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llvm-project/lld/ELF/SymbolTable.cpp

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//===- SymbolTable.cpp ----------------------------------------------------===//
//
// The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Symbol table is a bag of all known symbols. We put all symbols of
// all input files to the symbol table. The symbol table is basically
// a hash table with the logic to resolve symbol name conflicts using
// the symbol types.
//
//===----------------------------------------------------------------------===//
#include "SymbolTable.h"
#include "Config.h"
#include "Error.h"
#include "LinkerScript.h"
#include "Strings.h"
#include "SymbolListFile.h"
#include "Symbols.h"
#include "llvm/Bitcode/ReaderWriter.h"
#include "llvm/Support/StringSaver.h"
using namespace llvm;
using namespace llvm::object;
using namespace llvm::ELF;
using namespace lld;
using namespace lld::elf;
// 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.
template <class ELFT> static bool isCompatible(InputFile *F) {
if (!isa<ELFFileBase<ELFT>>(F) && !isa<BitcodeFile>(F))
return true;
if (F->EKind == Config->EKind && F->EMachine == Config->EMachine)
return true;
StringRef A = F->getName();
StringRef B = Config->Emulation;
if (B.empty())
B = Config->FirstElf->getName();
error(A + " is incompatible with " + B);
return false;
}
// Add symbols in File to the symbol table.
template <class ELFT>
void SymbolTable<ELFT>::addFile(std::unique_ptr<InputFile> File) {
InputFile *FileP = File.get();
if (!isCompatible<ELFT>(FileP))
return;
// .a file
if (auto *F = dyn_cast<ArchiveFile>(FileP)) {
ArchiveFiles.emplace_back(cast<ArchiveFile>(File.release()));
F->parse<ELFT>();
return;
}
// Lazy object file
if (auto *F = dyn_cast<LazyObjectFile>(FileP)) {
LazyObjectFiles.emplace_back(cast<LazyObjectFile>(File.release()));
F->parse<ELFT>();
return;
}
if (Config->Trace)
llvm::outs() << getFilename(FileP) << "\n";
// .so file
if (auto *F = dyn_cast<SharedFile<ELFT>>(FileP)) {
// DSOs are uniquified not by filename but by soname.
F->parseSoName();
if (!SoNames.insert(F->getSoName()).second)
return;
SharedFiles.emplace_back(cast<SharedFile<ELFT>>(File.release()));
F->parseRest();
return;
}
// LLVM bitcode file
if (auto *F = dyn_cast<BitcodeFile>(FileP)) {
BitcodeFiles.emplace_back(cast<BitcodeFile>(File.release()));
F->parse<ELFT>(ComdatGroups);
return;
}
// Regular object file
auto *F = cast<ObjectFile<ELFT>>(FileP);
ObjectFiles.emplace_back(cast<ObjectFile<ELFT>>(File.release()));
F->parse(ComdatGroups);
}
// This function is where all the optimizations of link-time
// optimization happens. When LTO is in use, some input files are
// not in native object file format but in the LLVM bitcode format.
// This function compiles bitcode files into a few big native files
// using LLVM functions and replaces bitcode symbols with the results.
// Because all bitcode files that consist of a program are passed
// to the compiler at once, it can do whole-program optimization.
template <class ELFT> void SymbolTable<ELFT>::addCombinedLtoObject() {
if (BitcodeFiles.empty())
return;
// Compile bitcode files.
Lto.reset(new BitcodeCompiler);
for (const std::unique_ptr<BitcodeFile> &F : BitcodeFiles)
Lto->add(*F);
std::vector<std::unique_ptr<InputFile>> IFs = Lto->compile();
// Replace bitcode symbols.
