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ELFFile.h
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ELFFile.h
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//===- lib/ReaderWriter/ELF/ELFFile.h -------------------------------------===//
//
// The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#ifndef LLD_READER_WRITER_ELF_FILE_H
#define LLD_READER_WRITER_ELF_FILE_H
#include "Atoms.h"
#include <llvm/ADT/MapVector.h>
#include <map>
#include <unordered_map>
namespace lld {
namespace elf {
/// \brief Read a binary, find out based on the symbol table contents what kind
/// of symbol it is and create corresponding atoms for it
template <class ELFT> class ELFFile : public File {
typedef llvm::object::Elf_Sym_Impl<ELFT> Elf_Sym;
typedef llvm::object::Elf_Shdr_Impl<ELFT> Elf_Shdr;
typedef llvm::object::Elf_Rel_Impl<ELFT, false> Elf_Rel;
typedef llvm::object::Elf_Rel_Impl<ELFT, true> Elf_Rela;
typedef typename llvm::object::ELFFile<ELFT>::Elf_Sym_Iter Elf_Sym_Iter;
typedef typename llvm::object::ELFFile<ELFT>::Elf_Rela_Iter Elf_Rela_Iter;
typedef typename llvm::object::ELFFile<ELFT>::Elf_Rel_Iter Elf_Rel_Iter;
typedef typename llvm::object::ELFFile<ELFT>::Elf_Word Elf_Word;
// A Map is used to hold the atoms that have been divided up
// after reading the section that contains Merge String attributes
struct MergeSectionKey {
MergeSectionKey(const Elf_Shdr *shdr, int64_t offset)
: _shdr(shdr), _offset(offset) {}
// Data members
const Elf_Shdr *_shdr;
int64_t _offset;
};
struct MergeSectionEq {
int64_t operator()(const MergeSectionKey &k) const {
return llvm::hash_combine((int64_t)(k._shdr->sh_name),
(int64_t)k._offset);
}
bool operator()(const MergeSectionKey &lhs,
const MergeSectionKey &rhs) const {
return ((lhs._shdr->sh_name == rhs._shdr->sh_name) &&
(lhs._offset == rhs._offset));
}
};
struct MergeString {
MergeString(int64_t offset, StringRef str, const Elf_Shdr *shdr,
StringRef sectionName)
: _offset(offset), _string(str), _shdr(shdr),
_sectionName(sectionName) {}
// the offset of this atom
int64_t _offset;
// The content
StringRef _string;
// Section header
const Elf_Shdr *_shdr;
// Section name
StringRef _sectionName;
};
// This is used to find the MergeAtom given a relocation
// offset
typedef std::vector<ELFMergeAtom<ELFT> *> MergeAtomsT;
/// \brief find a mergeAtom given a start offset
struct FindByOffset {
const Elf_Shdr *_shdr;
int64_t _offset;
FindByOffset(const Elf_Shdr *shdr, int64_t offset)
: _shdr(shdr), _offset(offset) {}
bool operator()(const ELFMergeAtom<ELFT> *a) {
int64_t off = a->offset();
return (_shdr->sh_name == a->section()) &&
((_offset >= off) && (_offset <= off + (int64_t)a->size()));
}
};
/// \brief find a merge atom given a offset
ELFMergeAtom<ELFT> *findMergeAtom(const Elf_Shdr *shdr, uint64_t offset) {
auto it = std::find_if(_mergeAtoms.begin(), _mergeAtoms.end(),
FindByOffset(shdr, offset));
assert(it != _mergeAtoms.end());
return *it;
}
typedef std::unordered_map<MergeSectionKey, DefinedAtom *, MergeSectionEq,
MergeSectionEq> MergedSectionMapT;
typedef typename MergedSectionMapT::iterator MergedSectionMapIterT;
public:
ELFFile(StringRef name, ELFLinkingContext &ctx)
: File(name, kindObject), _ordinal(0),
_doStringsMerge(ctx.mergeCommonStrings()), _useWrap(false), _ctx(ctx) {
setLastError(std::error_code());
}
ELFFile(std::unique_ptr<MemoryBuffer> mb, ELFLinkingContext &ctx)
: File(mb->getBufferIdentifier(), kindObject), _mb(std::move(mb)),
_ordinal(0), _doStringsMerge(ctx.mergeCommonStrings()),
_useWrap(ctx.wrapCalls().size()), _ctx(ctx) {}
static ErrorOr<std::unique_ptr<ELFFile>>
create(std::unique_ptr<MemoryBuffer> mb, ELFLinkingContext &ctx);
virtual Reference::KindArch kindArch();
/// \brief Create symbols from LinkingContext.
std::error_code createAtomsFromContext();
/// \brief Read input sections and populate necessary data structures
/// to read them later and create atoms
std::error_code createAtomizableSections();
/// \brief Create mergeable atoms from sections that have the merge attribute
/// set
std::error_code createMergeableAtoms();
/// \brief Add the symbols that the sections contain. The symbols will be
/// converted to atoms for
/// Undefined symbols, absolute symbols
std::error_code createSymbolsFromAtomizableSections();
/// \brief Create individual atoms
std::error_code createAtoms();
const atom_collection<DefinedAtom> &defined() const override {
return _definedAtoms;
}
const atom_collection<UndefinedAtom> &undefined() const override {
return _undefinedAtoms;
}
const atom_collection<SharedLibraryAtom> &sharedLibrary() const override {
return _sharedLibraryAtoms;
}
const atom_collection<AbsoluteAtom> &absolute() const override {
return _absoluteAtoms;
}
Atom *findAtom(const Elf_Sym *sourceSymbol, const Elf_Sym *targetSymbol) {
// All references to atoms inside a group are through undefined atoms.
