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/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/Analysis/ObjectUtils.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/MC/StringTableBuilder.h"
26 #include "llvm/Object/IRSymtab.h"
27 #include "llvm/Object/ModuleSymbolTable.h"
28 #include "llvm/Object/SymbolicFile.h"
29 #include "llvm/Support/Allocator.h"
30 #include "llvm/Support/Casting.h"
31 #include "llvm/Support/Error.h"
32 #include "llvm/Support/raw_ostream.h"
33 #include "llvm/Support/StringSaver.h"
34 #include <cassert>
35 #include <string>
36 #include <utility>
37 #include <vector>
38 
39 using namespace llvm;
40 using namespace irsymtab;
41 
42 namespace {
43 
44 /// Stores the temporary state that is required to build an IR symbol table.
45 struct Builder {
46   SmallVector<char, 0> &Symtab;
47   SmallVector<char, 0> &Strtab;
48 
49   Builder(SmallVector<char, 0> &Symtab, SmallVector<char, 0> &Strtab)
50       : Symtab(Symtab), Strtab(Strtab) {}
51 
52   StringTableBuilder StrtabBuilder{StringTableBuilder::RAW};
53 
54   BumpPtrAllocator Alloc;
55   StringSaver Saver{Alloc};
56 
57   DenseMap<const Comdat *, unsigned> ComdatMap;
58   Mangler Mang;
59   Triple TT;
60 
61   std::vector<storage::Comdat> Comdats;
62   std::vector<storage::Module> Mods;
63   std::vector<storage::Symbol> Syms;
64   std::vector<storage::Uncommon> Uncommons;
65 
66   std::string COFFLinkerOpts;
67   raw_string_ostream COFFLinkerOptsOS{COFFLinkerOpts};
68 
69   void setStr(storage::Str &S, StringRef Value) {
70     S.Offset = StrtabBuilder.add(Value);
71     S.Size = Value.size();
72   }
73 
74   template <typename T>
75   void writeRange(storage::Range<T> &R, const std::vector<T> &Objs) {
76     R.Offset = Symtab.size();
77     R.Size = Objs.size();
78     Symtab.insert(Symtab.end(), reinterpret_cast<const char *>(Objs.data()),
79                   reinterpret_cast<const char *>(Objs.data() + Objs.size()));
80   }
81 
82   Error addModule(Module *M);
83   Error addSymbol(const ModuleSymbolTable &Msymtab,
84                   const SmallPtrSet<GlobalValue *, 8> &Used,
85                   ModuleSymbolTable::Symbol Sym);
86 
87   Error build(ArrayRef<Module *> Mods);
88 };
89 
90 Error Builder::addModule(Module *M) {
91   SmallPtrSet<GlobalValue *, 8> Used;
92   collectUsedGlobalVariables(*M, Used, /*CompilerUsed*/ false);
93 
94   ModuleSymbolTable Msymtab;
95   Msymtab.addModule(M);
96 
97   storage::Module Mod;
98   Mod.Begin = Syms.size();
99   Mod.End = Syms.size() + Msymtab.symbols().size();
100   Mod.UncBegin = Uncommons.size();
101   Mods.push_back(Mod);
102 
103   if (TT.isOSBinFormatCOFF()) {
104     if (auto E = M->materializeMetadata())
105       return E;
106     if (Metadata *Val = M->getModuleFlag("Linker Options")) {
107       MDNode *LinkerOptions = cast<MDNode>(Val);
108       for (const MDOperand &MDOptions : LinkerOptions->operands())
109         for (const MDOperand &MDOption : cast<MDNode>(MDOptions)->operands())
110           COFFLinkerOptsOS << " " << cast<MDString>(MDOption)->getString();
111     }
112   }
113 
114   for (ModuleSymbolTable::Symbol Msym : Msymtab.symbols())
115     if (Error Err = addSymbol(Msymtab, Used, Msym))
116       return Err;
117 
118   return Error::success();
119 }
120 
121 Error Builder::addSymbol(const ModuleSymbolTable &Msymtab,
122                          const SmallPtrSet<GlobalValue *, 8> &Used,
123                          ModuleSymbolTable::Symbol Msym) {
124   Syms.emplace_back();
125   storage::Symbol &Sym = Syms.back();
126   Sym = {};
127 
128   storage::Uncommon *Unc = nullptr;
129   auto Uncommon = [&]() -> storage::Uncommon & {
130     if (Unc)
131       return *Unc;
132     Sym.Flags |= 1 << storage::Symbol::FB_has_uncommon;
133     Uncommons.emplace_back();
134     Unc = &Uncommons.back();
135     *Unc = {};
136     setStr(Unc->COFFWeakExternFallbackName, "");
137     return *Unc;
138   };
139 
140   SmallString<64> Name;
141   {
142     raw_svector_ostream OS(Name);
143     Msymtab.printSymbolName(OS, Msym);
144   }
145   setStr(Sym.Name, Saver.save(StringRef(Name)));
146 
147   auto Flags = Msymtab.getSymbolFlags(Msym);
148   if (Flags & object::BasicSymbolRef::SF_Undefined)
149     Sym.Flags |= 1 << storage::Symbol::FB_undefined;
150   if (Flags & object::BasicSymbolRef::SF_Weak)
151     Sym.Flags |= 1 << storage::Symbol::FB_weak;
152   if (Flags & object::BasicSymbolRef::SF_Common)
153     Sym.Flags |= 1 << storage::Symbol::FB_common;
154   if (Flags & object::BasicSymbolRef::SF_Indirect)
155     Sym.Flags |= 1 << storage::Symbol::FB_indirect;
156   if (Flags & object::BasicSymbolRef::SF_Global)
157     Sym.Flags |= 1 << storage::Symbol::FB_global;
158   if (Flags & object::BasicSymbolRef::SF_FormatSpecific)
159     Sym.Flags |= 1 << storage::Symbol::FB_format_specific;
160   if (Flags & object::BasicSymbolRef::SF_Executable)
161     Sym.Flags |= 1 << storage::Symbol::FB_executable;
162 
163   Sym.ComdatIndex = -1;
164   auto *GV = Msym.dyn_cast<GlobalValue *>();
165   if (!GV) {
166     // Undefined module asm symbols act as GC roots and are implicitly used.
