blob: 4dd9621493a0e5be546cc2db6686f3a81bb4a11d [file] [log] [blame]
//===- Driver.cpp ---------------------------------------------------------===//
// The LLVM Linker
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// 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 "Error.h"
#include "Filesystem.h"
#include "ICF.h"
#include "InputFiles.h"
#include "InputSection.h"
#include "LinkerScript.h"
#include "Memory.h"
#include "OutputSections.h"
#include "ScriptParser.h"
#include "Strings.h"
#include "SymbolTable.h"
#include "Target.h"
#include "Threads.h"
#include "Writer.h"
#include "lld/Config/Version.h"
#include "lld/Driver/Driver.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/StringSwitch.h"
#include "llvm/Object/Decompressor.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compression.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/TarWriter.h"
#include "llvm/Support/TargetSelect.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 lld;
using namespace lld::elf;
Configuration *elf::Config;
LinkerDriver *elf::Driver;
BumpPtrAllocator elf::BAlloc;
StringSaver elf::Saver{BAlloc};
std::vector<SpecificAllocBase *> elf::SpecificAllocBase::Instances;
static void setConfigs();
bool elf::link(ArrayRef<const char *> Args, bool CanExitEarly,
raw_ostream &Error) {
ErrorCount = 0;
ErrorOS = &Error;
Argv0 = Args[0];
Tar = nullptr;
Config = make<Configuration>();
Driver = make<LinkerDriver>();
Script = make<LinkerScript>();
Driver->main(Args, CanExitEarly);
return !ErrorCount;
// 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})
.Case("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("elf32ppc", {ELF32BEKind, EM_PPC})
.Case("elf64btsmip", {ELF64BEKind, EM_MIPS})
.Case("elf64ltsmip", {ELF64LEKind, EM_MIPS})
.Case("elf64ppc", {ELF64BEKind, EM_PPC64})
.Cases("elf_amd64", "elf_x86_64", {ELF64LEKind, EM_X86_64})
.Case("elf_i386", {ELF32LEKind, EM_386})
.Case("elf_iamcu", {ELF32LEKind, EM_IAMCU})
.Default({ELFNoneKind, EM_NONE});
if (Ret.first == ELFNoneKind) {
if (S == "i386pe" || S == "i386pep" || S == "thumb2pe")
error("Windows targets are not supported on the ELF frontend: " + Emul);
error("unknown emulation: " + Emul);
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();
for (const ErrorOr<Archive::Child> &COrErr : File->children(Err)) {
Archive::Child C =
check(COrErr, MB.getBufferIdentifier() +
": could not get the child of the archive");
MemoryBufferRef MBRef =
MB.getBufferIdentifier() +
": could not get the buffer for a child of the archive");
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 (InBinary) {
switch (identify_magic(MBRef.getBuffer())) {
case file_magic::unknown:
case file_magic::archive: {
// Handle -whole-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->hasSymbolTable()) {
for (const auto &P : getArchiveMembers(MBRef))
Files.push_back(make<LazyObjectFile>(P.first, Path, P.second));
// Handle the regular case.
case file_magic::elf_shared_object:
if (Config->Relocatable) {
error("attempted static link of dynamic object " + Path);
// DSOs usually have DT_SONAME tags in their ELF headers, and the
// sonames are used to identify DSOs. But if they are missing,
// they are identified by filenames. We don't know whether the new
// file has a DT_SONAME or not because we haven't parsed it yet.
// Here, we set the default soname for the file because we might
// need it later.
// If a file was specified by -lfoo, the directory part is not
// significant, as a user did not specify it. This behavior is
// compatible with GNU.
MBRef, WithLOption ? sys::path::filename(Path) : Path));
if (InLib)
Files.push_back(make<LazyObjectFile>(MBRef, "", 0));
// 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);
// 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(opt::InputArgList &Args) {
// Parse and evaluate -mllvm options.
std::vector<const char *> V;
V.push_back("lld (LLVM option parsing)");
for (auto *Arg : Args.filtered(OPT_mllvm))
// Some command line options or some combinations of them are not allowed.
