1//===- IRSymtab.h - data definitions for IR symbol tables -------*- 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// This file contains data definitions and a reader and builder for a symbol
10// table for LLVM IR. Its purpose is to allow linkers and other consumers of
11// bitcode files to efficiently read the symbol table for symbol resolution
12// purposes without needing to construct a module in memory.
13//
14// As with most object files the symbol table has two parts: the symbol table
15// itself and a string table which is referenced by the symbol table.
16//
17// A symbol table corresponds to a single bitcode file, which may consist of
18// multiple modules, so symbol tables may likewise contain symbols for multiple
19// modules.
20//
21//===----------------------------------------------------------------------===//
22
23#ifndef LLVM_OBJECT_IRSYMTAB_H
24#define LLVM_OBJECT_IRSYMTAB_H
25
26#include "llvm/ADT/ArrayRef.h"
27#include "llvm/ADT/StringRef.h"
28#include "llvm/ADT/iterator_range.h"
29#include "llvm/IR/Comdat.h"
30#include "llvm/IR/GlobalValue.h"
31#include "llvm/Object/SymbolicFile.h"
32#include "llvm/Support/Allocator.h"
33#include "llvm/Support/Endian.h"
34#include "llvm/Support/Error.h"
35#include <cassert>
36#include <cstdint>
37#include <vector>
38
39namespace llvm {
40
41struct BitcodeFileContents;
42class StringTableBuilder;
43
44namespace irsymtab {
45
46namespace storage {
47
48// The data structures in this namespace define the low-level serialization
49// format. Clients that just want to read a symbol table should use the
50// irsymtab::Reader class.
51
52using Word = support::ulittle32_t;
53
54/// A reference to a string in the string table.
55struct Str {
56 Word Offset, Size;
57
58 StringRef get(StringRef Strtab) const {
59 return {Strtab.data() + Offset, Size};
60 }
61};
62
63/// A reference to a range of objects in the symbol table.
64template <typename T> struct Range {
65 Word Offset, Size;
66
67 ArrayRef<T> get(StringRef Symtab) const {
68 return {reinterpret_cast<const T *>(Symtab.data() + Offset), Size};
69 }
70};
71
72/// Describes the range of a particular module's symbols within the symbol
73/// table.
74struct Module {
75 Word Begin, End;
76
77 /// The index of the first Uncommon for this Module.
78 Word UncBegin;
79};
80
81/// This is equivalent to an IR comdat.
82struct Comdat {
83 Str Name;
84
85 // llvm::Comdat::SelectionKind
86 Word SelectionKind;
87};
88
89/// Contains the information needed by linkers for symbol resolution, as well as
90/// by the LTO implementation itself.
91struct Symbol {
92 /// The mangled symbol name.
93 Str Name;
94
95 /// The unmangled symbol name, or the empty string if this is not an IR
96 /// symbol.
97 Str IRName;
98
99 /// The index into Header::Comdats, or -1 if not a comdat member.
100 Word ComdatIndex;
101
102 Word Flags;
103 enum FlagBits {
104 FB_visibility, // 2 bits
105 FB_has_uncommon = FB_visibility + 2,
106 FB_undefined,
107 FB_weak,
108 FB_common,
109 FB_indirect,
110 FB_used,
111 FB_tls,
112 FB_may_omit,
113 FB_global,
114 FB_format_specific,
115 FB_unnamed_addr,
116 FB_executable,
117 };
118};
119
120/// This data structure contains rarely used symbol fields and is optionally
121/// referenced by a Symbol.
122struct Uncommon {
123 Word CommonSize, CommonAlign;
124
125 /// COFF-specific: the name of the symbol that a weak external resolves to
126 /// if not defined.
127 Str COFFWeakExternFallbackName;
128
129 /// Specified section name, if any.
130 Str SectionName;
131};
132
133
134struct Header {
135 /// Version number of the symtab format. This number should be incremented
136 /// when the format changes, but it does not need to be incremented if a
137 /// change to LLVM would cause it to create a different symbol table.
138 Word Version;
139 enum { kCurrentVersion = 3 };
140
141 /// The producer's version string (LLVM_VERSION_STRING " " LLVM_REVISION).
142 /// Consumers should rebuild the symbol table from IR if the producer's
143 /// version does not match the consumer's version due to potential differences
144 /// in symbol table format, symbol enumeration order and so on.
145 Str Producer;
146
147 Range<Module> Modules;
148 Range<Comdat> Comdats;
149 Range<Symbol> Symbols;
150 Range<Uncommon> Uncommons;
151
152 Str TargetTriple, SourceFileName;
153
154 /// COFF-specific: linker directives.