Atom *targetAtom = _symbolToAtomMapping.lookup(targetSymbol);
StringRef targetSymbolName = targetAtom->name();
if (targetAtom->definition() != Atom::definitionRegular)
return targetAtom;
if ((llvm::dyn_cast<DefinedAtom>(targetAtom))->scope() ==
DefinedAtom::scopeTranslationUnit)
return targetAtom;
if (!redirectReferenceUsingUndefAtom(sourceSymbol, targetSymbol))
return targetAtom;
auto undefForGroupchild = _undefAtomsForGroupChild.find(targetSymbolName);
if (undefForGroupchild != _undefAtomsForGroupChild.end())
return undefForGroupchild->getValue();
auto undefGroupChildAtom =
new (_readerStorage) SimpleUndefinedAtom(*this, targetSymbolName);
_undefinedAtoms._atoms.push_back(undefGroupChildAtom);
return (_undefAtomsForGroupChild[targetSymbolName] = undefGroupChildAtom);
}
protected:
ELFDefinedAtom<ELFT> *createDefinedAtomAndAssignRelocations(
StringRef symbolName, StringRef sectionName, const Elf_Sym *symbol,
const Elf_Shdr *section, ArrayRef<uint8_t> symContent,
ArrayRef<uint8_t> secContent);
std::error_code doParse() override;
/// \brief Iterate over Elf_Rela relocations list and create references.
virtual void createRelocationReferences(const Elf_Sym *symbol,
ArrayRef<uint8_t> content,
range<Elf_Rela_Iter> rels);
/// \brief Iterate over Elf_Rel relocations list and create references.
virtual void createRelocationReferences(const Elf_Sym *symbol,
ArrayRef<uint8_t> symContent,
ArrayRef<uint8_t> secContent,
range<Elf_Rel_Iter> rels);
/// \brief After all the Atoms and References are created, update each
/// Reference's target with the Atom pointer it refers to.
void updateReferences();
/// \brief Update the reference if the access corresponds to a merge string
/// section.
void updateReferenceForMergeStringAccess(ELFReference<ELFT> *ref,
const Elf_Sym *symbol,
const Elf_Shdr *shdr);
/// \brief Do we want to ignore the section. Ignored sections are
/// not processed to create atoms
bool isIgnoredSection(const Elf_Shdr *section);
/// \brief Is the current section be treated as a mergeable string section.
/// The contents of a mergeable string section are null-terminated strings.
/// If the section have mergeable strings, the linker would need to split
/// the section into multiple atoms and mark them mergeByContent.
bool isMergeableStringSection(const Elf_Shdr *section);
/// \brief Returns a new anonymous atom whose size is equal to the
/// section size. That atom will be used to represent the entire
/// section that have no symbols.
ELFDefinedAtom<ELFT> *createSectionAtom(const Elf_Shdr *section,
StringRef sectionName,
ArrayRef<uint8_t> contents);
/// Returns the symbol's content size. The nextSymbol should be null if the
/// symbol is the last one in the section.
uint64_t symbolContentSize(const Elf_Shdr *section,
const Elf_Sym *symbol,
const Elf_Sym *nextSymbol);
void createEdge(ELFDefinedAtom<ELFT> *from, ELFDefinedAtom<ELFT> *to,
uint32_t edgeKind);
/// Get the section name for a section.
ErrorOr<StringRef> getSectionName(const Elf_Shdr *shdr) const {
if (!shdr)
return StringRef();
return _objFile->getSectionName(shdr);
}
/// Determines if the section occupy memory space.
bool sectionOccupiesMemorySpace(const Elf_Shdr *shdr) const {
return (shdr->sh_type != llvm::ELF::SHT_NOBITS);
}
/// Return the section contents.
ErrorOr<ArrayRef<uint8_t>> getSectionContents(const Elf_Shdr *shdr) const {
if (!shdr || !sectionOccupiesMemorySpace(shdr))
return ArrayRef<uint8_t>();
return _objFile->getSectionContents(shdr);
}
/// Returns true if the symbol is a undefined symbol.
bool isUndefinedSymbol(const Elf_Sym *sym) const {
return (sym->st_shndx == llvm::ELF::SHN_UNDEF);
}
/// Determines if the target wants to create an atom for a section that has no
/// symbol references.
bool handleSectionWithNoSymbols(const Elf_Shdr *shdr,
std::vector<Elf_Sym_Iter> &syms) const {
return shdr && (shdr->sh_type == llvm::ELF::SHT_PROGBITS) && syms.empty();
}
/// Handle creation of atoms for .gnu.linkonce sections.
std::error_code handleGnuLinkOnceSection(
StringRef sectionName,
llvm::StringMap<std::vector<ELFDefinedAtom<ELFT> *>> &atomsForSection,
const Elf_Shdr *shdr);
// Handle Section groups/COMDAT scetions.
std::error_code handleSectionGroup(
StringRef signature, StringRef groupSectionName,
llvm::StringMap<std::vector<ELFDefinedAtom<ELFT> *>> &atomsForSection,
llvm::DenseMap<const Elf_Shdr *, std::vector<StringRef>> &comdatSections,
const Elf_Shdr *shdr);
/// Process the Undefined symbol and create an atom for it.
