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llvm-project/lld/ELF/Driver.cpp

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//===- Driver.cpp ---------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// 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/Threads.h"
#include "lld/Common/Version.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/StringSwitch.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compression.h"
#include "llvm/Support/GlobPattern.h"
#include "llvm/Support/LEB128.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 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 &error) {
errorHandler().logName = args::getFilenameWithoutExe(args[0]);
errorHandler().errorLimitExceededMsg =
"too many errors emitted, stopping now (use "
"-error-limit=0 to see all errors)";
errorHandler().errorOS = &error;
errorHandler().exitEarly = canExitEarly;
errorHandler().colorDiagnostics = error.has_colors();
inputSections.clear();
outputSections.clear();
binaryFiles.clear();
bitcodeFiles.clear();
objectFiles.clear();
sharedFiles.clear();
config = make<Configuration>();
driver = make<LinkerDriver>();
script = make<LinkerScript>();
symtab = make<SymbolTable>();
tar = nullptr;
memset(&in, 0, sizeof(in));
partitions = {Partition()};
SharedFile::vernauxNum = 0;
config->progName = args[0];
driver->main(args);
// 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);
freeArena();
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);
osabi = ELFOSABI_FREEBSD;
}
std::pair<ELFKind, uint16_t> ret =
StringSwitch<std::pair<ELFKind, uint16_t>>(s)
.Cases("aarch64elf", "aarch64linux", "aarch64_elf64_le_vec",
{ELF64LEKind, 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})
.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})
.Default({ELFNoneKind, EM_NONE});
if (ret.first == ELFNoneKind)
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 =
CHECK(Archive::create(mb),
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 ErrorOr<Archive::Child> &cOrErr : file->children(err)) {
Archive::Child c =
CHECK(cOrErr, mb.getBufferIdentifier() +
": could not get the child of the archive");
MemoryBufferRef mbref =
CHECK(c.getMemoryBufferRef(),
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: " +
toString(std::move(err)));
// Take ownership of memory buffers created for members of thin archives.
for (std::unique_ptr<MemoryBuffer> &mb : file->takeThinBuffers())
make<std::unique_ptr<MemoryBuffer>>(std::move(mb));
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())
return;
MemoryBufferRef mbref = *buffer;
if (config->formatBinary) {
files.push_back(make<BinaryFile>(mbref));
return;
}
switch (identify_magic(mbref.getBuffer())) {
case file_magic::unknown:
readLinkerScript(mbref);
return;
case file_magic::archive: {
// Handle -whole-archive.
if (inWholeArchive) {
for (const auto &p : getArchiveMembers(mbref))
files.push_back(createObjectFile(p.first, path, p.second));
return;
}
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 :
getArchiveMembers(mbref))
if (identify_magic(p.first.getBuffer()) != file_magic::bitcode) {
error(path + ": archive has no index; run ranlib to add one");
return;
}
for (const std::pair<MemoryBufferRef, uint64_t> &p :
getArchiveMembers(mbref))
files.push_back(make<LazyObjFile>(p.first, path, p.second));
return;
}
// Handle the regular case.
files.push_back(make<ArchiveFile>(std::move(file)));
return;
}
case file_magic::elf_shared_object:
if (config->isStatic || config->relocatable) {
error("attempted static link of dynamic object " + path);
return;
}
// 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.
