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/PointerUnion.h"
18 #include "llvm/ADT/StringMap.h"
19 #include "llvm/MC/MCAssembler.h"
20 #include "llvm/MC/MCExpr.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 // Special sentinal value for the absolute pseudo section.
52 // FIXME: Use a PointerInt wrapper for this?
53 static MCSection *AbsolutePseudoSection;
55 /// If a symbol has a Fragment, the section is implied, so we only need
57 /// FIXME: We might be able to simplify this by having the asm streamer create
59 /// If this is a section, then it gives the symbol is defined in. This is null
60 /// for undefined symbols, and the special AbsolutePseudoSection value for
61 /// absolute symbols. If this is a variable symbol, this caches the variable
64 /// If this is a fragment, then it gives the fragment this symbol's value is
65 /// relative to, if any.
66 mutable PointerUnion<MCSection *, MCFragment *> SectionOrFragment;
68 /// IsTemporary - True if this is an assembler temporary label, which
69 /// typically does not survive in the .o file's symbol table. Usually
71 unsigned IsTemporary : 1;
73 /// \brief True if this symbol can be redefined.
74 unsigned IsRedefinable : 1;
76 /// IsUsed - True if this symbol has been used.
77 mutable unsigned IsUsed : 1;
79 mutable bool IsRegistered : 1;
81 /// This symbol is visible outside this translation unit.
82 mutable unsigned IsExternal : 1;
84 /// This symbol is private extern.
85 mutable unsigned IsPrivateExtern : 1;
87 /// True if this symbol is named.
88 /// A named symbol will have a pointer to the name allocated in the bytes
89 /// immediately prior to the MCSymbol.
92 /// LLVM RTTI discriminator. This is actually a SymbolKind enumerator, but is
93 /// unsigned to avoid sign extension and achieve better bitpacking with MSVC.
96 /// A symbol can contain an Offset, or Value, or be Common, but never more
97 /// than one of these.
98 enum Contents : uint8_t {
105 Contents SymbolContents : 2;
107 /// Index field, for use by the object file implementation.
108 mutable uint32_t Index = 0;
111 /// The offset to apply to the fragment address to form this symbol's value.
114 /// The size of the symbol, if it is 'common'.
117 /// If non-null, the value for a variable symbol.
121 /// The alignment of the symbol, if it is 'common', or -1.
123 // FIXME: Pack this in with other fields?
124 unsigned CommonAlign = -1U;
126 /// The Flags field is used by object file implementations to store
127 /// additional per symbol information which is not easily classified.
128 mutable uint32_t Flags = 0;
130 protected: // MCContext creates and uniques these.
132 friend class MCContext;
134 /// \brief The name for a symbol.
135 /// MCSymbol contains a uint64_t so is probably aligned to 8. On a 32-bit
136 /// system, the name is a pointer so isn't going to satisfy the 8 byte
137 /// alignment of uint64_t. Account for that here.
139 const StringMapEntry<bool> *NameEntry;
140 uint64_t AlignmentPadding;
141 } NameEntryStorageTy;
143 MCSymbol(SymbolKind Kind, const StringMapEntry<bool> *Name, bool isTemporary)
144 : IsTemporary(isTemporary),
145 IsRedefinable(false), IsUsed(false), IsRegistered(false),
146 IsExternal(false), IsPrivateExtern(false), HasName(!!Name),
147 Kind(Kind), SymbolContents(SymContentsUnset) {
150 getNameEntryPtr() = Name;
153 // Provide custom new/delete as we will only allocate space for a name
155 void *operator new(size_t s, const StringMapEntry<bool> *Name,
160 void operator delete(void *);
161 /// \brief Placement delete - required by std, but never called.
162 void operator delete(void*, unsigned) {
163 llvm_unreachable("Constructor throws?");
165 /// \brief Placement delete - required by std, but never called.
166 void operator delete(void*, unsigned, bool) {
167 llvm_unreachable("Constructor throws?");
170 MCSymbol(const MCSymbol &) = delete;
171 void operator=(const MCSymbol &) = delete;
172 MCSection *getSectionPtr() const {
173 if (MCFragment *F = getFragment())
174 return F->getParent();
175 assert(!SectionOrFragment.is<MCFragment *>() && "Section or null expected");
176 MCSection *Section = SectionOrFragment.dyn_cast<MCSection *>();
177 if (Section || !isVariable())
179 return Section = getVariableValue()->findAssociatedSection();
182 /// \brief Get a reference to the name field. Requires that we have a name
183 const StringMapEntry<bool> *&getNameEntryPtr() {
184 assert(HasName && "Name is required");
185 NameEntryStorageTy *Name = reinterpret_cast<NameEntryStorageTy *>(this);
186 return (*(Name - 1)).NameEntry;
188 const StringMapEntry<bool> *&getNameEntryPtr() const {
189 return const_cast<MCSymbol*>(this)->getNameEntryPtr();
193 /// getName - Get the symbol name.
194 StringRef getName() const {
198 return getNameEntryPtr()->first();
201 bool isRegistered() const { return IsRegistered; }
202 void setIsRegistered(bool Value) const { IsRegistered = Value; }
207 /// isTemporary - Check if this is an assembler temporary symbol.
208 bool isTemporary() const { return IsTemporary; }
210 /// isUsed - Check if this is used.
211 bool isUsed() const { return IsUsed; }
212 void setUsed(bool Value) const { IsUsed = Value; }
214 /// \brief Check if this symbol is redefinable.
