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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/ELFLinkingContext.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;
typedef typename llvm::object::ELFFile<ELFT>::Elf_Sym_Iter Elf_Sym_Iter;
// 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;
/// \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
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)
: File(name, kindObject), _ordinal(0), _doStringsMerge(false),
_targetHandler(nullptr) {}
ELFFile(std::unique_ptr<MemoryBuffer> mb, bool atomizeStrings,
TargetHandlerBase *handler, error_code &ec)
: File(mb->getBufferIdentifier(), kindObject), _ordinal(0),
_doStringsMerge(atomizeStrings),
_targetHandler(reinterpret_cast<TargetHandler<ELFT> *>(handler)) {
_objFile.reset(new llvm::object::ELFFile<ELFT>(mb.release(), ec));
if (ec)
return;
// Read input sections from the input file that need to be converted to
// atoms
if (auto err = createAtomizableSections()) {
ec = err;
return;
}
// For mergeable strings, we would need to split the section into various
// atoms
if (auto err = createMergeableAtoms()) {
ec = err;
return;
}
// Create the necessary symbols that are part of the section that we
// created in createAtomizableSections function
if (auto err = createSymbolsFromAtomizableSections()) {
ec = err;
return;
}
// Create the appropriate atoms from the file
if (auto err = createAtoms()) {
ec = err;
return;
}
}
Reference::KindArch 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_PPC:
return Reference::KindArch::PowerPC;
case llvm::ELF::EM_HEXAGON:
return Reference::KindArch::Hexagon;
case llvm::ELF::EM_MIPS:
return Reference::KindArch::Mips;
}
llvm_unreachable("unsupported e_machine value");
}
/// \brief Read input sections and populate necessary data structures
/// to read them later and create atoms
error_code 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 (auto sit = _objFile->begin_sections(),
sie = _objFile->end_sections(); sit != sie; ++sit) {
const Elf_Shdr *section = &*sit;
if (isIgnoredSection(section))
continue;
if (isMergeableStringSection(section)) {
_mergeStringSections.push_back(section);
continue;
}
// Create a sectionSymbols entry for every progbits section.
if ((section->sh_type == llvm::ELF::SHT_PROGBITS) ||
(section->sh_type == llvm::ELF::SHT_INIT_ARRAY) ||
(section->sh_type == llvm::ELF::SHT_FINI_ARRAY))
_sectionSymbols[section];
if (section->sh_type == llvm::ELF::SHT_RELA) {
auto sHdr = _objFile->getSection(section->sh_info);
auto sectionName = _objFile->getSectionName(sHdr);
if (error_code ec = sectionName.getError())
return ec;
auto rai(_objFile->begin_rela(section));
auto rae(_objFile->end_rela(section));
_relocationAddendReferences[*sectionName] = make_range(rai, rae);
totalRelocs += std::distance(rai, rae);
}
if (section->sh_type == llvm::ELF::SHT_REL) {
auto sHdr = _objFile->getSection(section->sh_info);
auto sectionName = _objFile->getSectionName(sHdr);
if (error_code ec = sectionName.getError())
return ec;
auto ri(_objFile->begin_rel(section));
auto re(_objFile->end_rel(section));
_relocationReferences[*sectionName] = make_range(ri, re);
totalRelocs += std::distance(ri, re);
}
}
_references.reserve(totalRelocs);
return error_code::success();
}
/// \brief Create mergeable atoms from sections that have the merge attribute
/// set
error_code 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 = _objFile->getSectionName(msi);
if (error_code ec = sectionName.getError())
return ec;
auto sectionContents = _objFile->getSectionContents(msi);
if (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());
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));
mergeAtom->setOrdinal(++_ordinal);
_definedAtoms._atoms.push_back(mergeAtom);
_mergeAtoms.push_back(mergeAtom);
}
return error_code::success();
}
/// \brief Add the symbols that the sections contain. The symbols will be
/// converted to atoms for
/// Undefined symbols, absolute symbols
error_code 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 (error_code ec = symbolName.getError())
return ec;
if (SymI->st_shndx == llvm::ELF::SHN_ABS) {
// Create an absolute atom.
auto *newAtom = new (_readerStorage)
ELFAbsoluteAtom<ELFT>(*this, *symbolName, &*SymI, SymI->st_value);
_absoluteAtoms._atoms.push_back(newAtom);
_symbolToAtomMapping.insert(std::make_pair(&*SymI, newAtom));
} else if (SymI->st_shndx == llvm::ELF::SHN_UNDEF) {
// Create an undefined atom.
