llvm-project/lld/wasm/Symbols.h

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//===- Symbols.h ------------------------------------------------*- C++ -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//
#ifndef LLD_WASM_SYMBOLS_H
#define LLD_WASM_SYMBOLS_H
#include "Config.h"
#include "lld/Common/LLVM.h"
#include "llvm/ADT/Optional.h"
#include "llvm/Object/Archive.h"
#include "llvm/Object/Wasm.h"
namespace lld {
namespace wasm {
// Shared string constants
// The default module name to use for symbol imports.
extern const char *defaultModule;
// The name under which to import or export the wasm table.
extern const char *functionTableName;
using llvm::wasm::WasmSymbolType;
class InputFile;
class InputChunk;
class InputSegment;
class InputFunction;
class InputGlobal;
class InputTag;
class InputSection;
class InputTable;
class OutputSection;
#define INVALID_INDEX UINT32_MAX
// The base class for real symbol classes.
class Symbol {
public:
enum Kind : uint8_t {
DefinedFunctionKind,
DefinedDataKind,
DefinedGlobalKind,
DefinedTagKind,
DefinedTableKind,
SectionKind,
OutputSectionKind,
UndefinedFunctionKind,
UndefinedDataKind,
UndefinedGlobalKind,
UndefinedTableKind,
LazyKind,
};
Kind kind() const { return symbolKind; }
bool isDefined() const { return !isLazy() && !isUndefined(); }
bool isUndefined() const {
return symbolKind == UndefinedFunctionKind ||
symbolKind == UndefinedDataKind ||
symbolKind == UndefinedGlobalKind ||
symbolKind == UndefinedTableKind;
}
bool isLazy() const { return symbolKind == LazyKind; }
bool isLocal() const;
bool isWeak() const;
bool isHidden() const;
// Returns true if this symbol exists in a discarded (due to COMDAT) section
bool isDiscarded() const;
// True if this is an undefined weak symbol. This only works once
// all input files have been added.
bool isUndefWeak() const {
// See comment on lazy symbols for details.
return isWeak() && (isUndefined() || isLazy());
}
// 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;
bool isExportedExplicit() const;
// Indicates that the symbol is used in an __attribute__((used)) directive
// or similar.
bool isNoStrip() const;
const WasmSignature* getSignature() const;
uint32_t getGOTIndex() const {
assert(gotIndex != INVALID_INDEX);
return gotIndex;
}
void setGOTIndex(uint32_t index);
bool hasGOTIndex() const { return gotIndex != INVALID_INDEX; }
protected:
Symbol(StringRef name, Kind k, uint32_t flags, InputFile *f)
: name(name), file(f), symbolKind(k), referenced(!config->gcSections),
requiresGOT(false), isUsedInRegularObj(false), forceExport(false),
canInline(false), traced(false), isStub(false), flags(flags) {}
StringRef name;
InputFile *file;
uint32_t outputSymbolIndex = INVALID_INDEX;
uint32_t gotIndex = INVALID_INDEX;
Kind symbolKind;
public:
bool referenced : 1;
// True for data symbols that needs a dummy GOT entry. Used for static
// linking of GOT accesses.
bool requiresGOT : 1;
// True if the symbol was used for linking and thus need to be added to the
// output file's symbol table. This is true for all symbols except for
// unreferenced DSO symbols, lazy (archive) symbols, and bitcode symbols that
// are unreferenced except by other bitcode objects.
bool isUsedInRegularObj : 1;
// True if ths symbol is explicitly marked for export (i.e. via the
// -e/--export command line flag)
bool forceExport : 1;
// False if LTO shouldn't inline whatever this symbol points to. If a symbol
// is overwritten after LTO, LTO shouldn't inline the symbol because it
// doesn't know the final contents of the symbol.
bool canInline : 1;
// True if this symbol is specified by --trace-symbol option.
bool traced : 1;
// True if this symbol is a linker-synthesized stub function (traps when
// called) and should otherwise be treated as missing/undefined. See
// SymbolTable::replaceWithUndefined.