ErrorOr<ELFUndefinedAtom<ELFT> *>
handleUndefinedSymbol(StringRef symName, const Elf_Sym *sym) {
return new (_readerStorage) ELFUndefinedAtom<ELFT>(*this, symName, sym);
}
/// Returns true if the symbol is a absolute symbol.
bool isAbsoluteSymbol(const Elf_Sym *sym) const {
return (sym->st_shndx == llvm::ELF::SHN_ABS);
}
/// Process the Absolute symbol and create an atom for it.
ErrorOr<ELFAbsoluteAtom<ELFT> *>
handleAbsoluteSymbol(StringRef symName, const Elf_Sym *sym, int64_t value) {
return new (_readerStorage)
ELFAbsoluteAtom<ELFT>(*this, symName, sym, value);
}
/// Returns true if the symbol is common symbol. A common symbol represents a
/// tentive definition in C. It has name, size and alignment constraint, but
/// actual storage has not yet been allocated. (The linker will allocate
/// storage for them in the later pass after coalescing tentative symbols by
/// name.)
virtual bool isCommonSymbol(const Elf_Sym *symbol) const {
return symbol->getType() == llvm::ELF::STT_COMMON ||
symbol->st_shndx == llvm::ELF::SHN_COMMON;
}
/// Returns true if the section is a gnulinkonce section.
bool isGnuLinkOnceSection(StringRef sectionName) const {
return sectionName.startswith(".gnu.linkonce.");
}
/// Returns true if the section is a COMDAT group section.
bool isGroupSection(const Elf_Shdr *shdr) const {
return (shdr->sh_type == llvm::ELF::SHT_GROUP);
}
/// Returns true if the section is a member of some group.
bool isSectionMemberOfGroup(const Elf_Shdr *shdr) const {
return (shdr->sh_flags & llvm::ELF::SHF_GROUP);
}
/// Returns correct st_value for the symbol depending on the architecture.
/// For most architectures it's just a regular st_value with no changes.
virtual uint64_t getSymbolValue(const Elf_Sym *symbol) const {
return symbol->st_value;
}
/// Returns initial addend
virtual Reference::Addend getInitialAddend(ArrayRef<uint8_t> symContent,
uint64_t symbolValue,
const Elf_Rel& reference) const {
return *(symContent.data() + reference.r_offset - symbolValue);
}
/// Process the common symbol and create an atom for it.
virtual ErrorOr<ELFCommonAtom<ELFT> *>
handleCommonSymbol(StringRef symName, const Elf_Sym *sym) {
return new (_readerStorage) ELFCommonAtom<ELFT>(*this, symName, sym);
}
/// Returns true if the symbol is a defined symbol.
virtual bool isDefinedSymbol(const Elf_Sym *sym) const {
return (sym->getType() == llvm::ELF::STT_NOTYPE ||
sym->getType() == llvm::ELF::STT_OBJECT ||
sym->getType() == llvm::ELF::STT_FUNC ||
sym->getType() == llvm::ELF::STT_GNU_IFUNC ||
sym->getType() == llvm::ELF::STT_SECTION ||
sym->getType() == llvm::ELF::STT_FILE ||
sym->getType() == llvm::ELF::STT_TLS);
}
/// Process the Defined symbol and create an atom for it.
virtual ErrorOr<ELFDefinedAtom<ELFT> *>
handleDefinedSymbol(StringRef symName, StringRef sectionName,
const Elf_Sym *sym, const Elf_Shdr *sectionHdr,
ArrayRef<uint8_t> contentData,
unsigned int referenceStart, unsigned int referenceEnd,
std::vector<ELFReference<ELFT> *> &referenceList) {
return new (_readerStorage) ELFDefinedAtom<ELFT>(
*this, symName, sectionName, sym, sectionHdr, contentData,
referenceStart, referenceEnd, referenceList);
}
/// Process the Merge string and create an atom for it.
ErrorOr<ELFMergeAtom<ELFT> *>
handleMergeString(StringRef sectionName, const Elf_Shdr *sectionHdr,
ArrayRef<uint8_t> contentData, unsigned int offset) {
ELFMergeAtom<ELFT> *mergeAtom = new (_readerStorage)
ELFMergeAtom<ELFT>(*this, sectionName, sectionHdr, contentData, offset);
const MergeSectionKey mergedSectionKey(sectionHdr, offset);
if (_mergedSectionMap.find(mergedSectionKey) == _mergedSectionMap.end())
_mergedSectionMap.insert(std::make_pair(mergedSectionKey, mergeAtom));
return mergeAtom;
}
/// References to the sections comprising a group, from sections
/// outside the group, must be made via global UNDEF symbols,
/// referencing global symbols defined as addresses in the group
/// sections. They may not reference local symbols for addresses in
/// the group's sections, including section symbols.