files.push_back(
make<SharedFile>(mbref, withLOption ? path::filename(path) : path));
return;
case file_magic::bitcode:
case file_magic::elf_relocatable:
if (inLib)
files.push_back(make<LazyObjFile>(mbref, "", 0));
else
files.push_back(createObjectFile(mbref));
break;
default:
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);
else
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() {
InitializeAllTargets();
InitializeAllTargetMCs();
InitializeAllAsmPrinters();
InitializeAllAsmParsers();
}
// 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->tocOptimize && config->emachine != EM_PPC64)
error("--toc-optimize is only supported on the PowerPC64 target");
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->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->gcSections)
error("-r and --gc-sections 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->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->requireCET)
error("--require-cet may not be used with -z retpolineplt");
if (config->emachine != EM_AARCH64) {
if (config->pacPlt)
error("--pac-plt only supported on AArch64");
if (config->forceBTI)
error("--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 bool isKnownZFlag(StringRef s) {
return s == "combreloc" || s == "copyreloc" || s == "defs" ||
s == "execstack" || s == "global" || s == "hazardplt" ||
s == "ifunc-noplt" || s == "initfirst" || s == "interpose" ||
s == "keep-text-section-prefix" || s == "lazy" || s == "muldefs" ||
s == "nocombreloc" || s == "nocopyreloc" || s == "nodefaultlib" ||
s == "nodelete" || s == "nodlopen" || s == "noexecstack" ||
s == "nokeep-text-section-prefix" || s == "norelro" || s == "notext" ||
s == "now" || s == "origin" || s == "relro" || s == "retpolineplt" ||
s == "rodynamic" || s == "text" || s == "wxneeded" ||
s.startswith("common-page-size") || s.startswith("max-page-size=") ||
s.startswith("stack-size=");
}
// Report an error for an unknown -z option.
static void checkZOptions(opt::InputArgList &args) {
for (auto *arg : args.filtered(OPT_z))
if (!isKnownZFlag(arg->getValue()))
error("unknown -z value: " + StringRef(arg->getValue()));
}
void LinkerDriver::main(ArrayRef<const char *> argsArr) {
ELFOptTable parser;
opt::InputArgList args = parser.parse(argsArr.slice(1));
// Interpret this flag early because error() depends on them.
errorHandler().errorLimit = args::getInteger(args, OPT_error_limit, 20);
checkZOptions(args);
// Handle -help
if (args.hasArg(OPT_help)) {
printHelp();
return;
}
// 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)");
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");
} else {
error("--reproduce: " + toString(errOrWriter.takeError()));
}
}
readConfigs(args);
// 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))
return;
if (args.hasArg(OPT_version))
return;
initLLVM();
createFiles(args);
if (errorCount())
return;
inferMachineType();
setConfigs(args);
checkOptions();
if (errorCount())
return;
// 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:
link<ELF32LE>(args);
return;
case ELF32BEKind:
link<ELF32BE>(args);
return;
case ELF64LEKind:
link<ELF64LE>(args);
return;
case ELF64BEKind:
link<ELF64BE>(args);
return;
default:
llvm_unreachable("unknown Config->EKind");
}
}
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 UnresolvedPolicy getUnresolvedSymbolPolicy(opt::InputArgList &args) {
UnresolvedPolicy errorOrWarn = args.hasFlag(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);
continue;
}
case OPT_no_undefined:
return errorOrWarn;
case OPT_z:
if (StringRef(arg->getValue()) == "defs")
return errorOrWarn;
continue;
}
}
// -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 = 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) {
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 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;
}
maybeWarnUnorderableSymbol(sym);
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");
return;
}
if (InputSectionBase *from = findSection(fields[0]))
if (InputSectionBase *to = findSection(fields[1]))
config->callGraphProfile[std::make_pair(from, to)] += count;
}
}
template <class ELFT> static void readCallGraphsFromObjectFiles() {
for (auto file : objectFiles) {
auto *obj = cast<ObjFile<ELFT>>(file);
for (const Elf_CGProfile_Impl<ELFT> &cgpe : obj->cgProfile) {
auto *fromSym = dyn_cast<Defined>(&obj->getSymbol(cgpe.cgp_from));
auto *toSym = dyn_cast<Defined>(&obj->getSymbol(cgpe.cgp_to));
if (!fromSym || !toSym)
continue;
