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/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 /// Stores the temporary state that is required to build an IR symbol table.
47 struct Builder {
48   SmallVector<char, 0> &Symtab;
49   StringTableBuilder &StrtabBuilder;
50   StringSaver Saver;
51 
52   // This ctor initializes a StringSaver using the passed in BumpPtrAllocator.
53   // The StringTableBuilder does not create a copy of any strings added to it,
54   // so this provides somewhere to store any strings that we create.
55   Builder(SmallVector<char, 0> &Symtab, StringTableBuilder &StrtabBuilder,
56           BumpPtrAllocator &Alloc)
57       : Symtab(Symtab), StrtabBuilder(StrtabBuilder), Saver(Alloc) {}
58 
59   DenseMap<const Comdat *, unsigned> ComdatMap;
60   Mangler Mang;
61   Triple TT;
62 
63   std::vector<storage::Comdat> Comdats;
64   std::vector<storage::Module> Mods;
65   std::vector<storage::Symbol> Syms;
66   std::vector<storage::Uncommon> Uncommons;
67 
68   std::string COFFLinkerOpts;
69   raw_string_ostream COFFLinkerOptsOS{COFFLinkerOpts};
70 
71   void setStr(storage::Str &S, StringRef Value) {
72     S.Offset = StrtabBuilder.add(Value);
73     S.Size = Value.size();
74   }
75 
76   template <typename T>
77   void writeRange(storage::Range<T> &R, const std::vector<T> &Objs) {
78     R.Offset = Symtab.size();
79     R.Size = Objs.size();
80     Symtab.insert(Symtab.end(), reinterpret_cast<const char *>(Objs.data()),
81                   reinterpret_cast<const char *>(Objs.data() + Objs.size()));
82   }
83 
84   Error addModule(Module *M);
85   Error addSymbol(const ModuleSymbolTable &Msymtab,
86                   const SmallPtrSet<GlobalValue *, 8> &Used,
87                   ModuleSymbolTable::Symbol Sym);
88 
89   Error build(ArrayRef<Module *> Mods);
90 };
91 
92 Error Builder::addModule(Module *M) {
93   if (M->getDataLayoutStr().empty())
94     return make_error<StringError>("input module has no datalayout",
95                                    inconvertibleErrorCode());
96 
97   SmallPtrSet<GlobalValue *, 8> Used;
98   collectUsedGlobalVariables(*M, Used, /*CompilerUsed*/ false);
99 
100   ModuleSymbolTable Msymtab;
101   Msymtab.addModule(M);
102 
103   storage::Module Mod;
104   Mod.Begin = Syms.size();
105   Mod.End = Syms.size() + Msymtab.symbols().size();
106   Mod.UncBegin = Uncommons.size();
107   Mods.push_back(Mod);
108 
109   if (TT.isOSBinFormatCOFF()) {
110     if (auto E = M->materializeMetadata())
111       return E;
112     if (NamedMDNode *LinkerOptions =
113             M->getNamedMetadata("llvm.linker.options")) {
114       for (MDNode *MDOptions : LinkerOptions->operands())
115         for (const MDOperand &MDOption : cast<MDNode>(MDOptions)->operands())
116           COFFLinkerOptsOS << " " << cast<MDString>(MDOption)->getString();
117     }
118   }
119 
120   for (ModuleSymbolTable::Symbol Msym : Msymtab.symbols())
121     if (Error Err = addSymbol(Msymtab, Used, Msym))
122       return Err;
123 
124   return Error::success();
125 }
126 
127 Error Builder::addSymbol(const ModuleSymbolTable &Msymtab,
128                          const SmallPtrSet<GlobalValue *, 8> &Used,
129                          ModuleSymbolTable::Symbol Msym) {
130   Syms.emplace_back();
