[llvm-dev] LLVM plugin: access function signature of a function pointer parameter

[Marc via llvm-dev]

As an additional question is there a way how I can detect if a call
parameter is actually a function pointer?

On 08.02.21 18:30, Johannes Doerfert wrote:
> Going through the callee value, as you did.:
>
> Value *Callee = CI->getCalledValue();

getCalledValue() seems to have been renamed to getCalledOperand()

> PointerType *CalleePtrTy = dyn_cast<PointerType>(Callee->getType());
> if (!CalleePtrTy) ...
> FunctionType *CalleeFnTy =
> dyn_cast<FunctionType>(CalleePtrTy->getPointerElementType());
> if (!CalleeFnTy) ...
> if (CalleeFnTy->getNumParams() > idx)
>   return CalleFnTy->getParamTy(idx);

that would be getParamType(1), it returns
void (i32)*

... and I am back at square one :-(

Regards,
Marc

> On 2/8/21 10:20 AM, Marc via llvm-dev wrote:
>> Hi,
>>
>> I am unable to find any information on how to extract the function
>> signature from calls that receive a function pointer. e.g.:
>>
>> C code:
>>    signal(SIG_TERM, a_function_ptr);
>>
>> IR:
>>    %call = call void (i32)* @signal(i32 4, void (i32)* %1) #3, !dbg !26
>>
>> And Value* of callInst->GetOperand(1) resulting in: void (i32)*
>>
>> How can I extract that (i32) information, so basically the function
>> parameter signature?
>>
>> I want to add a feature into an llvm plugin that parses all calls,
>> identifies function pointers and then dumps the function signature.
>> (Yes if a function point is hidden to be a size_t* bitcast and
>> transfered I will not be able to see this, but in cases where this is
>> visible I would like to get that information.
>>
>> Thank you!
>>
>> Regards,
>> Marc
>>

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