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 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(arg->getSpelling() + " 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 void parseClangOption(StringRef opt, const Twine &msg) {
std::string err;
raw_string_ostream os(err);
const char *argv[] = {config->progName.data(), opt.data()};
if (cl::ParseCommandLineOptions(2, argv, "", &os))
return;
os.flush();
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().fatalWarnings =
args.hasFlag(OPT_fatal_warnings, OPT_no_fatal_warnings, false);
errorHandler().vsDiagnostics =
args.hasArg(OPT_visual_studio_diagnostics_format, false);
threadsEnabled = args.hasFlag(OPT_threads, OPT_no_threads, true);
config->allowMultipleDefinition =
args.hasFlag(OPT_allow_multiple_definition,
OPT_no_allow_multiple_definition, false) ||
hasZOption(args, "muldefs");
config->allowShlibUndefined =
args.hasFlag(OPT_allow_shlib_undefined, OPT_no_allow_shlib_undefined,
args.hasArg(OPT_shared));
config->auxiliaryList = args::getStrings(args, OPT_auxiliary);
config->bsymbolic = args.hasArg(OPT_Bsymbolic);
config->bsymbolicFunctions = args.hasArg(OPT_Bsymbolic_functions);
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.hasFlag(OPT_cref, OPT_no_cref, false);
config->defineCommon = args.hasFlag(OPT_define_common, OPT_no_define_common,
!args.hasArg(OPT_relocatable));
config->demangle = args.hasFlag(OPT_demangle, OPT_no_demangle, true);
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);
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->forceBTI = args.hasArg(OPT_force_bti);
config->requireCET = args.hasArg(OPT_require_cet);
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 =
args.hasArg(OPT_ignore_data_address_equality);
config->ignoreFunctionAddressEquality =
args.hasArg(OPT_ignore_function_address_equality);
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->ltoDebugPassManager = args.hasArg(OPT_lto_debug_pass_manager);
config->ltoNewPassManager = args.hasArg(OPT_lto_new_pass_manager);
config->ltoNewPmPasses = args.getLastArgValue(OPT_lto_newpm_passes);
config->ltoo = args::getInteger(args, OPT_lto_O, 2);
config->ltoObjPath = args.getLastArgValue(OPT_plugin_opt_obj_path_eq);
config->ltoPartitions = args::getInteger(args, OPT_lto_partitions, 1);
config->ltoSampleProfile = args.getLastArgValue(OPT_lto_sample_profile);
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->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);
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->pacPlt = args.hasArg(OPT_pac_plt);
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->printSymbolOrder =
args.getLastArgValue(OPT_print_symbol_order);
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.hasArg(OPT_no_rosegment);
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(
parseCachePruningPolicy(args.getLastArgValue(OPT_thinlto_cache_policy)),
"--thinlto-cache-policy: invalid cache policy");
config->thinLTOEmitImportsFiles =
args.hasArg(OPT_plugin_opt_thinlto_emit_imports_files);
config->thinLTOIndexOnly = args.hasArg(OPT_plugin_opt_thinlto_index_only) ||
args.hasArg(OPT_plugin_opt_thinlto_index_only_eq);
config->thinLTOIndexOnlyArg =
args.getLastArgValue(OPT_plugin_opt_thinlto_index_only_eq);
config->thinLTOJobs = args::getInteger(args, OPT_thinlto_jobs, -1u);
config->thinLTOObjectSuffixReplace =
getOldNewOptions(args, OPT_plugin_opt_thinlto_object_suffix_replace_eq);
config->thinLTOPrefixReplace =
getOldNewOptions(args, OPT_plugin_opt_thinlto_prefix_replace_eq);
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->useAndroidRelrTags = args.hasFlag(
OPT_use_android_relr_tags, OPT_no_use_android_relr_tags, false);
config->unresolvedSymbols = getUnresolvedSymbolPolicy(args);
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->warnIfuncTextrel =
args.hasFlag(OPT_warn_ifunc_textrel, OPT_no_warn_ifunc_textrel, false);
config->warnSymbolOrdering =
args.hasFlag(OPT_warn_symbol_ordering, OPT_no_warn_symbol_ordering, true);
config->zCombreloc = getZFlag(args, "combreloc", "nocombreloc", true);
config->zCopyreloc = getZFlag(args, "copyreloc", "nocopyreloc", true);
config->zExecstack = getZFlag(args, "execstack", "noexecstack", false);
config->zGlobal = hasZOption(args, "global");
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->zRelro = getZFlag(args, "relro", "norelro", true);
config->zRetpolineplt = hasZOption(args, "retpolineplt");
config->zRodynamic = hasZOption(args, "rodynamic");
config->zStackSize = args::getZOptionValue(args, OPT_z, "stack-size", 0);
config->zText = getZFlag(args, "text", "notext", true);
config->zWxneeded = hasZOption(args, "wxneeded");
// Parse LTO options.
