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llvm-project/lld/ELF/InputFiles.cpp

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//===- InputFiles.cpp -----------------------------------------------------===//
//
// The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "InputFiles.h"
#include "InputSection.h"
#include "LinkerScript.h"
#include "SymbolTable.h"
#include "Symbols.h"
#include "SyntheticSections.h"
#include "lld/Common/ErrorHandler.h"
#include "lld/Common/Memory.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/CodeGen/Analysis.h"
#include "llvm/DebugInfo/DWARF/DWARFContext.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/LTO/LTO.h"
#include "llvm/MC/StringTableBuilder.h"
#include "llvm/Object/ELFObjectFile.h"
#include "llvm/Support/ARMAttributeParser.h"
#include "llvm/Support/ARMBuildAttributes.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/TarWriter.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
using namespace llvm::ELF;
using namespace llvm::object;
using namespace llvm::sys;
using namespace llvm::sys::fs;
using namespace lld;
using namespace lld::elf;
std::vector<BinaryFile *> elf::BinaryFiles;
std::vector<BitcodeFile *> elf::BitcodeFiles;
std::vector<InputFile *> elf::ObjectFiles;
std::vector<InputFile *> elf::SharedFiles;
TarWriter *elf::Tar;
InputFile::InputFile(Kind K, MemoryBufferRef M) : MB(M), FileKind(K) {}
Optional<MemoryBufferRef> elf::readFile(StringRef Path) {
// The --chroot option changes our virtual root directory.
// This is useful when you are dealing with files created by --reproduce.
if (!Config->Chroot.empty() && Path.startswith("/"))
Path = Saver.save(Config->Chroot + Path);
log(Path);
auto MBOrErr = MemoryBuffer::getFile(Path);
if (auto EC = MBOrErr.getError()) {
error("cannot open " + Path + ": " + EC.message());
return None;
}
std::unique_ptr<MemoryBuffer> &MB = *MBOrErr;
MemoryBufferRef MBRef = MB->getMemBufferRef();
make<std::unique_ptr<MemoryBuffer>>(std::move(MB)); // take MB ownership
if (Tar)
Tar->append(relativeToRoot(Path), MBRef.getBuffer());
return MBRef;
}
// Concatenates arguments to construct a string representing an error location.
static std::string createFileLineMsg(StringRef Path, unsigned Line) {
std::string Filename = path::filename(Path);
std::string Lineno = ":" + std::to_string(Line);
if (Filename == Path)
return Filename + Lineno;
return Filename + Lineno + " (" + Path.str() + Lineno + ")";
}
template <class ELFT>
static std::string getSrcMsgAux(ObjFile<ELFT> &File, const Symbol &Sym,
InputSectionBase &Sec, uint64_t Offset) {
// In DWARF, functions and variables are stored to different places.
// First, lookup a function for a given offset.
if (Optional<DILineInfo> Info = File.getDILineInfo(&Sec, Offset))
return createFileLineMsg(Info->FileName, Info->Line);
// If it failed, lookup again as a variable.
if (Optional<std::pair<std::string, unsigned>> FileLine =
File.getVariableLoc(Sym.getName()))
return createFileLineMsg(FileLine->first, FileLine->second);
// File.SourceFile contains STT_FILE symbol, and that is a last resort.
return File.SourceFile;
}
std::string InputFile::getSrcMsg(const Symbol &Sym, InputSectionBase &Sec,
uint64_t Offset) {
if (kind() != ObjKind)
return "";
switch (Config->EKind) {
default:
llvm_unreachable("Invalid kind");
case ELF32LEKind:
return getSrcMsgAux(cast<ObjFile<ELF32LE>>(*this), Sym, Sec, Offset);
case ELF32BEKind:
return getSrcMsgAux(cast<ObjFile<ELF32BE>>(*this), Sym, Sec, Offset);
case ELF64LEKind:
return getSrcMsgAux(cast<ObjFile<ELF64LE>>(*this), Sym, Sec, Offset);
case ELF64BEKind:
return getSrcMsgAux(cast<ObjFile<ELF64BE>>(*this), Sym, Sec, Offset);
}
}
template <class ELFT> void ObjFile<ELFT>::initializeDwarf() {
DWARFContext Dwarf(make_unique<LLDDwarfObj<ELFT>>(this));
const DWARFObject &Obj = Dwarf.getDWARFObj();
DwarfLine.reset(new DWARFDebugLine);
DWARFDataExtractor LineData(Obj, Obj.getLineSection(), Config->IsLE,
Config->Wordsize);
// The second parameter is offset in .debug_line section
// for compilation unit (CU) of interest. We have only one
// CU (object file), so offset is always 0.
const DWARFDebugLine::LineTable *LT =
DwarfLine->getOrParseLineTable(LineData, 0, Dwarf, nullptr);
if (!LT)
return;
// Return if there is no debug information about CU available.
if (!Dwarf.getNumCompileUnits())
return;
// Loop over variable records and insert them to VariableLoc.
DWARFCompileUnit *CU = Dwarf.getCompileUnitAtIndex(0);
for (const auto &Entry : CU->dies()) {
DWARFDie Die(CU, &Entry);
// Skip all tags that are not variables.
if (Die.getTag() != dwarf::DW_TAG_variable)
continue;
// Skip if a local variable because we don't need them for generating error
// messages. In general, only non-local symbols can fail to be linked.
if (!dwarf::toUnsigned(Die.find(dwarf::DW_AT_external), 0))
continue;
// Get the source filename index for the variable.
unsigned File = dwarf::toUnsigned(Die.find(dwarf::DW_AT_decl_file), 0);
if (!LT->hasFileAtIndex(File))
continue;
// Get the line number on which the variable is declared.
unsigned Line = dwarf::toUnsigned(Die.find(dwarf::DW_AT_decl_line), 0);
// Get the name of the variable and add the collected information to
// VariableLoc. Usually Name is non-empty, but it can be empty if the input
// object file lacks some debug info.
