There are several compiler helper functions that the compiler uses to handle operations that do not have a short machine code equivalent. For example, integer divide uses a function that is implicitly called by the compiler if there is no divide instruction available in the target instruction set. (ARMv7-R and ARMv7-M architectures use the instructions SDIV and UDIV in Thumb state. Other versions of the ARM architecture also use compiler functions that are implicitly invoked.)

Integer divide, and all the floating-point functions if you use a floating-point mode that involves throwing exceptions, require __rt_raise() to handle math errors. Re-implementing __rt_raise() enables all the math functions, and it avoids having to link in all the signal-handling library code.