1 //===- IRSymtab.cpp - implementation of IR symbol tables ------------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 
10 #include "llvm/Object/IRSymtab.h"
11 #include "llvm/ADT/ArrayRef.h"
12 #include "llvm/ADT/DenseMap.h"
13 #include "llvm/ADT/SmallPtrSet.h"
14 #include "llvm/ADT/SmallString.h"
15 #include "llvm/ADT/SmallVector.h"
16 #include "llvm/ADT/StringRef.h"
17 #include "llvm/ADT/Triple.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 namespace {
45 
46 const char *getExpectedProducerName() {
47   static char DefaultName[] = LLVM_VERSION_STRING
48 #ifdef LLVM_REVISION
49       " " LLVM_REVISION
50 #endif
51       ;
52   // Allows for testing of the irsymtab writer and upgrade mechanism. This
53   // environment variable should not be set by users.
54   if (char *OverrideName = getenv("LLVM_OVERRIDE_PRODUCER"))
55     return OverrideName;
56   return DefaultName;
57 }
58 
59 const char *kExpectedProducerName = getExpectedProducerName();
60 
61 /// Stores the temporary state that is required to build an IR symbol table.
62 struct Builder {
63   SmallVector<char, 0> &Symtab;
64   StringTableBuilder &StrtabBuilder;
65   StringSaver Saver;
66 
67   // This ctor initializes a StringSaver using the passed in BumpPtrAllocator.
68   // The StringTableBuilder does not create a copy of any strings added to it,
69   // so this provides somewhere to store any strings that we create.
70   Builder(SmallVector<char, 0> &Symtab, StringTableBuilder &StrtabBuilder,
71           BumpPtrAllocator &Alloc)
72       : Symtab(Symtab), StrtabBuilder(StrtabBuilder), Saver(Alloc) {}
73 
74   DenseMap<const Comdat *, int> ComdatMap;
75   Mangler Mang;
76   Triple TT;
77 
78   std::vector<storage::Comdat> Comdats;
79   std::vector<storage::Module> Mods;
80   std::vector<storage::Symbol> Syms;
81   std::vector<storage::Uncommon> Uncommons;
82 
83   std::string COFFLinkerOpts;
84   raw_string_ostream COFFLinkerOptsOS{COFFLinkerOpts};
85 
86   void setStr(storage::Str &S, StringRef Value) {
87     S.Offset = StrtabBuilder.add(Value);
88     S.Size = Value.size();
89   }
90 
91   template <typename T>
92   void writeRange(storage::Range<T> &R, const std::vector<T> &Objs) {
93     R.Offset = Symtab.size();
94     R.Size = Objs.size();
95     Symtab.insert(Symtab.end(), reinterpret_cast<const char *>(Objs.data()),
96                   reinterpret_cast<const char *>(Objs.data() + Objs.size()));
97   }
98 
99   Expected<int> getComdatIndex(const Comdat *C, const Module *M);
100 
101   Error addModule(Module *M);
102   Error addSymbol(const ModuleSymbolTable &Msymtab,
103                   const SmallPtrSet<GlobalValue *, 8> &Used,
104                   ModuleSymbolTable::Symbol Sym);
105 
106   Error build(ArrayRef<Module *> Mods);
107 };
108 
109 Error Builder::addModule(Module *M) {
110   if (M->getDataLayoutStr().empty())
111     return make_error<StringError>("input module has no datalayout",
112                                    inconvertibleErrorCode());
113 
114   SmallPtrSet<GlobalValue *, 8> Used;
115   collectUsedGlobalVariables(*M, Used, /*CompilerUsed*/ false);
116 
117   ModuleSymbolTable Msymtab;
118   Msymtab.addModule(M);
119 
120   storage::Module Mod;
121   Mod.Begin = Syms.size();
122   Mod.End = Syms.size() + Msymtab.symbols().size();
123   Mod.UncBegin = Uncommons.size();
124   Mods.push_back(Mod);
125 
126   if (TT.isOSBinFormatCOFF()) {
127     if (auto E = M->materializeMetadata())
