// Scan the object code to find the first argument to ProtoMember for a given CAG
private static int getProtoMemberArgument(CustomAttributeData att, long protoMemberCtor)
{
// Disassemble the CAG
var code = asm.Disassemble(att.GetMethodBody(), (long)att.VirtualAddress.Start);
var insIndex = -1;
var disp = 0;
// Step forwards through each instruction
while (++insIndex < code.Length && disp == 0)
{
var ins = code[insIndex];
// Look for JMP and CALL instructions to the ProtoMember constructor
if ((ins.Id == X86InstructionId.X86_INS_JMP || ins.Id == X86InstructionId.X86_INS_CALL) &&
ins.Details.Operands[0].Immediate == protoMemberCtor)
{
// Now step backwards looking for the most recent LEA EDX instruction
while (--insIndex >= 0 && disp == 0)
{
ins = code[insIndex];
if (ins.Id == X86InstructionId.X86_INS_LEA &&
ins.Details.ExplicitlyWrittenRegisters[0].Id == X86RegisterId.X86_REG_EDX)
{
// The instruction is LEA EDX, [R8 + disp]
// We know that R8 is zero so the displacement is the field number
disp = (int)ins.Details.Displacement;
}
}
if (insIndex == -1)
{
throw new InvalidOperationException("Unable to determine ProtoMember field number");
}
}
}
return(disp);
}