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llvm-project/lld/ELF/InputFiles.cpp

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//===- InputFiles.cpp -----------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "InputFiles.h"
#include "Driver.h"
#include "InputSection.h"
#include "LinkerScript.h"
#include "SymbolTable.h"
#include "Symbols.h"
#include "SyntheticSections.h"
#include "lld/Common/ErrorHandler.h"
#include "lld/Common/Memory.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/CodeGen/Analysis.h"
#include "llvm/DebugInfo/DWARF/DWARFContext.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/LTO/LTO.h"
#include "llvm/MC/StringTableBuilder.h"
#include "llvm/Object/ELFObjectFile.h"
#include "llvm/Support/ARMAttributeParser.h"
#include "llvm/Support/ARMBuildAttributes.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/TarWriter.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
using namespace llvm::ELF;
using namespace llvm::object;
using namespace llvm::sys;
using namespace llvm::sys::fs;
using namespace llvm::support::endian;
using namespace lld;
using namespace lld::elf;
bool InputFile::IsInGroup;
uint32_t InputFile::NextGroupId;
std::vector<BinaryFile *> elf::BinaryFiles;
std::vector<BitcodeFile *> elf::BitcodeFiles;
std::vector<LazyObjFile *> elf::LazyObjFiles;
std::vector<InputFile *> elf::ObjectFiles;
std::vector<SharedFile *> elf::SharedFiles;
std::unique_ptr<TarWriter> elf::Tar;
static ELFKind getELFKind(MemoryBufferRef MB, StringRef ArchiveName) {
unsigned char Size;
unsigned char Endian;
std::tie(Size, Endian) = getElfArchType(MB.getBuffer());
auto Fatal = [&](StringRef Msg) {
StringRef Filename = MB.getBufferIdentifier();
if (ArchiveName.empty())
fatal(Filename + ": " + Msg);
else
fatal(ArchiveName + "(" + Filename + "): " + Msg);
};
if (!MB.getBuffer().startswith(ElfMagic))
Fatal("not an ELF file");
if (Endian != ELFDATA2LSB && Endian != ELFDATA2MSB)
Fatal("corrupted ELF file: invalid data encoding");
if (Size != ELFCLASS32 && Size != ELFCLASS64)
Fatal("corrupted ELF file: invalid file class");
size_t BufSize = MB.getBuffer().size();
if ((Size == ELFCLASS32 && BufSize < sizeof(Elf32_Ehdr)) ||
(Size == ELFCLASS64 && BufSize < sizeof(Elf64_Ehdr)))
Fatal("corrupted ELF file: file is too short");
if (Size == ELFCLASS32)
return (Endian == ELFDATA2LSB) ? ELF32LEKind : ELF32BEKind;
return (Endian == ELFDATA2LSB) ? ELF64LEKind : ELF64BEKind;
}
InputFile::InputFile(Kind K, MemoryBufferRef M)
: MB(M), GroupId(NextGroupId), FileKind(K) {
// All files within the same --{start,end}-group get the same group ID.
// Otherwise, a new file will get a new group ID.
if (!IsInGroup)
++NextGroupId;
}
Optional<MemoryBufferRef> elf::readFile(StringRef Path) {
// The --chroot option changes our virtual root directory.
// This is useful when you are dealing with files created by --reproduce.
if (!Config->Chroot.empty() && Path.startswith("/"))
Path = Saver.save(Config->Chroot + Path);
log(Path);
auto MBOrErr = MemoryBuffer::getFile(Path, -1, false);
if (auto EC = MBOrErr.getError()) {
error("cannot open " + Path + ": " + EC.message());
return None;
}
std::unique_ptr<MemoryBuffer> &MB = *MBOrErr;
MemoryBufferRef MBRef = MB->getMemBufferRef();
make<std::unique_ptr<MemoryBuffer>>(std::move(MB)); // take MB ownership
if (Tar)
Tar->append(relativeToRoot(Path), MBRef.getBuffer());
return MBRef;
}
// All input object files must be for the same architecture
// (e.g. it does not make sense to link x86 object files with
// MIPS object files.) This function checks for that error.
static bool isCompatible(InputFile *File) {
if (!File->isElf() && !isa<BitcodeFile>(File))
return true;
if (File->EKind == Config->EKind && File->EMachine == Config->EMachine) {
if (Config->EMachine != EM_MIPS)
return true;
if (isMipsN32Abi(File) == Config->MipsN32Abi)
return true;
}
if (!Config->Emulation.empty()) {
error(toString(File) + " is incompatible with " + Config->Emulation);
} else {
InputFile *Existing;
if (!ObjectFiles.empty())
Existing = ObjectFiles[0];
else if (!SharedFiles.empty())
Existing = SharedFiles[0];
else
Existing = BitcodeFiles[0];
error(toString(File) + " is incompatible with " + toString(Existing));
}
return false;
}
template <class ELFT> static void doParseFile(InputFile *File) {
if (!isCompatible(File))
return;
// Binary file
if (auto *F = dyn_cast<BinaryFile>(File)) {
BinaryFiles.push_back(F);
F->parse();
return;
}
// .a file
if (auto *F = dyn_cast<ArchiveFile>(File)) {
F->parse();
return;
}
// Lazy object file
if (auto *F = dyn_cast<LazyObjFile>(File)) {
LazyObjFiles.push_back(F);
F->parse<ELFT>();
return;
}
if (Config->Trace)
message(toString(File));
// .so file
if (auto *F = dyn_cast<SharedFile>(File)) {
F->parse<ELFT>();
return;
}
// LLVM bitcode file
if (auto *F = dyn_cast<BitcodeFile>(File)) {
BitcodeFiles.push_back(F);
F->parse<ELFT>();
return;
}
// Regular object file
ObjectFiles.push_back(File);
cast<ObjFile<ELFT>>(File)->parse();
}
// Add symbols in File to the symbol table.
void elf::parseFile(InputFile *File) {
switch (Config->EKind) {
case ELF32LEKind:
doParseFile<ELF32LE>(File);
return;
case ELF32BEKind:
doParseFile<ELF32BE>(File);
return;
case ELF64LEKind:
doParseFile<ELF64LE>(File);
return;
case ELF64BEKind:
doParseFile<ELF64BE>(File);
return;
default:
llvm_unreachable("unknown ELFT");
}
}
// Concatenates arguments to construct a string representing an error location.
static std::string createFileLineMsg(StringRef Path, unsigned Line) {
std::string Filename = path::filename(Path);
std::string Lineno = ":" + std::to_string(Line);
if (Filename == Path)
return Filename + Lineno;
return Filename + Lineno + " (" + Path.str() + Lineno + ")";
}
template <class ELFT>
static std::string getSrcMsgAux(ObjFile<ELFT> &File, const Symbol &Sym,
InputSectionBase &Sec, uint64_t Offset) {
// In DWARF, functions and variables are stored to different places.
