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llvm-project/lld/ELF/Driver.cpp

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//===- 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 "Filesystem.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/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/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);
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));
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})
.Case("elf32ppc", {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()) {
for (const auto &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->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(
createSharedFile(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(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->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->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");
}
}
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 == "initfirst" || S == "interpose" ||
S == "keep-text-section-prefix" || S == "lazy" || S == "muldefs" ||
S == "nocombreloc" || S == "nocopyreloc" || 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("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);
// 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)");
// 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;
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");
make<std::unique_ptr<TarWriter>>(std::move(*ErrOrWriter));
} else {
error(Twine("--reproduce: failed to open ") + Path + ": " +
toString(ErrOrWriter.takeError()));
}
}
readConfigs(Args);
checkZOptions(Args);
initLLVM();
createFiles(Args);
if (errorCount())
return;
inferMachineType();
setConfigs(Args);
checkOptions(Args);
if (errorCount())
return;
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, 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: " + 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 = 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, const Symbol *> SymbolNameToSymbol;
for (InputFile *File : ObjectFiles)
for (Symbol *Sym : File->getSymbols())
SymbolNameToSymbol[Sym->getName()] = Sym;
auto FindSection = [&](StringRef SymName) -> InputSectionBase * {
const Symbol *Sym = SymbolNameToSymbol.lookup(SymName);
if (Sym)
warnUnorderableSymbol(Sym);
else if (Config->WarnSymbolOrdering)
warn(MB.getBufferIdentifier() + ": no such symbol: " + SymName);
if (const Defined *DR = dyn_cast_or_null<Defined>(Sym))
return dyn_cast_or_null<InputSectionBase>(DR->Section);
return nullptr;
};
for (StringRef L : args::getLines(MB)) {
SmallVector<StringRef, 3> Fields;
L.split(Fields, ' ');
uint64_t Count;
if (Fields.size() != 3 || !to_integer(Fields[2], Count))
fatal(MB.getBufferIdentifier() + ": parse error");
if (const InputSectionBase *FromSB = FindSection(Fields[0]))
if (const InputSectionBase *ToSB = FindSection(Fields[1]))
Config->CallGraphProfile[std::make_pair(FromSB, ToSB)] += Count;
}
}
template <class ELFT> static void readCallGraphsFromObjectFiles() {
auto FindSection = [&](const Symbol *Sym) -> const InputSectionBase * {
warnUnorderableSymbol(Sym);
if (const auto *SymD = dyn_cast<Defined>(Sym))
return dyn_cast_or_null<InputSectionBase>(SymD->Section);
return nullptr;
};
for (auto File : ObjectFiles) {
auto *Obj = cast<ObjFile<ELFT>>(File);
for (const Elf_CGProfile_Impl<ELFT> &CGPE : Obj->CGProfile) {
const InputSectionBase *FromSB =
FindSection(&Obj->getSymbol(CGPE.cgp_from));
const InputSectionBase *ToSB = FindSection(&Obj->getSymbol(CGPE.cgp_to));
if (!FromSB || !ToSB)
continue;
Config->CallGraphProfile[{FromSB, ToSB}] += 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.
