MISRA-C and Zephyr

Flavio Ceolin

Hi guys,

Recently I start working on Zephyr to be compliant with MISRA-C. I'd
like to give you a brief overview about MISRA-C and why this is valuable
to Zephyr.

MISRA-C is code guideline that define a subset of C that aims to make
embedded software safer, more secure and especially more portable. It
does it defining a set of guidelines that try to fill the gaps between C
specification and different implementations, it means things with
undefined behavior, unspecified behavior and things that the
compiler implementation is free to choose the behavior.

That's been said, every MISRA-C guideline is classified as rule or
directive. These rules and directives are classified in mandatory,
required or advisory. Mandatory means that the code must be compliant
with the guideline, required the code also must be compliant but it's
possible creating a deviation, advisory are recommendations and don't
need a formal deviation if ignored.

So, what about Zephyr ? Zephyr currently contains ~8k violations and
approximately half are either required or mandatory (~10). I'm filling
issues on github
(https://github.com/zephyrproject-rtos/zephyr/labels/MISRA-C) that
contains (I hope) enough information about the problem and some
suggestions to approach them. I ask everybody to take a look on them and
give opinions. Some of them required collaboration of diverse code-owners
and developers.

To finish, why MISRA-C is valuable to Zephyr ?

- Following a standard helps with maintainability of the code.
- Process standards like ISO26262 and IEC61508 used to develop critical
products require that the code follows a code guideline (ISO26262
explicitly recommends MISRA-C).
- Other proprietary RTOs are MISRA-C compliant, if we want to be more
with them, is good too.
- It'll help us spot problems bugs and avoid them. I've worked this week
in two guidelines that are not that intrusive and I found at least
three real bugs.
- We'll have less problems with different compilers, the mandatory
violations are regarding using specific gcc builtin functions.

If you have any questions regarding MISRA-C lets discuss it :)

Flavio Ceolin

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