1 //===- Symbols.h ------------------------------------------------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8
9 #ifndef LLD_COFF_SYMBOLS_H
10 #define LLD_COFF_SYMBOLS_H
11
12 #include "Chunks.h"
13 #include "Config.h"
14 #include "lld/Common/LLVM.h"
15 #include "lld/Common/Memory.h"
16 #include "llvm/ADT/ArrayRef.h"
17 #include "llvm/Object/Archive.h"
18 #include "llvm/Object/COFF.h"
19 #include <atomic>
20 #include <memory>
21 #include <vector>
22
23 namespace lld {
24
25 std::string toString(coff::Symbol &b);
26
27 // There are two different ways to convert an Archive::Symbol to a string:
28 // One for Microsoft name mangling and one for Itanium name mangling.
29 // Call the functions toCOFFString and toELFString, not just toString.
30 std::string toCOFFString(const coff::Archive::Symbol &b);
31
32 namespace coff {
33
34 using llvm::object::Archive;
35 using llvm::object::COFFSymbolRef;
36 using llvm::object::coff_import_header;
37 using llvm::object::coff_symbol_generic;
38
39 class ArchiveFile;
40 class InputFile;
41 class ObjFile;
42 class SymbolTable;
43
44 // The base class for real symbol classes.
45 class Symbol {
46 public:
47 enum Kind {
48 // The order of these is significant. We start with the regular defined
49 // symbols as those are the most prevalent and the zero tag is the cheapest
50 // to set. Among the defined kinds, the lower the kind is preferred over
51 // the higher kind when testing whether one symbol should take precedence
52 // over another.
53 DefinedRegularKind = 0,
54 DefinedCommonKind,
55 DefinedLocalImportKind,
56 DefinedImportThunkKind,
57 DefinedImportDataKind,
58 DefinedAbsoluteKind,
59 DefinedSyntheticKind,
60
61 UndefinedKind,
62 LazyArchiveKind,
63 LazyObjectKind,
64 LazyDLLSymbolKind,
65
66 LastDefinedCOFFKind = DefinedCommonKind,
67 LastDefinedKind = DefinedSyntheticKind,
68 };
69
kind()70 Kind kind() const { return static_cast<Kind>(symbolKind); }
71
72 // Returns the symbol name.
getName()73 StringRef getName() {
74 // COFF symbol names are read lazily for a performance reason.
75 // Non-external symbol names are never used by the linker except for logging
76 // or debugging. Their internal references are resolved not by name but by
77 // symbol index. And because they are not external, no one can refer them by
78 // name. Object files contain lots of non-external symbols, and creating
79 // StringRefs for them (which involves lots of strlen() on the string table)
80 // is a waste of time.
81 if (nameData == nullptr)
82 computeName();
83 return StringRef(nameData, nameSize);
84 }
85
86 void replaceKeepingName(Symbol *other, size_t size);
87
88 // Returns the file from which this symbol was created.
89 InputFile *getFile();
90
91 // Indicates that this symbol will be included in the final image. Only valid
92 // after calling markLive.
93 bool isLive() const;
94
isLazy()95 bool isLazy() const {
96 return symbolKind == LazyArchiveKind || symbolKind == LazyObjectKind ||
97 symbolKind == LazyDLLSymbolKind;
98 }
99
100 private:
101 void computeName();
102
103 protected:
104 friend SymbolTable;
105 explicit Symbol(Kind k, StringRef n = "")
symbolKind(k)106 : symbolKind(k), isExternal(true), isCOMDAT(false),
107 writtenToSymtab(false), pendingArchiveLoad(false), isGCRoot(false),
108 isRuntimePseudoReloc(false), deferUndefined(false), canInline(true),
109 nameSize(n.size()), nameData(n.empty() ? nullptr : n.data()) {}
110
111 const unsigned symbolKind : 8;
112 unsigned isExternal : 1;
113
114 public:
115 // This bit is used by the \c DefinedRegular subclass.
116 unsigned isCOMDAT : 1;
117
118 // This bit is used by Writer::createSymbolAndStringTable() to prevent
119 // symbols from being written to the symbol table more than once.
120 unsigned writtenToSymtab : 1;
121
122 // True if this symbol was referenced by a regular (non-bitcode) object.