// First, lookup a function for a given offset.
if (Optional<DILineInfo> Info = File.getDILineInfo(&Sec, Offset))
return createFileLineMsg(Info->FileName, Info->Line);
// If it failed, lookup again as a variable.
if (Optional<std::pair<std::string, unsigned>> FileLine =
File.getVariableLoc(Sym.getName()))
return createFileLineMsg(FileLine->first, FileLine->second);
// File.SourceFile contains STT_FILE symbol, and that is a last resort.
return File.SourceFile;
}
std::string InputFile::getSrcMsg(const Symbol &Sym, InputSectionBase &Sec,
uint64_t Offset) {
if (kind() != ObjKind)
return "";
switch (Config->EKind) {
default:
llvm_unreachable("Invalid kind");
case ELF32LEKind:
return getSrcMsgAux(cast<ObjFile<ELF32LE>>(*this), Sym, Sec, Offset);
case ELF32BEKind:
return getSrcMsgAux(cast<ObjFile<ELF32BE>>(*this), Sym, Sec, Offset);
case ELF64LEKind:
return getSrcMsgAux(cast<ObjFile<ELF64LE>>(*this), Sym, Sec, Offset);
case ELF64BEKind:
return getSrcMsgAux(cast<ObjFile<ELF64BE>>(*this), Sym, Sec, Offset);
}
}
template <class ELFT> void ObjFile<ELFT>::initializeDwarf() {
Dwarf = llvm::make_unique<DWARFContext>(make_unique<LLDDwarfObj<ELFT>>(this));
for (std::unique_ptr<DWARFUnit> &CU : Dwarf->compile_units()) {
auto Report = [](Error Err) {
handleAllErrors(std::move(Err),
[](ErrorInfoBase &Info) { warn(Info.message()); });
};
Expected<const DWARFDebugLine::LineTable *> ExpectedLT =
Dwarf->getLineTableForUnit(CU.get(), Report);
const DWARFDebugLine::LineTable *LT = nullptr;
if (ExpectedLT)
LT = *ExpectedLT;
else
Report(ExpectedLT.takeError());
if (!LT)
continue;
LineTables.push_back(LT);
// Loop over variable records and insert them to VariableLoc.
for (const auto &Entry : CU->dies()) {
DWARFDie Die(CU.get(), &Entry);
// Skip all tags that are not variables.
if (Die.getTag() != dwarf::DW_TAG_variable)
continue;
// Skip if a local variable because we don't need them for generating
// error messages. In general, only non-local symbols can fail to be
// linked.
if (!dwarf::toUnsigned(Die.find(dwarf::DW_AT_external), 0))
continue;
// Get the source filename index for the variable.
unsigned File = dwarf::toUnsigned(Die.find(dwarf::DW_AT_decl_file), 0);
if (!LT->hasFileAtIndex(File))
continue;
// Get the line number on which the variable is declared.
unsigned Line = dwarf::toUnsigned(Die.find(dwarf::DW_AT_decl_line), 0);
// Here we want to take the variable name to add it into VariableLoc.
// Variable can have regular and linkage name associated. At first, we try
// to get linkage name as it can be different, for example when we have
// two variables in different namespaces of the same object. Use common
// name otherwise, but handle the case when it also absent in case if the
// input object file lacks some debug info.
StringRef Name =
dwarf::toString(Die.find(dwarf::DW_AT_linkage_name),
dwarf::toString(Die.find(dwarf::DW_AT_name), ""));
if (!Name.empty())
VariableLoc.insert({Name, {LT, File, Line}});
}
}
}
// Returns the pair of file name and line number describing location of data
// object (variable, array, etc) definition.
template <class ELFT>
Optional<std::pair<std::string, unsigned>>
ObjFile<ELFT>::getVariableLoc(StringRef Name) {
llvm::call_once(InitDwarfLine, [this]() { initializeDwarf(); });
// Return if we have no debug information about data object.
auto It = VariableLoc.find(Name);
if (It == VariableLoc.end())
return None;
// Take file name string from line table.
std::string FileName;
if (!It->second.LT->getFileNameByIndex(
It->second.File, nullptr,
DILineInfoSpecifier::FileLineInfoKind::AbsoluteFilePath, FileName))
return None;
return std::make_pair(FileName, It->second.Line);
}
// Returns source line information for a given offset
// using DWARF debug info.
template <class ELFT>
Optional<DILineInfo> ObjFile<ELFT>::getDILineInfo(InputSectionBase *S,
uint64_t Offset) {
llvm::call_once(InitDwarfLine, [this]() { initializeDwarf(); });
// Detect SectionIndex for specified section.
uint64_t SectionIndex = object::SectionedAddress::UndefSection;
ArrayRef<InputSectionBase *> Sections = S->File->getSections();
for (uint64_t CurIndex = 0; CurIndex < Sections.size(); ++CurIndex) {
if (S == Sections[CurIndex]) {
SectionIndex = CurIndex;
break;
}
}
// Use fake address calcuated by adding section file offset and offset in
// section. See comments for ObjectInfo class.
DILineInfo Info;
for (const llvm::DWARFDebugLine::LineTable *LT : LineTables) {
if (LT->getFileLineInfoForAddress(
{S->getOffsetInFile() + Offset, SectionIndex}, nullptr,
DILineInfoSpecifier::FileLineInfoKind::AbsoluteFilePath, Info))
return Info;
}
return None;
}
// Returns "<internal>", "foo.a(bar.o)" or "baz.o".
std::string lld::toString(const InputFile *F) {
if (!F)
return "<internal>";
if (F->ToStringCache.empty()) {
if (F->ArchiveName.empty())
F->ToStringCache = F->getName();
else
F->ToStringCache = (F->ArchiveName + "(" + F->getName() + ")").str();
}
return F->ToStringCache;
}
ELFFileBase::ELFFileBase(Kind K, MemoryBufferRef MB) : InputFile(K, MB) {
EKind = getELFKind(MB, "");
switch (EKind) {
case ELF32LEKind:
init<ELF32LE>();
break;
case ELF32BEKind:
init<ELF32BE>();
break;
case ELF64LEKind:
init<ELF64LE>();
break;
case ELF64BEKind:
init<ELF64BE>();
break;
default:
llvm_unreachable("getELFKind");
}
}
template <typename Elf_Shdr>
static const Elf_Shdr *findSection(ArrayRef<Elf_Shdr> Sections, uint32_t Type) {
for (const Elf_Shdr &Sec : Sections)
if (Sec.sh_type == Type)
return &Sec;
return nullptr;
}
template <class ELFT> void ELFFileBase::init() {
using Elf_Shdr = typename ELFT::Shdr;
using Elf_Sym = typename ELFT::Sym;
// Initialize trivial attributes.
const ELFFile<ELFT> &Obj = getObj<ELFT>();
EMachine = Obj.getHeader()->e_machine;
OSABI = Obj.getHeader()->e_ident[llvm::ELF::EI_OSABI];
ABIVersion = Obj.getHeader()->e_ident[llvm::ELF::EI_ABIVERSION];
ArrayRef<Elf_Shdr> Sections = CHECK(Obj.sections(), this);
// Find a symbol table.
bool IsDSO =
(identify_magic(MB.getBuffer()) == file_magic::elf_shared_object);
const Elf_Shdr *SymtabSec =
findSection(Sections, IsDSO ? SHT_DYNSYM : SHT_SYMTAB);
if (!SymtabSec)
return;
// Initialize members corresponding to a symbol table.
FirstGlobal = SymtabSec->sh_info;
ArrayRef<Elf_Sym> ESyms = CHECK(Obj.symbols(SymtabSec), this);
if (FirstGlobal == 0 || FirstGlobal > ESyms.size())
fatal(toString(this) + ": invalid sh_info in symbol table");
ELFSyms = reinterpret_cast<const void *>(ESyms.data());
NumELFSyms = ESyms.size();
StringTable = CHECK(Obj.getStringTableForSymtab(*SymtabSec, Sections), this);
}
template <class ELFT>
uint32_t ObjFile<ELFT>::getSectionIndex(const Elf_Sym &Sym) const {
return CHECK(
this->getObj().getSectionIndex(&Sym, getELFSyms<ELFT>(), ShndxTable),
this);
}
template <class ELFT> ArrayRef<Symbol *> ObjFile<ELFT>::getLocalSymbols() {
if (this->Symbols.empty())
return {};
return makeArrayRef(this->Symbols).slice(1, this->FirstGlobal - 1);
}
template <class ELFT> ArrayRef<Symbol *> ObjFile<ELFT>::getGlobalSymbols() {
return makeArrayRef(this->Symbols).slice(this->FirstGlobal);
}
template <class ELFT> void ObjFile<ELFT>::parse(bool IgnoreComdats) {
// Read a section table. JustSymbols is usually false.
if (this->JustSymbols)
initializeJustSymbols();
else
initializeSections(IgnoreComdats);
// Read a symbol table.
initializeSymbols();
}
// Sections with SHT_GROUP and comdat bits define comdat section groups.
