Re: [PATCH] docs/misra: add exceptions to rules

[Jan Beulich <jbeulich@xxxxxxxx>]

(re-adding xen-devel@)

On 22.08.2023 17:09, Nicola Vetrini wrote:
> 
>>>> +         - Switch with a controlling value incompatible with labeled
>>>> +           statements
>>>
>>> What does this mean?
>>
>> I am not certain about this one actually. It could be when we have:
>>
>> switch (var) {
>>   case 1:
>>       something();
>>       break;
>>   case 2:
>>       something();
>>       break;
>> }
>>
>> and var could be 3 in theory?
>>
>> Nicola, please confirm.
>>
>>
> 
> This one is about case labels that are statically determined not to be 
> reachable (and hence
> saying that the code under that label is unreachable is not inaccurate) 
> because the
> controlling expression of the switch statement can never have such 
> value. An example below:
> 
> $ cat p.c
> int f(void) {
>    char c;
>    switch (c) {
>      case 260:
>        return 260;
>      case 4:
>        return 4;
>    }
> }
> 
> $ eclair_env -enable=MC3.R2.1,B.REPORT.TXT -- gcc -c p.c
> violation for rule MC3.R2.1: (required) A project shall not contain 
> unreachable code. (untagged)
> p.c:3.3-3.8: Loc #1 [culprit: `switch' statement has a controlling value 
> incompatible with labeled statement]
>    switch (c) {
>    <~~~~>
> p.c:5.14-5.16: Loc #2 [evidence: integer literal is unreachable]
>        return 260;
>               <~>
> 
> This is also true for things like
> 
> switch(sizeof(int)) {
>    case 2:
>      ...
>    case 4:
>      ...
> }

Ah yes, we certainly have quite a few of those. Not sure how to best
describe such for the doc, but what was suggested (still visible at
the top) doesn't get this across, I'm afraid,

Jan