llvm-project/lld/ELF/Symbols.h

467 lines
16 KiB
C++

//===- Symbols.h ------------------------------------------------*- C++ -*-===//
//
// The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// All symbols are handled as SymbolBodies regardless of their types.
// This file defines various types of SymbolBodies.
//
//===----------------------------------------------------------------------===//
#ifndef LLD_ELF_SYMBOLS_H
#define LLD_ELF_SYMBOLS_H
#include "InputSection.h"
#include "lld/Core/LLVM.h"
#include "llvm/Object/Archive.h"
#include "llvm/Object/ELF.h"
#include "llvm/Support/AlignOf.h"
namespace lld {
namespace elf {
class ArchiveFile;
class BitcodeFile;
class InputFile;
class LazyObjectFile;
class SymbolBody;
template <class ELFT> class ObjectFile;
template <class ELFT> class OutputSection;
template <class ELFT> class OutputSectionBase;
template <class ELFT> class SharedFile;
// Returns a demangled C++ symbol name. If Name is not a mangled
// name or the system does not provide __cxa_demangle function,
// it returns the unmodified string.
std::string demangle(StringRef Name);
struct Symbol;
// The base class for real symbol classes.
class SymbolBody {
public:
enum Kind {
DefinedFirst,
DefinedRegularKind = DefinedFirst,
SharedKind,
DefinedCommonKind,
DefinedBitcodeKind,
DefinedSyntheticKind,
DefinedLast = DefinedSyntheticKind,
UndefinedKind,
LazyArchiveKind,
LazyObjectKind,
};
Symbol *symbol();
const Symbol *symbol() const {
return const_cast<SymbolBody *>(this)->symbol();
}
Kind kind() const { return static_cast<Kind>(SymbolKind); }
bool isUndefined() const { return SymbolKind == UndefinedKind; }
bool isDefined() const { return SymbolKind <= DefinedLast; }
bool isCommon() const { return SymbolKind == DefinedCommonKind; }
bool isLazy() const {
return SymbolKind == LazyArchiveKind || SymbolKind == LazyObjectKind;
}
bool isShared() const { return SymbolKind == SharedKind; }
bool isLocal() const { return IsLocal; }
bool isPreemptible() const;
// Returns the symbol name.
StringRef getName() const {
assert(!isLocal());
return StringRef(Name.S, Name.Len);
}
uint32_t getNameOffset() const {
assert(isLocal());
return NameOffset;
}
uint8_t getVisibility() const { return StOther & 0x3; }
unsigned DynsymIndex = 0;
uint32_t GotIndex = -1;
uint32_t GotPltIndex = -1;
uint32_t PltIndex = -1;
uint32_t ThunkIndex = -1;
uint32_t GlobalDynIndex = -1;
bool isInGot() const { return GotIndex != -1U; }
bool isInPlt() const { return PltIndex != -1U; }
bool hasThunk() const { return ThunkIndex != -1U; }
template <class ELFT>
typename ELFT::uint getVA(typename ELFT::uint Addend = 0) const;
template <class ELFT> typename ELFT::uint getGotOffset() const;
template <class ELFT> typename ELFT::uint getGotVA() const;
template <class ELFT> typename ELFT::uint getGotPltOffset() const;
template <class ELFT> typename ELFT::uint getGotPltVA() const;
template <class ELFT> typename ELFT::uint getPltVA() const;
template <class ELFT> typename ELFT::uint getThunkVA() const;
template <class ELFT> typename ELFT::uint getSize() const;
// Returns the file from which the symbol was created.
// For logging purpose only.
template <class ELFT> InputFile *getSourceFile();
protected:
SymbolBody(Kind K, StringRef Name, uint8_t StOther, uint8_t Type);
SymbolBody(Kind K, uint32_t NameOffset, uint8_t StOther, uint8_t Type);
const unsigned SymbolKind : 8;
public:
// True if the linker has to generate a copy relocation for this shared
// symbol or if the symbol should point to its plt entry.
unsigned NeedsCopyOrPltAddr : 1;
// True if this is a local symbol.
unsigned IsLocal : 1;
// The following fields have the same meaning as the ELF symbol attributes.
