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//===- Symbols.h ------------------------------------------------*- C++ -*-===//
// The LLVM Linker
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
#include "Config.h"
#include "lld/Common/LLVM.h"
#include "llvm/Object/Archive.h"
#include "llvm/Object/Wasm.h"
using llvm::object::Archive;
using llvm::object::WasmSymbol;
using llvm::wasm::WasmGlobal;
using llvm::wasm::WasmGlobalType;
using llvm::wasm::WasmSignature;
using llvm::wasm::WasmSymbolType;
namespace lld {
namespace wasm {
class InputFile;
class InputChunk;
class InputSegment;
class InputFunction;
class InputGlobal;
class InputSection;
// The base class for real symbol classes.
class Symbol {
enum Kind {
Kind kind() const { return SymbolKind; }
bool isDefined() const {
return SymbolKind == DefinedFunctionKind || SymbolKind == DefinedDataKind ||
SymbolKind == DefinedGlobalKind || SymbolKind == SectionKind;
bool isUndefined() const {
return SymbolKind == UndefinedFunctionKind ||
SymbolKind == UndefinedDataKind || SymbolKind == UndefinedGlobalKind;
bool isLazy() const { return SymbolKind == LazyKind; }
bool isLocal() const;
bool isWeak() const;
bool isHidden() const;
// Returns the symbol name.
StringRef getName() const { return Name; }
// Returns the file from which this symbol was created.
InputFile *getFile() const { return File; }
InputChunk *getChunk() const;
// Indicates that the section or import for this symbol will be included in
// the final image.
bool isLive() const;
// Marks the symbol's InputChunk as Live, so that it will be included in the
// final image.
void markLive();
void setHidden(bool IsHidden);
// Get/set the index in the output symbol table. This is only used for
// relocatable output.
uint32_t getOutputSymbolIndex() const;
void setOutputSymbolIndex(uint32_t Index);
WasmSymbolType getWasmType() const;
bool isExported() const;
// True if this symbol was referenced by a regular (non-bitcode) object.
unsigned IsUsedInRegularObj : 1;
unsigned ForceExport : 1;
Symbol(StringRef Name, Kind K, uint32_t Flags, InputFile *F)
: IsUsedInRegularObj(false), ForceExport(false), Name(Name),
SymbolKind(K), Flags(Flags), File(F), Referenced(!Config->GcSections) {}
StringRef Name;
Kind SymbolKind;
uint32_t Flags;
InputFile *File;
uint32_t OutputSymbolIndex = INVALID_INDEX;
bool Referenced;
class FunctionSymbol : public Symbol {
static bool classof(const Symbol *S) {
return S->kind() == DefinedFunctionKind ||
S->kind() == UndefinedFunctionKind;
// Get/set the table index
void setTableIndex(uint32_t Index);
uint32_t getTableIndex() const;
bool hasTableIndex() const;
// Get/set the function index
uint32_t getFunctionIndex() const;
void setFunctionIndex(uint32_t Index);
bool hasFunctionIndex() const;
const WasmSignature *FunctionType;
FunctionSymbol(StringRef Name, Kind K, uint32_t Flags, InputFile *F,
const WasmSignature *Type)
: Symbol(Name, K, Flags, F), FunctionType(Type) {}
uint32_t TableIndex = INVALID_INDEX;
uint32_t FunctionIndex = INVALID_INDEX;
class DefinedFunction : public FunctionSymbol {
DefinedFunction(StringRef Name, uint32_t Flags, InputFile *F,
InputFunction *Function);
static bool classof(const Symbol *S) {
return S->kind() == DefinedFunctionKind;
InputFunction *Function;
class UndefinedFunction : public FunctionSymbol {
UndefinedFunction(StringRef Name, uint32_t Flags, InputFile *File = nullptr,
const WasmSignature *Type = nullptr)
: FunctionSymbol(Name, UndefinedFunctionKind, Flags, File, Type) {}
static bool classof(const Symbol *S) {
return S->kind() == UndefinedFunctionKind;
class SectionSymbol : public Symbol {
static bool classof(const Symbol *S) { return S->kind() == SectionKind; }
SectionSymbol(StringRef Name, uint32_t Flags, const InputSection *S,
InputFile *F = nullptr)
: Symbol(Name, SectionKind, Flags, F), Section(S) {}
const InputSection *Section;
uint32_t getOutputSectionIndex() const;
void setOutputSectionIndex(uint32_t Index);
uint32_t OutputSectionIndex = INVALID_INDEX;
class DataSymbol : public Symbol {
static bool classof(const Symbol *S) {
return S->kind() == DefinedDataKind || S->kind() == UndefinedDataKind;
DataSymbol(StringRef Name, Kind K, uint32_t Flags, InputFile *F)
: Symbol(Name, K, Flags, F) {}
class DefinedData : public DataSymbol {
// Constructor for regular data symbols originating from input files.
DefinedData(StringRef Name, uint32_t Flags, InputFile *F,
InputSegment *Segment, uint32_t Offset, uint32_t Size)
: DataSymbol(Name, DefinedDataKind, Flags, F), Segment(Segment),
Offset(Offset), Size(Size) {}
// Constructor for linker synthetic data symbols.
