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/Bitcode/BitcodeReader.h"
18 #include "llvm/Config/llvm-config.h"
19 #include "llvm/IR/Comdat.h"
20 #include "llvm/IR/DataLayout.h"
21 #include "llvm/IR/GlobalAlias.h"
22 #include "llvm/IR/GlobalObject.h"
23 #include "llvm/IR/Mangler.h"
24 #include "llvm/IR/Metadata.h"
25 #include "llvm/IR/Module.h"
26 #include "llvm/MC/StringTableBuilder.h"
27 #include "llvm/Object/ModuleSymbolTable.h"
28 #include "llvm/Object/SymbolicFile.h"
29 #include "llvm/Support/Allocator.h"
30 #include "llvm/Support/Casting.h"
31 #include "llvm/Support/CommandLine.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 cl::opt<bool> DisableBitcodeVersionUpgrade(
45 "disable-bitcode-version-upgrade", cl::init(false), cl::Hidden,
46 cl::desc("Disable automatic bitcode upgrade for version mismatch"));
47
48 static const char *PreservedSymbols[] = {
49 #define HANDLE_LIBCALL(code, name) name,
50 #include "llvm/IR/RuntimeLibcalls.def"
51 #undef HANDLE_LIBCALL
52 // There are global variables, so put it here instead of in
53 // RuntimeLibcalls.def.
54 // TODO: Are there similar such variables?
55 "__ssp_canary_word",
56 "__stack_chk_guard",
57 };
58
59 namespace {
60
getExpectedProducerName()61 const char *getExpectedProducerName() {
62 static char DefaultName[] = LLVM_VERSION_STRING
63 #ifdef LLVM_REVISION
64 " " LLVM_REVISION
65 #endif
66 ;
67 // Allows for testing of the irsymtab writer and upgrade mechanism. This
68 // environment variable should not be set by users.
69 if (char *OverrideName = getenv("LLVM_OVERRIDE_PRODUCER"))
70 return OverrideName;
71 return DefaultName;
72 }
73
74 const char *kExpectedProducerName = getExpectedProducerName();
75
76 /// Stores the temporary state that is required to build an IR symbol table.
77 struct Builder {
78 SmallVector<char, 0> &Symtab;
79 StringTableBuilder &StrtabBuilder;
80 StringSaver Saver;
81
82 // This ctor initializes a StringSaver using the passed in BumpPtrAllocator.
83 // The StringTableBuilder does not create a copy of any strings added to it,
84 // so this provides somewhere to store any strings that we create.
Builder__anonfe214dc10111::Builder85 Builder(SmallVector<char, 0> &Symtab, StringTableBuilder &StrtabBuilder,
86 BumpPtrAllocator &Alloc)
87 : Symtab(Symtab), StrtabBuilder(StrtabBuilder), Saver(Alloc) {}
88
89 DenseMap<const Comdat *, int> ComdatMap;
90 Mangler Mang;
91 Triple TT;
92
93 std::vector<storage::Comdat> Comdats;
94 std::vector<storage::Module> Mods;
95 std::vector<storage::Symbol> Syms;
96 std::vector<storage::Uncommon> Uncommons;
97
98 std::string COFFLinkerOpts;
99 raw_string_ostream COFFLinkerOptsOS{COFFLinkerOpts};
100
101 std::vector<storage::Str> DependentLibraries;
102
setStr__anonfe214dc10111::Builder103 void setStr(storage::Str &S, StringRef Value) {
104 S.Offset = StrtabBuilder.add(Value);
105 S.Size = Value.size();
106 }
107
108 template <typename T>
writeRange__anonfe214dc10111::Builder109 void writeRange(storage::Range<T> &R, const std::vector<T> &Objs) {
110 R.Offset = Symtab.size();
111 R.Size = Objs.size();
112 Symtab.insert(Symtab.end(), reinterpret_cast<const char *>(Objs.data()),
113 reinterpret_cast<const char *>(Objs.data() + Objs.size()));
114 }
115