// These stubs never appear in the table and any table index relocations
// against them will produce address 0 (The table index representing
// the null function pointer).
bool isStub : 1;
uint32_t flags;
};
class FunctionSymbol : public Symbol {
public:
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 *signature;
protected:
FunctionSymbol(StringRef name, Kind k, uint32_t flags, InputFile *f,
const WasmSignature *sig)
: Symbol(name, k, flags, f), signature(sig) {}
uint32_t tableIndex = INVALID_INDEX;
uint32_t functionIndex = INVALID_INDEX;
};
class DefinedFunction : public FunctionSymbol {
public:
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 {
public:
UndefinedFunction(StringRef name, llvm::Optional<StringRef> importName,
llvm::Optional<StringRef> importModule, uint32_t flags,
InputFile *file = nullptr,
const WasmSignature *type = nullptr,
bool isCalledDirectly = true)
: FunctionSymbol(name, UndefinedFunctionKind, flags, file, type),
importName(importName), importModule(importModule),
isCalledDirectly(isCalledDirectly) {}
static bool classof(const Symbol *s) {
return s->kind() == UndefinedFunctionKind;
}
llvm::Optional<StringRef> importName;
llvm::Optional<StringRef> importModule;
DefinedFunction *stubFunction = nullptr;
bool isCalledDirectly;
};
// Section symbols for output sections are different from those for input
// section. These are generated by the linker and point the OutputSection
// rather than an InputSection.
class OutputSectionSymbol : public Symbol {
public:
OutputSectionSymbol(const OutputSection *s)
: Symbol("", OutputSectionKind, llvm::wasm::WASM_SYMBOL_BINDING_LOCAL,
nullptr),
section(s) {}
static bool classof(const Symbol *s) {
return s->kind() == OutputSectionKind;
}
const OutputSection *section;
};
class SectionSymbol : public Symbol {
public:
SectionSymbol(uint32_t flags, const InputChunk *s, InputFile *f = nullptr)
: Symbol("", SectionKind, flags, f), section(s) {}
static bool classof(const Symbol *s) { return s->kind() == SectionKind; }
const OutputSectionSymbol *getOutputSectionSymbol() const;
const InputChunk *section;
};
class DataSymbol : public Symbol {
public:
static bool classof(const Symbol *s) {
return s->kind() == DefinedDataKind || s->kind() == UndefinedDataKind;
}
protected:
DataSymbol(StringRef name, Kind k, uint32_t flags, InputFile *f)
: Symbol(name, k, flags, f) {}
};
class DefinedData : public DataSymbol {
public:
2018-04-27 13:50:40 +08:00
// Constructor for regular data symbols originating from input files.
DefinedData(StringRef name, uint32_t flags, InputFile *f, InputChunk *segment,
uint64_t value, uint64_t size)
: DataSymbol(name, DefinedDataKind, flags, f), segment(segment),
value(value), 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.
uint64_t getVA() const;
void setVA(uint64_t va);
// Returns the offset of a defined data symbol within its OutputSegment.
