1 //===-- ModuleUtils.cpp - Functions to manipulate Modules -----------------===//
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 // This family of functions perform manipulations on Modules.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/Transforms/Utils/ModuleUtils.h"
15 #include "llvm/IR/DerivedTypes.h"
16 #include "llvm/IR/Function.h"
17 #include "llvm/IR/IRBuilder.h"
18 #include "llvm/IR/Module.h"
19 #include "llvm/Support/raw_ostream.h"
20 
21 using namespace llvm;
22 
23 static void appendToGlobalArray(const char *Array, Module &M, Function *F,
24                                 int Priority, Constant *Data) {
25   IRBuilder<> IRB(M.getContext());
26   FunctionType *FnTy = FunctionType::get(IRB.getVoidTy(), false);
27 
28   // Get the current set of static global constructors and add the new ctor
29   // to the list.
30   SmallVector<Constant *, 16> CurrentCtors;
31   StructType *EltTy;
32   if (GlobalVariable *GVCtor = M.getNamedGlobal(Array)) {
33     ArrayType *ATy = cast<ArrayType>(GVCtor->getValueType());
34     StructType *OldEltTy = cast<StructType>(ATy->getElementType());
35     // Upgrade a 2-field global array type to the new 3-field format if needed.
36     if (Data && OldEltTy->getNumElements() < 3)
37       EltTy = StructType::get(IRB.getInt32Ty(), PointerType::getUnqual(FnTy),
38                               IRB.getInt8PtrTy(), nullptr);
39     else
40       EltTy = OldEltTy;
41     if (Constant *Init = GVCtor->getInitializer()) {
42       unsigned n = Init->getNumOperands();
43       CurrentCtors.reserve(n + 1);
44       for (unsigned i = 0; i != n; ++i) {
45         auto Ctor = cast<Constant>(Init->getOperand(i));
46         if (EltTy != OldEltTy)
47           Ctor = ConstantStruct::get(
48               EltTy, Ctor->getAggregateElement((unsigned)0),
49               Ctor->getAggregateElement(1),
50               Constant::getNullValue(IRB.getInt8PtrTy()), nullptr);
51         CurrentCtors.push_back(Ctor);
52       }
53     }
54     GVCtor->eraseFromParent();
55   } else {
56     // Use the new three-field struct if there isn't one already.
57     EltTy = StructType::get(IRB.getInt32Ty(), PointerType::getUnqual(FnTy),
58                             IRB.getInt8PtrTy(), nullptr);
59   }
60 
61   // Build a 2 or 3 field global_ctor entry.  We don't take a comdat key.
62   Constant *CSVals[3];
63   CSVals[0] = IRB.getInt32(Priority);
64   CSVals[1] = F;
65   // FIXME: Drop support for the two element form in LLVM 4.0.
66   if (EltTy->getNumElements() >= 3)
67     CSVals[2] = Data ? ConstantExpr::getPointerCast(Data, IRB.getInt8PtrTy())
68                      : Constant::getNullValue(IRB.getInt8PtrTy());
69   Constant *RuntimeCtorInit =
70       ConstantStruct::get(EltTy, makeArrayRef(CSVals, EltTy->getNumElements()));
71 
72   CurrentCtors.push_back(RuntimeCtorInit);
73 
74   // Create a new initializer.
75   ArrayType *AT = ArrayType::get(EltTy, CurrentCtors.size());
76   Constant *NewInit = ConstantArray::get(AT, CurrentCtors);
77 
78   // Create the new global variable and replace all uses of
79   // the old global variable with the new one.
80   (void)new GlobalVariable(M, NewInit->getType(), false,
81                            GlobalValue::AppendingLinkage, NewInit, Array);
82 }
83 
84 void llvm::appendToGlobalCtors(Module &M, Function *F, int Priority, Constant *Data) {
85   appendToGlobalArray("llvm.global_ctors", M, F, Priority, Data);
86 }
87 
88 void llvm::appendToGlobalDtors(Module &M, Function *F, int Priority, Constant *Data) {
89   appendToGlobalArray("llvm.global_dtors", M, F, Priority, Data);
90 }
91 
92 static void appendToUsedList(Module &M, StringRef Name, ArrayRef<GlobalValue *> Values) {
93   GlobalVariable *GV = M.getGlobalVariable(Name);
94   SmallPtrSet<Constant *, 16> InitAsSet;
95   SmallVector<Constant *, 16> Init;
96   if (GV) {
97     ConstantArray *CA = dyn_cast<ConstantArray>(GV->getInitializer());
98     for (auto &Op : CA->operands()) {
99       Constant *C = cast_or_null<Constant>(Op);
100       if (InitAsSet.insert(C).second)
101         Init.push_back(C);
102     }
103     GV->eraseFromParent();
104   }
105 
106   Type *Int8PtrTy = llvm::Type::getInt8PtrTy(M.getContext());
107   for (auto *V : Values) {
108     Constant *C = ConstantExpr::getBitCast(V, Int8PtrTy);
109     if (InitAsSet.insert(C).second)
110       Init.push_back(C);
111   }
112 
113   if (Init.empty())
114     return;
115 
116   ArrayType *ATy = ArrayType::get(Int8PtrTy, Init.size());