// This function checks for such errors.
static void checkOptions(opt::InputArgList &Args) {
// 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->Pie && Config->Shared)
error("-shared and -pie may not be used together");
if (!Config->Shared && !Config->AuxiliaryList.empty())
error("-f may not be used without -shared");
if (Config->Relocatable) {
if (Config->Shared)
error("-r and -shared may not be used together");
if (Config->GcSections)
error("-r and --gc-sections may not be used together");
if (Config->ICF)
error("-r and --icf may not be used together");
if (Config->Pie)
error("-r and -pie may not be used together");
static StringRef getString(opt::InputArgList &Args, unsigned Key,
StringRef Default = "") {
if (auto *Arg = Args.getLastArg(Key))
return Arg->getValue();
return Default;
static int getInteger(opt::InputArgList &Args, unsigned Key, int Default) {
int V = Default;
if (auto *Arg = Args.getLastArg(Key)) {
StringRef S = Arg->getValue();
if (S.getAsInteger(10, V))
error(Arg->getSpelling() + ": number expected, but got " + S);
return V;
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 uint64_t getZOptionValue(opt::InputArgList &Args, StringRef Key,
uint64_t Default) {
for (auto *Arg : Args.filtered(OPT_z)) {
StringRef Value = Arg->getValue();
size_t Pos = Value.find("=");
if (Pos != StringRef::npos && Key == Value.substr(0, Pos)) {
Value = Value.substr(Pos + 1);
uint64_t Result;
if (Value.getAsInteger(0, Result))
error("invalid " + Key + ": " + Value);
return Result;
return Default;
void LinkerDriver::main(ArrayRef<const char *> ArgsArr, bool CanExitEarly) {
ELFOptTable Parser;
opt::InputArgList Args = Parser.parse(ArgsArr.slice(1));
// Interpret this flag early because error() depends on them.
Config->ErrorLimit = getInteger(Args, OPT_error_limit, 20);
// 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 2.4.6 (released in February 2014 and
// still the newest version in March 2017) or earlier to recognize LLD as
// a GNU compatible linker. As long as an output for the -v option
// contains "GNU" or "with BFD", they recognize us as GNU-compatible.
// 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)");
// ld.bfd always exits after printing out the version string.
// proceeds if a given option is -v. Because gold's behavior
// is more permissive than ld.bfd, we chose what gold does here.
if (Args.hasArg(OPT_version))
Config->ExitEarly = CanExitEarly && !Args.hasArg(OPT_full_shutdown);
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 = ErrOrWriter->get();
Tar->append("response.txt", createResponseFile(Args));
Tar->append("version.txt", getLLDVersion() + "\n");
} else {
error(Twine("--reproduce: failed to open ") + Path + ": " +
if (ErrorCount)
switch (Config->EKind) {
case ELF32LEKind:
case ELF32BEKind:
case ELF64LEKind:
case ELF64BEKind:
llvm_unreachable("unknown Config->EKind");
static bool getArg(opt::InputArgList &Args, unsigned K1, unsigned K2,
bool Default) {
if (auto *Arg = Args.getLastArg(K1, K2))
return Arg->getOption().getID() == K1;
return Default;
static std::vector<StringRef> getArgs(opt::InputArgList &Args, int Id) {
std::vector<StringRef> V;
for (auto *Arg : Args.filtered(Id))
return V;
static std::string getRpath(opt::InputArgList &Args) {
std::vector<StringRef> V = getArgs(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 UnresolvedPolicy getUnresolvedSymbolPolicy(opt::InputArgList &Args) {
// -noinhibit-exec or -r imply some default values.
if (Args.hasArg(OPT_noinhibit_exec))
return UnresolvedPolicy::WarnAll;
if (Args.hasArg(OPT_relocatable))
return UnresolvedPolicy::IgnoreAll;
UnresolvedPolicy ErrorOrWarn = getArg(Args, OPT_error_unresolved_symbols,
OPT_warn_unresolved_symbols, true)
? UnresolvedPolicy::ReportError
: UnresolvedPolicy::Warn;
// Process the last of -unresolved-symbols, -no-undefined or -z defs.
