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

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//===- lib/ReaderWriter/ELF/DefaultLayout.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_DEFAULT_LAYOUT_H
#define LLD_READER_WRITER_ELF_DEFAULT_LAYOUT_H
#include "Chunk.h"
#include "HeaderChunks.h"
#include "Layout.h"
#include "SectionChunks.h"
#include "SegmentChunks.h"
#include "lld/Core/Instrumentation.h"
#include "lld/Core/STDExtras.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/Hashing.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/StringSwitch.h"
#include "llvm/Support/Errc.h"
#include "llvm/Support/Format.h"
#include <map>
#include <memory>
#include <tuple>
#include <unordered_map>
namespace lld {
namespace elf {
/// \brief The DefaultLayout class is used by the Writer to arrange
/// sections and segments in the order determined by the target ELF
/// format. The writer creates a single instance of the DefaultLayout
/// class
template<class ELFT>
class DefaultLayout : public Layout {
public:
// The order in which the sections appear in the output file
// If its determined, that the layout needs to change
// just changing the order of enumerations would essentially
// change the layout in the output file
// Change the enumerations so that Target can override and stick
// a section anywhere it wants to
enum DefaultSectionOrder {
ORDER_NOT_DEFINED = 0,
ORDER_INTERP = 10,
ORDER_RO_NOTE = 15,
ORDER_HASH = 30,
ORDER_DYNAMIC_SYMBOLS = 40,
ORDER_DYNAMIC_STRINGS = 50,
ORDER_DYNAMIC_RELOCS = 52,
ORDER_DYNAMIC_PLT_RELOCS = 54,
ORDER_INIT = 60,
ORDER_PLT = 70,
ORDER_TEXT = 80,
ORDER_FINI = 90,
ORDER_REL = 95,
ORDER_RODATA = 100,
ORDER_EH_FRAME = 110,
ORDER_EH_FRAMEHDR = 120,
ORDER_TDATA = 124,
ORDER_TBSS = 128,
ORDER_CTORS = 130,
ORDER_DTORS = 140,
ORDER_INIT_ARRAY = 150,
ORDER_FINI_ARRAY = 160,
ORDER_DYNAMIC = 170,
ORDER_GOT = 180,
ORDER_GOT_PLT = 190,
ORDER_DATA = 200,
ORDER_RW_NOTE = 205,
ORDER_BSS = 210,
ORDER_NOALLOC = 215,
ORDER_OTHER = 220,
ORDER_SECTION_STRINGS = 230,
ORDER_SYMBOL_TABLE = 240,
ORDER_STRING_TABLE = 250,
ORDER_SECTION_HEADERS = 260
};
public:
// The Key used for creating Sections
// The sections are created using
// SectionName, contentPermissions
struct SectionKey {
SectionKey(StringRef name, DefinedAtom::ContentPermissions perm)
: _name(name), _perm(perm) {
}
// Data members
StringRef _name;
DefinedAtom::ContentPermissions _perm;
};
struct SectionKeyHash {
int64_t operator()(const SectionKey &k) const {
return llvm::hash_combine(k._name, k._perm);
}
};
struct SectionKeyEq {
bool operator()(const SectionKey &lhs, const SectionKey &rhs) const {
return ((lhs._name == rhs._name) && (lhs._perm == rhs._perm));
}
};
typedef typename std::vector<Chunk<ELFT> *>::iterator ChunkIter;
typedef typename std::vector<Segment<ELFT> *>::iterator SegmentIter;
// The additional segments are used to figure out
// if there is a segment by that type already created
// For example : PT_TLS, we have two sections .tdata/.tbss
// that are part of PT_TLS, we need to create this additional
// segment only once
typedef std::pair<int64_t, int64_t> AdditionalSegmentKey;
// The segments are created using
// SegmentName, Segment flags
typedef std::pair<StringRef, int64_t> SegmentKey;
// HashKey for the Segment
class SegmentHashKey {
public:
int64_t operator() (const SegmentKey &k) const {
// k.first = SegmentName
// k.second = SegmentFlags
return llvm::hash_combine(k.first, k.second);
}
};
class AdditionalSegmentHashKey {
public:
int64_t operator() (int64_t segmentType, int64_t segmentFlag) const {
// k.first = SegmentName
// k.second = SegmentFlags
return llvm::hash_combine(segmentType, segmentFlag);
}
};
