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/ADT/Triple.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/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 static const char *LibcallRoutineNames[] = {
45 #define HANDLE_LIBCALL(code, name) name,
46 #include "llvm/IR/RuntimeLibcalls.def"
47 #undef HANDLE_LIBCALL
48 };
49 
50 namespace {
51 
52 const char *getExpectedProducerName() {
53   static char DefaultName[] = LLVM_VERSION_STRING
54 #ifdef LLVM_REVISION
55       " " LLVM_REVISION
56 #endif
57       ;
58   // Allows for testing of the irsymtab writer and upgrade mechanism. This
59   // environment variable should not be set by users.
60   if (char *OverrideName = getenv("LLVM_OVERRIDE_PRODUCER"))
61     return OverrideName;
62   return DefaultName;
63 }
64 
65 const char *kExpectedProducerName = getExpectedProducerName();
66 
67 /// Stores the temporary state that is required to build an IR symbol table.
68 struct Builder {
69   SmallVector<char, 0> &Symtab;
70   StringTableBuilder &StrtabBuilder;
71   StringSaver Saver;
72 
73   // This ctor initializes a StringSaver using the passed in BumpPtrAllocator.
74   // The StringTableBuilder does not create a copy of any strings added to it,
75   // so this provides somewhere to store any strings that we create.
76   Builder(SmallVector<char, 0> &Symtab, StringTableBuilder &StrtabBuilder,
77           BumpPtrAllocator &Alloc)
78       : Symtab(Symtab), StrtabBuilder(StrtabBuilder), Saver(Alloc) {}
79 
80   DenseMap<const Comdat *, int> ComdatMap;
81   Mangler Mang;
82   Triple TT;
83 
84   std::vector<storage::Comdat> Comdats;
85   std::vector<storage::Module> Mods;
86   std::vector<storage::Symbol> Syms;
87   std::vector<storage::Uncommon> Uncommons;
88 
89   std::string COFFLinkerOpts;
90   raw_string_ostream COFFLinkerOptsOS{COFFLinkerOpts};
91 
92   void setStr(storage::Str &S, StringRef Value) {
93     S.Offset = StrtabBuilder.add(Value);
94     S.Size = Value.size();
95   }
96 
97   template <typename T>
98   void writeRange(storage::Range<T> &R, const std::vector<T> &Objs) {
99     R.Offset = Symtab.size();
100     R.Size = Objs.size();
101     Symtab.insert(Symtab.end(), reinterpret_cast<const char *>(Objs.data()),
102                   reinterpret_cast<const char *>(Objs.data() + Objs.size()));
103   }
104 
105   Expected<int> getComdatIndex(const Comdat *C, const Module *M);
106 
107   Error addModule(Module *M);
108   Error addSymbol(const ModuleSymbolTable &Msymtab,
109                   const SmallPtrSet<GlobalValue *, 8> &Used,
110                   ModuleSymbolTable::Symbol Sym);
111 
112   Error build(ArrayRef<Module *> Mods);
113 };
114 
115 Error Builder::addModule(Module *M) {
116   if (M->getDataLayoutStr().empty())
117     return make_error<StringError>("input module has no datalayout",
118                                    inconvertibleErrorCode());
119 
120   SmallPtrSet<GlobalValue *, 8> Used;
121   collectUsedGlobalVariables(*M, Used, /*CompilerUsed*/ false);
122 
123   ModuleSymbolTable Msymtab;
124   Msymtab.addModule(M);
125 
126   storage::Module Mod;
127   Mod.Begin = Syms.size();
128   Mod.End = Syms.size() + Msymtab.symbols().size();
129   Mod.UncBegin = Uncommons.size();
130   Mods.push_back(Mod);
131 
132   if (TT.isOSBinFormatCOFF()) {
133     if (auto E = M->materializeMetadata())
134       return E;
135     if (NamedMDNode *LinkerOptions =
136             M->getNamedMetadata("llvm.linker.options")) {
137       for (MDNode *MDOptions : LinkerOptions->operands())
138         for (const MDOperand &MDOption : cast<MDNode>(MDOptions)->operands())
139           COFFLinkerOptsOS << " " << cast<MDString>(MDOption)->getString();
140     }
141   }
142 
143   for (ModuleSymbolTable::Symbol Msym : Msymtab.symbols())
144     if (Error Err = addSymbol(Msymtab, Used, Msym))
145       return Err;
146 
147   return Error::success();
148 }
149 
150 Expected<int> Builder::getComdatIndex(const Comdat *C, const Module *M) {
151   auto P = ComdatMap.insert(std::make_pair(C, Comdats.size()));
152   if (P.second) {
153     std::string Name;
154     if (TT.isOSBinFormatCOFF()) {
155       const GlobalValue *GV = M->getNamedValue(C->getName());
156       if (!GV)
157         return make_error<StringError>("Could not find leader",
158                                        inconvertibleErrorCode());
159       // Internal leaders do not affect symbol resolution, therefore they do not
160       // appear in the symbol table.
