1 //===- IRSymtab.cpp - implementation of IR symbol tables ------------------===//
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 #include "llvm/Object/IRSymtab.h"
10 #include "llvm/ADT/ArrayRef.h"
11 #include "llvm/ADT/DenseMap.h"
12 #include "llvm/ADT/SmallPtrSet.h"
13 #include "llvm/ADT/SmallString.h"
14 #include "llvm/ADT/SmallVector.h"
15 #include "llvm/ADT/StringRef.h"
16 #include "llvm/ADT/Triple.h"
17 #include "llvm/Config/llvm-config.h"
18 #include "llvm/IR/Comdat.h"
19 #include "llvm/IR/DataLayout.h"
20 #include "llvm/IR/GlobalAlias.h"
21 #include "llvm/IR/GlobalObject.h"
22 #include "llvm/IR/Mangler.h"
23 #include "llvm/IR/Metadata.h"
24 #include "llvm/IR/Module.h"
25 #include "llvm/Bitcode/BitcodeReader.h"
26 #include "llvm/MC/StringTableBuilder.h"
27 #include "llvm/Object/IRObjectFile.h"
28 #include "llvm/Object/ModuleSymbolTable.h"
29 #include "llvm/Object/SymbolicFile.h"
30 #include "llvm/Support/Allocator.h"
31 #include "llvm/Support/Casting.h"
32 #include "llvm/Support/Error.h"
33 #include "llvm/Support/StringSaver.h"
34 #include "llvm/Support/VCSRevision.h"
35 #include "llvm/Support/raw_ostream.h"
36 #include <cassert>
37 #include <string>
38 #include <utility>
39 #include <vector>
40
41 using namespace llvm;
42 using namespace irsymtab;
43
44 static const char *LibcallRoutineNames[] = {
45 #define HANDLE_LIBCALL(code, name) name,
46 #include "llvm/IR/RuntimeLibcalls.def"
47 #undef HANDLE_LIBCALL
48 };
49
50 namespace {
51
getExpectedProducerName()52 const char *getExpectedProducerName() {
53 static char DefaultName[] = LLVM_VERSION_STRING
54 #ifdef LLVM_REVISION
55 " " LLVM_REVISION
56 #endif
57 ;
58 // Allows for testing of the irsymtab writer and upgrade mechanism. This
59 // environment variable should not be set by users.
60 if (char *OverrideName = getenv("LLVM_OVERRIDE_PRODUCER"))
61 return OverrideName;
62 return DefaultName;
63 }
64
65 const char *kExpectedProducerName = getExpectedProducerName();
66
67 /// Stores the temporary state that is required to build an IR symbol table.
68 struct Builder {
69 SmallVector<char, 0> &Symtab;
70 StringTableBuilder &StrtabBuilder;
71 StringSaver Saver;
72
73 // This ctor initializes a StringSaver using the passed in BumpPtrAllocator.
74 // The StringTableBuilder does not create a copy of any strings added to it,
75 // so this provides somewhere to store any strings that we create.
