Re: [XEN PATCH v2 1/3] EFI: address a violation of MISRA C Rule 13.6

[Roberto Bagnara <roberto.bagnara@xxxxxxxxxxx>]

On 2024-09-30 15:07, Jan Beulich wrote:
> On 30.09.2024 14:49, Federico Serafini wrote:
> > guest_handle_ok()'s expansion contains a sizeof() involving its
> > first argument which is guest_handle_cast().
> > The expansion of the latter, in turn, contains a variable
> > initialization.
> >
> > Since MISRA considers the initialization (even of a local variable)
> > a side effect, the chain of expansions mentioned above violates
> > MISRA C:2012 Rule 13.6 (The operand of the `sizeof' operator shall not
> > contain any expression which has potential side effect).
> I'm afraid I need to ask for clarification of terminology and alike here.
> While the Misra doc has a section on Persistent Side Effects in its
> Glossary appendix, what constitutes a side effect from its pov isn't
> really spelled out anywhere. Which in turn raises the question whether it
> is indeed Misra (and not just Eclair) which deems initialization a side
> effect. This is even more so relevant as 13.6 talks of only expressions,
> yet initializers fall under declarations (in turn involving an expression
> on the rhs of the equal sign).
>
> All the same of course affects patch 2 then, too.
MISRA C leaves the definition of "side effect" to the C Standard.
E.g., C18 5.1.2.3p2:

  Accessing a volatile object, modifying an object, modifying a file,
  or calling a function that does any of those operations are all
  side effects,[omitted irrelevant footnote reference] which are
  changes in the state of the execution environment.

The MISRA C:2012/2023 Glossary entry for "Persistent side effect"
indirectly confirms that initialization is always a side effect.

Kind regards,

   Roberto