1 //===- MCSymbol.h - Machine Code Symbols ------------------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file contains the declaration of the MCSymbol class.
12 //===----------------------------------------------------------------------===//
14 #ifndef LLVM_MC_MCSYMBOL_H
15 #define LLVM_MC_MCSYMBOL_H
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"
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.
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.
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.
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 {
59 // Special sentinal value for the absolute pseudo section.
61 // FIXME: Use a PointerInt wrapper for this?
62 static MCSection *AbsolutePseudoSection;
64 /// If a symbol has a Fragment, the section is implied, so we only need
66 /// FIXME: We might be able to simplify this by having the asm streamer create
68 /// If this is a section, then it gives the symbol is defined in. This is null
69 /// for undefined symbols, and the special AbsolutePseudoSection value for
70 /// absolute symbols. If this is a variable symbol, this caches the variable
73 /// If this is a fragment, then it gives the fragment this symbol's value is
74 /// relative to, if any.
76 /// For the 'HasName' integer, this is true if this symbol is named.
77 /// A named symbol will have a pointer to the name allocated in the bytes
78 /// immediately prior to the MCSymbol.
79 mutable PointerIntPair<PointerUnion<MCSection *, MCFragment *>, 1>
80 SectionOrFragmentAndHasName;
82 /// IsTemporary - True if this is an assembler temporary label, which
83 /// typically does not survive in the .o file's symbol table. Usually
85 unsigned IsTemporary : 1;
87 /// \brief True if this symbol can be redefined.
88 unsigned IsRedefinable : 1;
90 /// IsUsed - True if this symbol has been used.
91 mutable unsigned IsUsed : 1;
93 mutable bool IsRegistered : 1;
95 /// This symbol is visible outside this translation unit.
96 mutable unsigned IsExternal : 1;
98 /// This symbol is private extern.
99 mutable unsigned IsPrivateExtern : 1;
101 /// LLVM RTTI discriminator. This is actually a SymbolKind enumerator, but is
102 /// unsigned to avoid sign extension and achieve better bitpacking with MSVC.
105 /// True if we have created a relocation that uses this symbol.
106 mutable unsigned IsUsedInReloc : 1;
108 /// This is actually a Contents enumerator, but is unsigned to avoid sign
109 /// extension and achieve better bitpacking with MSVC.
110 unsigned SymbolContents : 2;
112 /// The alignment of the symbol, if it is 'common', or -1.
114 /// The alignment is stored as log2(align) + 1. This allows all values from
115 /// 0 to 2^31 to be stored which is every power of 2 representable by an
117 static const unsigned NumCommonAlignmentBits = 5;
118 unsigned CommonAlignLog2 : NumCommonAlignmentBits;
120 /// The Flags field is used by object file implementations to store
121 /// additional per symbol information which is not easily classified.
122 static const unsigned NumFlagsBits = 16;
123 mutable uint32_t Flags : NumFlagsBits;
125 /// Index field, for use by the object file implementation.
126 mutable uint32_t Index = 0;
129 /// The offset to apply to the fragment address to form this symbol's value.
132 /// The size of the symbol, if it is 'common'.
135 /// If non-null, the value for a variable symbol.
139 protected: // MCContext creates and uniques these.
141 friend class MCContext;
143 /// \brief The name for a symbol.
144 /// MCSymbol contains a uint64_t so is probably aligned to 8. On a 32-bit
145 /// system, the name is a pointer so isn't going to satisfy the 8 byte
146 /// alignment of uint64_t. Account for that here.
148 const StringMapEntry<bool> *NameEntry;
149 uint64_t AlignmentPadding;
150 } NameEntryStorageTy;
152 MCSymbol(SymbolKind Kind, const StringMapEntry<bool> *Name, bool isTemporary)
153 : IsTemporary(isTemporary), IsRedefinable(false), IsUsed(false),
154 IsRegistered(false), IsExternal(false), IsPrivateExtern(false),
155 Kind(Kind), IsUsedInReloc(false), SymbolContents(SymContentsUnset),
156 CommonAlignLog2(0), Flags(0) {
158 SectionOrFragmentAndHasName.setInt(!!Name);
160 getNameEntryPtr() = Name;
163 // Provide custom new/delete as we will only allocate space for a name
165 void *operator new(size_t s, const StringMapEntry<bool> *Name,
170 void operator delete(void *);
171 /// \brief Placement delete - required by std, but never called.
