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/Bitcode/BitcodeReader.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/MC/StringTableBuilder.h"
26#include "llvm/Object/ModuleSymbolTable.h"
27#include "llvm/Object/SymbolicFile.h"
28#include "llvm/Support/Allocator.h"
29#include "llvm/Support/Casting.h"
30#include "llvm/Support/CommandLine.h"
31#include "llvm/Support/Error.h"
32#include "llvm/Support/StringSaver.h"
33#include "llvm/Support/VCSRevision.h"
34#include "llvm/Support/raw_ostream.h"
35#include "llvm/TargetParser/Triple.h"
36#include <cassert>
37#include <string>
38#include <utility>
39#include <vector>
40
41using namespace llvm;
42using namespace irsymtab;
43
44static cl::opt<bool> DisableBitcodeVersionUpgrade(
45 "disable-bitcode-version-upgrade", cl::Hidden,
46 cl::desc("Disable automatic bitcode upgrade for version mismatch"));
47
48static 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
59namespace {
60
61const 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(name: "LLVM_OVERRIDE_PRODUCER"))
70 return OverrideName;
71 return DefaultName;
72}
73
74const char *kExpectedProducerName = getExpectedProducerName();
75
76/// Stores the temporary state that is required to build an IR symbol table.
77struct 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.
85 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
103 void setStr(storage::Str &S, StringRef Value) {
104 S.Offset = StrtabBuilder.add(S: Value);
105 S.Size = Value.size();
106 }
107
108 template <typename T>
109 void writeRange(storage::Range<T> &R, const std::vector<T> &Objs) {
110 R.Offset = Symtab.size();
111 R.Size = Objs.size();
112 Symtab.insert(I: Symtab.end(), From: reinterpret_cast<const char *>(Objs.data()),
113 To: 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
126Error Builder::addModule(Module *M) {
127 if (M->getDataLayoutStr().empty())
128 return make_error<StringError>(Args: "input module has no datalayout",
129 Args: 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: *M, Vec&: UsedV, /*CompilerUsed=*/false);
144 collectUsedGlobalVariables(M: *M, Vec&: 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(x: Mod);
155
156 if (TT.isOSBinFormatCOFF()) {
157 if (auto E = M->materializeMetadata())
158 return E;
159 if (NamedMDNode *LinkerOptions =
160 M->getNamedMetadata(Name: "llvm.linker.options")) {
161 for (MDNode *MDOptions : LinkerOptions->operands())
162 for (const MDOperand &MDOption : cast<MDNode>(Val: MDOptions)->operands())
163 COFFLinkerOptsOS << " " << cast<MDString>(Val: MDOption)->getString();
164 }
165 }
166
167 if (TT.isOSBinFormatELF()) {
168 if (auto E = M->materializeMetadata())
169 return E;
170 if (NamedMDNode *N = M->getNamedMetadata(Name: "llvm.dependent-libraries")) {
171 for (MDNode *MDOptions : N->operands()) {
172 const auto OperandStr =
173 cast<MDString>(Val: cast<MDNode>(Val: MDOptions)->getOperand(I: 0))->getString();
174 storage::Str Specifier;