StringRef Name = dwarf::toString(Die.find(dwarf::DW_AT_name), "");
if (!Name.empty())
VariableLoc.insert({Name, {File, Line}});
}
}
// Returns the pair of file name and line number describing location of data
// object (variable, array, etc) definition.
template <class ELFT>
Optional<std::pair<std::string, unsigned>>
ObjFile<ELFT>::getVariableLoc(StringRef Name) {
llvm::call_once(InitDwarfLine, [this]() { initializeDwarf(); });
// There is always only one CU so it's offset is 0.
const DWARFDebugLine::LineTable *LT = DwarfLine->getLineTable(0);
if (!LT)
return None;
// Return if we have no debug information about data object.
auto It = VariableLoc.find(Name);
if (It == VariableLoc.end())
return None;
// Take file name string from line table.
std::string FileName;
if (!LT->getFileNameByIndex(
It->second.first /* File */, nullptr,
DILineInfoSpecifier::FileLineInfoKind::AbsoluteFilePath, FileName))
return None;
return std::make_pair(FileName, It->second.second /*Line*/);
}
// Returns source line information for a given offset
// using DWARF debug info.
template <class ELFT>
Optional<DILineInfo> ObjFile<ELFT>::getDILineInfo(InputSectionBase *S,
uint64_t Offset) {
llvm::call_once(InitDwarfLine, [this]() { initializeDwarf(); });
// The offset to CU is 0.
const DWARFDebugLine::LineTable *Tbl = DwarfLine->getLineTable(0);
if (!Tbl)
return None;
// Use fake address calcuated by adding section file offset and offset in
// section. See comments for ObjectInfo class.
DILineInfo Info;
Tbl->getFileLineInfoForAddress(
S->getOffsetInFile() + Offset, nullptr,
DILineInfoSpecifier::FileLineInfoKind::AbsoluteFilePath, Info);
if (Info.Line == 0)
return None;
return Info;
}
// Returns source line information for a given offset using DWARF debug info.
template <class ELFT>
std::string ObjFile<ELFT>::getLineInfo(InputSectionBase *S, uint64_t Offset) {
if (Optional<DILineInfo> Info = getDILineInfo(S, Offset))
return Info->FileName + ":" + std::to_string(Info->Line);
return "";
}
// Returns "<internal>", "foo.a(bar.o)" or "baz.o".
std::string lld::toString(const InputFile *F) {
if (!F)
return "<internal>";
if (F->ToStringCache.empty()) {
if (F->ArchiveName.empty())
F->ToStringCache = F->getName();
else
F->ToStringCache = (F->ArchiveName + "(" + F->getName() + ")").str();
}
return F->ToStringCache;
}
template <class ELFT>
ELFFileBase<ELFT>::ELFFileBase(Kind K, MemoryBufferRef MB) : InputFile(K, MB) {
if (ELFT::TargetEndianness == support::little)
EKind = ELFT::Is64Bits ? ELF64LEKind : ELF32LEKind;
else
EKind = ELFT::Is64Bits ? ELF64BEKind : ELF32BEKind;
EMachine = getObj().getHeader()->e_machine;
OSABI = getObj().getHeader()->e_ident[llvm::ELF::EI_OSABI];
}
template <class ELFT>
typename ELFT::SymRange ELFFileBase<ELFT>::getGlobalELFSyms() {
return makeArrayRef(ELFSyms.begin() + FirstNonLocal, ELFSyms.end());
}
template <class ELFT>
uint32_t ELFFileBase<ELFT>::getSectionIndex(const Elf_Sym &Sym) const {
return CHECK(getObj().getSectionIndex(&Sym, ELFSyms, SymtabSHNDX), this);
}
template <class ELFT>
void ELFFileBase<ELFT>::initSymtab(ArrayRef<Elf_Shdr> Sections,
const Elf_Shdr *Symtab) {
FirstNonLocal = Symtab->sh_info;
ELFSyms = CHECK(getObj().symbols(Symtab), this);
if (FirstNonLocal == 0 || FirstNonLocal > ELFSyms.size())
fatal(toString(this) + ": invalid sh_info in symbol table");
StringTable =
CHECK(getObj().getStringTableForSymtab(*Symtab, Sections), this);
}
template <class ELFT>
ObjFile<ELFT>::ObjFile(MemoryBufferRef M, StringRef ArchiveName)
: ELFFileBase<ELFT>(Base::ObjKind, M) {
this->ArchiveName = ArchiveName;
}
template <class ELFT> ArrayRef<Symbol *> ObjFile<ELFT>::getLocalSymbols() {
if (this->Symbols.empty())
return {};
return makeArrayRef(this->Symbols).slice(1, this->FirstNonLocal - 1);
}
template <class ELFT>
void ObjFile<ELFT>::parse(DenseSet<CachedHashStringRef> &ComdatGroups) {
// Read section and symbol tables.
initializeSections(ComdatGroups);
initializeSymbols();
}
// Sections with SHT_GROUP and comdat bits define comdat section groups.
// They are identified and deduplicated by group name. This function
// returns a group name.
template <class ELFT>
StringRef ObjFile<ELFT>::getShtGroupSignature(ArrayRef<Elf_Shdr> Sections,
const Elf_Shdr &Sec) {
// Group signatures are stored as symbol names in object files.
// sh_info contains a symbol index, so we fetch a symbol and read its name.
if (this->ELFSyms.empty())
this->initSymtab(
Sections, CHECK(object::getSection<ELFT>(Sections, Sec.sh_link), this));
const Elf_Sym *Sym =
CHECK(object::getSymbol<ELFT>(this->ELFSyms, Sec.sh_info), this);
StringRef Signature = CHECK(Sym->getName(this->StringTable), this);
// As a special case, if a symbol is a section symbol and has no name,
// we use a section name as a signature.
//
// Such SHT_GROUP sections are invalid from the perspective of the ELF
// standard, but GNU gold 1.14 (the newest version as of July 2017) or
// older produce such sections as outputs for the -r option, so we need
// a bug-compatibility.
if (Signature.empty() && Sym->getType() == STT_SECTION)
return getSectionName(Sec);
return Signature;
}
template <class ELFT>
ArrayRef<typename ObjFile<ELFT>::Elf_Word>
ObjFile<ELFT>::getShtGroupEntries(const Elf_Shdr &Sec) {
const ELFFile<ELFT> &Obj = this->getObj();
ArrayRef<Elf_Word> Entries =
CHECK(Obj.template getSectionContentsAsArray<Elf_Word>(&Sec), this);
if (Entries.empty() || Entries[0] != GRP_COMDAT)
fatal(toString(this) + ": unsupported SHT_GROUP format");
return Entries.slice(1);
}
template <class ELFT> bool ObjFile<ELFT>::shouldMerge(const Elf_Shdr &Sec) {
// We don't merge sections if -O0 (default is -O1). This makes sometimes
// the linker significantly faster, although the output will be bigger.
if (Config->Optimize == 0)
return false;
// A mergeable section with size 0 is useless because they don't have
// any data to merge. A mergeable string section with size 0 can be
// argued as invalid because it doesn't end with a null character.