for (auto &IF : IFs) {
ObjectFile<ELFT> *Obj = cast<ObjectFile<ELFT>>(IF.release());
llvm::DenseSet<StringRef> DummyGroups;
Obj->parse(DummyGroups);
ObjectFiles.emplace_back(Obj);
}
}
template <class ELFT>
DefinedRegular<ELFT> *SymbolTable<ELFT>::addAbsolute(StringRef Name,
uint8_t Visibility) {
return cast<DefinedRegular<ELFT>>(
addRegular(Name, STB_GLOBAL, Visibility)->body());
}
// Add Name as an "ignored" symbol. An ignored symbol is a regular
// linker-synthesized defined symbol, but is only defined if needed.
template <class ELFT>
DefinedRegular<ELFT> *SymbolTable<ELFT>::addIgnored(StringRef Name,
uint8_t Visibility) {
if (!find(Name))
return nullptr;
return addAbsolute(Name, Visibility);
}
// Rename SYM as __wrap_SYM. The original symbol is preserved as __real_SYM.
// Used to implement --wrap.
template <class ELFT> void SymbolTable<ELFT>::wrap(StringRef Name) {
SymbolBody *B = find(Name);
if (!B)
return;
StringSaver Saver(Alloc);
Symbol *Sym = B->symbol();
Symbol *Real = addUndefined(Saver.save("__real_" + Name));
Symbol *Wrap = addUndefined(Saver.save("__wrap_" + Name));
// We rename symbols by replacing the old symbol's SymbolBody with the new
// symbol's SymbolBody. This causes all SymbolBody pointers referring to the
// old symbol to instead refer to the new symbol.
memcpy(Real->Body.buffer, Sym->Body.buffer, sizeof(Sym->Body));
memcpy(Sym->Body.buffer, Wrap->Body.buffer, sizeof(Wrap->Body));
}
static uint8_t getMinVisibility(uint8_t VA, uint8_t VB) {
if (VA == STV_DEFAULT)
return VB;
if (VB == STV_DEFAULT)
return VA;
return std::min(VA, VB);
}
// A symbol version may be included in a symbol name as a suffix after '@'.
// This function parses that part and returns a version ID number.
static uint16_t getVersionId(Symbol *Sym, StringRef Name) {
size_t VersionBegin = Name.find('@');
if (VersionBegin == StringRef::npos)
return Config->DefaultSymbolVersion;
// If symbol name contains '@' or '@@' we can assign its version id right
// here. '@@' means the default version. It is usually the most recent one.
// VERSYM_HIDDEN flag should be set for all non-default versions.
StringRef Version = Name.drop_front(VersionBegin + 1);
bool Default = Version.startswith("@");
if (Default)
Version = Version.drop_front();
for (VersionDefinition &V : Config->VersionDefinitions)
if (V.Name == Version)
return Default ? V.Id : (V.Id | VERSYM_HIDDEN);
// If we are not building shared and version script
// is not specified, then it is not a error, it is
// in common not to use script for linking executables.
// In this case we just create new version.
if (!Config->Shared && !Config->HasVersionScript) {
size_t Id = defineSymbolVersion(Version);
return Default ? Id : (Id | VERSYM_HIDDEN);
}
error("symbol " + Name + " has undefined version " + Version);
return 0;
}
// Find an existing symbol or create and insert a new one.
template <class ELFT>
std::pair<Symbol *, bool> SymbolTable<ELFT>::insert(StringRef Name) {
unsigned NumSyms = SymVector.size();
auto P = Symtab.insert(std::make_pair(Name, NumSyms));
Symbol *Sym;
if (P.second) {
Sym = new (Alloc) Symbol;
Sym->Binding = STB_WEAK;
Sym->Visibility = STV_DEFAULT;
Sym->IsUsedInRegularObj = false;
Sym->ExportDynamic = false;
Sym->VersionId = getVersionId(Sym, Name);
Sym->VersionedName =
Sym->VersionId != VER_NDX_LOCAL && Sym->VersionId != VER_NDX_GLOBAL;
SymVector.push_back(Sym);
} else {
Sym = SymVector[P.first->second];
}
return {Sym, P.second};
}
// Find an existing symbol or create and insert a new one, then apply the given
// attributes.
template <class ELFT>
std::pair<Symbol *, bool>
SymbolTable<ELFT>::insert(StringRef Name, uint8_t Type, uint8_t Visibility,
bool CanOmitFromDynSym, bool IsUsedInRegularObj,
InputFile *File) {
Symbol *S;
bool WasInserted;
std::tie(S, WasInserted) = insert(Name);
// Merge in the new symbol's visibility.
