OP solved it, closing

Close enough, but you missed this part If the **final result** is longer than 140 chars it must return false.

thank you!

That's a problem with your code, not a kata issue, you only test match doesn't return null and then you work with the original string. While chaining methods seems nice, it makes more difficult to know where your code is wrong. Only chain when you're sure about what your code does.

Thanks for the clarification. For some reason I expected that it is intended to use the RDI-pointer not only for the length but also for the result arr. Have a nice day.

The result is a dynamically allocated (e.g., with malloc) array. The address of this array should be returned in rax. The length of this array should be written into [rdi].

I recommend to solve this kata in C first because the C version has the same requirements as NASM.

Because your code is too slow for big inputs:

Take a look at performance: some lists have thousands of elements.