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llvm-project/lld/lib/ReaderWriter/ELF/File.h

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//===- lib/ReaderWriter/ELF/File.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 "lld/Core/File.h"
#include "lld/Core/Reference.h"
#include "lld/ReaderWriter/ELFTargetInfo.h"
#include "lld/ReaderWriter/ReaderArchive.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Object/ELF.h"
#include "llvm/Object/ObjectFile.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/ELF.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/ErrorOr.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/Memory.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Support/system_error.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;
// 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, int32_t offset)
: _shdr(shdr), _offset(offset) {
}
// Data members
const Elf_Shdr *_shdr;
int32_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(int32_t offset, StringRef str, const Elf_Shdr *shdr,
StringRef sectionName)
: _offset(offset), _string(str), _shdr(shdr),
_sectionName(sectionName) {
}
// the offset of this atom
int32_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;
typedef typename MergeAtomsT::iterator MergeAtomsIter;
/// \brief find a mergeAtom given a start offset
struct FindByOffset {
const Elf_Shdr *_shdr;
uint64_t _offset;
FindByOffset(const Elf_Shdr *shdr, uint64_t offset)
: _shdr(shdr), _offset(offset) {
}
bool operator()(const ELFMergeAtom<ELFT> *a) {
uint64_t off = a->offset();
return (_shdr->sh_name == a->section()) &&
((_offset >= off) && (_offset <= off + a->size()));
}
};
/// \brief find a merge atom given a offset
MergeAtomsIter findMergeAtom(const Elf_Shdr *shdr, uint64_t offset) {
return std::find_if(_mergeAtoms.begin(), _mergeAtoms.end(),
FindByOffset(shdr, offset));
}
typedef std::unordered_map<MergeSectionKey, DefinedAtom *, MergeSectionEq,
MergeSectionEq> MergedSectionMapT;
typedef typename MergedSectionMapT::iterator MergedSectionMapIterT;
public:
ELFFile(const ELFTargetInfo &ti, StringRef name)
: File(name), _elfTargetInfo(ti) {
}
ELFFile(const ELFTargetInfo &ti, std::unique_ptr<llvm::MemoryBuffer> MB,
llvm::error_code &EC)
: File(MB->getBufferIdentifier()), _elfTargetInfo(ti) {
static uint32_t lastOrdinal = 0;
_ordinal = lastOrdinal++;
llvm::OwningPtr<llvm::object::Binary> binaryFile;
EC = createBinary(MB.release(), binaryFile);
if (EC)
return;
// Point Obj to correct class and bitwidth ELF object
_objFile.reset(
llvm::dyn_cast<llvm::object::ELFObjectFile<ELFT> >(binaryFile.get()));
if (!_objFile) {
EC = make_error_code(llvm::object::object_error::invalid_file_type);
return;
}
binaryFile.take();
std::map<const Elf_Shdr *, std::vector<const Elf_Sym *> > sectionSymbols;
// Sections that have merge string property
std::vector<const Elf_Shdr *> mergeStringSections;
bool doStringsMerge = _elfTargetInfo.getLinkerOptions()._mergeCommonStrings;
// 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.
llvm::object::section_iterator sit(_objFile->begin_sections());
llvm::object::section_iterator sie(_objFile->end_sections());
for (; sit != sie; sit.increment(EC)) {
if (EC)
return;
const Elf_Shdr *section = _objFile->getElfSection(sit);
switch (section->sh_type) {
case llvm::ELF::SHT_NOTE:
case llvm::ELF::SHT_STRTAB:
case llvm::ELF::SHT_SYMTAB:
case llvm::ELF::SHT_SYMTAB_SHNDX:
continue;
}
if (section->sh_size == 0)
continue;
if (doStringsMerge) {
int64_t sectionFlags = section->sh_flags;
sectionFlags &= ~llvm::ELF::SHF_ALLOC;
// If the section have mergeable strings, the linker would
// need to split the section into multiple atoms and mark them
// mergeByContent
if ((section->sh_entsize < 2) &&
(sectionFlags == (llvm::ELF::SHF_MERGE | llvm::ELF::SHF_STRINGS))) {
mergeStringSections.push_back(section);
continue;
}
}
// Create a sectionSymbols entry for every progbits section.