DefinedData(StringRef Name, uint32_t Flags)
: DataSymbol(Name, DefinedDataKind, Flags, nullptr) {}
static bool classof(const Symbol *S) { return S->kind() == DefinedDataKind; }
// Returns the output virtual address of a defined data symbol.
uint32_t getVirtualAddress() const;
void setVirtualAddress(uint32_t VA);
// Returns the offset of a defined data symbol within its OutputSegment.
uint32_t getOutputSegmentOffset() const;
uint32_t getOutputSegmentIndex() const;
uint32_t getSize() const { return Size; }
InputSegment *Segment = nullptr;
uint32_t Offset = 0;
uint32_t Size = 0;
class UndefinedData : public DataSymbol {
UndefinedData(StringRef Name, uint32_t Flags, InputFile *File = nullptr)
: DataSymbol(Name, UndefinedDataKind, Flags, File) {}
static bool classof(const Symbol *S) {
return S->kind() == UndefinedDataKind;
class GlobalSymbol : public Symbol {
static bool classof(const Symbol *S) {
return S->kind() == DefinedGlobalKind || S->kind() == UndefinedGlobalKind;
const WasmGlobalType *getGlobalType() const { return GlobalType; }
// Get/set the global index
uint32_t getGlobalIndex() const;
void setGlobalIndex(uint32_t Index);
bool hasGlobalIndex() const;
GlobalSymbol(StringRef Name, Kind K, uint32_t Flags, InputFile *F,
const WasmGlobalType *GlobalType)
: Symbol(Name, K, Flags, F), GlobalType(GlobalType) {}
// Explicit function type, needed for undefined or synthetic functions only.
// For regular defined globals this information comes from the InputChunk.
const WasmGlobalType *GlobalType;
uint32_t GlobalIndex = INVALID_INDEX;
class DefinedGlobal : public GlobalSymbol {
DefinedGlobal(StringRef Name, uint32_t Flags, InputFile *File,
InputGlobal *Global);
static bool classof(const Symbol *S) {
return S->kind() == DefinedGlobalKind;
InputGlobal *Global;
class UndefinedGlobal : public GlobalSymbol {
UndefinedGlobal(StringRef Name, uint32_t Flags, InputFile *File = nullptr,
const WasmGlobalType *Type = nullptr)
: GlobalSymbol(Name, UndefinedGlobalKind, Flags, File, Type) {}
static bool classof(const Symbol *S) {
return S->kind() == UndefinedGlobalKind;
class LazySymbol : public Symbol {
LazySymbol(StringRef Name, InputFile *File, const Archive::Symbol &Sym)
: Symbol(Name, LazyKind, 0, File), ArchiveSymbol(Sym) {}
static bool classof(const Symbol *S) { return S->kind() == LazyKind; }
void fetch();
Archive::Symbol ArchiveSymbol;
// linker-generated symbols
struct WasmSym {
// __stack_pointer
// Global that holds the address of the top of the explicit value stack in
// linear memory.
static DefinedGlobal *StackPointer;
// __data_end
// Symbol marking the end of the data and bss.
static DefinedData *DataEnd;
// __heap_base
// Symbol marking the end of the data, bss and explicit stack. Any linear
// memory following this address is not used by the linked code and can
// therefore be used as a backing store for brk()/malloc() implementations.
static DefinedData *HeapBase;
// __wasm_call_ctors
// Function that directly calls all ctors in priority order.
static DefinedFunction *CallCtors;
// __dso_handle
// Symbol used in calls to __cxa_atexit to determine current DLL
static DefinedData *DsoHandle;
// A buffer class that is large enough to hold any Symbol-derived
// object. We allocate memory using this class and instantiate a symbol
// using the placement new.
union SymbolUnion {
alignas(DefinedFunction) char A[sizeof(DefinedFunction)];
alignas(DefinedData) char B[sizeof(DefinedData)];
alignas(DefinedGlobal) char C[sizeof(DefinedGlobal)];
alignas(LazySymbol) char D[sizeof(LazySymbol)];
alignas(UndefinedFunction) char E[sizeof(UndefinedFunction)];
alignas(UndefinedData) char F[sizeof(UndefinedData)];
alignas(UndefinedGlobal) char G[sizeof(UndefinedGlobal)];
alignas(SectionSymbol) char I[sizeof(SectionSymbol)];
template <typename T, typename... ArgT>
T *replaceSymbol(Symbol *S, ArgT &&... Arg) {
"Symbol types must be trivially destructible");
static_assert(sizeof(T) <= sizeof(SymbolUnion), "Symbol too small");
static_assert(alignof(T) <= alignof(SymbolUnion),
"SymbolUnion not aligned enough");
assert(static_cast<Symbol *>(static_cast<T *>(nullptr)) == nullptr &&
"Not a Symbol");
Symbol SymCopy = *S;
T *S2 = new (S) T(std::forward<ArgT>(Arg)...);
S2->IsUsedInRegularObj = SymCopy.IsUsedInRegularObj;
S2->ForceExport = SymCopy.ForceExport;
return S2;
} // namespace wasm
// Returns a symbol name for an error message.
std::string toString(const wasm::Symbol &Sym);
std::string toString(wasm::Symbol::Kind Kind);
} // namespace lld