if (auto *arg = args.getLastArg(OPT_plugin_opt_mcpu_eq))
parseClangOption(saver.save("-mcpu=" + StringRef(arg->getValue())),
arg->getSpelling());
for (auto *arg : args.filtered(OPT_plugin_opt))
parseClangOption(arg->getValue(), arg->getSpelling());
// Parse -mllvm options.
for (auto *arg : args.filtered(OPT_mllvm))
parseClangOption(arg->getValue(), arg->getSpelling());
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 (config->thinLTOJobs == 0)
error("--thinlto-jobs: number of threads must be > 0");
if (config->splitStackAdjustSize < 0)
error("--split-stack-adjust-size: size must be >= 0");
// 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) =
parseEmulation(s);
config->mipsN32Abi = (s == "elf32btsmipn32" || s == "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;
else
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) =
getPackDynRelocs(args);
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;
}
}
// 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 : args::getLines(*buffer))
config->versionScriptGlobals.push_back(
{s, /*IsExternCpp*/ false, /*HasWildcard*/ false});
}
bool hasExportDynamic =
args.hasFlag(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()))
readDynamicList(*buffer);
for (auto *arg : args.filtered(OPT_export_dynamic_symbol))
config->dynamicList.push_back(
{arg->getValue(), /*IsExternCpp*/ false, /*HasWildcard*/ false});
}
// If --export-dynamic-symbol=foo is given and symbol foo is defined in
// an object file in an archive file, that object file should be pulled
// out and linked. (It doesn't have to behave like that from technical
// point of view, but this is needed for compatibility with GNU.)
for (auto *arg : args.filtered(OPT_export_dynamic_symbol))
config->undefined.push_back(arg->getValue());
for (auto *arg : args.filtered(OPT_version_script))
if (Optional<std::string> path = searchScript(arg->getValue())) {
if (Optional<MemoryBufferRef> buffer = readFile(*path))
readVersionScript(*buffer);
} 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.
// 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 don't know why ELF defined two
// different mechanisms in the first place, but this is how the spec is
// defined.
//
// You cannot choose which one, Rel or Rela, you want to use. Instead each
// ABI defines which one you need to use. The following expression expresses
// that.
config->isRela = m == EM_AARCH64 || m == EM_AMDGPU || m == EM_HEXAGON ||
m == EM_PPC || m == EM_PPC64 || m == EM_RISCV ||
m == EM_X86_64;
// 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) ||
!config->isRela;
config->tocOptimize =
args.hasFlag(OPT_toc_optimize, OPT_no_toc_optimize, m == EM_PPC64);
}
// Returns a value of "-format" option.