155 Str COFFLinkerOpts;
156
157 /// Dependent Library Specifiers
158 Range<Str> DependentLibraries;
159};
160
161} // end namespace storage
162
163/// Fills in Symtab and StrtabBuilder with a valid symbol and string table for
164/// Mods.
165Error build(ArrayRef<Module *> Mods, SmallVector<char, 0> &Symtab,
166 StringTableBuilder &StrtabBuilder, BumpPtrAllocator &Alloc);
167
168/// This represents a symbol that has been read from a storage::Symbol and
169/// possibly a storage::Uncommon.
170struct Symbol {
171 // Copied from storage::Symbol.
172 StringRef Name, IRName;
173 int ComdatIndex;
174 uint32_t Flags;
175
176 // Copied from storage::Uncommon.
177 uint32_t CommonSize, CommonAlign;
178 StringRef COFFWeakExternFallbackName;
179 StringRef SectionName;
180
181 /// Returns the mangled symbol name.
182 StringRef getName() const { return Name; }
183
184 /// Returns the unmangled symbol name, or the empty string if this is not an
185 /// IR symbol.
186 StringRef getIRName() const { return IRName; }
187
188 /// Returns the index into the comdat table (see Reader::getComdatTable()), or
189 /// -1 if not a comdat member.
190 int getComdatIndex() const { return ComdatIndex; }
191
192 using S = storage::Symbol;
193
194 GlobalValue::VisibilityTypes getVisibility() const {
195 return GlobalValue::VisibilityTypes((Flags >> S::FB_visibility) & 3);
196 }
197
198 bool isUndefined() const { return (Flags >> S::FB_undefined) & 1; }
199 bool isWeak() const { return (Flags >> S::FB_weak) & 1; }
200 bool isCommon() const { return (Flags >> S::FB_common) & 1; }
201 bool isIndirect() const { return (Flags >> S::FB_indirect) & 1; }
202 bool isUsed() const { return (Flags >> S::FB_used) & 1; }
203 bool isTLS() const { return (Flags >> S::FB_tls) & 1; }
204
205 bool canBeOmittedFromSymbolTable() const {
206 return (Flags >> S::FB_may_omit) & 1;
207 }
208
209 bool isGlobal() const { return (Flags >> S::FB_global) & 1; }
210 bool isFormatSpecific() const { return (Flags >> S::FB_format_specific) & 1; }
211 bool isUnnamedAddr() const { return (Flags >> S::FB_unnamed_addr) & 1; }
212 bool isExecutable() const { return (Flags >> S::FB_executable) & 1; }
213
214 uint64_t getCommonSize() const {
215 assert(isCommon());
216 return CommonSize;
217 }
218
219 uint32_t getCommonAlignment() const {
220 assert(isCommon());
221 return CommonAlign;
222 }
223
224 /// COFF-specific: for weak externals, returns the name of the symbol that is
225 /// used as a fallback if the weak external remains undefined.
226 StringRef getCOFFWeakExternalFallback() const {
227 assert(isWeak() && isIndirect());
228 return COFFWeakExternFallbackName;
229 }
230
231 StringRef getSectionName() const { return SectionName; }
232};
233
234/// This class can be used to read a Symtab and Strtab produced by
235/// irsymtab::build.
236class Reader {
237 StringRef Symtab, Strtab;
238
239 ArrayRef<storage::Module> Modules;
240 ArrayRef<storage::Comdat> Comdats;
241 ArrayRef<storage::Symbol> Symbols;
242 ArrayRef<storage::Uncommon> Uncommons;
243 ArrayRef<storage::Str> DependentLibraries;
244
245 StringRef str(storage::Str S) const { return S.get(Strtab); }
246
247 template <typename T> ArrayRef<T> range(storage::Range<T> R) const {
248 return R.get(Symtab);
249 }
250
251 const storage::Header &header() const {
252 return *reinterpret_cast<const storage::Header *>(Symtab.data());
253 }
254
255public:
256 class SymbolRef;
257
258 Reader() = default;
259 Reader(StringRef Symtab, StringRef Strtab) : Symtab(Symtab), Strtab(Strtab) {
260 Modules = range(R: header().Modules);
261 Comdats = range(R: header().Comdats);
262 Symbols = range(R: header().Symbols);
263 Uncommons = range(R: header().Uncommons);
264 DependentLibraries = range(R: header().DependentLibraries);
265 }
266
267 using symbol_range = iterator_range<object::content_iterator<SymbolRef>>;
268
269 /// Returns the symbol table for the entire bitcode file.