// They are identified and deduplicated by group name. This function
// returns a group name.
template <class ELFT>
StringRef ObjFile<ELFT>::getShtGroupSignature(ArrayRef<Elf_Shdr> Sections,
const Elf_Shdr &Sec) {
const Elf_Sym *Sym =
CHECK(object::getSymbol<ELFT>(this->getELFSyms<ELFT>(), Sec.sh_info), this);
StringRef Signature = CHECK(Sym->getName(this->StringTable), this);
// As a special case, if a symbol is a section symbol and has no name,
// we use a section name as a signature.
//
// Such SHT_GROUP sections are invalid from the perspective of the ELF
// standard, but GNU gold 1.14 (the newest version as of July 2017) or
// older produce such sections as outputs for the -r option, so we need
// a bug-compatibility.
if (Signature.empty() && Sym->getType() == STT_SECTION)
return getSectionName(Sec);
return Signature;
}
template <class ELFT> bool ObjFile<ELFT>::shouldMerge(const Elf_Shdr &Sec) {
// On a regular link we don't merge sections if -O0 (default is -O1). This
// sometimes makes the linker significantly faster, although the output will
// be bigger.
//
// Doing the same for -r would create a problem as it would combine sections
// with different sh_entsize. One option would be to just copy every SHF_MERGE
// section as is to the output. While this would produce a valid ELF file with
// usable SHF_MERGE sections, tools like (llvm-)?dwarfdump get confused when
// they see two .debug_str. We could have separate logic for combining
// SHF_MERGE sections based both on their name and sh_entsize, but that seems
// to be more trouble than it is worth. Instead, we just use the regular (-O1)
// logic for -r.
if (Config->Optimize == 0 && !Config->Relocatable)
return false;
// A mergeable section with size 0 is useless because they don't have
// any data to merge. A mergeable string section with size 0 can be
// argued as invalid because it doesn't end with a null character.
// We'll avoid a mess by handling them as if they were non-mergeable.
if (Sec.sh_size == 0)
return false;
// Check for sh_entsize. The ELF spec is not clear about the zero
// sh_entsize. It says that "the member [sh_entsize] contains 0 if
// the section does not hold a table of fixed-size entries". We know
// that Rust 1.13 produces a string mergeable section with a zero
// sh_entsize. Here we just accept it rather than being picky about it.
uint64_t EntSize = Sec.sh_entsize;
if (EntSize == 0)
return false;
if (Sec.sh_size % EntSize)
fatal(toString(this) +
": SHF_MERGE section size must be a multiple of sh_entsize");
uint64_t Flags = Sec.sh_flags;
if (!(Flags & SHF_MERGE))
return false;
if (Flags & SHF_WRITE)
fatal(toString(this) + ": writable SHF_MERGE section is not supported");
return true;
}
// This is for --just-symbols.
//
// --just-symbols is a very minor feature that allows you to link your
// output against other existing program, so that if you load both your
// program and the other program into memory, your output can refer the
// other program's symbols.
//
// When the option is given, we link "just symbols". The section table is
// initialized with null pointers.
template <class ELFT> void ObjFile<ELFT>::initializeJustSymbols() {
ArrayRef<Elf_Shdr> Sections = CHECK(this->getObj().sections(), this);
this->Sections.resize(Sections.size());
}
// An ELF object file may contain a `.deplibs` section. If it exists, the
// section contains a list of library specifiers such as `m` for libm. This
// function resolves a given name by finding the first matching library checking
// the various ways that a library can be specified to LLD. This ELF extension
// is a form of autolinking and is called `dependent libraries`. It is currently
// unique to LLVM and lld.
static void addDependentLibrary(StringRef Specifier, const InputFile *F) {
if (!Config->DependentLibraries)
return;
if (fs::exists(Specifier))
Driver->addFile(Specifier, /*WithLOption=*/false);
else if (Optional<std::string> S = findFromSearchPaths(Specifier))
Driver->addFile(*S, /*WithLOption=*/true);
else if (Optional<std::string> S = searchLibraryBaseName(Specifier))
Driver->addFile(*S, /*WithLOption=*/true);
else
error(toString(F) +
": unable to find library from dependent library specifier: " +
Specifier);
}
template <class ELFT>
void ObjFile<ELFT>::initializeSections(bool IgnoreComdats) {
const ELFFile<ELFT> &Obj = this->getObj();
ArrayRef<Elf_Shdr> ObjSections = CHECK(Obj.sections(), this);
uint64_t Size = ObjSections.size();
this->Sections.resize(Size);
this->SectionStringTable =
CHECK(Obj.getSectionStringTable(ObjSections), this);
for (size_t I = 0, E = ObjSections.size(); I < E; I++) {
if (this->Sections[I] == &InputSection::Discarded)
continue;
const Elf_Shdr &Sec = ObjSections[I];
if (Sec.sh_type == ELF::SHT_LLVM_CALL_GRAPH_PROFILE)
CGProfile =
check(Obj.template getSectionContentsAsArray<Elf_CGProfile>(&Sec));
// SHF_EXCLUDE'ed sections are discarded by the linker. However,
// if -r is given, we'll let the final link discard such sections.
// This is compatible with GNU.
if ((Sec.sh_flags & SHF_EXCLUDE) && !Config->Relocatable) {
if (Sec.sh_type == SHT_LLVM_ADDRSIG) {
// We ignore the address-significance table if we know that the object
// file was created by objcopy or ld -r. This is because these tools
// will reorder the symbols in the symbol table, invalidating the data
// in the address-significance table, which refers to symbols by index.
if (Sec.sh_link != 0)
this->AddrsigSec = &Sec;
else if (Config->ICF == ICFLevel::Safe)
warn(toString(this) + ": --icf=safe is incompatible with object "
"files created using objcopy or ld -r");
}
this->Sections[I] = &InputSection::Discarded;
continue;
}
switch (Sec.sh_type) {
case SHT_GROUP: {
// De-duplicate section groups by their signatures.
StringRef Signature = getShtGroupSignature(ObjSections, Sec);
this->Sections[I] = &InputSection::Discarded;
ArrayRef<Elf_Word> Entries =
CHECK(Obj.template getSectionContentsAsArray<Elf_Word>(&Sec), this);
if (Entries.empty())
fatal(toString(this) + ": empty SHT_GROUP");
// The first word of a SHT_GROUP section contains flags. Currently,
// the standard defines only "GRP_COMDAT" flag for the COMDAT group.
// An group with the empty flag doesn't define anything; such sections
// are just skipped.
if (Entries[0] == 0)
continue;
if (Entries[0] != GRP_COMDAT)
fatal(toString(this) + ": unsupported SHT_GROUP format");
bool IsNew =
IgnoreComdats ||
Symtab->ComdatGroups.try_emplace(CachedHashStringRef(Signature), this)
.second;
if (IsNew) {
if (Config->Relocatable)
this->Sections[I] = createInputSection(Sec);
continue;
}
// Otherwise, discard group members.
for (uint32_t SecIndex : Entries.slice(1)) {
if (SecIndex >= Size)
fatal(toString(this) +
": invalid section index in group: " + Twine(SecIndex));
this->Sections[SecIndex] = &InputSection::Discarded;
}
break;
}
case SHT_SYMTAB_SHNDX:
ShndxTable = CHECK(Obj.getSHNDXTable(Sec, ObjSections), this);
break;
case SHT_SYMTAB:
case SHT_STRTAB:
case SHT_NULL:
break;
default:
this->Sections[I] = createInputSection(Sec);
}
// .ARM.exidx sections have a reverse dependency on the InputSection they
// have a SHF_LINK_ORDER dependency, this is identified by the sh_link.