167     if (Flags & object::BasicSymbolRef::SF_Undefined)
168       Sym.Flags |= 1 << storage::Symbol::FB_used;
169     setStr(Sym.IRName, "");
170     return Error::success();
171   }
172 
173   setStr(Sym.IRName, GV->getName());
174 
175   if (Used.count(GV))
176     Sym.Flags |= 1 << storage::Symbol::FB_used;
177   if (GV->isThreadLocal())
178     Sym.Flags |= 1 << storage::Symbol::FB_tls;
179   if (GV->hasGlobalUnnamedAddr())
180     Sym.Flags |= 1 << storage::Symbol::FB_unnamed_addr;
181   if (canBeOmittedFromSymbolTable(GV))
182     Sym.Flags |= 1 << storage::Symbol::FB_may_omit;
183   Sym.Flags |= unsigned(GV->getVisibility()) << storage::Symbol::FB_visibility;
184 
185   if (Flags & object::BasicSymbolRef::SF_Common) {
186     Uncommon().CommonSize = GV->getParent()->getDataLayout().getTypeAllocSize(
187         GV->getType()->getElementType());
188     Uncommon().CommonAlign = GV->getAlignment();
189   }
190 
191   const GlobalObject *Base = GV->getBaseObject();
192   if (!Base)
193     return make_error<StringError>("Unable to determine comdat of alias!",
194                                    inconvertibleErrorCode());
195   if (const Comdat *C = Base->getComdat()) {
196     auto P = ComdatMap.insert(std::make_pair(C, Comdats.size()));
197     Sym.ComdatIndex = P.first->second;
198 
199     if (P.second) {
200       storage::Comdat Comdat;
201       setStr(Comdat.Name, C->getName());
202       Comdats.push_back(Comdat);
203     }
204   }
205 
206   if (TT.isOSBinFormatCOFF()) {
207     emitLinkerFlagsForGlobalCOFF(COFFLinkerOptsOS, GV, TT, Mang);
208 
209     if ((Flags & object::BasicSymbolRef::SF_Weak) &&
210         (Flags & object::BasicSymbolRef::SF_Indirect)) {
211       std::string FallbackName;
212       raw_string_ostream OS(FallbackName);
213       Msymtab.printSymbolName(
214           OS, cast<GlobalValue>(
215                   cast<GlobalAlias>(GV)->getAliasee()->stripPointerCasts()));
216       OS.flush();
217       setStr(Uncommon().COFFWeakExternFallbackName, Saver.save(FallbackName));
218     }
219   }
220 
221   return Error::success();
222 }
223 
224 Error Builder::build(ArrayRef<Module *> IRMods) {
225   storage::Header Hdr;
226 
227   assert(!IRMods.empty());
228   setStr(Hdr.TargetTriple, IRMods[0]->getTargetTriple());
229   setStr(Hdr.SourceFileName, IRMods[0]->getSourceFileName());
230   TT = Triple(IRMods[0]->getTargetTriple());
231 
232   for (auto *M : IRMods)
233     if (Error Err = addModule(M))
234       return Err;
235 
236   COFFLinkerOptsOS.flush();
237   setStr(Hdr.COFFLinkerOpts, COFFLinkerOpts);
238 
239   // We are about to fill in the header's range fields, so reserve space for it
240   // and copy it in afterwards.
241   Symtab.resize(sizeof(storage::Header));
242   writeRange(Hdr.Modules, Mods);
243   writeRange(Hdr.Comdats, Comdats);
244   writeRange(Hdr.Symbols, Syms);
245   writeRange(Hdr.Uncommons, Uncommons);
246 
247   *reinterpret_cast<storage::Header *>(Symtab.data()) = Hdr;
248 
249   raw_svector_ostream OS(Strtab);
250   StrtabBuilder.finalizeInOrder();
251   StrtabBuilder.write(OS);
252 
253   return Error::success();
254 }
255 
256 } // end anonymous namespace
257 
258 Error irsymtab::build(ArrayRef<Module *> Mods, SmallVector<char, 0> &Symtab,
259                       SmallVector<char, 0> &Strtab) {
260   return Builder(Symtab, Strtab).build(Mods);
261 }
262