1 //===- IRSymtab.cpp - implementation of IR symbol tables --------*- C++ -*-===//
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/Analysis/ObjectUtils.h"
12 #include "llvm/IR/Mangler.h"
13 #include "llvm/IR/Module.h"
14 #include "llvm/MC/StringTableBuilder.h"
15 #include "llvm/Object/ModuleSymbolTable.h"
16 #include "llvm/Support/Allocator.h"
17 #include "llvm/Support/StringSaver.h"
18 
19 using namespace llvm;
20 using namespace irsymtab;
21 
22 namespace {
23 
24 /// Stores the temporary state that is required to build an IR symbol table.
25 struct Builder {
26   SmallVector<char, 0> &Symtab;
27   SmallVector<char, 0> &Strtab;
28   Builder(SmallVector<char, 0> &Symtab, SmallVector<char, 0> &Strtab)
29       : Symtab(Symtab), Strtab(Strtab) {}
30 
31   StringTableBuilder StrtabBuilder{StringTableBuilder::ELF};
32 
33   BumpPtrAllocator Alloc;
34   StringSaver Saver{Alloc};
35 
36   DenseMap<const Comdat *, unsigned> ComdatMap;
37   ModuleSymbolTable Msymtab;
38   SmallPtrSet<GlobalValue *, 8> Used;
39   Mangler Mang;
40   Triple TT;
41 
42   std::vector<storage::Comdat> Comdats;
43   std::vector<storage::Module> Mods;
44   std::vector<storage::Symbol> Syms;
45   std::vector<storage::Uncommon> Uncommons;
46 
47   std::string COFFLinkerOpts;
48   raw_string_ostream COFFLinkerOptsOS{COFFLinkerOpts};
49 
50   void setStr(storage::Str &S, StringRef Value) {
51     S.Offset = StrtabBuilder.add(Value);
52   }
53   template <typename T>
54   void writeRange(storage::Range<T> &R, const std::vector<T> &Objs) {
55     R.Offset = Symtab.size();
56     R.Size = Objs.size();
57     Symtab.insert(Symtab.end(), reinterpret_cast<const char *>(Objs.data()),
58                   reinterpret_cast<const char *>(Objs.data() + Objs.size()));
59   }
60 
61   Error addModule(Module *M);
62   Error addSymbol(ModuleSymbolTable::Symbol Sym);
63 
64   Error build(ArrayRef<Module *> Mods);
65 };
66 
67 Error Builder::addModule(Module *M) {
68   collectUsedGlobalVariables(*M, Used, /*CompilerUsed*/ false);
69 
70   storage::Module Mod;
71   Mod.Begin = Msymtab.symbols().size();
72   Msymtab.addModule(M);
73   Mod.End = Msymtab.symbols().size();
74   Mods.push_back(Mod);
75 
76   if (TT.isOSBinFormatCOFF()) {
77     if (auto E = M->materializeMetadata())
78       return E;
79     if (Metadata *Val = M->getModuleFlag("Linker Options")) {
80       MDNode *LinkerOptions = cast<MDNode>(Val);
81       for (const MDOperand &MDOptions : LinkerOptions->operands())
82         for (const MDOperand &MDOption : cast<MDNode>(MDOptions)->operands())
83           COFFLinkerOptsOS << " " << cast<MDString>(MDOption)->getString();
84     }
85   }
86 
87   return Error::success();
88 }
89 
90 Error Builder::addSymbol(ModuleSymbolTable::Symbol Msym) {
91   Syms.emplace_back();
92   storage::Symbol &Sym = Syms.back();
93   Sym = {};
94 
95   Sym.UncommonIndex = -1;
96   storage::Uncommon *Unc = nullptr;
97   auto Uncommon = [&]() -> storage::Uncommon & {
98     if (Unc)
99       return *Unc;
100     Sym.UncommonIndex = Uncommons.size();
101     Uncommons.emplace_back();
102     Unc = &Uncommons.back();
103     *Unc = {};
104     setStr(Unc->COFFWeakExternFallbackName, "");
105     return *Unc;
106   };
107 
108   SmallString<64> Name;
109   {
110     raw_svector_ostream OS(Name);
111     Msymtab.printSymbolName(OS, Msym);
112   }
113   setStr(Sym.Name, Saver.save(StringRef(Name)));
114 
115   auto Flags = Msymtab.getSymbolFlags(Msym);
116   if (Flags & object::BasicSymbolRef::SF_Undefined)
117     Sym.Flags |= 1 << storage::Symbol::FB_undefined;
118   if (Flags & object::BasicSymbolRef::SF_Weak)
119     Sym.Flags |= 1 << storage::Symbol::FB_weak;
120   if (Flags & object::BasicSymbolRef::SF_Common)
121     Sym.Flags |= 1 << storage::Symbol::FB_common;
122   if (Flags & object::BasicSymbolRef::SF_Indirect)