// We'll avoid a mess by handling them as if they were non-mergeable.
if (Sec.sh_size == 0)
return false;
// Check for sh_entsize. The ELF spec is not clear about the zero
// sh_entsize. It says that "the member [sh_entsize] contains 0 if
// the section does not hold a table of fixed-size entries". We know
// that Rust 1.13 produces a string mergeable section with a zero
// sh_entsize. Here we just accept it rather than being picky about it.
uint64_t EntSize = Sec.sh_entsize;
if (EntSize == 0)
return false;
if (Sec.sh_size % EntSize)
fatal(toString(this) +
": SHF_MERGE section size must be a multiple of sh_entsize");
uint64_t Flags = Sec.sh_flags;
if (!(Flags & SHF_MERGE))
return false;
if (Flags & SHF_WRITE)
fatal(toString(this) + ": writable SHF_MERGE section is not supported");
return true;
}
template <class ELFT>
void ObjFile<ELFT>::initializeSections(
DenseSet<CachedHashStringRef> &ComdatGroups) {
const ELFFile<ELFT> &Obj = this->getObj();
ArrayRef<Elf_Shdr> ObjSections = CHECK(this->getObj().sections(), this);
uint64_t Size = ObjSections.size();
this->Sections.resize(Size);
this->SectionStringTable =
CHECK(Obj.getSectionStringTable(ObjSections), this);
for (size_t I = 0, E = ObjSections.size(); I < E; I++) {
if (this->Sections[I] == &InputSection::Discarded)
continue;
const Elf_Shdr &Sec = ObjSections[I];
// SHF_EXCLUDE'ed sections are discarded by the linker. However,
// if -r is given, we'll let the final link discard such sections.
// This is compatible with GNU.
if ((Sec.sh_flags & SHF_EXCLUDE) && !Config->Relocatable) {
this->Sections[I] = &InputSection::Discarded;
continue;
}
switch (Sec.sh_type) {
case SHT_GROUP: {
// De-duplicate section groups by their signatures.
StringRef Signature = getShtGroupSignature(ObjSections, Sec);
bool IsNew = ComdatGroups.insert(CachedHashStringRef(Signature)).second;
this->Sections[I] = &InputSection::Discarded;
// If it is a new section group, we want to keep group members.
// Group leader sections, which contain indices of group members, are
// discarded because they are useless beyond this point. The only
// exception is the -r option because in order to produce re-linkable
// object files, we want to pass through basically everything.
if (IsNew) {
if (Config->Relocatable)
this->Sections[I] = createInputSection(Sec);
continue;
}
// Otherwise, discard group members.
for (uint32_t SecIndex : getShtGroupEntries(Sec)) {
if (SecIndex >= Size)
fatal(toString(this) +
": invalid section index in group: " + Twine(SecIndex));
this->Sections[SecIndex] = &InputSection::Discarded;
}
break;
}
case SHT_SYMTAB:
this->initSymtab(ObjSections, &Sec);
break;
case SHT_SYMTAB_SHNDX:
this->SymtabSHNDX = CHECK(Obj.getSHNDXTable(Sec, ObjSections), this);
break;
case SHT_STRTAB:
case SHT_NULL:
break;
default:
this->Sections[I] = createInputSection(Sec);
}
// .ARM.exidx sections have a reverse dependency on the InputSection they
// have a SHF_LINK_ORDER dependency, this is identified by the sh_link.
if (Sec.sh_flags & SHF_LINK_ORDER) {
if (Sec.sh_link >= this->Sections.size())
fatal(toString(this) +
": invalid sh_link index: " + Twine(Sec.sh_link));
InputSectionBase *LinkSec = this->Sections[Sec.sh_link];
InputSection *IS = cast<InputSection>(this->Sections[I]);
LinkSec->DependentSections.push_back(IS);
if (!isa<InputSection>(LinkSec))
error("a section " + IS->Name +
" with SHF_LINK_ORDER should not refer a non-regular "
"section: " +
toString(LinkSec));
}
}
}
// The ARM support in lld makes some use of instructions that are not available
// on all ARM architectures. Namely:
// - Use of BLX instruction for interworking between ARM and Thumb state.
// - Use of the extended Thumb branch encoding in relocation.
// - Use of the MOVT/MOVW instructions in Thumb Thunks.
// The ARM Attributes section contains information about the architecture chosen
// at compile time. We follow the convention that if at least one input object
// is compiled with an architecture that supports these features then lld is
// permitted to use them.
static void updateSupportedARMFeatures(const ARMAttributeParser &Attributes) {
if (!Attributes.hasAttribute(ARMBuildAttrs::CPU_arch))
return;
auto Arch = Attributes.getAttributeValue(ARMBuildAttrs::CPU_arch);
switch (Arch) {
case ARMBuildAttrs::Pre_v4:
case ARMBuildAttrs::v4:
case ARMBuildAttrs::v4T:
// Architectures prior to v5 do not support BLX instruction
break;
case ARMBuildAttrs::v5T:
case ARMBuildAttrs::v5TE:
case ARMBuildAttrs::v5TEJ:
case ARMBuildAttrs::v6:
case ARMBuildAttrs::v6KZ:
case ARMBuildAttrs::v6K:
Config->ARMHasBlx = true;
// Architectures used in pre-Cortex processors do not support
// The J1 = 1 J2 = 1 Thumb branch range extension, with the exception
// of Architecture v6T2 (arm1156t2-s and arm1156t2f-s) that do.
break;
default:
// All other Architectures have BLX and extended branch encoding
Config->ARMHasBlx = true;
Config->ARMJ1J2BranchEncoding = true;
if (Arch != ARMBuildAttrs::v6_M && Arch != ARMBuildAttrs::v6S_M)
// All Architectures used in Cortex processors with the exception
// of v6-M and v6S-M have the MOVT and MOVW instructions.