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) {
// For --{push,pop}-state.
std::vector<std::tuple<bool, bool, bool>> stack;
// Iterate over argv to process input files and positional arguments.
for (auto *arg : args) {
switch (arg->getOption().getID()) {
case OPT_library:
addLibrary(arg->getValue());
break;
case OPT_INPUT:
addFile(arg->getValue(), /*withLOption=*/false);
break;
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()));
else
readDefsym(from, MemoryBufferRef(to, "-defsym"));
break;
}
case OPT_script:
if (Optional<std::string> path = searchScript(arg->getValue())) {
if (Optional<MemoryBufferRef> mb = readFile(*path))
readLinkerScript(*mb);
break;
}
error(Twine("cannot find linker script ") + arg->getValue());
break;
case OPT_as_needed:
config->asNeeded = true;
break;
case OPT_format:
config->formatBinary = isFormatBinary(arg->getValue());
break;
case OPT_no_as_needed:
config->asNeeded = false;
break;
case OPT_Bstatic:
case OPT_omagic:
case OPT_nmagic:
config->isStatic = true;
break;
case OPT_Bdynamic:
config->isStatic = false;
break;
case OPT_whole_archive:
inWholeArchive = true;
break;
case OPT_no_whole_archive:
inWholeArchive = false;
break;
case OPT_just_symbols:
if (Optional<MemoryBufferRef> mb = readFile(arg->getValue())) {
files.push_back(createObjectFile(*mb));
files.back()->justSymbols = true;
}
break;
case OPT_start_group:
if (InputFile::isInGroup)
error("nested --start-group");
InputFile::isInGroup = true;
break;
case OPT_end_group:
if (!InputFile::isInGroup)
error("stray --end-group");
InputFile::isInGroup = false;
++InputFile::nextGroupId;
break;
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;
break;
case OPT_end_lib:
if (!inLib)
error("stray --end-lib");
inLib = false;
InputFile::isInGroup = false;
++InputFile::nextGroupId;
break;
case OPT_push_state:
stack.emplace_back(config->asNeeded, config->isStatic, inWholeArchive);
break;
case OPT_pop_state:
if (stack.empty()) {
error("unbalanced --push-state/--pop-state");
break;
}
std::tie(config->asNeeded, config->isStatic, inWholeArchive) = stack.back();
stack.pop_back();
break;
}
}
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)
return;
for (InputFile *f : files) {
if (f->ekind == ELFNoneKind)
continue;
config->ekind = f->ekind;
config->emachine = f->emachine;
config->osabi = f->osabi;
config->mipsN32Abi = config->emachine == EM_MIPS && isMipsN32Abi(f);
return;
}
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",
target->defaultMaxPageSize);
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",
target->defaultCommonPageSize);
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)
break;
ret.insert(s.substr(0, pos));
s = s.substr(pos + 1);
}
ret.insert(s);
}
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->isLocal() && sym->file == file)
sym->versionId = VER_NDX_LOCAL;
};
for (InputFile *file : objectFiles)
visit(file);
for (BitcodeFile *file : bitcodeFiles)
visit(file);
}
// Force Sym to be entered in the output. Used for -u or equivalent.
static void handleUndefined(Symbol *sym) {
// 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())
sym->fetch();
}
// As an extention 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()));
return;
}
std::vector<Symbol *> syms;
symtab->forEachSymbol([&](Symbol *sym) {
// Calling Sym->fetch() from here is not safe because it may
// add new symbols to the symbol table, invalidating the
// current iterator. So we just keep a note.
if (pat->match(sym->getName()))
syms.push_back(sym);
});
for (Symbol *sym : syms)
handleUndefined(sym);
}
static void handleLibcall(StringRef name) {
Symbol *sym = symtab->find(name);
if (!sym || !sym->isLazy())
return;
MemoryBufferRef mb;
if (auto *lo = dyn_cast<LazyObject>(sym))
mb = lo->file->mb;
else
mb = cast<LazyArchive>(sym)->getMemberBuffer();
if (isBitcode(mb))
sym->fetch();
}
// 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() {
symtab->forEachSymbol([](Symbol *sym) {
auto *s = dyn_cast<CommonSymbol>(sym);
if (!s)
return;
auto *bss = make<BssSection>("COMMON", s->size, s->alignment);
bss->file = s->file;
bss->markDead();
inputSections.push_back(bss);
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() {
symtab->forEachSymbol([](Symbol *sym) {
auto *s = dyn_cast<SharedSymbol>(sym);
if (!s || s->getFile().isNeeded)
return;
bool used = s->used;
s->replace(Undefined{nullptr, s->getName(), STB_WEAK, s->stOther, s->type});
s->used = used;
});
}
// 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");
continue;
}
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)
return;
// Symbols in the dynsym could be address-significant in other executables
// or DSOs, so we conservatively mark them as address-significant.
