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



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



 


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