for (auto *Arg : llvm::reverse(Args)) {
switch (Arg->getOption().getID()) {
case OPT_unresolved_symbols: {
StringRef S = Arg->getValue();
if (S == "ignore-all" || S == "ignore-in-object-files")
return UnresolvedPolicy::Ignore;
if (S == "ignore-in-shared-libs" || S == "report-all")
return ErrorOrWarn;
error("unknown --unresolved-symbols value: " + S);
case OPT_no_undefined:
return ErrorOrWarn;
case OPT_z:
if (StringRef(Arg->getValue()) == "defs")
return ErrorOrWarn;
// -shared implies -unresolved-symbols=ignore-all because missing
// symbols are likely to be resolved at runtime using other DSOs.
if (Config->Shared)
return UnresolvedPolicy::Ignore;
return ErrorOrWarn;
static Target2Policy getTarget2(opt::InputArgList &Args) {
StringRef S = getString(Args, 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) {
if (auto *Arg = Args.getLastArg(OPT_oformat)) {
StringRef S = Arg->getValue();
if (S == "binary")
return true;
error("unknown --oformat value: " + S);
return false;
static DiscardPolicy getDiscard(opt::InputArgList &Args) {
if (Args.hasArg(OPT_relocatable))
return DiscardPolicy::None;
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 || Arg->getOption().getID() == OPT_no_dynamic_linker)
return "";
return Arg->getValue();
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::Arg *Arg) {
uint64_t VA = 0;
if (S.startswith("0x"))
S = S.drop_front(2);
if (S.getAsInteger(16, VA))
error("invalid argument: " + toString(Arg));
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, Arg);
if (auto *Arg = Args.getLastArg(OPT_Ttext))
Ret[".text"] = parseSectionAddress(Arg->getValue(), Arg);
if (auto *Arg = Args.getLastArg(OPT_Tdata))
Ret[".data"] = parseSectionAddress(Arg->getValue(), Arg);
if (auto *Arg = Args.getLastArg(OPT_Tbss))
Ret[".bss"] = parseSectionAddress(Arg->getValue(), Arg);
return Ret;
static SortSectionPolicy getSortSection(opt::InputArgList &Args) {
StringRef S = getString(Args, 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 std::pair<bool, bool> getHashStyle(opt::InputArgList &Args) {
StringRef S = getString(Args, OPT_hash_style, "sysv");
if (S == "sysv")
return {true, false};
if (S == "gnu")
return {false, true};
if (S != "both")
error("unknown -hash-style: " + S);
return {true, true};
// 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) {
if (Args.hasArg(OPT_build_id))
return {BuildIdKind::Fast, {}};
StringRef S = getString(Args, OPT_build_id_eq, "none");
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::vector<StringRef> getLines(MemoryBufferRef MB) {
SmallVector<StringRef, 0> Arr;
MB.getBuffer().split(Arr, '\n');
std::vector<StringRef> Ret;
for (StringRef S : Arr) {
S = S.trim();
if (!S.empty())
return Ret;
static bool getCompressDebugSections(opt::InputArgList &Args) {
StringRef S = getString(Args, 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;
// Initializes Config members by the command line options.