S->Visibility = getMinVisibility(S->Visibility, Visibility);
if (!CanOmitFromDynSym && (Config->Shared || Config->ExportDynamic))
S->ExportDynamic = true;
if (IsUsedInRegularObj)
S->IsUsedInRegularObj = true;
if (!WasInserted && S->body()->Type != SymbolBody::UnknownType &&
((Type == STT_TLS) != S->body()->isTls()))
error("TLS attribute mismatch for symbol: " +
conflictMsg(S->body(), File));
return {S, WasInserted};
}
// Construct a string in the form of "Sym in File1 and File2".
// Used to construct an error message.
template <typename ELFT>
std::string SymbolTable<ELFT>::conflictMsg(SymbolBody *Existing,
InputFile *NewFile) {
std::string Sym = Existing->getName();
if (Config->Demangle)
Sym = demangle(Sym);
return Sym + " in " + getFilename(Existing->getSourceFile<ELFT>()) + " and " +
getFilename(NewFile);
}
template <class ELFT> Symbol *SymbolTable<ELFT>::addUndefined(StringRef Name) {
return addUndefined(Name, STB_GLOBAL, STV_DEFAULT, /*Type*/ 0,
/*CanOmitFromDynSym*/ false, /*File*/ nullptr);
}
template <class ELFT>
Symbol *SymbolTable<ELFT>::addUndefined(StringRef Name, uint8_t Binding,
uint8_t StOther, uint8_t Type,
bool CanOmitFromDynSym,
InputFile *File) {
Symbol *S;
bool WasInserted;
std::tie(S, WasInserted) =
insert(Name, Type, StOther & 3, CanOmitFromDynSym,
/*IsUsedInRegularObj*/ !File || !isa<BitcodeFile>(File), File);
if (WasInserted) {
S->Binding = Binding;
replaceBody<Undefined>(S, Name, StOther, Type);
cast<Undefined>(S->body())->File = File;
return S;
}
if (Binding != STB_WEAK) {
if (S->body()->isShared() || S->body()->isLazy())
S->Binding = Binding;
if (auto *SS = dyn_cast<SharedSymbol<ELFT>>(S->body()))
SS->File->IsUsed = true;
}
if (auto *L = dyn_cast<Lazy>(S->body())) {
// An undefined weak will not fetch archive members, but we have to remember
// its type. See also comment in addLazyArchive.
if (S->isWeak())
L->Type = Type;
else if (auto F = L->getFile())
addFile(std::move(F));
}
return S;
}
// We have a new defined symbol with the specified binding. Return 1 if the new
// symbol should win, -1 if the new symbol should lose, or 0 if both symbols are
// strong defined symbols.
static int compareDefined(Symbol *S, bool WasInserted, uint8_t Binding) {
if (WasInserted)
return 1;
SymbolBody *Body = S->body();
if (Body->isLazy() || Body->isUndefined() || Body->isShared())
return 1;
if (Binding == STB_WEAK)
return -1;
if (S->isWeak())
return 1;
return 0;
}
// We have a new non-common defined symbol with the specified binding. Return 1
// if the new symbol should win, -1 if the new symbol should lose, or 0 if there
// is a conflict. If the new symbol wins, also update the binding.
static int compareDefinedNonCommon(Symbol *S, bool WasInserted, uint8_t Binding) {
if (int Cmp = compareDefined(S, WasInserted, Binding)) {
if (Cmp > 0)
S->Binding = Binding;
return Cmp;
}
if (isa<DefinedCommon>(S->body())) {
// Non-common symbols take precedence over common symbols.
