
OPT_no_lto_pgo_warn_mismatch, true);
config->ltoDebugPassManager = args.hasArg(OPT_lto_debug_pass_manager);
config->ltoEmitAsm = args.hasArg(OPT_lto_emit_asm);
config->ltoNewPassManager =
args.hasFlag(OPT_no_lto_legacy_pass_manager, OPT_lto_legacy_pass_manager,
config->ltoNewPmPasses = args.getLastArgValue(OPT_lto_newpm_passes);
config->ltoWholeProgramVisibility =
OPT_no_lto_whole_program_visibility, false);
config->ltoo = args::getInteger(args, OPT_lto_O, 2);
config->ltoObjPath = args.getLastArgValue(OPT_lto_obj_path_eq);
config->ltoPartitions = args::getInteger(args, OPT_lto_partitions, 1);
config->ltoSampleProfile = args.getLastArgValue(OPT_lto_sample_profile);
config->ltoBasicBlockSections =
config->ltoUniqueBasicBlockSectionNames =
OPT_no_lto_unique_basic_block_section_names, false);
config->mapFile = args.getLastArgValue(OPT_Map);
config->mipsGotSize = args::getInteger(args, OPT_mips_got_size, 0xfff0);
config->mergeArmExidx =
args.hasFlag(OPT_merge_exidx_entries, OPT_no_merge_exidx_entries, true);
config->mmapOutputFile =
args.hasFlag(OPT_mmap_output_file, OPT_no_mmap_output_file, true);
config->nmagic = args.hasFlag(OPT_nmagic, OPT_no_nmagic, false);
config->noinhibitExec = args.hasArg(OPT_noinhibit_exec);
config->nostdlib = args.hasArg(OPT_nostdlib);
config->oFormatBinary = isOutputFormatBinary(args);
config->omagic = args.hasFlag(OPT_omagic, OPT_no_omagic, false);
config->optRemarksFilename = args.getLastArgValue(OPT_opt_remarks_filename);
// Parse remarks hotness threshold. Valid value is either integer or 'auto'.
if (auto *arg = args.getLastArg(OPT_opt_remarks_hotness_threshold)) {
auto resultOrErr = remarks::parseHotnessThresholdOption(arg->getValue());
if (!resultOrErr)
error(arg->getSpelling() + ": invalid argument '" + arg->getValue() +
"', only integer or 'auto' is supported");
config->optRemarksHotnessThreshold = *resultOrErr;
config->optRemarksPasses = args.getLastArgValue(OPT_opt_remarks_passes);
config->optRemarksWithHotness = args.hasArg(OPT_opt_remarks_with_hotness);
config->optRemarksFormat = args.getLastArgValue(OPT_opt_remarks_format);
config->optimize = args::getInteger(args, OPT_O, 1);
config->orphanHandling = getOrphanHandling(args);
config->outputFile = args.getLastArgValue(OPT_o);
config->pie = args.hasFlag(OPT_pie, OPT_no_pie, false);
config->printIcfSections =
args.hasFlag(OPT_print_icf_sections, OPT_no_print_icf_sections, false);
config->printGcSections =
args.hasFlag(OPT_print_gc_sections, OPT_no_print_gc_sections, false);
config->printArchiveStats = args.getLastArgValue(OPT_print_archive_stats);
config->printSymbolOrder =
config->relax = args.hasFlag(OPT_relax, OPT_no_relax, true);
config->rpath = getRpath(args);
config->relocatable = args.hasArg(OPT_relocatable);
config->saveTemps = args.hasArg(OPT_save_temps);
config->searchPaths = args::getStrings(args, OPT_library_path);
config->sectionStartMap = getSectionStartMap(args);
config->shared = args.hasArg(OPT_shared);
config->singleRoRx = !args.hasFlag(OPT_rosegment, OPT_no_rosegment, true);
config->soName = args.getLastArgValue(OPT_soname);
config->sortSection = getSortSection(args);
config->splitStackAdjustSize = args::getInteger(args, OPT_split_stack_adjust_size, 16384);
config->strip = getStrip(args);
config->sysroot = args.getLastArgValue(OPT_sysroot);
config->target1Rel = args.hasFlag(OPT_target1_rel, OPT_target1_abs, false);
config->target2 = getTarget2(args);
config->thinLTOCacheDir = args.getLastArgValue(OPT_thinlto_cache_dir);
config->thinLTOCachePolicy = CHECK(
"--thinlto-cache-policy: invalid cache policy");
config->thinLTOEmitImportsFiles = args.hasArg(OPT_thinlto_emit_imports_files);
config->thinLTOIndexOnly = args.hasArg(OPT_thinlto_index_only) ||
config->thinLTOIndexOnlyArg = args.getLastArgValue(OPT_thinlto_index_only_eq);
config->thinLTOObjectSuffixReplace =
getOldNewOptions(args, OPT_thinlto_object_suffix_replace_eq);
config->thinLTOPrefixReplace =
getOldNewOptions(args, OPT_thinlto_prefix_replace_eq);
config->thinLTOModulesToCompile =
args::getStrings(args, OPT_thinlto_single_module_eq);
config->timeTraceEnabled = args.hasArg(OPT_time_trace);
config->timeTraceGranularity =
args::getInteger(args, OPT_time_trace_granularity, 500);
config->trace = args.hasArg(OPT_trace);
config->undefined = args::getStrings(args, OPT_undefined);
config->undefinedVersion =
args.hasFlag(OPT_undefined_version, OPT_no_undefined_version, true);
config->unique = args.hasArg(OPT_unique);
config->useAndroidRelrTags = args.hasFlag(
OPT_use_android_relr_tags, OPT_no_use_android_relr_tags, false);
config->warnBackrefs =
args.hasFlag(OPT_warn_backrefs, OPT_no_warn_backrefs, false);
config->warnCommon = args.hasFlag(OPT_warn_common, OPT_no_warn_common, false);
config->warnSymbolOrdering =
args.hasFlag(OPT_warn_symbol_ordering, OPT_no_warn_symbol_ordering, true);
config->whyExtract = args.getLastArgValue(OPT_why_extract);
config->zCombreloc = getZFlag(args, "combreloc", "nocombreloc", true);
config->zCopyreloc = getZFlag(args, "copyreloc", "nocopyreloc", true);
config->zForceBti = hasZOption(args, "force-bti");
config->zForceIbt = hasZOption(args, "force-ibt");
config->zGlobal = hasZOption(args, "global");
config->zGnustack = getZGnuStack(args);
config->zHazardplt = hasZOption(args, "hazardplt");
config->zIfuncNoplt = hasZOption(args, "ifunc-noplt");
config->zInitfirst = hasZOption(args, "initfirst");
