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//===- MCSymbol.h - Machine Code Symbols ------------------------*- 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
//
//===----------------------------------------------------------------------===//
//
// This file contains the declaration of the MCSymbol class.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_MC_MCSYMBOL_H
#define LLVM_MC_MCSYMBOL_H
#include "llvm/ADT/StringMapEntry.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCFragment.h"
#include "llvm/MC/MCSymbolTableEntry.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MathExtras.h"
#include <cassert>
#include <cstddef>
#include <cstdint>
namespace llvm {
class MCAsmInfo;
class MCContext;
class MCSection;
class raw_ostream;
/// MCSymbol - Instances of this class represent a symbol name in the MC file,
/// and MCSymbols are created and uniqued by the MCContext class. MCSymbols
/// should only be constructed with valid names for the object file.
///
/// If the symbol is defined/emitted into the current translation unit, the
/// Section member is set to indicate what section it lives in. Otherwise, if
/// it is a reference to an external entity, it has a null section.
class MCSymbol {
protected:
/// The kind of the symbol. If it is any value other than unset then this
/// class is actually one of the appropriate subclasses of MCSymbol.
enum SymbolKind {
SymbolKindUnset,
SymbolKindCOFF,
SymbolKindELF,
SymbolKindGOFF,
SymbolKindMachO,
SymbolKindWasm,
SymbolKindXCOFF,
};
/// A symbol can contain an Offset, or Value, or be Common, but never more
/// than one of these.
enum Contents : uint8_t {
SymContentsUnset,
SymContentsOffset,
SymContentsVariable,
SymContentsCommon,
SymContentsTargetCommon, // Index stores the section index
};
// Special sentinel value for the absolute pseudo fragment.
static MCFragment *AbsolutePseudoFragment;
/// If a symbol has a Fragment, the section is implied, so we only need
/// one pointer.
/// The special AbsolutePseudoFragment value is for absolute symbols.
/// If this is a variable symbol, this caches the variable value's fragment.
/// FIXME: We might be able to simplify this by having the asm streamer create
/// dummy fragments.
/// If this is a section, then it gives the symbol is defined in. This is null
/// for undefined symbols.
///
/// If this is a fragment, then it gives the fragment this symbol's value is
/// relative to, if any.
mutable MCFragment *Fragment = nullptr;
/// True if this symbol is named. A named symbol will have a pointer to the
/// name allocated in the bytes immediately prior to the MCSymbol.
unsigned HasName : 1;
/// IsTemporary - True if this is an assembler temporary label, which
/// typically does not survive in the .o file's symbol table. Usually
/// "Lfoo" or ".foo".
unsigned IsTemporary : 1;
/// True if this symbol can be redefined.
unsigned IsRedefinable : 1;
/// IsUsed - True if this symbol has been used.
mutable unsigned IsUsed : 1;
mutable unsigned IsRegistered : 1;
/// True if this symbol is visible outside this translation unit. Note: ELF
/// uses binding instead of this bit.
mutable unsigned IsExternal : 1;
/// Mach-O specific: This symbol is private extern.
mutable unsigned IsPrivateExtern : 1;
/// This symbol is weak external.
mutable unsigned IsWeakExternal : 1;
/// LLVM RTTI discriminator. This is actually a SymbolKind enumerator, but is
/// unsigned to avoid sign extension and achieve better bitpacking with MSVC.
unsigned Kind : 3;
/// True if we have created a relocation that uses this symbol.
mutable unsigned IsUsedInReloc : 1;
/// This is actually a Contents enumerator, but is unsigned to avoid sign
/// extension and achieve better bitpacking with MSVC.
unsigned SymbolContents : 3;
/// The alignment of the symbol if it is 'common'.
///
/// Internally, this is stored as log2(align) + 1.
/// We reserve 5 bits to encode this value which allows the following values
/// 0b00000 -> unset
/// 0b00001 -> 1ULL << 0 = 1
/// 0b00010 -> 1ULL << 1 = 2
/// 0b00011 -> 1ULL << 2 = 4
/// ...
/// 0b11111 -> 1ULL << 30 = 1 GiB
enum : unsigned { NumCommonAlignmentBits = 5 };
unsigned CommonAlignLog2 : NumCommonAlignmentBits;
/// The Flags field is used by object file implementations to store
/// additional per symbol information which is not easily classified.
enum : unsigned { NumFlagsBits = 16 };
mutable uint32_t Flags : NumFlagsBits;
/// Index field, for use by the object file implementation.
mutable uint32_t Index = 0;
union {
/// The offset to apply to the fragment address to form this symbol's value.
uint64_t Offset;
/// The size of the symbol, if it is 'common'.
uint64_t CommonSize;
/// If non-null, the value for a variable symbol.
const MCExpr *Value;
};
// MCContext creates and uniques these.
friend class MCExpr;
friend class MCContext;
/// The name for a symbol.