117   GV = new llvm::GlobalVariable(M, ATy, false, GlobalValue::AppendingLinkage,
118                                 ConstantArray::get(ATy, Init), Name);
119   GV->setSection("llvm.metadata");
120 }
121 
122 void llvm::appendToUsed(Module &M, ArrayRef<GlobalValue *> Values) {
123   appendToUsedList(M, "llvm.used", Values);
124 }
125 
126 void llvm::appendToCompilerUsed(Module &M, ArrayRef<GlobalValue *> Values) {
127   appendToUsedList(M, "llvm.compiler.used", Values);
128 }
129 
130 Function *llvm::checkSanitizerInterfaceFunction(Constant *FuncOrBitcast) {
131   if (isa<Function>(FuncOrBitcast))
132     return cast<Function>(FuncOrBitcast);
133   FuncOrBitcast->print(errs());
134   errs() << '\n';
135   std::string Err;
136   raw_string_ostream Stream(Err);
137   Stream << "Sanitizer interface function redefined: " << *FuncOrBitcast;
138   report_fatal_error(Err);
139 }
140 
141 std::pair<Function *, Function *> llvm::createSanitizerCtorAndInitFunctions(
142     Module &M, StringRef CtorName, StringRef InitName,
143     ArrayRef<Type *> InitArgTypes, ArrayRef<Value *> InitArgs,
144     StringRef VersionCheckName) {
145   assert(!InitName.empty() && "Expected init function name");
146   assert(InitArgs.size() == InitArgTypes.size() &&
147          "Sanitizer's init function expects different number of arguments");
148   Function *Ctor = Function::Create(
149       FunctionType::get(Type::getVoidTy(M.getContext()), false),
150       GlobalValue::InternalLinkage, CtorName, &M);
151   BasicBlock *CtorBB = BasicBlock::Create(M.getContext(), "", Ctor);
152   IRBuilder<> IRB(ReturnInst::Create(M.getContext(), CtorBB));
153   Function *InitFunction =
154       checkSanitizerInterfaceFunction(M.getOrInsertFunction(
155           InitName, FunctionType::get(IRB.getVoidTy(), InitArgTypes, false),
156           AttributeSet()));
157   InitFunction->setLinkage(Function::ExternalLinkage);
158   IRB.CreateCall(InitFunction, InitArgs);
159   if (!VersionCheckName.empty()) {
160     Function *VersionCheckFunction =
161         checkSanitizerInterfaceFunction(M.getOrInsertFunction(
162             VersionCheckName, FunctionType::get(IRB.getVoidTy(), {}, false),
163             AttributeSet()));
164     IRB.CreateCall(VersionCheckFunction, {});
165   }
166   return std::make_pair(Ctor, InitFunction);
167 }
168 
169 void llvm::filterDeadComdatFunctions(
170     Module &M, SmallVectorImpl<Function *> &DeadComdatFunctions) {
171   // Build a map from the comdat to the number of entries in that comdat we
172   // think are dead. If this fully covers the comdat group, then the entire
173   // group is dead. If we find another entry in the comdat group though, we'll
174   // have to preserve the whole group.
175   SmallDenseMap<Comdat *, int, 16> ComdatEntriesCovered;
176   for (Function *F : DeadComdatFunctions) {
177     Comdat *C = F->getComdat();
178     assert(C && "Expected all input GVs to be in a comdat!");
179     ComdatEntriesCovered[C] += 1;
180   }
181 
182   auto CheckComdat = [&](Comdat &C) {
183     auto CI = ComdatEntriesCovered.find(&C);
184     if (CI == ComdatEntriesCovered.end())
185       return;
186 
187     // If this could have been covered by a dead entry, just subtract one to
188     // account for it.
189     if (CI->second > 0) {
190       CI->second -= 1;
191       return;
192     }
193 
194     // If we've already accounted for all the entries that were dead, the
195     // entire comdat is alive so remove it from the map.
196     ComdatEntriesCovered.erase(CI);
197   };
198 
199   auto CheckAllComdats = [&] {
200     for (Function &F : M.functions())
201       if (Comdat *C = F.getComdat()) {
202         CheckComdat(*C);
203         if (ComdatEntriesCovered.empty())
204           return;
205       }
206     for (GlobalVariable &GV : M.globals())
207       if (Comdat *C = GV.getComdat()) {
208         CheckComdat(*C);
209         if (ComdatEntriesCovered.empty())
210           return;
211       }
212     for (GlobalAlias &GA : M.aliases())
213       if (Comdat *C = GA.getComdat()) {
214         CheckComdat(*C);
215         if (ComdatEntriesCovered.empty())
216           return;
217       }
218   };
219   CheckAllComdats();
220 
221   if (ComdatEntriesCovered.empty()) {
222     DeadComdatFunctions.clear();
223     return;
224   }
225 
226   // Remove the entries that were not covering.
227   erase_if(DeadComdatFunctions, [&](GlobalValue *GV) {
228     return ComdatEntriesCovered.find(GV->getComdat()) ==
229            ComdatEntriesCovered.end();
230   });
231 }
232