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      1 //===- MCSymbol.h - Machine Code Symbols ------------------------*- C++ -*-===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This file contains the declaration of the MCSymbol class.
     11 //
     12 //===----------------------------------------------------------------------===//
     13 
     14 #ifndef LLVM_MC_MCSYMBOL_H
     15 #define LLVM_MC_MCSYMBOL_H
     16 
     17 #include "llvm/ADT/PointerIntPair.h"
     18 #include "llvm/ADT/PointerUnion.h"
     19 #include "llvm/ADT/StringMap.h"
     20 #include "llvm/MC/MCAssembler.h"
     21 #include "llvm/Support/Compiler.h"
     22 
     23 namespace llvm {
     24 class MCAsmInfo;
     25 class MCExpr;
     26 class MCSymbol;
     27 class MCFragment;
     28 class MCSection;
     29 class MCContext;
     30 class raw_ostream;
     31 
     32 /// MCSymbol - Instances of this class represent a symbol name in the MC file,
     33 /// and MCSymbols are created and uniqued by the MCContext class.  MCSymbols
     34 /// should only be constructed with valid names for the object file.
     35 ///
     36 /// If the symbol is defined/emitted into the current translation unit, the
     37 /// Section member is set to indicate what section it lives in.  Otherwise, if
     38 /// it is a reference to an external entity, it has a null section.
     39 class MCSymbol {
     40 protected:
     41   /// The kind of the symbol.  If it is any value other than unset then this
     42   /// class is actually one of the appropriate subclasses of MCSymbol.
     43   enum SymbolKind {
     44     SymbolKindUnset,
     45     SymbolKindCOFF,
     46     SymbolKindELF,
     47     SymbolKindMachO,
     48   };
     49 
     50   /// A symbol can contain an Offset, or Value, or be Common, but never more
     51   /// than one of these.
     52   enum Contents : uint8_t {
     53     SymContentsUnset,
     54     SymContentsOffset,
     55     SymContentsVariable,
     56     SymContentsCommon,
     57   };
     58 
     59   // Special sentinal value for the absolute pseudo fragment.
     60   static MCFragment *AbsolutePseudoFragment;
     61 
     62   /// If a symbol has a Fragment, the section is implied, so we only need
     63   /// one pointer.
     64   /// The special AbsolutePseudoFragment value is for absolute symbols.
     65   /// If this is a variable symbol, this caches the variable value's fragment.
     66   /// FIXME: We might be able to simplify this by having the asm streamer create
     67   /// dummy fragments.
     68   /// If this is a section, then it gives the symbol is defined in. This is null
     69   /// for undefined symbols.
     70   ///
     71   /// If this is a fragment, then it gives the fragment this symbol's value is
     72   /// relative to, if any.
     73   ///
     74   /// For the 'HasName' integer, this is true if this symbol is named.
     75   /// A named symbol will have a pointer to the name allocated in the bytes
     76   /// immediately prior to the MCSymbol.
     77   mutable PointerIntPair<MCFragment *, 1> FragmentAndHasName;
     78 
     79   /// IsTemporary - True if this is an assembler temporary label, which
     80   /// typically does not survive in the .o file's symbol table.  Usually
     81   /// "Lfoo" or ".foo".
     82   unsigned IsTemporary : 1;
     83 
     84   /// \brief True if this symbol can be redefined.
     85   unsigned IsRedefinable : 1;
     86 
     87   /// IsUsed - True if this symbol has been used.
     88   mutable unsigned IsUsed : 1;
     89 
     90   mutable bool IsRegistered : 1;
     91 
     92   /// This symbol is visible outside this translation unit.
     93   mutable unsigned IsExternal : 1;
     94 
     95   /// This symbol is private extern.
     96   mutable unsigned IsPrivateExtern : 1;
     97 
     98   /// LLVM RTTI discriminator. This is actually a SymbolKind enumerator, but is
     99   /// unsigned to avoid sign extension and achieve better bitpacking with MSVC.
    100   unsigned Kind : 2;
    101 
    102   /// True if we have created a relocation that uses this symbol.
    103   mutable unsigned IsUsedInReloc : 1;
    104 
    105   /// This is actually a Contents enumerator, but is unsigned to avoid sign
    106   /// extension and achieve better bitpacking with MSVC.