// Merged Sections contain the map of Sectionnames to a vector of sections,
// that have been merged to form a single section
typedef std::map<StringRef, MergedSections<ELFT> *> MergedSectionMapT;
typedef typename std::vector<MergedSections<ELFT> *>::iterator
MergedSectionIter;
typedef std::unordered_map<SectionKey, AtomSection<ELFT> *, SectionKeyHash,
SectionKeyEq> SectionMapT;
typedef std::map<AdditionalSegmentKey, Segment<ELFT> *> AdditionalSegmentMapT;
typedef std::unordered_map<SegmentKey, Segment<ELFT> *, SegmentHashKey>
SegmentMapT;
/// \brief find a absolute atom pair given a absolute atom name
struct FindByName {
const std::string _name;
FindByName(StringRef name) : _name(name) {}
bool operator()(const lld::AtomLayout *j) { return j->_atom->name() == _name; }
};
typedef typename std::vector<lld::AtomLayout *>::iterator AbsoluteAtomIterT;
DefaultLayout(const ELFLinkingContext &context) : _context(context) {}
/// \brief Return the section order for a input section
SectionOrder getSectionOrder(StringRef name, int32_t contentType,
int32_t contentPermissions) override;
/// \brief This maps the input sections to the output section names
virtual StringRef getSectionName(const DefinedAtom *da) const;
/// \brief Gets or creates a section.
AtomSection<ELFT> *getSection(
StringRef name, int32_t contentType,
DefinedAtom::ContentPermissions contentPermissions);
/// \brief Gets the segment for a output section
virtual Layout::SegmentType getSegmentType(Section<ELFT> *section) const;
/// \brief Returns true/false depending on whether the section has a Output
// segment or not
static bool hasOutputSegment(Section<ELFT> *section);
// Adds an atom to the section
ErrorOr<const lld::AtomLayout &> addAtom(const Atom *atom) override;
/// \brief Find an output Section given a section name.
MergedSections<ELFT> *findOutputSection(StringRef name) {
auto iter = _mergedSectionMap.find(name);
if (iter == _mergedSectionMap.end())
return nullptr;
return iter->second;
}
/// \brief find a absolute atom given a name
AbsoluteAtomIterT findAbsoluteAtom(StringRef name) {
return std::find_if(_absoluteAtoms.begin(), _absoluteAtoms.end(),
FindByName(name));
}
// Merge sections with the same name into a MergedSections
void mergeSimilarSections();
void assignSectionsToSegments() override;
void assignVirtualAddress() override;
void assignOffsetsForMiscSections();
void assignFileOffsets() override;
/// Inline functions
inline range<AbsoluteAtomIterT> absoluteAtoms() { return _absoluteAtoms; }
inline void addSection(Chunk<ELFT> *c) {
_sections.push_back(c);
}
inline void finalize() {
ScopedTask task(getDefaultDomain(), "Finalize layout");
for (auto &si : _sections)
si->finalize();
}
inline void doPreFlight() {
for (auto &si : _sections)
si->doPreFlight();
}
inline bool findAtomAddrByName(StringRef name, uint64_t &addr) override {
for (auto sec : _sections)
if (auto section = dyn_cast<Section<ELFT> >(sec))
if (section->findAtomAddrByName(name, addr))
return true;
return false;
}
inline void setHeader(ELFHeader<ELFT> *elfHeader) { _elfHeader = elfHeader; }
inline void setProgramHeader(ProgramHeader<ELFT> *p) {
_programHeader = p;
}
inline range<MergedSectionIter> mergedSections() { return _mergedSections; }
inline range<ChunkIter> sections() { return _sections; }
inline range<SegmentIter> segments() { return _segments; }
inline ELFHeader<ELFT> *getHeader() { return _elfHeader; }
inline ProgramHeader<ELFT> *getProgramHeader() {
return _programHeader;
}
bool hasDynamicRelocationTable() const { return !!_dynamicRelocationTable; }
bool hasPLTRelocationTable() const { return !!_pltRelocationTable; }
/// \brief Get or create the dynamic relocation table. All relocations in this
/// table are processed at startup.
