lld/MachO/Symbols.h - llvm-project - Git at Google

 //===- 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_MACHO_SYMBOLS_H
 #define LLD_MACHO_SYMBOLS_H

 #include "Config.h"
 #include "InputFiles.h"
 #include "Target.h"
 #include "lld/Common/ErrorHandler.h"
 #include "lld/Common/Strings.h"
 #include "llvm/Object/Archive.h"
 #include "llvm/Support/MathExtras.h"

 namespace lld {
 namespace macho {

 class MachHeaderSection;

 struct StringRefZ {
   StringRefZ(const char *s) : data(s), size(-1) {}
   StringRefZ(StringRef s) : data(s.data()), size(s.size()) {}

   const char *data;
   const uint32_t size;
 };

 class Symbol {
 public:
   enum Kind {
     DefinedKind,
     UndefinedKind,
     CommonKind,
     DylibKind,
     LazyKind,
   };

   virtual ~Symbol() {}

   Kind kind() const { return symbolKind; }

   StringRef getName() const {
     if (nameSize == (uint32_t)-1)
       nameSize = strlen(nameData);
     return {nameData, nameSize};
   }

   bool isLive() const { return used; }

   virtual uint64_t getVA() const { return 0; }

   virtual bool isWeakDef() const { llvm_unreachable("cannot be weak def"); }

   // Only undefined or dylib symbols can be weak references. A weak reference
   // need not be satisfied at runtime, e.g. due to the symbol not being
   // available on a given target platform.
   virtual bool isWeakRef() const { llvm_unreachable("cannot be a weak ref"); }

   virtual bool isTlv() const { llvm_unreachable("cannot be TLV"); }

   // Whether this symbol is in the GOT or TLVPointer sections.
   bool isInGot() const { return gotIndex != UINT32_MAX; }

   // Whether this symbol is in the StubsSection.
   bool isInStubs() const { return stubsIndex != UINT32_MAX; }

   uint64_t getStubVA() const;
   uint64_t getGotVA() const;
   uint64_t getTlvVA() const;
   uint64_t resolveBranchVA() const {
     assert(isa<Defined>(this) || isa<DylibSymbol>(this));
     return isInStubs() ? getStubVA() : getVA();
   }
   uint64_t resolveGotVA() const { return isInGot() ? getGotVA() : getVA(); }
   uint64_t resolveTlvVA() const { return isInGot() ? getTlvVA() : getVA(); }

   // The index of this symbol in the GOT or the TLVPointer section, depending
   // on whether it is a thread-local. A given symbol cannot be referenced by
   // both these sections at once.
   uint32_t gotIndex = UINT32_MAX;

   uint32_t stubsIndex = UINT32_MAX;

   uint32_t symtabIndex = UINT32_MAX;

   InputFile *getFile() const { return file; }

 protected:
   Symbol(Kind k, StringRefZ name, InputFile *file)
       : symbolKind(k), nameData(name.data), file(file), nameSize(name.size),
         isUsedInRegularObj(!file || isa<ObjFile>(file)),
         used(!config->deadStrip) {}

   Kind symbolKind;
   const char *nameData;
   InputFile *file;
   mutable uint32_t nameSize;

 public:
   // True if this symbol was referenced by a regular (non-bitcode) object.
   bool isUsedInRegularObj : 1;

   // True if an undefined or dylib symbol is used from a live section.
   bool used : 1;
 };

 class Defined : public Symbol {
 public:
   Defined(StringRefZ name, InputFile *file, InputSection *isec, uint64_t value,
           uint64_t size, bool isWeakDef, bool isExternal, bool isPrivateExtern,
           bool isThumb, bool isReferencedDynamically, bool noDeadStrip,
           bool canOverrideWeakDef = false, bool isWeakDefCanBeHidden = false);

   bool isWeakDef() const override { return weakDef; }
   bool isExternalWeakDef() const {
     return isWeakDef() && isExternal() && !privateExtern;
   }
   bool isTlv() const override;

   bool isExternal() const { return external; }
   bool isAbsolute() const { return isec == nullptr; }

   uint64_t getVA() const override;

