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 *, unsigned> 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   Error addModule(Module *M);
101   Error addSymbol(const ModuleSymbolTable &Msymtab,
102                   const SmallPtrSet<GlobalValue *, 8> &Used,
103                   ModuleSymbolTable::Symbol Sym);
104 
105   Error build(ArrayRef<Module *> Mods);
106 };
107 
108 Error Builder::addModule(Module *M) {
109   if (M->getDataLayoutStr().empty())
110     return make_error<StringError>("input module has no datalayout",
111                                    inconvertibleErrorCode());
112 
113   SmallPtrSet<GlobalValue *, 8> Used;
114   collectUsedGlobalVariables(*M, Used, /*CompilerUsed*/ false);
115 
116   ModuleSymbolTable Msymtab;
117   Msymtab.addModule(M);
118 
119   storage::Module Mod;
120   Mod.Begin = Syms.size();
121   Mod.End = Syms.size() + Msymtab.symbols().size();
122   Mod.UncBegin = Uncommons.size();
123   Mods.push_back(Mod);
124 
125   if (TT.isOSBinFormatCOFF()) {
126     if (auto E = M->materializeMetadata())
127       return E;
128     if (NamedMDNode *LinkerOptions =
129             M->getNamedMetadata("llvm.linker.options")) {
130       for (MDNode *MDOptions : LinkerOptions->operands())
131         for (const MDOperand &MDOption : cast<MDNode>(MDOptions)->operands())
132           COFFLinkerOptsOS << " " << cast<MDString>(MDOption)->getString();
133     }
134   }
135 
136   for (ModuleSymbolTable::Symbol Msym : Msymtab.symbols())
137     if (Error Err = addSymbol(Msymtab, Used, Msym))
138       return Err;
139 
140   return Error::success();
141 }
142 
143 Error Builder::addSymbol(const ModuleSymbolTable &Msymtab,
144                          const SmallPtrSet<GlobalValue *, 8> &Used,
145                          ModuleSymbolTable::Symbol Msym) {
146   Syms.emplace_back();
147   storage::Symbol &Sym = Syms.back();
148   Sym = {};
149 
150   storage::Uncommon *Unc = nullptr;
151   auto Uncommon = [&]() -> storage::Uncommon & {
152     if (Unc)
153       return *Unc;
154     Sym.Flags |= 1 << storage::Symbol::FB_has_uncommon;
155     Uncommons.emplace_back();
156     Unc = &Uncommons.back();
157     *Unc = {};
158     setStr(Unc->COFFWeakExternFallbackName, "");
159     setStr(Unc->SectionName, "");
160     return *Unc;
161   };
162 
163   SmallString<64> Name;
164   {
165     raw_svector_ostream OS(Name);
166     Msymtab.printSymbolName(OS, Msym);
167   }
168   setStr(Sym.Name, Saver.save(StringRef(Name)));
169 
170   auto Flags = Msymtab.getSymbolFlags(Msym);
171   if (Flags & object::BasicSymbolRef::SF_Undefined)
172     Sym.Flags |= 1 << storage::Symbol::FB_undefined;
173   if (Flags & object::BasicSymbolRef::SF_Weak)
174     Sym.Flags |= 1 << storage::Symbol::FB_weak;
175   if (Flags & object::BasicSymbolRef::SF_Common)
176     Sym.Flags |= 1 << storage::Symbol::FB_common;
177   if (Flags & object::BasicSymbolRef::SF_Indirect)
178     Sym.Flags |= 1 << storage::Symbol::FB_indirect;
179   if (Flags & object::BasicSymbolRef::SF_Global)
180     Sym.Flags |= 1 << storage::Symbol::FB_global;
181   if (Flags & object::BasicSymbolRef::SF_FormatSpecific)
182     Sym.Flags |= 1 << storage::Symbol::FB_format_specific;
183   if (Flags & object::BasicSymbolRef::SF_Executable)
184     Sym.Flags |= 1 << storage::Symbol::FB_executable;
185 
186   Sym.ComdatIndex = -1;
187   auto *GV = Msym.dyn_cast<GlobalValue *>();
188   if (!GV) {
189     // Undefined module asm symbols act as GC roots and are implicitly used.