uint64_t getOutputSegmentOffset() const;
uint64_t getOutputSegmentIndex() const;
uint64_t getSize() const { return size; }
InputChunk *segment = nullptr;
uint64_t value = 0;
protected:
uint64_t size = 0;
};
class UndefinedData : public DataSymbol {
public:
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 {
public:
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;
protected:
GlobalSymbol(StringRef name, Kind k, uint32_t flags, InputFile *f,
const WasmGlobalType *globalType)
: Symbol(name, k, flags, f), globalType(globalType) {}
const WasmGlobalType *globalType;
uint32_t globalIndex = INVALID_INDEX;
};
class DefinedGlobal : public GlobalSymbol {
public:
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 {
public:
UndefinedGlobal(StringRef name, llvm::Optional<StringRef> importName,
llvm::Optional<StringRef> importModule, uint32_t flags,
InputFile *file = nullptr,
const WasmGlobalType *type = nullptr)
: GlobalSymbol(name, UndefinedGlobalKind, flags, file, type),
importName(importName), importModule(importModule) {}
static bool classof(const Symbol *s) {
return s->kind() == UndefinedGlobalKind;
}
llvm::Optional<StringRef> importName;
llvm::Optional<StringRef> importModule;
};
class TableSymbol : public Symbol {
public:
static bool classof(const Symbol *s) {
return s->kind() == DefinedTableKind || s->kind() == UndefinedTableKind;
}
const WasmTableType *getTableType() const { return tableType; }
void setLimits(const WasmLimits &limits);
// Get/set the table number
uint32_t getTableNumber() const;
void setTableNumber(uint32_t number);
bool hasTableNumber() const;
protected:
TableSymbol(StringRef name, Kind k, uint32_t flags, InputFile *f,
const WasmTableType *type)
: Symbol(name, k, flags, f), tableType(type) {}
const WasmTableType *tableType;
uint32_t tableNumber = INVALID_INDEX;
};
class DefinedTable : public TableSymbol {
public:
DefinedTable(StringRef name, uint32_t flags, InputFile *file,
InputTable *table);
static bool classof(const Symbol *s) { return s->kind() == DefinedTableKind; }
InputTable *table;
};
class UndefinedTable : public TableSymbol {
public:
UndefinedTable(StringRef name, llvm::Optional<StringRef> importName,
llvm::Optional<StringRef> importModule, uint32_t flags,
InputFile *file, const WasmTableType *type)
: TableSymbol(name, UndefinedTableKind, flags, file, type),
importName(importName), importModule(importModule) {}
static bool classof(const Symbol *s) {
return s->kind() == UndefinedTableKind;
}
llvm::Optional<StringRef> importName;
llvm::Optional<StringRef> importModule;
};
// A tag is a general format to distinguish typed entities. Each tag has an
// attribute and a type. Currently the attribute can only specify that the tag
// is for an exception tag.
//
// In exception handling, tags are used to distinguish different kinds of
// exceptions. For example, they can be used to distinguish different language's
// exceptions, e.g., all C++ exceptions have the same tag and Java exceptions
// would have a distinct tag. Wasm can filter the exceptions it catches based on
// their tag.
//
// A single TagSymbol object represents a single tag. The C++ exception symbol
// is a weak symbol generated in every object file in which exceptions are used,
// and is named '__cpp_exception' for linking.
class TagSymbol : public Symbol {
public:
static bool classof(const Symbol *s) { return s->kind() == DefinedTagKind; }
const WasmTagType *getTagType() const { return tagType; }
// Get/set the tag index
uint32_t getTagIndex() const;
void setTagIndex(uint32_t index);
bool hasTagIndex() const;
const WasmSignature *signature;
protected:
TagSymbol(StringRef name, Kind k, uint32_t flags, InputFile *f,
const WasmTagType *tagType, const WasmSignature *sig)
: Symbol(name, k, flags, f), signature(sig), tagType(tagType) {}
const WasmTagType *tagType;
uint32_t tagIndex = INVALID_INDEX;
};
class DefinedTag : public TagSymbol {
public:
DefinedTag(StringRef name, uint32_t flags, InputFile *file, InputTag *tag);
static bool classof(const Symbol *s) { return s->kind() == DefinedTagKind; }
InputTag *tag;
};
// LazySymbol represents a symbol that is not yet in the link, but we know where
// to find it if needed. If the resolver finds both Undefined and Lazy for the
// same name, it will ask the Lazy to load a file.