   // Ensure this symbol's pointers to InputSections point to their canonical
   // copies.
   void canonicalize();

   static bool classof(const Symbol *s) { return s->kind() == DefinedKind; }

   // Place the bitfields first so that they can get placed in the tail padding
   // of the parent class, on platforms which support it.
   bool overridesWeakDef : 1;
   // Whether this symbol should appear in the output binary's export trie.
   bool privateExtern : 1;
   // Whether this symbol should appear in the output symbol table.
   bool includeInSymtab : 1;
   // Only relevant when compiling for Thumb-supporting arm32 archs.
   bool thumb : 1;
   // Symbols marked referencedDynamically won't be removed from the output's
   // symbol table by tools like strip. In theory, this could be set on arbitrary
   // symbols in input object files. In practice, it's used solely for the
   // synthetic __mh_execute_header symbol.
   // This is information for the static linker, and it's also written to the
   // output file's symbol table for tools running later (such as `strip`).
   bool referencedDynamically : 1;
   // Set on symbols that should not be removed by dead code stripping.
   // Set for example on `__attribute__((used))` globals, or on some Objective-C
   // metadata. This is information only for the static linker and not written
   // to the output.
   bool noDeadStrip : 1;

   bool weakDefCanBeHidden : 1;

 private:
   const bool weakDef : 1;
   const bool external : 1;

 public:
   InputSection *isec;
   // Contains the offset from the containing subsection. Note that this is
   // different from nlist::n_value, which is the absolute address of the symbol.
   uint64_t value;
   // size is only calculated for regular (non-bitcode) symbols.
   uint64_t size;
   ConcatInputSection *unwindEntry = nullptr;
 };

 // This enum does double-duty: as a symbol property, it indicates whether & how
 // a dylib symbol is referenced. As a DylibFile property, it indicates the kind
 // of referenced symbols contained within the file. If there are both weak
 // and strong references to the same file, we will count the file as
 // strongly-referenced.
 enum class RefState : uint8_t { Unreferenced = 0, Weak = 1, Strong = 2 };

 class Undefined : public Symbol {
 public:
   Undefined(StringRefZ name, InputFile *file, RefState refState)
       : Symbol(UndefinedKind, name, file), refState(refState) {
     assert(refState != RefState::Unreferenced);
   }

   bool isWeakRef() const override { return refState == RefState::Weak; }

   static bool classof(const Symbol *s) { return s->kind() == UndefinedKind; }

   RefState refState : 2;
 };

 // On Unix, it is traditionally allowed to write variable definitions without
 // initialization expressions (such as "int foo;") to header files. These are
 // called tentative definitions.
 //
 // Using tentative definitions is usually considered a bad practice; you should
 // write only declarations (such as "extern int foo;") to header files.
 // Nevertheless, the linker and the compiler have to do something to support
 // bad code by allowing duplicate definitions for this particular case.
 //
 // The compiler creates common symbols when it sees tentative definitions.
 // (You can suppress this behavior and let the compiler create a regular
 // defined symbol by passing -fno-common. -fno-common is the default in clang
 // as of LLVM 11.0.) When linking the final binary, if there are remaining
 // common symbols after name resolution is complete, the linker converts them
 // to regular defined symbols in a __common section.
 class CommonSymbol : public Symbol {
 public:
   CommonSymbol(StringRefZ name, InputFile *file, uint64_t size, uint32_t align,
                bool isPrivateExtern)
       : Symbol(CommonKind, name, file), size(size),
         align(align != 1 ? align : llvm::PowerOf2Ceil(size)),
         privateExtern(isPrivateExtern) {
     // TODO: cap maximum alignment
   }

   static bool classof(const Symbol *s) { return s->kind() == CommonKind; }

   const uint64_t size;
   const uint32_t align;
   const bool privateExtern;
 };

 class DylibSymbol : public Symbol {
 public:
   DylibSymbol(DylibFile *file, StringRefZ name, bool isWeakDef,
               RefState refState, bool isTlv)
       : Symbol(DylibKind, name, file), refState(refState), weakDef(isWeakDef),
         tlv(isTlv) {
     if (file && refState > RefState::Unreferenced)
       file->numReferencedSymbols++;
   }

   uint64_t getVA() const override;
   bool isWeakDef() const override { return weakDef; }
   bool isWeakRef() const override { return refState == RefState::Weak; }
   bool isReferenced() const { return refState != RefState::Unreferenced; }
   bool isTlv() const override { return tlv; }
   bool isDynamicLookup() const { return file == nullptr; }
   bool hasStubsHelper() const { return stubsHelperIndex != UINT32_MAX; }