/// ABI Doc : https://mentorembedded.github.io/cxx-abi/abi/prop-72-comdat.html
/// Does the atom need to be redirected using a separate undefined atom?
bool redirectReferenceUsingUndefAtom(const Elf_Sym *sourceSymbol,
const Elf_Sym *targetSymbol) const;
void addReferenceToSymbol(const ELFReference<ELFT> *r, const Elf_Sym *sym) {
_referenceToSymbol[r] = sym;
}
const Elf_Sym *findSymbolForReference(const ELFReference<ELFT> *r) const {
auto elfReferenceToSymbol = _referenceToSymbol.find(r);
if (elfReferenceToSymbol != _referenceToSymbol.end())
return elfReferenceToSymbol->second;
return nullptr;
}
llvm::BumpPtrAllocator _readerStorage;
std::unique_ptr<llvm::object::ELFFile<ELFT> > _objFile;
atom_collection_vector<DefinedAtom> _definedAtoms;
atom_collection_vector<UndefinedAtom> _undefinedAtoms;
atom_collection_vector<SharedLibraryAtom> _sharedLibraryAtoms;
atom_collection_vector<AbsoluteAtom> _absoluteAtoms;
/// \brief _relocationAddendReferences and _relocationReferences contain the
/// list of relocations references. In ELF, if a section named, ".text" has
/// relocations will also have a section named ".rel.text" or ".rela.text"
/// which will hold the entries.
std::unordered_map<StringRef, range<Elf_Rela_Iter>>
_relocationAddendReferences;
MergedSectionMapT _mergedSectionMap;
std::unordered_map<StringRef, range<Elf_Rel_Iter>> _relocationReferences;
std::vector<ELFReference<ELFT> *> _references;
llvm::DenseMap<const Elf_Sym *, Atom *> _symbolToAtomMapping;
llvm::DenseMap<const ELFReference<ELFT> *, const Elf_Sym *>
_referenceToSymbol;
// Group child atoms have a pair corresponding to the signature and the
// section header of the section that was used for generating the signature.
llvm::DenseMap<const Elf_Sym *, std::pair<StringRef, const Elf_Shdr *>>
_groupChild;
llvm::StringMap<Atom *> _undefAtomsForGroupChild;
/// \brief Atoms that are created for a section that has the merge property
/// set
MergeAtomsT _mergeAtoms;
/// \brief the section and the symbols that are contained within it to create
/// used to create atoms
llvm::MapVector<const Elf_Shdr *, std::vector<Elf_Sym_Iter>> _sectionSymbols;
/// \brief Sections that have merge string property
std::vector<const Elf_Shdr *> _mergeStringSections;
std::unique_ptr<MemoryBuffer> _mb;
int64_t _ordinal;
/// \brief the cached options relevant while reading the ELF File
bool _doStringsMerge;
/// \brief Is --wrap on?
bool _useWrap;
/// \brief The LinkingContext.
ELFLinkingContext &_ctx;
// Wrap map
llvm::StringMap<UndefinedAtom *> _wrapSymbolMap;
};
/// \brief All atoms are owned by a File. To add linker specific atoms
/// the atoms need to be inserted to a file called (RuntimeFile) which
/// are basically additional symbols required by libc and other runtime
/// libraries part of executing a program. This class provides support
/// for adding absolute symbols and undefined symbols
template <class ELFT> class RuntimeFile : public ELFFile<ELFT> {
public:
typedef llvm::object::Elf_Sym_Impl<ELFT> Elf_Sym;
RuntimeFile(ELFLinkingContext &context, StringRef name)
: ELFFile<ELFT>(name, context) {}
/// \brief add a global absolute atom
virtual Atom *addAbsoluteAtom(StringRef symbolName) {
assert(!symbolName.empty() && "AbsoluteAtoms must have a name");
Elf_Sym *symbol = new (this->_readerStorage) Elf_Sym;
symbol->st_name = 0;
symbol->st_value = 0;
symbol->st_shndx = llvm::ELF::SHN_ABS;
symbol->setBindingAndType(llvm::ELF::STB_GLOBAL, llvm::ELF::STT_OBJECT);
symbol->setVisibility(llvm::ELF::STV_DEFAULT);
symbol->st_size = 0;
auto newAtom = this->handleAbsoluteSymbol(symbolName, symbol, -1);
this->_absoluteAtoms._atoms.push_back(*newAtom);
return *newAtom;
}
/// \brief add an undefined atom
virtual Atom *addUndefinedAtom(StringRef symbolName) {
assert(!symbolName.empty() && "UndefinedAtoms must have a name");
Elf_Sym *symbol = new (this->_readerStorage) Elf_Sym;
symbol->st_name = 0;
symbol->st_value = 0;
symbol->st_shndx = llvm::ELF::SHN_UNDEF;
symbol->setBindingAndType(llvm::ELF::STB_GLOBAL, llvm::ELF::STT_NOTYPE);
symbol->setVisibility(llvm::ELF::STV_DEFAULT);
symbol->st_size = 0;
auto newAtom = this->handleUndefinedSymbol(symbolName, symbol);
this->_undefinedAtoms._atoms.push_back(*newAtom);
return *newAtom;
}
// cannot add atoms to Runtime file
virtual void addAtom(const Atom &) {
llvm_unreachable("cannot add atoms to Runtime files");
}
};
template <class ELFT>
ErrorOr<std::unique_ptr<ELFFile<ELFT>>>