116 Expected<int> getComdatIndex(const Comdat *C, const Module *M);
117
118 Error addModule(Module *M);
119 Error addSymbol(const ModuleSymbolTable &Msymtab,
120 const SmallPtrSet<GlobalValue *, 4> &Used,
121 ModuleSymbolTable::Symbol Sym);
122
123 Error build(ArrayRef<Module *> Mods);
124 };
125
addModule(Module * M)126 Error Builder::addModule(Module *M) {
127 if (M->getDataLayoutStr().empty())
128 return make_error<StringError>("input module has no datalayout",
129 inconvertibleErrorCode());
130
131 // Symbols in the llvm.used list will get the FB_Used bit and will not be
132 // internalized. We do this for llvm.compiler.used as well:
133 //
134 // IR symbol table tracks module-level asm symbol references but not inline
135 // asm. A symbol only referenced by inline asm is not in the IR symbol table,
136 // so we may not know that the definition (in another translation unit) is
137 // referenced. That definition may have __attribute__((used)) (which lowers to
138 // llvm.compiler.used on ELF targets) to communicate to the compiler that it
139 // may be used by inline asm. The usage is perfectly fine, so we treat
140 // llvm.compiler.used conservatively as llvm.used to work around our own
141 // limitation.
142 SmallVector<GlobalValue *, 4> UsedV;
143 collectUsedGlobalVariables(*M, UsedV, /*CompilerUsed=*/false);
144 collectUsedGlobalVariables(*M, UsedV, /*CompilerUsed=*/true);
145 SmallPtrSet<GlobalValue *, 4> Used(UsedV.begin(), UsedV.end());
146
147 ModuleSymbolTable Msymtab;
148 Msymtab.addModule(M);
149
150 storage::Module Mod;
151 Mod.Begin = Syms.size();
152 Mod.End = Syms.size() + Msymtab.symbols().size();
153 Mod.UncBegin = Uncommons.size();
154 Mods.push_back(Mod);
155
156 if (TT.isOSBinFormatCOFF()) {
157 if (auto E = M->materializeMetadata())
158 return E;
159 if (NamedMDNode *LinkerOptions =
160 M->getNamedMetadata("llvm.linker.options")) {
161 for (MDNode *MDOptions : LinkerOptions->operands())
162 for (const MDOperand &MDOption : cast<MDNode>(MDOptions)->operands())
163 COFFLinkerOptsOS << " " << cast<MDString>(MDOption)->getString();
164 }
165 }
166
167 if (TT.isOSBinFormatELF()) {
168 if (auto E = M->materializeMetadata())
169 return E;
170 if (NamedMDNode *N = M->getNamedMetadata("llvm.dependent-libraries")) {
171 for (MDNode *MDOptions : N->operands()) {
172 const auto OperandStr =
173 cast<MDString>(cast<MDNode>(MDOptions)->getOperand(0))->getString();
174 storage::Str Specifier;
175 setStr(Specifier, OperandStr);
176 DependentLibraries.emplace_back(Specifier);
177 }
178 }
179 }
180
181 for (ModuleSymbolTable::Symbol Msym : Msymtab.symbols())
182 if (Error Err = addSymbol(Msymtab, Used, Msym))
183 return Err;
184
185 return Error::success();
186 }
187
getComdatIndex(const Comdat * C,const Module * M)188 Expected<int> Builder::getComdatIndex(const Comdat *C, const Module *M) {
189 auto P = ComdatMap.insert(std::make_pair(C, Comdats.size()));
190 if (P.second) {
191 std::string Name;
192 if (TT.isOSBinFormatCOFF()) {
193 const GlobalValue *GV = M->getNamedValue(C->getName());
194 if (!GV)
195 return make_error<StringError>("Could not find leader",
196 inconvertibleErrorCode());
197 // Internal leaders do not affect symbol resolution, therefore they do not
198 // appear in the symbol table.