Config->ARMHasMovtMovw = true;
break;
}
}
template <class ELFT>
InputSectionBase *ObjFile<ELFT>::getRelocTarget(const Elf_Shdr &Sec) {
uint32_t Idx = Sec.sh_info;
if (Idx >= this->Sections.size())
fatal(toString(this) + ": invalid relocated section index: " + Twine(Idx));
InputSectionBase *Target = this->Sections[Idx];
// Strictly speaking, a relocation section must be included in the
// group of the section it relocates. However, LLVM 3.3 and earlier
// would fail to do so, so we gracefully handle that case.
if (Target == &InputSection::Discarded)
return nullptr;
if (!Target)
fatal(toString(this) + ": unsupported relocation reference");
return Target;
}
// Create a regular InputSection class that has the same contents
// as a given section.
static InputSection *toRegularSection(MergeInputSection *Sec) {
return make<InputSection>(Sec->File, Sec->Flags, Sec->Type, Sec->Alignment,
Sec->Data, Sec->Name);
}
template <class ELFT>
InputSectionBase *ObjFile<ELFT>::createInputSection(const Elf_Shdr &Sec) {
StringRef Name = getSectionName(Sec);
switch (Sec.sh_type) {
case SHT_ARM_ATTRIBUTES: {
if (Config->EMachine != EM_ARM)
break;
ARMAttributeParser Attributes;
ArrayRef<uint8_t> Contents = check(this->getObj().getSectionContents(&Sec));
Attributes.Parse(Contents, /*isLittle*/ Config->EKind == ELF32LEKind);
updateSupportedARMFeatures(Attributes);
// FIXME: Retain the first attribute section we see. The eglibc ARM
// dynamic loaders require the presence of an attribute section for dlopen
// to work. In a full implementation we would merge all attribute sections.
if (InX::ARMAttributes == nullptr) {
InX::ARMAttributes = make<InputSection>(*this, Sec, Name);
return InX::ARMAttributes;
}
return &InputSection::Discarded;
}
case SHT_RELA:
case SHT_REL: {
// Find the relocation target section and associate this
// section with it. Target can be discarded, for example
// if it is a duplicated member of SHT_GROUP section, we
// do not create or proccess relocatable sections then.
InputSectionBase *Target = getRelocTarget(Sec);
if (!Target)
return nullptr;
// This section contains relocation information.
// If -r is given, we do not interpret or apply relocation
// but just copy relocation sections to output.
if (Config->Relocatable)
return make<InputSection>(*this, Sec, Name);
if (Target->FirstRelocation)
fatal(toString(this) +
": multiple relocation sections to one section are not supported");
// Mergeable sections with relocations are tricky because relocations
// need to be taken into account when comparing section contents for
// merging. It's not worth supporting such mergeable sections because
// they are rare and it'd complicates the internal design (we usually
// have to determine if two sections are mergeable early in the link
// process much before applying relocations). We simply handle mergeable
// sections with relocations as non-mergeable.
if (auto *MS = dyn_cast<MergeInputSection>(Target)) {
Target = toRegularSection(MS);
this->Sections[Sec.sh_info] = Target;
}
size_t NumRelocations;
if (Sec.sh_type == SHT_RELA) {
ArrayRef<Elf_Rela> Rels = CHECK(this->getObj().relas(&Sec), this);
Target->FirstRelocation = Rels.begin();
NumRelocations = Rels.size();
Target->AreRelocsRela = true;
} else {
ArrayRef<Elf_Rel> Rels = CHECK(this->getObj().rels(&Sec), this);
Target->FirstRelocation = Rels.begin();
NumRelocations = Rels.size();
Target->AreRelocsRela = false;
}
assert(isUInt<31>(NumRelocations));
Target->NumRelocations = NumRelocations;
// Relocation sections processed by the linker are usually removed
// from the output, so returning `nullptr` for the normal case.
// However, if -emit-relocs is given, we need to leave them in the output.
// (Some post link analysis tools need this information.)
if (Config->EmitRelocs) {
InputSection *RelocSec = make<InputSection>(*this, Sec, Name);
// We will not emit relocation section if target was discarded.
Target->DependentSections.push_back(RelocSec);
return RelocSec;
}
return nullptr;
}
}
// The GNU linker uses .note.GNU-stack section as a marker indicating
// that the code in the object file does not expect that the stack is
// executable (in terms of NX bit). If all input files have the marker,
// the GNU linker adds a PT_GNU_STACK segment to tells the loader to
// make the stack non-executable. Most object files have this section as
// of 2017.
//
// But making the stack non-executable is a norm today for security
// reasons. Failure to do so may result in a serious security issue.
// Therefore, we make LLD always add PT_GNU_STACK unless it is
// explicitly told to do otherwise (by -z execstack). Because the stack
// executable-ness is controlled solely by command line options,
// .note.GNU-stack sections are simply ignored.
if (Name == ".note.GNU-stack")
return &InputSection::Discarded;
// Split stacks is a feature to support a discontiguous stack. At least
// as of 2017, it seems that the feature is not being used widely.
// Only GNU gold supports that. We don't. For the details about that,
// see https://gcc.gnu.org/wiki/SplitStacks
if (Name == ".note.GNU-split-stack") {
error(toString(this) +
": object file compiled with -fsplit-stack is not supported");
return &InputSection::Discarded;
}
// The linkonce feature is a sort of proto-comdat. Some glibc i386 object
// files contain definitions of symbol "__x86.get_pc_thunk.bx" in linkonce
// sections. Drop those sections to avoid duplicate symbol errors.
// FIXME: This is glibc PR20543, we should remove this hack once that has been
// fixed for a while.
if (Name.startswith(".gnu.linkonce."))
return &InputSection::Discarded;
// If we are creating a new .build-id section, strip existing .build-id
// sections so that the output won't have more than one .build-id.
