CODEWITHSUNDEEP
llvm
Alex
Alex

Reputation: 360

llvm get annotations

I updated my previous question under a new form. Hello everyone,

I have the following 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"

I need to get @f (or maybe I can get somehow the definition of @f = global i32 0, align 4 ) and also I need to get "DS" from @.str. In my target code I have :

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

I have problems to parse @llvm.global.annotations and I assume I will have with @.str. What I tried:

1.

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";

RESULT :

  [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.

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

RESULT :

[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 }]

Any help is welcomed ! Thank you !

Upvotes: 3

Views: 2717

Answers (3)

Nachshon Cohen
Nachshon Cohen

Reputation: 113

Quite a late answer, but Google led me here and I thought that providing a full LLVM pass that discovers free text annotation would be helpful. This LLVM pass would instrument only function marked with __attribute((annotate("someFreeTextAnnotation"))). The code follows:

#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 */);

Upvotes: 5

Alex
Alex

Reputation: 360

I solved it. I cast the entire annotated expression to Value*. Then, in order to avoid ugly things like getAsString(), I check if V->getValueID() == Value::ConstantArrayVal in order to cast it to ConstantArray. Because it contains only array[0], I cast array0>getOperand(0) to ConstantStruct. Therefore, from ConstantStruct you can get all the four operands. Now to do is only to get the names of @f, @str from every field. This is done by ConstantStruct->getOperand(0)->getOperand(0).

Upvotes: 0

user2022455
user2022455

Reputation:

Use runOnModule() instead of runOnFunction() if you are doing so. Alternatively, you can take the module. llvm.global.annotations is defined outside functions. Inside do something like:

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
}

}

Upvotes: 1

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