    107   unsigned SymbolContents : 2;
    108 
    109   /// The alignment of the symbol, if it is 'common', or -1.
    110   ///
    111   /// The alignment is stored as log2(align) + 1.  This allows all values from
    112   /// 0 to 2^31 to be stored which is every power of 2 representable by an
    113   /// unsigned.
    114   enum : unsigned { NumCommonAlignmentBits = 5 };
    115   unsigned CommonAlignLog2 : NumCommonAlignmentBits;
    116 
    117   /// The Flags field is used by object file implementations to store
    118   /// additional per symbol information which is not easily classified.
    119   enum : unsigned { NumFlagsBits = 16 };
    120   mutable uint32_t Flags : NumFlagsBits;
    121 
    122   /// Index field, for use by the object file implementation.
    123   mutable uint32_t Index = 0;
    124 
    125   union {
    126     /// The offset to apply to the fragment address to form this symbol's value.
    127     uint64_t Offset;
    128 
    129     /// The size of the symbol, if it is 'common'.
    130     uint64_t CommonSize;
    131 
    132     /// If non-null, the value for a variable symbol.
    133     const MCExpr *Value;
    134   };
    135 
    136 protected: // MCContext creates and uniques these.
    137   friend class MCExpr;
    138   friend class MCContext;
    139 
    140   /// \brief The name for a symbol.
    141   /// MCSymbol contains a uint64_t so is probably aligned to 8.  On a 32-bit
    142   /// system, the name is a pointer so isn't going to satisfy the 8 byte
    143   /// alignment of uint64_t.  Account for that here.
    144   typedef union {
    145     const StringMapEntry<bool> *NameEntry;
    146     uint64_t AlignmentPadding;
    147   } NameEntryStorageTy;
    148 
    149   MCSymbol(SymbolKind Kind, const StringMapEntry<bool> *Name, bool isTemporary)
    150       : IsTemporary(isTemporary), IsRedefinable(false), IsUsed(false),
    151         IsRegistered(false), IsExternal(false), IsPrivateExtern(false),
    152         Kind(Kind), IsUsedInReloc(false), SymbolContents(SymContentsUnset),
    153         CommonAlignLog2(0), Flags(0) {
    154     Offset = 0;
    155     FragmentAndHasName.setInt(!!Name);
    156     if (Name)
    157       getNameEntryPtr() = Name;
    158   }
    159 
    160   // Provide custom new/delete as we will only allocate space for a name
    161   // if we need one.
    162   void *operator new(size_t s, const StringMapEntry<bool> *Name,
    163                      MCContext &Ctx);
    164 
    165 private:
    166 
    167   void operator delete(void *);
    168   /// \brief Placement delete - required by std, but never called.
    169   void operator delete(void*, unsigned) {
    170     llvm_unreachable("Constructor throws?");
    171   }
    172   /// \brief Placement delete - required by std, but never called.
    173   void operator delete(void*, unsigned, bool) {
    174     llvm_unreachable("Constructor throws?");
    175   }
    176 
    177   MCSymbol(const MCSymbol &) = delete;
    178   void operator=(const MCSymbol &) = delete;
    179   MCSection *getSectionPtr(bool SetUsed = true) const {
    180     if (MCFragment *F = getFragment(SetUsed)) {
    181       assert(F != AbsolutePseudoFragment);
    182       return F->getParent();
    183     }
    184     return nullptr;
    185   }
    186 
    187   /// \brief Get a reference to the name field.  Requires that we have a name
    188   const StringMapEntry<bool> *&getNameEntryPtr() {
    189     assert(FragmentAndHasName.getInt() && "Name is required");
    190     NameEntryStorageTy *Name = reinterpret_cast<NameEntryStorageTy *>(this);
    191     return (*(Name - 1)).NameEntry;
    192   }
    193   const StringMapEntry<bool> *&getNameEntryPtr() const {
    194     return const_cast<MCSymbol*>(this)->getNameEntryPtr();
    195   }
    196 
    197 public:
    198   /// getName - Get the symbol name.