if (Config->WarnCommon)
warning("common " + S->body()->getName() + " is overridden");
return 1;
}
return 0;
}
template <class ELFT>
Symbol *SymbolTable<ELFT>::addCommon(StringRef N, uint64_t Size,
uint64_t Alignment, uint8_t Binding,
uint8_t StOther, uint8_t Type,
InputFile *File) {
Symbol *S;
bool WasInserted;
std::tie(S, WasInserted) =
insert(N, Type, StOther & 3, /*CanOmitFromDynSym*/ false,
/*IsUsedInRegularObj*/ true, File);
int Cmp = compareDefined(S, WasInserted, Binding);
if (Cmp > 0) {
S->Binding = Binding;
replaceBody<DefinedCommon>(S, N, Size, Alignment, StOther, Type);
} else if (Cmp == 0) {
auto *C = dyn_cast<DefinedCommon>(S->body());
if (!C) {
// Non-common symbols take precedence over common symbols.
if (Config->WarnCommon)
warning("common " + S->body()->getName() + " is overridden");
return S;
}
if (Config->WarnCommon)
warning("multiple common of " + S->body()->getName());
C->Size = std::max(C->Size, Size);
C->Alignment = std::max(C->Alignment, Alignment);
}
return S;
}
template <class ELFT>
void SymbolTable<ELFT>::reportDuplicate(SymbolBody *Existing,
InputFile *NewFile) {
std::string Msg = "duplicate symbol: " + conflictMsg(Existing, NewFile);
if (Config->AllowMultipleDefinition)
warning(Msg);
else
error(Msg);
}
template <typename ELFT>
Symbol *SymbolTable<ELFT>::addRegular(StringRef Name, const Elf_Sym &Sym,
InputSectionBase<ELFT> *Section) {
Symbol *S;
bool WasInserted;
std::tie(S, WasInserted) =
insert(Name, Sym.getType(), Sym.getVisibility(),
/*CanOmitFromDynSym*/ false, /*IsUsedInRegularObj*/ true,
Section ? Section->getFile() : nullptr);
int Cmp = compareDefinedNonCommon(S, WasInserted, Sym.getBinding());
if (Cmp > 0)
replaceBody<DefinedRegular<ELFT>>(S, Name, Sym, Section);
else if (Cmp == 0)
reportDuplicate(S->body(), Section->getFile());
return S;
}
template <typename ELFT>
Symbol *SymbolTable<ELFT>::addRegular(StringRef Name, uint8_t Binding,
uint8_t StOther) {
Symbol *S;
bool WasInserted;
std::tie(S, WasInserted) =
insert(Name, STT_NOTYPE, StOther & 3, /*CanOmitFromDynSym*/ false,
/*IsUsedInRegularObj*/ true, nullptr);
int Cmp = compareDefinedNonCommon(S, WasInserted, Binding);
if (Cmp > 0)
replaceBody<DefinedRegular<ELFT>>(S, Name, StOther);
else if (Cmp == 0)
reportDuplicate(S->body(), nullptr);
return S;
}
template <typename ELFT>
Symbol *SymbolTable<ELFT>::addSynthetic(StringRef N,
OutputSectionBase<ELFT> *Section,
uintX_t Value) {
Symbol *S;
bool WasInserted;
std::tie(S, WasInserted) =
insert(N, STT_NOTYPE, STV_HIDDEN, /*CanOmitFromDynSym*/ false,
/*IsUsedInRegularObj*/ true, nullptr);
int Cmp = compareDefinedNonCommon(S, WasInserted, STB_GLOBAL);
if (Cmp > 0)
replaceBody<DefinedSynthetic<ELFT>>(S, N, Value, Section);
else if (Cmp == 0)
reportDuplicate(S->body(), nullptr);
return S;
}
template <typename ELFT>
void SymbolTable<ELFT>::addShared(SharedFile<ELFT> *F, StringRef Name,
const Elf_Sym &Sym,
const typename ELFT::Verdef *Verdef) {
// DSO symbols do not affect visibility in the output, so we pass STV_DEFAULT
// as the visibility, which will leave the visibility in the symbol table
// unchanged.