Builder__anon76d26b6c0111::Builder76 Builder(SmallVector<char, 0> &Symtab, StringTableBuilder &StrtabBuilder,
77 BumpPtrAllocator &Alloc)
78 : Symtab(Symtab), StrtabBuilder(StrtabBuilder), Saver(Alloc) {}
79
80 DenseMap<const Comdat *, int> ComdatMap;
81 Mangler Mang;
82 Triple TT;
83
84 std::vector<storage::Comdat> Comdats;
85 std::vector<storage::Module> Mods;
86 std::vector<storage::Symbol> Syms;
87 std::vector<storage::Uncommon> Uncommons;
88
89 std::string COFFLinkerOpts;
90 raw_string_ostream COFFLinkerOptsOS{COFFLinkerOpts};
91
92 std::vector<storage::Str> DependentLibraries;
93
setStr__anon76d26b6c0111::Builder94 void setStr(storage::Str &S, StringRef Value) {
95 S.Offset = StrtabBuilder.add(Value);
96 S.Size = Value.size();
97 }
98
99 template <typename T>
writeRange__anon76d26b6c0111::Builder100 void writeRange(storage::Range<T> &R, const std::vector<T> &Objs) {
101 R.Offset = Symtab.size();
102 R.Size = Objs.size();
103 Symtab.insert(Symtab.end(), reinterpret_cast<const char *>(Objs.data()),
104 reinterpret_cast<const char *>(Objs.data() + Objs.size()));
105 }
106
107 Expected<int> getComdatIndex(const Comdat *C, const Module *M);
108
109 Error addModule(Module *M);
110 Error addSymbol(const ModuleSymbolTable &Msymtab,
111 const SmallPtrSet<GlobalValue *, 4> &Used,
112 ModuleSymbolTable::Symbol Sym);
113
114 Error build(ArrayRef<Module *> Mods);
115 };
116
addModule(Module * M)117 Error Builder::addModule(Module *M) {
118 if (M->getDataLayoutStr().empty())
119 return make_error<StringError>("input module has no datalayout",
120 inconvertibleErrorCode());
121
122 // Symbols in the llvm.used list will get the FB_Used bit and will not be
123 // internalized. We do this for llvm.compiler.used as well:
124 //
125 // IR symbol table tracks module-level asm symbol references but not inline
126 // asm. A symbol only referenced by inline asm is not in the IR symbol table,
127 // so we may not know that the definition (in another translation unit) is
128 // referenced. That definition may have __attribute__((used)) (which lowers to
129 // llvm.compiler.used on ELF targets) to communicate to the compiler that it
130 // may be used by inline asm. The usage is perfectly fine, so we treat
131 // llvm.compiler.used conservatively as llvm.used to work around our own
132 // limitation.
133 SmallVector<GlobalValue *, 4> UsedV;
134 collectUsedGlobalVariables(*M, UsedV, /*CompilerUsed=*/false);
135 collectUsedGlobalVariables(*M, UsedV, /*CompilerUsed=*/true);
136 SmallPtrSet<GlobalValue *, 4> Used(UsedV.begin(), UsedV.end());
137
138 ModuleSymbolTable Msymtab;
139 Msymtab.addModule(M);
140
141 storage::Module Mod;
142 Mod.Begin = Syms.size();
143 Mod.End = Syms.size() + Msymtab.symbols().size();
144 Mod.UncBegin = Uncommons.size();
145 Mods.push_back(Mod);
146
147 if (TT.isOSBinFormatCOFF()) {
148 if (auto E = M->materializeMetadata())
149 return E;
150 if (NamedMDNode *LinkerOptions =
151 M->getNamedMetadata("llvm.linker.options")) {
152 for (MDNode *MDOptions : LinkerOptions->operands())
153 for (const MDOperand &MDOption : cast<MDNode>(MDOptions)->operands())
154 COFFLinkerOptsOS << " " << cast<MDString>(MDOption)->getString();
155 }
156 }
157
158 if (TT.isOSBinFormatELF()) {
159 if (auto E = M->materializeMetadata())
160 return E;
161 if (NamedMDNode *N = M->getNamedMetadata("llvm.dependent-libraries")) {
162 for (MDNode *MDOptions : N->operands()) {
163 const auto OperandStr =
164 cast<MDString>(cast<MDNode>(MDOptions)->getOperand(0))->getString();
165 storage::Str Specifier;
166 setStr(Specifier, OperandStr);
167 DependentLibraries.emplace_back(Specifier);
168 }
169 }
170 }
171
172 for (ModuleSymbolTable::Symbol Msym : Msymtab.symbols())
173 if (Error Err = addSymbol(Msymtab, Used, Msym))
174 return Err;
175
176 return Error::success();
177 }
178
getComdatIndex(const Comdat * C,const Module * M)179 Expected<int> Builder::getComdatIndex(const Comdat *C, const Module *M) {
180 auto P = ComdatMap.insert(std::make_pair(C, Comdats.size()));
181 if (P.second) {
182 std::string Name;
183 if (TT.isOSBinFormatCOFF()) {
184 const GlobalValue *GV = M->getNamedValue(C->getName());
185 if (!GV)
186 return make_error<StringError>("Could not find leader",
187 inconvertibleErrorCode());
188 // Internal leaders do not affect symbol resolution, therefore they do not
189 // appear in the symbol table.