config->zInterpose = hasZOption(args, "interpose");
config->zKeepTextSectionPrefix = getZFlag(
args, "keep-text-section-prefix", "nokeep-text-section-prefix", false);
config->zNodefaultlib = hasZOption(args, "nodefaultlib");
config->zNodelete = hasZOption(args, "nodelete");
config->zNodlopen = hasZOption(args, "nodlopen");
config->zNow = getZFlag(args, "now", "lazy", false);
config->zOrigin = hasZOption(args, "origin");
config->zPacPlt = hasZOption(args, "pac-plt");
config->zRelro = getZFlag(args, "relro", "norelro", true);
config->zRetpolineplt = hasZOption(args, "retpolineplt");
config->zRodynamic = hasZOption(args, "rodynamic");
config->zSeparate = getZSeparate(args);
config->zShstk = hasZOption(args, "shstk");
config->zStackSize = args::getZOptionValue(args, OPT_z, "stack-size", 0);
config->zStartStopGC =
getZFlag(args, "start-stop-gc", "nostart-stop-gc", true);
config->zStartStopVisibility = getZStartStopVisibility(args);
config->zText = getZFlag(args, "text", "notext", true);
config->zWxneeded = hasZOption(args, "wxneeded");
config->power10Stubs = args.getLastArgValue(OPT_power10_stubs_eq) != "no";
if (opt::Arg *arg = args.getLastArg(OPT_eb, OPT_el)) {
if (arg->getOption().matches(OPT_eb))
config->optEB = true;
config->optEL = true;
for (opt::Arg *arg : args.filtered(OPT_shuffle_sections)) {
constexpr StringRef errPrefix = "--shuffle-sections=: ";
std::pair<StringRef, StringRef> kv = StringRef(arg->getValue()).split('=');
if (kv.first.empty() || kv.second.empty()) {
error(errPrefix + "expected <section_glob>=<seed>, but got '" +
arg->getValue() + "'");
// Signed so that <section_glob>=-1 is allowed.
int64_t v;
if (!to_integer(kv.second, v))
error(errPrefix + "expected an integer, but got '" + kv.second + "'");
else if (Expected<GlobPattern> pat = GlobPattern::create(kv.first))
config->shuffleSections.emplace_back(std::move(*pat), uint32_t(v));
error(errPrefix + toString(pat.takeError()));
for (opt::Arg *arg : args.filtered(OPT_z)) {
std::pair<StringRef, StringRef> option =
if (option.first != "dead-reloc-in-nonalloc")
constexpr StringRef errPrefix = "-z dead-reloc-in-nonalloc=: ";
std::pair<StringRef, StringRef> kv = option.second.split('=');
if (kv.first.empty() || kv.second.empty()) {
error(errPrefix + "expected <section_glob>=<value>");
uint64_t v;
if (!to_integer(kv.second, v))
error(errPrefix + "expected a non-negative integer, but got '" +
kv.second + "'");
else if (Expected<GlobPattern> pat = GlobPattern::create(kv.first))
config->deadRelocInNonAlloc.emplace_back(std::move(*pat), v);
error(errPrefix + toString(pat.takeError()));
// Parse LTO options.
if (auto *arg = args.getLastArg(OPT_plugin_opt_mcpu_eq))
parseClangOption("-mcpu=" + StringRef(arg->getValue())),
for (opt::Arg *arg : args.filtered(OPT_plugin_opt_eq_minus))
parseClangOption(std::string("-") + arg->getValue(), arg->getSpelling());
// GCC collect2 passes -plugin-opt=path/to/lto-wrapper with an absolute or
// relative path. Just ignore. If not ended with "lto-wrapper", consider it an
// unsupported option and error.
for (opt::Arg *arg : args.filtered(OPT_plugin_opt_eq))
if (!StringRef(arg->getValue()).endswith("lto-wrapper"))
error(arg->getSpelling() + ": unknown plugin option '" + arg->getValue() +
// Parse -mllvm options.
for (auto *arg : args.filtered(OPT_mllvm))
parseClangOption(arg->getValue(), arg->getSpelling());
// --threads= takes a positive integer and provides the default value for
// --thinlto-jobs=.
if (auto *arg = args.getLastArg(OPT_threads)) {
StringRef v(arg->getValue());
unsigned threads = 0;
if (!llvm::to_integer(v, threads, 0) || threads == 0)
error(arg->getSpelling() + ": expected a positive integer, but got '" +
arg->getValue() + "'");
parallel::strategy = hardware_concurrency(threads);
config->thinLTOJobs = v;
if (auto *arg = args.getLastArg(OPT_thinlto_jobs))
config->thinLTOJobs = arg->getValue();
if (config->ltoo > 3)
error("invalid optimization level for LTO: " + Twine(config->ltoo));
if (config->ltoPartitions == 0)
error("--lto-partitions: number of threads must be > 0");
if (!get_threadpool_strategy(config->thinLTOJobs))
error("--thinlto-jobs: invalid job count: " + config->thinLTOJobs);
if (config->splitStackAdjustSize < 0)
error("--split-stack-adjust-size: size must be >= 0");
// The text segment is traditionally the first segment, whose address equals
// the base address. However, lld places the R PT_LOAD first. -Ttext-segment
// is an old-fashioned option that does not play well with lld's layout.
// Suggest --image-base as a likely alternative.
if (args.hasArg(OPT_Ttext_segment))
error("-Ttext-segment is not supported. Use --image-base if you "
"intend to set the base address");
// Parse ELF{32,64}{LE,BE} and CPU type.
if (auto *arg = args.getLastArg(OPT_m)) {
StringRef s = arg->getValue();
std::tie(config->ekind, config->emachine, config->osabi) =
config->mipsN32Abi =
(s.startswith("elf32btsmipn32") || s.startswith("elf32ltsmipn32"));
config->emulation = s;
// Parse --hash-style={sysv,gnu,both}.
if (auto *arg = args.getLastArg(OPT_hash_style)) {
StringRef s = arg->getValue();
if (s == "sysv")
config->sysvHash = true;
else if (s == "gnu")
config->gnuHash = true;
else if (s == "both")
config->sysvHash = config->gnuHash = true;
error("unknown --hash-style: " + s);
if (args.hasArg(OPT_print_map))
config->mapFile = "-";
// Page alignment can be disabled by the -n (--nmagic) and -N (--omagic).
