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$$foo
and the original definition of
foo()
must be a global or weak definition:
$Super$$foo
Identifies the original unpatched function
foo()
. Use this to call the original function directly.$Sub$$foo
Identifies the new function that is called instead of the original function
foo()
. Use this to add processing before or after the original function.
Note
The$Sub$$
and $Super$$
mechanism only works at static
link time, $Super$$
references cannot be imported or exported into the
dynamic symbol table.
Example
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. */ }