190 if (GV->hasLocalLinkage()) {
191 P.first->second = -1;
192 return -1;
193 }
194 llvm::raw_string_ostream OS(Name);
195 Mang.getNameWithPrefix(OS, GV, false);
196 } else {
197 Name = std::string(C->getName());
198 }
199
200 storage::Comdat Comdat;
201 setStr(Comdat.Name, Saver.save(Name));
202 Comdats.push_back(Comdat);
203 }
204
205 return P.first->second;
206 }
207
addSymbol(const ModuleSymbolTable & Msymtab,const SmallPtrSet<GlobalValue *,4> & Used,ModuleSymbolTable::Symbol Msym)208 Error Builder::addSymbol(const ModuleSymbolTable &Msymtab,
209 const SmallPtrSet<GlobalValue *, 4> &Used,
210 ModuleSymbolTable::Symbol Msym) {
211 Syms.emplace_back();
212 storage::Symbol &Sym = Syms.back();
213 Sym = {};
214
215 storage::Uncommon *Unc = nullptr;
216 auto Uncommon = [&]() -> storage::Uncommon & {
217 if (Unc)
218 return *Unc;
219 Sym.Flags |= 1 << storage::Symbol::FB_has_uncommon;
220 Uncommons.emplace_back();
221 Unc = &Uncommons.back();
222 *Unc = {};
223 setStr(Unc->COFFWeakExternFallbackName, "");
224 setStr(Unc->SectionName, "");
225 return *Unc;
226 };
227
228 SmallString<64> Name;
229 {
230 raw_svector_ostream OS(Name);
231 Msymtab.printSymbolName(OS, Msym);
232 }
233 setStr(Sym.Name, Saver.save(StringRef(Name)));
234
235 auto Flags = Msymtab.getSymbolFlags(Msym);
236 if (Flags & object::BasicSymbolRef::SF_Undefined)
237 Sym.Flags |= 1 << storage::Symbol::FB_undefined;
238 if (Flags & object::BasicSymbolRef::SF_Weak)
239 Sym.Flags |= 1 << storage::Symbol::FB_weak;
240 if (Flags & object::BasicSymbolRef::SF_Common)
241 Sym.Flags |= 1 << storage::Symbol::FB_common;
242 if (Flags & object::BasicSymbolRef::SF_Indirect)
243 Sym.Flags |= 1 << storage::Symbol::FB_indirect;
244 if (Flags & object::BasicSymbolRef::SF_Global)
245 Sym.Flags |= 1 << storage::Symbol::FB_global;
246 if (Flags & object::BasicSymbolRef::SF_FormatSpecific)
247 Sym.Flags |= 1 << storage::Symbol::FB_format_specific;
248 if (Flags & object::BasicSymbolRef::SF_Executable)
249 Sym.Flags |= 1 << storage::Symbol::FB_executable;
250
251 Sym.ComdatIndex = -1;
252 auto *GV = Msym.dyn_cast<GlobalValue *>();
253 if (!GV) {
254 // Undefined module asm symbols act as GC roots and are implicitly used.