if (Sec.sh_flags & SHF_LINK_ORDER) {
InputSectionBase *LinkSec = nullptr;
if (Sec.sh_link < this->Sections.size())
LinkSec = this->Sections[Sec.sh_link];
if (!LinkSec)
fatal(toString(this) +
": invalid sh_link index: " + Twine(Sec.sh_link));
InputSection *IS = cast<InputSection>(this->Sections[I]);
LinkSec->DependentSections.push_back(IS);
if (!isa<InputSection>(LinkSec))
error("a section " + IS->Name +
" with SHF_LINK_ORDER should not refer a non-regular "
"section: " +
toString(LinkSec));
}
}
}
// For ARM only, to set the EF_ARM_ABI_FLOAT_SOFT or EF_ARM_ABI_FLOAT_HARD
// flag in the ELF Header we need to look at Tag_ABI_VFP_args to find out how
// the input objects have been compiled.
static void updateARMVFPArgs(const ARMAttributeParser &Attributes,
const InputFile *F) {
if (!Attributes.hasAttribute(ARMBuildAttrs::ABI_VFP_args))
// If an ABI tag isn't present then it is implicitly given the value of 0
// which maps to ARMBuildAttrs::BaseAAPCS. However many assembler files,
// including some in glibc that don't use FP args (and should have value 3)
// don't have the attribute so we do not consider an implicit value of 0
// as a clash.
return;
unsigned VFPArgs = Attributes.getAttributeValue(ARMBuildAttrs::ABI_VFP_args);
ARMVFPArgKind Arg;
switch (VFPArgs) {
case ARMBuildAttrs::BaseAAPCS:
Arg = ARMVFPArgKind::Base;
break;
case ARMBuildAttrs::HardFPAAPCS:
Arg = ARMVFPArgKind::VFP;
break;
case ARMBuildAttrs::ToolChainFPPCS:
// Tool chain specific convention that conforms to neither AAPCS variant.
Arg = ARMVFPArgKind::ToolChain;
break;
case ARMBuildAttrs::CompatibleFPAAPCS:
// Object compatible with all conventions.
return;
default:
error(toString(F) + ": unknown Tag_ABI_VFP_args value: " + Twine(VFPArgs));
return;
}
// Follow ld.bfd and error if there is a mix of calling conventions.
if (Config->ARMVFPArgs != Arg && Config->ARMVFPArgs != ARMVFPArgKind::Default)
error(toString(F) + ": incompatible Tag_ABI_VFP_args");
else
Config->ARMVFPArgs = Arg;
}
// The ARM support in lld makes some use of instructions that are not available
// on all ARM architectures. Namely:
// - Use of BLX instruction for interworking between ARM and Thumb state.
// - Use of the extended Thumb branch encoding in relocation.
// - Use of the MOVT/MOVW instructions in Thumb Thunks.
// The ARM Attributes section contains information about the architecture chosen
// at compile time. We follow the convention that if at least one input object
// is compiled with an architecture that supports these features then lld is
// permitted to use them.
static void updateSupportedARMFeatures(const ARMAttributeParser &Attributes) {
if (!Attributes.hasAttribute(ARMBuildAttrs::CPU_arch))
return;
auto Arch = Attributes.getAttributeValue(ARMBuildAttrs::CPU_arch);
switch (Arch) {
case ARMBuildAttrs::Pre_v4:
case ARMBuildAttrs::v4:
case ARMBuildAttrs::v4T:
// Architectures prior to v5 do not support BLX instruction
break;
case ARMBuildAttrs::v5T:
case ARMBuildAttrs::v5TE:
case ARMBuildAttrs::v5TEJ:
case ARMBuildAttrs::v6:
case ARMBuildAttrs::v6KZ:
case ARMBuildAttrs::v6K:
Config->ARMHasBlx = true;
// Architectures used in pre-Cortex processors do not support
// The J1 = 1 J2 = 1 Thumb branch range extension, with the exception
// of Architecture v6T2 (arm1156t2-s and arm1156t2f-s) that do.
break;
default:
// All other Architectures have BLX and extended branch encoding
Config->ARMHasBlx = true;
Config->ARMJ1J2BranchEncoding = true;
if (Arch != ARMBuildAttrs::v6_M && Arch != ARMBuildAttrs::v6S_M)
// All Architectures used in Cortex processors with the exception
// of v6-M and v6S-M have the MOVT and MOVW instructions.
Config->ARMHasMovtMovw = true;
break;
}
}
// If a source file is compiled with x86 hardware-assisted call flow control
// enabled, the generated object file contains feature flags indicating that
// fact. This function reads the feature flags and returns it.
//
// Essentially we want to read a single 32-bit value in this function, but this
// function is rather complicated because the value is buried deep inside a
// .note.gnu.property section.
//
// The section consists of one or more NOTE records. Each NOTE record consists
// of zero or more type-length-value fields. We want to find a field of a
// certain type. It seems a bit too much to just store a 32-bit value, perhaps
// the ABI is unnecessarily complicated.
template <class ELFT>
static uint32_t readAndFeatures(ObjFile<ELFT> *Obj, ArrayRef<uint8_t> Data) {
using Elf_Nhdr = typename ELFT::Nhdr;
using Elf_Note = typename ELFT::Note;
uint32_t FeaturesSet = 0;
while (!Data.empty()) {
// Read one NOTE record.
if (Data.size() < sizeof(Elf_Nhdr))
fatal(toString(Obj) + ": .note.gnu.property: section too short");
auto *Nhdr = reinterpret_cast<const Elf_Nhdr *>(Data.data());
if (Data.size() < Nhdr->getSize())
fatal(toString(Obj) + ": .note.gnu.property: section too short");
Elf_Note Note(*Nhdr);
if (Nhdr->n_type != NT_GNU_PROPERTY_TYPE_0 || Note.getName() != "GNU") {
Data = Data.slice(Nhdr->getSize());
continue;
}
uint32_t FeatureAndType = Config->EMachine == EM_AARCH64
? GNU_PROPERTY_AARCH64_FEATURE_1_AND
: GNU_PROPERTY_X86_FEATURE_1_AND;
// Read a body of a NOTE record, which consists of type-length-value fields.
ArrayRef<uint8_t> Desc = Note.getDesc();
while (!Desc.empty()) {
if (Desc.size() < 8)
fatal(toString(Obj) + ": .note.gnu.property: section too short");
uint32_t Type = read32le(Desc.data());
uint32_t Size = read32le(Desc.data() + 4);
if (Type == FeatureAndType) {
// We found a FEATURE_1_AND field. There may be more than one of these
// in a .note.gnu.propery section, for a relocatable object we
// accumulate the bits set.
FeaturesSet |= read32le(Desc.data() + 8);
}
// On 64-bit, a payload may be followed by a 4-byte padding to make its
// size a multiple of 8.
if (ELFT::Is64Bits)
Size = alignTo(Size, 8);
Desc = Desc.slice(Size + 8); // +8 for Type and Size
}
// Go to next NOTE record to look for more FEATURE_1_AND descriptions.