ELFFile<ELFT>::create(std::unique_ptr<MemoryBuffer> mb,
ELFLinkingContext &ctx) {
std::unique_ptr<ELFFile<ELFT>> file(new ELFFile<ELFT>(std::move(mb), ctx));
return std::move(file);
}
template <class ELFT>
std::error_code ELFFile<ELFT>::doParse() {
std::error_code ec;
_objFile.reset(new llvm::object::ELFFile<ELFT>(_mb->getBuffer(), ec));
if (ec)
return ec;
if ((ec = createAtomsFromContext()))
return ec;
// Read input sections from the input file that need to be converted to
// atoms
if ((ec = createAtomizableSections()))
return ec;
// For mergeable strings, we would need to split the section into various
// atoms
if ((ec = createMergeableAtoms()))
return ec;
// Create the necessary symbols that are part of the section that we
// created in createAtomizableSections function
if ((ec = createSymbolsFromAtomizableSections()))
return ec;
// Create the appropriate atoms from the file
if ((ec = createAtoms()))
return ec;
return std::error_code();
}
template <class ELFT> Reference::KindArch ELFFile<ELFT>::kindArch() {
switch (_objFile->getHeader()->e_machine) {
case llvm::ELF::EM_X86_64:
return Reference::KindArch::x86_64;
case llvm::ELF::EM_386:
return Reference::KindArch::x86;
case llvm::ELF::EM_ARM:
return Reference::KindArch::ARM;
case llvm::ELF::EM_HEXAGON:
return Reference::KindArch::Hexagon;
case llvm::ELF::EM_MIPS:
return Reference::KindArch::Mips;
case llvm::ELF::EM_AARCH64:
return Reference::KindArch::AArch64;
}
llvm_unreachable("unsupported e_machine value");
}
template <class ELFT>
std::error_code ELFFile<ELFT>::createAtomizableSections() {
// Handle: SHT_REL and SHT_RELA sections:
// Increment over the sections, when REL/RELA section types are found add
// the contents to the RelocationReferences map.
// Record the number of relocs to guess at preallocating the buffer.
uint64_t totalRelocs = 0;
for (const Elf_Shdr §ion : _objFile->sections()) {
if (isIgnoredSection(§ion))
continue;
if (isMergeableStringSection(§ion)) {
_mergeStringSections.push_back(§ion);
continue;
}
if (section.sh_type == llvm::ELF::SHT_RELA) {
auto sHdr = _objFile->getSection(section.sh_info);
auto sectionName = _objFile->getSectionName(sHdr);
if (std::error_code ec = sectionName.getError())
return ec;
auto rai(_objFile->begin_rela(§ion));
auto rae(_objFile->end_rela(§ion));
_relocationAddendReferences[*sectionName] = make_range(rai, rae);
totalRelocs += std::distance(rai, rae);
} else if (section.sh_type == llvm::ELF::SHT_REL) {
auto sHdr = _objFile->getSection(section.sh_info);
auto sectionName = _objFile->getSectionName(sHdr);
if (std::error_code ec = sectionName.getError())
return ec;
auto ri(_objFile->begin_rel(§ion));
auto re(_objFile->end_rel(§ion));
_relocationReferences[*sectionName] = make_range(ri, re);
totalRelocs += std::distance(ri, re);
} else {
_sectionSymbols[§ion];
}
}
_references.reserve(totalRelocs);
return std::error_code();
}
template <class ELFT> std::error_code ELFFile<ELFT>::createMergeableAtoms() {
// Divide the section that contains mergeable strings into tokens
// TODO
// a) add resolver support to recognize multibyte chars
// b) Create a separate section chunk to write mergeable atoms
std::vector<MergeString *> tokens;
for (const Elf_Shdr *msi : _mergeStringSections) {
auto sectionName = getSectionName(msi);
if (std::error_code ec = sectionName.getError())
return ec;
auto sectionContents = getSectionContents(msi);
if (std::error_code ec = sectionContents.getError())
return ec;
StringRef secCont(reinterpret_cast<const char *>(sectionContents->begin()),
sectionContents->size());
unsigned int prev = 0;
for (std::size_t i = 0, e = sectionContents->size(); i != e; ++i) {
if ((*sectionContents)[i] == '\0') {
tokens.push_back(new (_readerStorage) MergeString(
prev, secCont.slice(prev, i + 1), msi, *sectionName));
prev = i + 1;
}
}
}
// Create Mergeable atoms
for (const MergeString *tai : tokens) {
ArrayRef<uint8_t> content((const uint8_t *)tai->_string.data(),
tai->_string.size());
ErrorOr<ELFMergeAtom<ELFT> *> mergeAtom =
handleMergeString(tai->_sectionName, tai->_shdr, content, tai->_offset);
(*mergeAtom)->setOrdinal(++_ordinal);
_definedAtoms._atoms.push_back(*mergeAtom);
_mergeAtoms.push_back(*mergeAtom);
}
return std::error_code();
}
template <class ELFT>
std::error_code ELFFile<ELFT>::createSymbolsFromAtomizableSections() {
// Increment over all the symbols collecting atoms and symbol names for
// later use.