// As PT_GNU_RELRO relies on Paging, do not create it when we have disabled
// it.
if (config->nmagic || config->omagic)
config->zRelro = false;
std::tie(config->buildId, config->buildIdVector) = getBuildId(args);
std::tie(config->androidPackDynRelocs, config->relrPackDynRelocs) =
if (auto *arg = args.getLastArg(OPT_symbol_ordering_file)){
if (args.hasArg(OPT_call_graph_ordering_file))
error("--symbol-ordering-file and --call-graph-order-file "
"may not be used together");
if (Optional<MemoryBufferRef> buffer = readFile(arg->getValue())){
config->symbolOrderingFile = getSymbolOrderingFile(*buffer);
// Also need to disable CallGraphProfileSort to prevent
// LLD order symbols with CGProfile
config->callGraphProfileSort = false;
{"local", (uint16_t)VER_NDX_LOCAL, {}, {}});
{"global", (uint16_t)VER_NDX_GLOBAL, {}, {}});
// If --retain-symbol-file is used, we'll keep only the symbols listed in
// the file and discard all others.
if (auto *arg = args.getLastArg(OPT_retain_symbols_file)) {
{"*", /*isExternCpp=*/false, /*hasWildcard=*/true});
if (Optional<MemoryBufferRef> buffer = readFile(arg->getValue()))
for (StringRef s : args::getLines(*buffer))
{s, /*isExternCpp=*/false, /*hasWildcard=*/false});
for (opt::Arg *arg : args.filtered(OPT_warn_backrefs_exclude)) {
StringRef pattern(arg->getValue());
if (Expected<GlobPattern> pat = GlobPattern::create(pattern))
error(arg->getSpelling() + ": " + toString(pat.takeError()));
// For -no-pie and -pie, --export-dynamic-symbol specifies defined symbols
// which should be exported. For -shared, references to matched non-local
// STV_DEFAULT symbols are not bound to definitions within the shared object,
// even if other options express a symbolic intention: -Bsymbolic,
// -Bsymbolic-functions (if STT_FUNC), --dynamic-list.
for (auto *arg : args.filtered(OPT_export_dynamic_symbol))
{arg->getValue(), /*isExternCpp=*/false,
// --export-dynamic-symbol-list specifies a list of --export-dynamic-symbol
// patterns. --dynamic-list is --export-dynamic-symbol-list plus -Bsymbolic
// like semantics.
config->symbolic =
config->bsymbolic == BsymbolicKind::All || args.hasArg(OPT_dynamic_list);
for (auto *arg :
args.filtered(OPT_dynamic_list, OPT_export_dynamic_symbol_list))
if (Optional<MemoryBufferRef> buffer = readFile(arg->getValue()))
for (auto *arg : args.filtered(OPT_version_script))
if (Optional<std::string> path = searchScript(arg->getValue())) {
if (Optional<MemoryBufferRef> buffer = readFile(*path))
} else {
error(Twine("cannot find version script ") + arg->getValue());
// Some Config members do not directly correspond to any particular
// command line options, but computed based on other Config values.
// This function initialize such members. See Config.h for the details
// of these values.
static void setConfigs(opt::InputArgList &args) {
ELFKind k = config->ekind;
uint16_t m = config->emachine;
config->copyRelocs = (config->relocatable || config->emitRelocs);
config->is64 = (k == ELF64LEKind || k == ELF64BEKind);
config->isLE = (k == ELF32LEKind || k == ELF64LEKind);
config->endianness = config->isLE ? endianness::little : endianness::big;
config->isMips64EL = (k == ELF64LEKind && m == EM_MIPS);
config->isPic = config->pie || config->shared;
config->picThunk = args.hasArg(OPT_pic_veneer, config->isPic);
config->wordsize = config->is64 ? 8 : 4;
// ELF defines two different ways to store relocation addends as shown below:
// Rel: Addends are stored to the location where relocations are applied. It
// cannot pack the full range of addend values for all relocation types, but
// this only affects relocation types that we don't support emitting as
// dynamic relocations (see getDynRel).
// Rela: Addends are stored as part of relocation entry.
// In other words, Rela makes it easy to read addends at the price of extra
// 4 or 8 byte for each relocation entry.
// We pick the format for dynamic relocations according to the psABI for each
// processor, but a contrary choice can be made if the dynamic loader
// supports.
config->isRela = getIsRela(args);
// If the output uses REL relocations we must store the dynamic relocation
// addends to the output sections. We also store addends for RELA relocations
// if --apply-dynamic-relocs is used.
// We default to not writing the addends when using RELA relocations since
// any standard conforming tool can find it in r_addend.
config->writeAddends = args.hasFlag(OPT_apply_dynamic_relocs,
OPT_no_apply_dynamic_relocs, false) ||
// Validation of dynamic relocation addends is on by default for assertions
// builds (for supported targets) and disabled otherwise. Ideally we would
// enable the debug checks for all targets, but currently not all targets
// have support for reading Elf_Rel addends, so we only enable for a subset.
#ifndef NDEBUG
bool checkDynamicRelocsDefault = m == EM_ARM || m == EM_386 || m == EM_MIPS ||
m == EM_X86_64 || m == EM_RISCV;
bool checkDynamicRelocsDefault = false;
config->checkDynamicRelocs =
OPT_no_check_dynamic_relocations, checkDynamicRelocsDefault);
config->tocOptimize =
args.hasFlag(OPT_toc_optimize, OPT_no_toc_optimize, m == EM_PPC64);
config->pcRelOptimize =
args.hasFlag(OPT_pcrel_optimize, OPT_no_pcrel_optimize, m == EM_PPC64);
static bool isFormatBinary(StringRef s) {
if (s == "binary")
return true;
if (s == "elf" || s == "default")
return false;
error("unknown --format value: " + s +
" (supported formats: elf, default, binary)");
return false;
void LinkerDriver::createFiles(opt::InputArgList &args) {
llvm::TimeTraceScope timeScope("Load input files");
// For --{push,pop}-state.
std::vector<std::tuple<bool, bool, bool>> stack;
// Iterate over argv to process input files and positional arguments.