if (section->sh_type == llvm::ELF::SHT_PROGBITS)
sectionSymbols[section];
if (section->sh_type == llvm::ELF::SHT_RELA) {
StringRef sectionName;
if ((EC = _objFile->getSectionName(section, sectionName)))
return;
// Get rid of the leading .rela so Atoms can use their own section
// name to find the relocs.
sectionName = sectionName.drop_front(5);
auto rai(_objFile->beginELFRela(section));
auto rae(_objFile->endELFRela(section));
auto &Ref = _relocationAddendRefences[sectionName];
for (; rai != rae; ++rai) {
Ref.push_back(&*rai);
}
}
if (section->sh_type == llvm::ELF::SHT_REL) {
StringRef sectionName;
if ((EC = _objFile->getSectionName(section, sectionName)))
return;
// Get rid of the leading .rel so Atoms can use their own section
// name to find the relocs.
sectionName = sectionName.drop_front(4);
auto ri(_objFile->beginELFRel(section));
auto re(_objFile->endELFRel(section));
auto &Ref = _relocationReferences[sectionName];
for (; ri != re; ++ri) {
Ref.push_back(&*ri);
}
}
}
// Divide the section that contains mergeable strings into tokens
// TODO
// a) add resolver support to recognize multibyte chars
// b) Create a seperate section chunk to write mergeable atoms
std::vector<MergeString *> tokens;
for (auto msi : mergeStringSections) {
StringRef sectionContents;
StringRef sectionName;
if ((EC = _objFile->getSectionName(msi, sectionName)))
return;
if ((EC = _objFile->getSectionContents(msi, sectionContents)))
return;
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, sectionContents.slice(prev, i + 1), msi, sectionName));
prev = i + 1;
}
}
}
// Create Mergeable atoms
for (auto tai : tokens) {
ArrayRef<uint8_t> content((const uint8_t *)tai->_string.data(),
tai->_string.size());
ELFMergeAtom<ELFT> *mergeAtom = new (_readerStorage) ELFMergeAtom<ELFT>(
*this, tai->_sectionName, tai->_shdr, content, tai->_offset);
const MergeSectionKey mergedSectionKey(tai->_shdr, tai->_offset);
if (_mergedSectionMap.find(mergedSectionKey) == _mergedSectionMap.end())
_mergedSectionMap.insert(std::make_pair(mergedSectionKey, mergeAtom));
_definedAtoms._atoms.push_back(mergeAtom);
_mergeAtoms.push_back(mergeAtom);
}
// Increment over all the symbols collecting atoms and symbol names for
// later use.
llvm::object::symbol_iterator it(_objFile->begin_symbols());
llvm::object::symbol_iterator ie(_objFile->end_symbols());
for (; it != ie; it.increment(EC)) {
if (EC)
return;
if ((EC = it->getSection(sit)))
return;
const Elf_Shdr *section = _objFile->getElfSection(sit);
const Elf_Sym *symbol = _objFile->getElfSymbol(it);
// If its a merge section, the atoms have already
// been created, lets not create the atoms again
if (doStringsMerge) {
int64_t sectionFlags = section->sh_flags;
sectionFlags &= ~llvm::ELF::SHF_ALLOC;
if ((section->sh_entsize < 2) &&
(sectionFlags == (llvm::ELF::SHF_MERGE | llvm::ELF::SHF_STRINGS))) {
continue;
}
}
StringRef symbolName;
if ((EC = _objFile->getSymbolName(section, symbol, symbolName)))
return;
if (symbol->st_shndx == llvm::ELF::SHN_ABS) {
// Create an absolute atom.
