Re: [PATCH 1/2] automation/eclair_analysis: deviate MISRA C Rule 21.2

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 20 Jun 2024, Jan Beulich wrote:
> On 19.06.2024 19:09, Alessandro Zucchelli wrote:
> > Rule 21.2 reports identifiers reserved for the C and POSIX standard
> > libraries: all xen's translation units are compiled with option
> > -nostdinc, this guarantees that these libraries are not used, therefore
> > a justification is provided for allowing uses of such identifiers in
> > the project.
> > Builtins starting with "__builtin_" still remain available.
> > 
> > No functional change.
> > 
> > Signed-off-by: Alessandro Zucchelli <alessandro.zucchelli@xxxxxxxxxxx>
> > ---
> >  automation/eclair_analysis/ECLAIR/deviations.ecl | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> > 
> > diff --git a/automation/eclair_analysis/ECLAIR/deviations.ecl 
> > b/automation/eclair_analysis/ECLAIR/deviations.ecl
> > index 447c1e6661..9fa9a7f01c 100644
> > --- a/automation/eclair_analysis/ECLAIR/deviations.ecl
> > +++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
> > @@ -487,6 +487,17 @@ leads to a violation of the Rule are deviated."
> >  # Series 21.
> >  #
> >  
> > +-doc_begin="Rules 21.1 and 21.2 report identifiers reserved for the C and 
> > POSIX
> > +standard libraries: if these libraries are not used there is no reason to 
> > avoid such
> > +identifiers. All xen's translation units are compiled with option 
> > -nostdinc,
> > +this guarantees that these libraries are not used. Some compilers could 
> > perform
> > +optimization using built-in functions: this risk is partially addressed by
> > +using the compilation option -fno-builtin. Builtins starting with 
> > \"__builtin_\"
> > +still remain available."
> 
> While the sub-section "Reserved Identifiers" is part of Section 7,
> "Library", close coordination is needed between the library and the
> compiler, which only together form an "implementation". Therefore any
> use of identifiers beginning with two underscores or beginning with an
> underscore and an upper case letter is at risk of colliding not only
> with a particular library implementation (which we don't use), but
> also of such with a particular compiler implementation (which we cannot
> avoid to use). How can we permit use of such potentially problematic
> identifiers?

Alternative question: is there a way we can check if there is clash of
some sort between a compiler implementation of something and a MACRO or
identifier we have in Xen? An error or a warning from the compiler for
instance? That could be an easy way to prove we are safe.

Also, can we use the fact that the compiler we use is the same compiler
used to compile Linux, and Linux makes extensive use of identifiers and
macros starting with underscores as one of the reason for being safe
from clashes?