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llvm-project/lld/ELF/InputFiles.cpp

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//===- InputFiles.cpp -----------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "InputFiles.h"
#include "Config.h"
#include "DWARF.h"
#include "Driver.h"
#include "InputSection.h"
#include "LinkerScript.h"
#include "SymbolTable.h"
#include "Symbols.h"
#include "SyntheticSections.h"
#include "Target.h"
#include "lld/Common/CommonLinkerContext.h"
#include "lld/Common/DWARF.h"
#include "llvm/ADT/CachedHashString.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/LTO/LTO.h"
#include "llvm/Object/IRObjectFile.h"
#include "llvm/Support/ARMAttributeParser.h"
#include "llvm/Support/ARMBuildAttributes.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/RISCVAttributeParser.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 llvm::support::endian;
using namespace lld;
using namespace lld::elf;
bool InputFile::isInGroup;
uint32_t InputFile::nextGroupId;
std::unique_ptr<TarWriter> elf::tar;
// Returns "<internal>", "foo.a(bar.o)" or "baz.o".
std::string lld::toString(const InputFile *f) {
static std::mutex mu;
if (!f)
return "<internal>";
{
std::lock_guard<std::mutex> lock(mu);
if (f->toStringCache.empty()) {
if (f->archiveName.empty())
f->toStringCache = f->getName();
else
(f->archiveName + "(" + f->getName() + ")").toVector(f->toStringCache);
}
}
return std::string(f->toStringCache);
}
static ELFKind getELFKind(MemoryBufferRef mb, StringRef archiveName) {
unsigned char size;
unsigned char endian;
std::tie(size, endian) = getElfArchType(mb.getBuffer());
auto report = [&](StringRef msg) {
StringRef filename = mb.getBufferIdentifier();
if (archiveName.empty())
fatal(filename + ": " + msg);
else
fatal(archiveName + "(" + filename + "): " + msg);
};
if (!mb.getBuffer().startswith(ElfMagic))
report("not an ELF file");
if (endian != ELFDATA2LSB && endian != ELFDATA2MSB)
report("corrupted ELF file: invalid data encoding");
if (size != ELFCLASS32 && size != ELFCLASS64)
report("corrupted ELF file: invalid file class");
size_t bufSize = mb.getBuffer().size();
if ((size == ELFCLASS32 && bufSize < sizeof(Elf32_Ehdr)) ||
(size == ELFCLASS64 && bufSize < sizeof(Elf64_Ehdr)))
report("corrupted ELF file: file is too short");
if (size == ELFCLASS32)
return (endian == ELFDATA2LSB) ? ELF32LEKind : ELF32BEKind;
return (endian == ELFDATA2LSB) ? ELF64LEKind : ELF64BEKind;
}
// For ARM only, to set the EF_ARM_ABI_FLOAT_SOFT or EF_ARM_ABI_FLOAT_HARD
// flag in the ELF Header we need to look at Tag_ABI_VFP_args to find out how
// the input objects have been compiled.
static void updateARMVFPArgs(const ARMAttributeParser &attributes,
const InputFile *f) {
Optional<unsigned> attr =
attributes.getAttributeValue(ARMBuildAttrs::ABI_VFP_args);
if (!attr)
// If an ABI tag isn't present then it is implicitly given the value of 0
// which maps to ARMBuildAttrs::BaseAAPCS. However many assembler files,
// including some in glibc that don't use FP args (and should have value 3)
// don't have the attribute so we do not consider an implicit value of 0
// as a clash.
return;
unsigned vfpArgs = *attr;
ARMVFPArgKind arg;
switch (vfpArgs) {
case ARMBuildAttrs::BaseAAPCS:
arg = ARMVFPArgKind::Base;
break;
case ARMBuildAttrs::HardFPAAPCS:
arg = ARMVFPArgKind::VFP;
break;
case ARMBuildAttrs::ToolChainFPPCS:
// Tool chain specific convention that conforms to neither AAPCS variant.
arg = ARMVFPArgKind::ToolChain;
break;
case ARMBuildAttrs::CompatibleFPAAPCS:
// Object compatible with all conventions.
return;
default:
error(toString(f) + ": unknown Tag_ABI_VFP_args value: " + Twine(vfpArgs));
return;
}
// Follow ld.bfd and error if there is a mix of calling conventions.
if (config->armVFPArgs != arg && config->armVFPArgs != ARMVFPArgKind::Default)
error(toString(f) + ": incompatible Tag_ABI_VFP_args");
else
config->armVFPArgs = arg;
}
// 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) {
Optional<unsigned> attr =
attributes.getAttributeValue(ARMBuildAttrs::CPU_arch);
if (!attr)
return;
auto arch = attr.value();
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;
}
}
InputFile::InputFile(Kind k, MemoryBufferRef m)
: mb(m), groupId(nextGroupId), fileKind(k) {
// All files within the same --{start,end}-group get the same group ID.
// Otherwise, a new file will get a new group ID.
if (!isInGroup)
++nextGroupId;
}
Optional<MemoryBufferRef> elf::readFile(StringRef path) {
llvm::TimeTraceScope timeScope("Load input files", 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);
config->dependencyFiles.insert(llvm::CachedHashString(path));
auto mbOrErr = MemoryBuffer::getFile(path, /*IsText=*/false,
/*RequiresNullTerminator=*/false);
if (auto ec = mbOrErr.getError()) {
error("cannot open " + path + ": " + ec.message());
return None;
}
MemoryBufferRef mbref = (*mbOrErr)->getMemBufferRef();
ctx->memoryBuffers.push_back(std::move(*mbOrErr)); // take MB ownership
if (tar)
tar->append(relativeToRoot(path), mbref.getBuffer());
return mbref;
}
// All input object files must be for the same architecture
// (e.g. it does not make sense to link x86 object files with
// MIPS object files.) This function checks for that error.
static bool isCompatible(InputFile *file) {
if (!file->isElf() && !isa<BitcodeFile>(file))
return true;
if (file->ekind == config->ekind && file->emachine == config->emachine) {
if (config->emachine != EM_MIPS)
return true;
if (isMipsN32Abi(file) == config->mipsN32Abi)
return true;
}
StringRef target =
!config->bfdname.empty() ? config->bfdname : config->emulation;
if (!target.empty()) {
error(toString(file) + " is incompatible with " + target);
return false;
}
InputFile *existing = nullptr;
if (!ctx->objectFiles.empty())
existing = ctx->objectFiles[0];
else if (!ctx->sharedFiles.empty())
existing = ctx->sharedFiles[0];
else if (!ctx->bitcodeFiles.empty())
existing = ctx->bitcodeFiles[0];
std::string with;
if (existing)
with = " with " + toString(existing);
error(toString(file) + " is incompatible" + with);
return false;
}
template <class ELFT> static void doParseFile(InputFile *file) {
if (!isCompatible(file))
return;
// Binary file
if (auto *f = dyn_cast<BinaryFile>(file)) {
ctx->binaryFiles.push_back(f);
f->parse();
return;
}
// Lazy object file
if (file->lazy) {
if (auto *f = dyn_cast<BitcodeFile>(file)) {
ctx->lazyBitcodeFiles.push_back(f);
f->parseLazy();
} else {
cast<ObjFile<ELFT>>(file)->parseLazy();
}
return;
}
if (config->trace)
message(toString(file));
// .so file
if (auto *f = dyn_cast<SharedFile>(file)) {
f->parse<ELFT>();
return;
}
// LLVM bitcode file
if (auto *f = dyn_cast<BitcodeFile>(file)) {
ctx->bitcodeFiles.push_back(f);
f->parse();
return;
}
// Regular object file
ctx->objectFiles.push_back(cast<ELFFileBase>(file));
cast<ObjFile<ELFT>>(file)->parse();
}
// Add symbols in File to the symbol table.