auto *newAtom = new (_readerStorage)
ELFAbsoluteAtom<ELFT>(*this, symbolName, symbol, symbol->st_value);
_absoluteAtoms._atoms.push_back(newAtom);
_symbolToAtomMapping.insert(std::make_pair(symbol, newAtom));
} else if (symbol->st_shndx == llvm::ELF::SHN_UNDEF) {
// Create an undefined atom.
auto *newAtom = new (_readerStorage)
ELFUndefinedAtom<ELFT>(*this, symbolName, symbol);
_undefinedAtoms._atoms.push_back(newAtom);
_symbolToAtomMapping.insert(std::make_pair(symbol, newAtom));
} else {
// This is actually a defined symbol. Add it to its section's list of
// symbols.
if (symbol->getType() == llvm::ELF::STT_NOTYPE || symbol->getType() ==
llvm::ELF::STT_OBJECT || symbol->getType() == llvm::ELF::STT_FUNC ||
symbol->getType() == llvm::ELF::STT_GNU_IFUNC ||
symbol->getType() == llvm::ELF::STT_SECTION || symbol->getType() ==
llvm::ELF::STT_FILE || symbol->getType() == llvm::ELF::STT_TLS ||
symbol->getType() == llvm::ELF::STT_COMMON ||
symbol->st_shndx == llvm::ELF::SHN_COMMON) {
sectionSymbols[section].push_back(symbol);
} else {
llvm::errs() << "Unable to create atom for: " << symbolName << "\n";
EC = llvm::object::object_error::parse_failed;
return;
}
}
}
for (auto &i : sectionSymbols) {
auto &symbols = i.second;
// Sort symbols by position.
std::stable_sort(symbols.begin(), symbols.end(),
[](const Elf_Sym * A, const Elf_Sym * B) {
return A->st_value < B->st_value;
});
StringRef sectionContents;
if ((EC = _objFile->getSectionContents(i.first, sectionContents)))
return;
StringRef sectionName;
if ((EC = _objFile->getSectionName(i.first, sectionName)))
return;
// If the section has no symbols, create a custom atom for it.
if (i.first->sh_type == llvm::ELF::SHT_PROGBITS && symbols.empty() &&
!sectionContents.empty()) {
Elf_Sym *sym = new (_readerStorage) Elf_Sym;
sym->st_name = 0;
sym->setBindingAndType(llvm::ELF::STB_LOCAL, llvm::ELF::STT_SECTION);
sym->st_other = 0;
sym->st_shndx = 0;
sym->st_value = 0;
sym->st_size = 0;
ArrayRef<uint8_t> content((const uint8_t *)sectionContents.data(),
sectionContents.size());
_definedAtoms._atoms.push_back(
new (_readerStorage)
ELFDefinedAtom<ELFT>(*this, sectionName, sectionName, sym, i.first,
content, 0, 0, _references));
}
ELFDefinedAtom<ELFT> *previous_atom = nullptr;
// i.first is the section the symbol lives in
for (auto si = symbols.begin(), se = symbols.end(); si != se; ++si) {
StringRef symbolName;
if ((EC = _objFile->getSymbolName(i.first, *si, symbolName)))
return;
bool isCommon = (*si)->getType() == llvm::ELF::STT_COMMON ||
(*si)->st_shndx == llvm::ELF::SHN_COMMON;
DefinedAtom::ContentType c;
if (((*si)->st_shndx >= llvm::ELF::SHN_LOPROC) &&
((*si)->st_shndx <= llvm::ELF::SHN_HIPROC)) {
TargetHandler<ELFT> &TargetHandler =
_elfTargetInfo.getTargetHandler<ELFT>();
TargetAtomHandler<ELFT> &elfAtomHandler =
TargetHandler.targetAtomHandler();
c = elfAtomHandler.contentType(*si);
if (c == DefinedAtom::typeZeroFill ||
c == DefinedAtom::typeTLVInitialZeroFill)
isCommon = true;
}
// Get the symbol's content:
uint64_t contentSize;
if (si + 1 == se) {
// if this is the last symbol, take up the remaining data.
