MISRA C Do not use recursions

[ceolin]

MISRA-C does not allows that a function call themselves, either directly or indirectly. Currently there is only one spot in Zephyr doing it _rb_walk().

rule 17.2

part of: #9552

[ceolin]

@andyross if you have time can you take a look on this ?

[andyross]

MISRA exists just to make my life miserable, doesn't it?

(FWIW: I know of at least one other in mempool, though that one is proper tail recursion and maybe MISRA has an exception for that?)

Yeah, I'll take it. FWIW: there is a non-recursive walker (a FOREACH kind of thing), but it's got significantly higher code size.

[ceolin]

it does feel to be in my shoes :)

Yeah, I'm sorry for that, I know that not using recursion here will increase and make it more complicated.

[pfalcon]

MISRA exists just to make my life miserable, doesn't it?

Everyone's.

proper tail recursion and maybe MISRA has an exception for that?

I'm sure tail recursion doesn't exist in MISRA's world. And speaking seriously, C doesn't guarantee tail-recursive optimization, so... just don't tell anyone there's another func like that ;-).

[andyross]

Actually looking at this more carefully, this should be doable for 1.14. The two spots I know of are rb_walk above, and a tail recursion case in mempool. The latter can be turned into iteration with 2-3 lines of code and an extra level of indentation, and it turns out the former is in fact no longer used in the tree beyond the test case (I needed it in the scheduler at one point, but I don't think that usage ever even merged). Will submit a patch.