RelocationTable<ELFT> *getDynamicRelocationTable() {
if (!_dynamicRelocationTable) {
_dynamicRelocationTable.reset(new (_allocator) RelocationTable<ELFT>(
_context, _context.isRelaOutputFormat() ? ".rela.dyn" : ".rel.dyn",
ORDER_DYNAMIC_RELOCS));
addSection(_dynamicRelocationTable.get());
}
return _dynamicRelocationTable.get();
}
/// \brief Get or create the PLT relocation table. Referenced by DT_JMPREL.
RelocationTable<ELFT> *getPLTRelocationTable() {
if (!_pltRelocationTable) {
_pltRelocationTable.reset(new (_allocator) RelocationTable<ELFT>(
_context, _context.isRelaOutputFormat() ? ".rela.plt" : ".rel.plt",
ORDER_DYNAMIC_PLT_RELOCS));
addSection(_pltRelocationTable.get());
}
return _pltRelocationTable.get();
}
uint64_t getTLSSize() const {
for (const auto &phdr : *_programHeader)
if (phdr->p_type == llvm::ELF::PT_TLS)
return phdr->p_memsz;
return 0;
}
protected:
/// \brief Allocate a new section.
virtual AtomSection<ELFT> *createSection(
StringRef name, int32_t contentType,
DefinedAtom::ContentPermissions contentPermissions,
SectionOrder sectionOrder);
protected:
llvm::BumpPtrAllocator _allocator;
SectionMapT _sectionMap;
MergedSectionMapT _mergedSectionMap;
AdditionalSegmentMapT _additionalSegmentMap;
SegmentMapT _segmentMap;
std::vector<Chunk<ELFT> *> _sections;
std::vector<Segment<ELFT> *> _segments;
std::vector<MergedSections<ELFT> *> _mergedSections;
ELFHeader<ELFT> *_elfHeader;
ProgramHeader<ELFT> *_programHeader;
LLD_UNIQUE_BUMP_PTR(RelocationTable<ELFT>) _dynamicRelocationTable;
LLD_UNIQUE_BUMP_PTR(RelocationTable<ELFT>) _pltRelocationTable;
std::vector<lld::AtomLayout *> _absoluteAtoms;
const ELFLinkingContext &_context;
};
/// \brief Handle linker scripts. TargetLayouts would derive
/// from this class to override some of the functionalities.
