6.7 Use of $Super$$ and $Sub$$ to patch symbol definitions

There are special patterns you can use for situations where an existing symbol cannot be modified.

An existing symbol cannot be modified, for example, if it is located in an external library or in ROM code. In such cases you can use the $Super$$ and $Sub$$ patterns to patch an existing symbol.

To patch the definition of the function foo(), $Sub$$foo and the original definition of foo() must be a global or weak definition:


Identifies the original unpatched function foo(). Use this to call the original function directly.


Identifies the new function that is called instead of the original function foo(). Use this to add processing before or after the original function.


The $Sub$$ and $Super$$ mechanism only works at static link time, $Super$$ references cannot be imported or exported into the dynamic symbol table.


The following example shows how to use $Super$$ and $Sub$$ to insert a call to the function ExtraFunc() before the call to the legacy function foo().

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$$foo();  /* calls the original foo() function */
                  /* To avoid calling the original foo() function
                   * omit the $Super$$foo(); function call.
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