128       return E;
129     if (NamedMDNode *LinkerOptions =
130             M->getNamedMetadata("llvm.linker.options")) {
131       for (MDNode *MDOptions : LinkerOptions->operands())
132         for (const MDOperand &MDOption : cast<MDNode>(MDOptions)->operands())
133           COFFLinkerOptsOS << " " << cast<MDString>(MDOption)->getString();
134     }
135   }
136 
137   for (ModuleSymbolTable::Symbol Msym : Msymtab.symbols())
138     if (Error Err = addSymbol(Msymtab, Used, Msym))
139       return Err;
140 
141   return Error::success();
142 }
143 
144 Expected<int> Builder::getComdatIndex(const Comdat *C, const Module *M) {
145   auto P = ComdatMap.insert(std::make_pair(C, Comdats.size()));
146   if (P.second) {
147     std::string Name;
148     if (TT.isOSBinFormatCOFF()) {
149       const GlobalValue *GV = M->getNamedValue(C->getName());
150       if (!GV)
151         return make_error<StringError>("Could not find leader",
152                                        inconvertibleErrorCode());
153       // Internal leaders do not affect symbol resolution, therefore they do not
154       // appear in the symbol table.
155       if (GV->hasLocalLinkage()) {
156         P.first->second = -1;
157         return -1;
158       }
159       llvm::raw_string_ostream OS(Name);
160       Mang.getNameWithPrefix(OS, GV, false);
161     } else {
162       Name = C->getName();
163     }
164 
165     storage::Comdat Comdat;
166     setStr(Comdat.Name, Saver.save(Name));
167     Comdats.push_back(Comdat);
168   }
169 
170   return P.first->second;
171 }
172 
173 Error Builder::addSymbol(const ModuleSymbolTable &Msymtab,
174                          const SmallPtrSet<GlobalValue *, 8> &Used,
175                          ModuleSymbolTable::Symbol Msym) {
176   Syms.emplace_back();
177   storage::Symbol &Sym = Syms.back();
178   Sym = {};
179 
180   storage::Uncommon *Unc = nullptr;
181   auto Uncommon = [&]() -> storage::Uncommon & {
182     if (Unc)
183       return *Unc;
184     Sym.Flags |= 1 << storage::Symbol::FB_has_uncommon;
185     Uncommons.emplace_back();
186     Unc = &Uncommons.back();
187     *Unc = {};
188     setStr(Unc->COFFWeakExternFallbackName, "");
189     setStr(Unc->SectionName, "");
190     return *Unc;
191   };
192 
193   SmallString<64> Name;
194   {
195     raw_svector_ostream OS(Name);
196     Msymtab.printSymbolName(OS, Msym);
197   }
198   setStr(Sym.Name, Saver.save(StringRef(Name)));
199 
200   auto Flags = Msymtab.getSymbolFlags(Msym);
201   if (Flags & object::BasicSymbolRef::SF_Undefined)
202     Sym.Flags |= 1 << storage::Symbol::FB_undefined;
203   if (Flags & object::BasicSymbolRef::SF_Weak)
204     Sym.Flags |= 1 << storage::Symbol::FB_weak;
205   if (Flags & object::BasicSymbolRef::SF_Common)
206     Sym.Flags |= 1 << storage::Symbol::FB_common;
207   if (Flags & object::BasicSymbolRef::SF_Indirect)
208     Sym.Flags |= 1 << storage::Symbol::FB_indirect;
209   if (Flags & object::BasicSymbolRef::SF_Global)
210     Sym.Flags |= 1 << storage::Symbol::FB_global;
211   if (Flags & object::BasicSymbolRef::SF_FormatSpecific)
212     Sym.Flags |= 1 << storage::Symbol::FB_format_specific;
213   if (Flags & object::BasicSymbolRef::SF_Executable)
214     Sym.Flags |= 1 << storage::Symbol::FB_executable;
215 
216   Sym.ComdatIndex = -1;
217   auto *GV = Msym.dyn_cast<GlobalValue *>();
218   if (!GV) {
219     // Undefined module asm symbols act as GC roots and are implicitly used.