Data = Data.slice(Nhdr->getSize());
}
return FeaturesSet;
}
template <class ELFT>
InputSectionBase *ObjFile<ELFT>::getRelocTarget(const Elf_Shdr &Sec) {
uint32_t Idx = Sec.sh_info;
if (Idx >= this->Sections.size())
fatal(toString(this) + ": invalid relocated section index: " + Twine(Idx));
InputSectionBase *Target = this->Sections[Idx];
// Strictly speaking, a relocation section must be included in the
// group of the section it relocates. However, LLVM 3.3 and earlier
// would fail to do so, so we gracefully handle that case.
if (Target == &InputSection::Discarded)
return nullptr;
if (!Target)
fatal(toString(this) + ": unsupported relocation reference");
return Target;
}
// Create a regular InputSection class that has the same contents
// as a given section.
static InputSection *toRegularSection(MergeInputSection *Sec) {
return make<InputSection>(Sec->File, Sec->Flags, Sec->Type, Sec->Alignment,
Sec->data(), Sec->Name);
}
template <class ELFT>
InputSectionBase *ObjFile<ELFT>::createInputSection(const Elf_Shdr &Sec) {
StringRef Name = getSectionName(Sec);
switch (Sec.sh_type) {
case SHT_ARM_ATTRIBUTES: {
if (Config->EMachine != EM_ARM)
break;
ARMAttributeParser Attributes;
ArrayRef<uint8_t> Contents = check(this->getObj().getSectionContents(&Sec));
Attributes.Parse(Contents, /*isLittle*/ Config->EKind == ELF32LEKind);
updateSupportedARMFeatures(Attributes);
updateARMVFPArgs(Attributes, this);
// FIXME: Retain the first attribute section we see. The eglibc ARM
// dynamic loaders require the presence of an attribute section for dlopen
// to work. In a full implementation we would merge all attribute sections.
if (In.ARMAttributes == nullptr) {
In.ARMAttributes = make<InputSection>(*this, Sec, Name);
return In.ARMAttributes;
}
return &InputSection::Discarded;
}
case SHT_LLVM_DEPENDENT_LIBRARIES: {
if (Config->Relocatable)
break;
ArrayRef<char> Data =
CHECK(this->getObj().template getSectionContentsAsArray<char>(&Sec), this);
if (!Data.empty() && Data.back() != '\0') {
error(toString(this) +
": corrupted dependent libraries section (unterminated string): " +
Name);
return &InputSection::Discarded;
}
for (const char *D = Data.begin(), *E = Data.end(); D < E;) {
StringRef S(D);
addDependentLibrary(S, this);
D += S.size() + 1;
}
return &InputSection::Discarded;
}
case SHT_RELA:
case SHT_REL: {
// Find a relocation target section and associate this section with that.
// Target may have been discarded if it is in a different section group
// and the group is discarded, even though it's a violation of the
// spec. We handle that situation gracefully by discarding dangling
// relocation sections.
InputSectionBase *Target = getRelocTarget(Sec);
if (!Target)
return nullptr;
// This section contains relocation information.
// If -r is given, we do not interpret or apply relocation
// but just copy relocation sections to output.
if (Config->Relocatable) {
InputSection *RelocSec = make<InputSection>(*this, Sec, Name);
// We want to add a dependency to target, similar like we do for
// -emit-relocs below. This is useful for the case when linker script
// contains the "/DISCARD/". It is perhaps uncommon to use a script with
// -r, but we faced it in the Linux kernel and have to handle such case
// and not to crash.
Target->DependentSections.push_back(RelocSec);
return RelocSec;
}
if (Target->FirstRelocation)
fatal(toString(this) +
": multiple relocation sections to one section are not supported");
// ELF spec allows mergeable sections with relocations, but they are
// rare, and it is in practice hard to merge such sections by contents,
// because applying relocations at end of linking changes section
// contents. So, we simply handle such sections as non-mergeable ones.
// Degrading like this is acceptable because section merging is optional.
if (auto *MS = dyn_cast<MergeInputSection>(Target)) {
Target = toRegularSection(MS);
this->Sections[Sec.sh_info] = Target;
}
if (Sec.sh_type == SHT_RELA) {
ArrayRef<Elf_Rela> Rels = CHECK(getObj().relas(&Sec), this);
Target->FirstRelocation = Rels.begin();
Target->NumRelocations = Rels.size();
Target->AreRelocsRela = true;
} else {
ArrayRef<Elf_Rel> Rels = CHECK(getObj().rels(&Sec), this);
Target->FirstRelocation = Rels.begin();
Target->NumRelocations = Rels.size();
Target->AreRelocsRela = false;
}
assert(isUInt<31>(Target->NumRelocations));
// Relocation sections processed by the linker are usually removed
// from the output, so returning `nullptr` for the normal case.
// However, if -emit-relocs is given, we need to leave them in the output.
// (Some post link analysis tools need this information.)
if (Config->EmitRelocs) {
InputSection *RelocSec = make<InputSection>(*this, Sec, Name);
// We will not emit relocation section if target was discarded.
Target->DependentSections.push_back(RelocSec);
return RelocSec;
}
return nullptr;
}
}
// The GNU linker uses .note.GNU-stack section as a marker indicating
// that the code in the object file does not expect that the stack is
// executable (in terms of NX bit). If all input files have the marker,
// the GNU linker adds a PT_GNU_STACK segment to tells the loader to
// make the stack non-executable. Most object files have this section as
// of 2017.
//
// But making the stack non-executable is a norm today for security
// reasons. Failure to do so may result in a serious security issue.
// Therefore, we make LLD always add PT_GNU_STACK unless it is
// explicitly told to do otherwise (by -z execstack). Because the stack
// executable-ness is controlled solely by command line options,
// .note.GNU-stack sections are simply ignored.
if (Name == ".note.GNU-stack")
return &InputSection::Discarded;
// Object files that use processor features such as Intel Control-Flow
// Enforcement (CET) or AArch64 Branch Target Identification BTI, use a
// .note.gnu.property section containing a bitfield of feature bits like the
// GNU_PROPERTY_X86_FEATURE_1_IBT flag. Read a bitmap containing the flag.
//
// Since we merge bitmaps from multiple object files to create a new
// .note.gnu.property containing a single AND'ed bitmap, we discard an input
// file's .note.gnu.property section.
if (Name == ".note.gnu.property") {
ArrayRef<uint8_t> Contents = check(this->getObj().getSectionContents(&Sec));
this->AndFeatures = readAndFeatures(this, Contents);
return &InputSection::Discarded;
}
// Split stacks is a feature to support a discontiguous stack,
// commonly used in the programming language Go. For the details,
// see https://gcc.gnu.org/wiki/SplitStacks. An object file compiled
// for split stack will include a .note.GNU-split-stack section.
if (Name == ".note.GNU-split-stack") {
if (Config->Relocatable) {
error("cannot mix split-stack and non-split-stack in a relocatable link");
return &InputSection::Discarded;
}
this->SplitStack = true;
return &InputSection::Discarded;
}
// An object file cmpiled for split stack, but where some of the
// functions were compiled with the no_split_stack_attribute will
// include a .note.GNU-no-split-stack section.
if (Name == ".note.GNU-no-split-stack") {
this->SomeNoSplitStack = true;
return &InputSection::Discarded;
}
// The linkonce feature is a sort of proto-comdat. Some glibc i386 object
// files contain definitions of symbol "__x86.get_pc_thunk.bx" in linkonce
// sections. Drop those sections to avoid duplicate symbol errors.
// FIXME: This is glibc PR20543, we should remove this hack once that has been
// fixed for a while.
if (Name == ".gnu.linkonce.t.__x86.get_pc_thunk.bx" ||
Name == ".gnu.linkonce.t.__i686.get_pc_thunk.bx")
return &InputSection::Discarded;
// If we are creating a new .build-id section, strip existing .build-id
// sections so that the output won't have more than one .build-id.