172 void operator delete(void*, unsigned) {
173 llvm_unreachable("Constructor throws?");
175 /// \brief Placement delete - required by std, but never called.
176 void operator delete(void*, unsigned, bool) {
177 llvm_unreachable("Constructor throws?");
180 MCSymbol(const MCSymbol &) = delete;
181 void operator=(const MCSymbol &) = delete;
182 MCSection *getSectionPtr() const {
183 if (MCFragment *F = getFragment())
184 return F->getParent();
185 const auto &SectionOrFragment = SectionOrFragmentAndHasName.getPointer();
186 assert(!SectionOrFragment.is<MCFragment *>() && "Section or null expected");
187 MCSection *Section = SectionOrFragment.dyn_cast<MCSection *>();
188 if (Section || !isVariable())
190 return Section = getVariableValue()->findAssociatedSection();
193 /// \brief Get a reference to the name field. Requires that we have a name
194 const StringMapEntry<bool> *&getNameEntryPtr() {
195 assert(SectionOrFragmentAndHasName.getInt() && "Name is required");
196 NameEntryStorageTy *Name = reinterpret_cast<NameEntryStorageTy *>(this);
197 return (*(Name - 1)).NameEntry;
199 const StringMapEntry<bool> *&getNameEntryPtr() const {
200 return const_cast<MCSymbol*>(this)->getNameEntryPtr();
204 /// getName - Get the symbol name.
205 StringRef getName() const {
206 if (!SectionOrFragmentAndHasName.getInt())
209 return getNameEntryPtr()->first();
212 bool isRegistered() const { return IsRegistered; }
213 void setIsRegistered(bool Value) const { IsRegistered = Value; }
215 void setUsedInReloc() const { IsUsedInReloc = true; }
216 bool isUsedInReloc() const { return IsUsedInReloc; }
221 /// isTemporary - Check if this is an assembler temporary symbol.
222 bool isTemporary() const { return IsTemporary; }
224 /// isUsed - Check if this is used.
225 bool isUsed() const { return IsUsed; }
226 void setUsed(bool Value) const { IsUsed = Value; }
228 /// \brief Check if this symbol is redefinable.
229 bool isRedefinable() const { return IsRedefinable; }
230 /// \brief Mark this symbol as redefinable.
231 void setRedefinable(bool Value) { IsRedefinable = Value; }
232 /// \brief Prepare this symbol to be redefined.
233 void redefineIfPossible() {
235 if (SymbolContents == SymContentsVariable) {
237 SymbolContents = SymContentsUnset;
240 IsRedefinable = false;
245 /// \name Associated Sections
248 /// isDefined - Check if this symbol is defined (i.e., it has an address).
250 /// Defined symbols are either absolute or in some section.
251 bool isDefined() const { return getSectionPtr() != nullptr; }
253 /// isInSection - Check if this symbol is defined in some section (i.e., it
254 /// is defined but not absolute).
255 bool isInSection() const { return isDefined() && !isAbsolute(); }
257 /// isUndefined - Check if this symbol undefined (i.e., implicitly defined).
258 bool isUndefined() const { return !isDefined(); }
260 /// isAbsolute - Check if this is an absolute symbol.
261 bool isAbsolute() const { return getSectionPtr() == AbsolutePseudoSection; }
263 /// Get the section associated with a defined, non-absolute symbol.
264 MCSection &getSection() const {
265 assert(isInSection() && "Invalid accessor!");
266 return *getSectionPtr();
269 /// Mark the symbol as defined in the section \p S.
270 void setSection(MCSection &S) {
271 assert(!isVariable() && "Cannot set section of variable");
272 assert(!SectionOrFragmentAndHasName.getPointer().is<MCFragment *>() &&
273 "Section or null expected");
274 SectionOrFragmentAndHasName.setPointer(&S);
277 /// Mark the symbol as undefined.
