Re: [PATCH] misra: add deviation for PrintErrMesg() function

[Jan Beulich <jbeulich@xxxxxxxx>]

On 19.08.2025 15:12, Dmytro Prokopchuk1 wrote:
> MISRA C Rule 2.1 states: "A project shall not contain unreachable code."
> 
> The function 'PrintErrMesg()' is implemented to never return control to
> its caller. At the end of its execution, it calls 'blexit()', which, in
> turn, invokes '__builtin_unreachable()'. This makes the 'return false;'
> statement in 'read_file()' function unreachable.

I'm disappointed. In earlier review comments I pointed out that there are
two. Yet you say "the", without further disambiguation.

> --- a/automation/eclair_analysis/ECLAIR/deviations.ecl
> +++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
> @@ -41,6 +41,10 @@ not executable, and therefore it is safe for them to be 
> unreachable."
>  
> -call_properties+={"name(__builtin_unreachable)&&stmt(begin(any_exp(macro(name(ASSERT_UNREACHABLE)))))",
>  {"noreturn(false)"}}
>  -doc_end
>  
> +-doc_begin="Unreachability caused by the call to the 'PrintErrMesg()' 
> function is deliberate, as it terminates execution, ensuring no control flow 
> continues past this point."
> +-config=MC3A2.R2.1,reports+={deliberate, "any_area(^.*PrintErrMesg.*$ && 
> any_loc(file(^xen/common/efi/boot\\.c$)))"}
> +-doc_end

I don't understand the description here, nor ...

> --- a/docs/misra/deviations.rst
> +++ b/docs/misra/deviations.rst
> @@ -97,6 +97,13 @@ Deviations related to MISRA C:2012 Rules:
>         Xen expects developers to ensure code remains safe and reliable in 
> builds,
>         even when debug-only assertions like `ASSERT_UNREACHABLE() are 
> removed.
>  
> +   * - R2.1
> +     - Function `PrintErrMesg()` terminates execution (at the end it calls
> +       `blexit()`, which, in turn, invokes `__builtin_unreachable()`), 
> ensuring
> +       no code beyond this point is ever reached. This guarantees that 
> execution
> +       won't incorrectly proceed or introduce unwanted behavior.
> +     - Tagged as `deliberate` for ECLAIR.

.. the text here. PrintErrMesg() is noreturn. Why would anything need saying 
about
it? Isn't the problem here solely with the tail of read_file(), while other uses
of PrintErrMesg() are okay?

Jan