220     if (Flags & object::BasicSymbolRef::SF_Undefined)
221       Sym.Flags |= 1 << storage::Symbol::FB_used;
222     setStr(Sym.IRName, "");
223     return Error::success();
224   }
225 
226   setStr(Sym.IRName, GV->getName());
227 
228   if (Used.count(GV))
229     Sym.Flags |= 1 << storage::Symbol::FB_used;
230   if (GV->isThreadLocal())
231     Sym.Flags |= 1 << storage::Symbol::FB_tls;
232   if (GV->hasGlobalUnnamedAddr())
233     Sym.Flags |= 1 << storage::Symbol::FB_unnamed_addr;
234   if (GV->canBeOmittedFromSymbolTable())
235     Sym.Flags |= 1 << storage::Symbol::FB_may_omit;
236   Sym.Flags |= unsigned(GV->getVisibility()) << storage::Symbol::FB_visibility;
237 
238   if (Flags & object::BasicSymbolRef::SF_Common) {
239     Uncommon().CommonSize = GV->getParent()->getDataLayout().getTypeAllocSize(
240         GV->getType()->getElementType());
241     Uncommon().CommonAlign = GV->getAlignment();
242   }
243 
244   const GlobalObject *Base = GV->getBaseObject();
245   if (!Base)
246     return make_error<StringError>("Unable to determine comdat of alias!",
247                                    inconvertibleErrorCode());
248   if (const Comdat *C = Base->getComdat()) {
249     Expected<int> ComdatIndexOrErr = getComdatIndex(C, GV->getParent());
250     if (!ComdatIndexOrErr)
251       return ComdatIndexOrErr.takeError();
252     Sym.ComdatIndex = *ComdatIndexOrErr;
253   }
254 
255   if (TT.isOSBinFormatCOFF()) {
256     emitLinkerFlagsForGlobalCOFF(COFFLinkerOptsOS, GV, TT, Mang);
257 
258     if ((Flags & object::BasicSymbolRef::SF_Weak) &&
259         (Flags & object::BasicSymbolRef::SF_Indirect)) {
260       auto *Fallback = dyn_cast<GlobalValue>(
261           cast<GlobalAlias>(GV)->getAliasee()->stripPointerCasts());
262       if (!Fallback)
263         return make_error<StringError>("Invalid weak external",
264                                        inconvertibleErrorCode());
265       std::string FallbackName;
266       raw_string_ostream OS(FallbackName);
267       Msymtab.printSymbolName(OS, Fallback);
268       OS.flush();
269       setStr(Uncommon().COFFWeakExternFallbackName, Saver.save(FallbackName));
270     }
271   }
272 
273   if (!Base->getSection().empty())
274     setStr(Uncommon().SectionName, Saver.save(Base->getSection()));
275 
276   return Error::success();
277 }
278 
279 Error Builder::build(ArrayRef<Module *> IRMods) {
280   storage::Header Hdr;
281 
282   assert(!IRMods.empty());
283   Hdr.Version = storage::Header::kCurrentVersion;
284   setStr(Hdr.Producer, kExpectedProducerName);
285   setStr(Hdr.TargetTriple, IRMods[0]->getTargetTriple());
286   setStr(Hdr.SourceFileName, IRMods[0]->getSourceFileName());
287   TT = Triple(IRMods[0]->getTargetTriple());
288 
289   for (auto *M : IRMods)
290     if (Error Err = addModule(M))
291       return Err;
292 
293   COFFLinkerOptsOS.flush();
294   setStr(Hdr.COFFLinkerOpts, Saver.save(COFFLinkerOpts));
295 
296   // We are about to fill in the header's range fields, so reserve space for it
297   // and copy it in afterwards.
