14.1.2.9 interrupt
To declare a C function as an interrupt handler, tag the function with
the interrupt attribute.
For example: void __attribute__((interrupt))
_StackErrorTrap(void);
For attribute syntax, see 15.3.2 Syntax for Writing ISRs.
Note:
Interrupt functions must not be C++ functions; define them in a C module or use an
extern "C" block.