17.9 Definition of Subr Argument Lists

When the advice facility constructs the combined definition, it needs to know the argument list of the original function. This is not always possible for primitive functions. When advice cannot determine the argument list, it uses (&rest ad-subr-args), which always works but is inefficient because it constructs a list of the argument values. You can use ad-define-subr-args to declare the proper argument names for a primitive function:

Function: ad-define-subr-args function arglist

This function specifies that arglist should be used as the argument list for function function.

For example,

(ad-define-subr-args 'fset '(sym newdef))

specifies the argument list for the function fset.