void elf::parseFile(InputFile *file) { invokeELFT(doParseFile, file); }
// Concatenates arguments to construct a string representing an error location.
static std::string createFileLineMsg(StringRef path, unsigned line) {
std::string filename = std::string(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, look up a function for a given offset.
if (Optional<DILineInfo> info = file.getDILineInfo(&sec, offset))
return createFileLineMsg(info->FileName, info->Line);
// If it failed, look up 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 std::string(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);
}
}
StringRef InputFile::getNameForScript() const {
if (archiveName.empty())
return getName();
if (nameForScriptCache.empty())
nameForScriptCache = (archiveName + Twine(':') + getName()).str();
return nameForScriptCache;
}
// An ELF object file may contain a `.deplibs` section. If it exists, the
// section contains a list of library specifiers such as `m` for libm. This
// function resolves a given name by finding the first matching library checking
// the various ways that a library can be specified to LLD. This ELF extension
// is a form of autolinking and is called `dependent libraries`. It is currently
// unique to LLVM and lld.
static void addDependentLibrary(StringRef specifier, const InputFile *f) {
if (!config->dependentLibraries)
return;
if (Optional<std::string> s = searchLibraryBaseName(specifier))
driver->addFile(saver().save(*s), /*withLOption=*/true);
else if (Optional<std::string> s = findFromSearchPaths(specifier))
driver->addFile(saver().save(*s), /*withLOption=*/true);
else if (fs::exists(specifier))
driver->addFile(specifier, /*withLOption=*/false);
else
error(toString(f) +
": unable to find library from dependent library specifier: " +
specifier);
}
// Record the membership of a section group so that in the garbage collection
// pass, section group members are kept or discarded as a unit.
template <class ELFT>
static void handleSectionGroup(ArrayRef<InputSectionBase *> sections,
ArrayRef<typename ELFT::Word> entries) {
bool hasAlloc = false;
for (uint32_t index : entries.slice(1)) {
if (index >= sections.size())
return;
if (InputSectionBase *s = sections[index])
if (s != &InputSection::discarded && s->flags & SHF_ALLOC)
hasAlloc = true;
}
// If any member has the SHF_ALLOC flag, the whole group is subject to garbage
// collection. See the comment in markLive(). This rule retains .debug_types
// and .rela.debug_types.
if (!hasAlloc)
return;
// Connect the members in a circular doubly-linked list via
// nextInSectionGroup.
InputSectionBase *head;
InputSectionBase *prev = nullptr;
for (uint32_t index : entries.slice(1)) {
InputSectionBase *s = sections[index];
if (!s || s == &InputSection::discarded)
continue;
if (prev)
prev->nextInSectionGroup = s;
else
head = s;
prev = s;
}
if (prev)
prev->nextInSectionGroup = head;
}
template <class ELFT> DWARFCache *ObjFile<ELFT>::getDwarf() {
llvm::call_once(initDwarf, [this]() {
dwarf = std::make_unique<DWARFCache>(std::make_unique<DWARFContext>(
std::make_unique<LLDDwarfObj<ELFT>>(this), "",
[&](Error err) { warn(getName() + ": " + toString(std::move(err))); },
[&](Error warning) {
warn(getName() + ": " + toString(std::move(warning)));
}));
});
return dwarf.get();
}
// 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) {
return getDwarf()->getVariableLoc(name);
}
// 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) {
// Detect SectionIndex for specified section.
uint64_t sectionIndex = object::SectionedAddress::UndefSection;
ArrayRef<InputSectionBase *> sections = s->file->getSections();
for (uint64_t curIndex = 0; curIndex < sections.size(); ++curIndex) {
if (s == sections[curIndex]) {
sectionIndex = curIndex;
break;
}
}
return getDwarf()->getDILineInfo(offset, sectionIndex);
}
ELFFileBase::ELFFileBase(Kind k, MemoryBufferRef mb) : InputFile(k, mb) {
ekind = getELFKind(mb, "");
switch (ekind) {
case ELF32LEKind:
init<ELF32LE>(k);
break;
case ELF32BEKind:
init<ELF32BE>(k);
break;
case ELF64LEKind:
init<ELF64LE>(k);
break;
case ELF64BEKind:
init<ELF64BE>(k);
break;
default:
llvm_unreachable("getELFKind");
}
}
template <typename Elf_Shdr>
static const Elf_Shdr *findSection(ArrayRef<Elf_Shdr> sections, uint32_t type) {
for (const Elf_Shdr &sec : sections)
if (sec.sh_type == type)
return &sec;
return nullptr;
}
template <class ELFT> void ELFFileBase::init(InputFile::Kind k) {
using Elf_Shdr = typename ELFT::Shdr;
using Elf_Sym = typename ELFT::Sym;
// Initialize trivial attributes.
const ELFFile<ELFT> &obj = getObj<ELFT>();
emachine = obj.getHeader().e_machine;
osabi = obj.getHeader().e_ident[llvm::ELF::EI_OSABI];
abiVersion = obj.getHeader().e_ident[llvm::ELF::EI_ABIVERSION];
ArrayRef<Elf_Shdr> sections = CHECK(obj.sections(), this);
elfShdrs = sections.data();
numELFShdrs = sections.size();
// Find a symbol table.
const Elf_Shdr *symtabSec =
findSection(sections, k == SharedKind ? SHT_DYNSYM : SHT_SYMTAB);
if (!symtabSec)
return;
// Initialize members corresponding to a symbol table.
firstGlobal = symtabSec->sh_info;
ArrayRef<Elf_Sym> eSyms = CHECK(obj.symbols(symtabSec), this);
if (firstGlobal == 0 || firstGlobal > eSyms.size())
fatal(toString(this) + ": invalid sh_info in symbol table");
elfSyms = reinterpret_cast<const void *>(eSyms.data());
numELFSyms = uint32_t(eSyms.size());
stringTable = CHECK(obj.getStringTableForSymtab(*symtabSec, sections), this);
}
template <class ELFT>
uint32_t ObjFile<ELFT>::getSectionIndex(const Elf_Sym &sym) const {
return CHECK(
this->getObj().getSectionIndex(sym, getELFSyms<ELFT>(), shndxTable),
this);
}
template <class ELFT> void ObjFile<ELFT>::parse(bool ignoreComdats) {
object::ELFFile<ELFT> obj = this->getObj();
// Read a section table. justSymbols is usually false.
if (this->justSymbols) {
initializeJustSymbols();
initializeSymbols(obj);
return;
}
// Handle dependent libraries and selection of section groups as these are not
// done in parallel.
