__attribute__((used))

Prevents a function or static variable from being dead-stripped.

  function-declaration __attribute__((used));  

  function-definition __attribute__((used));  

  variable-declaration __attribute__((used));  

  variable-definition __attribute__((used));  

This attribute specifies that the linker must not dead-strip a function or static variable even if the linker determines that the rest of the program does not refer to the object.