199 if (GV->hasLocalLinkage()) {
200 P.first->second = -1;
201 return -1;
202 }
203 llvm::raw_string_ostream OS(Name);
204 Mang.getNameWithPrefix(OS, GV, false);
205 } else {
206 Name = std::string(C->getName());
207 }
208
209 storage::Comdat Comdat;
210 setStr(Comdat.Name, Saver.save(Name));
211 Comdat.SelectionKind = C->getSelectionKind();
212 Comdats.push_back(Comdat);
213 }
214
215 return P.first->second;
216 }
217
addSymbol(const ModuleSymbolTable & Msymtab,const SmallPtrSet<GlobalValue *,4> & Used,ModuleSymbolTable::Symbol Msym)218 Error Builder::addSymbol(const ModuleSymbolTable &Msymtab,
219 const SmallPtrSet<GlobalValue *, 4> &Used,
220 ModuleSymbolTable::Symbol Msym) {
221 Syms.emplace_back();
222 storage::Symbol &Sym = Syms.back();
223 Sym = {};
224
225 storage::Uncommon *Unc = nullptr;
226 auto Uncommon = [&]() -> storage::Uncommon & {
227 if (Unc)
228 return *Unc;
229 Sym.Flags |= 1 << storage::Symbol::FB_has_uncommon;
230 Uncommons.emplace_back();
231 Unc = &Uncommons.back();
232 *Unc = {};
233 setStr(Unc->COFFWeakExternFallbackName, "");
234 setStr(Unc->SectionName, "");
235 return *Unc;
236 };
237
238 SmallString<64> Name;
239 {
240 raw_svector_ostream OS(Name);
241 Msymtab.printSymbolName(OS, Msym);
242 }
243 setStr(Sym.Name, Saver.save(Name.str()));
244
245 auto Flags = Msymtab.getSymbolFlags(Msym);
246 if (Flags & object::BasicSymbolRef::SF_Undefined)
247 Sym.Flags |= 1 << storage::Symbol::FB_undefined;
248 if (Flags & object::BasicSymbolRef::SF_Weak)
249 Sym.Flags |= 1 << storage::Symbol::FB_weak;
250 if (Flags & object::BasicSymbolRef::SF_Common)
251 Sym.Flags |= 1 << storage::Symbol::FB_common;
252 if (Flags & object::BasicSymbolRef::SF_Indirect)
253 Sym.Flags |= 1 << storage::Symbol::FB_indirect;
254 if (Flags & object::BasicSymbolRef::SF_Global)
255 Sym.Flags |= 1 << storage::Symbol::FB_global;
256 if (Flags & object::BasicSymbolRef::SF_FormatSpecific)
257 Sym.Flags |= 1 << storage::Symbol::FB_format_specific;
258 if (Flags & object::BasicSymbolRef::SF_Executable)
259 Sym.Flags |= 1 << storage::Symbol::FB_executable;
260
261 Sym.ComdatIndex = -1;
262 auto *GV = Msym.dyn_cast<GlobalValue *>();
263 if (!GV) {
264 // Undefined module asm symbols act as GC roots and are implicitly used.