// This is not usually a problem because input object files normally don't
// have .build-id sections, but you can create such files by
// "ld.{bfd,gold,lld} -r --build-id", and we want to guard against it.
if (Name == ".note.gnu.build-id" && Config->BuildId != BuildIdKind::None)
return &InputSection::Discarded;
// The linker merges EH (exception handling) frames and creates a
// .eh_frame_hdr section for runtime. So we handle them with a special
// class. For relocatable outputs, they are just passed through.
if (Name == ".eh_frame" && !Config->Relocatable)
return make<EhInputSection>(*this, Sec, Name);
if (shouldMerge(Sec))
return make<MergeInputSection>(*this, Sec, Name);
return make<InputSection>(*this, Sec, Name);
}
template <class ELFT>
StringRef ObjFile<ELFT>::getSectionName(const Elf_Shdr &Sec) {
return CHECK(this->getObj().getSectionName(&Sec, SectionStringTable), this);
}
template <class ELFT> void ObjFile<ELFT>::initializeSymbols() {
this->Symbols.reserve(this->ELFSyms.size());
for (const Elf_Sym &Sym : this->ELFSyms)
this->Symbols.push_back(createSymbol(&Sym));
}
template <class ELFT> Symbol *ObjFile<ELFT>::createSymbol(const Elf_Sym *Sym) {
int Binding = Sym->getBinding();
uint32_t SecIdx = this->getSectionIndex(*Sym);
if (SecIdx >= this->Sections.size())
fatal(toString(this) + ": invalid section index: " + Twine(SecIdx));
InputSectionBase *Sec = this->Sections[SecIdx];
uint8_t StOther = Sym->st_other;
uint8_t Type = Sym->getType();
uint64_t Value = Sym->st_value;
uint64_t Size = Sym->st_size;
if (Binding == STB_LOCAL) {
if (Sym->getType() == STT_FILE)
SourceFile = CHECK(Sym->getName(this->StringTable), this);
if (this->StringTable.size() <= Sym->st_name)
fatal(toString(this) + ": invalid symbol name offset");
StringRefZ Name = this->StringTable.data() + Sym->st_name;
if (Sym->st_shndx == SHN_UNDEF)
return make<Undefined>(this, Name, Binding, StOther, Type);
return make<Defined>(this, Name, Binding, StOther, Type, Value, Size, Sec);
}
StringRef Name = CHECK(Sym->getName(this->StringTable), this);
switch (Sym->st_shndx) {
case SHN_UNDEF:
return Symtab->addUndefined<ELFT>(Name, Binding, StOther, Type,
/*CanOmitFromDynSym=*/false, this);
case SHN_COMMON:
if (Value == 0 || Value >= UINT32_MAX)
fatal(toString(this) + ": common symbol '" + Name +
"' has invalid alignment: " + Twine(Value));
return Symtab->addCommon(Name, Size, Value, Binding, StOther, Type, *this);
}
switch (Binding) {
default:
fatal(toString(this) + ": unexpected binding: " + Twine(Binding));
case STB_GLOBAL:
case STB_WEAK:
case STB_GNU_UNIQUE:
if (Sec == &InputSection::Discarded)
return Symtab->addUndefined<ELFT>(Name, Binding, StOther, Type,
/*CanOmitFromDynSym=*/false, this);
return Symtab->addRegular(Name, StOther, Type, Value, Size, Binding, Sec,
this);
}
}
ArchiveFile::ArchiveFile(std::unique_ptr<Archive> &&File)
: InputFile(ArchiveKind, File->getMemoryBufferRef()),
File(std::move(File)) {}
template <class ELFT> void ArchiveFile::parse() {
for (const Archive::Symbol &Sym : File->symbols())
Symtab->addLazyArchive<ELFT>(Sym.getName(), *this, Sym);
}
// Returns a buffer pointing to a member file containing a given symbol.
std::pair<MemoryBufferRef, uint64_t>
ArchiveFile::getMember(const Archive::Symbol *Sym) {
Archive::Child C =
CHECK(Sym->getMember(), toString(this) +
": could not get the member for symbol " +
Sym->getName());
if (!Seen.insert(C.getChildOffset()).second)
return {MemoryBufferRef(), 0};
MemoryBufferRef Ret =
CHECK(C.getMemoryBufferRef(),
toString(this) +
": could not get the buffer for the member defining symbol " +
Sym->getName());
if (C.getParent()->isThin() && Tar)
Tar->append(relativeToRoot(CHECK(C.getFullName(), this)), Ret.getBuffer());
if (C.getParent()->isThin())
return {Ret, 0};
return {Ret, C.getChildOffset()};
}
template <class ELFT>
SharedFile<ELFT>::SharedFile(MemoryBufferRef M, StringRef DefaultSoName)
: ELFFileBase<ELFT>(Base::SharedKind, M), SoName(DefaultSoName),
IsNeeded(!Config->AsNeeded) {}
// Partially parse the shared object file so that we can call
// getSoName on this object.
template <class ELFT> void SharedFile<ELFT>::parseSoName() {
const Elf_Shdr *DynamicSec = nullptr;
const ELFFile<ELFT> Obj = this->getObj();
ArrayRef<Elf_Shdr> Sections = CHECK(Obj.sections(), this);
// Search for .dynsym, .dynamic, .symtab, .gnu.version and .gnu.version_d.
for (const Elf_Shdr &Sec : Sections) {
switch (Sec.sh_type) {
default:
continue;
case SHT_DYNSYM:
this->initSymtab(Sections, &Sec);
break;
case SHT_DYNAMIC:
DynamicSec = &Sec;
break;
case SHT_SYMTAB_SHNDX:
this->SymtabSHNDX = CHECK(Obj.getSHNDXTable(Sec, Sections), this);
break;
case SHT_GNU_versym:
this->VersymSec = &Sec;
break;
case SHT_GNU_verdef:
this->VerdefSec = &Sec;
break;
}
}
if (this->VersymSec && this->ELFSyms.empty())
error("SHT_GNU_versym should be associated with symbol table");
// Search for a DT_SONAME tag to initialize this->SoName.
if (!DynamicSec)
return;
ArrayRef<Elf_Dyn> Arr =
CHECK(Obj.template getSectionContentsAsArray<Elf_Dyn>(DynamicSec), this);
for (const Elf_Dyn &Dyn : Arr) {
if (Dyn.d_tag == DT_SONAME) {
uint64_t Val = Dyn.getVal();
if (Val >= this->StringTable.size())
fatal(toString(this) + ": invalid DT_SONAME entry");
SoName = this->StringTable.data() + Val;
return;
}
}
}
// Parse the version definitions in the object file if present. Returns a vector
// whose nth element contains a pointer to the Elf_Verdef for version identifier
// n. Version identifiers that are not definitions map to nullptr. The array
// always has at least length 1.
