/// <summary>
/// This method starts from an API call instruction and goes backward to locate the instruction that
/// pushes the "this" object into stack. We insert out instrumentation patch at that point so that
/// the interception method can access the "this" object. After the interception method ends, we
/// push the "this" object to stack again so that the original API call can continue.
/// </summary>
/// <param name="callInstruction">Instruction that calls the API.</param>
/// <returns>The instruction that pushes the "this" object into stack.</returns>
private Instruction LocateLoadThisInstruction(Instruction callInstruction)
{
Tuple <int, int> poppedPushed = MSILHelper.GetStackTransition(callInstruction);
int toPop = poppedPushed.Item1;
Instruction current = callInstruction.Previous;
while (toPop > 1)
{
poppedPushed = MSILHelper.GetStackTransition(current);
toPop += poppedPushed.Item1;
toPop -= poppedPushed.Item2;
current = current.Previous;
}
return(current);
}
public static Instruction LocateLoadThisInstruction(ILProcessor ilProcessor, Instruction callInstruction)
{
Dictionary <Instruction, int> stackSize = new Dictionary <Instruction, int>();
Tuple <int, int> poppedPushed = MSILHelper.GetStackTransition(callInstruction);
int toPop = poppedPushed.Item1;
stackSize[callInstruction] = toPop;
if (callInstruction.Previous == null)
{
ilProcessor.InsertBefore(callInstruction, ilProcessor.Create(OpCodes.Nop));
}
Instruction current = callInstruction.Previous;
// fail if there current is a branch instruction
if (current.OpCode.FlowControl != FlowControl.Next)
{
return(null);
}
while (toPop > 1)
{
if (IsStackEmptyingInstruction(current))
{
Instruction branchSrc;
Instruction branchDst;
GetNextBranchDestinationInstruction(current, callInstruction, out branchSrc, out branchDst);
if (branchDst != null)
{
current = branchSrc;
toPop = stackSize[branchDst];
}
}
poppedPushed = MSILHelper.GetStackTransition(current);
toPop += poppedPushed.Item1;
toPop -= poppedPushed.Item2;
stackSize[current] = toPop;
if (current.Previous == null)
{
ilProcessor.InsertBefore(current, ilProcessor.Create(OpCodes.Nop));
}
current = current.Previous;
// fail if there current is a branch instruction
if (current.OpCode.FlowControl != FlowControl.Next)
{
return(null);
}
}
if (current.OpCode == OpCodes.Constrained)
{
current = current.Previous;
// fail if there current is a branch instruction
if (current.OpCode.FlowControl != FlowControl.Next)
{
return(null);
}
}
return(current);
}