symtab->forEachSymbol([&](Symbol *sym) {
if (sym->includeInDynsym())
markAddrsig(sym);
});
// 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 =
check(obj->getObj().getSectionContents(obj->addrsigSec));
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);
markAddrsig(syms[symIndex]);
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)
markAddrsig(s);
}
}
}
// This function reads a symbol partition specification section. These sections
// are used to control which partition a symbol is allocated to. See
// https://lld.llvm.org/Partitions.html 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;
if (s->areRelocsRela)
sym = &s->getFile<ELFT>()->getRelocTargetSym(s->template relas<ELFT>()[0]);
else
sym = &s->getFile<ELFT>()->getRelocTargetSym(s->template rels<ELFT>()[0]);
if (!isa<Defined>(sym) || !sym->includeInDynsym())
return;
StringRef partName = reinterpret_cast<const char *>(s->data().data());
for (Partition &part : partitions) {
if (part.name == partName) {
sym->partition = part.getNumber();
return;
}
}
// 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");
partitions.emplace_back();
Partition &newPart = partitions.back();
newPart.name = partName;
sym->partition = newPart.getNumber();
}
static Symbol *addUndefined(StringRef name) {
return symtab->addSymbol(
Undefined{nullptr, name, STB_GLOBAL, STV_DEFAULT, 0});
}
// 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() {
// Compile bitcode files and replace bitcode symbols.
lto.reset(new BitcodeCompiler);
for (BitcodeFile *file : bitcodeFiles)
lto->add(*file);
for (InputFile *file : lto->compile()) {
auto *obj = cast<ObjFile<ELFT>>(file);
obj->parse(/*ignoreComdats=*/true);
for (Symbol *sym : obj->getGlobalSymbols())
sym->parseSymbolVersion();
objectFiles.push_back(file);
}
}
// 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)
continue;
Symbol *sym = symtab->find(name);
if (!sym)
continue;
Symbol *real = addUndefined(saver.save("__real_" + name));
Symbol *wrap = addUndefined(saver.save("__wrap_" + name));
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;
wrap->isUsedInRegularObj = true;
}
return v;
}
// Do renaming for -wrap 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 wrapSymbols(ArrayRef<WrappedSymbol> wrapped) {
DenseMap<Symbol *, Symbol *> map;
for (const WrappedSymbol &w : wrapped) {
map[w.sym] = w.wrap;
map[w.real] = w.sym;
}
// 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 function returns the merged feature flags. If 0, we cannot enable CET.
// This is also the case with AARCH64's BTI and PAC which use the similar
// GNU_PROPERTY_AARCH64_FEATURE_1_AND mechanism.
//
// Note that the CET-aware PLT is not implemented yet. We do error
// check only.
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->forceBTI && !(features & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) {
warn(toString(f) + ": --force-bti: file does not have BTI property");
features |= GNU_PROPERTY_AARCH64_FEATURE_1_BTI;
} else if (!features && config->requireCET)
error(toString(f) + ": --require-cet: file is not compatible with CET");
ret &= features;
}
// Force enable pointer authentication Plt, we don't warn in this case as
// this does not require support in the object for correctness.
if (config->pacPlt)
ret |= GNU_PROPERTY_AARCH64_FEATURE_1_PAC;
return ret;
}
static const char *libcallRoutineNames[] = {
#define HANDLE_LIBCALL(code, name) name,
#include "llvm/IR/RuntimeLibcalls.def"
#undef HANDLE_LIBCALL
};
// 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) {
// 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;
else
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.