template <class ELFT>
std::vector<const typename ELFT::Verdef *>
SharedFile<ELFT>::parseVerdefs(const Elf_Versym *&Versym) {
std::vector<const Elf_Verdef *> Verdefs(1);
// We only need to process symbol versions for this DSO if it has both a
// versym and a verdef section, which indicates that the DSO contains symbol
// version definitions.
if (!VersymSec || !VerdefSec)
return Verdefs;
// The location of the first global versym entry.
const char *Base = this->MB.getBuffer().data();
Versym = reinterpret_cast<const Elf_Versym *>(Base + VersymSec->sh_offset) +
this->FirstNonLocal;
// We cannot determine the largest verdef identifier without inspecting
// every Elf_Verdef, but both bfd and gold assign verdef identifiers
// sequentially starting from 1, so we predict that the largest identifier
// will be VerdefCount.
unsigned VerdefCount = VerdefSec->sh_info;
Verdefs.resize(VerdefCount + 1);
// Build the Verdefs array by following the chain of Elf_Verdef objects
// from the start of the .gnu.version_d section.
const char *Verdef = Base + VerdefSec->sh_offset;
for (unsigned I = 0; I != VerdefCount; ++I) {
auto *CurVerdef = reinterpret_cast<const Elf_Verdef *>(Verdef);
Verdef += CurVerdef->vd_next;
unsigned VerdefIndex = CurVerdef->vd_ndx;
if (Verdefs.size() <= VerdefIndex)
Verdefs.resize(VerdefIndex + 1);
Verdefs[VerdefIndex] = CurVerdef;
}
return Verdefs;
}
// Fully parse the shared object file. This must be called after parseSoName().
template <class ELFT> void SharedFile<ELFT>::parseRest() {
// Create mapping from version identifiers to Elf_Verdef entries.
const Elf_Versym *Versym = nullptr;
Verdefs = parseVerdefs(Versym);
ArrayRef<Elf_Shdr> Sections = CHECK(this->getObj().sections(), this);
// Add symbols to the symbol table.
Elf_Sym_Range Syms = this->getGlobalELFSyms();
for (const Elf_Sym &Sym : Syms) {
unsigned VersymIndex = VER_NDX_GLOBAL;
if (Versym) {
VersymIndex = Versym->vs_index;
++Versym;
}
bool Hidden = VersymIndex & VERSYM_HIDDEN;
VersymIndex = VersymIndex & ~VERSYM_HIDDEN;
StringRef Name = CHECK(Sym.getName(this->StringTable), this);
if (Sym.isUndefined()) {
Symbol *S = Symtab->addUndefined<ELFT>(Name, Sym.getBinding(),
Sym.st_other, Sym.getType(),
/*CanOmitFromDynSym=*/false, this);
S->ExportDynamic = true;
continue;
}
// ELF spec requires that all local symbols precede weak or global
// symbols in each symbol table, and the index of first non-local symbol
// is stored to sh_info. If a local symbol appears after some non-local
// symbol, that's a violation of the spec.
if (Sym.getBinding() == STB_LOCAL) {
warn("found local symbol '" + Name +
"' in global part of symbol table in file " + toString(this));
continue;
}
if (Config->EMachine == EM_MIPS) {
// FIXME: MIPS BFD linker puts _gp_disp symbol into DSO files
// and incorrectly assigns VER_NDX_LOCAL to this section global
// symbol. Here is a workaround for this bug.
if (Versym && VersymIndex == VER_NDX_LOCAL && Name == "_gp_disp")
continue;
}
const Elf_Verdef *Ver = nullptr;
if (VersymIndex != VER_NDX_GLOBAL) {
if (VersymIndex >= Verdefs.size() || VersymIndex == VER_NDX_LOCAL) {
error("corrupt input file: version definition index " +
Twine(VersymIndex) + " for symbol " + Name +
" is out of bounds\n>>> defined in " + toString(this));
continue;
}
Ver = Verdefs[VersymIndex];
} else {
VersymIndex = 0;
}
// We do not usually care about alignments of data in shared object
// files because the loader takes care of it. However, if we promote a
// DSO symbol to point to .bss due to copy relocation, we need to keep
// the original alignment requirements. We infer it here.
uint64_t Alignment = 1;
if (Sym.st_value)
Alignment = 1ULL << countTrailingZeros((uint64_t)Sym.st_value);
if (0 < Sym.st_shndx && Sym.st_shndx < Sections.size()) {
uint64_t SecAlign = Sections[Sym.st_shndx].sh_addralign;
Alignment = std::min(Alignment, SecAlign);
}
if (Alignment > UINT32_MAX)
error(toString(this) + ": alignment too large: " + Name);
if (!Hidden)
Symtab->addShared(Name, *this, Sym, Alignment, VersymIndex);
// Also add the symbol with the versioned name to handle undefined symbols
// with explicit versions.
if (Ver) {
StringRef VerName = this->StringTable.data() + Ver->getAux()->vda_name;
Name = Saver.save(Name + "@" + VerName);
Symtab->addShared(Name, *this, Sym, Alignment, VersymIndex);
}
}
}
static ELFKind getBitcodeELFKind(const Triple &T) {
if (T.isLittleEndian())
return T.isArch64Bit() ? ELF64LEKind : ELF32LEKind;
return T.isArch64Bit() ? ELF64BEKind : ELF32BEKind;
}
static uint8_t getBitcodeMachineKind(StringRef Path, const Triple &T) {
switch (T.getArch()) {
case Triple::aarch64:
return EM_AARCH64;
case Triple::arm:
case Triple::thumb:
return EM_ARM;
case Triple::avr:
return EM_AVR;
case Triple::mips:
case Triple::mipsel:
case Triple::mips64:
case Triple::mips64el:
return EM_MIPS;
case Triple::ppc:
return EM_PPC;
case Triple::ppc64:
return EM_PPC64;
case Triple::x86:
return T.isOSIAMCU() ? EM_IAMCU : EM_386;
case Triple::x86_64:
return EM_X86_64;
default:
fatal(Path + ": could not infer e_machine from bitcode target triple " +
T.str());
}
}
BitcodeFile::BitcodeFile(MemoryBufferRef MB, StringRef ArchiveName,
uint64_t OffsetInArchive)
: InputFile(BitcodeKind, MB) {
this->ArchiveName = ArchiveName;
// Here we pass a new MemoryBufferRef which is identified by ArchiveName
// (the fully resolved path of the archive) + member name + offset of the
// member in the archive.