// This is not usually a problem because input object files normally don't
// have .build-id sections, but you can create such files by
// "ld.{bfd,gold,lld} -r --build-id", and we want to guard against it.
if (Name == ".note.gnu.build-id" && Config->BuildId != BuildIdKind::None)
return &InputSection::Discarded;
// The linker merges EH (exception handling) frames and creates a
// .eh_frame_hdr section for runtime. So we handle them with a special
// class. For relocatable outputs, they are just passed through.
if (Name == ".eh_frame" && !Config->Relocatable)
return make<EhInputSection>(*this, Sec, Name);
if (shouldMerge(Sec))
return make<MergeInputSection>(*this, Sec, Name);
return make<InputSection>(*this, Sec, Name);
}
template <class ELFT>
StringRef ObjFile<ELFT>::getSectionName(const Elf_Shdr &Sec) {
return CHECK(getObj().getSectionName(&Sec, SectionStringTable), this);
}
// Initialize this->Symbols. this->Symbols is a parallel array as
// its corresponding ELF symbol table.
template <class ELFT> void ObjFile<ELFT>::initializeSymbols() {
ArrayRef<Elf_Sym> ESyms = this->getELFSyms<ELFT>();
this->Symbols.resize(ESyms.size());
// Our symbol table may have already been partially initialized
// because of LazyObjFile.
for (size_t I = 0, End = ESyms.size(); I != End; ++I)
if (!this->Symbols[I] && ESyms[I].getBinding() != STB_LOCAL)
this->Symbols[I] =
Symtab->insert(CHECK(ESyms[I].getName(this->StringTable), this));
// Fill this->Symbols. A symbol is either local or global.
for (size_t I = 0, End = ESyms.size(); I != End; ++I) {
const Elf_Sym &ESym = ESyms[I];
// Read symbol attributes.
uint32_t SecIdx = getSectionIndex(ESym);
if (SecIdx >= this->Sections.size())
fatal(toString(this) + ": invalid section index: " + Twine(SecIdx));
InputSectionBase *Sec = this->Sections[SecIdx];
uint8_t Binding = ESym.getBinding();
uint8_t StOther = ESym.st_other;
uint8_t Type = ESym.getType();
uint64_t Value = ESym.st_value;
uint64_t Size = ESym.st_size;
StringRefZ Name = this->StringTable.data() + ESym.st_name;
// Handle local symbols. Local symbols are not added to the symbol
// table because they are not visible from other object files. We
// allocate symbol instances and add their pointers to Symbols.
if (Binding == STB_LOCAL) {
if (ESym.getType() == STT_FILE)
SourceFile = CHECK(ESym.getName(this->StringTable), this);
if (this->StringTable.size() <= ESym.st_name)
fatal(toString(this) + ": invalid symbol name offset");
if (ESym.st_shndx == SHN_UNDEF)
this->Symbols[I] = make<Undefined>(this, Name, Binding, StOther, Type);
else if (Sec == &InputSection::Discarded)
this->Symbols[I] = make<Undefined>(this, Name, Binding, StOther, Type,
/*DiscardedSecIdx=*/SecIdx);
else
this->Symbols[I] =
make<Defined>(this, Name, Binding, StOther, Type, Value, Size, Sec);
continue;
}
// Handle global undefined symbols.
if (ESym.st_shndx == SHN_UNDEF) {
this->Symbols[I]->resolve(Undefined{this, Name, Binding, StOther, Type});
continue;
}
// Handle global common symbols.
if (ESym.st_shndx == SHN_COMMON) {
if (Value == 0 || Value >= UINT32_MAX)
fatal(toString(this) + ": common symbol '" + StringRef(Name.Data) +
"' has invalid alignment: " + Twine(Value));
this->Symbols[I]->resolve(
CommonSymbol{this, Name, Binding, StOther, Type, Value, Size});
continue;
}
// If a defined symbol is in a discarded section, handle it as if it
// were an undefined symbol. Such symbol doesn't comply with the
// standard, but in practice, a .eh_frame often directly refer
// COMDAT member sections, and if a comdat group is discarded, some
// defined symbol in a .eh_frame becomes dangling symbols.
if (Sec == &InputSection::Discarded) {
this->Symbols[I]->resolve(
Undefined{this, Name, Binding, StOther, Type, SecIdx});
continue;
}
// Handle global defined symbols.
if (Binding == STB_GLOBAL || Binding == STB_WEAK ||
Binding == STB_GNU_UNIQUE) {
this->Symbols[I]->resolve(
Defined{this, Name, Binding, StOther, Type, Value, Size, Sec});
continue;
}
fatal(toString(this) + ": unexpected binding: " + Twine((int)Binding));
}
}
ArchiveFile::ArchiveFile(std::unique_ptr<Archive> &&File)
: InputFile(ArchiveKind, File->getMemoryBufferRef()),
File(std::move(File)) {}
void ArchiveFile::parse() {
for (const Archive::Symbol &Sym : File->symbols())
Symtab->addSymbol(LazyArchive{*this, Sym});
}
// Returns a buffer pointing to a member file containing a given symbol.
void ArchiveFile::fetch(const Archive::Symbol &Sym) {
Archive::Child C =
CHECK(Sym.getMember(), toString(this) +
": could not get the member for symbol " +
Sym.getName());
if (!Seen.insert(C.getChildOffset()).second)
return;
MemoryBufferRef MB =
CHECK(C.getMemoryBufferRef(),
toString(this) +
": could not get the buffer for the member defining symbol " +
Sym.getName());
if (Tar && C.getParent()->isThin())
Tar->append(relativeToRoot(CHECK(C.getFullName(), this)), MB.getBuffer());
InputFile *File = createObjectFile(
MB, getName(), C.getParent()->isThin() ? 0 : C.getChildOffset());
File->GroupId = GroupId;
parseFile(File);
}
unsigned SharedFile::VernauxNum;
// Parse the version definitions in the object file if present, and return a
// vector whose nth element contains a pointer to the Elf_Verdef for version
// identifier n. Version identifiers that are not definitions map to nullptr.
template <typename ELFT>
static std::vector<const void *> parseVerdefs(const uint8_t *Base,
const typename ELFT::Shdr *Sec) {
if (!Sec)
return {};
// We cannot determine the largest verdef identifier without inspecting
// every Elf_Verdef, but both bfd and gold assign verdef identifiers
// sequentially starting from 1, so we predict that the largest identifier
// will be VerdefCount.
unsigned VerdefCount = Sec->sh_info;
std::vector<const void *> Verdefs(VerdefCount + 1);
// Build the Verdefs array by following the chain of Elf_Verdef objects
// from the start of the .gnu.version_d section.
const uint8_t *Verdef = Base + Sec->sh_offset;
for (unsigned I = 0; I != VerdefCount; ++I) {
auto *CurVerdef = reinterpret_cast<const typename ELFT::Verdef *>(Verdef);
Verdef += CurVerdef->vd_next;
unsigned VerdefIndex = CurVerdef->vd_ndx;
Verdefs.resize(VerdefIndex + 1);
Verdefs[VerdefIndex] = CurVerdef;
}
return Verdefs;
}
// We do not usually care about alignments of data in shared object
// files because the loader takes care of it. However, if we promote a
// DSO symbol to point to .bss due to copy relocation, we need to keep
// the original alignment requirements. We infer it in this function.
template <typename ELFT>
static uint64_t getAlignment(ArrayRef<typename ELFT::Shdr> Sections,
const typename ELFT::Sym &Sym) {
uint64_t Ret = UINT64_MAX;
if (Sym.st_value)
Ret = 1ULL << countTrailingZeros((uint64_t)Sym.st_value);
if (0 < Sym.st_shndx && Sym.st_shndx < Sections.size())
Ret = std::min<uint64_t>(Ret, Sections[Sym.st_shndx].sh_addralign);
return (Ret > UINT32_MAX) ? 0 : Ret;
}
// Fully parse the shared object file.
//
// This function parses symbol versions. If a DSO has version information,
// the file has a ".gnu.version_d" section which contains symbol version
// definitions. Each symbol is associated to one version through a table in
// ".gnu.version" section. That table is a parallel array for the symbol
// table, and each table entry contains an index in ".gnu.version_d".
//
// The special index 0 is reserved for VERF_NDX_LOCAL and 1 is for
// VER_NDX_GLOBAL. There's no table entry for these special versions in
// ".gnu.version_d".