ArrayRef<Elf_Shdr> objSections = getELFShdrs<ELFT>();
StringRef shstrtab = CHECK(obj.getSectionStringTable(objSections), this);
uint64_t size = objSections.size();
sections.resize(size);
for (size_t i = 0; i != size; ++i) {
const Elf_Shdr &sec = objSections[i];
if (sec.sh_type == SHT_LLVM_DEPENDENT_LIBRARIES && !config->relocatable) {
StringRef name = check(obj.getSectionName(sec, shstrtab));
ArrayRef<char> data = CHECK(
this->getObj().template getSectionContentsAsArray<char>(sec), this);
if (!data.empty() && data.back() != '\0') {
error(
toString(this) +
": corrupted dependent libraries section (unterminated string): " +
name);
} else {
for (const char *d = data.begin(), *e = data.end(); d < e;) {
StringRef s(d);
addDependentLibrary(s, this);
d += s.size() + 1;
}
}
this->sections[i] = &InputSection::discarded;
continue;
}
if (sec.sh_type == SHT_ARM_ATTRIBUTES && config->emachine == EM_ARM) {
ARMAttributeParser attributes;
ArrayRef<uint8_t> contents =
check(this->getObj().getSectionContents(sec));
StringRef name = check(obj.getSectionName(sec, shstrtab));
this->sections[i] = &InputSection::discarded;
if (Error e = attributes.parse(contents, config->ekind == ELF32LEKind
? support::little
: support::big)) {
InputSection isec(*this, sec, name);
warn(toString(&isec) + ": " + llvm::toString(std::move(e)));
} else {
updateSupportedARMFeatures(attributes);
updateARMVFPArgs(attributes, this);
// 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 (in.attributes == nullptr) {
in.attributes = std::make_unique<InputSection>(*this, sec, name);
this->sections[i] = in.attributes.get();
}
}
}
if (sec.sh_type == SHT_RISCV_ATTRIBUTES && config->emachine == EM_RISCV) {
RISCVAttributeParser attributes;
ArrayRef<uint8_t> contents =
check(this->getObj().getSectionContents(sec));
StringRef name = check(obj.getSectionName(sec, shstrtab));
this->sections[i] = &InputSection::discarded;
if (Error e = attributes.parse(contents, support::little)) {
InputSection isec(*this, sec, name);
warn(toString(&isec) + ": " + llvm::toString(std::move(e)));
} else {
// FIXME: Validate arch tag contains C if and only if EF_RISCV_RVC is
// present.
// FIXME: Retain the first attribute section we see. Tools such as
// llvm-objdump make use of the attribute section to determine which
// standard extensions to enable. In a full implementation we would
// merge all attribute sections.
if (in.attributes == nullptr) {
in.attributes = std::make_unique<InputSection>(*this, sec, name);
this->sections[i] = in.attributes.get();
}
}
}
if (sec.sh_type != SHT_GROUP)
continue;
StringRef signature = getShtGroupSignature(objSections, sec);
ArrayRef<Elf_Word> entries =
CHECK(obj.template getSectionContentsAsArray<Elf_Word>(sec), this);
if (entries.empty())
fatal(toString(this) + ": empty SHT_GROUP");
Elf_Word flag = entries[0];
if (flag && flag != GRP_COMDAT)
fatal(toString(this) + ": unsupported SHT_GROUP format");
bool keepGroup =
(flag & GRP_COMDAT) == 0 || ignoreComdats ||
symtab->comdatGroups.try_emplace(CachedHashStringRef(signature), this)
.second;
if (keepGroup) {
if (config->relocatable)
this->sections[i] = createInputSection(
i, sec, check(obj.getSectionName(sec, shstrtab)));
continue;
}
// Otherwise, discard group members.
for (uint32_t secIndex : entries.slice(1)) {
if (secIndex >= size)
fatal(toString(this) +
": invalid section index in group: " + Twine(secIndex));
this->sections[secIndex] = &InputSection::discarded;
}
}
// Read a symbol table.
initializeSymbols(obj);
}
// 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) {
typename ELFT::SymRange symbols = this->getELFSyms<ELFT>();
if (sec.sh_info >= symbols.size())
fatal(toString(this) + ": invalid symbol index");
const typename ELFT::Sym &sym = symbols[sec.sh_info];
return CHECK(sym.getName(this->stringTable), this);
}
template <class ELFT>
bool ObjFile<ELFT>::shouldMerge(const Elf_Shdr &sec, StringRef name) {
// On a regular link we don't merge sections if -O0 (default is -O1). This
// sometimes makes the linker significantly faster, although the output will
// be bigger.
//
// Doing the same for -r would create a problem as it would combine sections
// with different sh_entsize. One option would be to just copy every SHF_MERGE
// section as is to the output. While this would produce a valid ELF file with
// usable SHF_MERGE sections, tools like (llvm-)?dwarfdump get confused when
// they see two .debug_str. We could have separate logic for combining
// SHF_MERGE sections based both on their name and sh_entsize, but that seems
// to be more trouble than it is worth. Instead, we just use the regular (-O1)
// logic for -r.
if (config->optimize == 0 && !config->relocatable)
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) + ":(" + name + "): SHF_MERGE section size (" +
Twine(sec.sh_size) + ") must be a multiple of sh_entsize (" +
Twine(entSize) + ")");
if (sec.sh_flags & SHF_WRITE)
fatal(toString(this) + ":(" + name +
"): writable SHF_MERGE section is not supported");
return true;
}
// This is for --just-symbols.
//
// --just-symbols is a very minor feature that 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 refer the
// other program's symbols.
//
// When the option is given, we link "just symbols". The section table is
// initialized with null pointers.
template <class ELFT> void ObjFile<ELFT>::initializeJustSymbols() {
sections.resize(numELFShdrs);
}
template <class ELFT>
void ObjFile<ELFT>::initializeSections(bool ignoreComdats,
const llvm::object::ELFFile<ELFT> &obj) {
ArrayRef<Elf_Shdr> objSections = getELFShdrs<ELFT>();
StringRef shstrtab = CHECK(obj.getSectionStringTable(objSections), this);
uint64_t size = objSections.size();
SmallVector<ArrayRef<Elf_Word>, 0> selectedGroups;
for (size_t i = 0; i != size; ++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) {
if (sec.sh_type == SHT_LLVM_CALL_GRAPH_PROFILE)
cgProfileSectionIndex = i;
if (sec.sh_type == SHT_LLVM_ADDRSIG) {
// We ignore the address-significance table if we know that the object
// file was created by objcopy or ld -r. This is because these tools
// will reorder the symbols in the symbol table, invalidating the data
// in the address-significance table, which refers to symbols by index.
if (sec.sh_link != 0)
this->addrsigSec = &sec;
else if (config->icf == ICFLevel::Safe)
warn(toString(this) +
": --icf=safe conservatively ignores "
"SHT_LLVM_ADDRSIG [index " +
Twine(i) +
"] with sh_link=0 "
"(likely created using objcopy or ld -r)");
}
this->sections[i] = &InputSection::discarded;
continue;
}
switch (sec.sh_type) {
case SHT_GROUP: {
if (!config->relocatable)
sections[i] = &InputSection::discarded;
StringRef signature =
cantFail(this->getELFSyms<ELFT>()[sec.sh_info].getName(stringTable));
ArrayRef<Elf_Word> entries =
cantFail(obj.template getSectionContentsAsArray<Elf_Word>(sec));
if ((entries[0] & GRP_COMDAT) == 0 || ignoreComdats ||
symtab->comdatGroups.find(CachedHashStringRef(signature))->second ==
this)
selectedGroups.push_back(entries);
break;
}
case SHT_SYMTAB_SHNDX:
shndxTable = CHECK(obj.getSHNDXTable(sec, objSections), this);
break;
case SHT_SYMTAB:
case SHT_STRTAB:
case SHT_REL:
case SHT_RELA:
case SHT_NULL:
break;
case SHT_LLVM_SYMPART:
ctx->hasSympart.store(true, std::memory_order_relaxed);
[[fallthrough]];
default:
this->sections[i] =
createInputSection(i, sec, check(obj.getSectionName(sec, shstrtab)));
}
}
// We have a second loop. It is used to:
// 1) handle SHF_LINK_ORDER sections.