131   storage::Symbol &Sym = Syms.back();
132   Sym = {};
133 
134   storage::Uncommon *Unc = nullptr;
135   auto Uncommon = [&]() -> storage::Uncommon & {
136     if (Unc)
137       return *Unc;
138     Sym.Flags |= 1 << storage::Symbol::FB_has_uncommon;
139     Uncommons.emplace_back();
140     Unc = &Uncommons.back();
141     *Unc = {};
142     setStr(Unc->COFFWeakExternFallbackName, "");
143     return *Unc;
144   };
145 
146   SmallString<64> Name;
147   {
148     raw_svector_ostream OS(Name);
149     Msymtab.printSymbolName(OS, Msym);
150   }
151   setStr(Sym.Name, Saver.save(StringRef(Name)));
152 
153   auto Flags = Msymtab.getSymbolFlags(Msym);
154   if (Flags & object::BasicSymbolRef::SF_Undefined)
155     Sym.Flags |= 1 << storage::Symbol::FB_undefined;
156   if (Flags & object::BasicSymbolRef::SF_Weak)
157     Sym.Flags |= 1 << storage::Symbol::FB_weak;
158   if (Flags & object::BasicSymbolRef::SF_Common)
159     Sym.Flags |= 1 << storage::Symbol::FB_common;
160   if (Flags & object::BasicSymbolRef::SF_Indirect)
161     Sym.Flags |= 1 << storage::Symbol::FB_indirect;
162   if (Flags & object::BasicSymbolRef::SF_Global)
163     Sym.Flags |= 1 << storage::Symbol::FB_global;
164   if (Flags & object::BasicSymbolRef::SF_FormatSpecific)
165     Sym.Flags |= 1 << storage::Symbol::FB_format_specific;
166   if (Flags & object::BasicSymbolRef::SF_Executable)
167     Sym.Flags |= 1 << storage::Symbol::FB_executable;
168 
169   Sym.ComdatIndex = -1;
170   auto *GV = Msym.dyn_cast<GlobalValue *>();
171   if (!GV) {
172     // Undefined module asm symbols act as GC roots and are implicitly used.
173     if (Flags & object::BasicSymbolRef::SF_Undefined)
174       Sym.Flags |= 1 << storage::Symbol::FB_used;
175     setStr(Sym.IRName, "");
176     return Error::success();
177   }
178 
179   setStr(Sym.IRName, GV->getName());
180 
181   if (Used.count(GV))
182     Sym.Flags |= 1 << storage::Symbol::FB_used;
183   if (GV->isThreadLocal())
184     Sym.Flags |= 1 << storage::Symbol::FB_tls;
185   if (GV->hasGlobalUnnamedAddr())
186     Sym.Flags |= 1 << storage::Symbol::FB_unnamed_addr;
187   if (canBeOmittedFromSymbolTable(GV))
188     Sym.Flags |= 1 << storage::Symbol::FB_may_omit;
189   Sym.Flags |= unsigned(GV->getVisibility()) << storage::Symbol::FB_visibility;
190 
191   if (Flags & object::BasicSymbolRef::SF_Common) {
192     Uncommon().CommonSize = GV->getParent()->getDataLayout().getTypeAllocSize(
193         GV->getType()->getElementType());
194     Uncommon().CommonAlign = GV->getAlignment();
195   }
196 
197   const GlobalObject *Base = GV->getBaseObject();
198   if (!Base)
199     return make_error<StringError>("Unable to determine comdat of alias!",
200                                    inconvertibleErrorCode());
201   if (const Comdat *C = Base->getComdat()) {
202     auto P = ComdatMap.insert(std::make_pair(C, Comdats.size()));
203     Sym.ComdatIndex = P.first->second;
204 
205     if (P.second) {
206       storage::Comdat Comdat;
207       setStr(Comdat.Name, C->getName());
208       Comdats.push_back(Comdat);
209     }
210   }
211 
212   if (TT.isOSBinFormatCOFF()) {
213     emitLinkerFlagsForGlobalCOFF(COFFLinkerOptsOS, GV, TT, Mang);
214 
215     if ((Flags & object::BasicSymbolRef::SF_Weak) &&
216         (Flags & object::BasicSymbolRef::SF_Indirect)) {