auto *newAtom = new (_readerStorage)
ELFUndefinedAtom<ELFT>(*this, *symbolName, &*SymI);
_undefinedAtoms._atoms.push_back(newAtom);
_symbolToAtomMapping.insert(std::make_pair(&*SymI, newAtom));
} else if (isCommonSymbol(&*SymI)) {
auto *newAtom = new (_readerStorage)
ELFCommonAtom<ELFT>(*this, *symbolName, &*SymI);
newAtom->setOrdinal(++_ordinal);
_definedAtoms._atoms.push_back(newAtom);
_symbolToAtomMapping.insert(std::make_pair(&*SymI, newAtom));
} else {
assert(section && "Symbol not defined in a section!");
// This is actually a defined symbol. Add it to its section's list of
// symbols.
if (SymI->getType() == llvm::ELF::STT_NOTYPE ||
SymI->getType() == llvm::ELF::STT_OBJECT ||
SymI->getType() == llvm::ELF::STT_FUNC ||
SymI->getType() == llvm::ELF::STT_GNU_IFUNC ||
SymI->getType() == llvm::ELF::STT_SECTION ||
SymI->getType() == llvm::ELF::STT_FILE ||
SymI->getType() == llvm::ELF::STT_TLS) {
_sectionSymbols[section].push_back(SymI);
} else {
llvm::errs() << "Unable to create atom for: " << *symbolName << "\n";
return llvm::object::object_error::parse_failed;
}
}
}
return error_code::success();
}
/// \brief Create individual atoms
error_code createAtoms() {
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(),
[](Elf_Sym_Iter A, Elf_Sym_Iter B) {
return A->st_value < B->st_value;
});
auto sectionName = section ? _objFile->getSectionName(section)
: StringRef();
if (error_code ec = sectionName.getError())
return ec;
auto sectionContents =
(section && section->sh_type != llvm::ELF::SHT_NOBITS)
? _objFile->getSectionContents(section)
: ArrayRef<uint8_t>();
if (error_code ec = sectionContents.getError())
return ec;
StringRef secCont(
reinterpret_cast<const char *>(sectionContents->begin()),
sectionContents->size());
// If the section has no symbols, create a custom atom for it.
if (section && section->sh_type == llvm::ELF::SHT_PROGBITS &&
symbols.empty()) {
ELFDefinedAtom<ELFT> *newAtom = createSectionAtom(
section, *sectionName, secCont);
_definedAtoms._atoms.push_back(newAtom);
newAtom->setOrdinal(++_ordinal);
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 (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(
(uint8_t *)sectionContents->data() + symbol->st_value, 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 = new (_readerStorage) ELFDefinedAtom<ELFT>(
*this, symbolName, *sectionName, &**si, section, symbolData,
_references.size(), _references.size(), _references);
_definedAtoms._atoms.push_back(definedMergeAtom);
definedMergeAtom->setOrdinal(++_ordinal);
}
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 && contentSize != 0) {
// 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);
anonAtom->setOrdinal(++_ordinal);
symbolData = ArrayRef<uint8_t>();
if (previousAtom)
createEdge(anonAtom, previousAtom,
lld::Reference::kindLayoutBefore);
// 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);
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);
// Add a preceded-by reference only if the current atom is not a weak
// atom.
if (symbol->getBinding() != llvm::ELF::STB_WEAK)
createEdge(newAtom, previousAtom,
lld::Reference::kindLayoutBefore);
}
// The previous atom is always the atom created before unless the atom
// is a weak atom.
previousAtom = anonAtom ? anonAtom : newAtom;
_definedAtoms._atoms.push_back(newAtom);
_symbolToAtomMapping.insert(std::make_pair(&*symbol, newAtom));
if (anonAtom)
_definedAtoms._atoms.push_back(anonAtom);
}
}
updateReferences();
return error_code::success();
}
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;
}
TargetHandler<ELFT> *targetHandler() const { return _targetHandler; }
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 = _relocationAddendReferences.find(sectionName);
if (rari != _relocationAddendReferences.end()) {
for (const Elf_Rela &rai : rari->second) {
if (rai.r_offset < symbol->st_value ||
symbol->st_value + content.size() <= rai.r_offset)
continue;
bool isMips64EL = _objFile->isMips64EL();
uint32_t symbolIndex = rai.getSymbol(isMips64EL);
auto *ERef = new (_readerStorage) ELFReference<ELFT>(
&rai, rai.r_offset - symbol->st_value, kindArch(),
rai.getType(isMips64EL), symbolIndex);
_references.push_back(ERef);
}
}
// Add Rel references.