// 2) create SHT_REL[A] sections. In some cases the section header index of a
// relocation section may be smaller than that of the relocated section. In
// such cases, the relocation section would attempt to reference a target
// section that has not yet been created. For simplicity, delay creation of
// relocation sections until now.
for (size_t i = 0; i != size; ++i) {
if (this->sections[i] == &InputSection::discarded)
continue;
const Elf_Shdr &sec = objSections[i];
if (sec.sh_type == SHT_REL || sec.sh_type == SHT_RELA) {
// Find a relocation target section and associate this section with that.
// Target may have been discarded if it is in a different section group
// and the group is discarded, even though it's a violation of the spec.
// We handle that situation gracefully by discarding dangling relocation
// sections.
const uint32_t info = sec.sh_info;
InputSectionBase *s = getRelocTarget(i, sec, info);
if (!s)
continue;
// ELF spec allows mergeable sections with relocations, but they are rare,
// and it is in practice hard to merge such sections by contents, because
// applying relocations at end of linking changes section contents. So, we
// simply handle such sections as non-mergeable ones. Degrading like this
// is acceptable because section merging is optional.
if (auto *ms = dyn_cast<MergeInputSection>(s)) {
s = makeThreadLocal<InputSection>(ms->file, ms->flags, ms->type,
ms->alignment, ms->data(), ms->name);
sections[info] = s;
}
if (s->relSecIdx != 0)
error(
toString(s) +
": multiple relocation sections to one section are not supported");
s->relSecIdx = i;
// Relocation sections are usually removed from the output, so return
// `nullptr` for the normal case. However, if -r or --emit-relocs is
// specified, we need to copy them to the output. (Some post link analysis
// tools specify --emit-relocs to obtain the information.)
if (config->copyRelocs) {
auto *isec = makeThreadLocal<InputSection>(
*this, sec, check(obj.getSectionName(sec, shstrtab)));
// If the relocated section is discarded (due to /DISCARD/ or
// --gc-sections), the relocation section should be discarded as well.
s->dependentSections.push_back(isec);
sections[i] = isec;
}
continue;
}
// A SHF_LINK_ORDER section with sh_link=0 is handled as if it did not have
// the flag.
if (!sec.sh_link || !(sec.sh_flags & SHF_LINK_ORDER))
continue;
InputSectionBase *linkSec = nullptr;
if (sec.sh_link < size)
linkSec = this->sections[sec.sh_link];
if (!linkSec)
fatal(toString(this) + ": invalid sh_link index: " + Twine(sec.sh_link));
// A SHF_LINK_ORDER section is discarded if its linked-to section is
// discarded.
InputSection *isec = cast<InputSection>(this->sections[i]);
linkSec->dependentSections.push_back(isec);
if (!isa<InputSection>(linkSec))
error("a section " + isec->name +
" with SHF_LINK_ORDER should not refer a non-regular section: " +
toString(linkSec));
}
for (ArrayRef<Elf_Word> entries : selectedGroups)
handleSectionGroup<ELFT>(this->sections, entries);
}
// If a source file is compiled with x86 hardware-assisted call flow control
// enabled, the generated object file contains feature flags indicating that
// fact. This function reads the feature flags and returns it.
//
// Essentially we want to read a single 32-bit value in this function, but this
// function is rather complicated because the value is buried deep inside a
// .note.gnu.property section.
//
// The section consists of one or more NOTE records. Each NOTE record consists
// of zero or more type-length-value fields. We want to find a field of a
// certain type. It seems a bit too much to just store a 32-bit value, perhaps
// the ABI is unnecessarily complicated.
template <class ELFT> static uint32_t readAndFeatures(const InputSection &sec) {
using Elf_Nhdr = typename ELFT::Nhdr;
using Elf_Note = typename ELFT::Note;
uint32_t featuresSet = 0;
ArrayRef<uint8_t> data = sec.rawData;
auto reportFatal = [&](const uint8_t *place, const char *msg) {
fatal(toString(sec.file) + ":(" + sec.name + "+0x" +
Twine::utohexstr(place - sec.rawData.data()) + "): " + msg);
};
while (!data.empty()) {
// Read one NOTE record.
auto *nhdr = reinterpret_cast<const Elf_Nhdr *>(data.data());
if (data.size() < sizeof(Elf_Nhdr) || data.size() < nhdr->getSize())
reportFatal(data.data(), "data is too short");
Elf_Note note(*nhdr);
if (nhdr->n_type != NT_GNU_PROPERTY_TYPE_0 || note.getName() != "GNU") {
data = data.slice(nhdr->getSize());
continue;
}
uint32_t featureAndType = config->emachine == EM_AARCH64
? GNU_PROPERTY_AARCH64_FEATURE_1_AND
: GNU_PROPERTY_X86_FEATURE_1_AND;
// Read a body of a NOTE record, which consists of type-length-value fields.
ArrayRef<uint8_t> desc = note.getDesc();
while (!desc.empty()) {
const uint8_t *place = desc.data();
if (desc.size() < 8)
reportFatal(place, "program property is too short");
uint32_t type = read32<ELFT::TargetEndianness>(desc.data());
uint32_t size = read32<ELFT::TargetEndianness>(desc.data() + 4);
desc = desc.slice(8);
if (desc.size() < size)
reportFatal(place, "program property is too short");
if (type == featureAndType) {
// We found a FEATURE_1_AND field. There may be more than one of these
// in a .note.gnu.property section, for a relocatable object we
// accumulate the bits set.
if (size < 4)
reportFatal(place, "FEATURE_1_AND entry is too short");
featuresSet |= read32<ELFT::TargetEndianness>(desc.data());
}
// Padding is present in the note descriptor, if necessary.
desc = desc.slice(alignTo<(ELFT::Is64Bits ? 8 : 4)>(size));
}
// Go to next NOTE record to look for more FEATURE_1_AND descriptions.
data = data.slice(nhdr->getSize());
}
return featuresSet;
}
template <class ELFT>
InputSectionBase *ObjFile<ELFT>::getRelocTarget(uint32_t idx,
const Elf_Shdr &sec,
uint32_t info) {
if (info < this->sections.size()) {
InputSectionBase *target = this->sections[info];
// 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 != nullptr)
return target;
}
error(toString(this) + Twine(": relocation section (index ") + Twine(idx) +
") has invalid sh_info (" + Twine(info) + ")");
return nullptr;
}
// The function may be called concurrently for different input files. For
// allocation, prefer makeThreadLocal which does not require holding a lock.
template <class ELFT>
InputSectionBase *ObjFile<ELFT>::createInputSection(uint32_t idx,
const Elf_Shdr &sec,
StringRef name) {
if (name.startswith(".n")) {
// 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;
// Object files that use processor features such as Intel Control-Flow
// Enforcement (CET) or AArch64 Branch Target Identification BTI, use a
// .note.gnu.property section containing a bitfield of feature bits like the
// GNU_PROPERTY_X86_FEATURE_1_IBT flag. Read a bitmap containing the flag.