uint8_t Type; // symbol type
uint8_t StOther; // st_other field value
// The Type field may also have this value. It means that we have not yet seen
// a non-Lazy symbol with this name, so we don't know what its type is. The
// Type field is normally set to this value for Lazy symbols unless we saw a
// weak undefined symbol first, in which case we need to remember the original
// symbol's type in order to check for TLS mismatches.
enum { UnknownType = 255 };
bool isSection() const { return Type == llvm::ELF::STT_SECTION; }
bool isTls() const { return Type == llvm::ELF::STT_TLS; }
bool isFunc() const { return Type == llvm::ELF::STT_FUNC; }
bool isGnuIFunc() const { return Type == llvm::ELF::STT_GNU_IFUNC; }
bool isObject() const { return Type == llvm::ELF::STT_OBJECT; }
bool isFile() const { return Type == llvm::ELF::STT_FILE; }
protected:
struct Str {
const char *S;
size_t Len;
};
union {
Str Name;
uint32_t NameOffset;
};
};
// The base class for any defined symbols.
class Defined : public SymbolBody {
public:
Defined(Kind K, StringRef Name, uint8_t StOther, uint8_t Type);
Defined(Kind K, uint32_t NameOffset, uint8_t StOther, uint8_t Type);
static bool classof(const SymbolBody *S) { return S->isDefined(); }
};
// The defined symbol in LLVM bitcode files.
class DefinedBitcode : public Defined {
public:
DefinedBitcode(StringRef Name, uint8_t StOther, uint8_t Type, BitcodeFile *F);
static bool classof(const SymbolBody *S);
BitcodeFile *File;
};
class DefinedCommon : public Defined {
public:
DefinedCommon(StringRef N, uint64_t Size, uint64_t Alignment, uint8_t StOther,
uint8_t Type);
static bool classof(const SymbolBody *S) {
return S->kind() == SymbolBody::DefinedCommonKind;
}
// The output offset of this common symbol in the output bss. Computed by the
// writer.
uint64_t OffsetInBss;
// The maximum alignment we have seen for this symbol.
uint64_t Alignment;
uint64_t Size;
};
// Regular defined symbols read from object file symbol tables.
template <class ELFT> class DefinedRegular : public Defined {
typedef typename ELFT::Sym Elf_Sym;
typedef typename ELFT::uint uintX_t;
public:
DefinedRegular(StringRef Name, const Elf_Sym &Sym,
InputSectionBase<ELFT> *Section)
: Defined(SymbolBody::DefinedRegularKind, Name, Sym.st_other,
Sym.getType()),
Value(Sym.st_value), Size(Sym.st_size),
Section(Section ? Section->Repl : NullInputSection) {}
DefinedRegular(const Elf_Sym &Sym, InputSectionBase<ELFT> *Section)
: Defined(SymbolBody::DefinedRegularKind, Sym.st_name, Sym.st_other,
Sym.getType()),
Value(Sym.st_value), Size(Sym.st_size),
Section(Section ? Section->Repl : NullInputSection) {
assert(isLocal());
}
DefinedRegular(StringRef Name, uint8_t StOther)
: Defined(SymbolBody::DefinedRegularKind, Name, StOther,
llvm::ELF::STT_NOTYPE),
Value(0), Size(0), Section(NullInputSection) {}
static bool classof(const SymbolBody *S) {
return S->kind() == SymbolBody::DefinedRegularKind;
}
uintX_t Value;
uintX_t Size;
// The input section this symbol belongs to. Notice that this is
// a reference to a pointer. We are using two levels of indirections
// because of ICF. If ICF decides two sections need to be merged, it
// manipulates this Section pointers so that they point to the same
// section. This is a bit tricky, so be careful to not be confused.
// If this is null, the symbol is an absolute symbol.
InputSectionBase<ELFT> *&Section;
private:
static InputSectionBase<ELFT> *NullInputSection;
};
template <class ELFT>
InputSectionBase<ELFT> *DefinedRegular<ELFT>::NullInputSection;
// DefinedSynthetic is a class to represent linker-generated ELF symbols.
// The difference from the regular symbol is that DefinedSynthetic symbols
// don't belong to any input files or sections. Thus, its constructor
// takes an output section to calculate output VA, etc.