217       std::string FallbackName;
218       raw_string_ostream OS(FallbackName);
219       Msymtab.printSymbolName(
220           OS, cast<GlobalValue>(
221                   cast<GlobalAlias>(GV)->getAliasee()->stripPointerCasts()));
222       OS.flush();
223       setStr(Uncommon().COFFWeakExternFallbackName, Saver.save(FallbackName));
224     }
225   }
226 
227   return Error::success();
228 }
229 
230 Error Builder::build(ArrayRef<Module *> IRMods) {
231   storage::Header Hdr;
232 
233   assert(!IRMods.empty());
234   setStr(Hdr.TargetTriple, IRMods[0]->getTargetTriple());
235   setStr(Hdr.SourceFileName, IRMods[0]->getSourceFileName());
236   TT = Triple(IRMods[0]->getTargetTriple());
237 
238   for (auto *M : IRMods)
239     if (Error Err = addModule(M))
240       return Err;
241 
242   COFFLinkerOptsOS.flush();
243   setStr(Hdr.COFFLinkerOpts, Saver.save(COFFLinkerOpts));
244 
245   // We are about to fill in the header's range fields, so reserve space for it
246   // and copy it in afterwards.
247   Symtab.resize(sizeof(storage::Header));
248   writeRange(Hdr.Modules, Mods);
249   writeRange(Hdr.Comdats, Comdats);
250   writeRange(Hdr.Symbols, Syms);
251   writeRange(Hdr.Uncommons, Uncommons);
252 
253   *reinterpret_cast<storage::Header *>(Symtab.data()) = Hdr;
254   return Error::success();
255 }
256 
257 } // end anonymous namespace
258 
259 Error irsymtab::build(ArrayRef<Module *> Mods, SmallVector<char, 0> &Symtab,
260                       StringTableBuilder &StrtabBuilder,
261                       BumpPtrAllocator &Alloc) {
262   return Builder(Symtab, StrtabBuilder, Alloc).build(Mods);
263 }
264 
265 // Upgrade a vector of bitcode modules created by an old version of LLVM by
266 // creating an irsymtab for them in the current format.
267 static Expected<FileContents> upgrade(ArrayRef<BitcodeModule> BMs) {
268   FileContents FC;
269 
270   LLVMContext Ctx;
271   std::vector<Module *> Mods;
272   std::vector<std::unique_ptr<Module>> OwnedMods;
273   for (auto BM : BMs) {
274     Expected<std::unique_ptr<Module>> MOrErr =
275         BM.getLazyModule(Ctx, /*ShouldLazyLoadMetadata*/ true,
276                          /*IsImporting*/ false);
277     if (!MOrErr)
278       return MOrErr.takeError();
279 
280     Mods.push_back(MOrErr->get());
281     OwnedMods.push_back(std::move(*MOrErr));
282   }
283 
284   StringTableBuilder StrtabBuilder(StringTableBuilder::RAW);
285   BumpPtrAllocator Alloc;
286   if (Error E = build(Mods, FC.Symtab, StrtabBuilder, Alloc))
287     return std::move(E);
288 
289   StrtabBuilder.finalizeInOrder();
290   FC.Strtab.resize(StrtabBuilder.getSize());
291   StrtabBuilder.write((uint8_t *)FC.Strtab.data());
292 
293   FC.TheReader = {{FC.Symtab.data(), FC.Symtab.size()},
294                   {FC.Strtab.data(), FC.Strtab.size()}};
295   return std::move(FC);
296 }
297 
298 Expected<FileContents> irsymtab::readBitcode(const BitcodeFileContents &BFC) {
299   if (BFC.Mods.empty())
300     return make_error<StringError>("Bitcode file does not contain any modules",
301                                    inconvertibleErrorCode());
302 
303   // Right now we have no on-disk representation of symbol tables, so we always
304   // upgrade.
305   return upgrade(BFC.Mods);
306 }
307