Using $Super$$ and $Sub$$ to override symbol definitions

There are situations where an existing symbol cannot be modified because, for example, it is located in an external library or in ROM code.

Use the $Super$$ and $Sub$$ patterns to patch an existing symbol.

For example, to patch the definition of a function foo(), use $Super$$foo() and $Sub$$foo() as follows:

Example 4.6 shows the legacy function foo() modified to result in a call to ExtraFunc() and a call to foo(). For more information, see the ARM ELF specification, aaelf.pdf, on the ARM website.

extern void ExtraFunc(void);
extern void $Super$$foo(void):

/* this function is called instead of the original foo() */
void $Sub$$foo(void)
{
  ExtraFunc();    /* does some extra setup work */
  $Super$$foo();  /* calls the original foo() function */
}