[LLVMdev] Instrumenting virtual function calls

[Robert Zeh]

I'm attempting to instrument virtual function calls in my code.  After  
each virtual call I'm calling my own registerMethod function, with an  
integer marking the location of the call and a pointer to the function  
that was called.

However, and this is where I get confused, the function pointer  
doesn't match any of the functions in my module.  I'd hoped to call  
ExecutionEngine::getGlobalValueAtAddress to get a Function* for the  
virtual function, but ExecutionEngine::getGlobalValueAtAddress returns  
null.

If I look up the virtual function that is getting called (with  
ExeuctionEngine::getPointerToFunction) it doesn't match the arguments  
being passed to my instrumentation. What's a little strange is that  
the pointers are somewhat close: getPointerToFunction returns  
0x47829a0, but my instrumentation gets 0x477fc10.

What am I missing?

Lines starting with "!" are the instrumented lines.

define double @Return() {
entry:
	%this = load  
%"struct.Q::BinaryOperation<bool,bool,bool,Q::AddOperator>"**  
@q_constant2		; < 
%"struct.Q::BinaryOperation<bool,bool,bool,Q::AddOperator>"*> [#uses=2]
	%tmp9.i = getelementptr  
%"struct.Q::BinaryOperation<bool,bool,bool,Q::AddOperator>"* %this,  
i32 0, i32 2, i32 0		; <%"struct.Q::Function"**> [#uses=1]
	%tmp10.i = load %"struct.Q::Function"** %tmp9.i, align 4		; < 
%"struct.Q::Function"*> [#uses=2]
	%tmp17.i = getelementptr  
%"struct.Q::BinaryOperation<bool,bool,bool,Q::AddOperator>"* %this,  
i32 0, i32 1, i32 0		; <%"struct.Q::Function"**> [#uses=1]
	%tmp18.i = load %"struct.Q::Function"** %tmp17.i, align 4		; < 
%"struct.Q::Function"*> [#uses=2]
	%tmp33.i = getelementptr %"struct.Q::Function"* %tmp18.i, i32 0, i32  
0, i32 0, i32 0, i32 0		; <i32 (...)***> [#uses=1]
	%tmp34.i = load i32 (...)*** %tmp33.i, align 4		; <i32 (...)**>  
[#uses=1]
	%tmp35.i = getelementptr i32 (...)** %tmp34.i, i32 9		; <i32 (...)**>  
[#uses=1]
	%tmp36.i = load i32 (...)** %tmp35.i, align 4		; <i32 (...)*> [#uses=1]
	%tmp3637.i = bitcast i32 (...)* %tmp36.i to double  
(%"struct.Q::Function"*)*		; <double (%"struct.Q::Function"*)*>  
[#uses=2]
	%tmp39.i = call double %tmp3637.i( %"struct.Q::Function"*  
%tmp18.i )		; <double> [#uses=1]
!	bitcast double (%"struct.Q::Function"*)* %tmp3637.i to i8*		; <i8*>: 
0 [#uses=1]
!	call void @registerMethod( i64 73846672, i8* %0 )
	%tmp49.i = getelementptr %"struct.Q::Function"* %tmp10.i, i32 0, i32  
0, i32 0, i32 0, i32 0		; <i32 (...)***> [#uses=1]
	%tmp50.i = load i32 (...)*** %tmp49.i, align 4		; <i32 (...)**>  
[#uses=1]
	%tmp51.i = getelementptr i32 (...)** %tmp50.i, i32 9		; <i32 (...)**>  
[#uses=1]
	%tmp52.i = load i32 (...)** %tmp51.i, align 4		; <i32 (...)*> [#uses=1]
	%tmp5253.i = bitcast i32 (...)* %tmp52.i to i32  
(%"struct.Q::Function"*)*		; <i32 (%"struct.Q::Function"*)*> [#uses=2]
	%tmp55.i = call i32 %tmp5253.i( %"struct.Q::Function"* %tmp10.i )		;  
<i32> [#uses=1]
!	bitcast i32 (%"struct.Q::Function"*)* %tmp5253.i to i8*		; <i8*>:1  
[#uses=1]
!	call void @registerMethod( i64 73865808, i8* %1 )
	%tmp5859.i = sitofp i32 %tmp55.i to double		; <double> [#uses=1]
	%tmp61.i = add double %tmp39.i, %tmp5859.i		; <double> [#uses=1]
	ret double %tmp61.i
}

Robert
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