/// MCSymbol contains a uint64_t so is probably aligned to 8. On a 32-bit
/// system, the name is a pointer so isn't going to satisfy the 8 byte
/// alignment of uint64_t. Account for that here.
using NameEntryStorageTy = union {
const MCSymbolTableEntry *NameEntry;
uint64_t AlignmentPadding;
};
MCSymbol(SymbolKind Kind, const MCSymbolTableEntry *Name, bool isTemporary)
: IsTemporary(isTemporary), IsRedefinable(false), IsUsed(false),
IsRegistered(false), IsExternal(false), IsPrivateExtern(false),
IsWeakExternal(false), Kind(Kind), IsUsedInReloc(false),
SymbolContents(SymContentsUnset), CommonAlignLog2(0), Flags(0) {
Offset = 0;
HasName = !!Name;
if (Name)
getNameEntryPtr() = Name;
}
// Provide custom new/delete as we will only allocate space for a name
// if we need one.
void *operator new(size_t s, const MCSymbolTableEntry *Name, MCContext &Ctx);
private:
void operator delete(void *);
/// Placement delete - required by std, but never called.
void operator delete(void*, unsigned) {
llvm_unreachable("Constructor throws?");
}
/// Placement delete - required by std, but never called.
void operator delete(void*, unsigned, bool) {
llvm_unreachable("Constructor throws?");
}
/// Get a reference to the name field. Requires that we have a name
const MCSymbolTableEntry *&getNameEntryPtr() {
assert(HasName && "Name is required");
NameEntryStorageTy *Name = reinterpret_cast<NameEntryStorageTy *>(this);
return (*(Name - 1)).NameEntry;
}
const MCSymbolTableEntry *&getNameEntryPtr() const {
return const_cast<MCSymbol*>(this)->getNameEntryPtr();
}
public:
MCSymbol(const MCSymbol &) = delete;
MCSymbol &operator=(const MCSymbol &) = delete;
/// getName - Get the symbol name.
StringRef getName() const {
if (!HasName)
return StringRef();
return getNameEntryPtr()->first();
}
bool isRegistered() const { return IsRegistered; }
void setIsRegistered(bool Value) const { IsRegistered = Value; }
void setUsedInReloc() const { IsUsedInReloc = true; }
bool isUsedInReloc() const { return IsUsedInReloc; }
/// \name Accessors
/// @{
/// isTemporary - Check if this is an assembler temporary symbol.
bool isTemporary() const { return IsTemporary; }
/// isUsed - Check if this is used.
bool isUsed() const { return IsUsed; }
/// Check if this symbol is redefinable.
bool isRedefinable() const { return IsRedefinable; }
/// Mark this symbol as redefinable.
void setRedefinable(bool Value) { IsRedefinable = Value; }
/// Prepare this symbol to be redefined.
void redefineIfPossible() {
if (IsRedefinable) {
if (SymbolContents == SymContentsVariable) {
Value = nullptr;
SymbolContents = SymContentsUnset;
}
setUndefined();
IsRedefinable = false;
}
}
/// @}
/// \name Associated Sections
/// @{
/// isDefined - Check if this symbol is defined (i.e., it has an address).
///
/// Defined symbols are either absolute or in some section.
bool isDefined() const { return !isUndefined(); }
/// isInSection - Check if this symbol is defined in some section (i.e., it
/// is defined but not absolute).
bool isInSection() const {
return isDefined() && !isAbsolute();
}
/// isUndefined - Check if this symbol undefined (i.e., implicitly defined).
bool isUndefined(bool SetUsed = true) const {
return getFragment(SetUsed) == nullptr;
}
/// isAbsolute - Check if this is an absolute symbol.
bool isAbsolute() const {
return getFragment() == AbsolutePseudoFragment;
}
/// Get the section associated with a defined, non-absolute symbol.