265 if (Flags & object::BasicSymbolRef::SF_Undefined)
266 Sym.Flags |= 1 << storage::Symbol::FB_used;
267 setStr(Sym.IRName, "");
268 return Error::success();
269 }
270
271 setStr(Sym.IRName, GV->getName());
272
273 bool IsPreservedSymbol = llvm::is_contained(PreservedSymbols, GV->getName());
274
275 if (Used.count(GV) || IsPreservedSymbol)
276 Sym.Flags |= 1 << storage::Symbol::FB_used;
277 if (GV->isThreadLocal())
278 Sym.Flags |= 1 << storage::Symbol::FB_tls;
279 if (GV->hasGlobalUnnamedAddr())
280 Sym.Flags |= 1 << storage::Symbol::FB_unnamed_addr;
281 if (GV->canBeOmittedFromSymbolTable())
282 Sym.Flags |= 1 << storage::Symbol::FB_may_omit;
283 Sym.Flags |= unsigned(GV->getVisibility()) << storage::Symbol::FB_visibility;
284
285 if (Flags & object::BasicSymbolRef::SF_Common) {
286 auto *GVar = dyn_cast<GlobalVariable>(GV);
287 if (!GVar)
288 return make_error<StringError>("Only variables can have common linkage!",
289 inconvertibleErrorCode());
290 Uncommon().CommonSize =
291 GV->getParent()->getDataLayout().getTypeAllocSize(GV->getValueType());
292 Uncommon().CommonAlign = GVar->getAlign() ? GVar->getAlign()->value() : 0;
293 }
294
295 const GlobalObject *GO = GV->getAliaseeObject();
296 if (!GO) {
297 if (isa<GlobalIFunc>(GV))
298 GO = cast<GlobalIFunc>(GV)->getResolverFunction();
299 if (!GO)
300 return make_error<StringError>("Unable to determine comdat of alias!",
301 inconvertibleErrorCode());
302 }
303 if (const Comdat *C = GO->getComdat()) {
304 Expected<int> ComdatIndexOrErr = getComdatIndex(C, GV->getParent());
305 if (!ComdatIndexOrErr)
306 return ComdatIndexOrErr.takeError();
307 Sym.ComdatIndex = *ComdatIndexOrErr;
308 }
309
310 if (TT.isOSBinFormatCOFF()) {
311 emitLinkerFlagsForGlobalCOFF(COFFLinkerOptsOS, GV, TT, Mang);
312
313 if ((Flags & object::BasicSymbolRef::SF_Weak) &&
314 (Flags & object::BasicSymbolRef::SF_Indirect)) {
315 auto *Fallback = dyn_cast<GlobalValue>(
316 cast<GlobalAlias>(GV)->getAliasee()->stripPointerCasts());
317 if (!Fallback)
318 return make_error<StringError>("Invalid weak external",
319 inconvertibleErrorCode());
320 std::string FallbackName;
321 raw_string_ostream OS(FallbackName);
322 Msymtab.printSymbolName(OS, Fallback);
323 OS.flush();
324 setStr(Uncommon().COFFWeakExternFallbackName, Saver.save(FallbackName));
325 }
326 }
327
328 if (!GO->getSection().empty())
329 setStr(Uncommon().SectionName, Saver.save(GO->getSection()));
330
331 return Error::success();
332 }
333
build(ArrayRef<Module * > IRMods)334 Error Builder::build(ArrayRef<Module *> IRMods) {
335 storage::Header Hdr;
336
337 assert(!IRMods.empty());
338 Hdr.Version = storage::Header::kCurrentVersion;
339 setStr(Hdr.Producer, kExpectedProducerName);
340 setStr(Hdr.TargetTriple, IRMods[0]->getTargetTriple());
341 setStr(Hdr.SourceFileName, IRMods[0]->getSourceFileName());
342 TT = Triple(IRMods[0]->getTargetTriple());
343
344 for (auto *M : IRMods)
345 if (Error Err = addModule(M))
346 return Err;
347
348 COFFLinkerOptsOS.flush();
349 setStr(Hdr.COFFLinkerOpts, Saver.save(COFFLinkerOpts));
350
351 // We are about to fill in the header's range fields, so reserve space for it
352 // and copy it in afterwards.