//
// The file format for symbol versioning is perhaps a bit more complicated
// than necessary, but you can easily understand the code if you wrap your
// head around the data structure described above.
template <class ELFT> void SharedFile::parse() {
using Elf_Dyn = typename ELFT::Dyn;
using Elf_Shdr = typename ELFT::Shdr;
using Elf_Sym = typename ELFT::Sym;
using Elf_Verdef = typename ELFT::Verdef;
using Elf_Versym = typename ELFT::Versym;
ArrayRef<Elf_Dyn> DynamicTags;
const ELFFile<ELFT> Obj = this->getObj<ELFT>();
ArrayRef<Elf_Shdr> Sections = CHECK(Obj.sections(), this);
const Elf_Shdr *VersymSec = nullptr;
const Elf_Shdr *VerdefSec = nullptr;
// Search for .dynsym, .dynamic, .symtab, .gnu.version and .gnu.version_d.
for (const Elf_Shdr &Sec : Sections) {
switch (Sec.sh_type) {
default:
continue;
case SHT_DYNAMIC:
DynamicTags =
CHECK(Obj.template getSectionContentsAsArray<Elf_Dyn>(&Sec), this);
break;
case SHT_GNU_versym:
VersymSec = &Sec;
break;
case SHT_GNU_verdef:
VerdefSec = &Sec;
break;
}
}
if (VersymSec && NumELFSyms == 0) {
error("SHT_GNU_versym should be associated with symbol table");
return;
}
// Search for a DT_SONAME tag to initialize this->SoName.
for (const Elf_Dyn &Dyn : DynamicTags) {
if (Dyn.d_tag == DT_NEEDED) {
uint64_t Val = Dyn.getVal();
if (Val >= this->StringTable.size())
fatal(toString(this) + ": invalid DT_NEEDED entry");
DtNeeded.push_back(this->StringTable.data() + Val);
} else if (Dyn.d_tag == DT_SONAME) {
uint64_t Val = Dyn.getVal();
if (Val >= this->StringTable.size())
fatal(toString(this) + ": invalid DT_SONAME entry");
SoName = this->StringTable.data() + Val;
}
}
// DSOs are uniquified not by filename but by soname.
DenseMap<StringRef, SharedFile *>::iterator It;
bool WasInserted;
std::tie(It, WasInserted) = Symtab->SoNames.try_emplace(SoName, this);
// If a DSO appears more than once on the command line with and without
// --as-needed, --no-as-needed takes precedence over --as-needed because a
// user can add an extra DSO with --no-as-needed to force it to be added to
// the dependency list.
It->second->IsNeeded |= IsNeeded;
if (!WasInserted)
return;
SharedFiles.push_back(this);
Verdefs = parseVerdefs<ELFT>(Obj.base(), VerdefSec);
// Parse ".gnu.version" section which is a parallel array for the symbol
// table. If a given file doesn't have a ".gnu.version" section, we use
// VER_NDX_GLOBAL.
size_t Size = NumELFSyms - FirstGlobal;
std::vector<uint32_t> Versyms(Size, VER_NDX_GLOBAL);
if (VersymSec) {
ArrayRef<Elf_Versym> Versym =
CHECK(Obj.template getSectionContentsAsArray<Elf_Versym>(VersymSec),
this)
.slice(FirstGlobal);
for (size_t I = 0; I < Size; ++I)
Versyms[I] = Versym[I].vs_index;
}
// System libraries can have a lot of symbols with versions. Using a
// fixed buffer for computing the versions name (foo@ver) can save a
// lot of allocations.
SmallString<0> VersionedNameBuffer;
// Add symbols to the symbol table.
ArrayRef<Elf_Sym> Syms = this->getGlobalELFSyms<ELFT>();
for (size_t I = 0; I < Syms.size(); ++I) {
const Elf_Sym &Sym = Syms[I];
// ELF spec requires that all local symbols precede weak or global
// symbols in each symbol table, and the index of first non-local symbol
// is stored to sh_info. If a local symbol appears after some non-local
// symbol, that's a violation of the spec.
StringRef Name = CHECK(Sym.getName(this->StringTable), this);
if (Sym.getBinding() == STB_LOCAL) {
warn("found local symbol '" + Name +
"' in global part of symbol table in file " + toString(this));
continue;
}
if (Sym.isUndefined()) {
Symbol *S = Symtab->addSymbol(
Undefined{this, Name, Sym.getBinding(), Sym.st_other, Sym.getType()});
S->ExportDynamic = true;
continue;
}
// MIPS BFD linker puts _gp_disp symbol into DSO files and incorrectly
// assigns VER_NDX_LOCAL to this section global symbol. Here is a
// workaround for this bug.
uint32_t Idx = Versyms[I] & ~VERSYM_HIDDEN;
if (Config->EMachine == EM_MIPS && Idx == VER_NDX_LOCAL &&
Name == "_gp_disp")
continue;
uint32_t Alignment = getAlignment<ELFT>(Sections, Sym);
if (!(Versyms[I] & VERSYM_HIDDEN)) {
Symtab->addSymbol(SharedSymbol{*this, Name, Sym.getBinding(),
Sym.st_other, Sym.getType(), Sym.st_value,
Sym.st_size, Alignment, Idx});
}
// Also add the symbol with the versioned name to handle undefined symbols
// with explicit versions.
if (Idx == VER_NDX_GLOBAL)
continue;
if (Idx >= Verdefs.size() || Idx == VER_NDX_LOCAL) {
error("corrupt input file: version definition index " + Twine(Idx) +
" for symbol " + Name + " is out of bounds\n>>> defined in " +
toString(this));
continue;
}
StringRef VerName =
this->StringTable.data() +
reinterpret_cast<const Elf_Verdef *>(Verdefs[Idx])->getAux()->vda_name;
VersionedNameBuffer.clear();
Name = (Name + "@" + VerName).toStringRef(VersionedNameBuffer);
Symtab->addSymbol(SharedSymbol{*this, Saver.save(Name), Sym.getBinding(),
Sym.st_other, Sym.getType(), Sym.st_value,
Sym.st_size, Alignment, Idx});
}
}
static ELFKind getBitcodeELFKind(const Triple &T) {
if (T.isLittleEndian())
return T.isArch64Bit() ? ELF64LEKind : ELF32LEKind;
return T.isArch64Bit() ? ELF64BEKind : ELF32BEKind;
}
static uint8_t getBitcodeMachineKind(StringRef Path, const Triple &T) {
switch (T.getArch()) {
case Triple::aarch64:
return EM_AARCH64;
case Triple::amdgcn:
case Triple::r600:
return EM_AMDGPU;
case Triple::arm:
case Triple::thumb:
return EM_ARM;
case Triple::avr:
return EM_AVR;
case Triple::mips:
case Triple::mipsel:
case Triple::mips64:
case Triple::mips64el:
return EM_MIPS;
case Triple::msp430:
return EM_MSP430;
case Triple::ppc:
return EM_PPC;
case Triple::ppc64:
case Triple::ppc64le:
return EM_PPC64;
case Triple::x86:
return T.isOSIAMCU() ? EM_IAMCU : EM_386;
case Triple::x86_64:
return EM_X86_64;
default:
error(Path + ": could not infer e_machine from bitcode target triple " +
T.str());
return EM_NONE;
}
}
BitcodeFile::BitcodeFile(MemoryBufferRef MB, StringRef ArchiveName,
uint64_t OffsetInArchive)
: InputFile(BitcodeKind, MB) {
this->ArchiveName = ArchiveName;
std::string Path = MB.getBufferIdentifier().str();
if (Config->ThinLTOIndexOnly)
Path = replaceThinLTOSuffix(MB.getBufferIdentifier());
// ThinLTO assumes that all MemoryBufferRefs given to it have a unique
// name. If two archives define two members with the same name, this
// causes a collision which result in only one of the objects being taken
// into consideration at LTO time (which very likely causes undefined
// symbols later in the link stage). So we append file offset to make
// filename unique.
