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/Analysis/ObjectUtils.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/Bitcode/BitcodeReader.h"
27 #include "llvm/MC/StringTableBuilder.h"
28 #include "llvm/Object/IRObjectFile.h"
29 #include "llvm/Object/ModuleSymbolTable.h"
30 #include "llvm/Object/SymbolicFile.h"
31 #include "llvm/Support/Allocator.h"
32 #include "llvm/Support/Casting.h"
33 #include "llvm/Support/Error.h"
34 #include "llvm/Support/StringSaver.h"
35 #include "llvm/Support/VCSRevision.h"
36 #include "llvm/Support/raw_ostream.h"
37 #include <cassert>
38 #include <string>
39 #include <utility>
40 #include <vector>
41 
42 using namespace llvm;
43 using namespace irsymtab;
44 
45 namespace {
46 
47 const char *getExpectedProducerName() {
48   static char DefaultName[] = LLVM_VERSION_STRING
49 #ifdef LLVM_REVISION
50       " " LLVM_REVISION
51 #endif
52       ;
53   // Allows for testing of the irsymtab writer and upgrade mechanism. This
54   // environment variable should not be set by users.
55   if (char *OverrideName = getenv("LLVM_OVERRIDE_PRODUCER"))
56     return OverrideName;
57   return DefaultName;
58 }
59 
60 const char *kExpectedProducerName = getExpectedProducerName();
61 
62 /// Stores the temporary state that is required to build an IR symbol table.
63 struct Builder {
64   SmallVector<char, 0> &Symtab;
65   StringTableBuilder &StrtabBuilder;
66   StringSaver Saver;
67 
68   // This ctor initializes a StringSaver using the passed in BumpPtrAllocator.
69   // The StringTableBuilder does not create a copy of any strings added to it,
70   // so this provides somewhere to store any strings that we create.
71   Builder(SmallVector<char, 0> &Symtab, StringTableBuilder &StrtabBuilder,
72           BumpPtrAllocator &Alloc)
73       : Symtab(Symtab), StrtabBuilder(StrtabBuilder), Saver(Alloc) {}
74 
75   DenseMap<const Comdat *, int> ComdatMap;
76   Mangler Mang;
77   Triple TT;
78 
79   std::vector<storage::Comdat> Comdats;
80   std::vector<storage::Module> Mods;
81   std::vector<storage::Symbol> Syms;
82   std::vector<storage::Uncommon> Uncommons;
83 
84   std::string COFFLinkerOpts;
85   raw_string_ostream COFFLinkerOptsOS{COFFLinkerOpts};
86 
87   void setStr(storage::Str &S, StringRef Value) {
88     S.Offset = StrtabBuilder.add(Value);
89     S.Size = Value.size();
90   }
91 
92   template <typename T>
93   void writeRange(storage::Range<T> &R, const std::vector<T> &Objs) {
94     R.Offset = Symtab.size();
95     R.Size = Objs.size();
96     Symtab.insert(Symtab.end(), reinterpret_cast<const char *>(Objs.data()),
97                   reinterpret_cast<const char *>(Objs.data() + Objs.size()));
98   }
99 
100   Expected<int> getComdatIndex(const Comdat *C, const Module *M);
101 
102   Error addModule(Module *M);
103   Error addSymbol(const ModuleSymbolTable &Msymtab,
104                   const SmallPtrSet<GlobalValue *, 8> &Used,
105                   ModuleSymbolTable::Symbol Sym);
106 
107   Error build(ArrayRef<Module *> Mods);
108 };
109 
110 Error Builder::addModule(Module *M) {
111   if (M->getDataLayoutStr().empty())
112     return make_error<StringError>("input module has no datalayout",
113                                    inconvertibleErrorCode());
114 
115   SmallPtrSet<GlobalValue *, 8> Used;
116   collectUsedGlobalVariables(*M, Used, /*CompilerUsed*/ false);
117 
118   ModuleSymbolTable Msymtab;
119   Msymtab.addModule(M);
120 
121   storage::Module Mod;
122   Mod.Begin = Syms.size();
123   Mod.End = Syms.size() + Msymtab.symbols().size();
124   Mod.UncBegin = Uncommons.size();