270 /// The symbols enumerated by this method are ephemeral, but they can be
271 /// copied into an irsymtab::Symbol object.
272 symbol_range symbols() const;
273
274 size_t getNumModules() const { return Modules.size(); }
275
276 /// Returns a slice of the symbol table for the I'th module in the file.
277 /// The symbols enumerated by this method are ephemeral, but they can be
278 /// copied into an irsymtab::Symbol object.
279 symbol_range module_symbols(unsigned I) const;
280
281 StringRef getTargetTriple() const { return str(S: header().TargetTriple); }
282
283 /// Returns the source file path specified at compile time.
284 StringRef getSourceFileName() const { return str(S: header().SourceFileName); }
285
286 /// Returns a table with all the comdats used by this file.
287 std::vector<std::pair<StringRef, llvm::Comdat::SelectionKind>>
288 getComdatTable() const {
289 std::vector<std::pair<StringRef, llvm::Comdat::SelectionKind>> ComdatTable;
290 ComdatTable.reserve(n: Comdats.size());
291 for (auto C : Comdats)
292 ComdatTable.push_back(x: {str(S: C.Name), llvm::Comdat::SelectionKind(
293 uint32_t(C.SelectionKind))});
294 return ComdatTable;
295 }
296
297 /// COFF-specific: returns linker options specified in the input file.
298 StringRef getCOFFLinkerOpts() const { return str(S: header().COFFLinkerOpts); }
299
300 /// Returns dependent library specifiers
301 std::vector<StringRef> getDependentLibraries() const {
302 std::vector<StringRef> Specifiers;
303 Specifiers.reserve(n: DependentLibraries.size());
304 for (auto S : DependentLibraries) {
305 Specifiers.push_back(x: str(S));
306 }
307 return Specifiers;
308 }
309};
310
311/// Ephemeral symbols produced by Reader::symbols() and
312/// Reader::module_symbols().
313class Reader::SymbolRef : public Symbol {
314 const storage::Symbol *SymI, *SymE;
315 const storage::Uncommon *UncI;
316 const Reader *R;
317
318 void read() {
319 if (SymI == SymE)
320 return;
321
322 Name = R->str(S: SymI->Name);
323 IRName = R->str(S: SymI->IRName);
324 ComdatIndex = SymI->ComdatIndex;
325 Flags = SymI->Flags;
326
327 if (Flags & (1 << storage::Symbol::FB_has_uncommon)) {
328 CommonSize = UncI->CommonSize;
329 CommonAlign = UncI->CommonAlign;
330 COFFWeakExternFallbackName = R->str(S: UncI->COFFWeakExternFallbackName);
331 SectionName = R->str(S: UncI->SectionName);
332 } else
333 // Reset this field so it can be queried unconditionally for all symbols.
334 SectionName = "";
335 }
336
337public:
338 SymbolRef(const storage::Symbol *SymI, const storage::Symbol *SymE,
339 const storage::Uncommon *UncI, const Reader *R)
340 : SymI(SymI), SymE(SymE), UncI(UncI), R(R) {
341 read();
342 }
343
344 void moveNext() {
345 ++SymI;
346 if (Flags & (1 << storage::Symbol::FB_has_uncommon))
347 ++UncI;
348 read();
349 }
350
351 bool operator==(const SymbolRef &Other) const { return SymI == Other.SymI; }
352};
353
354inline Reader::symbol_range Reader::symbols() const {
355 return {SymbolRef(Symbols.begin(), Symbols.end(), Uncommons.begin(), this),
356 SymbolRef(Symbols.end(), Symbols.end(), nullptr, this)};
357}
358
359inline Reader::symbol_range Reader::module_symbols(unsigned I) const {
360 const storage::Module &M = Modules[I];
361 const storage::Symbol *MBegin = Symbols.begin() + M.Begin,
362 *MEnd = Symbols.begin() + M.End;
363 return {SymbolRef(MBegin, MEnd, Uncommons.begin() + M.UncBegin, this),
364 SymbolRef(MEnd, MEnd, nullptr, this)};
365}
366
367/// The contents of the irsymtab in a bitcode file. Any underlying data for the
368/// irsymtab are owned by Symtab and Strtab.
369struct FileContents {
370 SmallVector<char, 0> Symtab, Strtab;
371 Reader TheReader;
372};
373
374/// Reads the contents of a bitcode file, creating its irsymtab if necessary.
375Expected<FileContents> readBitcode(const BitcodeFileContents &BFC);
376
377} // end namespace irsymtab
378} // end namespace llvm
379
380#endif // LLVM_OBJECT_IRSYMTAB_H
381