auto rri = _relocationReferences.find(sectionName);
if (rri != _relocationReferences.end()) {
for (const Elf_Rel &ri : rri->second) {
if (ri.r_offset < symbol->st_value ||
symbol->st_value + content.size() <= ri.r_offset)
continue;
bool isMips64EL = _objFile->isMips64EL();
uint32_t symbolIndex = ri.getSymbol(isMips64EL);
auto *ERef = new (_readerStorage) ELFReference<ELFT>(
&ri, ri.r_offset - symbol->st_value, kindArch(),
ri.getType(isMips64EL), symbolIndex);
// Read the addend from the section contents
// TODO : We should move the way lld reads relocations totally from
// ELFFile
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);
}
/// \brief After all the Atoms and References are created, update each
/// Reference's target with the Atom pointer it refers to.
void updateReferences() {
/// cached value of target relocation handler
assert(_targetHandler);
const TargetRelocationHandler<ELFT> &targetRelocationHandler =
_targetHandler->getRelocationHandler();
for (auto &ri : _references) {
if (ri->kindNamespace() == lld::Reference::KindNamespace::ELF) {
const Elf_Sym *symbol = _objFile->getSymbol(ri->targetSymbolIndex());
const Elf_Shdr *shdr = _objFile->getSection(symbol);
// If the atom is not in mergeable string section, the target atom is
// simply that atom.
if (!isMergeableStringSection(shdr)) {
ri->setTarget(findAtom(symbol));
continue;
}
// If the target atom is mergeable string atom, the atom might have been
// merged with other atom having the same contents. Try to find the
// merged one if that's the case.
int64_t relocAddend = targetRelocationHandler.relocAddend(*ri);
uint64_t addend = ri->addend() + relocAddend;
const MergeSectionKey ms(shdr, addend);
auto msec = _mergedSectionMap.find(ms);
if (msec != _mergedSectionMap.end()) {
ri->setTarget(msec->second);
continue;
}
// The target atom was not merged. Mergeable atoms are not in
// _symbolToAtomMapping, so we cannot find it by calling findAtom(). We
// instead call findMergeAtom().
if (symbol->getType() != llvm::ELF::STT_SECTION)
addend = symbol->st_value + addend;
ELFMergeAtom<ELFT> *mergedAtom = findMergeAtom(shdr, addend);
ri->setOffset(addend - mergedAtom->offset());
ri->setAddend(0);
ri->setTarget(mergedAtom);
}
}
}
/// \brief Return true if the symbol is corresponding to an architecture
/// specific section. We will let the TargetHandler handle such atoms.
inline bool isTargetSpecificAtom(const Elf_Shdr *shdr,
const Elf_Sym *sym) {
return ((shdr && (shdr->sh_flags & llvm::ELF::SHF_MASKPROC)) ||
(sym->st_shndx >= llvm::ELF::SHN_LOPROC &&
sym->st_shndx <= llvm::ELF::SHN_HIPROC));
}
/// \brief Do we want to ignore the section. Ignored sections are
/// not processed to create atoms
bool isIgnoredSection(const Elf_Shdr *section) {
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:
return true;
default:
break;
}
return false;
}
/// \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) {
if (_doStringsMerge && section) {
int64_t sectionFlags = section->sh_flags;
sectionFlags &= ~llvm::ELF::SHF_ALLOC;
// Mergeable string sections have both SHF_MERGE and SHF_STRINGS flags
// set. sh_entsize is the size of each character which is normally 1.
if ((section->sh_entsize < 2) &&
(sectionFlags == (llvm::ELF::SHF_MERGE | llvm::ELF::SHF_STRINGS))) {
return true;
}
}
return false;
}
/// \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,
StringRef sectionContents) {
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());
auto *newAtom = new (_readerStorage) ELFDefinedAtom<ELFT>(
*this, "", sectionName, sym, section, content, 0, 0, _references);
newAtom->setOrdinal(++_ordinal);
return newAtom;
}
/// 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.)