template<class ELFT>
class ScriptLayout: public DefaultLayout<ELFT> {
public:
ScriptLayout(const ELFLinkingContext &context)
: DefaultLayout<ELFT>(context)
{}
};
template <class ELFT>
Layout::SectionOrder DefaultLayout<ELFT>::getSectionOrder(
StringRef name, int32_t contentType, int32_t contentPermissions) {
switch (contentType) {
case DefinedAtom::typeResolver:
case DefinedAtom::typeCode:
return llvm::StringSwitch<Layout::SectionOrder>(name)
.StartsWith(".eh_frame_hdr", ORDER_EH_FRAMEHDR)
.StartsWith(".eh_frame", ORDER_EH_FRAME)
.StartsWith(".init", ORDER_INIT)
.StartsWith(".fini", ORDER_FINI)
.StartsWith(".hash", ORDER_HASH)
.Default(ORDER_TEXT);
case DefinedAtom::typeConstant:
return ORDER_RODATA;
case DefinedAtom::typeData:
case DefinedAtom::typeDataFast:
return llvm::StringSwitch<Layout::SectionOrder>(name)
.StartsWith(".init_array", ORDER_INIT_ARRAY)
.StartsWith(".fini_array", ORDER_FINI_ARRAY)
.Default(ORDER_DATA);
case DefinedAtom::typeZeroFill:
case DefinedAtom::typeZeroFillFast:
return ORDER_BSS;
case DefinedAtom::typeGOT:
return llvm::StringSwitch<Layout::SectionOrder>(name)
.StartsWith(".got.plt", ORDER_GOT_PLT)
.Default(ORDER_GOT);
case DefinedAtom::typeStub:
return ORDER_PLT;
case DefinedAtom::typeRONote:
return ORDER_RO_NOTE;
case DefinedAtom::typeRWNote:
return ORDER_RW_NOTE;
case DefinedAtom::typeNoAlloc:
return ORDER_NOALLOC;
case DefinedAtom::typeThreadData:
return ORDER_TDATA;
case DefinedAtom::typeThreadZeroFill:
return ORDER_TBSS;
default:
// If we get passed in a section push it to OTHER
if (contentPermissions == DefinedAtom::perm___)
return ORDER_OTHER;
return ORDER_NOT_DEFINED;
}
}
/// \brief This maps the input sections to the output section names
template <class ELFT>
StringRef DefaultLayout<ELFT>::getSectionName(const DefinedAtom *da) const {
if (da->sectionChoice() == DefinedAtom::sectionBasedOnContent) {
switch (da->contentType()) {
case DefinedAtom::typeCode:
return ".text";
case DefinedAtom::typeData:
return ".data";
case DefinedAtom::typeConstant:
return ".rodata";
case DefinedAtom::typeZeroFill:
return ".bss";
case DefinedAtom::typeThreadData:
return ".tdata";
case DefinedAtom::typeThreadZeroFill:
return ".tbss";
default:
break;
}
}
return llvm::StringSwitch<StringRef>(da->customSectionName())
.StartsWith(".text", ".text")
.StartsWith(".rodata", ".rodata")
.StartsWith(".gcc_except_table", ".gcc_except_table")
.StartsWith(".data.rel.ro", ".data.rel.ro")
.StartsWith(".data.rel.local", ".data.rel.local")
.StartsWith(".data", ".data")
.StartsWith(".tdata", ".tdata")
.StartsWith(".tbss", ".tbss")
.StartsWith(".init_array", ".init_array")
.StartsWith(".fini_array", ".fini_array")
.Default(da->customSectionName());
}
/// \brief Gets the segment for a output section
template <class ELFT>
Layout::SegmentType DefaultLayout<ELFT>::getSegmentType(
Section<ELFT> *section) const {
switch (section->order()) {
case ORDER_INTERP:
return llvm::ELF::PT_INTERP;
case ORDER_TEXT:
case ORDER_HASH:
case ORDER_DYNAMIC_SYMBOLS:
case ORDER_DYNAMIC_STRINGS:
case ORDER_DYNAMIC_RELOCS:
case ORDER_DYNAMIC_PLT_RELOCS:
