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      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/ADT/SmallPtrSet.h"
     16 #include "llvm/IR/DerivedTypes.h"
     17 #include "llvm/IR/Function.h"
     18 #include "llvm/IR/IRBuilder.h"
     19 #include "llvm/IR/Module.h"
     20 #include "llvm/Support/raw_ostream.h"
     21 
     22 using namespace llvm;
     23 
     24 static void appendToGlobalArray(const char *Array,
     25                                 Module &M, Function *F, int Priority) {
     26   IRBuilder<> IRB(M.getContext());
     27   FunctionType *FnTy = FunctionType::get(IRB.getVoidTy(), false);
     28 
     29   // Get the current set of static global constructors and add the new ctor
     30   // to the list.
     31   SmallVector<Constant *, 16> CurrentCtors;
     32   StructType *EltTy;
     33   if (GlobalVariable *GVCtor = M.getNamedGlobal(Array)) {
     34     // If there is a global_ctors array, use the existing struct type, which can
     35     // have 2 or 3 fields.
     36     ArrayType *ATy = cast<ArrayType>(GVCtor->getType()->getElementType());
     37     EltTy = cast<StructType>(ATy->getElementType());
     38     if (Constant *Init = GVCtor->getInitializer()) {
     39       unsigned n = Init->getNumOperands();
     40       CurrentCtors.reserve(n + 1);
     41       for (unsigned i = 0; i != n; ++i)
     42         CurrentCtors.push_back(cast<Constant>(Init->getOperand(i)));
     43     }
     44     GVCtor->eraseFromParent();
     45   } else {
     46     // Use the new three-field struct if there isn't one already.
     47     EltTy = StructType::get(IRB.getInt32Ty(), PointerType::getUnqual(FnTy),
     48                             IRB.getInt8PtrTy(), nullptr);
     49   }
     50 
     51   // Build a 2 or 3 field global_ctor entry.  We don't take a comdat key.
     52   Constant *CSVals[3];
     53   CSVals[0] = IRB.getInt32(Priority);
     54   CSVals[1] = F;
     55   // FIXME: Drop support for the two element form in LLVM 4.0.
     56   if (EltTy->getNumElements() >= 3)
     57     CSVals[2] = llvm::Constant::getNullValue(IRB.getInt8PtrTy());
     58   Constant *RuntimeCtorInit =
     59       ConstantStruct::get(EltTy, makeArrayRef(CSVals, EltTy->getNumElements()));
     60 
     61   CurrentCtors.push_back(RuntimeCtorInit);
     62 
     63   // Create a new initializer.
     64   ArrayType *AT = ArrayType::get(EltTy, CurrentCtors.size());
     65   Constant *NewInit = ConstantArray::get(AT, CurrentCtors);
     66 
     67   // Create the new global variable and replace all uses of
     68   // the old global variable with the new one.
     69   (void)new GlobalVariable(M, NewInit->getType(), false,
     70                            GlobalValue::AppendingLinkage, NewInit, Array);
     71 }
     72 
     73 void llvm::appendToGlobalCtors(Module &M, Function *F, int Priority) {
     74   appendToGlobalArray("llvm.global_ctors", M, F, Priority);
     75 }
     76 
     77 void llvm::appendToGlobalDtors(Module &M, Function *F, int Priority) {
     78   appendToGlobalArray("llvm.global_dtors", M, F, Priority);
     79 }
     80 
     81 GlobalVariable *
     82 llvm::collectUsedGlobalVariables(Module &M, SmallPtrSetImpl<GlobalValue *> &Set,
     83                                  bool CompilerUsed) {
     84   const char *Name = CompilerUsed ? "llvm.compiler.used" : "llvm.used";
     85   GlobalVariable *GV = M.getGlobalVariable(Name);
     86   if (!GV || !GV->hasInitializer())
     87     return GV;
     88 
     89   const ConstantArray *Init = cast<ConstantArray>(GV->getInitializer());
     90   for (unsigned I = 0, E = Init->getNumOperands(); I != E; ++I) {
     91     Value *Op = Init->getOperand(I);
     92     GlobalValue *G = cast<GlobalValue>(Op->stripPointerCastsNoFollowAliases());
     93     Set.insert(G);
     94   }
     95   return GV;
     96 }
     97 
     98 Function *llvm::checkSanitizerInterfaceFunction(Constant *FuncOrBitcast) {
     99   if (isa<Function>(FuncOrBitcast))
    100     return cast<Function>(FuncOrBitcast);
    101   FuncOrBitcast->dump();
    102   std::string Err;
    103   raw_string_ostream Stream(Err);
    104   Stream << "Sanitizer interface function redefined: " << *FuncOrBitcast;
    105   report_fatal_error(Err);
    106 }
    107 
    108 std::pair<Function *, Function *> llvm::createSanitizerCtorAndInitFunctions(
    109     Module &M, StringRef CtorName, StringRef InitName,
    110     ArrayRef<Type *> InitArgTypes, ArrayRef<Value *> InitArgs,
    111     StringRef VersionCheckName) {
    112   assert(!InitName.empty() && "Expected init function name");
    113   assert(InitArgTypes.size() == InitArgTypes.size() &&
    114          "Sanitizer's init function expects different number of arguments");
    115   Function *Ctor = Function::Create(
    116       FunctionType::get(Type::getVoidTy(M.getContext()), false),
    117       GlobalValue::InternalLinkage, CtorName, &M);
    118   BasicBlock *CtorBB = BasicBlock::Create(M.getContext(), "", Ctor);
    119   IRBuilder<> IRB(ReturnInst::Create(M.getContext(), CtorBB));
    120   Function *InitFunction =
    121       checkSanitizerInterfaceFunction(M.getOrInsertFunction(
    122           InitName, FunctionType::get(IRB.getVoidTy(), InitArgTypes, false),
    123           AttributeSet()));
    124   InitFunction->setLinkage(Function::ExternalLinkage);
    125   IRB.CreateCall(InitFunction, InitArgs);
    126   if (!VersionCheckName.empty()) {
    127     Function *VersionCheckFunction =
    128         checkSanitizerInterfaceFunction(M.getOrInsertFunction(
    129             VersionCheckName, FunctionType::get(IRB.getVoidTy(), {}, false),
    130             AttributeSet()));
    131     IRB.CreateCall(VersionCheckFunction, {});
    132   }
    133   return std::make_pair(Ctor, InitFunction);
    134 }
    135 
    136