contentSize = isCommon ? 0 : i.first->sh_size - (*si)->st_value;
} else {
contentSize = isCommon ? 0 : (*(si + 1))->st_value - (*si)->st_value;
}
// 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;
if ((*si)->getBinding() == llvm::ELF::STB_WEAK && contentSize != 0) {
// Create a new non-weak ELF symbol.
auto sym = new (_readerStorage) Elf_Sym;
*sym = **si;
sym->setBinding(llvm::ELF::STB_GLOBAL);
anonAtom = createDefinedAtomAndAssignRelocations(
"", sectionName, sym, i.first,
ArrayRef<uint8_t>((uint8_t *)sectionContents.data() +
(*si)->st_value, contentSize));
contentSize = 0;
}
ArrayRef<uint8_t> symbolData = ArrayRef<uint8_t>(
(uint8_t *)sectionContents.data() + (*si)->st_value, contentSize);
// Check to see if we need to add the FollowOn Reference
// We dont want to do for symbols that are
// a) common symbols
// so, lets add a follow-on reference from the previous atom to the
// current atom as well as lets add a preceded-by reference from the
// current atom to the previous atom, so that the previous atom
// is not removed in any case
ELFReference<ELFT> *followOn = nullptr;
if (!isCommon && previous_atom) {
followOn = new (_readerStorage)
ELFReference<ELFT>(lld::Reference::kindLayoutAfter);
previous_atom->addReference(followOn);
}
auto newAtom = createDefinedAtomAndAssignRelocations(
symbolName, sectionName, *si, i.first, symbolData);
// If we are inserting a followOn reference, lets add a precededBy
// reference too
if (followOn) {
ELFReference<ELFT> *precededby = nullptr;
followOn->setTarget(newAtom);
// Add a preceded by reference only if the current atom is not a
// weak atom
if ((*si)->getBinding() != llvm::ELF::STB_WEAK) {
precededby = new (_readerStorage)
ELFReference<ELFT>(lld::Reference::kindLayoutBefore);
precededby->setTarget(previous_atom);
newAtom->addReference(precededby);
}
}
// The previous atom is always the atom created before unless
// the atom is a weak atom
if ((*si)->getBinding() != llvm::ELF::STB_WEAK)
previous_atom = newAtom;
_definedAtoms._atoms.push_back(newAtom);
_symbolToAtomMapping.insert(std::make_pair((*si), newAtom));
if (anonAtom)
_definedAtoms._atoms.push_back(anonAtom);
}
}
// All the Atoms and References are created. Now update each Reference's
// target with the Atom pointer it refers to.
for (auto &ri : _references) {
if (ri->kind() >= lld::Reference::kindTargetLow) {
const Elf_Sym *Symbol = _objFile->getElfSymbol(ri->targetSymbolIndex());
const Elf_Shdr *shdr = _objFile->getSection(Symbol);
int64_t sectionFlags = 0;
if (shdr)
sectionFlags = shdr->sh_flags;
sectionFlags &= ~llvm::ELF::SHF_ALLOC;
// If the section has mergeable strings, then make the relocation
// refer to the MergeAtom to allow deduping
if (doStringsMerge && shdr && (shdr->sh_entsize < 2) &&
(sectionFlags == (llvm::ELF::SHF_MERGE | llvm::ELF::SHF_STRINGS))) {
const MergeSectionKey ms(shdr, ri->addend());
if (_mergedSectionMap.find(ms) == _mergedSectionMap.end()) {
uint64_t addend = ri->addend();
if (Symbol->getType() != llvm::ELF::STT_SECTION)
addend = Symbol->st_value + ri->addend();
MergeAtomsIter mai = findMergeAtom(shdr, addend);
if (mai != _mergeAtoms.end()) {
ri->setOffset(addend - ((*mai)->offset()));
ri->setAddend(0);
ri->setTarget(*mai);
} // check
else
llvm_unreachable("unable to find a merge atom");
} // find
else
ri->setTarget(_mergedSectionMap[ms]);