//
// A special complication is the handling of weak undefined symbols. They should
// not load a file, but we have to remember we have seen both the weak undefined
// and the lazy. We represent that with a lazy symbol with a weak binding. This
// means that code looking for undefined symbols normally also has to take lazy
// symbols into consideration.
class LazySymbol : public Symbol {
public:
LazySymbol(StringRef name, uint32_t flags, InputFile *file,
const llvm::object::Archive::Symbol &sym)
: Symbol(name, LazyKind, flags, file), archiveSymbol(sym) {}
static bool classof(const Symbol *s) { return s->kind() == LazyKind; }
void fetch();
void setWeak();
MemoryBufferRef getMemberBuffer();
// Lazy symbols can have a signature because they can replace an
// UndefinedFunction which which case we need to be able to preserve the
// signature.
// TODO(sbc): This repetition of the signature field is inelegant. Revisit
// the use of class hierarchy to represent symbol taxonomy.
const WasmSignature *signature = nullptr;
private:
llvm::object::Archive::Symbol archiveSymbol;
};
// linker-generated symbols
struct WasmSym {
// __global_base
// Symbol marking the start of the global section.
static DefinedData *globalBase;
// __stack_pointer
// Global that holds the address of the top of the explicit value stack in
// linear memory.
static GlobalSymbol *stackPointer;
[WebAssembly] Implement thread-local storage (local-exec model) Summary: Thread local variables are placed inside a `.tdata` segment. Their symbols are offsets from the start of the segment. The address of a thread local variable is computed as `__tls_base` + the offset from the start of the segment. `.tdata` segment is a passive segment and `memory.init` is used once per thread to initialize the thread local storage. `__tls_base` is a wasm global. Since each thread has its own wasm instance, it is effectively thread local. Currently, `__tls_base` must be initialized at thread startup, and so cannot be used with dynamic libraries. `__tls_base` is to be initialized with a new linker-synthesized function, `__wasm_init_tls`, which takes as an argument a block of memory to use as the storage for thread locals. It then initializes the block of memory and sets `__tls_base`. As `__wasm_init_tls` will handle the memory initialization, the memory does not have to be zeroed. To help allocating memory for thread-local storage, a new compiler intrinsic is introduced: `__builtin_wasm_tls_size()`. This instrinsic function returns the size of the thread-local storage for the current function. The expected usage is to run something like the following upon thread startup: __wasm_init_tls(malloc(__builtin_wasm_tls_size())); Reviewers: tlively, aheejin, kripken, sbc100 Subscribers: dschuff, jgravelle-google, hiraditya, sunfish, jfb, cfe-commits, llvm-commits Tags: #clang, #llvm Differential Revision: https://reviews.llvm.org/D64537 llvm-svn: 366272
2019-07-17 06:00:45 +08:00
// __tls_base
// Global that holds the address of the base of the current thread's
// TLS block.
static GlobalSymbol *tlsBase;
// __tls_size
// Symbol whose value is the size of the TLS block.
static GlobalSymbol *tlsSize;
// __tls_size
// Symbol whose value is the alignment of the TLS block.
static GlobalSymbol *tlsAlign;
// __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_init_memory_flag
// Symbol whose contents are nonzero iff memory has already been initialized.
static DefinedData *initMemoryFlag;
// __wasm_init_memory
// Function that initializes passive data segments during instantiation.
static DefinedFunction *initMemory;
// __wasm_call_ctors
// Function that directly calls all ctors in priority order.
static DefinedFunction *callCtors;
// __wasm_call_dtors
// Function that calls the libc/etc. cleanup function.
static DefinedFunction *callDtors;
// __wasm_apply_data_relocs
// Function that applies relocations to data segment post-instantiation.
static DefinedFunction *applyDataRelocs;
// __wasm_apply_global_relocs
// Function that applies relocations to data segment post-instantiation.
