Re: [PATCH 1/3] misra: add deviation for rules 21.1 and 21.2

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 23 Apr 2025, Jan Beulich wrote:
> On 23.04.2025 01:43, victorm.lira@xxxxxxx wrote:
> > From: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
> > 
> > MISRA C Rules 21.1 ("#define and #undef shall not be used on a
> > reserved identifier or reserved macro name") and R21.2 ("A reserved
> > identifier or reserved macro name shall not be declared") violations
> > are not problematic for Xen, as it does not use the C or POSIX
> > libraries.
> 
> In the course of all the Misra discussions it was pointed out more than
> once that it's not just the titles which matter, but also the
> "Amplification" text. While the latter two of the three bullet points
> applying to both rules clearly are library-centric, the first one isn't.
> In that light it's entirely unclear to me how ...
> 
> > Xen uses -fno-builtin and -nostdinc to ensure this, but there are still
> > __builtin_* functions from the compiler that are available so
> > a deviation is formulated for all identifiers not starting with
> > "__builtin_".
> > 
> > The missing text of a deviation for Rule 21.2 is added to
> > docs/misra/deviations.rst.
> > 
> > To avoid regressions, tag both rules as clean and add them to the
> > monitored set.
> 
> ... our code base could be anywhere near clean towards these two rules.


Given the section these two rules belong to "Standard libraries" and
given the rest of the rule description, it is clear to me that the
conflicts and undefined behaviors the two rules are trying to prevent
are conflicts with C or POSIX libraries. Nicola is the original author
of the patch and he has more experience with MISRA and I would trust
his interpretation.