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