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   SmallVector<char, 0> &Strtab;
50 
51   Builder(SmallVector<char, 0> &Symtab, SmallVector<char, 0> &Strtab)
52       : Symtab(Symtab), Strtab(Strtab) {}
53 
54   StringTableBuilder StrtabBuilder{StringTableBuilder::RAW};
55 
56   BumpPtrAllocator Alloc;
57   StringSaver 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   SmallPtrSet<GlobalValue *, 8> Used;
94   collectUsedGlobalVariables(*M, Used, /*CompilerUsed*/ false);
95 
96   ModuleSymbolTable Msymtab;
97   Msymtab.addModule(M);
98 
99   storage::Module Mod;
100   Mod.Begin = Syms.size();
101   Mod.End = Syms.size() + Msymtab.symbols().size();
102   Mod.UncBegin = Uncommons.size();
103   Mods.push_back(Mod);
104 
105   if (TT.isOSBinFormatCOFF()) {
106     if (auto E = M->materializeMetadata())
107       return E;
108     if (Metadata *Val = M->getModuleFlag("Linker Options")) {
109       MDNode *LinkerOptions = cast<MDNode>(Val);
110       for (const MDOperand &MDOptions : LinkerOptions->operands())
111         for (const MDOperand &MDOption : cast<MDNode>(MDOptions)->operands())
112           COFFLinkerOptsOS << " " << cast<MDString>(MDOption)->getString();
113     }
114   }
115 
116   for (ModuleSymbolTable::Symbol Msym : Msymtab.symbols())
117     if (Error Err = addSymbol(Msymtab, Used, Msym))
118       return Err;
119 
120   return Error::success();
121 }
122 
123 Error Builder::addSymbol(const ModuleSymbolTable &Msymtab,
124                          const SmallPtrSet<GlobalValue *, 8> &Used,
125                          ModuleSymbolTable::Symbol Msym) {
126   Syms.emplace_back();
127   storage::Symbol &Sym = Syms.back();
128   Sym = {};
129 
130   storage::Uncommon *Unc = nullptr;
131   auto Uncommon = [&]() -> storage::Uncommon & {
132     if (Unc)
133       return *Unc;
134     Sym.Flags |= 1 << storage::Symbol::FB_has_uncommon;
135     Uncommons.emplace_back();
136     Unc = &Uncommons.back();
137     *Unc = {};
138     setStr(Unc->COFFWeakExternFallbackName, "");
139     return *Unc;
140   };
141 
142   SmallString<64> Name;
143   {
144     raw_svector_ostream OS(Name);
145     Msymtab.printSymbolName(OS, Msym);
146   }
147   setStr(Sym.Name, Saver.save(StringRef(Name)));
148 
149   auto Flags = Msymtab.getSymbolFlags(Msym);
150   if (Flags & object::BasicSymbolRef::SF_Undefined)
151     Sym.Flags |= 1 << storage::Symbol::FB_undefined;
152   if (Flags & object::BasicSymbolRef::SF_Weak)
153     Sym.Flags |= 1 << storage::Symbol::FB_weak;
154   if (Flags & object::BasicSymbolRef::SF_Common)
155     Sym.Flags |= 1 << storage::Symbol::FB_common;
156   if (Flags & object::BasicSymbolRef::SF_Indirect)
157     Sym.Flags |= 1 << storage::Symbol::FB_indirect;
158   if (Flags & object::BasicSymbolRef::SF_Global)
159     Sym.Flags |= 1 << storage::Symbol::FB_global;
160   if (Flags & object::BasicSymbolRef::SF_FormatSpecific)
161     Sym.Flags |= 1 << storage::Symbol::FB_format_specific;
162   if (Flags & object::BasicSymbolRef::SF_Executable)
163     Sym.Flags |= 1 << storage::Symbol::FB_executable;
164 
165   Sym.ComdatIndex = -1;
166   auto *GV = Msym.dyn_cast<GlobalValue *>();
167   if (!GV) {
168     // Undefined module asm symbols act as GC roots and are implicitly used.