//
// Since we merge bitmaps from multiple object files to create a new
// .note.gnu.property containing a single AND'ed bitmap, we discard an input
// file's .note.gnu.property section.
if (name == ".note.gnu.property") {
this->andFeatures = readAndFeatures<ELFT>(InputSection(*this, sec, name));
return &InputSection::discarded;
}
// Split stacks is a feature to support a discontiguous stack,
// commonly used in the programming language Go. For the details,
// see https://gcc.gnu.org/wiki/SplitStacks. An object file compiled
// for split stack will include a .note.GNU-split-stack section.
if (name == ".note.GNU-split-stack") {
if (config->relocatable) {
error(
"cannot mix split-stack and non-split-stack in a relocatable link");
return &InputSection::discarded;
}
this->splitStack = true;
return &InputSection::discarded;
}
// An object file compiled for split stack, but where some of the
// functions were compiled with the no_split_stack_attribute will
// include a .note.GNU-no-split-stack section.
if (name == ".note.GNU-no-split-stack") {
this->someNoSplitStack = true;
return &InputSection::discarded;
}
// Strip existing .note.gnu.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")
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 makeThreadLocal<EhInputSection>(*this, sec, name);
if ((sec.sh_flags & SHF_MERGE) && shouldMerge(sec, name))
return makeThreadLocal<MergeInputSection>(*this, sec, name);
return makeThreadLocal<InputSection>(*this, sec, name);
}
// Initialize this->Symbols. this->Symbols is a parallel array as
// its corresponding ELF symbol table.
template <class ELFT>
void ObjFile<ELFT>::initializeSymbols(const object::ELFFile<ELFT> &obj) {
SymbolTable &symtab = *elf::symtab;
ArrayRef<Elf_Sym> eSyms = this->getELFSyms<ELFT>();
symbols.resize(eSyms.size());
// Some entries have been filled by LazyObjFile.
for (size_t i = firstGlobal, end = eSyms.size(); i != end; ++i)
if (!symbols[i])
symbols[i] = symtab.insert(CHECK(eSyms[i].getName(stringTable), this));
// Perform symbol resolution on non-local symbols.
SmallVector<unsigned, 32> undefineds;
for (size_t i = firstGlobal, end = eSyms.size(); i != end; ++i) {
const Elf_Sym &eSym = eSyms[i];
uint32_t secIdx = eSym.st_shndx;
if (secIdx == SHN_UNDEF) {
undefineds.push_back(i);
continue;
}
uint8_t binding = eSym.getBinding();
uint8_t stOther = eSym.st_other;
uint8_t type = eSym.getType();
uint64_t value = eSym.st_value;
uint64_t size = eSym.st_size;
Symbol *sym = symbols[i];
sym->isUsedInRegularObj = true;
if (LLVM_UNLIKELY(eSym.st_shndx == SHN_COMMON)) {
if (value == 0 || value >= UINT32_MAX)
fatal(toString(this) + ": common symbol '" + sym->getName() +
"' has invalid alignment: " + Twine(value));
hasCommonSyms = true;
sym->resolve(
CommonSymbol{this, StringRef(), binding, stOther, type, value, size});
continue;
}
// Handle global defined symbols. Defined::section will be set in postParse.
sym->resolve(Defined{this, StringRef(), binding, stOther, type, value, size,
nullptr});
}
// Undefined symbols (excluding those defined relative to non-prevailing
// sections) can trigger recursive extract. Process defined symbols first so
// that the relative order between a defined symbol and an undefined symbol
// does not change the symbol resolution behavior. In addition, a set of
// interconnected symbols will all be resolved to the same file, instead of
// being resolved to different files.
for (unsigned i : undefineds) {
const Elf_Sym &eSym = eSyms[i];
Symbol *sym = symbols[i];
sym->resolve(Undefined{this, StringRef(), eSym.getBinding(), eSym.st_other,
eSym.getType()});
sym->isUsedInRegularObj = true;
sym->referenced = true;
}
}
template <class ELFT>
void ObjFile<ELFT>::initSectionsAndLocalSyms(bool ignoreComdats) {
if (!justSymbols)
initializeSections(ignoreComdats, getObj());
if (!firstGlobal)
return;
SymbolUnion *locals = makeThreadLocalN<SymbolUnion>(firstGlobal);
ArrayRef<Elf_Sym> eSyms = this->getELFSyms<ELFT>();
for (size_t i = 0, end = firstGlobal; i != end; ++i) {
const Elf_Sym &eSym = eSyms[i];
uint32_t secIdx = eSym.st_shndx;
if (LLVM_UNLIKELY(secIdx == SHN_XINDEX))
secIdx = check(getExtendedSymbolTableIndex<ELFT>(eSym, i, shndxTable));
else if (secIdx >= SHN_LORESERVE)
secIdx = 0;
if (LLVM_UNLIKELY(secIdx >= sections.size()))
fatal(toString(this) + ": invalid section index: " + Twine(secIdx));
if (LLVM_UNLIKELY(eSym.getBinding() != STB_LOCAL))
error(toString(this) + ": non-local symbol (" + Twine(i) +
") found at index < .symtab's sh_info (" + Twine(end) + ")");
InputSectionBase *sec = sections[secIdx];
uint8_t type = eSym.getType();
if (type == STT_FILE)
sourceFile = CHECK(eSym.getName(stringTable), this);
if (LLVM_UNLIKELY(stringTable.size() <= eSym.st_name))
fatal(toString(this) + ": invalid symbol name offset");
StringRef name(stringTable.data() + eSym.st_name);
symbols[i] = reinterpret_cast<Symbol *>(locals + i);
if (eSym.st_shndx == SHN_UNDEF || sec == &InputSection::discarded)
new (symbols[i]) Undefined(this, name, STB_LOCAL, eSym.st_other, type,
/*discardedSecIdx=*/secIdx);
else
new (symbols[i]) Defined(this, name, STB_LOCAL, eSym.st_other, type,
eSym.st_value, eSym.st_size, sec);
symbols[i]->isUsedInRegularObj = true;
}
}
// Called after all ObjFile::parse is called for all ObjFiles. This checks
// duplicate symbols and may do symbol property merge in the future.
template <class ELFT> void ObjFile<ELFT>::postParse() {
static std::mutex mu;
ArrayRef<Elf_Sym> eSyms = this->getELFSyms<ELFT>();
for (size_t i = firstGlobal, end = eSyms.size(); i != end; ++i) {
const Elf_Sym &eSym = eSyms[i];
Symbol &sym = *symbols[i];
uint32_t secIdx = eSym.st_shndx;
uint8_t binding = eSym.getBinding();
if (LLVM_UNLIKELY(binding != STB_GLOBAL && binding != STB_WEAK &&
binding != STB_GNU_UNIQUE))
errorOrWarn(toString(this) + ": symbol (" + Twine(i) +
") has invalid binding: " + Twine((int)binding));
// st_value of STT_TLS represents the assigned offset, not the actual
// address which is used by STT_FUNC and STT_OBJECT. STT_TLS symbols can
// only be referenced by special TLS relocations. It is usually an error if
// a STT_TLS symbol is replaced by a non-STT_TLS symbol, vice versa.
if (LLVM_UNLIKELY(sym.isTls()) && eSym.getType() != STT_TLS &&
eSym.getType() != STT_NOTYPE)
errorOrWarn("TLS attribute mismatch: " + toString(sym) + "\n>>> in " +
toString(sym.file) + "\n>>> in " + toString(this));
// Handle non-COMMON defined symbol below. !sym.file allows a symbol
// assignment to redefine a symbol without an error.
if (!sym.file || !sym.isDefined() || secIdx == SHN_UNDEF ||
secIdx == SHN_COMMON)
continue;
if (LLVM_UNLIKELY(secIdx == SHN_XINDEX))
secIdx = check(getExtendedSymbolTableIndex<ELFT>(eSym, i, shndxTable));
else if (secIdx >= SHN_LORESERVE)
secIdx = 0;
if (LLVM_UNLIKELY(secIdx >= sections.size()))
fatal(toString(this) + ": invalid section index: " + Twine(secIdx));
InputSectionBase *sec = sections[secIdx];
if (sec == &InputSection::discarded) {
if (sym.traced) {
printTraceSymbol(Undefined{this, sym.getName(), sym.binding,
sym.stOther, sym.type, secIdx},
sym.getName());
}
if (sym.file == this) {
std::lock_guard<std::mutex> lock(mu);
ctx->nonPrevailingSyms.emplace_back(&sym, secIdx);
}
continue;
}
if (sym.file == this) {
cast<Defined>(sym).section = sec;
continue;
}
if (binding == STB_WEAK)
continue;
std::lock_guard<std::mutex> lock(mu);
ctx->duplicates.push_back({&sym, this, sec, eSym.st_value});
}
}
// The handling of tentative definitions (COMMON symbols) in archives is murky.