   DylibFile *getFile() const {
     assert(!isDynamicLookup());
     return cast<DylibFile>(file);
   }

   static bool classof(const Symbol *s) { return s->kind() == DylibKind; }

   uint32_t stubsHelperIndex = UINT32_MAX;
   uint32_t lazyBindOffset = UINT32_MAX;

   RefState getRefState() const { return refState; }

   void reference(RefState newState) {
     assert(newState > RefState::Unreferenced);
     if (refState == RefState::Unreferenced && file)
       getFile()->numReferencedSymbols++;
     refState = std::max(refState, newState);
   }

   void unreference() {
     // dynamic_lookup symbols have no file.
     if (refState > RefState::Unreferenced && file) {
       assert(getFile()->numReferencedSymbols > 0);
       getFile()->numReferencedSymbols--;
     }
   }

 private:
   RefState refState : 2;
   const bool weakDef : 1;
   const bool tlv : 1;
 };

 class LazySymbol : public Symbol {
 public:
   LazySymbol(ArchiveFile *file, const llvm::object::Archive::Symbol &sym)
       : Symbol(LazyKind, sym.getName(), file), sym(sym) {}

   ArchiveFile *getFile() const { return cast<ArchiveFile>(file); }
   void fetchArchiveMember();

   static bool classof(const Symbol *s) { return s->kind() == LazyKind; }

 private:
   const llvm::object::Archive::Symbol sym;
 };

 union SymbolUnion {
   alignas(Defined) char a[sizeof(Defined)];
   alignas(Undefined) char b[sizeof(Undefined)];
   alignas(CommonSymbol) char c[sizeof(CommonSymbol)];
   alignas(DylibSymbol) char d[sizeof(DylibSymbol)];
   alignas(LazySymbol) char e[sizeof(LazySymbol)];
 };

 template <typename T, typename... ArgT>
 T *replaceSymbol(Symbol *s, ArgT &&...arg) {
   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");

   bool isUsedInRegularObj = s->isUsedInRegularObj;
   bool used = s->used;
   T *sym = new (s) T(std::forward<ArgT>(arg)...);
   sym->isUsedInRegularObj |= isUsedInRegularObj;
   sym->used |= used;
   return sym;
 }

 } // namespace macho

 std::string toString(const macho::Symbol &);
 std::string toMachOString(const llvm::object::Archive::Symbol &);

 } // namespace lld

 #endif
	//===- 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_MACHO_SYMBOLS_H
	#define LLD_MACHO_SYMBOLS_H

	#include "Config.h"
	#include "InputFiles.h"
	#include "Target.h"
	#include "lld/Common/ErrorHandler.h"
	#include "lld/Common/Strings.h"
	#include "llvm/Object/Archive.h"
	#include "llvm/Support/MathExtras.h"

	namespace lld {
	namespace macho {

	class MachHeaderSection;

	struct StringRefZ {
	StringRefZ(const char *s) : data(s), size(-1) {}
	StringRefZ(StringRef s) : data(s.data()), size(s.size()) {}

	const char *data;
	const uint32_t size;
	};

	class Symbol {
	public:
	enum Kind {
	DefinedKind,
	UndefinedKind,
	CommonKind,
	DylibKind,
	LazyKind,
	};

	virtual ~Symbol() {}

	Kind kind() const { return symbolKind; }

	StringRef getName() const {
	if (nameSize == (uint32_t)-1)
	nameSize = strlen(nameData);
	return {nameData, nameSize};
	}

	bool isLive() const { return used; }

	virtual uint64_t getVA() const { return 0; }

	virtual bool isWeakDef() const { llvm_unreachable("cannot be weak def"); }

	// Only undefined or dylib symbols can be weak references. A weak reference
	// need not be satisfied at runtime, e.g. due to the symbol not being
	// available on a given target platform.
	virtual bool isWeakRef() const { llvm_unreachable("cannot be a weak ref"); }

	virtual bool isTlv() const { llvm_unreachable("cannot be TLV"); }

	// Whether this symbol is in the GOT or TLVPointer sections.
	bool isInGot() const { return gotIndex != UINT32_MAX; }

	// Whether this symbol is in the StubsSection.
	bool isInStubs() const { return stubsIndex != UINT32_MAX; }

	uint64_t getStubVA() const;
	uint64_t getGotVA() const;
	uint64_t getTlvVA() const;
	uint64_t resolveBranchVA() const {
	assert(isa<Defined>(this) \|\| isa<DylibSymbol>(this));
	return isInStubs() ? getStubVA() : getVA();
	}
	uint64_t resolveGotVA() const { return isInGot() ? getGotVA() : getVA(); }
	uint64_t resolveTlvVA() const { return isInGot() ? getTlvVA() : getVA(); }

