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digitalmars.D.learn - Get relative offset portably.

I am doing some weird stuff. I duplicate functions and modify 
them in a portable way. One problem I have is that I cannot get 
data in a relative way to be able to access attached functional 

Here is an kinda of thought example,

void base(int a, int b, int c)

This function is duplicated byte wise using memcpy. Extra 
information is added to the these bytes that I would like to 
access in base, but no absolute addresses can be used and 
portability must be maintained. One can imagine the data attached 
to the start or end of the function.

Using assembly, it is relatively easy. Just get eip at start of 
function, get the length of the function, then access the data 
like mov eax, [eip+length]. This is not portable though.

The function signature cannot change either or, it too, would be 
easy as I could just pass the offsets. I have no control over the 
calling mechanism. I can only create a functional template then 
copy that and attach data that it can use. I have seen some 
methods to do this but they all are unsafe as they might create 
undefined behavior in specific instances.

Do I have any options?
Jul 18 2016