// A tentative definition will be promoted to a global definition if there are
// no non-tentative definitions to dominate it. When we hold a tentative
// definition to a symbol and are inspecting archive members for inclusion
// there are 2 ways we can proceed:
//
// 1) Consider the tentative definition a 'real' definition (ie promotion from
// tentative to real definition has already happened) and not inspect
// archive members for Global/Weak definitions to replace the tentative
// definition. An archive member would only be included if it satisfies some
// other undefined symbol. This is the behavior Gold uses.
//
// 2) Consider the tentative definition as still undefined (ie the promotion to
// a real definition happens only after all symbol resolution is done).
// The linker searches archive members for STB_GLOBAL definitions to
// replace the tentative definition with. This is the behavior used by
// GNU ld.
//
// The second behavior is inherited from SysVR4, which based it on the FORTRAN
// COMMON BLOCK model. This behavior is needed for proper initialization in old
// (pre F90) FORTRAN code that is packaged into an archive.
//
// The following functions search archive members for definitions to replace
// tentative definitions (implementing behavior 2).
static bool isBitcodeNonCommonDef(MemoryBufferRef mb, StringRef symName,
StringRef archiveName) {
IRSymtabFile symtabFile = check(readIRSymtab(mb));
for (const irsymtab::Reader::SymbolRef &sym :
symtabFile.TheReader.symbols()) {
if (sym.isGlobal() && sym.getName() == symName)
return !sym.isUndefined() && !sym.isWeak() && !sym.isCommon();
}
return false;
}
template <class ELFT>
static bool isNonCommonDef(MemoryBufferRef mb, StringRef symName,
StringRef archiveName) {
ObjFile<ELFT> *obj = make<ObjFile<ELFT>>(mb, archiveName);
StringRef stringtable = obj->getStringTable();
for (auto sym : obj->template getGlobalELFSyms<ELFT>()) {
Expected<StringRef> name = sym.getName(stringtable);
if (name && name.get() == symName)
return sym.isDefined() && sym.getBinding() == STB_GLOBAL &&
!sym.isCommon();
}
return false;
}
static bool isNonCommonDef(MemoryBufferRef mb, StringRef symName,
StringRef archiveName) {
switch (getELFKind(mb, archiveName)) {
case ELF32LEKind:
return isNonCommonDef<ELF32LE>(mb, symName, archiveName);
case ELF32BEKind:
return isNonCommonDef<ELF32BE>(mb, symName, archiveName);
case ELF64LEKind:
return isNonCommonDef<ELF64LE>(mb, symName, archiveName);
case ELF64BEKind:
return isNonCommonDef<ELF64BE>(mb, symName, archiveName);
default:
llvm_unreachable("getELFKind");
}
}
unsigned SharedFile::vernauxNum;
// Parse the version definitions in the object file if present, and return 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.
template <typename ELFT>
static SmallVector<const void *, 0>
parseVerdefs(const uint8_t *base, const typename ELFT::Shdr *sec) {
if (!sec)
return {};
// Build the Verdefs array by following the chain of Elf_Verdef objects
// from the start of the .gnu.version_d section.
SmallVector<const void *, 0> verdefs;
const uint8_t *verdef = base + sec->sh_offset;
for (unsigned i = 0, e = sec->sh_info; i != e; ++i) {
auto *curVerdef = reinterpret_cast<const typename ELFT::Verdef *>(verdef);
verdef += curVerdef->vd_next;
unsigned verdefIndex = curVerdef->vd_ndx;
if (verdefIndex >= verdefs.size())
verdefs.resize(verdefIndex + 1);
verdefs[verdefIndex] = curVerdef;
}
return verdefs;
}
// Parse SHT_GNU_verneed to properly set the name of a versioned undefined
// symbol. We detect fatal issues which would cause vulnerabilities, but do not
// implement sophisticated error checking like in llvm-readobj because the value
// of such diagnostics is low.
template <typename ELFT>
std::vector<uint32_t> SharedFile::parseVerneed(const ELFFile<ELFT> &obj,
const typename ELFT::Shdr *sec) {
if (!sec)
return {};
std::vector<uint32_t> verneeds;
ArrayRef<uint8_t> data = CHECK(obj.getSectionContents(*sec), this);
const uint8_t *verneedBuf = data.begin();
for (unsigned i = 0; i != sec->sh_info; ++i) {
if (verneedBuf + sizeof(typename ELFT::Verneed) > data.end())
fatal(toString(this) + " has an invalid Verneed");
auto *vn = reinterpret_cast<const typename ELFT::Verneed *>(verneedBuf);
const uint8_t *vernauxBuf = verneedBuf + vn->vn_aux;
for (unsigned j = 0; j != vn->vn_cnt; ++j) {
if (vernauxBuf + sizeof(typename ELFT::Vernaux) > data.end())
fatal(toString(this) + " has an invalid Vernaux");
auto *aux = reinterpret_cast<const typename ELFT::Vernaux *>(vernauxBuf);
if (aux->vna_name >= this->stringTable.size())
fatal(toString(this) + " has a Vernaux with an invalid vna_name");
uint16_t version = aux->vna_other & VERSYM_VERSION;
if (version >= verneeds.size())
verneeds.resize(version + 1);
verneeds[version] = aux->vna_name;
vernauxBuf += aux->vna_next;
}
verneedBuf += vn->vn_next;
}
return verneeds;
}
// 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 in this function.
template <typename ELFT>
static uint64_t getAlignment(ArrayRef<typename ELFT::Shdr> sections,
const typename ELFT::Sym &sym) {
uint64_t ret = UINT64_MAX;
if (sym.st_value)
ret = 1ULL << countTrailingZeros((uint64_t)sym.st_value);
if (0 < sym.st_shndx && sym.st_shndx < sections.size())
ret = std::min<uint64_t>(ret, sections[sym.st_shndx].sh_addralign);
return (ret > UINT32_MAX) ? 0 : ret;
}
// Fully parse the shared object file.
//
// This function parses symbol versions. If a DSO has version information,
// the file has a ".gnu.version_d" section which contains symbol version
// definitions. Each symbol is associated to one version through a table in
// ".gnu.version" section. That table is a parallel array for the symbol
// table, and each table entry contains an index in ".gnu.version_d".
//
// The special index 0 is reserved for VERF_NDX_LOCAL and 1 is for
// VER_NDX_GLOBAL. There's no table entry for these special versions in
// ".gnu.version_d".