InputFile::isInGroup = false;
for (auto *arg : args) {
switch (arg->getOption().getID()) {
case OPT_library:
addFile(arg->getValue(), /*withLOption=*/false);
case OPT_defsym: {
StringRef from;
StringRef to;
std::tie(from, to) = StringRef(arg->getValue()).split('=');
if (from.empty() || to.empty())
error("--defsym: syntax error: " + StringRef(arg->getValue()));
readDefsym(from, MemoryBufferRef(to, "--defsym"));
case OPT_script:
if (Optional<std::string> path = searchScript(arg->getValue())) {
if (Optional<MemoryBufferRef> mb = readFile(*path))
error(Twine("cannot find linker script ") + arg->getValue());
case OPT_as_needed:
config->asNeeded = true;
case OPT_format:
config->formatBinary = isFormatBinary(arg->getValue());
case OPT_no_as_needed:
config->asNeeded = false;
case OPT_Bstatic:
case OPT_omagic:
case OPT_nmagic:
config->isStatic = true;
case OPT_Bdynamic:
config->isStatic = false;
case OPT_whole_archive:
inWholeArchive = true;
case OPT_no_whole_archive:
inWholeArchive = false;
case OPT_just_symbols:
if (Optional<MemoryBufferRef> mb = readFile(arg->getValue())) {
files.back()->justSymbols = true;
case OPT_start_group:
if (InputFile::isInGroup)
error("nested --start-group");
InputFile::isInGroup = true;
case OPT_end_group:
if (!InputFile::isInGroup)
error("stray --end-group");
InputFile::isInGroup = false;
case OPT_start_lib:
if (inLib)
error("nested --start-lib");
if (InputFile::isInGroup)
error("may not nest --start-lib in --start-group");
inLib = true;
InputFile::isInGroup = true;
case OPT_end_lib:
if (!inLib)
error("stray --end-lib");
inLib = false;
InputFile::isInGroup = false;
case OPT_push_state:
stack.emplace_back(config->asNeeded, config->isStatic, inWholeArchive);
case OPT_pop_state:
if (stack.empty()) {
error("unbalanced --push-state/--pop-state");
std::tie(config->asNeeded, config->isStatic, inWholeArchive) = stack.back();
if (files.empty() && errorCount() == 0)
error("no input files");
// If -m <machine_type> was not given, infer it from object files.
void LinkerDriver::inferMachineType() {
if (config->ekind != ELFNoneKind)
for (InputFile *f : files) {
if (f->ekind == ELFNoneKind)
config->ekind = f->ekind;
config->emachine = f->emachine;
config->osabi = f->osabi;
config->mipsN32Abi = config->emachine == EM_MIPS && isMipsN32Abi(f);
error("target emulation unknown: -m or at least one .o file required");
// Parse -z max-page-size=<value>. The default value is defined by
// each target.
static uint64_t getMaxPageSize(opt::InputArgList &args) {
uint64_t val = args::getZOptionValue(args, OPT_z, "max-page-size",
if (!isPowerOf2_64(val))
error("max-page-size: value isn't a power of 2");
if (config->nmagic || config->omagic) {
if (val != target->defaultMaxPageSize)
warn("-z max-page-size set, but paging disabled by omagic or nmagic");
return 1;
return val;
// Parse -z common-page-size=<value>. The default value is defined by
// each target.
static uint64_t getCommonPageSize(opt::InputArgList &args) {
uint64_t val = args::getZOptionValue(args, OPT_z, "common-page-size",
if (!isPowerOf2_64(val))
error("common-page-size: value isn't a power of 2");
if (config->nmagic || config->omagic) {
if (val != target->defaultCommonPageSize)
warn("-z common-page-size set, but paging disabled by omagic or nmagic");
return 1;
// commonPageSize can't be larger than maxPageSize.
if (val > config->maxPageSize)
val = config->maxPageSize;
return val;
// Parses --image-base option.
static Optional<uint64_t> getImageBase(opt::InputArgList &args) {
// Because we are using "Config->maxPageSize" here, this function has to be
// called after the variable is initialized.
auto *arg = args.getLastArg(OPT_image_base);
if (!arg)
return None;
StringRef s = arg->getValue();
uint64_t v;
if (!to_integer(s, v)) {
error("--image-base: number expected, but got " + s);
return 0;
if ((v % config->maxPageSize) != 0)
warn("--image-base: address isn't multiple of page size: " + s);
return v;
// Parses `--exclude-libs=lib,lib,...`.
// The library names may be delimited by commas or colons.
static DenseSet<StringRef> getExcludeLibs(opt::InputArgList &args) {
DenseSet<StringRef> ret;
for (auto *arg : args.filtered(OPT_exclude_libs)) {
StringRef s = arg->getValue();
for (;;) {
size_t pos = s.find_first_of(",:");
if (pos == StringRef::npos)
ret.insert(s.substr(0, pos));
s = s.substr(pos + 1);
return ret;
// Handles the --exclude-libs option. If a static library file is specified
// by the --exclude-libs option, all public symbols from the archive become
// private unless otherwise specified by version scripts or something.
// A special library name "ALL" means all archive files.
// This is not a popular option, but some programs such as bionic libc use it.
static void excludeLibs(opt::InputArgList &args) {
DenseSet<StringRef> libs = getExcludeLibs(args);
bool all = libs.count("ALL");
auto visit = [&](InputFile *file) {
if (!file->archiveName.empty())
if (all || libs.count(path::filename(file->archiveName)))
for (Symbol *sym : file->getSymbols())
if (!sym->isUndefined() && !sym->isLocal() && sym->file == file)
sym->versionId = VER_NDX_LOCAL;
for (InputFile *file : objectFiles)
for (BitcodeFile *file : bitcodeFiles)
// Force Sym to be entered in the output.
static void handleUndefined(Symbol *sym, const char *option) {
// Since a symbol may not be used inside the program, LTO may
// eliminate it. Mark the symbol as "used" to prevent it.
sym->isUsedInRegularObj = true;
if (!sym->isLazy())
if (!config->whyExtract.empty())
whyExtract.emplace_back(option, sym->file, *sym);
// As an extension to GNU linkers, lld supports a variant of `-u`
// which accepts wildcard patterns. All symbols that match a given
// pattern are handled as if they were given by `-u`.
static void handleUndefinedGlob(StringRef arg) {
Expected<GlobPattern> pat = GlobPattern::create(arg);
if (!pat) {
error("--undefined-glob: " + toString(pat.takeError()));
// Calling sym->extract() in the loop is not safe because it may add new
// symbols to the symbol table, invalidating the current iterator.
std::vector<Symbol *> syms;
for (Symbol *sym : symtab->symbols())
if (pat->match(sym->getName()))
for (Symbol *sym : syms)
handleUndefined(sym, "--undefined-glob");
static void handleLibcall(StringRef name) {
Symbol *sym = symtab->find(name);
if (!sym || !sym->isLazy())
MemoryBufferRef mb;
if (auto *lo = dyn_cast<LazyObject>(sym))
mb = lo->file->mb;
mb = cast<LazyArchive>(sym)->getMemberBuffer();
if (isBitcode(mb))
// Handle --dependency-file=<path>. If that option is given, lld creates a
// file at a given path with the following contents:
// <output-file>: <input-file> ...