125   Mods.push_back(Mod);
126 
127   if (TT.isOSBinFormatCOFF()) {
128     if (auto E = M->materializeMetadata())
129       return E;
130     if (NamedMDNode *LinkerOptions =
131             M->getNamedMetadata("llvm.linker.options")) {
132       for (MDNode *MDOptions : LinkerOptions->operands())
133         for (const MDOperand &MDOption : cast<MDNode>(MDOptions)->operands())
134           COFFLinkerOptsOS << " " << cast<MDString>(MDOption)->getString();
135     }
136   }
137 
138   for (ModuleSymbolTable::Symbol Msym : Msymtab.symbols())
139     if (Error Err = addSymbol(Msymtab, Used, Msym))
140       return Err;
141 
142   return Error::success();
143 }
144 
145 Expected<int> Builder::getComdatIndex(const Comdat *C, const Module *M) {
146   auto P = ComdatMap.insert(std::make_pair(C, Comdats.size()));
147   if (P.second) {
148     std::string Name;
149     if (TT.isOSBinFormatCOFF()) {
150       const GlobalValue *GV = M->getNamedValue(C->getName());
151       if (!GV)
152         return make_error<StringError>("Could not find leader",
153                                        inconvertibleErrorCode());
154       // Internal leaders do not affect symbol resolution, therefore they do not
155       // appear in the symbol table.
156       if (GV->hasLocalLinkage()) {
157         P.first->second = -1;
158         return -1;
159       }
160       llvm::raw_string_ostream OS(Name);
161       Mang.getNameWithPrefix(OS, GV, false);
162     } else {
163       Name = C->getName();
164     }
165 
166     storage::Comdat Comdat;
167     setStr(Comdat.Name, Saver.save(Name));
168     Comdats.push_back(Comdat);
169   }
170 
171   return P.first->second;
172 }
173 
174 Error Builder::addSymbol(const ModuleSymbolTable &Msymtab,
175                          const SmallPtrSet<GlobalValue *, 8> &Used,
176                          ModuleSymbolTable::Symbol Msym) {
177   Syms.emplace_back();
178   storage::Symbol &Sym = Syms.back();
179   Sym = {};
180 
181   storage::Uncommon *Unc = nullptr;
182   auto Uncommon = [&]() -> storage::Uncommon & {
183     if (Unc)
184       return *Unc;
185     Sym.Flags |= 1 << storage::Symbol::FB_has_uncommon;
186     Uncommons.emplace_back();
187     Unc = &Uncommons.back();
188     *Unc = {};
189     setStr(Unc->COFFWeakExternFallbackName, "");
190     setStr(Unc->SectionName, "");
191     return *Unc;
192   };
193 
194   SmallString<64> Name;
195   {
196     raw_svector_ostream OS(Name);
197     Msymtab.printSymbolName(OS, Msym);
198   }
199   setStr(Sym.Name, Saver.save(StringRef(Name)));
200 
201   auto Flags = Msymtab.getSymbolFlags(Msym);
202   if (Flags & object::BasicSymbolRef::SF_Undefined)
203     Sym.Flags |= 1 << storage::Symbol::FB_undefined;
204   if (Flags & object::BasicSymbolRef::SF_Weak)
205     Sym.Flags |= 1 << storage::Symbol::FB_weak;
206   if (Flags & object::BasicSymbolRef::SF_Common)
207     Sym.Flags |= 1 << storage::Symbol::FB_common;
208   if (Flags & object::BasicSymbolRef::SF_Indirect)
209     Sym.Flags |= 1 << storage::Symbol::FB_indirect;
210   if (Flags & object::BasicSymbolRef::SF_Global)
211     Sym.Flags |= 1 << storage::Symbol::FB_global;
212   if (Flags & object::BasicSymbolRef::SF_FormatSpecific)
213     Sym.Flags |= 1 << storage::Symbol::FB_format_specific;
214   if (Flags & object::BasicSymbolRef::SF_Executable)
215     Sym.Flags |= 1 << storage::Symbol::FB_executable;
216 
217   Sym.ComdatIndex = -1;
218   auto *GV = Msym.dyn_cast<GlobalValue *>();
219   if (!GV) {
220     // Undefined module asm symbols act as GC roots and are implicitly used.