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())
return;
// 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;
// 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.
for (size_t i = 0; i < files.size(); ++i)
parseFile(files[i]);
// 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)
addUndefined(name);
// Handle the `--undefined <sym>` options.
for (StringRef arg : config->undefined)
if (Symbol *sym = symtab->find(arg))
handleUndefined(sym);
// If an entry symbol is in a static archive, pull out that file now.
if (Symbol *sym = symtab->find(config->entry))
handleUndefined(sym);
// Handle the `--undefined-glob <pattern>` options.
for (StringRef pat : args::getStrings(args, OPT_undefined_glob))
handleUndefinedGlob(pat);
// 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 (const char *s : libcallRoutineNames)
handleLibcall(s);
// Return if there were name resolution errors.
if (errorCount())
return;
// Now when we read all script files, we want to finalize order of linker
// script commands, which can be not yet final because of INSERT commands.
script->processInsertCommands();
// We want to declare linker script's symbols early,
// so that we can version them.
// They also might be exported if referenced by DSOs.
script->declareSymbols();
// Handle the -exclude-libs option.
if (args.hasArg(OPT_exclude_libs))
excludeLibs(args);
// 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);
Out::elfHeader->size = sizeof(typename ELFT::Ehdr);
// Create wrapped symbols for -wrap option.
std::vector<WrappedSymbol> wrapped = addWrappedSymbols(args);
// We need to create some reserved symbols such as _end. Create them.
if (!config->relocatable)
addReservedSymbols();
// 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)
symtab->scanVersionScript();
// 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.
compileBitcodeFiles<ELFT>();
if (errorCount())
return;
// If -thinlto-index-only is given, we should create only "index
// files" and not object files. Index file creation is already done
// in addCombinedLTOObject, so we are done if that's the case.
if (config->thinLTOIndexOnly)
return;
// Likewise, --plugin-opt=emit-llvm is an option to make LTO create
// an output file in bitcode and exit, so that you can just get a
// combined bitcode file.
if (config->emitLLVM)
return;
// Apply symbol renames for -wrap.
if (!wrapped.empty())
wrapSymbols(wrapped);
// 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)
inputSections.push_back(s);
for (BinaryFile *f : binaryFiles)
for (InputSectionBase *s : f->getSections())
inputSections.push_back(cast<InputSection>(s));
llvm::erase_if(inputSections, [](InputSectionBase *s) {
if (s->type == SHT_LLVM_SYMPART) {
readSymbolPartitionSection<ELFT>(s);
return true;
}
// We do not want to emit debug sections if --strip-all
// or -strip-debug are given.
return config->strip != StripPolicy::None &&
(s->name.startswith(".debug") || s->name.startswith(".zdebug"));
});
// Now that the number of partitions is fixed, save a pointer to the main
// partition.
mainPart = &partitions[0];
// Read .note.gnu.property 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. We have to add it
// before mergeSections because the .comment section is a mergeable section.
if (!config->relocatable)
inputSections.push_back(createCommentSection());
// Replace common symbols with regular symbols.
replaceCommonSymbols();
// Do size optimizations: garbage collection, merging of SHF_MERGE sections
// and identical code folding.
splitSections<ELFT>();
markLive<ELFT>();
demoteSharedSymbols();
mergeSections();
if (config->icf != ICFLevel::None) {
findKeepUniqueSections<ELFT>(args);
doIcf<ELFT>();
}
// Read the callgraph now that we know what was gced or icfed
if (config->callGraphProfileSort) {
if (auto *arg = args.getLastArg(OPT_call_graph_ordering_file))
if (Optional<MemoryBufferRef> buffer = readFile(arg->getValue()))
readCallGraph(*buffer);
readCallGraphsFromObjectFiles<ELFT>();
}
// Write the result to the file.
writeResult<ELFT>();
}
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