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   std::vector<storage::Str> DependentLibraries;
93 
94   void setStr(storage::Str &S, StringRef Value) {
95     S.Offset = StrtabBuilder.add(Value);
96     S.Size = Value.size();
97   }
98 
99   template <typename T>
100   void writeRange(storage::Range<T> &R, const std::vector<T> &Objs) {
101     R.Offset = Symtab.size();
102     R.Size = Objs.size();
103     Symtab.insert(Symtab.end(), reinterpret_cast<const char *>(Objs.data()),
104                   reinterpret_cast<const char *>(Objs.data() + Objs.size()));
105   }
106 
107   Expected<int> getComdatIndex(const Comdat *C, const Module *M);
108 
109   Error addModule(Module *M);
110   Error addSymbol(const ModuleSymbolTable &Msymtab,
111                   const SmallPtrSet<GlobalValue *, 4> &Used,
112                   ModuleSymbolTable::Symbol Sym);
113 
114   Error build(ArrayRef<Module *> Mods);
115 };
116 
117 Error Builder::addModule(Module *M) {
118   if (M->getDataLayoutStr().empty())
119     return make_error<StringError>("input module has no datalayout",
120                                    inconvertibleErrorCode());
121 
122   SmallVector<GlobalValue *, 4> UsedV;
123   collectUsedGlobalVariables(*M, UsedV, /*CompilerUsed=*/false);
124   SmallPtrSet<GlobalValue *, 4> Used(UsedV.begin(), UsedV.end());
125 
126   ModuleSymbolTable Msymtab;
127   Msymtab.addModule(M);
128 
129   storage::Module Mod;
130   Mod.Begin = Syms.size();
131   Mod.End = Syms.size() + Msymtab.symbols().size();
132   Mod.UncBegin = Uncommons.size();
133   Mods.push_back(Mod);
134 
135   if (TT.isOSBinFormatCOFF()) {
136     if (auto E = M->materializeMetadata())
137       return E;
138     if (NamedMDNode *LinkerOptions =
139             M->getNamedMetadata("llvm.linker.options")) {
140       for (MDNode *MDOptions : LinkerOptions->operands())
141         for (const MDOperand &MDOption : cast<MDNode>(MDOptions)->operands())
142           COFFLinkerOptsOS << " " << cast<MDString>(MDOption)->getString();
143     }
144   }
145 
146   if (TT.isOSBinFormatELF()) {
147     if (auto E = M->materializeMetadata())
148       return E;
149     if (NamedMDNode *N = M->getNamedMetadata("llvm.dependent-libraries")) {
150       for (MDNode *MDOptions : N->operands()) {
151         const auto OperandStr =
152             cast<MDString>(cast<MDNode>(MDOptions)->getOperand(0))->getString();
153         storage::Str Specifier;
154         setStr(Specifier, OperandStr);
155         DependentLibraries.emplace_back(Specifier);
156       }
157     }
158   }
159 
160   for (ModuleSymbolTable::Symbol Msym : Msymtab.symbols())
161     if (Error Err = addSymbol(Msymtab, Used, Msym))
162       return Err;
163 
164   return Error::success();
165 }
166 
167 Expected<int> Builder::getComdatIndex(const Comdat *C, const Module *M) {
168   auto P = ComdatMap.insert(std::make_pair(C, Comdats.size()));
169   if (P.second) {
170     std::string Name;
171     if (TT.isOSBinFormatCOFF()) {
172       const GlobalValue *GV = M->getNamedValue(C->getName());
173       if (!GV)
174         return make_error<StringError>("Could not find leader",
175                                        inconvertibleErrorCode());
176       // Internal leaders do not affect symbol resolution, therefore they do not
177       // appear in the symbol table.
