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("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(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(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
126Error 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
188Expected<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
218static DenseSet<StringRef> buildPreservedSymbolsSet() {
219  return DenseSet<StringRef>(std::begin(PreservedSymbols),
220                             std::end(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(Unc->COFFWeakExternFallbackName, "");
239    setStr(Unc->SectionName, "");
240    return *Unc;
241  };
242
243  SmallString<64> Name;
244  {
245    raw_svector_ostream OS(Name);
246    Msymtab.printSymbolName(OS, Msym);
247  }
248  setStr(Sym.Name, Saver.save(Name.str()));
249
250  auto Flags = Msymtab.getSymbolFlags(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 *>(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(Sym.IRName, "");
273    return Error::success();
274  }
275
276  setStr(Sym.IRName, GV->getName());
277
278  static const DenseSet<StringRef> PreservedSymbolsSet =
279      buildPreservedSymbolsSet();
280  bool IsPreservedSymbol = PreservedSymbolsSet.contains(GV->getName());
281
282  if (Used.count(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>(GV);
294    if (!GVar)
295      return make_error<StringError>("Only variables can have common linkage!",
296                                     inconvertibleErrorCode());
297    Uncommon().CommonSize =
298        GV->getParent()->getDataLayout().getTypeAllocSize(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>(GV))
305      GO = cast<GlobalIFunc>(GV)->getResolverFunction();
306    if (!GO)
307      return make_error<StringError>("Unable to determine comdat of alias!",
308                                     inconvertibleErrorCode());
309  }
310  if (const Comdat *C = GO->getComdat()) {
311    Expected<int> ComdatIndexOrErr = getComdatIndex(C, GV->getParent());
312    if (!ComdatIndexOrErr)
313      return ComdatIndexOrErr.takeError();
314    Sym.ComdatIndex = *ComdatIndexOrErr;
315  }
316
317  if (TT.isOSBinFormatCOFF()) {
318    emitLinkerFlagsForGlobalCOFF(COFFLinkerOptsOS, GV, TT, Mang);
319
320    if ((Flags & object::BasicSymbolRef::SF_Weak) &&
321        (Flags & object::BasicSymbolRef::SF_Indirect)) {
322      auto *Fallback = dyn_cast<GlobalValue>(
323          cast<GlobalAlias>(GV)->getAliasee()->stripPointerCasts());
324      if (!Fallback)
325        return make_error<StringError>("Invalid weak external",
326                                       inconvertibleErrorCode());
327      std::string FallbackName;
328      raw_string_ostream OS(FallbackName);
329      Msymtab.printSymbolName(OS, Fallback);
330      OS.flush();
331      setStr(Uncommon().COFFWeakExternFallbackName, Saver.save(FallbackName));
332    }
333  }
334
335  if (!GO->getSection().empty())
336    setStr(Uncommon().SectionName, Saver.save(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(Hdr.Producer, kExpectedProducerName);
347  setStr(Hdr.TargetTriple, IRMods[0]->getTargetTriple());
348  setStr(Hdr.SourceFileName, 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(Hdr.COFFLinkerOpts, Saver.save(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(sizeof(storage::Header));
361  writeRange(Hdr.Modules, Mods);
362  writeRange(Hdr.Comdats, Comdats);
363  writeRange(Hdr.Symbols, Syms);
364  writeRange(Hdr.Uncommons, Uncommons);
365  writeRange(Hdr.DependentLibraries, 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(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(Ctx, /*ShouldLazyLoadMetadata*/ true,
389                         /*IsImporting*/ false);
390    if (!MOrErr)
391      return MOrErr.takeError();
392
393    Mods.push_back(MOrErr->get());
394    OwnedMods.push_back(std::move(*MOrErr));
395  }
396
397  StringTableBuilder StrtabBuilder(StringTableBuilder::RAW);
398  BumpPtrAllocator Alloc;
399  if (Error E = build(Mods, FC.Symtab, StrtabBuilder, Alloc))
400    return std::move(E);
401
402  StrtabBuilder.finalizeInOrder();
403  FC.Strtab.resize(StrtabBuilder.getSize());
404  StrtabBuilder.write((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>("Bitcode file does not contain any modules",
414                                   inconvertibleErrorCode());
415
416  if (!DisableBitcodeVersionUpgrade) {
417    if (BFC.StrtabForSymtab.empty() ||
418        BFC.Symtab.size() < sizeof(storage::Header))
419      return upgrade(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(BFC.StrtabForSymtab);
428    if (Version != storage::Header::kCurrentVersion ||
429        Producer != kExpectedProducerName)
430      return upgrade(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(std::move(BFC.Mods));
443
444  return std::move(FC);
445}
446