123     Sym.Flags |= 1 << storage::Symbol::FB_indirect;
124   if (Flags & object::BasicSymbolRef::SF_Global)
125     Sym.Flags |= 1 << storage::Symbol::FB_global;
126   if (Flags & object::BasicSymbolRef::SF_FormatSpecific)
127     Sym.Flags |= 1 << storage::Symbol::FB_format_specific;
128 
129   Sym.ComdatIndex = -1;
130   auto *GV = Msym.dyn_cast<GlobalValue *>();
131   if (!GV) {
132     setStr(Sym.IRName, "");
133     return Error::success();
134   }
135 
136   setStr(Sym.IRName, GV->getName());
137 
138   if (Used.count(GV))
139     Sym.Flags |= 1 << storage::Symbol::FB_used;
140   if (GV->isThreadLocal())
141     Sym.Flags |= 1 << storage::Symbol::FB_tls;
142   if (GV->hasGlobalUnnamedAddr())
143     Sym.Flags |= 1 << storage::Symbol::FB_unnamed_addr;
144   if (canBeOmittedFromSymbolTable(GV))
145     Sym.Flags |= 1 << storage::Symbol::FB_may_omit;
146   Sym.Flags |= unsigned(GV->getVisibility()) << storage::Symbol::FB_visibility;
147 
148   if (Flags & object::BasicSymbolRef::SF_Common) {
149     Uncommon().CommonSize = GV->getParent()->getDataLayout().getTypeAllocSize(
150         GV->getType()->getElementType());
151     Uncommon().CommonAlign = GV->getAlignment();
152   }
153 
154   const GlobalObject *Base = GV->getBaseObject();
155   if (!Base)
156     return make_error<StringError>("Unable to determine comdat of alias!",
157                                    inconvertibleErrorCode());
158   if (const Comdat *C = Base->getComdat()) {
159     auto P = ComdatMap.insert(std::make_pair(C, Comdats.size()));
160     Sym.ComdatIndex = P.first->second;
161 
162     if (P.second) {
163       storage::Comdat Comdat;
164       setStr(Comdat.Name, C->getName());
165       Comdats.push_back(Comdat);
166     }
167   }
168 
169   if (TT.isOSBinFormatCOFF()) {
170     emitLinkerFlagsForGlobalCOFF(COFFLinkerOptsOS, GV, TT, Mang);
171 
172     if ((Flags & object::BasicSymbolRef::SF_Weak) &&
173         (Flags & object::BasicSymbolRef::SF_Indirect)) {
174       std::string FallbackName;
175       raw_string_ostream OS(FallbackName);
176       Msymtab.printSymbolName(
177           OS, cast<GlobalValue>(
178                   cast<GlobalAlias>(GV)->getAliasee()->stripPointerCasts()));
179       OS.flush();
180       setStr(Uncommon().COFFWeakExternFallbackName, Saver.save(FallbackName));
181     }
182   }
183 
184   return Error::success();
185 }
186 
187 Error Builder::build(ArrayRef<Module *> IRMods) {
188   storage::Header Hdr;
189 
190   assert(!IRMods.empty());
191   setStr(Hdr.SourceFileName, IRMods[0]->getSourceFileName());
192   TT = Triple(IRMods[0]->getTargetTriple());
193 
194   // This adds the symbols for each module to Msymtab.
195   for (auto *M : IRMods)
196     if (Error Err = addModule(M))
197       return Err;
198 
199   for (ModuleSymbolTable::Symbol Msym : Msymtab.symbols())
200     if (Error Err = addSymbol(Msym))
201       return Err;
202 
203   COFFLinkerOptsOS.flush();
204   setStr(Hdr.COFFLinkerOpts, COFFLinkerOpts);
205 
206   // We are about to fill in the header's range fields, so reserve space for it
207   // and copy it in afterwards.
208   Symtab.resize(sizeof(storage::Header));
209   writeRange(Hdr.Modules, Mods);
210   writeRange(Hdr.Comdats, Comdats);
211   writeRange(Hdr.Symbols, Syms);
212   writeRange(Hdr.Uncommons, Uncommons);
213 
214   *reinterpret_cast<storage::Header *>(Symtab.data()) = Hdr;
215 
216   raw_svector_ostream OS(Strtab);
217   StrtabBuilder.finalizeInOrder();
218   StrtabBuilder.write(OS);
219 
220   return Error::success();
221 }
222 
223 } // anonymous namespace
224 
225 Error irsymtab::build(ArrayRef<Module *> Mods, SmallVector<char, 0> &Symtab,
226                       SmallVector<char, 0> &Strtab) {
227   return Builder(Symtab, Strtab).build(Mods);
228 }
229