auto SymI = _objFile->begin_symbols(), SymE = _objFile->end_symbols();
// Skip over dummy sym.
if (SymI != SymE)
++SymI;
for (; SymI != SymE; ++SymI) {
const Elf_Shdr *section = _objFile->getSection(&*SymI);
auto symbolName = _objFile->getSymbolName(SymI);
if (std::error_code ec = symbolName.getError())
return ec;
if (isAbsoluteSymbol(&*SymI)) {
ErrorOr<ELFAbsoluteAtom<ELFT> *> absAtom =
handleAbsoluteSymbol(*symbolName, &*SymI, (int64_t)getSymbolValue(&*SymI));
_absoluteAtoms._atoms.push_back(*absAtom);
_symbolToAtomMapping.insert(std::make_pair(&*SymI, *absAtom));
} else if (isUndefinedSymbol(&*SymI)) {
if (_useWrap &&
(_wrapSymbolMap.find(*symbolName) != _wrapSymbolMap.end())) {
auto wrapAtom = _wrapSymbolMap.find(*symbolName);
_symbolToAtomMapping.insert(
std::make_pair(&*SymI, wrapAtom->getValue()));
continue;
}
ErrorOr<ELFUndefinedAtom<ELFT> *> undefAtom =
handleUndefinedSymbol(*symbolName, &*SymI);
_undefinedAtoms._atoms.push_back(*undefAtom);
_symbolToAtomMapping.insert(std::make_pair(&*SymI, *undefAtom));
} else if (isCommonSymbol(&*SymI)) {
ErrorOr<ELFCommonAtom<ELFT> *> commonAtom =
handleCommonSymbol(*symbolName, &*SymI);
(*commonAtom)->setOrdinal(++_ordinal);
_definedAtoms._atoms.push_back(*commonAtom);
_symbolToAtomMapping.insert(std::make_pair(&*SymI, *commonAtom));
} else if (isDefinedSymbol(&*SymI)) {
_sectionSymbols[section].push_back(SymI);
} else {
llvm::errs() << "Unable to create atom for: " << *symbolName << "\n";
return llvm::object::object_error::parse_failed;
}
}
return std::error_code();
}
template <class ELFT> std::error_code ELFFile<ELFT>::createAtoms() {
// Holds all the atoms that are part of the section. They are the targets of
// the kindGroupChild reference.
llvm::StringMap<std::vector<ELFDefinedAtom<ELFT> *>> atomsForSection;
// group sections have a mapping of the section header to the
// signature/section.
llvm::DenseMap<const Elf_Shdr *, std::pair<StringRef, StringRef>>
groupSections;
// Contains a list of comdat sections for a group.
llvm::DenseMap<const Elf_Shdr *, std::vector<StringRef>> comdatSections;
for (auto &i : _sectionSymbols) {
const Elf_Shdr *section = i.first;
std::vector<Elf_Sym_Iter> &symbols = i.second;
// Sort symbols by position.
std::stable_sort(symbols.begin(), symbols.end(),
[this](Elf_Sym_Iter a, Elf_Sym_Iter b) {
return getSymbolValue(&*a) < getSymbolValue(&*b);
});
ErrorOr<StringRef> sectionName = this->getSectionName(section);
if (std::error_code ec = sectionName.getError())
return ec;
auto sectionContents = getSectionContents(section);
if (std::error_code ec = sectionContents.getError())
return ec;
bool addAtoms = true;
// A section of type SHT_GROUP defines a grouping of sections. The name of a
// symbol from one of the containing object's symbol tables provides a
// signature
// for the section group. The section header of the SHT_GROUP section
// specifies
// the identifying symbol entry, as described : the sh_link member contains
// the section header index of the symbol table section that contains the
// entry.
// The sh_info member contains the symbol table index of the identifying
// entry.
// The sh_flags member of the section header contains 0. The name of the
// section
// (sh_name) is not specified.
