[LLVMdev] Finding Targets of a Function Pointer

[Vikram S. Adve]

Patrick,

DSA gives you this directly by getting the DS node pointed to by the  
function pointer and then getting the list of globals in that DS node.

As Luke said, this is incomplete if some functions are not available.   
But DSA will mark function pointers that "escape" to external code as  
'I'ncomplete (and otherwise it guarantees that the fptr doesn't point  
to any external functions).

--Vikram
Associate Professor, Computer Science
University of Illinois at Urbana-Champaign
http://llvm.org/~vadve



On Jul 14, 2009, at 2:47 PM, Luke Dalessandro wrote:

> Patrick Alexander Simmons wrote:
>> Hi all,
>>
>> I was wondering whether there's any existing code to find all  
>> possible
>> targets of a function pointer in LLVM, and, if not, if there were a
>> smarter way to go about writing something to accomplish this than the
>> obvious way of recursively following the def-use chains and  
>> creating an
>> aggregate set.
>
> I think the only way to do this is to use an alias analysis to create
> points-to sets. You can then run the analysis and ask it for may-alias
> results between function pointers at call sites, and the set of
> functions that you have available. Clearly you can have trouble if  
> there
> are functions that aren't currently available.
>
> You should probably look at the DSA stuff in poolalloc as I think that
> it does some of this, or at least contains infrastructure to do some  
> of
> this.
>
> One of the main reasons to want to do this is for member function call
> devirtualization. Unfortunately, the code generated by llvm-g++ isn't
> great for this task, since it erases all of the types in a vtable. If
> this is what you are doing then you are likely to run into trouble in
> moderate sized programs.
>
> Luke
>
>>
>> --Patrick
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