255 if (Flags & object::BasicSymbolRef::SF_Undefined)
256 Sym.Flags |= 1 << storage::Symbol::FB_used;
257 setStr(Sym.IRName, "");
258 return Error::success();
259 }
260
261 setStr(Sym.IRName, GV->getName());
262
263 bool IsBuiltinFunc = llvm::is_contained(LibcallRoutineNames, GV->getName());
264
265 if (Used.count(GV) || IsBuiltinFunc)
266 Sym.Flags |= 1 << storage::Symbol::FB_used;
267 if (GV->isThreadLocal())
268 Sym.Flags |= 1 << storage::Symbol::FB_tls;
269 if (GV->hasGlobalUnnamedAddr())
270 Sym.Flags |= 1 << storage::Symbol::FB_unnamed_addr;
271 if (GV->canBeOmittedFromSymbolTable())
272 Sym.Flags |= 1 << storage::Symbol::FB_may_omit;
273 Sym.Flags |= unsigned(GV->getVisibility()) << storage::Symbol::FB_visibility;
274
275 if (Flags & object::BasicSymbolRef::SF_Common) {
276 auto *GVar = dyn_cast<GlobalVariable>(GV);
277 if (!GVar)
278 return make_error<StringError>("Only variables can have common linkage!",
279 inconvertibleErrorCode());
280 Uncommon().CommonSize = GV->getParent()->getDataLayout().getTypeAllocSize(
281 GV->getType()->getElementType());
282 Uncommon().CommonAlign = GVar->getAlignment();
283 }
284
285 const GlobalObject *Base = GV->getBaseObject();
286 if (!Base)
287 return make_error<StringError>("Unable to determine comdat of alias!",
288 inconvertibleErrorCode());
289 if (const Comdat *C = Base->getComdat()) {
290 Expected<int> ComdatIndexOrErr = getComdatIndex(C, GV->getParent());
291 if (!ComdatIndexOrErr)
292 return ComdatIndexOrErr.takeError();
293 Sym.ComdatIndex = *ComdatIndexOrErr;
294 }
295
296 if (TT.isOSBinFormatCOFF()) {
297 emitLinkerFlagsForGlobalCOFF(COFFLinkerOptsOS, GV, TT, Mang);
298
299 if ((Flags & object::BasicSymbolRef::SF_Weak) &&
300 (Flags & object::BasicSymbolRef::SF_Indirect)) {
301 auto *Fallback = dyn_cast<GlobalValue>(
302 cast<GlobalAlias>(GV)->getAliasee()->stripPointerCasts());
303 if (!Fallback)
304 return make_error<StringError>("Invalid weak external",
305 inconvertibleErrorCode());
306 std::string FallbackName;
307 raw_string_ostream OS(FallbackName);
308 Msymtab.printSymbolName(OS, Fallback);
309 OS.flush();
310 setStr(Uncommon().COFFWeakExternFallbackName, Saver.save(FallbackName));
311 }
312 }
313
314 if (!Base->getSection().empty())
315 setStr(Uncommon().SectionName, Saver.save(Base->getSection()));
316
317 return Error::success();
318 }
319
build(ArrayRef<Module * > IRMods)320 Error Builder::build(ArrayRef<Module *> IRMods) {
321 storage::Header Hdr;
322
323 assert(!IRMods.empty());
324 Hdr.Version = storage::Header::kCurrentVersion;
325 setStr(Hdr.Producer, kExpectedProducerName);
326 setStr(Hdr.TargetTriple, IRMods[0]->getTargetTriple());
327 setStr(Hdr.SourceFileName, IRMods[0]->getSourceFileName());
328 TT = Triple(IRMods[0]->getTargetTriple());
329
330 for (auto *M : IRMods)
331 if (Error Err = addModule(M))
332 return Err;
333
334 COFFLinkerOptsOS.flush();
335 setStr(Hdr.COFFLinkerOpts, Saver.save(COFFLinkerOpts));
336
337 // We are about to fill in the header's range fields, so reserve space for it
338 // and copy it in afterwards.