// <input-file>:
// where <output-file> is a pathname of an output file and <input-file>
// ... is a list of pathnames of all input files. `make` command can read a
// file in the above format and interpret it as a dependency info. We write
// phony targets for every <input-file> to avoid an error when that file is
// removed.
// This option is useful if you want to make your final executable to depend
// on all input files including system libraries. Here is why.
// When you write a Makefile, you usually write it so that the final
// executable depends on all user-generated object files. Normally, you
// don't make your executable to depend on system libraries (such as libc)
// because you don't know the exact paths of libraries, even though system
// libraries that are linked to your executable statically are technically a
// part of your program. By using --dependency-file option, you can make
// lld to dump dependency info so that you can maintain exact dependencies
// easily.
static void writeDependencyFile() {
std::error_code ec;
raw_fd_ostream os(config->dependencyFile, ec, sys::fs::OF_None);
if (ec) {
error("cannot open " + config->dependencyFile + ": " + ec.message());
// We use the same escape rules as Clang/GCC which are accepted by Make/Ninja:
// * A space is escaped by a backslash which itself must be escaped.
// * A hash sign is escaped by a single backslash.
// * $ is escapes as $$.
auto printFilename = [](raw_fd_ostream &os, StringRef filename) {
llvm::SmallString<256> nativePath;
llvm::sys::path::native(filename.str(), nativePath);
llvm::sys::path::remove_dots(nativePath, /*remove_dot_dot=*/true);
for (unsigned i = 0, e = nativePath.size(); i != e; ++i) {
if (nativePath[i] == '#') {
os << '\\';
} else if (nativePath[i] == ' ') {
os << '\\';
unsigned j = i;
while (j > 0 && nativePath[--j] == '\\')
os << '\\';
} else if (nativePath[i] == '$') {
os << '$';
os << nativePath[i];
os << config->outputFile << ":";
for (StringRef path : config->dependencyFiles) {
os << " \\\n ";
printFilename(os, path);
os << "\n";
for (StringRef path : config->dependencyFiles) {
os << "\n";
printFilename(os, path);
os << ":\n";
// Replaces common symbols with defined symbols reside in .bss sections.
// This function is called after all symbol names are resolved. As a
// result, the passes after the symbol resolution won't see any
// symbols of type CommonSymbol.
static void replaceCommonSymbols() {
llvm::TimeTraceScope timeScope("Replace common symbols");
for (Symbol *sym : symtab->symbols()) {
auto *s = dyn_cast<CommonSymbol>(sym);
if (!s)
auto *bss = make<BssSection>("COMMON", s->size, s->alignment);
bss->file = s->file;
s->replace(Defined{s->file, s->getName(), s->binding, s->stOther, s->type,
/*value=*/0, s->size, bss});
// If all references to a DSO happen to be weak, the DSO is not added
// to DT_NEEDED. If that happens, we need to eliminate shared symbols
// created from the DSO. Otherwise, they become dangling references
// that point to a non-existent DSO.
static void demoteSharedSymbols() {
llvm::TimeTraceScope timeScope("Demote shared symbols");
for (Symbol *sym : symtab->symbols()) {
auto *s = dyn_cast<SharedSymbol>(sym);
if (!((s && !s->getFile().isNeeded) ||
(sym->isLazy() && sym->isUsedInRegularObj)))
bool used = sym->used;
Undefined{nullptr, sym->getName(), STB_WEAK, sym->stOther, sym->type});
sym->used = used;
sym->versionId = VER_NDX_GLOBAL;
// The section referred to by `s` is considered address-significant. Set the
// keepUnique flag on the section if appropriate.
static void markAddrsig(Symbol *s) {
if (auto *d = dyn_cast_or_null<Defined>(s))
if (d->section)
// We don't need to keep text sections unique under --icf=all even if they
// are address-significant.
if (config->icf == ICFLevel::Safe || !(d->section->flags & SHF_EXECINSTR))
d->section->keepUnique = true;
// Record sections that define symbols mentioned in --keep-unique <symbol>
// and symbols referred to by address-significance tables. These sections are
// ineligible for ICF.
template <class ELFT>
static void findKeepUniqueSections(opt::InputArgList &args) {
for (auto *arg : args.filtered(OPT_keep_unique)) {
StringRef name = arg->getValue();
auto *d = dyn_cast_or_null<Defined>(symtab->find(name));
if (!d || !d->section) {
warn("could not find symbol " + name + " to keep unique");
d->section->keepUnique = true;
// --icf=all --ignore-data-address-equality means that we can ignore
// the dynsym and address-significance tables entirely.
if (config->icf == ICFLevel::All && config->ignoreDataAddressEquality)
// Symbols in the dynsym could be address-significant in other executables
// or DSOs, so we conservatively mark them as address-significant.
for (Symbol *sym : symtab->symbols())
if (sym->includeInDynsym())
// Visit the address-significance table in each object file and mark each
// referenced symbol as address-significant.
for (InputFile *f : objectFiles) {
auto *obj = cast<ObjFile<ELFT>>(f);
ArrayRef<Symbol *> syms = obj->getSymbols();
if (obj->addrsigSec) {
ArrayRef<uint8_t> contents =
const uint8_t *cur = contents.begin();
while (cur != contents.end()) {
unsigned size;
const char *err;
uint64_t symIndex = decodeULEB128(cur, &size, contents.end(), &err);
if (err)
fatal(toString(f) + ": could not decode addrsig section: " + err);
cur += size;
} else {
// If an object file does not have an address-significance table,
// conservatively mark all of its symbols as address-significant.
for (Symbol *s : syms)
// This function reads a symbol partition specification section. These sections
// are used to control which partition a symbol is allocated to. See
// for more details on partitions.
template <typename ELFT>
static void readSymbolPartitionSection(InputSectionBase *s) {
// Read the relocation that refers to the partition's entry point symbol.