215 bool isRedefinable() const { return IsRedefinable; }
216 /// \brief Mark this symbol as redefinable.
217 void setRedefinable(bool Value) { IsRedefinable = Value; }
218 /// \brief Prepare this symbol to be redefined.
219 void redefineIfPossible() {
221 if (SymbolContents == SymContentsVariable) {
223 SymbolContents = SymContentsUnset;
225 SectionOrFragment = nullptr;
226 IsRedefinable = false;
231 /// \name Associated Sections
234 /// isDefined - Check if this symbol is defined (i.e., it has an address).
236 /// Defined symbols are either absolute or in some section.
237 bool isDefined() const { return getSectionPtr() != nullptr; }
239 /// isInSection - Check if this symbol is defined in some section (i.e., it
240 /// is defined but not absolute).
241 bool isInSection() const { return isDefined() && !isAbsolute(); }
243 /// isUndefined - Check if this symbol undefined (i.e., implicitly defined).
244 bool isUndefined() const { return !isDefined(); }
246 /// isAbsolute - Check if this is an absolute symbol.
247 bool isAbsolute() const { return getSectionPtr() == AbsolutePseudoSection; }
249 /// Get the section associated with a defined, non-absolute symbol.
250 MCSection &getSection() const {
251 assert(isInSection() && "Invalid accessor!");
252 return *getSectionPtr();
255 /// Mark the symbol as defined in the section \p S.
256 void setSection(MCSection &S) {
257 assert(!isVariable() && "Cannot set section of variable");
258 assert(!SectionOrFragment.is<MCFragment *>() && "Section or null expected");
259 SectionOrFragment = &S;
262 /// Mark the symbol as undefined.
263 void setUndefined() {
264 SectionOrFragment = nullptr;
267 bool isELF() const { return Kind == SymbolKindELF; }
269 bool isCOFF() const { return Kind == SymbolKindCOFF; }
271 bool isMachO() const { return Kind == SymbolKindMachO; }
274 /// \name Variable Symbols
277 /// isVariable - Check if this is a variable symbol.
278 bool isVariable() const {
279 return SymbolContents == SymContentsVariable;
282 /// getVariableValue() - Get the value for variable symbols.
283 const MCExpr *getVariableValue() const {
284 assert(isVariable() && "Invalid accessor!");
289 void setVariableValue(const MCExpr *Value);
293 /// Get the (implementation defined) index.
294 uint32_t getIndex() const {
298 /// Set the (implementation defined) index.
299 void setIndex(uint32_t Value) const {
303 uint64_t getOffset() const {
304 assert((SymbolContents == SymContentsUnset ||
305 SymbolContents == SymContentsOffset) &&
306 "Cannot get offset for a common/variable symbol");
309 void setOffset(uint64_t Value) {
310 assert((SymbolContents == SymContentsUnset ||
311 SymbolContents == SymContentsOffset) &&
312 "Cannot set offset for a common/variable symbol");
314 SymbolContents = SymContentsOffset;
317 /// Return the size of a 'common' symbol.
318 uint64_t getCommonSize() const {
319 assert(isCommon() && "Not a 'common' symbol!");
323 /// Mark this symbol as being 'common'.
325 /// \param Size - The size of the symbol.
326 /// \param Align - The alignment of the symbol.
327 void setCommon(uint64_t Size, unsigned Align) {
328 assert(getOffset() == 0);
331 SymbolContents = SymContentsCommon;
334 /// Return the alignment of a 'common' symbol.
335 unsigned getCommonAlignment() const {
336 assert(isCommon() && "Not a 'common' symbol!");
340 /// Declare this symbol as being 'common'.
342 /// \param Size - The size of the symbol.
343 /// \param Align - The alignment of the symbol.
344 /// \return True if symbol was already declared as a different type
345 bool declareCommon(uint64_t Size, unsigned Align) {
346 assert(isCommon() || getOffset() == 0);
348 if(CommonSize != Size || CommonAlign != Align)
351 setCommon(Size, Align);
355 /// Is this a 'common' symbol.
356 bool isCommon() const {
357 return SymbolContents == SymContentsCommon;
360 MCFragment *getFragment() const {
361 return SectionOrFragment.dyn_cast<MCFragment *>();
363 void setFragment(MCFragment *Value) const {
364 SectionOrFragment = Value;
367 bool isExternal() const { return IsExternal; }
368 void setExternal(bool Value) const { IsExternal = Value; }
370 bool isPrivateExtern() const { return IsPrivateExtern; }
371 void setPrivateExtern(bool Value) { IsPrivateExtern = Value; }
373 /// print - Print the value to the stream \p OS.
374 void print(raw_ostream &OS, const MCAsmInfo *MAI) const;
376 /// dump - Print the value to stderr.
380 /// Get the (implementation defined) symbol flags.
381 uint32_t getFlags() const { return Flags; }
383 /// Set the (implementation defined) symbol flags.
384 void setFlags(uint32_t Value) const { Flags = Value; }
386 /// Modify the flags via a mask
387 void modifyFlags(uint32_t Value, uint32_t Mask) const {
388 Flags = (Flags & ~Mask) | Value;
392 inline raw_ostream &operator<<(raw_ostream &OS, const MCSymbol &Sym) {
393 Sym.print(OS, nullptr);
396 } // end namespace llvm