298   Symtab.resize(sizeof(storage::Header));
299   writeRange(Hdr.Modules, Mods);
300   writeRange(Hdr.Comdats, Comdats);
301   writeRange(Hdr.Symbols, Syms);
302   writeRange(Hdr.Uncommons, Uncommons);
303 
304   *reinterpret_cast<storage::Header *>(Symtab.data()) = Hdr;
305   return Error::success();
306 }
307 
308 } // end anonymous namespace
309 
310 Error irsymtab::build(ArrayRef<Module *> Mods, SmallVector<char, 0> &Symtab,
311                       StringTableBuilder &StrtabBuilder,
312                       BumpPtrAllocator &Alloc) {
313   return Builder(Symtab, StrtabBuilder, Alloc).build(Mods);
314 }
315 
316 // Upgrade a vector of bitcode modules created by an old version of LLVM by
317 // creating an irsymtab for them in the current format.
318 static Expected<FileContents> upgrade(ArrayRef<BitcodeModule> BMs) {
319   FileContents FC;
320 
321   LLVMContext Ctx;
322   std::vector<Module *> Mods;
323   std::vector<std::unique_ptr<Module>> OwnedMods;
324   for (auto BM : BMs) {
325     Expected<std::unique_ptr<Module>> MOrErr =
326         BM.getLazyModule(Ctx, /*ShouldLazyLoadMetadata*/ true,
327                          /*IsImporting*/ false);
328     if (!MOrErr)
329       return MOrErr.takeError();
330 
331     Mods.push_back(MOrErr->get());
332     OwnedMods.push_back(std::move(*MOrErr));
333   }
334 
335   StringTableBuilder StrtabBuilder(StringTableBuilder::RAW);
336   BumpPtrAllocator Alloc;
337   if (Error E = build(Mods, FC.Symtab, StrtabBuilder, Alloc))
338     return std::move(E);
339 
340   StrtabBuilder.finalizeInOrder();
341   FC.Strtab.resize(StrtabBuilder.getSize());
342   StrtabBuilder.write((uint8_t *)FC.Strtab.data());
343 
344   FC.TheReader = {{FC.Symtab.data(), FC.Symtab.size()},
345                   {FC.Strtab.data(), FC.Strtab.size()}};
346   return std::move(FC);
347 }
348 
349 Expected<FileContents> irsymtab::readBitcode(const BitcodeFileContents &BFC) {
350   if (BFC.Mods.empty())
351     return make_error<StringError>("Bitcode file does not contain any modules",
352                                    inconvertibleErrorCode());
353 
354   if (BFC.StrtabForSymtab.empty() ||
355       BFC.Symtab.size() < sizeof(storage::Header))
356     return upgrade(BFC.Mods);
357 
358   // We cannot use the regular reader to read the version and producer, because
359   // it will expect the header to be in the current format. The only thing we
360   // can rely on is that the version and producer will be present as the first
361   // struct elements.
362   auto *Hdr = reinterpret_cast<const storage::Header *>(BFC.Symtab.data());
363   unsigned Version = Hdr->Version;
364   StringRef Producer = Hdr->Producer.get(BFC.StrtabForSymtab);
365   if (Version != storage::Header::kCurrentVersion ||
366       Producer != kExpectedProducerName)
367     return upgrade(BFC.Mods);
368 
369   FileContents FC;
370   FC.TheReader = {{BFC.Symtab.data(), BFC.Symtab.size()},
371                   {BFC.StrtabForSymtab.data(), BFC.StrtabForSymtab.size()}};
372 
373   // Finally, make sure that the number of modules in the symbol table matches
374   // the number of modules in the bitcode file. If they differ, it may mean that
375   // the bitcode file was created by binary concatenation, so we need to create
376   // a new symbol table from scratch.
377   if (FC.TheReader.getNumModules() != BFC.Mods.size())
378     return upgrade(std::move(BFC.Mods));
379 
380   return std::move(FC);
381 }
382