Using and Porting GNU CC
Using the built-in functions described below, you can record the arguments a function received, and call another function with the same arguments, without knowing the number or types of the arguments.
You can also record the return value of that function call, and later return that value, without knowing what data type the function tried to return (as long as your caller expects that data type).
void *to data describing how to perform a call with the same arguments as were passed to the current function.
The function saves the arg pointer register, structure value address, and all registers that might be used to pass arguments to a function into a block of memory allocated on the stack. Then it returns the address of that block.
__builtin_apply (function, arguments, size)
void (*)()) with a copy of the parameters described by arguments (type
void *) and size (type
The value of arguments should be the value returned by
__builtin_apply_args. The argument size specifies the size
of the stack argument data, in bytes.
This function returns a pointer of type
void * to data describing
how to return whatever value was returned by function. The data
is saved in a block of memory allocated on the stack.
It is not always simple to compute the proper value for size. The
value is used by
__builtin_apply to compute the amount of data
that should be pushed on the stack and copied from the incoming argument