Symbol *sym;
const RelsOrRelas<ELFT> rels = s->template relsOrRelas<ELFT>();
if (rels.areRelocsRel())
sym = &s->getFile<ELFT>()->getRelocTargetSym(rels.rels[0]);
sym = &s->getFile<ELFT>()->getRelocTargetSym(rels.relas[0]);
if (!isa<Defined>(sym) || !sym->includeInDynsym())
StringRef partName = reinterpret_cast<const char *>(s->data().data());
for (Partition &part : partitions) {
if ( == partName) {
sym->partition = part.getNumber();
// Forbid partitions from being used on incompatible targets, and forbid them
// from being used together with various linker features that assume a single
// set of output sections.
if (script->hasSectionsCommand)
error(toString(s->file) +
": partitions cannot be used with the SECTIONS command");
if (script->hasPhdrsCommands())
error(toString(s->file) +
": partitions cannot be used with the PHDRS command");
if (!config->sectionStartMap.empty())
error(toString(s->file) + ": partitions cannot be used with "
"--section-start, -Ttext, -Tdata or -Tbss");
if (config->emachine == EM_MIPS)
error(toString(s->file) + ": partitions cannot be used on this target");
// Impose a limit of no more than 254 partitions. This limit comes from the
// sizes of the Partition fields in InputSectionBase and Symbol, as well as
// the amount of space devoted to the partition number in RankFlags.
if (partitions.size() == 254)
fatal("may not have more than 254 partitions");
Partition &newPart = partitions.back(); = partName;
sym->partition = newPart.getNumber();
static Symbol *addUndefined(StringRef name) {
return symtab->addSymbol(
Undefined{nullptr, name, STB_GLOBAL, STV_DEFAULT, 0});
static Symbol *addUnusedUndefined(StringRef name,
uint8_t binding = STB_GLOBAL) {
Undefined sym{nullptr, name, binding, STV_DEFAULT, 0};
sym.isUsedInRegularObj = false;
return symtab->addSymbol(sym);
// This function is where all the optimizations of link-time
// optimization takes place. When LTO is in use, some input files are
// not in native object file format but in the LLVM bitcode format.
// This function compiles bitcode files into a few big native files
// using LLVM functions and replaces bitcode symbols with the results.
// Because all bitcode files that the program consists of are passed to
// the compiler at once, it can do a whole-program optimization.
template <class ELFT> void LinkerDriver::compileBitcodeFiles() {
llvm::TimeTraceScope timeScope("LTO");
// Compile bitcode files and replace bitcode symbols.
lto.reset(new BitcodeCompiler);
for (BitcodeFile *file : bitcodeFiles)
for (InputFile *file : lto->compile()) {
auto *obj = cast<ObjFile<ELFT>>(file);
// Parse '@' in symbol names for non-relocatable output.
if (!config->relocatable)
for (Symbol *sym : obj->getGlobalSymbols())
// The --wrap option is a feature to rename symbols so that you can write
// wrappers for existing functions. If you pass `--wrap=foo`, all
// occurrences of symbol `foo` are resolved to `__wrap_foo` (so, you are
// expected to write `__wrap_foo` function as a wrapper). The original
// symbol becomes accessible as `__real_foo`, so you can call that from your
// wrapper.
// This data structure is instantiated for each --wrap option.
struct WrappedSymbol {
Symbol *sym;
Symbol *real;
Symbol *wrap;
// Handles --wrap option.
// This function instantiates wrapper symbols. At this point, they seem
// like they are not being used at all, so we explicitly set some flags so
// that LTO won't eliminate them.
static std::vector<WrappedSymbol> addWrappedSymbols(opt::InputArgList &args) {
std::vector<WrappedSymbol> v;
DenseSet<StringRef> seen;
for (auto *arg : args.filtered(OPT_wrap)) {
StringRef name = arg->getValue();
if (!seen.insert(name).second)
Symbol *sym = symtab->find(name);
if (!sym)
Symbol *real = addUnusedUndefined("__real_" + name));
Symbol *wrap =
addUnusedUndefined("__wrap_" + name), sym->binding);
v.push_back({sym, real, wrap});
// We want to tell LTO not to inline symbols to be overwritten
// because LTO doesn't know the final symbol contents after renaming.
real->canInline = false;
sym->canInline = false;
// Tell LTO not to eliminate these symbols.
sym->isUsedInRegularObj = true;
// If sym is referenced in any object file, bitcode file or shared object,
// retain wrap which is the redirection target of sym. If the object file
// defining sym has sym references, we cannot easily distinguish the case
// from cases where sym is not referenced. Retain wrap because we choose to
// wrap sym references regardless of whether sym is defined
// (
if (sym->referenced || sym->isDefined())
wrap->isUsedInRegularObj = true;
return v;
// Do renaming for --wrap and foo@v1 by updating pointers to symbols.
// When this function is executed, only InputFiles and symbol table
// contain pointers to symbol objects. We visit them to replace pointers,
// so that wrapped symbols are swapped as instructed by the command line.
static void redirectSymbols(ArrayRef<WrappedSymbol> wrapped) {
llvm::TimeTraceScope timeScope("Redirect symbols");
DenseMap<Symbol *, Symbol *> map;
for (const WrappedSymbol &w : wrapped) {
map[w.sym] = w.wrap;
map[w.real] = w.sym;
for (Symbol *sym : symtab->symbols()) {
// Enumerate symbols with a non-default version (foo@v1).
StringRef name = sym->getName();
const char *suffix1 = sym->getVersionSuffix();
if (suffix1[0] != '@' || suffix1[1] == '@')
// Check the existing symbol foo. We have two special cases to handle:
// * There is a definition of foo@v1 and foo@@v1.
// * There is a definition of foo@v1 and foo.
Defined *sym2 = dyn_cast_or_null<Defined>(symtab->find(name));
if (!sym2)
const char *suffix2 = sym2->getVersionSuffix();
if (suffix2[0] == '@' && suffix2[1] == '@' &&
strcmp(suffix1 + 1, suffix2 + 2) == 0) {
// foo@v1 and foo@@v1 should be merged, so redirect foo@v1 to foo@@v1.
map.try_emplace(sym, sym2);
// If both foo@v1 and foo@@v1 are defined and non-weak, report a duplicate
// definition error.