case ORDER_REL:
case ORDER_INIT:
case ORDER_PLT:
case ORDER_FINI:
case ORDER_RODATA:
case ORDER_EH_FRAME:
return llvm::ELF::PT_LOAD;
case ORDER_RO_NOTE:
case ORDER_RW_NOTE:
return llvm::ELF::PT_NOTE;
case ORDER_DYNAMIC:
return llvm::ELF::PT_DYNAMIC;
case ORDER_CTORS:
case ORDER_DTORS:
return llvm::ELF::PT_GNU_RELRO;
case ORDER_EH_FRAMEHDR:
return llvm::ELF::PT_GNU_EH_FRAME;
case ORDER_GOT:
case ORDER_GOT_PLT:
case ORDER_DATA:
case ORDER_BSS:
case ORDER_INIT_ARRAY:
case ORDER_FINI_ARRAY:
return llvm::ELF::PT_LOAD;
case ORDER_TDATA:
case ORDER_TBSS:
return llvm::ELF::PT_TLS;
default:
return llvm::ELF::PT_NULL;
}
}
template <class ELFT>
bool DefaultLayout<ELFT>::hasOutputSegment(Section<ELFT> *section) {
switch (section->order()) {
case ORDER_INTERP:
case ORDER_HASH:
case ORDER_DYNAMIC_SYMBOLS:
case ORDER_DYNAMIC_STRINGS:
case ORDER_DYNAMIC_RELOCS:
case ORDER_DYNAMIC_PLT_RELOCS:
case ORDER_REL:
case ORDER_INIT:
case ORDER_PLT:
case ORDER_TEXT:
case ORDER_FINI:
case ORDER_RODATA:
case ORDER_EH_FRAME:
case ORDER_EH_FRAMEHDR:
case ORDER_TDATA:
case ORDER_TBSS:
case ORDER_RO_NOTE:
case ORDER_RW_NOTE:
case ORDER_DYNAMIC:
case ORDER_CTORS:
case ORDER_DTORS:
case ORDER_GOT:
case ORDER_GOT_PLT:
case ORDER_DATA:
case ORDER_INIT_ARRAY:
case ORDER_FINI_ARRAY:
case ORDER_BSS:
case ORDER_NOALLOC:
return true;
default:
return section->hasOutputSegment();
}
}
template <class ELFT>
AtomSection<ELFT> *DefaultLayout<ELFT>::createSection(
StringRef sectionName, int32_t contentType,
DefinedAtom::ContentPermissions permissions, SectionOrder sectionOrder) {
return new (_allocator) AtomSection<ELFT>(_context, sectionName, contentType,
permissions, sectionOrder);
}
template <class ELFT>
AtomSection<ELFT> *DefaultLayout<ELFT>::getSection(
StringRef sectionName, int32_t contentType,
DefinedAtom::ContentPermissions permissions) {
const SectionKey sectionKey(sectionName, permissions);
auto sec = _sectionMap.find(sectionKey);
if (sec != _sectionMap.end())
return sec->second;
SectionOrder sectionOrder =
getSectionOrder(sectionName, contentType, permissions);
AtomSection<ELFT> *newSec =
createSection(sectionName, contentType, permissions, sectionOrder);
newSec->setOrder(sectionOrder);
_sections.push_back(newSec);
_sectionMap.insert(std::make_pair(sectionKey, newSec));
return newSec;
}
template <class ELFT>
ErrorOr<const lld::AtomLayout &> DefaultLayout<ELFT>::addAtom(const Atom *atom) {
if (const DefinedAtom *definedAtom = dyn_cast<DefinedAtom>(atom)) {
// HACK: Ignore undefined atoms. We need to adjust the interface so that
// undefined atoms can still be included in the output symbol table for
// -noinhibit-exec.
if (definedAtom->contentType() == DefinedAtom::typeUnknown)
return make_error_code(llvm::errc::invalid_argument);
const DefinedAtom::ContentPermissions permissions =
definedAtom->permissions();
const DefinedAtom::ContentType contentType = definedAtom->contentType();
StringRef sectionName = getSectionName(definedAtom);
AtomSection<ELFT> *section =
getSection(sectionName, contentType, permissions);
// Add runtime relocations to the .rela section.