178       if (GV->hasLocalLinkage()) {
179         P.first->second = -1;
180         return -1;
181       }
182       llvm::raw_string_ostream OS(Name);
183       Mang.getNameWithPrefix(OS, GV, false);
184     } else {
185       Name = std::string(C->getName());
186     }
187 
188     storage::Comdat Comdat;
189     setStr(Comdat.Name, Saver.save(Name));
190     Comdats.push_back(Comdat);
191   }
192 
193   return P.first->second;
194 }
195 
196 Error Builder::addSymbol(const ModuleSymbolTable &Msymtab,
197                          const SmallPtrSet<GlobalValue *, 4> &Used,
198                          ModuleSymbolTable::Symbol Msym) {
199   Syms.emplace_back();
200   storage::Symbol &Sym = Syms.back();
201   Sym = {};
202 
203   storage::Uncommon *Unc = nullptr;
204   auto Uncommon = [&]() -> storage::Uncommon & {
205     if (Unc)
206       return *Unc;
207     Sym.Flags |= 1 << storage::Symbol::FB_has_uncommon;
208     Uncommons.emplace_back();
209     Unc = &Uncommons.back();
210     *Unc = {};
211     setStr(Unc->COFFWeakExternFallbackName, "");
212     setStr(Unc->SectionName, "");
213     return *Unc;
214   };
215 
216   SmallString<64> Name;
217   {
218     raw_svector_ostream OS(Name);
219     Msymtab.printSymbolName(OS, Msym);
220   }
221   setStr(Sym.Name, Saver.save(StringRef(Name)));
222 
223   auto Flags = Msymtab.getSymbolFlags(Msym);
224   if (Flags & object::BasicSymbolRef::SF_Undefined)
225     Sym.Flags |= 1 << storage::Symbol::FB_undefined;
226   if (Flags & object::BasicSymbolRef::SF_Weak)
227     Sym.Flags |= 1 << storage::Symbol::FB_weak;
228   if (Flags & object::BasicSymbolRef::SF_Common)
229     Sym.Flags |= 1 << storage::Symbol::FB_common;
230   if (Flags & object::BasicSymbolRef::SF_Indirect)
231     Sym.Flags |= 1 << storage::Symbol::FB_indirect;
232   if (Flags & object::BasicSymbolRef::SF_Global)
233     Sym.Flags |= 1 << storage::Symbol::FB_global;
234   if (Flags & object::BasicSymbolRef::SF_FormatSpecific)
235     Sym.Flags |= 1 << storage::Symbol::FB_format_specific;
236   if (Flags & object::BasicSymbolRef::SF_Executable)
237     Sym.Flags |= 1 << storage::Symbol::FB_executable;
238 
239   Sym.ComdatIndex = -1;
240   auto *GV = Msym.dyn_cast<GlobalValue *>();
241   if (!GV) {
242     // Undefined module asm symbols act as GC roots and are implicitly used.
243     if (Flags & object::BasicSymbolRef::SF_Undefined)
244       Sym.Flags |= 1 << storage::Symbol::FB_used;
245     setStr(Sym.IRName, "");
246     return Error::success();
247   }
248 
249   setStr(Sym.IRName, GV->getName());
250 
251   bool IsBuiltinFunc = llvm::is_contained(LibcallRoutineNames, GV->getName());
252 
253   if (Used.count(GV) || IsBuiltinFunc)
254     Sym.Flags |= 1 << storage::Symbol::FB_used;
255   if (GV->isThreadLocal())
256     Sym.Flags |= 1 << storage::Symbol::FB_tls;
257   if (GV->hasGlobalUnnamedAddr())
258     Sym.Flags |= 1 << storage::Symbol::FB_unnamed_addr;
259   if (GV->canBeOmittedFromSymbolTable())
260     Sym.Flags |= 1 << storage::Symbol::FB_may_omit;
261   Sym.Flags |= unsigned(GV->getVisibility()) << storage::Symbol::FB_visibility;
262 
263   if (Flags & object::BasicSymbolRef::SF_Common) {
264     auto *GVar = dyn_cast<GlobalVariable>(GV);
265     if (!GVar)
266       return make_error<StringError>("Only variables can have common linkage!",
267                                      inconvertibleErrorCode());
268     Uncommon().CommonSize = GV->getParent()->getDataLayout().getTypeAllocSize(
269         GV->getType()->getElementType());
270     Uncommon().CommonAlign = GVar->getAlignment();
271   }
272 
273   const GlobalObject *Base = GV->getBaseObject();
274   if (!Base)
275     return make_error<StringError>("Unable to determine comdat of alias!",
276                                    inconvertibleErrorCode());
277   if (const Comdat *C = Base->getComdat()) {
278     Expected<int> ComdatIndexOrErr = getComdatIndex(C, GV->getParent());
279     if (!ComdatIndexOrErr)
280       return ComdatIndexOrErr.takeError();
281     Sym.ComdatIndex = *ComdatIndexOrErr;
282   }
283 
284   if (TT.isOSBinFormatCOFF()) {
285     emitLinkerFlagsForGlobalCOFF(COFFLinkerOptsOS, GV, TT, Mang);
286 
287     if ((Flags & object::BasicSymbolRef::SF_Weak) &&
288         (Flags & object::BasicSymbolRef::SF_Indirect)) {
289       auto *Fallback = dyn_cast<GlobalValue>(
290           cast<GlobalAlias>(GV)->getAliasee()->stripPointerCasts());
291       if (!Fallback)
292         return make_error<StringError>("Invalid weak external",
293                                        inconvertibleErrorCode());
294       std::string FallbackName;
295       raw_string_ostream OS(FallbackName);
296       Msymtab.printSymbolName(OS, Fallback);
297       OS.flush();
298       setStr(Uncommon().COFFWeakExternFallbackName, Saver.save(FallbackName));
299     }
300   }
301 
302   if (!Base->getSection().empty())
303     setStr(Uncommon().SectionName, Saver.save(Base->getSection()));
304 
305   return Error::success();
306 }
307 
308 Error Builder::build(ArrayRef<Module *> IRMods) {
309   storage::Header Hdr;
310 
311   assert(!IRMods.empty());
312   Hdr.Version = storage::Header::kCurrentVersion;
313   setStr(Hdr.Producer, kExpectedProducerName);
314   setStr(Hdr.TargetTriple, IRMods[0]->getTargetTriple());
315   setStr(Hdr.SourceFileName, IRMods[0]->getSourceFileName());
316   TT = Triple(IRMods[0]->getTargetTriple());
317 
318   for (auto *M : IRMods)
319     if (Error Err = addModule(M))
320       return Err;
321 
322   COFFLinkerOptsOS.flush();
323   setStr(Hdr.COFFLinkerOpts, Saver.save(COFFLinkerOpts));
324 
325   // We are about to fill in the header's range fields, so reserve space for it
326   // and copy it in afterwards.