void LinkerDriver::readConfigs(opt::InputArgList &Args) {
Config->AllowMultipleDefinition = Args.hasArg(OPT_allow_multiple_definition);
Config->AuxiliaryList = getArgs(Args, OPT_auxiliary);
Config->Bsymbolic = Args.hasArg(OPT_Bsymbolic);
Config->BsymbolicFunctions = Args.hasArg(OPT_Bsymbolic_functions);
Config->CompressDebugSections = getCompressDebugSections(Args);
Config->DefineCommon = getArg(Args, OPT_define_common, OPT_no_define_common,
Config->Demangle = getArg(Args, OPT_demangle, OPT_no_demangle, true);
Config->DisableVerify = Args.hasArg(OPT_disable_verify);
Config->Discard = getDiscard(Args);
Config->DynamicLinker = getDynamicLinker(Args);
Config->EhFrameHdr = Args.hasArg(OPT_eh_frame_hdr);
Config->EmitRelocs = Args.hasArg(OPT_emit_relocs);
Config->EnableNewDtags = !Args.hasArg(OPT_disable_new_dtags);
Config->Entry = getString(Args, OPT_entry);
Config->ExportDynamic =
getArg(Args, OPT_export_dynamic, OPT_no_export_dynamic, false);
Config->FatalWarnings =
getArg(Args, OPT_fatal_warnings, OPT_no_fatal_warnings, false);
Config->Fini = getString(Args, OPT_fini, "_fini");
Config->GcSections = getArg(Args, OPT_gc_sections, OPT_no_gc_sections, false);
Config->GdbIndex = Args.hasArg(OPT_gdb_index);
Config->ICF = Args.hasArg(OPT_icf);
Config->Init = getString(Args, OPT_init, "_init");
Config->LTOAAPipeline = getString(Args, OPT_lto_aa_pipeline);
Config->LTONewPmPasses = getString(Args, OPT_lto_newpm_passes);
Config->LTOO = getInteger(Args, OPT_lto_O, 2);
Config->LTOPartitions = getInteger(Args, OPT_lto_partitions, 1);
Config->MapFile = getString(Args, OPT_Map);
Config->NoGnuUnique = Args.hasArg(OPT_no_gnu_unique);
Config->NoUndefinedVersion = Args.hasArg(OPT_no_undefined_version);
Config->Nostdlib = Args.hasArg(OPT_nostdlib);
Config->OFormatBinary = isOutputFormatBinary(Args);
Config->Omagic = Args.hasArg(OPT_omagic);
Config->OptRemarksFilename = getString(Args, OPT_opt_remarks_filename);
Config->OptRemarksWithHotness = Args.hasArg(OPT_opt_remarks_with_hotness);
Config->Optimize = getInteger(Args, OPT_O, 1);
Config->OutputFile = getString(Args, OPT_o);
Config->Pie = getArg(Args, OPT_pie, OPT_nopie, false);
Config->PrintGcSections = Args.hasArg(OPT_print_gc_sections);
Config->Rpath = getRpath(Args);
Config->ReadOnlyDynamic = Args.hasArg(OPT_rodynamic);
Config->Relocatable = Args.hasArg(OPT_relocatable);
Config->SaveTemps = Args.hasArg(OPT_save_temps);
Config->SearchPaths = getArgs(Args, OPT_L);
Config->SectionStartMap = getSectionStartMap(Args);
Config->Shared = Args.hasArg(OPT_shared);
Config->SingleRoRx = Args.hasArg(OPT_no_rosegment);
Config->SoName = getString(Args, OPT_soname);
Config->SortSection = getSortSection(Args);
Config->Strip = getStrip(Args);
Config->Sysroot = getString(Args, OPT_sysroot);
Config->Target1Rel = getArg(Args, OPT_target1_rel, OPT_target1_abs, false);
Config->Target2 = getTarget2(Args);
Config->ThinLTOCacheDir = getString(Args, OPT_thinlto_cache_dir);
Config->ThinLTOCachePolicy =
check(parseCachePruningPolicy(getString(Args, OPT_thinlto_cache_policy)),
"--thinlto-cache-policy: invalid cache policy");
Config->ThinLTOJobs = getInteger(Args, OPT_thinlto_jobs, -1u);
Config->Threads = getArg(Args, OPT_threads, OPT_no_threads, true);
Config->Trace = Args.hasArg(OPT_trace);
Config->Undefined = getArgs(Args, OPT_undefined);
Config->UnresolvedSymbols = getUnresolvedSymbolPolicy(Args);
Config->Verbose = Args.hasArg(OPT_verbose);
Config->WarnCommon = Args.hasArg(OPT_warn_common);
Config->ZCombreloc = !hasZOption(Args, "nocombreloc");
Config->ZExecstack = hasZOption(Args, "execstack");
Config->ZNocopyreloc = hasZOption(Args, "nocopyreloc");
Config->ZNodelete = hasZOption(Args, "nodelete");
Config->ZNodlopen = hasZOption(Args, "nodlopen");
Config->ZNow = hasZOption(Args, "now");
Config->ZOrigin = hasZOption(Args, "origin");
Config->ZRelro = !hasZOption(Args, "norelro");
Config->ZStackSize = getZOptionValue(Args, "stack-size", 0);
Config->ZText = !hasZOption(Args, "notext");
Config->ZWxneeded = hasZOption(Args, "wxneeded");
if (Config->LTOO > 3)
error("invalid optimization level for LTO: " + getString(Args, OPT_lto_O));
if (Config->LTOPartitions == 0)
error("--lto-partitions: number of threads must be > 0");
if (Config->ThinLTOJobs == 0)
error("--thinlto-jobs: number of threads must be > 0");
if (auto *Arg = Args.getLastArg(OPT_m)) {
// Parse ELF{32,64}{LE,BE} and CPU type.