//
// The file format for symbol versioning is perhaps a bit more complicated
// than necessary, but you can easily understand the code if you wrap your
// head around the data structure described above.
template <class ELFT> void SharedFile::parse() {
using Elf_Dyn = typename ELFT::Dyn;
using Elf_Shdr = typename ELFT::Shdr;
using Elf_Sym = typename ELFT::Sym;
using Elf_Verdef = typename ELFT::Verdef;
using Elf_Versym = typename ELFT::Versym;
ArrayRef<Elf_Dyn> dynamicTags;
const ELFFile<ELFT> obj = this->getObj<ELFT>();
ArrayRef<Elf_Shdr> sections = getELFShdrs<ELFT>();
const Elf_Shdr *versymSec = nullptr;
const Elf_Shdr *verdefSec = nullptr;
const Elf_Shdr *verneedSec = nullptr;
// 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_DYNAMIC:
dynamicTags =
CHECK(obj.template getSectionContentsAsArray<Elf_Dyn>(sec), this);
break;
case SHT_GNU_versym:
versymSec = &sec;
break;
case SHT_GNU_verdef:
verdefSec = &sec;
break;
case SHT_GNU_verneed:
verneedSec = &sec;
break;
}
}
if (versymSec && numELFSyms == 0) {
error("SHT_GNU_versym should be associated with symbol table");
return;
}
// Search for a DT_SONAME tag to initialize this->soName.
for (const Elf_Dyn &dyn : dynamicTags) {
if (dyn.d_tag == DT_NEEDED) {
uint64_t val = dyn.getVal();
if (val >= this->stringTable.size())
fatal(toString(this) + ": invalid DT_NEEDED entry");
dtNeeded.push_back(this->stringTable.data() + val);
} else 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;
}
}
// DSOs are uniquified not by filename but by soname.
DenseMap<CachedHashStringRef, SharedFile *>::iterator it;
bool wasInserted;
std::tie(it, wasInserted) =
symtab->soNames.try_emplace(CachedHashStringRef(soName), this);
// If a DSO appears more than once on the command line with and without
// --as-needed, --no-as-needed takes precedence over --as-needed because a
// user can add an extra DSO with --no-as-needed to force it to be added to
// the dependency list.
it->second->isNeeded |= isNeeded;
if (!wasInserted)
return;
ctx->sharedFiles.push_back(this);
verdefs = parseVerdefs<ELFT>(obj.base(), verdefSec);
std::vector<uint32_t> verneeds = parseVerneed<ELFT>(obj, verneedSec);
// Parse ".gnu.version" section which is a parallel array for the symbol
// table. If a given file doesn't have a ".gnu.version" section, we use
// VER_NDX_GLOBAL.
size_t size = numELFSyms - firstGlobal;
std::vector<uint16_t> versyms(size, VER_NDX_GLOBAL);
if (versymSec) {
ArrayRef<Elf_Versym> versym =
CHECK(obj.template getSectionContentsAsArray<Elf_Versym>(*versymSec),
this)
.slice(firstGlobal);
for (size_t i = 0; i < size; ++i)
versyms[i] = versym[i].vs_index;
}
// System libraries can have a lot of symbols with versions. Using a
// fixed buffer for computing the versions name (foo@ver) can save a
// lot of allocations.
SmallString<0> versionedNameBuffer;
// Add symbols to the symbol table.
SymbolTable &symtab = *elf::symtab;
ArrayRef<Elf_Sym> syms = this->getGlobalELFSyms<ELFT>();
for (size_t i = 0, e = syms.size(); i != e; ++i) {
const Elf_Sym &sym = syms[i];
// 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.
StringRef name = CHECK(sym.getName(stringTable), this);
if (sym.getBinding() == STB_LOCAL) {
errorOrWarn(toString(this) + ": invalid local symbol '" + name +
"' in global part of symbol table");
continue;
}
const uint16_t ver = versyms[i], idx = ver & ~VERSYM_HIDDEN;
if (sym.isUndefined()) {
// For unversioned undefined symbols, VER_NDX_GLOBAL makes more sense but
// as of binutils 2.34, GNU ld produces VER_NDX_LOCAL.
if (ver != VER_NDX_LOCAL && ver != VER_NDX_GLOBAL) {
if (idx >= verneeds.size()) {
error("corrupt input file: version need index " + Twine(idx) +
" for symbol " + name + " is out of bounds\n>>> defined in " +
toString(this));
continue;
}
StringRef verName = stringTable.data() + verneeds[idx];
versionedNameBuffer.clear();
name = saver().save(
(name + "@" + verName).toStringRef(versionedNameBuffer));
}
Symbol *s = symtab.addSymbol(
Undefined{this, name, sym.getBinding(), sym.st_other, sym.getType()});
s->exportDynamic = true;
if (s->isUndefined() && sym.getBinding() != STB_WEAK &&
config->unresolvedSymbolsInShlib != UnresolvedPolicy::Ignore)
requiredSymbols.push_back(s);
continue;
}
if (ver == VER_NDX_LOCAL ||
(ver != VER_NDX_GLOBAL && idx >= verdefs.size())) {
// In GNU ld < 2.31 (before 3be08ea4728b56d35e136af4e6fd3086ade17764), the
// MIPS port puts _gp_disp symbol into DSO files and incorrectly assigns
// VER_NDX_LOCAL. Workaround this bug.
if (config->emachine == EM_MIPS && name == "_gp_disp")
continue;
error("corrupt input file: version definition index " + Twine(idx) +
" for symbol " + name + " is out of bounds\n>>> defined in " +
toString(this));
continue;
}
uint32_t alignment = getAlignment<ELFT>(sections, sym);
if (ver == idx) {
auto *s = symtab.addSymbol(
SharedSymbol{*this, name, sym.getBinding(), sym.st_other,
sym.getType(), sym.st_value, sym.st_size, alignment});
if (s->file == this)
s->verdefIndex = ver;
}
// Also add the symbol with the versioned name to handle undefined symbols
// with explicit versions.
if (ver == VER_NDX_GLOBAL)
continue;
StringRef verName =
stringTable.data() +
reinterpret_cast<const Elf_Verdef *>(verdefs[idx])->getAux()->vda_name;
versionedNameBuffer.clear();
name = (name + "@" + verName).toStringRef(versionedNameBuffer);
auto *s = symtab.addSymbol(
SharedSymbol{*this, saver().save(name), sym.getBinding(), sym.st_other,
sym.getType(), sym.st_value, sym.st_size, alignment});
if (s->file == this)
s->verdefIndex = idx;
}
}
static ELFKind getBitcodeELFKind(const Triple &t) {
if (t.isLittleEndian())
return t.isArch64Bit() ? ELF64LEKind : ELF32LEKind;
return t.isArch64Bit() ? ELF64BEKind : ELF32BEKind;
}
static uint16_t getBitcodeMachineKind(StringRef path, const Triple &t) {
switch (t.getArch()) {
case Triple::aarch64:
case Triple::aarch64_be:
return EM_AARCH64;
case Triple::amdgcn:
case Triple::r600:
return EM_AMDGPU;
case Triple::arm:
case Triple::thumb:
return EM_ARM;
case Triple::avr:
return EM_AVR;
case Triple::hexagon:
return EM_HEXAGON;
case Triple::mips:
case Triple::mipsel:
case Triple::mips64:
case Triple::mips64el:
return EM_MIPS;
case Triple::msp430:
return EM_MSP430;
case Triple::ppc:
case Triple::ppcle:
return EM_PPC;
case Triple::ppc64:
case Triple::ppc64le:
return EM_PPC64;
case Triple::riscv32:
case Triple::riscv64:
return EM_RISCV;
case Triple::x86:
return t.isOSIAMCU() ? EM_IAMCU : EM_386;
case Triple::x86_64:
return EM_X86_64;
default:
error(path + ": could not infer e_machine from bitcode target triple " +
t.str());
return EM_NONE;
}
}
static uint8_t getOsAbi(const Triple &t) {
switch (t.getOS()) {
case Triple::AMDHSA:
return ELF::ELFOSABI_AMDGPU_HSA;
case Triple::AMDPAL:
return ELF::ELFOSABI_AMDGPU_PAL;
case Triple::Mesa3D:
return ELF::ELFOSABI_AMDGPU_MESA3D;
default:
return ELF::ELFOSABI_NONE;
}
}
BitcodeFile::BitcodeFile(MemoryBufferRef mb, StringRef archiveName,
uint64_t offsetInArchive, bool lazy)
: InputFile(BitcodeKind, mb) {
this->archiveName = archiveName;
this->lazy = lazy;
std::string path = mb.getBufferIdentifier().str();
if (config->thinLTOIndexOnly)
path = replaceThinLTOSuffix(mb.getBufferIdentifier());
// ThinLTO assumes that all MemoryBufferRefs given to it have a unique
// name. 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). So we append file offset to make
// filename unique.