327   Symtab.resize(sizeof(storage::Header));
328   writeRange(Hdr.Modules, Mods);
329   writeRange(Hdr.Comdats, Comdats);
330   writeRange(Hdr.Symbols, Syms);
331   writeRange(Hdr.Uncommons, Uncommons);
332   writeRange(Hdr.DependentLibraries, DependentLibraries);
333   *reinterpret_cast<storage::Header *>(Symtab.data()) = Hdr;
334   return Error::success();
335 }
336 
337 } // end anonymous namespace
338 
339 Error irsymtab::build(ArrayRef<Module *> Mods, SmallVector<char, 0> &Symtab,
340                       StringTableBuilder &StrtabBuilder,
341                       BumpPtrAllocator &Alloc) {
342   return Builder(Symtab, StrtabBuilder, Alloc).build(Mods);
343 }
344 
345 // Upgrade a vector of bitcode modules created by an old version of LLVM by
346 // creating an irsymtab for them in the current format.
347 static Expected<FileContents> upgrade(ArrayRef<BitcodeModule> BMs) {
348   FileContents FC;
349 
350   LLVMContext Ctx;
351   std::vector<Module *> Mods;
352   std::vector<std::unique_ptr<Module>> OwnedMods;
353   for (auto BM : BMs) {
354     Expected<std::unique_ptr<Module>> MOrErr =
355         BM.getLazyModule(Ctx, /*ShouldLazyLoadMetadata*/ true,
356                          /*IsImporting*/ false);
357     if (!MOrErr)
358       return MOrErr.takeError();
359 
360     Mods.push_back(MOrErr->get());
361     OwnedMods.push_back(std::move(*MOrErr));
362   }
363 
364   StringTableBuilder StrtabBuilder(StringTableBuilder::RAW);
365   BumpPtrAllocator Alloc;
366   if (Error E = build(Mods, FC.Symtab, StrtabBuilder, Alloc))
367     return std::move(E);
368 
369   StrtabBuilder.finalizeInOrder();
370   FC.Strtab.resize(StrtabBuilder.getSize());
371   StrtabBuilder.write((uint8_t *)FC.Strtab.data());
372 
373   FC.TheReader = {{FC.Symtab.data(), FC.Symtab.size()},
374                   {FC.Strtab.data(), FC.Strtab.size()}};
375   return std::move(FC);
376 }
377 
378 Expected<FileContents> irsymtab::readBitcode(const BitcodeFileContents &BFC) {
379   if (BFC.Mods.empty())
380     return make_error<StringError>("Bitcode file does not contain any modules",
381                                    inconvertibleErrorCode());
382 
383   if (BFC.StrtabForSymtab.empty() ||
384       BFC.Symtab.size() < sizeof(storage::Header))
385     return upgrade(BFC.Mods);
386 
387   // We cannot use the regular reader to read the version and producer, because
388   // it will expect the header to be in the current format. The only thing we
389   // can rely on is that the version and producer will be present as the first
390   // struct elements.
391   auto *Hdr = reinterpret_cast<const storage::Header *>(BFC.Symtab.data());
392   unsigned Version = Hdr->Version;
393   StringRef Producer = Hdr->Producer.get(BFC.StrtabForSymtab);
394   if (Version != storage::Header::kCurrentVersion ||
395       Producer != kExpectedProducerName)
396     return upgrade(BFC.Mods);
397 
398   FileContents FC;
399   FC.TheReader = {{BFC.Symtab.data(), BFC.Symtab.size()},
400                   {BFC.StrtabForSymtab.data(), BFC.StrtabForSymtab.size()}};
401 
402   // Finally, make sure that the number of modules in the symbol table matches
403   // the number of modules in the bitcode file. If they differ, it may mean that
404   // the bitcode file was created by binary concatenation, so we need to create
405   // a new symbol table from scratch.
406   if (FC.TheReader.getNumModules() != BFC.Mods.size())
407     return upgrade(std::move(BFC.Mods));
408 
409   return std::move(FC);
410 }
411