123 unsigned isUsedInRegularObj : 1;
124
125 // True if we've seen both a lazy and an undefined symbol with this symbol
126 // name, which means that we have enqueued an archive member load and should
127 // not load any more archive members to resolve the same symbol.
128 unsigned pendingArchiveLoad : 1;
129
130 /// True if we've already added this symbol to the list of GC roots.
131 unsigned isGCRoot : 1;
132
133 unsigned isRuntimePseudoReloc : 1;
134
135 // True if we want to allow this symbol to be undefined in the early
136 // undefined check pass in SymbolTable::reportUnresolvable(), as it
137 // might be fixed up later.
138 unsigned deferUndefined : 1;
139
140 // False if LTO shouldn't inline whatever this symbol points to. If a symbol
141 // is overwritten after LTO, LTO shouldn't inline the symbol because it
142 // doesn't know the final contents of the symbol.
143 unsigned canInline : 1;
144
145 protected:
146 // Symbol name length. Assume symbol lengths fit in a 32-bit integer.
147 uint32_t nameSize;
148
149 const char *nameData;
150 };
151
152 // The base class for any defined symbols, including absolute symbols,
153 // etc.
154 class Defined : public Symbol {
155 public:
Defined(Kind k,StringRef n)156 Defined(Kind k, StringRef n) : Symbol(k, n) {}
157
classof(const Symbol * s)158 static bool classof(const Symbol *s) { return s->kind() <= LastDefinedKind; }
159
160 // Returns the RVA (relative virtual address) of this symbol. The
161 // writer sets and uses RVAs.
162 uint64_t getRVA();
163
164 // Returns the chunk containing this symbol. Absolute symbols and __ImageBase
165 // do not have chunks, so this may return null.
166 Chunk *getChunk();
167 };
168
169 // Symbols defined via a COFF object file or bitcode file. For COFF files, this
170 // stores a coff_symbol_generic*, and names of internal symbols are lazily
171 // loaded through that. For bitcode files, Sym is nullptr and the name is stored
172 // as a decomposed StringRef.
173 class DefinedCOFF : public Defined {
174 friend Symbol;
175
176 public:
DefinedCOFF(Kind k,InputFile * f,StringRef n,const coff_symbol_generic * s)177 DefinedCOFF(Kind k, InputFile *f, StringRef n, const coff_symbol_generic *s)
178 : Defined(k, n), file(f), sym(s) {}
179
classof(const Symbol * s)180 static bool classof(const Symbol *s) {
181 return s->kind() <= LastDefinedCOFFKind;
182 }
183
getFile()184 InputFile *getFile() { return file; }
185
186 COFFSymbolRef getCOFFSymbol();
187
188 InputFile *file;
189
190 protected:
191 const coff_symbol_generic *sym;
192 };
193
194 // Regular defined symbols read from object file symbol tables.
195 class DefinedRegular : public DefinedCOFF {
196 public:
197 DefinedRegular(InputFile *f, StringRef n, bool isCOMDAT,
198 bool isExternal = false,
199 const coff_symbol_generic *s = nullptr,
200 SectionChunk *c = nullptr)
DefinedCOFF(DefinedRegularKind,f,n,s)201 : DefinedCOFF(DefinedRegularKind, f, n, s), data(c ? &c->repl : nullptr) {
202 this->isExternal = isExternal;
203 this->isCOMDAT = isCOMDAT;
204 }
205
classof(const Symbol * s)206 static bool classof(const Symbol *s) {
207 return s->kind() == DefinedRegularKind;
208 }
209
getRVA()210 uint64_t getRVA() const { return (*data)->getRVA() + sym->Value; }
getChunk()211 SectionChunk *getChunk() const { return *data; }
getValue()212 uint32_t getValue() const { return sym->Value; }
213
214 SectionChunk **data;
215 };
216
217 class DefinedCommon : public DefinedCOFF {
218 public:
219 DefinedCommon(InputFile *f, StringRef n, uint64_t size,
220 const coff_symbol_generic *s = nullptr,
221 CommonChunk *c = nullptr)
DefinedCOFF(DefinedCommonKind,f,n,s)222 : DefinedCOFF(DefinedCommonKind, f, n, s), data(c), size(size) {
223 this->isExternal = true;
224 }
225
classof(const Symbol * s)226 static bool classof(const Symbol *s) {
227 return s->kind() == DefinedCommonKind;
228 }
229
getRVA()230 uint64_t getRVA() { return data->getRVA(); }
getChunk()231 CommonChunk *getChunk() { return data; }
232
233 private:
234 friend SymbolTable;
getSize()235 uint64_t getSize() const { return size; }
236 CommonChunk *data;
237 uint64_t size;
238 };
239
240 // Absolute symbols.