	// The index of this symbol in the GOT or the TLVPointer section, depending
	// on whether it is a thread-local. A given symbol cannot be referenced by
	// both these sections at once.
	uint32_t gotIndex = UINT32_MAX;

	uint32_t stubsIndex = UINT32_MAX;

	uint32_t symtabIndex = UINT32_MAX;

	InputFile *getFile() const { return file; }

	protected:
	Symbol(Kind k, StringRefZ name, InputFile *file)
	: symbolKind(k), nameData(name.data), file(file), nameSize(name.size),
	isUsedInRegularObj(!file \|\| isa<ObjFile>(file)),
	used(!config->deadStrip) {}

	Kind symbolKind;
	const char *nameData;
	InputFile *file;
	mutable uint32_t nameSize;

	public:
	// True if this symbol was referenced by a regular (non-bitcode) object.
	bool isUsedInRegularObj : 1;

	// True if an undefined or dylib symbol is used from a live section.
	bool used : 1;
	};

	class Defined : public Symbol {
	public:
	Defined(StringRefZ name, InputFile file, InputSection isec, uint64_t value,
	uint64_t size, bool isWeakDef, bool isExternal, bool isPrivateExtern,
	bool isThumb, bool isReferencedDynamically, bool noDeadStrip,
	bool canOverrideWeakDef = false, bool isWeakDefCanBeHidden = false);

	bool isWeakDef() const override { return weakDef; }
	bool isExternalWeakDef() const {
	return isWeakDef() && isExternal() && !privateExtern;
	}
	bool isTlv() const override;

	bool isExternal() const { return external; }
	bool isAbsolute() const { return isec == nullptr; }

	uint64_t getVA() const override;

	// Ensure this symbol's pointers to InputSections point to their canonical
	// copies.
	void canonicalize();

	static bool classof(const Symbol *s) { return s->kind() == DefinedKind; }

	// Place the bitfields first so that they can get placed in the tail padding
	// of the parent class, on platforms which support it.
	bool overridesWeakDef : 1;
	// Whether this symbol should appear in the output binary's export trie.
	bool privateExtern : 1;
	// Whether this symbol should appear in the output symbol table.
	bool includeInSymtab : 1;
	// Only relevant when compiling for Thumb-supporting arm32 archs.
	bool thumb : 1;
	// Symbols marked referencedDynamically won't be removed from the output's
	// symbol table by tools like strip. In theory, this could be set on arbitrary
	// symbols in input object files. In practice, it's used solely for the
	// synthetic __mh_execute_header symbol.
	// This is information for the static linker, and it's also written to the
	// output file's symbol table for tools running later (such as `strip`).
	bool referencedDynamically : 1;
	// Set on symbols that should not be removed by dead code stripping.
	// Set for example on `__attribute__((used))` globals, or on some Objective-C
	// metadata. This is information only for the static linker and not written
	// to the output.
	bool noDeadStrip : 1;

	bool weakDefCanBeHidden : 1;

	private:
	const bool weakDef : 1;
	const bool external : 1;

	public:
	InputSection *isec;
	// Contains the offset from the containing subsection. Note that this is
	// different from nlist::n_value, which is the absolute address of the symbol.
	uint64_t value;
	// size is only calculated for regular (non-bitcode) symbols.
	uint64_t size;
	ConcatInputSection *unwindEntry = nullptr;
	};

	// This enum does double-duty: as a symbol property, it indicates whether & how
	// a dylib symbol is referenced. As a DylibFile property, it indicates the kind
	// of referenced symbols contained within the file. If there are both weak
	// and strong references to the same file, we will count the file as
	// strongly-referenced.
	enum class RefState : uint8_t { Unreferenced = 0, Weak = 1, Strong = 2 };

	class Undefined : public Symbol {
	public:
	Undefined(StringRefZ name, InputFile *file, RefState refState)
	: Symbol(UndefinedKind, name, file), refState(refState) {
	assert(refState != RefState::Unreferenced);
	}

	bool isWeakRef() const override { return refState == RefState::Weak; }

	static bool classof(const Symbol *s) { return s->kind() == UndefinedKind; }

	RefState refState : 2;
	};