StringRef S = Arg->getValue();
std::tie(Config->EKind, Config->EMachine, Config->OSABI) =
Config->MipsN32Abi = (S == "elf32btsmipn32" || S == "elf32ltsmipn32");
Config->Emulation = S;
if (Args.hasArg(OPT_print_map))
Config->MapFile = "-";
// --omagic is an option to create old-fashioned executables in which
// .text segments are writable. Today, the option is still in use to
// create special-purpose programs such as boot loaders. It doesn't
// make sense to create PT_GNU_RELRO for such executables.
if (Config->Omagic)
Config->ZRelro = false;
std::tie(Config->SysvHash, Config->GnuHash) = getHashStyle(Args);
std::tie(Config->BuildId, Config->BuildIdVector) = getBuildId(Args);
if (auto *Arg = Args.getLastArg(OPT_symbol_ordering_file))
if (Optional<MemoryBufferRef> Buffer = readFile(Arg->getValue()))
Config->SymbolOrderingFile = getLines(*Buffer);
// 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)) {
Config->DefaultSymbolVersion = VER_NDX_LOCAL;
if (Optional<MemoryBufferRef> Buffer = readFile(Arg->getValue()))
for (StringRef S : getLines(*Buffer))
{S, /*IsExternCpp*/ false, /*HasWildcard*/ false});
bool HasExportDynamic =
getArg(Args, OPT_export_dynamic, OPT_no_export_dynamic, false);
// Parses -dynamic-list and -export-dynamic-symbol. They make some
// symbols private. Note that -export-dynamic takes precedence over them
// as it says all symbols should be exported.
if (!HasExportDynamic) {
for (auto *Arg : Args.filtered(OPT_dynamic_list))
if (Optional<MemoryBufferRef> Buffer = readFile(Arg->getValue()))
for (auto *Arg : Args.filtered(OPT_export_dynamic_symbol))
{Arg->getValue(), /*IsExternCpp*/ false, /*HasWildcard*/ false});
// Dynamic lists are a simplified linker script that doesn't need the
// "global:" and implicitly ends with a "local:*". Set the variables
// needed to simulate that.
if (Args.hasArg(OPT_dynamic_list) ||
Args.hasArg(OPT_export_dynamic_symbol)) {
Config->ExportDynamic = true;
if (!Config->Shared)
Config->DefaultSymbolVersion = VER_NDX_LOCAL;
if (auto *Arg = Args.getLastArg(OPT_version_script))
if (Optional<MemoryBufferRef> Buffer = readFile(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() {
ELFKind Kind = Config->EKind;
uint16_t Machine = Config->EMachine;
// There is an ILP32 ABI for x86-64, although it's not very popular.
// It is called the x32 ABI.
bool IsX32 = (Kind == ELF32LEKind && Machine == EM_X86_64);
Config->CopyRelocs = (Config->Relocatable || Config->EmitRelocs);
Config->Is64 = (Kind == ELF64LEKind || Kind == ELF64BEKind);
Config->IsLE = (Kind == ELF32LEKind || Kind == ELF64LEKind);
Config->Endianness =
Config->IsLE ? support::endianness::little : support::endianness::big;
Config->IsMips64EL = (Kind == ELF64LEKind && Machine == EM_MIPS);
Config->IsRela = Config->Is64 || IsX32 || Config->MipsN32Abi;
Config->Pic = Config->Pie || Config->Shared;
Config->Wordsize = Config->Is64 ? 8 : 4;
//MIPS must unconditionally set ReadOnlyDynamic
Config->ReadOnlyDynamic = Machine == EM_MIPS ? true : Config->ReadOnlyDynamic;
// Returns a value of "-format" option.