353 Symtab.resize(sizeof(storage::Header));
354 writeRange(Hdr.Modules, Mods);
355 writeRange(Hdr.Comdats, Comdats);
356 writeRange(Hdr.Symbols, Syms);
357 writeRange(Hdr.Uncommons, Uncommons);
358 writeRange(Hdr.DependentLibraries, DependentLibraries);
359 *reinterpret_cast<storage::Header *>(Symtab.data()) = Hdr;
360 return Error::success();
361 }
362
363 } // end anonymous namespace
364
build(ArrayRef<Module * > Mods,SmallVector<char,0> & Symtab,StringTableBuilder & StrtabBuilder,BumpPtrAllocator & Alloc)365 Error irsymtab::build(ArrayRef<Module *> Mods, SmallVector<char, 0> &Symtab,
366 StringTableBuilder &StrtabBuilder,
367 BumpPtrAllocator &Alloc) {
368 return Builder(Symtab, StrtabBuilder, Alloc).build(Mods);
369 }
370
371 // Upgrade a vector of bitcode modules created by an old version of LLVM by
372 // creating an irsymtab for them in the current format.
upgrade(ArrayRef<BitcodeModule> BMs)373 static Expected<FileContents> upgrade(ArrayRef<BitcodeModule> BMs) {
374 FileContents FC;
375
376 LLVMContext Ctx;
377 std::vector<Module *> Mods;
378 std::vector<std::unique_ptr<Module>> OwnedMods;
379 for (auto BM : BMs) {
380 Expected<std::unique_ptr<Module>> MOrErr =
381 BM.getLazyModule(Ctx, /*ShouldLazyLoadMetadata*/ true,
382 /*IsImporting*/ false);
383 if (!MOrErr)
384 return MOrErr.takeError();
385
386 Mods.push_back(MOrErr->get());
387 OwnedMods.push_back(std::move(*MOrErr));
388 }
389
390 StringTableBuilder StrtabBuilder(StringTableBuilder::RAW);
391 BumpPtrAllocator Alloc;
392 if (Error E = build(Mods, FC.Symtab, StrtabBuilder, Alloc))
393 return std::move(E);
394
395 StrtabBuilder.finalizeInOrder();
396 FC.Strtab.resize(StrtabBuilder.getSize());
397 StrtabBuilder.write((uint8_t *)FC.Strtab.data());
398
399 FC.TheReader = {{FC.Symtab.data(), FC.Symtab.size()},
400 {FC.Strtab.data(), FC.Strtab.size()}};
401 return std::move(FC);
402 }
403
readBitcode(const BitcodeFileContents & BFC)404 Expected<FileContents> irsymtab::readBitcode(const BitcodeFileContents &BFC) {
405 if (BFC.Mods.empty())
406 return make_error<StringError>("Bitcode file does not contain any modules",
407 inconvertibleErrorCode());
408
409 if (!DisableBitcodeVersionUpgrade) {
410 if (BFC.StrtabForSymtab.empty() ||
411 BFC.Symtab.size() < sizeof(storage::Header))
412 return upgrade(BFC.Mods);
413
414 // We cannot use the regular reader to read the version and producer,
415 // because it will expect the header to be in the current format. The only
416 // thing we can rely on is that the version and producer will be present as
417 // the first struct elements.
418 auto *Hdr = reinterpret_cast<const storage::Header *>(BFC.Symtab.data());
419 unsigned Version = Hdr->Version;
420 StringRef Producer = Hdr->Producer.get(BFC.StrtabForSymtab);
421 if (Version != storage::Header::kCurrentVersion ||
422 Producer != kExpectedProducerName)
423 return upgrade(BFC.Mods);
424 }
425
426 FileContents FC;
427 FC.TheReader = {{BFC.Symtab.data(), BFC.Symtab.size()},
428 {BFC.StrtabForSymtab.data(), BFC.StrtabForSymtab.size()}};
429
430 // Finally, make sure that the number of modules in the symbol table matches
431 // the number of modules in the bitcode file. If they differ, it may mean that
432 // the bitcode file was created by binary concatenation, so we need to create
433 // a new symbol table from scratch.
434 if (FC.TheReader.getNumModules() != BFC.Mods.size())
435 return upgrade(std::move(BFC.Mods));
436
437 return std::move(FC);
438 }
439