Symbol *S;
bool WasInserted;
std::tie(S, WasInserted) =
insert(Name, Sym.getType(), STV_DEFAULT, /*CanOmitFromDynSym*/ true,
/*IsUsedInRegularObj*/ false, F);
// Make sure we preempt DSO symbols with default visibility.
if (Sym.getVisibility() == STV_DEFAULT)
S->ExportDynamic = true;
if (WasInserted || isa<Undefined>(S->body())) {
replaceBody<SharedSymbol<ELFT>>(S, F, Name, Sym, Verdef);
if (!S->isWeak())
F->IsUsed = true;
}
}
template <class ELFT>
Symbol *SymbolTable<ELFT>::addBitcode(StringRef Name, bool IsWeak,
uint8_t StOther, uint8_t Type,
bool CanOmitFromDynSym, BitcodeFile *F) {
Symbol *S;
bool WasInserted;
std::tie(S, WasInserted) = insert(Name, Type, StOther & 3, CanOmitFromDynSym,
/*IsUsedInRegularObj*/ false, F);
int Cmp =
compareDefinedNonCommon(S, WasInserted, IsWeak ? STB_WEAK : STB_GLOBAL);
if (Cmp > 0)
replaceBody<DefinedBitcode>(S, Name, StOther, Type, F);
else if (Cmp == 0)
reportDuplicate(S->body(), F);
return S;
}
template <class ELFT> SymbolBody *SymbolTable<ELFT>::find(StringRef Name) {
auto It = Symtab.find(Name);
if (It == Symtab.end())
return nullptr;
return SymVector[It->second]->body();
}
// Returns a list of defined symbols that match with a given glob pattern.
template <class ELFT>
std::vector<SymbolBody *> SymbolTable<ELFT>::findAll(StringRef Pattern) {
std::vector<SymbolBody *> Res;
for (auto &It : Symtab) {
StringRef Name = It.first.Val;
SymbolBody *B = SymVector[It.second]->body();
if (!B->isUndefined() && globMatch(Pattern, Name))
Res.push_back(B);
}
return Res;
}
template <class ELFT>
void SymbolTable<ELFT>::addLazyArchive(
ArchiveFile *F, const llvm::object::Archive::Symbol Sym) {
Symbol *S;
bool WasInserted;
std::tie(S, WasInserted) = insert(Sym.getName());
if (WasInserted) {
replaceBody<LazyArchive>(S, *F, Sym, SymbolBody::UnknownType);
return;
}
if (!S->body()->isUndefined())
return;
// Weak undefined symbols should not fetch members from archives. If we were
// to keep old symbol we would not know that an archive member was available
// if a strong undefined symbol shows up afterwards in the link. If a strong
// undefined symbol never shows up, this lazy symbol will get to the end of
// the link and must be treated as the weak undefined one. We already marked
// this symbol as used when we added it to the symbol table, but we also need
// to preserve its type. FIXME: Move the Type field to Symbol.
if (S->isWeak()) {
replaceBody<LazyArchive>(S, *F, Sym, S->body()->Type);
return;
}
MemoryBufferRef MBRef = F->getMember(&Sym);
if (!MBRef.getBuffer().empty())
addFile(createObjectFile(MBRef, F->getName()));
}
template <class ELFT>
void SymbolTable<ELFT>::addLazyObject(StringRef Name, LazyObjectFile &Obj) {
Symbol *S;
bool WasInserted;
std::tie(S, WasInserted) = insert(Name);
if (WasInserted) {
replaceBody<LazyObject>(S, Name, Obj, SymbolBody::UnknownType);
return;
}
if (!S->body()->isUndefined())
return;
// See comment for addLazyArchive above.
if (S->isWeak()) {
replaceBody<LazyObject>(S, Name, Obj, S->body()->Type);
} else {
MemoryBufferRef MBRef = Obj.getBuffer();
if (!MBRef.getBuffer().empty())
addFile(createObjectFile(MBRef));
}
}
// Process undefined (-u) flags by loading lazy symbols named by those flags.
template <class ELFT> void SymbolTable<ELFT>::scanUndefinedFlags() {
for (StringRef S : Config->Undefined)
if (auto *L = dyn_cast_or_null<Lazy>(find(S)))
if (std::unique_ptr<InputFile> File = L->getFile())
addFile(std::move(File));
}
// This function takes care of the case in which shared libraries depend on
// the user program (not the other way, which is usual). Shared libraries
// may have undefined symbols, expecting that the user program provides
// the definitions for them. An example is BSD's __progname symbol.