    199   StringRef getName() const {
    200     if (!FragmentAndHasName.getInt())
    201       return StringRef();
    202 
    203     return getNameEntryPtr()->first();
    204   }
    205 
    206   bool isRegistered() const { return IsRegistered; }
    207   void setIsRegistered(bool Value) const { IsRegistered = Value; }
    208 
    209   void setUsedInReloc() const { IsUsedInReloc = true; }
    210   bool isUsedInReloc() const { return IsUsedInReloc; }
    211 
    212   /// \name Accessors
    213   /// @{
    214 
    215   /// isTemporary - Check if this is an assembler temporary symbol.
    216   bool isTemporary() const { return IsTemporary; }
    217 
    218   /// isUsed - Check if this is used.
    219   bool isUsed() const { return IsUsed; }
    220   void setUsed(bool Value) const { IsUsed |= Value; }
    221 
    222   /// \brief Check if this symbol is redefinable.
    223   bool isRedefinable() const { return IsRedefinable; }
    224   /// \brief Mark this symbol as redefinable.
    225   void setRedefinable(bool Value) { IsRedefinable = Value; }
    226   /// \brief Prepare this symbol to be redefined.
    227   void redefineIfPossible() {
    228     if (IsRedefinable) {
    229       if (SymbolContents == SymContentsVariable) {
    230         Value = nullptr;
    231         SymbolContents = SymContentsUnset;
    232       }
    233       setUndefined();
    234       IsRedefinable = false;
    235     }
    236   }
    237 
    238   /// @}
    239   /// \name Associated Sections
    240   /// @{
    241 
    242   /// isDefined - Check if this symbol is defined (i.e., it has an address).
    243   ///
    244   /// Defined symbols are either absolute or in some section.
    245   bool isDefined(bool SetUsed = true) const {
    246     return getFragment(SetUsed) != nullptr;
    247   }
    248 
    249   /// isInSection - Check if this symbol is defined in some section (i.e., it
    250   /// is defined but not absolute).
    251   bool isInSection(bool SetUsed = true) const {
    252     return isDefined(SetUsed) && !isAbsolute(SetUsed);
    253   }
    254 
    255   /// isUndefined - Check if this symbol undefined (i.e., implicitly defined).
    256   bool isUndefined(bool SetUsed = true) const { return !isDefined(SetUsed); }
    257 
    258   /// isAbsolute - Check if this is an absolute symbol.
    259   bool isAbsolute(bool SetUsed = true) const {
    260     return getFragment(SetUsed) == AbsolutePseudoFragment;
    261   }
    262 
    263   /// Get the section associated with a defined, non-absolute symbol.
    264   MCSection &getSection(bool SetUsed = true) const {
    265     assert(isInSection(SetUsed) && "Invalid accessor!");
    266     return *getSectionPtr(SetUsed);
    267   }
    268 
    269   /// Mark the symbol as defined in the fragment \p F.
    270   void setFragment(MCFragment *F) const {
    271     assert(!isVariable() && "Cannot set fragment of variable");
    272     FragmentAndHasName.setPointer(F);
    273   }
    274 
    275   /// Mark the symbol as undefined.
    276   void setUndefined() { FragmentAndHasName.setPointer(nullptr); }
    277 
    278   bool isELF() const { return Kind == SymbolKindELF; }
    279 
    280   bool isCOFF() const { return Kind == SymbolKindCOFF; }
    281 
    282   bool isMachO() const { return Kind == SymbolKindMachO; }
    283 
    284   /// @}
    285   /// \name Variable Symbols
    286   /// @{
    287 
    288   /// isVariable - Check if this is a variable symbol.
    289   bool isVariable() const {
    290     return SymbolContents == SymContentsVariable;
    291   }
    292 
    293   /// getVariableValue - Get the value for variable symbols.
    294   const MCExpr *getVariableValue(bool SetUsed = true) const {
    295     assert(isVariable() && "Invalid accessor!");
    296     IsUsed |= SetUsed;
    297     return Value;
    298   }
    299 
    300   void setVariableValue(const MCExpr *Value);
    301 
    302   /// @}
    303 
    304   /// Get the (implementation defined) index.
    305   uint32_t getIndex() const {
    306     return Index;
    307   }
    308 
    309   /// Set the (implementation defined) index.