bool isCommonSymbol(const Elf_Sym *symbol) {
// This method handles only architecture independent stuffs, and don't know
// whether an architecture dependent section is for common symbols or
// not. Let the TargetHandler to make a decision if that's the case.
if (isTargetSpecificAtom(nullptr, symbol)) {
assert(_targetHandler);
TargetAtomHandler<ELFT> &atomHandler =
_targetHandler->targetAtomHandler();
return atomHandler.getType(symbol) == llvm::ELF::STT_COMMON;
}
return symbol->getType() == llvm::ELF::STT_COMMON ||
symbol->st_shndx == llvm::ELF::SHN_COMMON;
}
/// 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) {
// if this is the last symbol, take up the remaining data.
return nextSymbol
? nextSymbol->st_value - symbol->st_value
: section->sh_size - symbol->st_value;
}
void createEdge(ELFDefinedAtom<ELFT> *from, ELFDefinedAtom<ELFT> *to,
uint32_t edgeKind) {
auto reference = new (_readerStorage) ELFReference<ELFT>(edgeKind);
reference->setTarget(to);
from->addReference(reference);
}
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. -- .rel or .rela is prepended to create
/// the SHT_REL(A) section name.
std::unordered_map<
StringRef,
range<typename llvm::object::ELFFile<ELFT>::Elf_Rela_Iter> >
_relocationAddendReferences;
MergedSectionMapT _mergedSectionMap;
std::unordered_map<
StringRef,
range<typename llvm::object::ELFFile<ELFT>::Elf_Rel_Iter> >
_relocationReferences;
std::vector<ELFReference<ELFT> *> _references;
llvm::DenseMap<const Elf_Sym *, Atom *> _symbolToAtomMapping;
/// \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
std::map<const Elf_Shdr *, std::vector<Elf_Sym_Iter>> _sectionSymbols;
/// \brief Sections that have merge string property
std::vector<const Elf_Shdr *> _mergeStringSections;
int64_t _ordinal;
/// \brief the cached options relevant while reading the ELF File
bool _doStringsMerge;
TargetHandler<ELFT> *_targetHandler;
};
/// \brief All atoms are owned by a File. To add linker specific atoms
/// the atoms need to be inserted to a file called (CRuntimeFile) 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 CRuntimeFile : public ELFFile<ELFT> {
public:
typedef llvm::object::Elf_Sym_Impl<ELFT> Elf_Sym;
CRuntimeFile(const ELFLinkingContext &context, StringRef name = "C runtime")
: ELFFile<ELFT>(name) {}
/// \brief add a global absolute atom
virtual Atom *addAbsoluteAtom(StringRef symbolName) {
assert(!symbolName.empty() && "AbsoluteAtoms must have a name");
Elf_Sym *symbol = new (_allocator) 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->st_other = llvm::ELF::STV_DEFAULT;
symbol->st_size = 0;
auto *newAtom =
new (_allocator) ELFAbsoluteAtom<ELFT>(*this, symbolName, symbol, -1);
_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 (_allocator) Elf_Sym;
symbol->st_name = 0;
symbol->st_value = 0;
symbol->st_shndx = llvm::ELF::SHN_UNDEF;
symbol->st_other = llvm::ELF::STV_DEFAULT;
symbol->st_size = 0;
auto *newAtom =
new (_allocator) ELFUndefinedAtom<ELFT>(*this, symbolName, symbol);
_undefinedAtoms._atoms.push_back(newAtom);
return newAtom;
}
virtual const File::atom_collection<DefinedAtom> &defined() const {
return _definedAtoms;
}
virtual const File::atom_collection<UndefinedAtom> &undefined() const {
return _undefinedAtoms;
}
virtual const File::atom_collection<SharedLibraryAtom> &
sharedLibrary() const {
return _sharedLibraryAtoms;
}
virtual const File::atom_collection<AbsoluteAtom> &absolute() const {
return _absoluteAtoms;
}
// cannot add atoms to C Runtime file
virtual void addAtom(const Atom &) {
llvm_unreachable("cannot add atoms to Runtime files");
}
protected:
llvm::BumpPtrAllocator _allocator;
File::atom_collection_vector<DefinedAtom> _definedAtoms;
File::atom_collection_vector<UndefinedAtom> _undefinedAtoms;
File::atom_collection_vector<SharedLibraryAtom> _sharedLibraryAtoms;
File::atom_collection_vector<AbsoluteAtom> _absoluteAtoms;
};
} // end namespace elf
} // end namespace lld
#endif
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