	// On Unix, it is traditionally allowed to write variable definitions without
	// initialization expressions (such as "int foo;") to header files. These are
	// called tentative definitions.
	//
	// Using tentative definitions is usually considered a bad practice; you should
	// write only declarations (such as "extern int foo;") to header files.
	// Nevertheless, the linker and the compiler have to do something to support
	// bad code by allowing duplicate definitions for this particular case.
	//
	// The compiler creates common symbols when it sees tentative definitions.
	// (You can suppress this behavior and let the compiler create a regular
	// defined symbol by passing -fno-common. -fno-common is the default in clang
	// as of LLVM 11.0.) When linking the final binary, if there are remaining
	// common symbols after name resolution is complete, the linker converts them
	// to regular defined symbols in a __common section.
	class CommonSymbol : public Symbol {
	public:
	CommonSymbol(StringRefZ name, InputFile *file, uint64_t size, uint32_t align,
	bool isPrivateExtern)
	: Symbol(CommonKind, name, file), size(size),
	align(align != 1 ? align : llvm::PowerOf2Ceil(size)),
	privateExtern(isPrivateExtern) {
	// TODO: cap maximum alignment
	}

	static bool classof(const Symbol *s) { return s->kind() == CommonKind; }

	const uint64_t size;
	const uint32_t align;
	const bool privateExtern;
	};

	class DylibSymbol : public Symbol {
	public:
	DylibSymbol(DylibFile *file, StringRefZ name, bool isWeakDef,
	RefState refState, bool isTlv)
	: Symbol(DylibKind, name, file), refState(refState), weakDef(isWeakDef),
	tlv(isTlv) {
	if (file && refState > RefState::Unreferenced)
	file->numReferencedSymbols++;
	}

	uint64_t getVA() const override;
	bool isWeakDef() const override { return weakDef; }
	bool isWeakRef() const override { return refState == RefState::Weak; }
	bool isReferenced() const { return refState != RefState::Unreferenced; }
	bool isTlv() const override { return tlv; }
	bool isDynamicLookup() const { return file == nullptr; }
	bool hasStubsHelper() const { return stubsHelperIndex != UINT32_MAX; }

	DylibFile *getFile() const {
	assert(!isDynamicLookup());
	return cast<DylibFile>(file);
	}

	static bool classof(const Symbol *s) { return s->kind() == DylibKind; }

	uint32_t stubsHelperIndex = UINT32_MAX;
	uint32_t lazyBindOffset = UINT32_MAX;

	RefState getRefState() const { return refState; }

	void reference(RefState newState) {
	assert(newState > RefState::Unreferenced);
	if (refState == RefState::Unreferenced && file)
	getFile()->numReferencedSymbols++;
	refState = std::max(refState, newState);
	}

	void unreference() {
	// dynamic_lookup symbols have no file.
	if (refState > RefState::Unreferenced && file) {
	assert(getFile()->numReferencedSymbols > 0);
	getFile()->numReferencedSymbols--;
	}
	}

	private:
	RefState refState : 2;
	const bool weakDef : 1;
	const bool tlv : 1;
	};

	class LazySymbol : public Symbol {
	public:
	LazySymbol(ArchiveFile *file, const llvm::object::Archive::Symbol &sym)
	: Symbol(LazyKind, sym.getName(), file), sym(sym) {}

	ArchiveFile *getFile() const { return cast<ArchiveFile>(file); }
	void fetchArchiveMember();

	static bool classof(const Symbol *s) { return s->kind() == LazyKind; }

	private:
	const llvm::object::Archive::Symbol sym;
	};

	union SymbolUnion {
	alignas(Defined) char a[sizeof(Defined)];
	alignas(Undefined) char b[sizeof(Undefined)];
	alignas(CommonSymbol) char c[sizeof(CommonSymbol)];
	alignas(DylibSymbol) char d[sizeof(DylibSymbol)];
	alignas(LazySymbol) char e[sizeof(LazySymbol)];
	};

	template <typename T, typename... ArgT>
	T replaceSymbol(Symbol s, ArgT &&...arg) {
	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");

	bool isUsedInRegularObj = s->isUsedInRegularObj;
	bool used = s->used;
	T *sym = new (s) T(std::forward<ArgT>(arg)...);
	sym->isUsedInRegularObj \|= isUsedInRegularObj;
	sym->used \|= used;
	return sym;
	}

	} // namespace macho

	std::string toString(const macho::Symbol &);
	std::string toMachOString(const llvm::object::Archive::Symbol &);

	} // namespace lld

	#endif