169     if (Flags & object::BasicSymbolRef::SF_Undefined)
170       Sym.Flags |= 1 << storage::Symbol::FB_used;
171     setStr(Sym.IRName, "");
172     return Error::success();
173   }
174 
175   setStr(Sym.IRName, GV->getName());
176 
177   if (Used.count(GV))
178     Sym.Flags |= 1 << storage::Symbol::FB_used;
179   if (GV->isThreadLocal())
180     Sym.Flags |= 1 << storage::Symbol::FB_tls;
181   if (GV->hasGlobalUnnamedAddr())
182     Sym.Flags |= 1 << storage::Symbol::FB_unnamed_addr;
183   if (canBeOmittedFromSymbolTable(GV))
184     Sym.Flags |= 1 << storage::Symbol::FB_may_omit;
185   Sym.Flags |= unsigned(GV->getVisibility()) << storage::Symbol::FB_visibility;
186 
187   if (Flags & object::BasicSymbolRef::SF_Common) {
188     Uncommon().CommonSize = GV->getParent()->getDataLayout().getTypeAllocSize(
189         GV->getType()->getElementType());
190     Uncommon().CommonAlign = GV->getAlignment();
191   }
192 
193   const GlobalObject *Base = GV->getBaseObject();
194   if (!Base)
195     return make_error<StringError>("Unable to determine comdat of alias!",
196                                    inconvertibleErrorCode());
197   if (const Comdat *C = Base->getComdat()) {
198     auto P = ComdatMap.insert(std::make_pair(C, Comdats.size()));
199     Sym.ComdatIndex = P.first->second;
200 
201     if (P.second) {
202       storage::Comdat Comdat;
203       setStr(Comdat.Name, C->getName());
204       Comdats.push_back(Comdat);
205     }
206   }
207 
208   if (TT.isOSBinFormatCOFF()) {
209     emitLinkerFlagsForGlobalCOFF(COFFLinkerOptsOS, GV, TT, Mang);
210 
211     if ((Flags & object::BasicSymbolRef::SF_Weak) &&
212         (Flags & object::BasicSymbolRef::SF_Indirect)) {
213       std::string FallbackName;
214       raw_string_ostream OS(FallbackName);
215       Msymtab.printSymbolName(
216           OS, cast<GlobalValue>(
217                   cast<GlobalAlias>(GV)->getAliasee()->stripPointerCasts()));
218       OS.flush();
219       setStr(Uncommon().COFFWeakExternFallbackName, Saver.save(FallbackName));
220     }
221   }
222 
223   return Error::success();
224 }
225 
226 Error Builder::build(ArrayRef<Module *> IRMods) {
227   storage::Header Hdr;
228 
229   assert(!IRMods.empty());
230   setStr(Hdr.TargetTriple, IRMods[0]->getTargetTriple());
231   setStr(Hdr.SourceFileName, IRMods[0]->getSourceFileName());
232   TT = Triple(IRMods[0]->getTargetTriple());
233 
234   for (auto *M : IRMods)
235     if (Error Err = addModule(M))
236       return Err;
237 
238   COFFLinkerOptsOS.flush();
239   setStr(Hdr.COFFLinkerOpts, COFFLinkerOpts);
240 
241   // We are about to fill in the header's range fields, so reserve space for it
242   // and copy it in afterwards.
243   Symtab.resize(sizeof(storage::Header));
244   writeRange(Hdr.Modules, Mods);
245   writeRange(Hdr.Comdats, Comdats);
246   writeRange(Hdr.Symbols, Syms);
247   writeRange(Hdr.Uncommons, Uncommons);
248 
249   *reinterpret_cast<storage::Header *>(Symtab.data()) = Hdr;
250 
251   raw_svector_ostream OS(Strtab);
252   StrtabBuilder.finalizeInOrder();
253   StrtabBuilder.write(OS);
254 
255   return Error::success();
256 }
257 
258 } // end anonymous namespace
259 
260 Error irsymtab::build(ArrayRef<Module *> Mods, SmallVector<char, 0> &Symtab,
261                       SmallVector<char, 0> &Strtab) {
262   return Builder(Symtab, Strtab).build(Mods);
263 }
264 
265 Expected<FileContents> irsymtab::readBitcode(ArrayRef<BitcodeModule> BMs) {
266   FileContents FC;
267   if (BMs.empty())
268     return make_error<StringError>("Bitcode file does not contain any modules",
269                                    inconvertibleErrorCode());
270 
271   LLVMContext Ctx;
272   std::vector<Module *> Mods;
273   std::vector<std::unique_ptr<Module>> OwnedMods;
274   for (auto BM : BMs) {
275     Expected<std::unique_ptr<Module>> MOrErr =
276         BM.getLazyModule(Ctx, /*ShouldLazyLoadMetadata*/ true,
277                          /*IsImporting*/ false);
278     if (!MOrErr)
279       return MOrErr.takeError();
280 
281     if ((*MOrErr)->getDataLayoutStr().empty())
282       return make_error<StringError>("input module has no datalayout",
283                                      inconvertibleErrorCode());
284 
285     Mods.push_back(MOrErr->get());
286     OwnedMods.push_back(std::move(*MOrErr));
287   }
288 
289   if (Error E = build(Mods, FC.Symtab, FC.Strtab))
290     return std::move(E);
291 
292   FC.TheReader = {{FC.Symtab.data(), FC.Symtab.size()},
293                   {FC.Strtab.data(), FC.Strtab.size()}};
294   return std::move(FC);
295 }
296