190     if (Flags & object::BasicSymbolRef::SF_Undefined)
191       Sym.Flags |= 1 << storage::Symbol::FB_used;
192     setStr(Sym.IRName, "");
193     return Error::success();
194   }
195 
196   setStr(Sym.IRName, GV->getName());
197 
198   if (Used.count(GV))
199     Sym.Flags |= 1 << storage::Symbol::FB_used;
200   if (GV->isThreadLocal())
201     Sym.Flags |= 1 << storage::Symbol::FB_tls;
202   if (GV->hasGlobalUnnamedAddr())
203     Sym.Flags |= 1 << storage::Symbol::FB_unnamed_addr;
204   if (canBeOmittedFromSymbolTable(GV))
205     Sym.Flags |= 1 << storage::Symbol::FB_may_omit;
206   Sym.Flags |= unsigned(GV->getVisibility()) << storage::Symbol::FB_visibility;
207 
208   if (Flags & object::BasicSymbolRef::SF_Common) {
209     Uncommon().CommonSize = GV->getParent()->getDataLayout().getTypeAllocSize(
210         GV->getType()->getElementType());
211     Uncommon().CommonAlign = GV->getAlignment();
212   }
213 
214   const GlobalObject *Base = GV->getBaseObject();
215   if (!Base)
216     return make_error<StringError>("Unable to determine comdat of alias!",
217                                    inconvertibleErrorCode());
218   if (const Comdat *C = Base->getComdat()) {
219     auto P = ComdatMap.insert(std::make_pair(C, Comdats.size()));
220     Sym.ComdatIndex = P.first->second;
221 
222     if (P.second) {
223       storage::Comdat Comdat;
224       setStr(Comdat.Name, C->getName());
225       Comdats.push_back(Comdat);
226     }
227   }
228 
229   if (TT.isOSBinFormatCOFF()) {
230     emitLinkerFlagsForGlobalCOFF(COFFLinkerOptsOS, GV, TT, Mang);
231 
232     if ((Flags & object::BasicSymbolRef::SF_Weak) &&
233         (Flags & object::BasicSymbolRef::SF_Indirect)) {
234       std::string FallbackName;
235       raw_string_ostream OS(FallbackName);
236       Msymtab.printSymbolName(
237           OS, cast<GlobalValue>(
238                   cast<GlobalAlias>(GV)->getAliasee()->stripPointerCasts()));
239       OS.flush();
240       setStr(Uncommon().COFFWeakExternFallbackName, Saver.save(FallbackName));
241     }
242   }
243 
244   if (!Base->getSection().empty())
245     setStr(Uncommon().SectionName, Saver.save(Base->getSection()));
246 
247   return Error::success();
248 }
249 
250 Error Builder::build(ArrayRef<Module *> IRMods) {
251   storage::Header Hdr;
252 
253   assert(!IRMods.empty());
254   Hdr.Version = storage::Header::kCurrentVersion;
255   setStr(Hdr.Producer, kExpectedProducerName);
256   setStr(Hdr.TargetTriple, IRMods[0]->getTargetTriple());
257   setStr(Hdr.SourceFileName, IRMods[0]->getSourceFileName());
258   TT = Triple(IRMods[0]->getTargetTriple());
259 
260   for (auto *M : IRMods)
261     if (Error Err = addModule(M))
262       return Err;
263 
264   COFFLinkerOptsOS.flush();
265   setStr(Hdr.COFFLinkerOpts, Saver.save(COFFLinkerOpts));
266 
267   // We are about to fill in the header's range fields, so reserve space for it
268   // and copy it in afterwards.