StringRef name = archiveName.empty()
? saver().save(path)
: saver().save(archiveName + "(" + path::filename(path) +
" at " + utostr(offsetInArchive) + ")");
MemoryBufferRef mbref(mb.getBuffer(), name);
obj = CHECK(lto::InputFile::create(mbref), this);
Triple t(obj->getTargetTriple());
ekind = getBitcodeELFKind(t);
emachine = getBitcodeMachineKind(mb.getBufferIdentifier(), t);
osabi = getOsAbi(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");
}
static void
createBitcodeSymbol(Symbol *&sym, const std::vector<bool> &keptComdats,
const lto::InputFile::Symbol &objSym, BitcodeFile &f) {
uint8_t binding = objSym.isWeak() ? STB_WEAK : STB_GLOBAL;
uint8_t type = objSym.isTLS() ? STT_TLS : STT_NOTYPE;
uint8_t visibility = mapVisibility(objSym.getVisibility());
if (!sym)
sym = symtab->insert(saver().save(objSym.getName()));
int c = objSym.getComdatIndex();
if (objSym.isUndefined() || (c != -1 && !keptComdats[c])) {
Undefined newSym(&f, StringRef(), binding, visibility, type);
sym->resolve(newSym);
sym->referenced = true;
return;
}
if (objSym.isCommon()) {
sym->resolve(CommonSymbol{&f, StringRef(), binding, visibility, STT_OBJECT,
objSym.getCommonAlignment(),
objSym.getCommonSize()});
} else {
Defined newSym(&f, StringRef(), binding, visibility, type, 0, 0, nullptr);
if (objSym.canBeOmittedFromSymbolTable())
newSym.exportDynamic = false;
sym->resolve(newSym);
}
}
void BitcodeFile::parse() {
for (std::pair<StringRef, Comdat::SelectionKind> s : obj->getComdatTable()) {
keptComdats.push_back(
s.second == Comdat::NoDeduplicate ||
symtab->comdatGroups.try_emplace(CachedHashStringRef(s.first), this)
.second);
}
symbols.resize(obj->symbols().size());
// Process defined symbols first. See the comment in
// ObjFile<ELFT>::initializeSymbols.
for (auto [i, irSym] : llvm::enumerate(obj->symbols()))
if (!irSym.isUndefined())
createBitcodeSymbol(symbols[i], keptComdats, irSym, *this);
for (auto [i, irSym] : llvm::enumerate(obj->symbols()))
if (irSym.isUndefined())
createBitcodeSymbol(symbols[i], keptComdats, irSym, *this);
for (auto l : obj->getDependentLibraries())
addDependentLibrary(l, this);
}
void BitcodeFile::parseLazy() {
SymbolTable &symtab = *elf::symtab;
symbols.resize(obj->symbols().size());
for (auto [i, irSym] : llvm::enumerate(obj->symbols()))
if (!irSym.isUndefined()) {
auto *sym = symtab.insert(saver().save(irSym.getName()));
sym->resolve(LazyObject{*this});
symbols[i] = sym;
}
}
void BitcodeFile::postParse() {
for (auto [i, irSym] : llvm::enumerate(obj->symbols())) {
const Symbol &sym = *symbols[i];
if (sym.file == this || !sym.isDefined() || irSym.isUndefined() ||
irSym.isCommon() || irSym.isWeak())
continue;
int c = irSym.getComdatIndex();
if (c != -1 && !keptComdats[c])
continue;
reportDuplicate(sym, this, nullptr, 0);
}
}
void BinaryFile::parse() {
ArrayRef<uint8_t> data = arrayRefFromStringRef(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] = '_';
llvm::StringSaver &saver = lld::saver();
symtab->addAndCheckDuplicate(Defined{nullptr, saver.save(s + "_start"),
STB_GLOBAL, STV_DEFAULT, STT_OBJECT, 0,
0, section});
symtab->addAndCheckDuplicate(Defined{nullptr, saver.save(s + "_end"),
STB_GLOBAL, STV_DEFAULT, STT_OBJECT,
data.size(), 0, section});
symtab->addAndCheckDuplicate(Defined{nullptr, saver.save(s + "_size"),
STB_GLOBAL, STV_DEFAULT, STT_OBJECT,
data.size(), 0, nullptr});
}
ELFFileBase *elf::createObjFile(MemoryBufferRef mb, StringRef archiveName,
bool lazy) {
ELFFileBase *f;
switch (getELFKind(mb, archiveName)) {
case ELF32LEKind:
f = make<ObjFile<ELF32LE>>(mb, archiveName);
break;
case ELF32BEKind:
f = make<ObjFile<ELF32BE>>(mb, archiveName);
break;
case ELF64LEKind:
f = make<ObjFile<ELF64LE>>(mb, archiveName);
break;
case ELF64BEKind:
f = make<ObjFile<ELF64BE>>(mb, archiveName);
break;
default:
llvm_unreachable("getELFKind");
}
f->lazy = lazy;
return f;
}
template <class ELFT> void ObjFile<ELFT>::parseLazy() {
const ArrayRef<typename ELFT::Sym> eSyms = this->getELFSyms<ELFT>();
SymbolTable &symtab = *elf::symtab;
symbols.resize(eSyms.size());
for (size_t i = firstGlobal, end = eSyms.size(); i != end; ++i)
if (eSyms[i].st_shndx != SHN_UNDEF)
symbols[i] = symtab.insert(CHECK(eSyms[i].getName(stringTable), this));
// Replace existing symbols with LazyObject symbols.
//
// resolve() may trigger this->extract() if an existing symbol is an undefined
// symbol. If that happens, this function has served its purpose, and we can
// exit from the loop early.
for (Symbol *sym : makeArrayRef(symbols).slice(firstGlobal))
if (sym) {
sym->resolve(LazyObject{*this});
if (!lazy)
return;
}
}
bool InputFile::shouldExtractForCommon(StringRef name) {
if (isa<BitcodeFile>(this))
return isBitcodeNonCommonDef(mb, name, archiveName);
return isNonCommonDef(mb, name, archiveName);
}
std::string elf::replaceThinLTOSuffix(StringRef path) {
StringRef suffix = config->thinLTOObjectSuffixReplace.first;
StringRef repl = config->thinLTOObjectSuffixReplace.second;
if (path.consume_back(suffix))
return (path + repl).str();
return std::string(path);
}
template class elf::ObjFile<ELF32LE>;
template class elf::ObjFile<ELF32BE>;
template class elf::ObjFile<ELF64LE>;
template class elf::ObjFile<ELF64BE>;
template void SharedFile::parse<ELF32LE>();
template void SharedFile::parse<ELF32BE>();
template void SharedFile::parse<ELF64LE>();
template void SharedFile::parse<ELF64BE>();
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