241 class DefinedAbsolute : public Defined {
242 public:
DefinedAbsolute(StringRef n,COFFSymbolRef s)243 DefinedAbsolute(StringRef n, COFFSymbolRef s)
244 : Defined(DefinedAbsoluteKind, n), va(s.getValue()) {
245 isExternal = s.isExternal();
246 }
247
DefinedAbsolute(StringRef n,uint64_t v)248 DefinedAbsolute(StringRef n, uint64_t v)
249 : Defined(DefinedAbsoluteKind, n), va(v) {}
250
classof(const Symbol * s)251 static bool classof(const Symbol *s) {
252 return s->kind() == DefinedAbsoluteKind;
253 }
254
getRVA()255 uint64_t getRVA() { return va - config->imageBase; }
setVA(uint64_t v)256 void setVA(uint64_t v) { va = v; }
getVA()257 uint64_t getVA() const { return va; }
258
259 // Section index relocations against absolute symbols resolve to
260 // this 16 bit number, and it is the largest valid section index
261 // plus one. This variable keeps it.
262 static uint16_t numOutputSections;
263
264 private:
265 uint64_t va;
266 };
267
268 // This symbol is used for linker-synthesized symbols like __ImageBase and
269 // __safe_se_handler_table.
270 class DefinedSynthetic : public Defined {
271 public:
DefinedSynthetic(StringRef name,Chunk * c)272 explicit DefinedSynthetic(StringRef name, Chunk *c)
273 : Defined(DefinedSyntheticKind, name), c(c) {}
274
classof(const Symbol * s)275 static bool classof(const Symbol *s) {
276 return s->kind() == DefinedSyntheticKind;
277 }
278
279 // A null chunk indicates that this is __ImageBase. Otherwise, this is some
280 // other synthesized chunk, like SEHTableChunk.
getRVA()281 uint32_t getRVA() { return c ? c->getRVA() : 0; }
getChunk()282 Chunk *getChunk() { return c; }
283
284 private:
285 Chunk *c;
286 };
287
288 // This class represents a symbol defined in an archive file. It is
289 // created from an archive file header, and it knows how to load an
290 // object file from an archive to replace itself with a defined
291 // symbol. If the resolver finds both Undefined and LazyArchive for
292 // the same name, it will ask the LazyArchive to load a file.
293 class LazyArchive : public Symbol {
294 public:
LazyArchive(ArchiveFile * f,const Archive::Symbol s)295 LazyArchive(ArchiveFile *f, const Archive::Symbol s)
296 : Symbol(LazyArchiveKind, s.getName()), file(f), sym(s) {}
297
classof(const Symbol * s)298 static bool classof(const Symbol *s) { return s->kind() == LazyArchiveKind; }
299
300 MemoryBufferRef getMemberBuffer();
301
302 ArchiveFile *file;
303 const Archive::Symbol sym;
304 };
305
306 class LazyObject : public Symbol {
307 public:
LazyObject(LazyObjFile * f,StringRef n)308 LazyObject(LazyObjFile *f, StringRef n)
309 : Symbol(LazyObjectKind, n), file(f) {}
classof(const Symbol * s)310 static bool classof(const Symbol *s) { return s->kind() == LazyObjectKind; }
311 LazyObjFile *file;
312 };
313
314 // MinGW only.
315 class LazyDLLSymbol : public Symbol {
316 public:
LazyDLLSymbol(DLLFile * f,DLLFile::Symbol * s,StringRef n)317 LazyDLLSymbol(DLLFile *f, DLLFile::Symbol *s, StringRef n)
318 : Symbol(LazyDLLSymbolKind, n), file(f), sym(s) {}
classof(const Symbol * s)319 static bool classof(const Symbol *s) {
320 return s->kind() == LazyDLLSymbolKind;
321 }
322
323 DLLFile *file;
324 DLLFile::Symbol *sym;
325 };
326
327 // Undefined symbols.