for (const auto &reloc : *definedAtom)
if (_context.isDynamicRelocation(*definedAtom, *reloc))
getDynamicRelocationTable()->addRelocation(*definedAtom, *reloc);
else if (_context.isPLTRelocation(*definedAtom, *reloc))
getPLTRelocationTable()->addRelocation(*definedAtom, *reloc);
return section->appendAtom(atom);
} else if (const AbsoluteAtom *absoluteAtom = dyn_cast<AbsoluteAtom>(atom)) {
// Absolute atoms are not part of any section, they are global for the whole
// link
_absoluteAtoms.push_back(new (_allocator)
lld::AtomLayout(absoluteAtom, 0, absoluteAtom->value()));
return *_absoluteAtoms.back();
} else {
llvm_unreachable("Only absolute / defined atoms can be added here");
}
}
/// Merge sections with the same name into a MergedSections
template<class ELFT>
void
DefaultLayout<ELFT>::mergeSimilarSections() {
MergedSections<ELFT> *mergedSection;
for (auto &si : _sections) {
const std::pair<StringRef, MergedSections<ELFT> *>
currentMergedSections(si->name(), nullptr);
std::pair<typename MergedSectionMapT::iterator, bool>
mergedSectionInsert
(_mergedSectionMap.insert(currentMergedSections));
if (!mergedSectionInsert.second) {
mergedSection = mergedSectionInsert.first->second;
} else {
mergedSection = new (_allocator.Allocate<MergedSections<ELFT>>())
MergedSections<ELFT>(si->name());
_mergedSections.push_back(mergedSection);
mergedSectionInsert.first->second = mergedSection;
}
mergedSection->appendSection(si);
}
}
template <class ELFT> void DefaultLayout<ELFT>::assignSectionsToSegments() {
ScopedTask task(getDefaultDomain(), "assignSectionsToSegments");
ELFLinkingContext::OutputMagic outputMagic = _context.getOutputMagic();
// TODO: Do we want to give a chance for the targetHandlers
// to sort segments in an arbitrary order?
// sort the sections by their order as defined by the layout
std::stable_sort(_sections.begin(), _sections.end(),
[](Chunk<ELFT> *A, Chunk<ELFT> *B) {
return A->order() < B->order();
});
// Merge all sections
mergeSimilarSections();
// Set the ordinal after sorting the sections
int ordinal = 1;
for (auto msi : _mergedSections) {
msi->setOrdinal(ordinal);
for (auto ai : msi->sections()) {
ai->setOrdinal(ordinal);
}
++ordinal;
}
for (auto msi : _mergedSections) {
for (auto ai : msi->sections()) {
if (auto section = dyn_cast<Section<ELFT> >(ai)) {
if (!hasOutputSegment(section))
continue;
msi->setLoadableSection(section->isLoadableSection());
// Get the segment type for the section
int64_t segmentType = getSegmentType(section);
msi->setHasSegment();
section->setSegmentType(segmentType);
StringRef segmentName = section->segmentKindToStr();
int64_t lookupSectionFlag = msi->flags();
if (!(lookupSectionFlag & llvm::ELF::SHF_WRITE))
lookupSectionFlag &= ~llvm::ELF::SHF_EXECINSTR;
// Merge string sections into Data segment itself
lookupSectionFlag &= ~(llvm::ELF::SHF_STRINGS | llvm::ELF::SHF_MERGE);
// Merge the TLS section into the DATA segment itself
lookupSectionFlag &= ~(llvm::ELF::SHF_TLS);
Segment<ELFT> *segment;
// We need a separate segment for sections that don't have
// the segment type to be PT_LOAD
if (segmentType != llvm::ELF::PT_LOAD) {
const AdditionalSegmentKey key(segmentType, lookupSectionFlag);
const std::pair<AdditionalSegmentKey, Segment<ELFT> *>
additionalSegment(key, nullptr);
std::pair<typename AdditionalSegmentMapT::iterator, bool>
additionalSegmentInsert(
_additionalSegmentMap.insert(additionalSegment));
if (!additionalSegmentInsert.second) {
segment = additionalSegmentInsert.first->second;
} else {
segment = new (_allocator) Segment<ELFT>(_context, segmentName,
segmentType);
additionalSegmentInsert.first->second = segment;
_segments.push_back(segment);
}
segment->append(section);
}
if (segmentType == llvm::ELF::PT_NULL)
continue;