221     if (Flags & object::BasicSymbolRef::SF_Undefined)
222       Sym.Flags |= 1 << storage::Symbol::FB_used;
223     setStr(Sym.IRName, "");
224     return Error::success();
225   }
226 
227   setStr(Sym.IRName, GV->getName());
228 
229   if (Used.count(GV))
230     Sym.Flags |= 1 << storage::Symbol::FB_used;
231   if (GV->isThreadLocal())
232     Sym.Flags |= 1 << storage::Symbol::FB_tls;
233   if (GV->hasGlobalUnnamedAddr())
234     Sym.Flags |= 1 << storage::Symbol::FB_unnamed_addr;
235   if (canBeOmittedFromSymbolTable(GV))
236     Sym.Flags |= 1 << storage::Symbol::FB_may_omit;
237   Sym.Flags |= unsigned(GV->getVisibility()) << storage::Symbol::FB_visibility;
238 
239   if (Flags & object::BasicSymbolRef::SF_Common) {
240     Uncommon().CommonSize = GV->getParent()->getDataLayout().getTypeAllocSize(
241         GV->getType()->getElementType());
242     Uncommon().CommonAlign = GV->getAlignment();
243   }
244 
245   const GlobalObject *Base = GV->getBaseObject();
246   if (!Base)
247     return make_error<StringError>("Unable to determine comdat of alias!",
248                                    inconvertibleErrorCode());
249   if (const Comdat *C = Base->getComdat()) {
250     Expected<int> ComdatIndexOrErr = getComdatIndex(C, GV->getParent());
251     if (!ComdatIndexOrErr)
252       return ComdatIndexOrErr.takeError();
253     Sym.ComdatIndex = *ComdatIndexOrErr;
254   }
255 
256   if (TT.isOSBinFormatCOFF()) {
257     emitLinkerFlagsForGlobalCOFF(COFFLinkerOptsOS, GV, TT, Mang);
258 
259     if ((Flags & object::BasicSymbolRef::SF_Weak) &&
260         (Flags & object::BasicSymbolRef::SF_Indirect)) {
261       auto *Fallback = dyn_cast<GlobalValue>(
262           cast<GlobalAlias>(GV)->getAliasee()->stripPointerCasts());
263       if (!Fallback)
264         return make_error<StringError>("Invalid weak external",
265                                        inconvertibleErrorCode());
266       std::string FallbackName;
267       raw_string_ostream OS(FallbackName);
268       Msymtab.printSymbolName(OS, Fallback);
269       OS.flush();
270       setStr(Uncommon().COFFWeakExternFallbackName, Saver.save(FallbackName));
271     }
272   }
273 
274   if (!Base->getSection().empty())
275     setStr(Uncommon().SectionName, Saver.save(Base->getSection()));
276 
277   return Error::success();
278 }
279 
280 Error Builder::build(ArrayRef<Module *> IRMods) {
281   storage::Header Hdr;
282 
283   assert(!IRMods.empty());
284   Hdr.Version = storage::Header::kCurrentVersion;
285   setStr(Hdr.Producer, kExpectedProducerName);
286   setStr(Hdr.TargetTriple, IRMods[0]->getTargetTriple());
287   setStr(Hdr.SourceFileName, IRMods[0]->getSourceFileName());
288   TT = Triple(IRMods[0]->getTargetTriple());
289 
290   for (auto *M : IRMods)
291     if (Error Err = addModule(M))
292       return Err;
293 
294   COFFLinkerOptsOS.flush();
295   setStr(Hdr.COFFLinkerOpts, Saver.save(COFFLinkerOpts));
296 
297   // We are about to fill in the header's range fields, so reserve space for it
298   // and copy it in afterwards.