// If Section is null, this symbol is relative to the image base.
template <class ELFT> class DefinedSynthetic : public Defined {
public:
typedef typename ELFT::uint uintX_t;
DefinedSynthetic(StringRef N, uintX_t Value,
OutputSectionBase<ELFT> *Section);
static bool classof(const SymbolBody *S) {
return S->kind() == SymbolBody::DefinedSyntheticKind;
}
// Special value designates that the symbol 'points'
// to the end of the section.
static const uintX_t SectionEnd = uintX_t(-1);
uintX_t Value;
const OutputSectionBase<ELFT> *Section;
};
class Undefined : public SymbolBody {
public:
Undefined(StringRef Name, uint8_t StOther, uint8_t Type);
Undefined(uint32_t NameOffset, uint8_t StOther, uint8_t Type);
static bool classof(const SymbolBody *S) {
return S->kind() == UndefinedKind;
}
// The file this undefined symbol was created from.
// For logging purpose only.
InputFile *File = nullptr;
};
template <class ELFT> class SharedSymbol : public Defined {
typedef typename ELFT::Sym Elf_Sym;
typedef typename ELFT::Verdef Elf_Verdef;
typedef typename ELFT::uint uintX_t;
public:
static bool classof(const SymbolBody *S) {
return S->kind() == SymbolBody::SharedKind;
}
SharedSymbol(SharedFile<ELFT> *F, StringRef Name, const Elf_Sym &Sym,
const Elf_Verdef *Verdef)
: Defined(SymbolBody::SharedKind, Name, Sym.st_other, Sym.getType()),
File(F), Sym(Sym), Verdef(Verdef) {
// IFuncs defined in DSOs are treated as functions by the static linker.
if (isGnuIFunc())
Type = llvm::ELF::STT_FUNC;
}
SharedFile<ELFT> *File;
const Elf_Sym &Sym;
// This field is initially a pointer to the symbol's version definition. As
// symbols are added to the version table, this field is replaced with the
// version identifier to be stored in .gnu.version in the output file.
union {
const Elf_Verdef *Verdef;
uint16_t VersionId;
};
// OffsetInBss is significant only when needsCopy() is true.
uintX_t OffsetInBss = 0;
bool needsCopy() const { return this->NeedsCopyOrPltAddr && !this->isFunc(); }
};
// This class represents a symbol defined in an archive file. It is
// created from an archive file header, and it knows how to load an
// object file from an archive to replace itself with a defined
// symbol. If the resolver finds both Undefined and Lazy for
// the same name, it will ask the Lazy to load a file.
class Lazy : public SymbolBody {
public:
Lazy(SymbolBody::Kind K, StringRef Name, uint8_t Type)
: SymbolBody(K, Name, llvm::ELF::STV_DEFAULT, Type) {}
static bool classof(const SymbolBody *S) { return S->isLazy(); }
// Returns an object file for this symbol, or a nullptr if the file
// was already returned.
std::unique_ptr<InputFile> getFile();
};
// LazyArchive symbols represents symbols in archive files.
class LazyArchive : public Lazy {
public:
LazyArchive(ArchiveFile &File, const llvm::object::Archive::Symbol S,
uint8_t Type)
: Lazy(LazyArchiveKind, S.getName(), Type), File(File), Sym(S) {}
static bool classof(const SymbolBody *S) {
return S->kind() == LazyArchiveKind;
}
std::unique_ptr<InputFile> getFile();
private:
ArchiveFile &File;
const llvm::object::Archive::Symbol Sym;
};
// LazyObject symbols represents symbols in object files between
// --start-lib and --end-lib options.
class LazyObject : public Lazy {
public:
LazyObject(StringRef Name, LazyObjectFile &File, uint8_t Type)
: Lazy(LazyObjectKind, Name, Type), File(File) {}
static bool classof(const SymbolBody *S) {
return S->kind() == LazyObjectKind;
}
std::unique_ptr<InputFile> getFile();
private:
LazyObjectFile &File;
};
// Some linker-generated symbols need to be created as
// DefinedRegular symbols.
template <class ELFT> struct ElfSym {
// The content for _etext and etext symbols.
