Retrieving the name of a indirect virtual method call in LLVM pass

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#1

Hi,

I have been implementing a CallGraphSCCPass that analyzes each function invocation. Direct calls are not a problem, but currently I also need to retrieve the name of the function in the case of virtual method calls. For example:

struct A {

A() {}

virtual foo() {}

virtual ~A() {}

};

int main() {

A* a = new A;

a->foo();

}

In the pass, I can determine the name of the indirect call by using CallInst::getCalledValue(), but that doesn’t give any information on the actual method that is being called, which should be foo(). The only “name” I can get is the type of the class, in which this case is class.A.

Is there any way I can get the name of the virtual method (foo) that is being invoked? It isn’t in the bitcode except for when it is defined. I tried taking a look at the whole-program-devirt source but can’t find where they are actually finding the names of the functions when building the virtual tables for each class.

I would greatly appreciate any help on this and if it is possible at all.

Thanks,

Ben Fu

#2

Sounds like maybe you’re trying to do something at a level where it’s not going to be practical - what’s your overall goal?

But no, at the LLVM IR level you can’t get the name of a virtual function being called - as you’ve seen, it’s a dynamic call through a table of function pointers & at LLVM’s level, those functions could have any names (or none at all - or at least none that makes sense in this translation unit/module because it’s a local symbol in some other module).

#3

The goal is to create a function call graph with the names of the functions, and the graph should include indirect calls too. I looked and saw that LLVM supports a metadata type called ‘callees’, but I don’t see that it’s currently being implemented by clang. Will this eventually be used?

Thanks,

Ben

#4

The goal is to create a function call graph with the names of the functions, and the graph should include indirect calls too.

That’s not possible in general - functions being called could come from external code, for example. (dlsym, for instance)

I looked and saw that LLVM supports a metadata type called ‘callees’, but I don’t see that it’s currently being implemented by clang. Will this eventually be used?

Not sure - I guess maybe if there were a constrained set of callees - but that’s not true of a polymorphic class hierarchy (there could always be another derived class in some external code - it’s not a closed group/set/collection/thing).