MCSection &getSection() const {
assert(isInSection() && "Invalid accessor!");
return *getFragment()->getParent();
}
/// Mark the symbol as defined in the fragment \p F.
void setFragment(MCFragment *F) const {
assert(!isVariable() && "Cannot set fragment of variable");
Fragment = F;
}
/// Mark the symbol as undefined.
void setUndefined() { Fragment = nullptr; }
bool isELF() const { return Kind == SymbolKindELF; }
bool isCOFF() const { return Kind == SymbolKindCOFF; }
bool isGOFF() const { return Kind == SymbolKindGOFF; }
bool isMachO() const { return Kind == SymbolKindMachO; }
bool isWasm() const { return Kind == SymbolKindWasm; }
bool isXCOFF() const { return Kind == SymbolKindXCOFF; }
/// @}
/// \name Variable Symbols
/// @{
/// isVariable - Check if this is a variable symbol.
bool isVariable() const {
return SymbolContents == SymContentsVariable;
}
/// getVariableValue - Get the value for variable symbols.
const MCExpr *getVariableValue(bool SetUsed = true) const {
assert(isVariable() && "Invalid accessor!");
IsUsed |= SetUsed;
return Value;
}
void setVariableValue(const MCExpr *Value);
/// @}
/// Get the (implementation defined) index.
uint32_t getIndex() const {
return Index;
}
/// Set the (implementation defined) index.
void setIndex(uint32_t Value) const {
Index = Value;
}
bool isUnset() const { return SymbolContents == SymContentsUnset; }
uint64_t getOffset() const {
assert((SymbolContents == SymContentsUnset ||
SymbolContents == SymContentsOffset) &&
"Cannot get offset for a common/variable symbol");
return Offset;
}
void setOffset(uint64_t Value) {
assert((SymbolContents == SymContentsUnset ||
SymbolContents == SymContentsOffset) &&
"Cannot set offset for a common/variable symbol");
Offset = Value;
SymbolContents = SymContentsOffset;
}
/// Return the size of a 'common' symbol.
uint64_t getCommonSize() const {
assert(isCommon() && "Not a 'common' symbol!");
return CommonSize;
}
/// Mark this symbol as being 'common'.
///
/// \param Size - The size of the symbol.
/// \param Alignment - The alignment of the symbol.
/// \param Target - Is the symbol a target-specific common-like symbol.
void setCommon(uint64_t Size, Align Alignment, bool Target = false) {
assert(getOffset() == 0);
CommonSize = Size;
SymbolContents = Target ? SymContentsTargetCommon : SymContentsCommon;
unsigned Log2Align = encode(Alignment);
assert(Log2Align < (1U << NumCommonAlignmentBits) &&
"Out of range alignment");
CommonAlignLog2 = Log2Align;
}
/// Return the alignment of a 'common' symbol.
MaybeAlign getCommonAlignment() const {
assert(isCommon() && "Not a 'common' symbol!");
return decodeMaybeAlign(CommonAlignLog2);
}
/// Declare this symbol as being 'common'.
///
/// \param Size - The size of the symbol.
/// \param Alignment - The alignment of the symbol.
/// \param Target - Is the symbol a target-specific common-like symbol.
/// \return True if symbol was already declared as a different type
bool declareCommon(uint64_t Size, Align Alignment, bool Target = false) {
assert(isCommon() || getOffset() == 0);
if(isCommon()) {
if (CommonSize != Size || getCommonAlignment() != Alignment ||
isTargetCommon() != Target)
return true;
} else
setCommon(Size, Alignment, Target);
return false;
}
/// Is this a 'common' symbol.
bool isCommon() const {
return SymbolContents == SymContentsCommon ||
SymbolContents == SymContentsTargetCommon;
}
/// Is this a target-specific common-like symbol.
bool isTargetCommon() const {
return SymbolContents == SymContentsTargetCommon;
}
MCFragment *getFragment(bool SetUsed = true) const {
if (Fragment || !isVariable() || isWeakExternal())
return Fragment;
// If the symbol is a non-weak alias, get information about
// the aliasee. (Don't try to resolve weak aliases.)
Fragment = getVariableValue(SetUsed)->findAssociatedFragment();
return Fragment;
}
// For ELF, use MCSymbolELF::setBinding instead.
bool isExternal() const { return IsExternal; }
void setExternal(bool Value) const { IsExternal = Value; }
// COFF-specific
bool isWeakExternal() const { return IsWeakExternal; }
/// print - Print the value to the stream \p OS.
void print(raw_ostream &OS, const MCAsmInfo *MAI) const;
/// dump - Print the value to stderr.
void dump() const;
protected:
/// Get the (implementation defined) symbol flags.
uint32_t getFlags() const { return Flags; }
/// Set the (implementation defined) symbol flags.
void setFlags(uint32_t Value) const {
assert(Value < (1U << NumFlagsBits) && "Out of range flags");
Flags = Value;
}
/// Modify the flags via a mask
void modifyFlags(uint32_t Value, uint32_t Mask) const {
assert(Value < (1U << NumFlagsBits) && "Out of range flags");
Flags = (Flags & ~Mask) | Value;
}
};
inline raw_ostream &operator<<(raw_ostream &OS, const MCSymbol &Sym) {
Sym.print(OS, nullptr);
return OS;
}
} // end namespace llvm
#endif // LLVM_MC_MCSYMBOL_H
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