static bool getBinaryOption(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) {
for (auto *Arg : Args) {
switch (Arg->getOption().getID()) {
case OPT_l:
addFile(Arg->getValue(), /*WithLOption=*/false);
case OPT_alias_script_T:
case OPT_script:
if (Optional<MemoryBufferRef> MB = readFile(Arg->getValue()))
case OPT_as_needed:
Config->AsNeeded = true;
case OPT_format:
InBinary = getBinaryOption(Arg->getValue());
case OPT_no_as_needed:
Config->AsNeeded = false;
case OPT_Bstatic:
Config->Static = true;
case OPT_Bdynamic:
Config->Static = false;
case OPT_whole_archive:
InWholeArchive = true;
case OPT_no_whole_archive:
InWholeArchive = false;
case OPT_start_lib:
InLib = true;
case OPT_end_lib:
InLib = false;
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 =
getZOptionValue(Args, "max-page-size", Target->DefaultMaxPageSize);
if (!isPowerOf2_64(Val))
error("max-page-size: value isn't a power of 2");
return Val;
// Parses -image-base option.
static uint64_t getImageBase(opt::InputArgList &Args) {
// Use default if no -image-base option is given.
// Because we are using "Target" here, this function
// has to be called after the variable is initialized.
auto *Arg = Args.getLastArg(OPT_image_base);
if (!Arg)
return Config->Pic ? 0 : Target->DefaultImageBase;
StringRef S = Arg->getValue();
uint64_t V;
if (S.getAsInteger(0, 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 --defsym=alias option.
static std::vector<std::pair<StringRef, StringRef>>
getDefsym(opt::InputArgList &Args) {
std::vector<std::pair<StringRef, StringRef>> Ret;
for (auto *Arg : Args.filtered(OPT_defsym)) {
StringRef From;
StringRef To;
std::tie(From, To) = StringRef(Arg->getValue()).split('=');
if (!isValidCIdentifier(To))
error("--defsym: symbol name expected, but got " + To);
Ret.push_back({From, To});
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) {
SymbolTable<ELFT> Symtab;
elf::Symtab<ELFT>::X = &Symtab;
Target = createTarget();
Config->MaxPageSize = getMaxPageSize(Args);
Config->ImageBase = getImageBase(Args);
// 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.
if (auto E = tryCreateFile(Config->OutputFile))
error("cannot open output file " + Config->OutputFile + ": " + E.message());
if (auto E = tryCreateFile(Config->MapFile))
error("cannot open map file " + Config->MapFile + ": " + E.message());
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))
// Add all files to the symbol table. This will add almost all
// symbols that we need to the symbol table.
for (InputFile *F : Files)
// If an entry symbol is in a static archive, pull out that file now
// to complete the symbol table. After this, no new names except a
// few linker-synthesized ones will be added to the symbol table.
if (Symtab.find(Config->Entry))
// Return if there were name resolution errors.
if (ErrorCount)
if (ErrorCount)
// 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 Sym : Script->Opt.ReferencedSymbols)
for (auto *Arg : Args.filtered(OPT_wrap))
// Handle --defsym=sym=alias option.
for (std::pair<StringRef, StringRef> &Def : getDefsym(Args))
Symtab.alias(Def.first, Def.second);
// 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 (elf::ObjectFile<ELFT> *F : Symtab.getObjectFiles())
for (InputSectionBase *S : F->getSections())
if (S && S != &InputSection::Discarded)
for (BinaryFile *F : Symtab.getBinaryFiles())
for (InputSectionBase *S : F->getSections())
// Do size optimizations: garbage collection and identical code folding.
if (Config->GcSections)
if (Config->ICF)
// MergeInputSection::splitIntoPieces needs to be called before
// any call of MergeInputSection::getOffset. Do that.
parallelForEach(InputSections.begin(), InputSections.end(),
[](InputSectionBase *S) {
if (!S->Live)
if (Decompressor::isCompressedELFSection(S->Flags, S->Name))
if (auto *MS = dyn_cast<MergeInputSection>(S))
// Write the result to the file.