if (isGroupSection(section)) {
const Elf_Word *groupMembers =
reinterpret_cast<const Elf_Word *>(sectionContents->data());
const long count = (section->sh_size) / sizeof(Elf_Word);
for (int i = 1; i < count; i++) {
const Elf_Shdr *sHdr = _objFile->getSection(groupMembers[i]);
ErrorOr<StringRef> sectionName = _objFile->getSectionName(sHdr);
if (std::error_code ec = sectionName.getError())
return ec;
comdatSections[section].push_back(*sectionName);
}
const Elf_Sym *symbol = _objFile->getSymbol(section->sh_info);
const Elf_Shdr *symtab = _objFile->getSection(section->sh_link);
ErrorOr<StringRef> symbolName = _objFile->getSymbolName(symtab, symbol);
if (std::error_code ec = symbolName.getError())
return ec;
groupSections.insert(
std::make_pair(section, std::make_pair(*symbolName, *sectionName)));
continue;
}
if (isGnuLinkOnceSection(*sectionName)) {
groupSections.insert(
std::make_pair(section, std::make_pair(*sectionName, *sectionName)));
addAtoms = false;
}
if (isSectionMemberOfGroup(section))
addAtoms = false;
if (handleSectionWithNoSymbols(section, symbols)) {
ELFDefinedAtom<ELFT> *newAtom =
createSectionAtom(section, *sectionName, *sectionContents);
newAtom->setOrdinal(++_ordinal);
if (addAtoms)
_definedAtoms._atoms.push_back(newAtom);
else
atomsForSection[*sectionName].push_back(newAtom);
continue;
}
ELFDefinedAtom<ELFT> *previousAtom = nullptr;
ELFReference<ELFT> *anonFollowedBy = nullptr;
for (auto si = symbols.begin(), se = symbols.end(); si != se; ++si) {
auto symbol = *si;
StringRef symbolName = "";
if (symbol->getType() != llvm::ELF::STT_SECTION) {
auto symName = _objFile->getSymbolName(symbol);
if (std::error_code ec = symName.getError())
return ec;
symbolName = *symName;
}
uint64_t contentSize = symbolContentSize(
section, &*symbol, (si + 1 == se) ? nullptr : &**(si + 1));
// Check to see if we need to add the FollowOn Reference
ELFReference<ELFT> *followOn = nullptr;
if (previousAtom) {
// Replace the followon atom with the anonymous atom that we created,
// so that the next symbol that we create is a followon from the
// anonymous atom.
if (anonFollowedBy) {
followOn = anonFollowedBy;
} else {
followOn = new (_readerStorage)
ELFReference<ELFT>(lld::Reference::kindLayoutAfter);
previousAtom->addReference(followOn);
}
}
ArrayRef<uint8_t> symbolData((const uint8_t *)sectionContents->data() +
getSymbolValue(&*symbol),
contentSize);
// If the linker finds that a section has global atoms that are in a
// mergeable section, treat them as defined atoms as they shouldn't be
// merged away as well as these symbols have to be part of symbol
// resolution
if (isMergeableStringSection(section)) {
if (symbol->getBinding() == llvm::ELF::STB_GLOBAL) {
auto definedMergeAtom = handleDefinedSymbol(
symbolName, *sectionName, &**si, section, symbolData,
_references.size(), _references.size(), _references);
(*definedMergeAtom)->setOrdinal(++_ordinal);
if (addAtoms)
_definedAtoms._atoms.push_back(*definedMergeAtom);
else
atomsForSection[*sectionName].push_back(*definedMergeAtom);
}
continue;
}
// Don't allocate content to a weak symbol, as they may be merged away.
// Create an anonymous atom to hold the data.
ELFDefinedAtom<ELFT> *anonAtom = nullptr;
anonFollowedBy = nullptr;
if (symbol->getBinding() == llvm::ELF::STB_WEAK) {
// Create anonymous new non-weak ELF symbol that holds the symbol
// data.
auto sym = new (_readerStorage) Elf_Sym(*symbol);
sym->setBinding(llvm::ELF::STB_GLOBAL);
anonAtom = createDefinedAtomAndAssignRelocations(
"", *sectionName, sym, section, symbolData, *sectionContents);
symbolData = ArrayRef<uint8_t>();
// If this is the last atom, let's not create a followon reference.
if (anonAtom && (si + 1) != se) {
anonFollowedBy = new (_readerStorage)
ELFReference<ELFT>(lld::Reference::kindLayoutAfter);
anonAtom->addReference(anonFollowedBy);
}
}
ELFDefinedAtom<ELFT> *newAtom = createDefinedAtomAndAssignRelocations(
symbolName, *sectionName, &*symbol, section, symbolData,
*sectionContents);
newAtom->setOrdinal(++_ordinal);
// If the atom was a weak symbol, let's create a followon reference to
// the anonymous atom that we created.
if (anonAtom)
createEdge(newAtom, anonAtom, Reference::kindLayoutAfter);
if (previousAtom) {
// Set the followon atom to the weak atom that we have created, so
// that they would alias when the file gets written.
followOn->setTarget(anonAtom ? anonAtom : newAtom);
}
// The previous atom is always the atom created before unless the atom
// is a weak atom.
previousAtom = anonAtom ? anonAtom : newAtom;
if (addAtoms)
_definedAtoms._atoms.push_back(newAtom);
else
atomsForSection[*sectionName].push_back(newAtom);
_symbolToAtomMapping.insert(std::make_pair(&*symbol, newAtom));
if (anonAtom) {
anonAtom->setOrdinal(++_ordinal);
if (addAtoms)
_definedAtoms._atoms.push_back(anonAtom);
else
atomsForSection[*sectionName].push_back(anonAtom);
}
}
}
// Iterate over all the group sections to create parent atoms pointing to
// group-child atoms.
for (auto § : groupSections) {
StringRef signature = sect.second.first;
StringRef groupSectionName = sect.second.second;
if (isGnuLinkOnceSection(signature))
handleGnuLinkOnceSection(signature, atomsForSection, sect.first);
else if (isGroupSection(sect.first))
handleSectionGroup(signature, groupSectionName, atomsForSection,
comdatSections, sect.first);
}
updateReferences();
return std::error_code();
}
template <class ELFT>
std::error_code ELFFile<ELFT>::handleGnuLinkOnceSection(
StringRef signature,
llvm::StringMap<std::vector<ELFDefinedAtom<ELFT> *>> &atomsForSection,
const Elf_Shdr *shdr) {
// TODO: Check for errors.
