you could use asprintf() that does allocation for you with right string size

Fixed

yeah, I've seen that happening in another kata.
I think when the test is called it loads to the register the bool expected on rdi, and since it does not get overwritten by the call to our function it just stays there hanging

ok I managed to fix my code, I had to put the size argument to malloc on rdi register before calling malloc, I was thinking that would go through the stack

yeah, try doing it in nasm and check how easy it is

Hey, i did this solution with nasm that shouldn't be passing.

https://www.codewars.com/kata/reviews/5fea23fed1f3e000018018f6/groups/60f6596739a54c000106df9c