// ThinLTO uses the MemoryBufferRef identifier to access its internal
// data structures and if two archives define two members with the same name,
// this causes a collision which result in only one of the objects being
// taken into consideration at LTO time (which very likely causes undefined
// symbols later in the link stage).
MemoryBufferRef MBRef(MB.getBuffer(),
Saver.save(ArchiveName + MB.getBufferIdentifier() +
utostr(OffsetInArchive)));
Obj = CHECK(lto::InputFile::create(MBRef), this);
Triple T(Obj->getTargetTriple());
EKind = getBitcodeELFKind(T);
EMachine = getBitcodeMachineKind(MB.getBufferIdentifier(), T);
}
static uint8_t mapVisibility(GlobalValue::VisibilityTypes GvVisibility) {
switch (GvVisibility) {
case GlobalValue::DefaultVisibility:
return STV_DEFAULT;
case GlobalValue::HiddenVisibility:
return STV_HIDDEN;
case GlobalValue::ProtectedVisibility:
return STV_PROTECTED;
}
llvm_unreachable("unknown visibility");
}
template <class ELFT>
static Symbol *createBitcodeSymbol(const std::vector<bool> &KeptComdats,
const lto::InputFile::Symbol &ObjSym,
BitcodeFile &F) {
StringRef NameRef = Saver.save(ObjSym.getName());
uint32_t Binding = ObjSym.isWeak() ? STB_WEAK : STB_GLOBAL;
uint8_t Type = ObjSym.isTLS() ? STT_TLS : STT_NOTYPE;
uint8_t Visibility = mapVisibility(ObjSym.getVisibility());
bool CanOmitFromDynSym = ObjSym.canBeOmittedFromSymbolTable();
int C = ObjSym.getComdatIndex();
if (C != -1 && !KeptComdats[C])
return Symtab->addUndefined<ELFT>(NameRef, Binding, Visibility, Type,
CanOmitFromDynSym, &F);
if (ObjSym.isUndefined())
return Symtab->addUndefined<ELFT>(NameRef, Binding, Visibility, Type,
CanOmitFromDynSym, &F);
if (ObjSym.isCommon())
return Symtab->addCommon(NameRef, ObjSym.getCommonSize(),
ObjSym.getCommonAlignment(), Binding, Visibility,
STT_OBJECT, F);
return Symtab->addBitcode(NameRef, Binding, Visibility, Type,
CanOmitFromDynSym, F);
}
template <class ELFT>
void BitcodeFile::parse(DenseSet<CachedHashStringRef> &ComdatGroups) {
std::vector<bool> KeptComdats;
for (StringRef S : Obj->getComdatTable())
KeptComdats.push_back(ComdatGroups.insert(CachedHashStringRef(S)).second);
for (const lto::InputFile::Symbol &ObjSym : Obj->symbols())
Symbols.push_back(createBitcodeSymbol<ELFT>(KeptComdats, ObjSym, *this));
}
static ELFKind getELFKind(MemoryBufferRef MB) {
unsigned char Size;
unsigned char Endian;
std::tie(Size, Endian) = getElfArchType(MB.getBuffer());
if (Endian != ELFDATA2LSB && Endian != ELFDATA2MSB)
fatal(MB.getBufferIdentifier() + ": invalid data encoding");
if (Size != ELFCLASS32 && Size != ELFCLASS64)
fatal(MB.getBufferIdentifier() + ": invalid file class");
size_t BufSize = MB.getBuffer().size();
if ((Size == ELFCLASS32 && BufSize < sizeof(Elf32_Ehdr)) ||
(Size == ELFCLASS64 && BufSize < sizeof(Elf64_Ehdr)))
fatal(MB.getBufferIdentifier() + ": file is too short");
if (Size == ELFCLASS32)
return (Endian == ELFDATA2LSB) ? ELF32LEKind : ELF32BEKind;
return (Endian == ELFDATA2LSB) ? ELF64LEKind : ELF64BEKind;
}
void BinaryFile::parse() {
ArrayRef<uint8_t> Data = toArrayRef(MB.getBuffer());
auto *Section = make<InputSection>(this, SHF_ALLOC | SHF_WRITE, SHT_PROGBITS,
8, Data, ".data");
Sections.push_back(Section);
// For each input file foo that is embedded to a result as a binary
// blob, we define _binary_foo_{start,end,size} symbols, so that
// user programs can access blobs by name. Non-alphanumeric
// characters in a filename are replaced with underscore.
std::string S = "_binary_" + MB.getBufferIdentifier().str();
for (size_t I = 0; I < S.size(); ++I)
if (!isAlnum(S[I]))
S[I] = '_';
Symtab->addRegular(Saver.save(S + "_start"), STV_DEFAULT, STT_OBJECT, 0, 0,
STB_GLOBAL, Section, nullptr);
Symtab->addRegular(Saver.save(S + "_end"), STV_DEFAULT, STT_OBJECT,
Data.size(), 0, STB_GLOBAL, Section, nullptr);
Symtab->addRegular(Saver.save(S + "_size"), STV_DEFAULT, STT_OBJECT,
Data.size(), 0, STB_GLOBAL, nullptr, nullptr);
}
static bool isBitcode(MemoryBufferRef MB) {
using namespace sys::fs;
return identify_magic(MB.getBuffer()) == file_magic::bitcode;
}
InputFile *elf::createObjectFile(MemoryBufferRef MB, StringRef ArchiveName,
uint64_t OffsetInArchive) {
if (isBitcode(MB))
return make<BitcodeFile>(MB, ArchiveName, OffsetInArchive);
switch (getELFKind(MB)) {
case ELF32LEKind:
return make<ObjFile<ELF32LE>>(MB, ArchiveName);
case ELF32BEKind:
return make<ObjFile<ELF32BE>>(MB, ArchiveName);
case ELF64LEKind:
return make<ObjFile<ELF64LE>>(MB, ArchiveName);
case ELF64BEKind:
return make<ObjFile<ELF64BE>>(MB, ArchiveName);
default:
llvm_unreachable("getELFKind");
}
}
InputFile *elf::createSharedFile(MemoryBufferRef MB, StringRef DefaultSoName) {
switch (getELFKind(MB)) {
case ELF32LEKind:
return make<SharedFile<ELF32LE>>(MB, DefaultSoName);
case ELF32BEKind:
return make<SharedFile<ELF32BE>>(MB, DefaultSoName);
case ELF64LEKind:
return make<SharedFile<ELF64LE>>(MB, DefaultSoName);
case ELF64BEKind:
return make<SharedFile<ELF64BE>>(MB, DefaultSoName);
default:
llvm_unreachable("getELFKind");
}
}
MemoryBufferRef LazyObjFile::getBuffer() {
if (Seen)
return MemoryBufferRef();
Seen = true;
return MB;
}
InputFile *LazyObjFile::fetch() {
MemoryBufferRef MBRef = getBuffer();
if (MBRef.getBuffer().empty())
return nullptr;
return createObjectFile(MBRef, ArchiveName, OffsetInArchive);
}
template <class ELFT> void LazyObjFile::parse() {
// A lazy object file wraps either a bitcode file or an ELF file.
