llvm得到annotations

原文

问题

我用一个新的表格更新了之前的问题。大家好,

我有以下LLVM IR:

@.str = private unnamed_addr constant [3 x i8] c"DS\00", section "llvm.metadata"
@llvm.global.annotations = appending global [1 x { i8*, i8*, i8*, i32 }] [{ i8*, i8*, i8*, i32 } { i8* bitcast (i32* @f to i8*), i8* getelementptr inbounds ([3 x i8]* @.str, i32 0, i32 0), i8* getelementptr inbounds ([9 x i8]* @.str1, i32 0, i32 0), i32 18 }], section "llvm.metadata"
           

我需要得到@f(或者我可以得到

@f = global i32 0, align 4

的定义)，我还需要从

@.str

得到“DS”。在我的目标代码中，我有:

__attribute__((annotate("DS"))) int f=0;

我无法解析

@llvm.global.annotations

，我想我会用

@.str

。我试着:

1. 代码

   for (Module::global_iterator I = F.global_begin(), E = F.global_end(); I != E; ++I) {
       if (I->getName() == "llvm.global.annotations") {
          Value *V = cast<Value>(I->getOperand(0));
           errs()<<"\n "<<*(V)<<"\n";
           errs()<<"\n "<<*(V->getType())<<"\n";
              

   结果：

   [1 x { i8*, i8*, i8*, i32 }] [{ i8*, i8*, i8*, i32 } { i8* bitcast (i32* @f to i8*), i8* getelementptr inbounds ([3 x i8]* @.str, i32 0, i32 0), i8* getelementptr inbounds ([9 x i8]* @.str1, i32 0, i32 0), i32 18 }]
   
    [1 x { i8*, i8*, i8*, i32 }]
              

2. 代码：

   errs()<<"\n "<<(V->getValueID())<<"\n";
   if(V->getValueID() == Value::ConstantArrayVal) {
               ConstantArray *ca = (ConstantArray *)V;
               errs()<<"\n "<<(ca[0])<<"\n";  }
              

   结果

   [1 x { i8*, i8*, i8*, i32 }] [{ i8*, i8*, i8*, i32 } { i8* bitcast (i32* @f to i8*), i8* getelementptr inbounds ([3 x i8]* @.str, i32 0, i32 0), i8* getelementptr inbounds ([9 x i8]* @.str1, i32 0, i32 0), i32 18 }]
              

欢迎任何帮助!谢谢你!

3个回答

1. 如果你做这项工作请使用runOnModule()而不是runOnFunction()。或者，您可以使用模块。llvm.global.annotations是在函数外部定义的。在内部做类似的事情:

   for (Module::global_iterator I = F.global_begin(), E = F.global_end(); I != E; ++I) {
   
   if (I->getName() == "llvm.global.annotations")
   {
       errs()<<"\nllvm.global.annotations\n";
       //1. find out what global variable is by "parsing" the IR
       //2. get through the module till you find a load @f 
       //3. you can add metadata to the load function and you can easily get the metadata from the normal pass
   }
   
   } 
              

2. 我解决了它。我将整个带注释的表达式转换为

   Value*

   。然后，为了避免像

   getAsString()

   这样难看的东西，我检查是否

   V->getValueID() == Value::ConstantArrayVal

   ，以便将它转换为

   ConstantArray

   。因为它只包含

   array[0]

   ，所以我将

   array0>getOperand(0)

   转换为

   ConstantStruct

   。因此，从

   ConstantStruct

   你可以获得所有四个操作数。现在要做的就是从每个字段中获取

   @f、@str

   的名称。这是由

   ConstantStruct->getOperand(0)->getOperand(0)

   完成的。
3. 这是一个很晚才给出的答案，但是谷歌把我带到这里，我认为提供一个完整的LLVM pass来发现免费的文本注释是有帮助的。这个LLVM pass将只测试用_attribute((annotate(“someFreeTextAnnotation”)标记的函数。代码如下:

   #include "llvm/Pass.h"
   #include "llvm/IR/Function.h"
   #include "llvm/Support/raw_ostream.h"
   #include "llvm/IR/Module.h"
   #include "llvm/IR/Constants.h"
   #include <set>
   
   using namespace llvm;
   const char *AnnotationString = "someFreeTextAnnotation";
   
   namespace {
   struct Hello : public FunctionPass {
       static char ID;
       Hello() : FunctionPass(ID) {}
       std::set<Function*> annotFuncs;
   
       virtual bool doInitialization(Module &M)override{
           getAnnotatedFunctions(&M);
           return false;
       }
       bool shouldInstrumentFunc(Function &F){
           return annotFuncs.find(&F)!=annotFuncs.end();
       }
       void getAnnotatedFunctions(Module *M){
           for (Module::global_iterator I = M->global_begin(),
                   E = M->global_end();
                   I != E;
                   ++I) {
   
               if (I->getName() == "llvm.global.annotations") {
                   ConstantArray *CA = dyn_cast<ConstantArray>(I->getOperand(0));
                   for(auto OI = CA->op_begin(); OI != CA->op_end(); ++OI){
                       ConstantStruct *CS = dyn_cast<ConstantStruct>(OI->get());
                       Function *FUNC = dyn_cast<Function>(CS->getOperand(0)->getOperand(0));
                       GlobalVariable *AnnotationGL = dyn_cast<GlobalVariable>(CS->getOperand(1)->getOperand(0));
                       StringRef annotation = dyn_cast<ConstantDataArray>(AnnotationGL->getInitializer())->getAsCString();
                       if(annotation.compare(AnnotationString)==0){
                           annotFuncs.insert(FUNC);
                           //errs() << "Found annotated function " << FUNC->getName()<<"\n";
                       }
                   }
               }
           }
       }
   
       bool runOnFunction(Function &F) override {
           if(shouldInstrumentFunc(F)==false)
               return false;
           errs() << "Instrumenting " << F.getName() << "\n";
   
           return false;
       }
   }; // end of struct Hello
   }  // end of anonymous namespace
   
   char Hello::ID = 0;
   static RegisterPass<Hello> X("hello", "Discover annotation attribute",
           false /* Only looks at CFG */,
           false /* Analysis Pass */);