// Unlike __wasm_apply_data_relocs this needs to run on every thread.
static DefinedFunction *applyGlobalRelocs;
[WebAssembly] Implement thread-local storage (local-exec model) Summary: Thread local variables are placed inside a `.tdata` segment. Their symbols are offsets from the start of the segment. The address of a thread local variable is computed as `__tls_base` + the offset from the start of the segment. `.tdata` segment is a passive segment and `memory.init` is used once per thread to initialize the thread local storage. `__tls_base` is a wasm global. Since each thread has its own wasm instance, it is effectively thread local. Currently, `__tls_base` must be initialized at thread startup, and so cannot be used with dynamic libraries. `__tls_base` is to be initialized with a new linker-synthesized function, `__wasm_init_tls`, which takes as an argument a block of memory to use as the storage for thread locals. It then initializes the block of memory and sets `__tls_base`. As `__wasm_init_tls` will handle the memory initialization, the memory does not have to be zeroed. To help allocating memory for thread-local storage, a new compiler intrinsic is introduced: `__builtin_wasm_tls_size()`. This instrinsic function returns the size of the thread-local storage for the current function. The expected usage is to run something like the following upon thread startup: __wasm_init_tls(malloc(__builtin_wasm_tls_size())); Reviewers: tlively, aheejin, kripken, sbc100 Subscribers: dschuff, jgravelle-google, hiraditya, sunfish, jfb, cfe-commits, llvm-commits Tags: #clang, #llvm Differential Revision: https://reviews.llvm.org/D64537 llvm-svn: 366272
2019-07-17 06:00:45 +08:00
// __wasm_init_tls
// Function that allocates thread-local storage and initializes it.
static DefinedFunction *initTLS;
// Pointer to the function that is to be used in the start section.
// (normally an alias of initMemory, or applyGlobalRelocs).
static DefinedFunction *startFunction;
// __dso_handle
// Symbol used in calls to __cxa_atexit to determine current DLL
static DefinedData *dsoHandle;
// __table_base
// Used in PIC code for offset of indirect function table
static UndefinedGlobal *tableBase;
static DefinedData *definedTableBase;
// 32-bit copy in wasm64 to work around init expr limitations.
// These can potentially be removed again once we have
// https://github.com/WebAssembly/extended-const
static UndefinedGlobal *tableBase32;
static DefinedData *definedTableBase32;
// __memory_base
// Used in PIC code for offset of global data
static UndefinedGlobal *memoryBase;
static DefinedData *definedMemoryBase;
// __indirect_function_table
// Used as an address space for function pointers, with each function that is
// used as a function pointer being allocated a slot.
static TableSymbol *indirectFunctionTable;
};
// 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(DefinedTag) char d[sizeof(DefinedTag)];
alignas(DefinedTable) char e[sizeof(DefinedTable)];
alignas(LazySymbol) char f[sizeof(LazySymbol)];
alignas(UndefinedFunction) char g[sizeof(UndefinedFunction)];
alignas(UndefinedData) char h[sizeof(UndefinedData)];
alignas(UndefinedGlobal) char i[sizeof(UndefinedGlobal)];
alignas(UndefinedTable) char j[sizeof(UndefinedTable)];
alignas(SectionSymbol) char k[sizeof(SectionSymbol)];
};
// It is important to keep the size of SymbolUnion small for performance and
// memory usage reasons. 96 bytes is a soft limit based on the size of
// UndefinedFunction on a 64-bit system.
static_assert(sizeof(SymbolUnion) <= 120, "SymbolUnion too large");
void printTraceSymbol(Symbol *sym);
void printTraceSymbolUndefined(StringRef name, const InputFile* file);
template <typename T, typename... ArgT>
T *replaceSymbol(Symbol *s, ArgT &&... arg) {
static_assert(std::is_trivially_destructible<T>(),
"Symbol types must be trivially destructible");
static_assert(sizeof(T) <= sizeof(SymbolUnion), "SymbolUnion 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;
s2->canInline = symCopy.canInline;
s2->traced = symCopy.traced;
// Print out a log message if --trace-symbol was specified.
// This is for debugging.
if (s2->traced)
printTraceSymbol(s2);
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);
std::string maybeDemangleSymbol(StringRef name);
} // namespace lld
#endif