help needed in modifying ix86_expand_epilogue/prologue

help needed in modifying ix86_expand_epilogue/prologue

[Vaibhav Shrimali]

I am doing my research in the area of System Security. Eventually I
have come to a point where I need to implement a dubious approach
which requires me to make changes in the ix86_expand_epilogue/prologue
functions of the i386.c file of the compiler.
I need to add another copy of return address before the pushing the
frame pointer on the stack. Then need to modify the copy of return
address return address. Then in the epilogue I need to track if there
is any modification to the copy of return address, if so then I need
to redirect the program flow.
I have got basic understanding of the two functions mentioned above
but haven't been able to determine how to get the job done since I
don't have much experience with the internals of GCC compiler.
Please help me out here. This is critical for my research.  I know it
doesn't require much modification to the compiler. Please guide me
through.
Thank You.
Hoping an urgent reply from the community.

--
Vaibhav Shrimali
BTech(ICT), DA-IICT
Gandhinagar