328 class Undefined : public Symbol {
329 public:
Undefined(StringRef n)330 explicit Undefined(StringRef n) : Symbol(UndefinedKind, n) {}
331
classof(const Symbol * s)332 static bool classof(const Symbol *s) { return s->kind() == UndefinedKind; }
333
334 // An undefined symbol can have a fallback symbol which gives an
335 // undefined symbol a second chance if it would remain undefined.
336 // If it remains undefined, it'll be replaced with whatever the
337 // Alias pointer points to.
338 Symbol *weakAlias = nullptr;
339
340 // If this symbol is external weak, try to resolve it to a defined
341 // symbol by searching the chain of fallback symbols. Returns the symbol if
342 // successful, otherwise returns null.
343 Defined *getWeakAlias();
344 };
345
346 // Windows-specific classes.
347
348 // This class represents a symbol imported from a DLL. This has two
349 // names for internal use and external use. The former is used for
350 // name resolution, and the latter is used for the import descriptor
351 // table in an output. The former has "__imp_" prefix.
352 class DefinedImportData : public Defined {
353 public:
DefinedImportData(StringRef n,ImportFile * f)354 DefinedImportData(StringRef n, ImportFile *f)
355 : Defined(DefinedImportDataKind, n), file(f) {
356 }
357
classof(const Symbol * s)358 static bool classof(const Symbol *s) {
359 return s->kind() == DefinedImportDataKind;
360 }
361
getRVA()362 uint64_t getRVA() { return file->location->getRVA(); }
getChunk()363 Chunk *getChunk() { return file->location; }
setLocation(Chunk * addressTable)364 void setLocation(Chunk *addressTable) { file->location = addressTable; }
365
getDLLName()366 StringRef getDLLName() { return file->dllName; }
getExternalName()367 StringRef getExternalName() { return file->externalName; }
getOrdinal()368 uint16_t getOrdinal() { return file->hdr->OrdinalHint; }
369
370 ImportFile *file;
371
372 // This is a pointer to the synthetic symbol associated with the load thunk
373 // for this symbol that will be called if the DLL is delay-loaded. This is
374 // needed for Control Flow Guard because if this DefinedImportData symbol is a
375 // valid call target, the corresponding load thunk must also be marked as a
376 // valid call target.
377 DefinedSynthetic *loadThunkSym = nullptr;
378 };
379
380 // This class represents a symbol for a jump table entry which jumps
381 // to a function in a DLL. Linker are supposed to create such symbols
382 // without "__imp_" prefix for all function symbols exported from
383 // DLLs, so that you can call DLL functions as regular functions with
384 // a regular name. A function pointer is given as a DefinedImportData.
385 class DefinedImportThunk : public Defined {
386 public:
387 DefinedImportThunk(StringRef name, DefinedImportData *s, uint16_t machine);
388
classof(const Symbol * s)389 static bool classof(const Symbol *s) {
390 return s->kind() == DefinedImportThunkKind;
391 }
392
getRVA()393 uint64_t getRVA() { return data->getRVA(); }
getChunk()394 Chunk *getChunk() { return data; }
395
396 DefinedImportData *wrappedSym;
397
398 private:
399 Chunk *data;
400 };
401
402 // If you have a symbol "foo" in your object file, a symbol name
403 // "__imp_foo" becomes automatically available as a pointer to "foo".
404 // This class is for such automatically-created symbols.
405 // Yes, this is an odd feature. We didn't intend to implement that.
406 // This is here just for compatibility with MSVC.