void LinkerDriver::readConfigs(opt::InputArgList &Args) {
errorHandler().Verbose = Args.hasArg(OPT_verbose);
errorHandler().FatalWarnings =
Args.hasFlag(OPT_fatal_warnings, OPT_no_fatal_warnings, 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->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->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->EmitRelocs = Args.hasArg(OPT_emit_relocs);
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->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->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->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->OptRemarksWithHotness = Args.hasArg(OPT_opt_remarks_with_hotness);
Config->Optimize = args::getInteger(Args, OPT_O, 1);
Config->OrphanHandling = getOrphanHandling(Args);
Config->OutputFile = Args.getLastArgValue(OPT_o);
Config->Pie = Args.hasFlag(OPT_pie, OPT_no_pie, false);
Config->PrintIcfSections =
Args.hasFlag(OPT_print_icf_sections, OPT_no_print_icf_sections, false);
Config->PrintGcSections =
Args.hasFlag(OPT_print_gc_sections, OPT_no_print_gc_sections, false);
Config->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->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->ZInitfirst = hasZOption(Args, "initfirst");
Config->ZInterpose = hasZOption(Args, "interpose");
Config->ZKeepTextSectionPrefix = getZFlag(
Args, "keep-text-section-prefix", "nokeep-text-section-prefix", false);
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");
// 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 = "-";
// --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->BuildId, Config->BuildIdVector) = getBuildId(Args);
std::tie(Config->AndroidPackDynRelocs, Config->RelrPackDynRelocs) =
getPackDynRelocs(Args);
if (auto *Arg = Args.getLastArg(OPT_symbol_ordering_file))
if (Optional<MemoryBufferRef> Buffer = readFile(Arg->getValue()))
Config->SymbolOrderingFile = getSymbolOrderingFile(*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 : 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->Pic = Config->Pie || Config->Shared;
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().getUnaliasedOption().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:
Config->Static = true;
break;
case OPT_Bdynamic:
Config->Static = 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->Static, InWholeArchive);
break;
case OPT_pop_state:
if (Stack.empty()) {
error("unbalanced --push-state/--pop-state");
break;
}
std::tie(Config->AsNeeded, Config->Static, 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");
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.
template <class ELFT>
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.
template <class ELFT> static void handleUndefined(StringRef Name) {
Symbol *Sym = Symtab->find(Name);
if (!Sym)
return;
// Since symbol S 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())
Symtab->fetchLazy<ELFT>(Sym);
}
template <class ELFT> 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))
Symtab->fetchLazy<ELFT>(Sym);
}
// 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.
template <class ELFT> static void demoteSharedSymbols() {
for (Symbol *Sym : Symtab->getSymbols()) {
if (auto *S = dyn_cast<SharedSymbol>(Sym)) {
if (!S->getFile<ELFT>().IsNeeded) {
bool Used = S->Used;
replaceSymbol<Undefined>(S, 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.
for (Symbol *S : Symtab->getSymbols())
if (S->includeInDynsym())
markAddrsig(S);
// 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);
}
}
}
// 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.
template <class ELFT>
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 = Symtab->addUndefined<ELFT>(Saver.save("__real_" + Name));
Symbol *Wrap = Symtab->addUndefined<ELFT>(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.
template <class ELFT> 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) {
std::vector<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);
}
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) {
Target = getTarget();
InX<ELFT>::VerSym = nullptr;
InX<ELFT>::VerNeed = nullptr;
Config->MaxPageSize = getMaxPageSize(Args);
Config->ImageBase = getImageBase(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->trace(Arg->getValue());
// Add all files to the symbol table. This will add almost all
// symbols that we need to the symbol table.
for (InputFile *F : Files)
Symtab->addFile<ELFT>(F);
// 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->Pic || 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 Sym : Script->ReferencedSymbols)
Symtab->addUndefined<ELFT>(Sym);
// Handle the `--undefined <sym>` options.
for (StringRef S : Config->Undefined)
handleUndefined<ELFT>(S);
// If an entry symbol is in a static archive, pull out that file now.
handleUndefined<ELFT>(Config->Entry);
// 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<ELFT>(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<ELFT>(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);
// 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();
// Create wrapped symbols for -wrap option.
std::vector<WrappedSymbol> Wrapped = addWrappedSymbols<ELFT>(Args);
// 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.
Symtab->addCombinedLTOObject<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;
// Apply symbol renames for -wrap.
if (!Wrapped.empty())
wrapSymbols<ELFT>(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));
// We do not want to emit debug sections if --strip-all
// or -strip-debug are given.
if (Config->Strip != StripPolicy::None)
llvm::erase_if(InputSections, [](InputSectionBase *S) {
return S->Name.startswith(".debug") || S->Name.startswith(".zdebug");
});
Config->EFlags = Target->calcEFlags();
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());
// Do size optimizations: garbage collection, merging of SHF_MERGE sections
// and identical code folding.
splitSections<ELFT>();
markLive<ELFT>();
demoteSharedSymbols<ELFT>();
mergeSections();
if (Config->ICF != ICFLevel::None) {
findKeepUniqueSections<ELFT>(Args);
doIcf<ELFT>();
}
// Read the callgraph now that we know what was gced or icfed
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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