} else
ri->setTarget(findAtom(Symbol));
}
}
}
virtual const atom_collection<DefinedAtom> &defined() const {
return _definedAtoms;
}
virtual const atom_collection<UndefinedAtom> &undefined() const {
return _undefinedAtoms;
}
virtual const atom_collection<SharedLibraryAtom> &sharedLibrary() const {
return _sharedLibraryAtoms;
}
virtual const atom_collection<AbsoluteAtom> &absolute() const {
return _absoluteAtoms;
}
virtual const ELFTargetInfo &getTargetInfo() const { return _elfTargetInfo; }
Atom *findAtom(const Elf_Sym *symbol) {
return _symbolToAtomMapping.lookup(symbol);
}
private:
ELFDefinedAtom<ELFT> *createDefinedAtomAndAssignRelocations(
StringRef symbolName, StringRef sectionName, const Elf_Sym *symbol,
const Elf_Shdr *section, ArrayRef<uint8_t> content) {
unsigned int referenceStart = _references.size();
// Only relocations that are inside the domain of the atom are added.
// Add Rela (those with r_addend) references:
auto rari = _relocationAddendRefences.find(sectionName);
auto rri = _relocationReferences.find(sectionName);
unsigned refs = 0;
if (rari != _relocationAddendRefences.end())
refs += rari->second.size();
if (rri != _relocationReferences.end())
refs += rri->second.size();
_references.reserve(_references.size() + refs);
if (rari != _relocationAddendRefences.end())
for (auto &rai : rari->second) {
if (!((rai->r_offset >= symbol->st_value) &&
(rai->r_offset < symbol->st_value + content.size())))
continue;
auto *ERef = new (_readerStorage)
ELFReference<ELFT>(rai, rai->r_offset - symbol->st_value, nullptr);
_references.push_back(ERef);
}
// Add Rel references.
if (rri != _relocationReferences.end())
for (auto &ri : rri->second) {
if ((ri->r_offset >= symbol->st_value) &&
(ri->r_offset < symbol->st_value + content.size())) {
auto *ERef = new (_readerStorage)
ELFReference<ELFT>(ri, ri->r_offset - symbol->st_value, nullptr);
// Read the addend from the section contents
// TODO : We should move the way lld reads relocations totally from
// ELFObjectFile
int32_t addend = *(content.data() + ri->r_offset - symbol->st_value);
ERef->setAddend(addend);
_references.push_back(ERef);
}
}
// Create the DefinedAtom and add it to the list of DefinedAtoms.
return new (_readerStorage) ELFDefinedAtom<
ELFT>(*this, symbolName, sectionName, symbol, section, content,
referenceStart, _references.size(), _references);
}
std::unique_ptr<llvm::object::ELFObjectFile<ELFT> > _objFile;
atom_collection_vector<DefinedAtom> _definedAtoms;
atom_collection_vector<UndefinedAtom> _undefinedAtoms;
atom_collection_vector<SharedLibraryAtom> _sharedLibraryAtoms;
atom_collection_vector<AbsoluteAtom> _absoluteAtoms;
/// \brief _relocationAddendRefences 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. -- .rel or .rela is prepended to create
/// the SHT_REL(A) section name.
std::unordered_map<StringRef,
std::vector<const Elf_Rela *> > _relocationAddendRefences;
MergedSectionMapT _mergedSectionMap;
std::unordered_map<StringRef,
std::vector<const Elf_Rel *> > _relocationReferences;
std::vector<ELFReference<ELFT> *> _references;
llvm::DenseMap<const Elf_Sym *, Atom *> _symbolToAtomMapping;
llvm::BumpPtrAllocator _readerStorage;
const ELFTargetInfo &_elfTargetInfo;
MergeAtomsT _mergeAtoms;
};
} // end namespace elf
} // end namespace lld
#endif
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