161       if (GV->hasLocalLinkage()) {
162         P.first->second = -1;
163         return -1;
164       }
165       llvm::raw_string_ostream OS(Name);
166       Mang.getNameWithPrefix(OS, GV, false);
167     } else {
168       Name = C->getName();
169     }
170 
171     storage::Comdat Comdat;
172     setStr(Comdat.Name, Saver.save(Name));
173     Comdats.push_back(Comdat);
174   }
175 
176   return P.first->second;
177 }
178 
179 Error Builder::addSymbol(const ModuleSymbolTable &Msymtab,
180                          const SmallPtrSet<GlobalValue *, 8> &Used,
181                          ModuleSymbolTable::Symbol Msym) {
182   Syms.emplace_back();
183   storage::Symbol &Sym = Syms.back();
184   Sym = {};
185 
186   storage::Uncommon *Unc = nullptr;
187   auto Uncommon = [&]() -> storage::Uncommon & {
188     if (Unc)
189       return *Unc;
190     Sym.Flags |= 1 << storage::Symbol::FB_has_uncommon;
191     Uncommons.emplace_back();
192     Unc = &Uncommons.back();
193     *Unc = {};
194     setStr(Unc->COFFWeakExternFallbackName, "");
195     setStr(Unc->SectionName, "");
196     return *Unc;
197   };
198 
199   SmallString<64> Name;
200   {
201     raw_svector_ostream OS(Name);
202     Msymtab.printSymbolName(OS, Msym);
203   }
204   setStr(Sym.Name, Saver.save(StringRef(Name)));
205 
206   auto Flags = Msymtab.getSymbolFlags(Msym);
207   if (Flags & object::BasicSymbolRef::SF_Undefined)
208     Sym.Flags |= 1 << storage::Symbol::FB_undefined;
209   if (Flags & object::BasicSymbolRef::SF_Weak)
210     Sym.Flags |= 1 << storage::Symbol::FB_weak;
211   if (Flags & object::BasicSymbolRef::SF_Common)
212     Sym.Flags |= 1 << storage::Symbol::FB_common;
213   if (Flags & object::BasicSymbolRef::SF_Indirect)
214     Sym.Flags |= 1 << storage::Symbol::FB_indirect;
215   if (Flags & object::BasicSymbolRef::SF_Global)
216     Sym.Flags |= 1 << storage::Symbol::FB_global;
217   if (Flags & object::BasicSymbolRef::SF_FormatSpecific)
218     Sym.Flags |= 1 << storage::Symbol::FB_format_specific;
219   if (Flags & object::BasicSymbolRef::SF_Executable)
220     Sym.Flags |= 1 << storage::Symbol::FB_executable;
221 
222   Sym.ComdatIndex = -1;
223   auto *GV = Msym.dyn_cast<GlobalValue *>();
224   if (!GV) {
225     // Undefined module asm symbols act as GC roots and are implicitly used.