// Eliminate foo@v1 from the symbol table.
sym->symbolKind = Symbol::PlaceholderKind;
} else if (auto *sym1 = dyn_cast<Defined>(sym)) {
if (sym2->versionId > VER_NDX_GLOBAL
? config->versionDefinitions[sym2->versionId].name == suffix1 + 1
: sym1->section == sym2->section && sym1->value == sym2->value) {
// Due to an assembler design flaw, if foo is defined, .symver foo,
// foo@v1 defines both foo and foo@v1. Unless foo is bound to a
// different version, GNU ld makes foo@v1 canonical and eliminates foo.
// Emulate its behavior, otherwise we would have foo or foo@@v1 beside
// foo@v1. foo@v1 and foo combining does not apply if they are not
// defined in the same place.
map.try_emplace(sym2, sym);
sym2->symbolKind = Symbol::PlaceholderKind;
if (map.empty())
// Update pointers in input files.
parallelForEach(objectFiles, [&](InputFile *file) {
MutableArrayRef<Symbol *> syms = file->getMutableSymbols();
for (size_t i = 0, e = syms.size(); i != e; ++i)
if (Symbol *s = map.lookup(syms[i]))
syms[i] = s;
// Update pointers in the symbol table.
for (const WrappedSymbol &w : wrapped)
symtab->wrap(w.sym, w.real, w.wrap);
// To enable CET (x86's hardware-assited control flow enforcement), each
// source file must be compiled with -fcf-protection. Object files compiled
// with the flag contain feature flags indicating that they are compatible
// with CET. We enable the feature only when all object files are compatible
// with CET.
// This is also the case with AARCH64's BTI and PAC which use the similar
template <class ELFT> static uint32_t getAndFeatures() {
if (config->emachine != EM_386 && config->emachine != EM_X86_64 &&
config->emachine != EM_AARCH64)
return 0;
uint32_t ret = -1;
for (InputFile *f : objectFiles) {
uint32_t features = cast<ObjFile<ELFT>>(f)->andFeatures;
if (config->zForceBti && !(features & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) {
warn(toString(f) + ": -z force-bti: file does not have "
} else if (config->zForceIbt &&
!(features & GNU_PROPERTY_X86_FEATURE_1_IBT)) {
warn(toString(f) + ": -z force-ibt: file does not have "
if (config->zPacPlt && !(features & GNU_PROPERTY_AARCH64_FEATURE_1_PAC)) {
warn(toString(f) + ": -z pac-plt: file does not have "
ret &= features;
// Force enable Shadow Stack.
if (config->zShstk)
return ret;
// Do actual linking. Note that when this function is called,
// all linker scripts have already been parsed.
template <class ELFT> void LinkerDriver::link(opt::InputArgList &args) {
llvm::TimeTraceScope timeScope("Link", StringRef("LinkerDriver::Link"));
// If a --hash-style option was not given, set to a default value,
// which varies depending on the target.
if (!args.hasArg(OPT_hash_style)) {
if (config->emachine == EM_MIPS)
config->sysvHash = true;
config->sysvHash = config->gnuHash = true;
// Default output filename is "a.out" by the Unix tradition.
if (config->outputFile.empty())
config->outputFile = "a.out";
// Fail early if the output file or map file is not writable. If a user has a
// long link, e.g. due to a large LTO link, they do not wish to run it and
// find that it failed because there was a mistake in their command-line.
llvm::TimeTraceScope timeScope("Create output files");
if (auto e = tryCreateFile(config->outputFile))
error("cannot open output file " + config->outputFile + ": " +
if (auto e = tryCreateFile(config->mapFile))
error("cannot open map file " + config->mapFile + ": " + e.message());
if (auto e = tryCreateFile(config->whyExtract))
error("cannot open --why-extract= file " + config->whyExtract + ": " +
if (errorCount())
// Use default entry point name if no name was given via the command
// line nor linker scripts. For some reason, MIPS entry point name is
// different from others.
config->warnMissingEntry =
(!config->entry.empty() || (!config->shared && !config->relocatable));
if (config->entry.empty() && !config->relocatable)
config->entry = (config->emachine == EM_MIPS) ? "__start" : "_start";
// Handle --trace-symbol.
for (auto *arg : args.filtered(OPT_trace_symbol))
symtab->insert(arg->getValue())->traced = true;
// Handle -u/--undefined before input files. If both a.a and define foo,
// -u foo a.a will extract a.a.
for (StringRef name : config->undefined)
addUnusedUndefined(name)->referenced = true;
// Add all files to the symbol table. This will add almost all
// symbols that we need to the symbol table. This process might
// add files to the link, via autolinking, these files are always
// appended to the Files vector.
llvm::TimeTraceScope timeScope("Parse input files");
for (size_t i = 0; i < files.size(); ++i) {
llvm::TimeTraceScope timeScope("Parse input files", files[i]->getName());
// Now that we have every file, we can decide if we will need a
// dynamic symbol table.
// We need one if we were asked to export dynamic symbols or if we are
// producing a shared library.
// We also need one if any shared libraries are used and for pie executables
// (probably because the dynamic linker needs it).
config->hasDynSymTab =
!sharedFiles.empty() || config->isPic || config->exportDynamic;
// Some symbols (such as __ehdr_start) are defined lazily only when there
// are undefined symbols for them, so we add these to trigger that logic.
for (StringRef name : script->referencedSymbols)
// Prevent LTO from removing any definition referenced by -u.
for (StringRef name : config->undefined)
if (Defined *sym = dyn_cast_or_null<Defined>(symtab->find(name)))
sym->isUsedInRegularObj = true;
// If an entry symbol is in a static archive, pull out that file now.
if (Symbol *sym = symtab->find(config->entry))
handleUndefined(sym, "--entry");
// Handle the `--undefined-glob <pattern>` options.
for (StringRef pat : args::getStrings(args, OPT_undefined_glob))
// Mark -init and -fini symbols so that the LTO doesn't eliminate them.
if (Symbol *sym = dyn_cast_or_null<Defined>(symtab->find(config->init)))
sym->isUsedInRegularObj = true;
if (Symbol *sym = dyn_cast_or_null<Defined>(symtab->find(config->fini)))
sym->isUsedInRegularObj = true;
// If any of our inputs are bitcode files, the LTO code generator may create
// references to certain library functions that might not be explicit in the
// bitcode file's symbol table. If any of those library functions are defined
// in a bitcode file in an archive member, we need to arrange to use LTO to
// compile those archive members by adding them to the link beforehand.
