Re: [XEN PATCH] misra: merge the two R14.3 invariant-condition deviations

[Jan Beulich <jbeulich@xxxxxxxx>]

On 26.10.2026 04:03, Shuaidong Chen wrote:
> MC3A2.R14.3 ("Controlling expressions shall not be invariant") is
> deviated by two separate entries.  One covers 'if' statements and
> conditional operators and places no restriction on where the invariant
> condition comes from.  The other covers 'switch' statements, but only
> when the controlling expression is a 'sizeof' operator.
> 
> The rationale recorded for the two is the same: the condition is
> deliberate.  Nothing about a 'switch' makes an invariant condition less
> deliberate than the same condition in an 'if', so the 'sizeof'
> restriction reads as an artefact of that entry having been added for
> read_atomic() and friends in arch/x86/include/asm/atomic.h rather than
> as a considered limit.

Well,

    if ( 1 )

can make sense, especially when 1 is the expansion of e.g. IS_ENABLED().
Otoh

    switch ( 1 )

doesn't make a lot of sense, even when it's as a result of the expanding
IS_ENABLED(). I agree that limiting to just sizeof() is unnecessarily
strict; alignof(), for example, should about always be usable where
sizeof() is. Yet making if() and switch() equal is imo going too far. I
realize though that it may be difficult to find a suitable boundary.
Stefano - do you possibly still have notes from the discussions long ago?

> Fold switch_stmt into the general entry and drop the 'sizeof'-restricted
> one, which the general predicate now subsumes.  Invariant 'switch'
> conditions that are not a 'sizeof' become deliberate as a result; that
> is the intent.
> 
> Signed-off-by: Shuaidong Chen <shuaidong.chen@xxxxxxx>

What you don't say at all: Does this help with any remaining violations?

Jan