175 setStr(S&: Specifier, Value: OperandStr);
176 DependentLibraries.emplace_back(args&: Specifier);
177 }
178 }
179 }
180
181 for (ModuleSymbolTable::Symbol Msym : Msymtab.symbols())
182 if (Error Err = addSymbol(Msymtab, Used, Sym: Msym))
183 return Err;
184
185 return Error::success();
186}
187
188Expected<int> Builder::getComdatIndex(const Comdat *C, const Module *M) {
189 auto P = ComdatMap.insert(KV: std::make_pair(x&: C, y: Comdats.size()));
190 if (P.second) {
191 std::string Name;
192 if (TT.isOSBinFormatCOFF()) {
193 const GlobalValue *GV = M->getNamedValue(Name: C->getName());
194 if (!GV)
195 return make_error<StringError>(Args: "Could not find leader",
196 Args: 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, CannotUsePrivateLabel: false);
205 } else {
206 Name = std::string(C->getName());
207 }
208
209 storage::Comdat Comdat;
210 setStr(S&: Comdat.Name, Value: Saver.save(S: Name));
211 Comdat.SelectionKind = C->getSelectionKind();
212 Comdats.push_back(x: Comdat);
213 }
214
215 return P.first->second;
216}
217
218static DenseSet<StringRef> buildPreservedSymbolsSet() {
219 return DenseSet<StringRef>(std::begin(arr&: PreservedSymbols),
220 std::end(arr&: PreservedSymbols));
221}
222
223Error Builder::addSymbol(const ModuleSymbolTable &Msymtab,
224 const SmallPtrSet<GlobalValue *, 4> &Used,
225 ModuleSymbolTable::Symbol Msym) {
226 Syms.emplace_back();
227 storage::Symbol &Sym = Syms.back();
228 Sym = {};
229
230 storage::Uncommon *Unc = nullptr;
231 auto Uncommon = [&]() -> storage::Uncommon & {
232 if (Unc)
233 return *Unc;
234 Sym.Flags |= 1 << storage::Symbol::FB_has_uncommon;
235 Uncommons.emplace_back();
236 Unc = &Uncommons.back();
237 *Unc = {};
238 setStr(S&: Unc->COFFWeakExternFallbackName, Value: "");
239 setStr(S&: Unc->SectionName, Value: "");
240 return *Unc;
241 };
242
243 SmallString<64> Name;
244 {
245 raw_svector_ostream OS(Name);
246 Msymtab.printSymbolName(OS, S: Msym);
247 }
248 setStr(S&: Sym.Name, Value: Saver.save(S: Name.str()));
249
250 auto Flags = Msymtab.getSymbolFlags(S: Msym);
251 if (Flags & object::BasicSymbolRef::SF_Undefined)
252 Sym.Flags |= 1 << storage::Symbol::FB_undefined;
253 if (Flags & object::BasicSymbolRef::SF_Weak)
254 Sym.Flags |= 1 << storage::Symbol::FB_weak;
255 if (Flags & object::BasicSymbolRef::SF_Common)
256 Sym.Flags |= 1 << storage::Symbol::FB_common;
257 if (Flags & object::BasicSymbolRef::SF_Indirect)
258 Sym.Flags |= 1 << storage::Symbol::FB_indirect;
259 if (Flags & object::BasicSymbolRef::SF_Global)
260 Sym.Flags |= 1 << storage::Symbol::FB_global;
261 if (Flags & object::BasicSymbolRef::SF_FormatSpecific)
262 Sym.Flags |= 1 << storage::Symbol::FB_format_specific;
263 if (Flags & object::BasicSymbolRef::SF_Executable)
264 Sym.Flags |= 1 << storage::Symbol::FB_executable;
265
266 Sym.ComdatIndex = -1;
267 auto *GV = dyn_cast_if_present<GlobalValue *>(Val&: Msym);
268 if (!GV) {
269 // Undefined module asm symbols act as GC roots and are implicitly used.