// If the output magic is set to OutputMagic::NMAGIC or
// OutputMagic::OMAGIC, Place the data alongside text in one single
// segment
if (outputMagic == ELFLinkingContext::OutputMagic::NMAGIC ||
outputMagic == ELFLinkingContext::OutputMagic::OMAGIC)
lookupSectionFlag = llvm::ELF::SHF_EXECINSTR | llvm::ELF::SHF_ALLOC |
llvm::ELF::SHF_WRITE;
// Use the flags of the merged Section for the segment
const SegmentKey key("PT_LOAD", lookupSectionFlag);
const std::pair<SegmentKey, Segment<ELFT> *> currentSegment(key,
nullptr);
std::pair<typename SegmentMapT::iterator, bool> segmentInsert(
_segmentMap.insert(currentSegment));
if (!segmentInsert.second) {
segment = segmentInsert.first->second;
} else {
segment = new (_allocator) Segment<ELFT>(_context, "PT_LOAD",
llvm::ELF::PT_LOAD);
segmentInsert.first->second = segment;
_segments.push_back(segment);
}
segment->append(section);
}
}
}
if (_context.isDynamic() && !_context.isDynamicLibrary()) {
Segment<ELFT> *segment =
new (_allocator) ProgramHeaderSegment<ELFT>(_context);
_segments.push_back(segment);
segment->append(_elfHeader);
segment->append(_programHeader);
}
}
template <class ELFT> void DefaultLayout<ELFT>::assignFileOffsets() {
// TODO: Do we want to give a chance for the targetHandlers
// to sort segments in an arbitrary order?
std::sort(_segments.begin(), _segments.end(), Segment<ELFT>::compareSegments);
int ordinal = 0;
// Compute the number of segments that might be needed, so that the
// size of the program header can be computed
uint64_t offset = 0;
for (auto si : _segments) {
si->setOrdinal(++ordinal);
// Don't assign offsets for segments that are not loadable
if (si->segmentType() != llvm::ELF::PT_LOAD)
continue;
si->assignOffsets(offset);
offset += si->fileSize();
}
}
template<class ELFT>
void
DefaultLayout<ELFT>::assignVirtualAddress() {
if (_segments.empty())
return;
uint64_t virtualAddress = _context.getBaseAddress();
ELFLinkingContext::OutputMagic outputMagic = _context.getOutputMagic();
// HACK: This is a super dirty hack. The elf header and program header are
// not part of a section, but we need them to be loaded at the base address
// so that AT_PHDR is set correctly by the loader and so they are accessible
// at runtime. To do this we simply prepend them to the first loadable Segment
// and let the layout logic take care of it.
Segment<ELFT> *firstLoadSegment = nullptr;
for (auto si : _segments) {
if (si->segmentType() == llvm::ELF::PT_LOAD) {
firstLoadSegment = si;
si->firstSection()->setAlign(si->align2());
break;
}
}
firstLoadSegment->prepend(_programHeader);
firstLoadSegment->prepend(_elfHeader);
bool newSegmentHeaderAdded = true;
while (true) {
for (auto si : _segments) {
si->finalize();
// Don't add PT_NULL segments into the program header
if (si->segmentType() != llvm::ELF::PT_NULL)
newSegmentHeaderAdded = _programHeader->addSegment(si);
}
if (!newSegmentHeaderAdded)
break;
uint64_t fileoffset = 0;
uint64_t address = virtualAddress;
// Fix the offsets after adding the program header
for (auto &si : _segments) {
if ((si->segmentType() != llvm::ELF::PT_LOAD) &&
(si->segmentType() != llvm::ELF::PT_NULL))
continue;
// Align the segment to a page boundary only if the output mode is
// not OutputMagic::NMAGIC/OutputMagic::OMAGIC
if (outputMagic != ELFLinkingContext::OutputMagic::NMAGIC &&
outputMagic != ELFLinkingContext::OutputMagic::OMAGIC)
fileoffset =
llvm::RoundUpToAlignment(fileoffset, _context.getPageSize());
si->assignOffsets(fileoffset);
fileoffset = si->fileOffset() + si->fileSize();
}
// start assigning virtual addresses
for (auto &si : _segments) {
if ((si->segmentType() != llvm::ELF::PT_LOAD) &&
(si->segmentType() != llvm::ELF::PT_NULL))
continue;
if (si->segmentType() == llvm::ELF::PT_NULL) {
// Handle Non allocatable sections.