static DefinedRegular<ELFT> *Etext;
static DefinedRegular<ELFT> *Etext2;
// The content for _edata and edata symbols.
static DefinedRegular<ELFT> *Edata;
static DefinedRegular<ELFT> *Edata2;
// The content for _end and end symbols.
static DefinedRegular<ELFT> *End;
static DefinedRegular<ELFT> *End2;
// The content for _gp_disp symbol for MIPS target.
static SymbolBody *MipsGpDisp;
};
template <class ELFT> DefinedRegular<ELFT> *ElfSym<ELFT>::Etext;
template <class ELFT> DefinedRegular<ELFT> *ElfSym<ELFT>::Etext2;
template <class ELFT> DefinedRegular<ELFT> *ElfSym<ELFT>::Edata;
template <class ELFT> DefinedRegular<ELFT> *ElfSym<ELFT>::Edata2;
template <class ELFT> DefinedRegular<ELFT> *ElfSym<ELFT>::End;
template <class ELFT> DefinedRegular<ELFT> *ElfSym<ELFT>::End2;
template <class ELFT> SymbolBody *ElfSym<ELFT>::MipsGpDisp;
// A real symbol object, SymbolBody, is usually stored within a Symbol. There's
// always one Symbol for each symbol name. The resolver updates the SymbolBody
// stored in the Body field of this object as it resolves symbols. Symbol also
// holds computed properties of symbol names.
struct Symbol {
// Symbol binding. This is on the Symbol to track changes during resolution.
// In particular:
// An undefined weak is still weak when it resolves to a shared library.
// An undefined weak will not fetch archive members, but we have to remember
// it is weak.
uint8_t Binding;
// Symbol visibility. This is the computed minimum visibility of all
// observed non-DSO symbols.
unsigned Visibility : 2;
// 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 and bitcode symbols that are unreferenced except
// by other bitcode objects.
unsigned IsUsedInRegularObj : 1;
// If this flag is true and the symbol has protected or default visibility, it
// will appear in .dynsym. This flag is set by interposable DSO symbols in
// executables, by most symbols in DSOs and executables built with
// --export-dynamic, and by dynamic lists.
unsigned ExportDynamic : 1;
// This flag acts as an additional filter on the dynamic symbol list. It is
// set if there is no version script, or if the symbol appears in the global
// section of the version script.
unsigned VersionScriptGlobal : 1;
bool includeInDynsym() const;
bool isWeak() const { return Binding == llvm::ELF::STB_WEAK; }
// This field is used to store the Symbol's SymbolBody. This instantiation of
// AlignedCharArrayUnion gives us a struct with a char array field that is
// large and aligned enough to store any derived class of SymbolBody. We
// assume that the size and alignment of ELF64LE symbols is sufficient for any
// ELFT, and we verify this with the static_asserts in replaceBody.
llvm::AlignedCharArrayUnion<
DefinedBitcode, DefinedCommon, DefinedRegular<llvm::object::ELF64LE>,
DefinedSynthetic<llvm::object::ELF64LE>, Undefined,
SharedSymbol<llvm::object::ELF64LE>, LazyArchive, LazyObject>
Body;
SymbolBody *body() { return reinterpret_cast<SymbolBody *>(Body.buffer); }
const SymbolBody *body() const { return const_cast<Symbol *>(this)->body(); }
};
template <typename T, typename... ArgT>
void replaceBody(Symbol *S, ArgT &&... Arg) {
static_assert(sizeof(T) <= sizeof(S->Body), "Body too small");
static_assert(llvm::AlignOf<T>::Alignment <=
llvm::AlignOf<decltype(S->Body)>::Alignment,
"Body not aligned enough");
assert(static_cast<SymbolBody *>(static_cast<T *>(nullptr)) == nullptr &&
"Not a SymbolBody");
new (S->Body.buffer) T(std::forward<ArgT>(Arg)...);
}
inline Symbol *SymbolBody::symbol() {
assert(!isLocal());
return reinterpret_cast<Symbol *>(reinterpret_cast<char *>(this) -
offsetof(Symbol, Body));
}
} // namespace elf
} // namespace lld
#endif