Re: [PATCH] Add more rules to docs/misra/rules.rst

[Stefano Stabellini <stefano.stabellini@xxxxxxx>]

On Thu, 26 Jan 2023, Jan Beulich wrote:
> On 25.01.2023 21:57, Stefano Stabellini wrote:
> > From: Stefano Stabellini <stefano.stabellini@xxxxxxx>
> > 
> > As agreed during the last MISRA C discussion, I am adding the following
> > MISRA C rules: 7.1, 7.3, 18.3.
> > 
> > I am also adding 13.1 and 18.2 that were "agreed pending an analysis on
> > the amount of violations".
> > 
> > In the case of 13.1 there are zero violations reported by cppcheck.
> > 
> > In the case of 18.2, there are zero violations reported by cppcheck
> > after deviating the linker symbols, as discussed.
> 
> I find this suspicious.

Hi Jan, you are right to be suspicious about 18.2 :-)  cppcheck is
clearly not doing a great job at finding violations. Here is the full
picture:

- cppcheck finds 3 violations, obviously related to linker symbols
specifically common/version.c:xen_build_init and
xen/lib/ctors.c:init_constructors

- Coverity finds 9 violations, not sure which ones

- Eclair finds 56 total on x86. Eclair is always the strictest of the
  three tools and is flagging:
  - the usage of the guest_mode macro in x86/traps.c and other places
  - the usage of the NEED_OP/NEED_IP macros in common/lzo.c
  the remaining violations should be less than 10


> See e.g. ((pg) - frame_table) expressions both Arm
> and x86 have. frame_table is neither a linker generated symbol, nor does
> it represent something that the compiler (or static analysis tools) would
> recognized as an "object". Still, the entire frame table of course
> effectively is an object (array), yet there's no way for any tool to
> actually recognize the array dimension.

I used cppcheck in my original email because it is the only tool today
where I can add a deviation as an in-code comment, re-run the scan,
and what happens (see the number of violations go down.)

However also considering that Coverity reports less than 10, and Eclair
reports more but due to only 2-3 macros, I think 18.2 should be
manageable.