uint64_t nonLoadableAddr = 0;
si->setVAddr(nonLoadableAddr);
si->assignVirtualAddress(nonLoadableAddr);
} else {
si->setVAddr(virtualAddress);
// The first segment has the virtualAddress set to the base address as
// we have added the file header and the program header don't align the
// first segment to the pagesize
si->assignVirtualAddress(address);
si->setMemSize(address - virtualAddress);
if (outputMagic != ELFLinkingContext::OutputMagic::NMAGIC &&
outputMagic != ELFLinkingContext::OutputMagic::OMAGIC)
virtualAddress =
llvm::RoundUpToAlignment(address, _context.getPageSize());
}
}
_programHeader->resetProgramHeaders();
}
Section<ELFT> *section;
// Fix the offsets of all the atoms within a section
for (auto &si : _sections) {
section = dyn_cast<Section<ELFT>>(si);
if (section && DefaultLayout<ELFT>::hasOutputSegment(section))
section->assignOffsets(section->fileOffset());
}
// Set the size of the merged Sections
for (auto msi : _mergedSections) {
uint64_t sectionfileoffset = 0;
uint64_t startFileOffset = 0;
uint64_t sectionsize = 0;
bool isFirstSection = true;
for (auto si : msi->sections()) {
if (isFirstSection) {
startFileOffset = si->fileOffset();
isFirstSection = false;
}
sectionfileoffset = si->fileOffset();
sectionsize = si->fileSize();
}
sectionsize = (sectionfileoffset - startFileOffset) + sectionsize;
msi->setFileOffset(startFileOffset);
msi->setSize(sectionsize);
}
// Set the virtual addr of the merged Sections
for (auto msi : _mergedSections) {
uint64_t sectionstartaddr = 0;
uint64_t startaddr = 0;
uint64_t sectionsize = 0;
bool isFirstSection = true;
for (auto si : msi->sections()) {
if (isFirstSection) {
startaddr = si->virtualAddr();
isFirstSection = false;
}
sectionstartaddr = si->virtualAddr();
sectionsize = si->memSize();
}
sectionsize = (sectionstartaddr - startaddr) + sectionsize;
msi->setMemSize(sectionsize);
msi->setAddr(startaddr);
}
}
template<class ELFT>
void
DefaultLayout<ELFT>::assignOffsetsForMiscSections() {
uint64_t fileoffset = 0;
uint64_t size = 0;
for (auto si : _segments) {
// Don't calculate offsets from non loadable segments
if ((si->segmentType() != llvm::ELF::PT_LOAD) &&
(si->segmentType() != llvm::ELF::PT_NULL))
continue;
fileoffset = si->fileOffset();
size = si->fileSize();
}
fileoffset = fileoffset + size;
Section<ELFT> *section;
for (auto si : _sections) {
section = dyn_cast<Section<ELFT>>(si);
if (section && DefaultLayout<ELFT>::hasOutputSegment(section))
continue;
fileoffset = llvm::RoundUpToAlignment(fileoffset, si->align2());
si->setFileOffset(fileoffset);
si->setVAddr(0);
fileoffset += si->fileSize();
}
}
} // end namespace elf
} // end namespace lld
#endif
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