if (isBitcode(this->MB)) {
std::unique_ptr<lto::InputFile> Obj =
CHECK(lto::InputFile::create(this->MB), this);
for (const lto::InputFile::Symbol &Sym : Obj->symbols())
if (!Sym.isUndefined())
Symtab->addLazyObject<ELFT>(Saver.save(Sym.getName()), *this);
return;
}
switch (getELFKind(this->MB)) {
case ELF32LEKind:
addElfSymbols<ELF32LE>();
return;
case ELF32BEKind:
addElfSymbols<ELF32BE>();
return;
case ELF64LEKind:
addElfSymbols<ELF64LE>();
return;
case ELF64BEKind:
addElfSymbols<ELF64BE>();
return;
default:
llvm_unreachable("getELFKind");
}
}
template <class ELFT> void LazyObjFile::addElfSymbols() {
ELFFile<ELFT> Obj = check(ELFFile<ELFT>::create(MB.getBuffer()));
ArrayRef<typename ELFT::Shdr> Sections = CHECK(Obj.sections(), this);
for (const typename ELFT::Shdr &Sec : Sections) {
if (Sec.sh_type != SHT_SYMTAB)
continue;
typename ELFT::SymRange Syms = CHECK(Obj.symbols(&Sec), this);
uint32_t FirstNonLocal = Sec.sh_info;
StringRef StringTable =
CHECK(Obj.getStringTableForSymtab(Sec, Sections), this);
for (const typename ELFT::Sym &Sym : Syms.slice(FirstNonLocal))
if (Sym.st_shndx != SHN_UNDEF)
Symtab->addLazyObject<ELFT>(CHECK(Sym.getName(StringTable), this),
*this);
return;
}
}
// This is for --just-symbols.
//
// This option allows you to link your output against other existing
// program, so that if you load both your program and the other program
// into memory, your output can use program's symbols.
//
// What we are doing here is to read defined symbols from a given ELF
// file and add them as absolute symbols.
template <class ELFT> void elf::readJustSymbolsFile(MemoryBufferRef MB) {
typedef typename ELFT::Shdr Elf_Shdr;
typedef typename ELFT::Sym Elf_Sym;
typedef typename ELFT::SymRange Elf_Sym_Range;
StringRef ObjName = MB.getBufferIdentifier();
ELFFile<ELFT> Obj = check(ELFFile<ELFT>::create(MB.getBuffer()));
ArrayRef<Elf_Shdr> Sections = CHECK(Obj.sections(), ObjName);
for (const Elf_Shdr &Sec : Sections) {
if (Sec.sh_type != SHT_SYMTAB)
continue;
Elf_Sym_Range Syms = CHECK(Obj.symbols(&Sec), ObjName);
uint32_t FirstNonLocal = Sec.sh_info;
StringRef StringTable =
CHECK(Obj.getStringTableForSymtab(Sec, Sections), ObjName);
for (const Elf_Sym &Sym : Syms.slice(FirstNonLocal))
if (Sym.st_shndx != SHN_UNDEF)
Symtab->addRegular(CHECK(Sym.getName(StringTable), ObjName),
Sym.st_other, Sym.getType(), Sym.st_value,
Sym.st_size, Sym.getBinding(), nullptr, nullptr);
return;
}
}
template void ArchiveFile::parse<ELF32LE>();
template void ArchiveFile::parse<ELF32BE>();
template void ArchiveFile::parse<ELF64LE>();
template void ArchiveFile::parse<ELF64BE>();
template void BitcodeFile::parse<ELF32LE>(DenseSet<CachedHashStringRef> &);
template void BitcodeFile::parse<ELF32BE>(DenseSet<CachedHashStringRef> &);
template void BitcodeFile::parse<ELF64LE>(DenseSet<CachedHashStringRef> &);
template void BitcodeFile::parse<ELF64BE>(DenseSet<CachedHashStringRef> &);
template void LazyObjFile::parse<ELF32LE>();
template void LazyObjFile::parse<ELF32BE>();
template void LazyObjFile::parse<ELF64LE>();
template void LazyObjFile::parse<ELF64BE>();
template class elf::ELFFileBase<ELF32LE>;
template class elf::ELFFileBase<ELF32BE>;
template class elf::ELFFileBase<ELF64LE>;
template class elf::ELFFileBase<ELF64BE>;
template class elf::ObjFile<ELF32LE>;
template class elf::ObjFile<ELF32BE>;
template class elf::ObjFile<ELF64LE>;
template class elf::ObjFile<ELF64BE>;
template class elf::SharedFile<ELF32LE>;
template class elf::SharedFile<ELF32BE>;
template class elf::SharedFile<ELF64LE>;
template class elf::SharedFile<ELF64BE>;
template void elf::readJustSymbolsFile<ELF32LE>(MemoryBufferRef);
template void elf::readJustSymbolsFile<ELF32BE>(MemoryBufferRef);
template void elf::readJustSymbolsFile<ELF64LE>(MemoryBufferRef);
template void elf::readJustSymbolsFile<ELF64BE>(MemoryBufferRef);
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