299   Symtab.resize(sizeof(storage::Header));
300   writeRange(Hdr.Modules, Mods);
301   writeRange(Hdr.Comdats, Comdats);
302   writeRange(Hdr.Symbols, Syms);
303   writeRange(Hdr.Uncommons, Uncommons);
304 
305   *reinterpret_cast<storage::Header *>(Symtab.data()) = Hdr;
306   return Error::success();
307 }
308 
309 } // end anonymous namespace
310 
311 Error irsymtab::build(ArrayRef<Module *> Mods, SmallVector<char, 0> &Symtab,
312                       StringTableBuilder &StrtabBuilder,
313                       BumpPtrAllocator &Alloc) {
314   return Builder(Symtab, StrtabBuilder, Alloc).build(Mods);
315 }
316 
317 // Upgrade a vector of bitcode modules created by an old version of LLVM by
318 // creating an irsymtab for them in the current format.
319 static Expected<FileContents> upgrade(ArrayRef<BitcodeModule> BMs) {
320   FileContents FC;
321 
322   LLVMContext Ctx;
323   std::vector<Module *> Mods;
324   std::vector<std::unique_ptr<Module>> OwnedMods;
325   for (auto BM : BMs) {
326     Expected<std::unique_ptr<Module>> MOrErr =
327         BM.getLazyModule(Ctx, /*ShouldLazyLoadMetadata*/ true,
328                          /*IsImporting*/ false);
329     if (!MOrErr)
330       return MOrErr.takeError();
331 
332     Mods.push_back(MOrErr->get());
333     OwnedMods.push_back(std::move(*MOrErr));
334   }
335 
336   StringTableBuilder StrtabBuilder(StringTableBuilder::RAW);
337   BumpPtrAllocator Alloc;
338   if (Error E = build(Mods, FC.Symtab, StrtabBuilder, Alloc))
339     return std::move(E);
340 
341   StrtabBuilder.finalizeInOrder();
342   FC.Strtab.resize(StrtabBuilder.getSize());
343   StrtabBuilder.write((uint8_t *)FC.Strtab.data());
344 
345   FC.TheReader = {{FC.Symtab.data(), FC.Symtab.size()},
346                   {FC.Strtab.data(), FC.Strtab.size()}};
347   return std::move(FC);
348 }
349 
350 Expected<FileContents> irsymtab::readBitcode(const BitcodeFileContents &BFC) {
351   if (BFC.Mods.empty())
352     return make_error<StringError>("Bitcode file does not contain any modules",
353                                    inconvertibleErrorCode());
354 
355   if (BFC.StrtabForSymtab.empty() ||
356       BFC.Symtab.size() < sizeof(storage::Header))
357     return upgrade(BFC.Mods);
358 
359   // We cannot use the regular reader to read the version and producer, because
360   // it will expect the header to be in the current format. The only thing we
361   // can rely on is that the version and producer will be present as the first
362   // struct elements.
363   auto *Hdr = reinterpret_cast<const storage::Header *>(BFC.Symtab.data());
364   unsigned Version = Hdr->Version;
365   StringRef Producer = Hdr->Producer.get(BFC.StrtabForSymtab);
366   if (Version != storage::Header::kCurrentVersion ||
367       Producer != kExpectedProducerName)
368     return upgrade(BFC.Mods);
369 
370   FileContents FC;
371   FC.TheReader = {{BFC.Symtab.data(), BFC.Symtab.size()},
372                   {BFC.StrtabForSymtab.data(), BFC.StrtabForSymtab.size()}};
373 
374   // Finally, make sure that the number of modules in the symbol table matches
375   // the number of modules in the bitcode file. If they differ, it may mean that
376   // the bitcode file was created by binary concatenation, so we need to create
377   // a new symbol table from scratch.
378   if (FC.TheReader.getNumModules() != BFC.Mods.size())
379     return upgrade(std::move(BFC.Mods));
380 
381   return std::move(FC);
382 }
383