我想更新LLVM IR中的全局变量值。 我在ModulePass中创建了新的全局变量:
bool runOnModule(llvm::Module &M) {
IRBuilder<> Builder(M.getContext());
Instruction *I = &*inst_begin(M.getFunction("main"));
Builder.SetInsertPoint(I);
M.getOrInsertGlobal("globalKey", Builder.getInt64Ty());
GlobalVariable* gVar = M.getNamedGlobal("globalKey");
gVar->setLinkage(GlobalValue::InternalLinkage);
gVar->setAlignment(Align(8));
gVar->setInitializer(Builder.getInt64(0));
gVar->setConstant(false);
for (Function &F : M.functions()) {
InstructionVisitor visitor(DL, getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F));
for (Instruction &I : instructions(F)) {
visitor.visit(I);
}
}
return true;
}
稍后在InstructionVisitor中,我尝试在每个分配上递增globalKey并使用printf函数进行打印:
Instruction* InstructionVisitor::print(Instruction* I, const char* text, Value* arg1, Value* arg2, Value* arg3, Value* arg4) {
Function* printfFn = I->getModule()->getFunction("printf");
if (printfFn) {
IRBuilder<> Builder(I->getContext());
Builder.SetInsertPoint(I->getNextNode());
Value* convertedText = Builder.CreateGlobalStringPtr(text);
std::vector <Value *> params;
params.push_back(convertedText);
if (arg1)
params.push_back(arg1);
if (arg2)
params.push_back(arg2);
if (arg3)
params.push_back(arg3);
if (arg4)
params.push_back(arg4);
return Builder.CreateCall(printfFn, params);
}
return I;
}
Instruction* InstructionVisitor::incrementGlobalKey(Instruction* I) {
IRBuilder<> Builder(I->getContext());
Builder.SetInsertPoint(I->getNextNode());
GlobalVariable* key = I->getModule()->getNamedGlobal("globalKey");
if (key) {
LoadInst* load = Builder.CreateLoad(key);
Value* inc = Builder.CreateAdd(load, Builder.getInt64(1));
StoreInst* store = Builder.CreateStore(inc, key);
return store;
}
return I;
}
void InstructionVisitor::visitCallInst(CallInst &CI) {
if (isAllocationFn(&CI, &TLI)) {
Value* allocatedAddress = &CI;
Instruction* I = &CI;
Value* allocatedSize = I->getOperand(0);
Instruction* next = incrementGlobalKey(I);
GlobalVariable* key = I->getModule()->getNamedGlobal("globalKey");
const char* message = "Allocated address: 0x%p, size: %d, key: 0x%x\n";
print(next, message, allocatedAddress, allocatedSize, key->getOperand(0));
}
}
我在执行检测代码(使用注入的printf调用)期间打印该全局变量。我通过key-> getOperand(0)来访问它的值(如上所示),但是它没有变化。我正在使用基于本教程https://llvm.org/docs/tutorial/BuildingAJIT2.html的ORC JIT,并且从本教程的optimizeModule函数运行ModulePass。
IR,可以在这里找到我正在检测的代码和程序输出: https://pastebin.com/JbDR2Wug
有人知道如何使它工作吗?我将感谢您的帮助!
答案 0 :(得分:1)
在@droptop有用的评论之后,我更改了代码以使用load指令实际加载全局变量的值。现在工作正常。如果有人需要,更新的代码如下所示:
Instruction* InstructionVisitor::getGlobalValue(Instruction* I, StringRef Name) {
IRBuilder<> Builder(I->getContext());
Builder.SetInsertPoint(I->getNextNode());
GlobalVariable* key = I->getModule()->getNamedGlobal(Name);
if (key) {
LoadInst* load = Builder.CreateLoad(key);
return load;
}
return nullptr;
}
void InstructionVisitor::visitCallInst(CallInst &CI) {
if (isAllocationFn(&CI, &TLI)) {
Value* allocatedAddress = &CI;
Instruction* I = &CI;
Value* allocatedSize = I->getOperand(0);
Instruction* next = incrementGlobalKey(I, allocatedAddress, allocatedSize);
Instruction* loadKey = getGlobalValue(next, "globalKey"); //here
const char* message = "Allocated address: 0x%p, size: %d, key: %lld\n";
next = print(loadKey, message, allocatedAddress, allocatedSize, loadKey);
}
}