// We need to put such symbols to the main program's .dynsym so that
// shared libraries can find them.
// Except this, we ignore undefined symbols in DSOs.
template <class ELFT> void SymbolTable<ELFT>::scanShlibUndefined() {
for (std::unique_ptr<SharedFile<ELFT>> &File : SharedFiles)
for (StringRef U : File->getUndefinedSymbols())
if (SymbolBody *Sym = find(U))
if (Sym->isDefined())
Sym->symbol()->ExportDynamic = true;
}
// This function process the dynamic list option by marking all the symbols
// to be exported in the dynamic table.
template <class ELFT> void SymbolTable<ELFT>::scanDynamicList() {
for (StringRef S : Config->DynamicList)
if (SymbolBody *B = find(S))
B->symbol()->ExportDynamic = true;
}
static bool hasWildcard(StringRef S) {
return S.find_first_of("?*") != StringRef::npos;
}
// This function processes the --version-script option by marking all global
// symbols with the VersionScriptGlobal flag, which acts as a filter on the
// dynamic symbol table.
template <class ELFT> void SymbolTable<ELFT>::scanVersionScript() {
// If version script does not contain versions declarations,
// we just should mark global symbols.
if (!Config->VersionScriptGlobals.empty()) {
for (StringRef S : Config->VersionScriptGlobals)
if (SymbolBody *B = find(S))
B->symbol()->VersionId = VER_NDX_GLOBAL;
return;
}
if (Config->VersionDefinitions.empty())
return;
// If we have symbols version declarations, we should
// assign version references for each symbol.
// Current rules are:
// * If there is an exact match for the mangled name, we use it.
// * Otherwise, we look through the wildcard patterns. We look through the
// version tags in reverse order. We use the first match we find (the last
// matching version tag in the file).
for (size_t I = 0, E = Config->VersionDefinitions.size(); I < E; ++I) {
VersionDefinition &V = Config->VersionDefinitions[I];
for (StringRef Name : V.Globals) {
if (hasWildcard(Name))
continue;
SymbolBody *B = find(Name);
if (!B || B->isUndefined()) {
if (Config->NoUndefinedVersion)
error("version script assignment of " + V.Name + " to symbol " +
Name + " failed: symbol not defined");
continue;
}
if (B->symbol()->VersionId != Config->DefaultSymbolVersion)
warning("duplicate symbol " + Name + " in version script");
B->symbol()->VersionId = V.Id;
}
}
for (size_t I = Config->VersionDefinitions.size() - 1; I != (size_t)-1; --I) {
VersionDefinition &V = Config->VersionDefinitions[I];
for (StringRef Name : V.Globals)
if (hasWildcard(Name))
for (SymbolBody *B : findAll(Name))
if (B->symbol()->VersionId == Config->DefaultSymbolVersion)
B->symbol()->VersionId = V.Id;
}
}
// Print the module names which define the notified
// symbols provided through -y or --trace-symbol option.
template <class ELFT> void SymbolTable<ELFT>::traceDefined() {
for (const auto &Symbol : Config->TraceSymbol)
if (SymbolBody *B = find(Symbol.getKey()))
if (B->isDefined() || B->isCommon())
if (InputFile *File = B->getSourceFile<ELFT>())
outs() << getFilename(File) << ": definition of "
<< B->getName() << "\n";
}
template class elf::SymbolTable<ELF32LE>;
template class elf::SymbolTable<ELF32BE>;
template class elf::SymbolTable<ELF64LE>;
template class elf::SymbolTable<ELF64BE>;
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