269   Symtab.resize(sizeof(storage::Header));
270   writeRange(Hdr.Modules, Mods);
271   writeRange(Hdr.Comdats, Comdats);
272   writeRange(Hdr.Symbols, Syms);
273   writeRange(Hdr.Uncommons, Uncommons);
274 
275   *reinterpret_cast<storage::Header *>(Symtab.data()) = Hdr;
276   return Error::success();
277 }
278 
279 } // end anonymous namespace
280 
281 Error irsymtab::build(ArrayRef<Module *> Mods, SmallVector<char, 0> &Symtab,
282                       StringTableBuilder &StrtabBuilder,
283                       BumpPtrAllocator &Alloc) {
284   return Builder(Symtab, StrtabBuilder, Alloc).build(Mods);
285 }
286 
287 // Upgrade a vector of bitcode modules created by an old version of LLVM by
288 // creating an irsymtab for them in the current format.
289 static Expected<FileContents> upgrade(ArrayRef<BitcodeModule> BMs) {
290   FileContents FC;
291 
292   LLVMContext Ctx;
293   std::vector<Module *> Mods;
294   std::vector<std::unique_ptr<Module>> OwnedMods;
295   for (auto BM : BMs) {
296     Expected<std::unique_ptr<Module>> MOrErr =
297         BM.getLazyModule(Ctx, /*ShouldLazyLoadMetadata*/ true,
298                          /*IsImporting*/ false);
299     if (!MOrErr)
300       return MOrErr.takeError();
301 
302     Mods.push_back(MOrErr->get());
303     OwnedMods.push_back(std::move(*MOrErr));
304   }
305 
306   StringTableBuilder StrtabBuilder(StringTableBuilder::RAW);
307   BumpPtrAllocator Alloc;
308   if (Error E = build(Mods, FC.Symtab, StrtabBuilder, Alloc))
309     return std::move(E);
310 
311   StrtabBuilder.finalizeInOrder();
312   FC.Strtab.resize(StrtabBuilder.getSize());
313   StrtabBuilder.write((uint8_t *)FC.Strtab.data());
314 
315   FC.TheReader = {{FC.Symtab.data(), FC.Symtab.size()},
316                   {FC.Strtab.data(), FC.Strtab.size()}};
317   return std::move(FC);
318 }
319 
320 Expected<FileContents> irsymtab::readBitcode(const BitcodeFileContents &BFC) {
321   if (BFC.Mods.empty())
322     return make_error<StringError>("Bitcode file does not contain any modules",
323                                    inconvertibleErrorCode());
324 
325   if (BFC.StrtabForSymtab.empty() ||
326       BFC.Symtab.size() < sizeof(storage::Header))
327     return upgrade(BFC.Mods);
328 
329   // We cannot use the regular reader to read the version and producer, because
330   // it will expect the header to be in the current format. The only thing we
331   // can rely on is that the version and producer will be present as the first
332   // struct elements.
333   auto *Hdr = reinterpret_cast<const storage::Header *>(BFC.Symtab.data());
334   unsigned Version = Hdr->Version;
335   StringRef Producer = Hdr->Producer.get(BFC.StrtabForSymtab);
336   if (Version != storage::Header::kCurrentVersion ||
337       Producer != kExpectedProducerName)
338     return upgrade(BFC.Mods);
339 
340   FileContents FC;
341   FC.TheReader = {{BFC.Symtab.data(), BFC.Symtab.size()},
342                   {BFC.StrtabForSymtab.data(), BFC.StrtabForSymtab.size()}};
343 
344   // Finally, make sure that the number of modules in the symbol table matches
345   // the number of modules in the bitcode file. If they differ, it may mean that
346   // the bitcode file was created by binary concatenation, so we need to create
347   // a new symbol table from scratch.
348   if (FC.TheReader.getNumModules() != BFC.Mods.size())
349     return upgrade(std::move(BFC.Mods));
350 
351   return std::move(FC);
352 }
353