LLVM's bitcode wrong detections of function's parameters - c++

Question

I'm using LLVM api in order to parse bitcode files. I have the following snippet and I'm using this command to generate the bitcode $CC -emit-llvm -c -g source.c where CC is set to the clang path.
#include <stdio.h>
struct Point {
int a;
int b;
};
int func_0(struct Point p, int x) {
return 0;
}
The TypeID is supposed to have a numeric value, based on the type of the parameter. However, both for the integer x and the struct Point I obtain the value of 10 which is referred as a TokenTyID. So, I decided to use the functions isIntegerTy() and isStructTy(), respectively, to see if at least in this case, I obtain the right result. This solution works for the integer parameter x, but not for the struct. How can I correctly identify structs and read their fields?
Just to completeness, to parse the bitcode I use this code:
using namespace llvm;
int main(int argc, char** argv) {
LLVMContext context;
OwningPtr<MemoryBuffer> mb;
MemoryBuffer::getFile(FileName, mb);
Module *m = ParseBitcodeFile(mb.get(), context);
for (Module::const_iterator i = m->getFunctionList().begin(), e = m->getFunctionList().end(); i != e; ++i) {
if (i->isDeclaration() || i->getName().str() == "main")
continue;
std::cout << i->getName().str() << std::endl;
Type* ret_type = i->getReturnType();
std::cout << "\t(ret) " << ret_type->getTypeID() << std::endl;
Function::const_arg_iterator ai;
Function::const_arg_iterator ae;
for (ai = i->arg_begin(), ae = i->arg_end(); ai != ae; ++ai) {
Type* t = ai->getType();
std::cout << "\t" << ai->getName().str() << " " << t->getTypeID()
<< "(" << t->getFunctionNumParams() << ")"
<< " is struct? " << (t->isStructTy() ? "Y" : "N")
<< " is int? " << (t->isIntegerTy() ? "Y" : "N")
<< "\n";
}
}
return 0;
}
I read this post Why does Clang coerce struct parameters to ints about the translation performed by clang with the structs and I'm pretty sure that is my same problem.

Answer 1

Since clang changes the function signature in the IR, you will have to get that information using debug info. Here is some rough code:
DITypeIdentifierMap TypeIdentifierMap;
DIType* getLowestDINode(DIType* Ty) {
if (Ty->getTag() == dwarf::DW_TAG_pointer_type ||
Ty->getTag() == dwarf::DW_TAG_member) {
DIType *baseTy =
dyn_cast<DIDerivedType>(Ty)->getBaseType().resolve(TypeIdentifierMap);
if (!baseTy) {
errs() << "Type : NULL - Nothing more to do\n";
return NULL;
}
//Skip all the DINodes with DW_TAG_typedef tag
while ((baseTy->getTag() == dwarf::DW_TAG_typedef || baseTy->getTag() == dwarf::DW_TAG_const_type
|| baseTy->getTag() == dwarf::DW_TAG_pointer_type)) {
if (DITypeRef temp = dyn_cast<DIDerivedType>(baseTy)->getBaseType())
baseTy = temp.resolve(TypeIdentifierMap);
else
break;
}
return baseTy;
}
return Ty;
}
int main(int argc, char** argv) {
LLVMContext context;
OwningPtr<MemoryBuffer> mb;
MemoryBuffer::getFile(FileName, mb);
Module *m = ParseBitcodeFile(mb.get(), context);
if (NamedMDNode *CU_Nodes = m.getNamedMetadata("llvm.dbg.cu")) {
TypeIdentifierMap = generateDITypeIdentifierMap(CU_Nodes);
}
SmallVector<std::pair<unsigned, MDNode *>, 4> MDs;
F.getAllMetadata(MDs);
for (auto &MD : MDs) {
if (MDNode *N = MD.second) {
if (auto *subRoutine = dyn_cast<DISubprogram>(N)->getType()) {
if (!subRoutine->getTypeArray()[0]) {
errs() << "return type \"void\" for Function : " << F.getName().str()
<< "\n";
}
const auto &TypeRef = subRoutine->getTypeArray();
for (int i=0; i<TypeRef.size(); i++) {
// Resolve the type
DIType *Ty = ArgTypeRef.resolve(TypeIdentifierMap);
DIType* baseTy = getLowestDINode(Ty);
if (!baseTy)
return;
// If that pointer is a struct
if (baseTy->getTag() == dwarf::DW_TAG_structure_type) {
std::cout << "structure type name: " << baseTy->getName().str() << std::endl();
}
}
}
}
}
}
I know it looks ugly but using debug info is not easy.