278 void setUndefined() {
279 SectionOrFragmentAndHasName.setPointer(
280 PointerUnion<MCSection *, MCFragment *>());
283 bool isELF() const { return Kind == SymbolKindELF; }
285 bool isCOFF() const { return Kind == SymbolKindCOFF; }
287 bool isMachO() const { return Kind == SymbolKindMachO; }
290 /// \name Variable Symbols
293 /// isVariable - Check if this is a variable symbol.
294 bool isVariable() const {
295 return SymbolContents == SymContentsVariable;
298 /// getVariableValue() - Get the value for variable symbols.
299 const MCExpr *getVariableValue() const {
300 assert(isVariable() && "Invalid accessor!");
305 void setVariableValue(const MCExpr *Value);
309 /// Get the (implementation defined) index.
310 uint32_t getIndex() const {
314 /// Set the (implementation defined) index.
315 void setIndex(uint32_t Value) const {
319 uint64_t getOffset() const {
320 assert((SymbolContents == SymContentsUnset ||
321 SymbolContents == SymContentsOffset) &&
322 "Cannot get offset for a common/variable symbol");
325 void setOffset(uint64_t Value) {
326 assert((SymbolContents == SymContentsUnset ||
327 SymbolContents == SymContentsOffset) &&
328 "Cannot set offset for a common/variable symbol");
330 SymbolContents = SymContentsOffset;
333 /// Return the size of a 'common' symbol.
334 uint64_t getCommonSize() const {
335 assert(isCommon() && "Not a 'common' symbol!");
339 /// Mark this symbol as being 'common'.
341 /// \param Size - The size of the symbol.
342 /// \param Align - The alignment of the symbol.
343 void setCommon(uint64_t Size, unsigned Align) {
344 assert(getOffset() == 0);
346 SymbolContents = SymContentsCommon;
348 assert((!Align || isPowerOf2_32(Align)) &&
349 "Alignment must be a power of 2");
350 unsigned Log2Align = Log2_32(Align) + 1;
351 assert(Log2Align < (1U << NumCommonAlignmentBits) &&
352 "Out of range alignment");
353 CommonAlignLog2 = Log2Align;
356 /// Return the alignment of a 'common' symbol.
357 unsigned getCommonAlignment() const {
358 assert(isCommon() && "Not a 'common' symbol!");
359 return CommonAlignLog2 ? (1U << (CommonAlignLog2 - 1)) : 0;
362 /// Declare this symbol as being 'common'.
364 /// \param Size - The size of the symbol.
365 /// \param Align - The alignment of the symbol.
366 /// \return True if symbol was already declared as a different type
367 bool declareCommon(uint64_t Size, unsigned Align) {
368 assert(isCommon() || getOffset() == 0);
370 if(CommonSize != Size || getCommonAlignment() != Align)
373 setCommon(Size, Align);
377 /// Is this a 'common' symbol.
378 bool isCommon() const {
379 return SymbolContents == SymContentsCommon;
382 MCFragment *getFragment() const {
383 return SectionOrFragmentAndHasName.getPointer().dyn_cast<MCFragment *>();
385 void setFragment(MCFragment *Value) const {
386 SectionOrFragmentAndHasName.setPointer(Value);
389 bool isExternal() const { return IsExternal; }
390 void setExternal(bool Value) const { IsExternal = Value; }
392 bool isPrivateExtern() const { return IsPrivateExtern; }
393 void setPrivateExtern(bool Value) { IsPrivateExtern = Value; }
395 /// print - Print the value to the stream \p OS.
396 void print(raw_ostream &OS, const MCAsmInfo *MAI) const;
398 /// dump - Print the value to stderr.
402 /// Get the (implementation defined) symbol flags.
403 uint32_t getFlags() const { return Flags; }
405 /// Set the (implementation defined) symbol flags.
406 void setFlags(uint32_t Value) const {
407 assert(Value < (1U << NumFlagsBits) && "Out of range flags");
411 /// Modify the flags via a mask
412 void modifyFlags(uint32_t Value, uint32_t Mask) const {
413 assert(Value < (1U << NumFlagsBits) && "Out of range flags");
414 Flags = (Flags & ~Mask) | Value;
418 inline raw_ostream &operator<<(raw_ostream &OS, const MCSymbol &Sym) {
419 Sym.print(OS, nullptr);
422 } // end namespace llvm