// However, adding all libcall symbols to the link can have undesired
// consequences. For example, the libgcc implementation of
// __sync_val_compare_and_swap_8 on 32-bit ARM pulls in an .init_array entry
// that aborts the program if the Linux kernel does not support 64-bit
// atomics, which would prevent the program from running even if it does not
// use 64-bit atomics.
// Therefore, we only add libcall symbols to the link before LTO if we have
// to, i.e. if the symbol's definition is in bitcode. Any other required
// libcall symbols will be added to the link after LTO when we add the LTO
// object file to the link.
if (!bitcodeFiles.empty())
for (auto *s : lto::LTO::getRuntimeLibcallSymbols())
// Return if there were name resolution errors.
if (errorCount())
// We want to declare linker script's symbols early,
// so that we can version them.
// They also might be exported if referenced by DSOs.
// Handle --exclude-libs. This is before scanVersionScript() due to a
// workaround for Android ndk: for a defined versioned symbol in an archive
// without a version node in the version script, Android does not expect a
// 'has undefined version' error in -shared --exclude-libs=ALL mode (PR36295).
// GNU ld errors in this case.
if (args.hasArg(OPT_exclude_libs))
// Create elfHeader early. We need a dummy section in
// addReservedSymbols to mark the created symbols as not absolute.
Out::elfHeader = make<OutputSection>("", 0, SHF_ALLOC);
std::vector<WrappedSymbol> wrapped = addWrappedSymbols(args);
// We need to create some reserved symbols such as _end. Create them.
if (!config->relocatable)
// Apply version scripts.
// For a relocatable output, version scripts don't make sense, and
// parsing a symbol version string (e.g. dropping "@ver1" from a symbol
// name "foo@ver1") rather do harm, so we don't call this if -r is given.
if (!config->relocatable) {
llvm::TimeTraceScope timeScope("Process symbol versions");
// Do link-time optimization if given files are LLVM bitcode files.
// This compiles bitcode files into real object files.
// With this the symbol table should be complete. After this, no new names
// except a few linker-synthesized ones will be added to the symbol table.
// Handle --exclude-libs again because lto.tmp may reference additional
// libcalls symbols defined in an excluded archive. This may override
// versionId set by scanVersionScript().
if (args.hasArg(OPT_exclude_libs))
// Symbol resolution finished. Report backward reference problems.
if (errorCount())
// If --thinlto-index-only is given, we should create only "index
// files" and not object files. Index file creation is already done
// in compileBitcodeFiles, so we are done if that's the case.
// Likewise, --plugin-opt=emit-llvm and --plugin-opt=emit-asm are the
// options to create output files in bitcode or assembly code
// respectively. No object files are generated.
// Also bail out here when only certain thinLTO modules are specified for
// compilation. The intermediate object file are the expected output.
if (config->thinLTOIndexOnly || config->emitLLVM || config->ltoEmitAsm ||
// Apply symbol renames for --wrap and combine foo@v1 and foo@@v1.
llvm::TimeTraceScope timeScope("Aggregate sections");
// Now that we have a complete list of input files.
// Beyond this point, no new files are added.
// Aggregate all input sections into one place.
for (InputFile *f : objectFiles)
for (InputSectionBase *s : f->getSections())
if (s && s != &InputSection::discarded)
for (BinaryFile *f : binaryFiles)
for (InputSectionBase *s : f->getSections())
llvm::TimeTraceScope timeScope("Strip sections");
llvm::erase_if(inputSections, [](InputSectionBase *s) {
if (s->type == SHT_LLVM_SYMPART) {
return true;
// We do not want to emit debug sections if --strip-all
// or --strip-debug are given.
if (config->strip == StripPolicy::None)
return false;
if (isDebugSection(*s))
return true;
if (auto *isec = dyn_cast<InputSection>(s))
if (InputSectionBase *rel = isec->getRelocatedSection())
if (isDebugSection(*rel))
return true;
return false;
// Since we now have a complete set of input files, we can create
// a .d file to record build dependencies.
if (!config->dependencyFile.empty())
// Now that the number of partitions is fixed, save a pointer to the main
// partition.
mainPart = &partitions[0];
// Read sections from input object files which
// contain a hint to tweak linker's and loader's behaviors.
config->andFeatures = getAndFeatures<ELFT>();
// The Target instance handles target-specific stuff, such as applying
// relocations or writing a PLT section. It also contains target-dependent
// values such as a default image base address.
target = getTarget();
config->eflags = target->calcEFlags();
// maxPageSize (sometimes called abi page size) is the maximum page size that
// the output can be run on. For example if the OS can use 4k or 64k page
// sizes then maxPageSize must be 64k for the output to be useable on both.
// All important alignment decisions must use this value.
config->maxPageSize = getMaxPageSize(args);
// commonPageSize is the most common page size that the output will be run on.
// For example if an OS can use 4k or 64k page sizes and 4k is more common
// than 64k then commonPageSize is set to 4k. commonPageSize can be used for
// optimizations such as DATA_SEGMENT_ALIGN in linker scripts. LLD's use of it
// is limited to writing trap instructions on the last executable segment.
config->commonPageSize = getCommonPageSize(args);
config->imageBase = getImageBase(args);
if (config->emachine == EM_ARM) {
// FIXME: These warnings can be removed when lld only uses these features
// when the input objects have been compiled with an architecture that
// supports them.
if (config->armHasBlx == false)
warn("lld uses blx instruction, no object with architecture supporting "
"feature detected");
// This adds a .comment section containing a version string.
if (!config->relocatable)
// Replace common symbols with regular symbols.
// Split SHF_MERGE and .eh_frame sections into pieces in preparation for garbage collection.
// Garbage collection and removal of shared symbols from unused shared objects.
// Make copies of any input sections that need to be copied into each
// partition.
// Create synthesized sections such as .got and .plt. This is called before
// processSectionCommands() so that they can be placed by SECTIONS commands.
// Some input sections that are used for exception handling need to be moved
// into synthetic sections. Do that now so that they aren't assigned to
// output sections in the usual way.
if (!config->relocatable)
llvm::TimeTraceScope timeScope("Assign sections");
// Create output sections described by SECTIONS commands.
// Linker scripts control how input sections are assigned to output
// sections. Input sections that were not handled by scripts are called
// "orphans", and they are assigned to output sections by the default rule.
// Process that.