339 Symtab.resize(sizeof(storage::Header));
340 writeRange(Hdr.Modules, Mods);
341 writeRange(Hdr.Comdats, Comdats);
342 writeRange(Hdr.Symbols, Syms);
343 writeRange(Hdr.Uncommons, Uncommons);
344 writeRange(Hdr.DependentLibraries, DependentLibraries);
345 *reinterpret_cast<storage::Header *>(Symtab.data()) = Hdr;
346 return Error::success();
347 }
348
349 } // end anonymous namespace
350
build(ArrayRef<Module * > Mods,SmallVector<char,0> & Symtab,StringTableBuilder & StrtabBuilder,BumpPtrAllocator & Alloc)351 Error irsymtab::build(ArrayRef<Module *> Mods, SmallVector<char, 0> &Symtab,
352 StringTableBuilder &StrtabBuilder,
353 BumpPtrAllocator &Alloc) {
354 return Builder(Symtab, StrtabBuilder, Alloc).build(Mods);
355 }
356
357 // Upgrade a vector of bitcode modules created by an old version of LLVM by
358 // creating an irsymtab for them in the current format.
upgrade(ArrayRef<BitcodeModule> BMs)359 static Expected<FileContents> upgrade(ArrayRef<BitcodeModule> BMs) {
360 FileContents FC;
361
362 LLVMContext Ctx;
363 std::vector<Module *> Mods;
364 std::vector<std::unique_ptr<Module>> OwnedMods;
365 for (auto BM : BMs) {
366 Expected<std::unique_ptr<Module>> MOrErr =
367 BM.getLazyModule(Ctx, /*ShouldLazyLoadMetadata*/ true,
368 /*IsImporting*/ false);
369 if (!MOrErr)
370 return MOrErr.takeError();
371
372 Mods.push_back(MOrErr->get());
373 OwnedMods.push_back(std::move(*MOrErr));
374 }
375
376 StringTableBuilder StrtabBuilder(StringTableBuilder::RAW);
377 BumpPtrAllocator Alloc;
378 if (Error E = build(Mods, FC.Symtab, StrtabBuilder, Alloc))
379 return std::move(E);
380
381 StrtabBuilder.finalizeInOrder();
382 FC.Strtab.resize(StrtabBuilder.getSize());
383 StrtabBuilder.write((uint8_t *)FC.Strtab.data());
384
385 FC.TheReader = {{FC.Symtab.data(), FC.Symtab.size()},
386 {FC.Strtab.data(), FC.Strtab.size()}};
387 return std::move(FC);
388 }
389
readBitcode(const BitcodeFileContents & BFC)390 Expected<FileContents> irsymtab::readBitcode(const BitcodeFileContents &BFC) {
391 if (BFC.Mods.empty())
392 return make_error<StringError>("Bitcode file does not contain any modules",
393 inconvertibleErrorCode());
394
395 if (BFC.StrtabForSymtab.empty() ||
396 BFC.Symtab.size() < sizeof(storage::Header))
397 return upgrade(BFC.Mods);
398
399 // We cannot use the regular reader to read the version and producer, because
400 // it will expect the header to be in the current format. The only thing we
401 // can rely on is that the version and producer will be present as the first
402 // struct elements.
403 auto *Hdr = reinterpret_cast<const storage::Header *>(BFC.Symtab.data());
404 unsigned Version = Hdr->Version;
405 StringRef Producer = Hdr->Producer.get(BFC.StrtabForSymtab);
406 if (Version != storage::Header::kCurrentVersion ||
407 Producer != kExpectedProducerName)
408 return upgrade(BFC.Mods);
409
410 FileContents FC;
411 FC.TheReader = {{BFC.Symtab.data(), BFC.Symtab.size()},
412 {BFC.StrtabForSymtab.data(), BFC.StrtabForSymtab.size()}};
413
414 // Finally, make sure that the number of modules in the symbol table matches
415 // the number of modules in the bitcode file. If they differ, it may mean that
416 // the bitcode file was created by binary concatenation, so we need to create
417 // a new symbol table from scratch.
418 if (FC.TheReader.getNumModules() != BFC.Mods.size())
419 return upgrade(std::move(BFC.Mods));
420
421 return std::move(FC);
422 }
423