226     if (Flags & object::BasicSymbolRef::SF_Undefined)
227       Sym.Flags |= 1 << storage::Symbol::FB_used;
228     setStr(Sym.IRName, "");
229     return Error::success();
230   }
231 
232   setStr(Sym.IRName, GV->getName());
233 
234   bool IsBuiltinFunc = false;
235 
236   for (const char *LibcallName : LibcallRoutineNames)
237     if (GV->getName() == LibcallName)
238       IsBuiltinFunc = true;
239 
240   if (Used.count(GV) || IsBuiltinFunc)
241     Sym.Flags |= 1 << storage::Symbol::FB_used;
242   if (GV->isThreadLocal())
243     Sym.Flags |= 1 << storage::Symbol::FB_tls;
244   if (GV->hasGlobalUnnamedAddr())
245     Sym.Flags |= 1 << storage::Symbol::FB_unnamed_addr;
246   if (GV->canBeOmittedFromSymbolTable())
247     Sym.Flags |= 1 << storage::Symbol::FB_may_omit;
248   Sym.Flags |= unsigned(GV->getVisibility()) << storage::Symbol::FB_visibility;
249 
250   if (Flags & object::BasicSymbolRef::SF_Common) {
251     Uncommon().CommonSize = GV->getParent()->getDataLayout().getTypeAllocSize(
252         GV->getType()->getElementType());
253     Uncommon().CommonAlign = GV->getAlignment();
254   }
255 
256   const GlobalObject *Base = GV->getBaseObject();
257   if (!Base)
258     return make_error<StringError>("Unable to determine comdat of alias!",
259                                    inconvertibleErrorCode());
260   if (const Comdat *C = Base->getComdat()) {
261     Expected<int> ComdatIndexOrErr = getComdatIndex(C, GV->getParent());
262     if (!ComdatIndexOrErr)
263       return ComdatIndexOrErr.takeError();
264     Sym.ComdatIndex = *ComdatIndexOrErr;
265   }
266 
267   if (TT.isOSBinFormatCOFF()) {
268     emitLinkerFlagsForGlobalCOFF(COFFLinkerOptsOS, GV, TT, Mang);
269 
270     if ((Flags & object::BasicSymbolRef::SF_Weak) &&
271         (Flags & object::BasicSymbolRef::SF_Indirect)) {
272       auto *Fallback = dyn_cast<GlobalValue>(
273           cast<GlobalAlias>(GV)->getAliasee()->stripPointerCasts());
274       if (!Fallback)
275         return make_error<StringError>("Invalid weak external",
276                                        inconvertibleErrorCode());
277       std::string FallbackName;
278       raw_string_ostream OS(FallbackName);
279       Msymtab.printSymbolName(OS, Fallback);
280       OS.flush();
281       setStr(Uncommon().COFFWeakExternFallbackName, Saver.save(FallbackName));
282     }
283   }
284 
285   if (!Base->getSection().empty())
286     setStr(Uncommon().SectionName, Saver.save(Base->getSection()));
287 
288   return Error::success();
289 }
290 
291 Error Builder::build(ArrayRef<Module *> IRMods) {
292   storage::Header Hdr;
293 
294   assert(!IRMods.empty());
295   Hdr.Version = storage::Header::kCurrentVersion;
296   setStr(Hdr.Producer, kExpectedProducerName);
297   setStr(Hdr.TargetTriple, IRMods[0]->getTargetTriple());
298   setStr(Hdr.SourceFileName, IRMods[0]->getSourceFileName());
299   TT = Triple(IRMods[0]->getTargetTriple());
300 
301   for (auto *M : IRMods)
302     if (Error Err = addModule(M))
303       return Err;
304 
305   COFFLinkerOptsOS.flush();
306   setStr(Hdr.COFFLinkerOpts, Saver.save(COFFLinkerOpts));
307 
308   // We are about to fill in the header's range fields, so reserve space for it
309   // and copy it in afterwards.