StringRef Name = ArchiveName.empty()
? Saver.save(Path)
: Saver.save(ArchiveName + "(" + Path + " at " +
utostr(OffsetInArchive) + ")");
MemoryBufferRef MBRef(MB.getBuffer(), Name);
Obj = CHECK(lto::InputFile::create(MBRef), this);
Triple T(Obj->getTargetTriple());
EKind = getBitcodeELFKind(T);
EMachine = getBitcodeMachineKind(MB.getBufferIdentifier(), T);
}
static uint8_t mapVisibility(GlobalValue::VisibilityTypes GvVisibility) {
switch (GvVisibility) {
case GlobalValue::DefaultVisibility:
return STV_DEFAULT;
case GlobalValue::HiddenVisibility:
return STV_HIDDEN;
case GlobalValue::ProtectedVisibility:
return STV_PROTECTED;
}
llvm_unreachable("unknown visibility");
}
template <class ELFT>
static Symbol *createBitcodeSymbol(const std::vector<bool> &KeptComdats,
const lto::InputFile::Symbol &ObjSym,
BitcodeFile &F) {
StringRef Name = Saver.save(ObjSym.getName());
uint8_t Binding = ObjSym.isWeak() ? STB_WEAK : STB_GLOBAL;
uint8_t Type = ObjSym.isTLS() ? STT_TLS : STT_NOTYPE;
uint8_t Visibility = mapVisibility(ObjSym.getVisibility());
bool CanOmitFromDynSym = ObjSym.canBeOmittedFromSymbolTable();
int C = ObjSym.getComdatIndex();
if (ObjSym.isUndefined() || (C != -1 && !KeptComdats[C])) {
Undefined New(&F, Name, Binding, Visibility, Type);
if (CanOmitFromDynSym)
New.ExportDynamic = false;
return Symtab->addSymbol(New);
}
if (ObjSym.isCommon())
return Symtab->addSymbol(
CommonSymbol{&F, Name, Binding, Visibility, STT_OBJECT,
ObjSym.getCommonAlignment(), ObjSym.getCommonSize()});
Defined New(&F, Name, Binding, Visibility, Type, 0, 0, nullptr);
if (CanOmitFromDynSym)
New.ExportDynamic = false;
return Symtab->addSymbol(New);
}
template <class ELFT> void BitcodeFile::parse() {
std::vector<bool> KeptComdats;
for (StringRef S : Obj->getComdatTable())
KeptComdats.push_back(
Symtab->ComdatGroups.try_emplace(CachedHashStringRef(S), this).second);
for (const lto::InputFile::Symbol &ObjSym : Obj->symbols())
Symbols.push_back(createBitcodeSymbol<ELFT>(KeptComdats, ObjSym, *this));
for (auto L : Obj->getDependentLibraries())
addDependentLibrary(L, this);
}
void BinaryFile::parse() {
ArrayRef<uint8_t> Data = arrayRefFromStringRef(MB.getBuffer());
auto *Section = make<InputSection>(this, SHF_ALLOC | SHF_WRITE, SHT_PROGBITS,
8, Data, ".data");
Sections.push_back(Section);
// For each input file foo that is embedded to a result as a binary
// blob, we define _binary_foo_{start,end,size} symbols, so that
// user programs can access blobs by name. Non-alphanumeric
// characters in a filename are replaced with underscore.
std::string S = "_binary_" + MB.getBufferIdentifier().str();
for (size_t I = 0; I < S.size(); ++I)
if (!isAlnum(S[I]))
S[I] = '_';
Symtab->addSymbol(Defined{nullptr, Saver.save(S + "_start"), STB_GLOBAL,
STV_DEFAULT, STT_OBJECT, 0, 0, Section});
Symtab->addSymbol(Defined{nullptr, Saver.save(S + "_end"), STB_GLOBAL,
STV_DEFAULT, STT_OBJECT, Data.size(), 0, Section});
Symtab->addSymbol(Defined{nullptr, Saver.save(S + "_size"), STB_GLOBAL,
STV_DEFAULT, STT_OBJECT, Data.size(), 0, nullptr});
}
InputFile *elf::createObjectFile(MemoryBufferRef MB, StringRef ArchiveName,
uint64_t OffsetInArchive) {
if (isBitcode(MB))
return make<BitcodeFile>(MB, ArchiveName, OffsetInArchive);
switch (getELFKind(MB, ArchiveName)) {
case ELF32LEKind:
return make<ObjFile<ELF32LE>>(MB, ArchiveName);
case ELF32BEKind:
return make<ObjFile<ELF32BE>>(MB, ArchiveName);
case ELF64LEKind:
return make<ObjFile<ELF64LE>>(MB, ArchiveName);
case ELF64BEKind:
return make<ObjFile<ELF64BE>>(MB, ArchiveName);
default:
llvm_unreachable("getELFKind");
}
}
void LazyObjFile::fetch() {
if (MB.getBuffer().empty())
return;
InputFile *File = createObjectFile(MB, ArchiveName, OffsetInArchive);
File->GroupId = GroupId;
MB = {};
// Copy symbol vector so that the new InputFile doesn't have to
// insert the same defined symbols to the symbol table again.
File->Symbols = std::move(Symbols);
parseFile(File);
}
template <class ELFT> void LazyObjFile::parse() {
using Elf_Sym = typename ELFT::Sym;
// A lazy object file wraps either a bitcode file or an ELF file.
if (isBitcode(this->MB)) {
std::unique_ptr<lto::InputFile> Obj =
CHECK(lto::InputFile::create(this->MB), this);
for (const lto::InputFile::Symbol &Sym : Obj->symbols()) {
if (Sym.isUndefined())
continue;
Symtab->addSymbol(LazyObject{*this, Saver.save(Sym.getName())});
}
return;
}
if (getELFKind(this->MB, ArchiveName) != Config->EKind) {
error("incompatible file: " + this->MB.getBufferIdentifier());
return;
}
// Find a symbol table.
ELFFile<ELFT> Obj = check(ELFFile<ELFT>::create(MB.getBuffer()));
ArrayRef<typename ELFT::Shdr> Sections = CHECK(Obj.sections(), this);
for (const typename ELFT::Shdr &Sec : Sections) {
if (Sec.sh_type != SHT_SYMTAB)
continue;
// A symbol table is found.
ArrayRef<Elf_Sym> ESyms = CHECK(Obj.symbols(&Sec), this);
uint32_t FirstGlobal = Sec.sh_info;
StringRef Strtab = CHECK(Obj.getStringTableForSymtab(Sec, Sections), this);
this->Symbols.resize(ESyms.size());
// Get existing symbols or insert placeholder symbols.
for (size_t I = FirstGlobal, End = ESyms.size(); I != End; ++I)
if (ESyms[I].st_shndx != SHN_UNDEF)
this->Symbols[I] = Symtab->insert(CHECK(ESyms[I].getName(Strtab), this));
// Replace existing symbols with LazyObject symbols.
//
// resolve() may trigger this->fetch() if an existing symbol is an
// undefined symbol. If that happens, this LazyObjFile has served
// its purpose, and we can exit from the loop early.
for (Symbol *Sym : this->Symbols) {
if (!Sym)
continue;
Sym->resolve(LazyObject{*this, Sym->getName()});
// MemoryBuffer is emptied if this file is instantiated as ObjFile.
if (MB.getBuffer().empty())
return;
}
return;
}
}
std::string elf::replaceThinLTOSuffix(StringRef Path) {
StringRef Suffix = Config->ThinLTOObjectSuffixReplace.first;
StringRef Repl = Config->ThinLTOObjectSuffixReplace.second;
if (Path.consume_back(Suffix))
return (Path + Repl).str();
return Path;
}
template void BitcodeFile::parse<ELF32LE>();
template void BitcodeFile::parse<ELF32BE>();
template void BitcodeFile::parse<ELF64LE>();
template void BitcodeFile::parse<ELF64BE>();
template void LazyObjFile::parse<ELF32LE>();
template void LazyObjFile::parse<ELF32BE>();
template void LazyObjFile::parse<ELF64LE>();
template void LazyObjFile::parse<ELF64BE>();
template class elf::ObjFile<ELF32LE>;
template class elf::ObjFile<ELF32BE>;
template class elf::ObjFile<ELF64LE>;
template class elf::ObjFile<ELF64BE>;
template void SharedFile::parse<ELF32LE>();
template void SharedFile::parse<ELF32BE>();
template void SharedFile::parse<ELF64LE>();
template void SharedFile::parse<ELF64BE>();
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