    310   void setIndex(uint32_t Value) const {
    311     Index = Value;
    312   }
    313 
    314   uint64_t getOffset() const {
    315     assert((SymbolContents == SymContentsUnset ||
    316             SymbolContents == SymContentsOffset) &&
    317            "Cannot get offset for a common/variable symbol");
    318     return Offset;
    319   }
    320   void setOffset(uint64_t Value) {
    321     assert((SymbolContents == SymContentsUnset ||
    322             SymbolContents == SymContentsOffset) &&
    323            "Cannot set offset for a common/variable symbol");
    324     Offset = Value;
    325     SymbolContents = SymContentsOffset;
    326   }
    327 
    328   /// Return the size of a 'common' symbol.
    329   uint64_t getCommonSize() const {
    330     assert(isCommon() && "Not a 'common' symbol!");
    331     return CommonSize;
    332   }
    333 
    334   /// Mark this symbol as being 'common'.
    335   ///
    336   /// \param Size - The size of the symbol.
    337   /// \param Align - The alignment of the symbol.
    338   void setCommon(uint64_t Size, unsigned Align) {
    339     assert(getOffset() == 0);
    340     CommonSize = Size;
    341     SymbolContents = SymContentsCommon;
    342 
    343     assert((!Align || isPowerOf2_32(Align)) &&
    344            "Alignment must be a power of 2");
    345     unsigned Log2Align = Log2_32(Align) + 1;
    346     assert(Log2Align < (1U << NumCommonAlignmentBits) &&
    347            "Out of range alignment");
    348     CommonAlignLog2 = Log2Align;
    349   }
    350 
    351   ///  Return the alignment of a 'common' symbol.
    352   unsigned getCommonAlignment() const {
    353     assert(isCommon() && "Not a 'common' symbol!");
    354     return CommonAlignLog2 ? (1U << (CommonAlignLog2 - 1)) : 0;
    355   }
    356 
    357   /// Declare this symbol as being 'common'.
    358   ///
    359   /// \param Size - The size of the symbol.
    360   /// \param Align - The alignment of the symbol.
    361   /// \return True if symbol was already declared as a different type
    362   bool declareCommon(uint64_t Size, unsigned Align) {
    363     assert(isCommon() || getOffset() == 0);
    364     if(isCommon()) {
    365       if(CommonSize != Size || getCommonAlignment() != Align)
    366        return true;
    367     } else
    368       setCommon(Size, Align);
    369     return false;
    370   }
    371 
    372   /// Is this a 'common' symbol.
    373   bool isCommon() const {
    374     return SymbolContents == SymContentsCommon;
    375   }
    376 
    377   MCFragment *getFragment(bool SetUsed = true) const {
    378     MCFragment *Fragment = FragmentAndHasName.getPointer();
    379     if (Fragment || !isVariable())
    380       return Fragment;
    381     Fragment = getVariableValue(SetUsed)->findAssociatedFragment();
    382     FragmentAndHasName.setPointer(Fragment);
    383     return Fragment;
    384   }
    385 
    386   bool isExternal() const { return IsExternal; }
    387   void setExternal(bool Value) const { IsExternal = Value; }
    388 
    389   bool isPrivateExtern() const { return IsPrivateExtern; }
    390   void setPrivateExtern(bool Value) { IsPrivateExtern = Value; }
    391 
    392   /// print - Print the value to the stream \p OS.
    393   void print(raw_ostream &OS, const MCAsmInfo *MAI) const;
    394 
    395   /// dump - Print the value to stderr.
    396   void dump() const;
    397 
    398 protected:
    399   /// Get the (implementation defined) symbol flags.
    400   uint32_t getFlags() const { return Flags; }
    401 
    402   /// Set the (implementation defined) symbol flags.
    403   void setFlags(uint32_t Value) const {
    404     assert(Value < (1U << NumFlagsBits) && "Out of range flags");
    405     Flags = Value;
    406   }
    407 
    408   /// Modify the flags via a mask
    409   void modifyFlags(uint32_t Value, uint32_t Mask) const {
    410     assert(Value < (1U << NumFlagsBits) && "Out of range flags");
    411     Flags = (Flags & ~Mask) | Value;
    412   }
    413 };
    414 
    415 inline raw_ostream &operator<<(raw_ostream &OS, const MCSymbol &Sym) {
    416   Sym.print(OS, nullptr);
    417   return OS;
    418 }
    419 } // end namespace llvm
    420 
    421 #endif
    422