310   Symtab.resize(sizeof(storage::Header));
311   writeRange(Hdr.Modules, Mods);
312   writeRange(Hdr.Comdats, Comdats);
313   writeRange(Hdr.Symbols, Syms);
314   writeRange(Hdr.Uncommons, Uncommons);
315 
316   *reinterpret_cast<storage::Header *>(Symtab.data()) = Hdr;
317   return Error::success();
318 }
319 
320 } // end anonymous namespace
321 
322 Error irsymtab::build(ArrayRef<Module *> Mods, SmallVector<char, 0> &Symtab,
323                       StringTableBuilder &StrtabBuilder,
324                       BumpPtrAllocator &Alloc) {
325   return Builder(Symtab, StrtabBuilder, Alloc).build(Mods);
326 }
327 
328 // Upgrade a vector of bitcode modules created by an old version of LLVM by
329 // creating an irsymtab for them in the current format.
330 static Expected<FileContents> upgrade(ArrayRef<BitcodeModule> BMs) {
331   FileContents FC;
332 
333   LLVMContext Ctx;
334   std::vector<Module *> Mods;
335   std::vector<std::unique_ptr<Module>> OwnedMods;
336   for (auto BM : BMs) {
337     Expected<std::unique_ptr<Module>> MOrErr =
338         BM.getLazyModule(Ctx, /*ShouldLazyLoadMetadata*/ true,
339                          /*IsImporting*/ false);
340     if (!MOrErr)
341       return MOrErr.takeError();
342 
343     Mods.push_back(MOrErr->get());
344     OwnedMods.push_back(std::move(*MOrErr));
345   }
346 
347   StringTableBuilder StrtabBuilder(StringTableBuilder::RAW);
348   BumpPtrAllocator Alloc;
349   if (Error E = build(Mods, FC.Symtab, StrtabBuilder, Alloc))
350     return std::move(E);
351 
352   StrtabBuilder.finalizeInOrder();
353   FC.Strtab.resize(StrtabBuilder.getSize());
354   StrtabBuilder.write((uint8_t *)FC.Strtab.data());
355 
356   FC.TheReader = {{FC.Symtab.data(), FC.Symtab.size()},
357                   {FC.Strtab.data(), FC.Strtab.size()}};
358   return std::move(FC);
359 }
360 
361 Expected<FileContents> irsymtab::readBitcode(const BitcodeFileContents &BFC) {
362   if (BFC.Mods.empty())
363     return make_error<StringError>("Bitcode file does not contain any modules",
364                                    inconvertibleErrorCode());
365 
366   if (BFC.StrtabForSymtab.empty() ||
367       BFC.Symtab.size() < sizeof(storage::Header))
368     return upgrade(BFC.Mods);
369 
370   // We cannot use the regular reader to read the version and producer, because
371   // it will expect the header to be in the current format. The only thing we
372   // can rely on is that the version and producer will be present as the first
373   // struct elements.
374   auto *Hdr = reinterpret_cast<const storage::Header *>(BFC.Symtab.data());
375   unsigned Version = Hdr->Version;
376   StringRef Producer = Hdr->Producer.get(BFC.StrtabForSymtab);
377   if (Version != storage::Header::kCurrentVersion ||
378       Producer != kExpectedProducerName)
379     return upgrade(BFC.Mods);
380 
381   FileContents FC;
382   FC.TheReader = {{BFC.Symtab.data(), BFC.Symtab.size()},
383                   {BFC.StrtabForSymtab.data(), BFC.StrtabForSymtab.size()}};
384 
385   // Finally, make sure that the number of modules in the symbol table matches
386   // the number of modules in the bitcode file. If they differ, it may mean that
387   // the bitcode file was created by binary concatenation, so we need to create
388   // a new symbol table from scratch.
389   if (FC.TheReader.getNumModules() != BFC.Mods.size())
390     return upgrade(std::move(BFC.Mods));
391 
392   return std::move(FC);
393 }
394