407 class DefinedLocalImport : public Defined {
408 public:
DefinedLocalImport(StringRef n,Defined * s)409 DefinedLocalImport(StringRef n, Defined *s)
410 : Defined(DefinedLocalImportKind, n), data(make<LocalImportChunk>(s)) {}
411
classof(const Symbol * s)412 static bool classof(const Symbol *s) {
413 return s->kind() == DefinedLocalImportKind;
414 }
415
getRVA()416 uint64_t getRVA() { return data->getRVA(); }
getChunk()417 Chunk *getChunk() { return data; }
418
419 private:
420 LocalImportChunk *data;
421 };
422
getRVA()423 inline uint64_t Defined::getRVA() {
424 switch (kind()) {
425 case DefinedAbsoluteKind:
426 return cast<DefinedAbsolute>(this)->getRVA();
427 case DefinedSyntheticKind:
428 return cast<DefinedSynthetic>(this)->getRVA();
429 case DefinedImportDataKind:
430 return cast<DefinedImportData>(this)->getRVA();
431 case DefinedImportThunkKind:
432 return cast<DefinedImportThunk>(this)->getRVA();
433 case DefinedLocalImportKind:
434 return cast<DefinedLocalImport>(this)->getRVA();
435 case DefinedCommonKind:
436 return cast<DefinedCommon>(this)->getRVA();
437 case DefinedRegularKind:
438 return cast<DefinedRegular>(this)->getRVA();
439 case LazyArchiveKind:
440 case LazyObjectKind:
441 case LazyDLLSymbolKind:
442 case UndefinedKind:
443 llvm_unreachable("Cannot get the address for an undefined symbol.");
444 }
445 llvm_unreachable("unknown symbol kind");
446 }
447
getChunk()448 inline Chunk *Defined::getChunk() {
449 switch (kind()) {
450 case DefinedRegularKind:
451 return cast<DefinedRegular>(this)->getChunk();
452 case DefinedAbsoluteKind:
453 return nullptr;
454 case DefinedSyntheticKind:
455 return cast<DefinedSynthetic>(this)->getChunk();
456 case DefinedImportDataKind:
457 return cast<DefinedImportData>(this)->getChunk();
458 case DefinedImportThunkKind:
459 return cast<DefinedImportThunk>(this)->getChunk();
460 case DefinedLocalImportKind:
461 return cast<DefinedLocalImport>(this)->getChunk();
462 case DefinedCommonKind:
463 return cast<DefinedCommon>(this)->getChunk();
464 case LazyArchiveKind:
465 case LazyObjectKind:
466 case LazyDLLSymbolKind:
467 case UndefinedKind:
468 llvm_unreachable("Cannot get the chunk of an undefined symbol.");
469 }
470 llvm_unreachable("unknown symbol kind");
471 }
472
473 // A buffer class that is large enough to hold any Symbol-derived
474 // object. We allocate memory using this class and instantiate a symbol
475 // using the placement new.
476 union SymbolUnion {
477 alignas(DefinedRegular) char a[sizeof(DefinedRegular)];
478 alignas(DefinedCommon) char b[sizeof(DefinedCommon)];
479 alignas(DefinedAbsolute) char c[sizeof(DefinedAbsolute)];
480 alignas(DefinedSynthetic) char d[sizeof(DefinedSynthetic)];
481 alignas(LazyArchive) char e[sizeof(LazyArchive)];
482 alignas(Undefined) char f[sizeof(Undefined)];
483 alignas(DefinedImportData) char g[sizeof(DefinedImportData)];
484 alignas(DefinedImportThunk) char h[sizeof(DefinedImportThunk)];
485 alignas(DefinedLocalImport) char i[sizeof(DefinedLocalImport)];
486 alignas(LazyObject) char j[sizeof(LazyObject)];
487 alignas(LazyDLLSymbol) char k[sizeof(LazyDLLSymbol)];
488 };
489
490 template <typename T, typename... ArgT>
replaceSymbol(Symbol * s,ArgT &&...arg)491 void replaceSymbol(Symbol *s, ArgT &&... arg) {
492 static_assert(std::is_trivially_destructible<T>(),
493 "Symbol types must be trivially destructible");
494 static_assert(sizeof(T) <= sizeof(SymbolUnion), "Symbol too small");
495 static_assert(alignof(T) <= alignof(SymbolUnion),
496 "SymbolUnion not aligned enough");
497 assert(static_cast<Symbol *>(static_cast<T *>(nullptr)) == nullptr &&
498 "Not a Symbol");
499 bool canInline = s->canInline;
500 new (s) T(std::forward<ArgT>(arg)...);
501 s->canInline = canInline;
502 }
503 } // namespace coff
504
505 } // namespace lld
506
507 #endif
508