270 if (Flags & object::BasicSymbolRef::SF_Undefined)
271 Sym.Flags |= 1 << storage::Symbol::FB_used;
272 setStr(S&: Sym.IRName, Value: "");
273 return Error::success();
274 }
275
276 setStr(S&: Sym.IRName, Value: GV->getName());
277
278 static const DenseSet<StringRef> PreservedSymbolsSet =
279 buildPreservedSymbolsSet();
280 bool IsPreservedSymbol = PreservedSymbolsSet.contains(V: GV->getName());
281
282 if (Used.count(Ptr: GV) || IsPreservedSymbol)
283 Sym.Flags |= 1 << storage::Symbol::FB_used;
284 if (GV->isThreadLocal())
285 Sym.Flags |= 1 << storage::Symbol::FB_tls;
286 if (GV->hasGlobalUnnamedAddr())
287 Sym.Flags |= 1 << storage::Symbol::FB_unnamed_addr;
288 if (GV->canBeOmittedFromSymbolTable())
289 Sym.Flags |= 1 << storage::Symbol::FB_may_omit;
290 Sym.Flags |= unsigned(GV->getVisibility()) << storage::Symbol::FB_visibility;
291
292 if (Flags & object::BasicSymbolRef::SF_Common) {
293 auto *GVar = dyn_cast<GlobalVariable>(Val: GV);
294 if (!GVar)
295 return make_error<StringError>(Args: "Only variables can have common linkage!",
296 Args: inconvertibleErrorCode());
297 Uncommon().CommonSize =
298 GV->getParent()->getDataLayout().getTypeAllocSize(Ty: GV->getValueType());
299 Uncommon().CommonAlign = GVar->getAlign() ? GVar->getAlign()->value() : 0;
300 }
301
302 const GlobalObject *GO = GV->getAliaseeObject();
303 if (!GO) {
304 if (isa<GlobalIFunc>(Val: GV))
305 GO = cast<GlobalIFunc>(Val: GV)->getResolverFunction();
306 if (!GO)
307 return make_error<StringError>(Args: "Unable to determine comdat of alias!",
308 Args: inconvertibleErrorCode());
309 }
310 if (const Comdat *C = GO->getComdat()) {
311 Expected<int> ComdatIndexOrErr = getComdatIndex(C, M: GV->getParent());
312 if (!ComdatIndexOrErr)
313 return ComdatIndexOrErr.takeError();
314 Sym.ComdatIndex = *ComdatIndexOrErr;
315 }
316
317 if (TT.isOSBinFormatCOFF()) {
318 emitLinkerFlagsForGlobalCOFF(OS&: COFFLinkerOptsOS, GV, TT, Mangler&: Mang);
319
320 if ((Flags & object::BasicSymbolRef::SF_Weak) &&
321 (Flags & object::BasicSymbolRef::SF_Indirect)) {
322 auto *Fallback = dyn_cast<GlobalValue>(
323 Val: cast<GlobalAlias>(Val: GV)->getAliasee()->stripPointerCasts());
324 if (!Fallback)
325 return make_error<StringError>(Args: "Invalid weak external",
326 Args: inconvertibleErrorCode());
327 std::string FallbackName;
328 raw_string_ostream OS(FallbackName);
329 Msymtab.printSymbolName(OS, S: Fallback);
330 OS.flush();
331 setStr(S&: Uncommon().COFFWeakExternFallbackName, Value: Saver.save(S: FallbackName));
332 }
333 }
334
335 if (!GO->getSection().empty())
336 setStr(S&: Uncommon().SectionName, Value: Saver.save(S: GO->getSection()));
337
338 return Error::success();
339}
340
341Error Builder::build(ArrayRef<Module *> IRMods) {
342 storage::Header Hdr;
343
344 assert(!IRMods.empty());
345 Hdr.Version = storage::Header::kCurrentVersion;
346 setStr(S&: Hdr.Producer, Value: kExpectedProducerName);
347 setStr(S&: Hdr.TargetTriple, Value: IRMods[0]->getTargetTriple());
348 setStr(S&: Hdr.SourceFileName, Value: IRMods[0]->getSourceFileName());
349 TT = Triple(IRMods[0]->getTargetTriple());
350
351 for (auto *M : IRMods)
352 if (Error Err = addModule(M))
353 return Err;
354
355 COFFLinkerOptsOS.flush();
356 setStr(S&: Hdr.COFFLinkerOpts, Value: Saver.save(S: COFFLinkerOpts));
357
358 // We are about to fill in the header's range fields, so reserve space for it
359 // and copy it in afterwards.