unsigned int referenceStart = _references.size();
std::vector<ELFReference<ELFT> *> refs;
for (auto ha : atomsForSection[signature]) {
_groupChild[ha->symbol()] = std::make_pair(signature, shdr);
ELFReference<ELFT> *ref =
new (_readerStorage) ELFReference<ELFT>(lld::Reference::kindGroupChild);
ref->setTarget(ha);
refs.push_back(ref);
}
atomsForSection[signature].clear();
// Create a gnu linkonce atom.
auto gnuLinkOnceAtom = handleDefinedSymbol(
signature, signature, nullptr, shdr, ArrayRef<uint8_t>(), referenceStart,
_references.size(), _references);
(*gnuLinkOnceAtom)->setOrdinal(++_ordinal);
_definedAtoms._atoms.push_back(*gnuLinkOnceAtom);
for (auto reference : refs)
(*gnuLinkOnceAtom)->addReference(reference);
return std::error_code();
}
template <class ELFT>
std::error_code ELFFile<ELFT>::handleSectionGroup(
StringRef signature, StringRef groupSectionName,
llvm::StringMap<std::vector<ELFDefinedAtom<ELFT> *>> &atomsForSection,
llvm::DenseMap<const Elf_Shdr *, std::vector<StringRef>> &comdatSections,
const Elf_Shdr *shdr) {
// TODO: Check for errors.
unsigned int referenceStart = _references.size();
std::vector<ELFReference<ELFT> *> refs;
auto sectionNamesInGroup = comdatSections[shdr];
for (auto sectionName : sectionNamesInGroup) {
for (auto ha : atomsForSection[sectionName]) {
_groupChild[ha->symbol()] = std::make_pair(signature, shdr);
ELFReference<ELFT> *ref = new (_readerStorage)
ELFReference<ELFT>(lld::Reference::kindGroupChild);
ref->setTarget(ha);
refs.push_back(ref);
}
atomsForSection[sectionName].clear();
}
// Create a gnu linkonce atom.
auto sectionGroupAtom = handleDefinedSymbol(
signature, groupSectionName, nullptr, shdr, ArrayRef<uint8_t>(),
referenceStart, _references.size(), _references);
(*sectionGroupAtom)->setOrdinal(++_ordinal);
_definedAtoms._atoms.push_back(*sectionGroupAtom);
for (auto reference : refs)
(*sectionGroupAtom)->addReference(reference);
return std::error_code();
}
template <class ELFT> std::error_code ELFFile<ELFT>::createAtomsFromContext() {
if (!_useWrap)
return std::error_code();
// Steps :-
// a) Create an undefined atom for the symbol specified by the --wrap option,
// as that
// may be needed to be pulled from an archive.
// b) Create an undefined atom for __wrap_<symbolname>.
// c) All references to the symbol specified by wrap should point to
// __wrap_<symbolname>
// d) All references to __real_symbol should point to the <symbol>
for (auto &wrapsym : _ctx.wrapCalls()) {
StringRef wrapStr = wrapsym.getKey();
// Create a undefined symbol fror the wrap symbol.
UndefinedAtom *wrapSymAtom =
new (_readerStorage) SimpleUndefinedAtom(*this, wrapStr);
StringRef wrapCallSym =
_ctx.allocateString((llvm::Twine("__wrap_") + wrapStr).str());
StringRef realCallSym =
_ctx.allocateString((llvm::Twine("__real_") + wrapStr).str());
UndefinedAtom *wrapCallAtom =
new (_readerStorage) SimpleUndefinedAtom(*this, wrapCallSym);
// Create maps, when there is call to sym, it should point to wrapCallSym.
_wrapSymbolMap.insert(std::make_pair(wrapStr, wrapCallAtom));
// Whenever there is a reference to realCall it should point to the symbol
// created for each wrap usage.
_wrapSymbolMap.insert(std::make_pair(realCallSym, wrapSymAtom));
_undefinedAtoms._atoms.push_back(wrapSymAtom);
_undefinedAtoms._atoms.push_back(wrapCallAtom);
}
return std::error_code();
}
template <class ELFT>
ELFDefinedAtom<ELFT> *ELFFile<ELFT>::createDefinedAtomAndAssignRelocations(
StringRef symbolName, StringRef sectionName, const Elf_Sym *symbol,
const Elf_Shdr *section, ArrayRef<uint8_t> symContent,
ArrayRef<uint8_t> secContent) {
unsigned int referenceStart = _references.size();
// Add Rela (those with r_addend) references:
auto rari = _relocationAddendReferences.find(sectionName);
if (rari != _relocationAddendReferences.end())
createRelocationReferences(symbol, symContent, rari->second);
// Add Rel references.
auto rri = _relocationReferences.find(sectionName);
if (rri != _relocationReferences.end())
createRelocationReferences(symbol, symContent, secContent, rri->second);