llvm dev - Jun 2018 - Retrieving the name of a indirect virtual method call in LLVM pass

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 

 

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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).

On Thu, Jun 7, 2018 at 9:40 AM via llvm-dev <llvm-dev at lists.llvm.org>
wrote:
> 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
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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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

 

From: David Blaikie <dblaikie at gmail.com> 
Sent: Friday, June 8, 2018 1:06 PM
To: ben_fu1 at utexas.edu
Cc: llvm-dev at lists.llvm.org
Subject: Re: [llvm-dev] Retrieving the name of a indirect virtual method call in
LLVM pass

 

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).

 

On Thu, Jun 7, 2018 at 9:40 AM via llvm-dev <llvm-dev at lists.llvm.org
<mailto:llvm-dev at lists.llvm.org> > wrote:

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 

 

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llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org> 
http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

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