360 Symtab.resize(N: sizeof(storage::Header));
361 writeRange(R&: Hdr.Modules, Objs: Mods);
362 writeRange(R&: Hdr.Comdats, Objs: Comdats);
363 writeRange(R&: Hdr.Symbols, Objs: Syms);
364 writeRange(R&: Hdr.Uncommons, Objs: Uncommons);
365 writeRange(R&: Hdr.DependentLibraries, Objs: DependentLibraries);
366 *reinterpret_cast<storage::Header *>(Symtab.data()) = Hdr;
367 return Error::success();
368}
369
370} // end anonymous namespace
371
372Error irsymtab::build(ArrayRef<Module *> Mods, SmallVector<char, 0> &Symtab,
373 StringTableBuilder &StrtabBuilder,
374 BumpPtrAllocator &Alloc) {
375 return Builder(Symtab, StrtabBuilder, Alloc).build(IRMods: Mods);
376}
377
378// Upgrade a vector of bitcode modules created by an old version of LLVM by
379// creating an irsymtab for them in the current format.
380static Expected<FileContents> upgrade(ArrayRef<BitcodeModule> BMs) {
381 FileContents FC;
382
383 LLVMContext Ctx;
384 std::vector<Module *> Mods;
385 std::vector<std::unique_ptr<Module>> OwnedMods;
386 for (auto BM : BMs) {
387 Expected<std::unique_ptr<Module>> MOrErr =
388 BM.getLazyModule(Context&: Ctx, /*ShouldLazyLoadMetadata*/ true,
389 /*IsImporting*/ false);
390 if (!MOrErr)
391 return MOrErr.takeError();
392
393 Mods.push_back(x: MOrErr->get());
394 OwnedMods.push_back(x: std::move(*MOrErr));
395 }
396
397 StringTableBuilder StrtabBuilder(StringTableBuilder::RAW);
398 BumpPtrAllocator Alloc;
399 if (Error E = build(Mods, Symtab&: FC.Symtab, StrtabBuilder, Alloc))
400 return std::move(E);
401
402 StrtabBuilder.finalizeInOrder();
403 FC.Strtab.resize(N: StrtabBuilder.getSize());
404 StrtabBuilder.write(Buf: (uint8_t *)FC.Strtab.data());
405
406 FC.TheReader = {{FC.Symtab.data(), FC.Symtab.size()},
407 {FC.Strtab.data(), FC.Strtab.size()}};
408 return std::move(FC);
409}
410
411Expected<FileContents> irsymtab::readBitcode(const BitcodeFileContents &BFC) {
412 if (BFC.Mods.empty())
413 return make_error<StringError>(Args: "Bitcode file does not contain any modules",
414 Args: inconvertibleErrorCode());
415
416 if (!DisableBitcodeVersionUpgrade) {
417 if (BFC.StrtabForSymtab.empty() ||
418 BFC.Symtab.size() < sizeof(storage::Header))
419 return upgrade(BMs: BFC.Mods);
420
421 // We cannot use the regular reader to read the version and producer,
422 // because it will expect the header to be in the current format. The only
423 // thing we can rely on is that the version and producer will be present as
424 // the first struct elements.
425 auto *Hdr = reinterpret_cast<const storage::Header *>(BFC.Symtab.data());
426 unsigned Version = Hdr->Version;
427 StringRef Producer = Hdr->Producer.get(Strtab: BFC.StrtabForSymtab);
428 if (Version != storage::Header::kCurrentVersion ||
429 Producer != kExpectedProducerName)
430 return upgrade(BMs: BFC.Mods);
431 }
432
433 FileContents FC;
434 FC.TheReader = {{BFC.Symtab.data(), BFC.Symtab.size()},
435 {BFC.StrtabForSymtab.data(), BFC.StrtabForSymtab.size()}};
436
437 // Finally, make sure that the number of modules in the symbol table matches
438 // the number of modules in the bitcode file. If they differ, it may mean that
439 // the bitcode file was created by binary concatenation, so we need to create
440 // a new symbol table from scratch.
441 if (FC.TheReader.getNumModules() != BFC.Mods.size())
442 return upgrade(BMs: std::move(BFC.Mods));
443
444 return std::move(FC);
445}
446

source code of llvm/lib/Object/IRSymtab.cpp