automation/eclair: generalize the noreturn function-pointer deviation

The R11.1 safe cast only matched void noreturn (*)(void *). Accept a
conversion where noreturn is omitted and the signature is otherwise
compatible. canonical() covers typeof destinations, and
compatible_deep_unqualified keeps the parameter and return types aligned.

Discarding noreturn does not change the calling convention. Code after
the call is unreachable when every possible callee is noreturn. Leaving
that code in place is a tolerated Rule 2.1 violation. The full rationale
is in docs/misra/deviations.rst.

Signed-off-by: Dmytro Prokopchuk <dmytro_prokopchuk1@epam.com>
Acked-by: Nicola Vetrini <nicola.vetrini@bugseng.com> # automation/eclair_analysis/.*
Acked-by: Jan Beulich <jbeulich@suse.com>

docs/misra/deviations.rst

@@ -392,10 +392,14 @@ Deviations related to MISRA C:2012 Rules:
      - Tagged as `safe` for ECLAIR.
 
    * - R11.1
-     - The conversion from 'void noreturn (*)(...)' to 'void (*)(...)' is safe
-       because the semantics of the 'noreturn' attribute do not alter the calling
-       convention or behavior of the resulting code, parameters handling remain
-       consistent.
+     - The conversion from a noreturn function pointer to a function pointer
+       with noreturn omitted but an otherwise compatible signature does not
+       alter the calling convention. The callee does not return, so code
+       following a call through the resulting pointer is unreachable. The
+       compiler may delete that unreachable code when it can see that all
+       of the possible callees are noreturn, or it may leave the code in
+       place. Xen's behavior is the same in either case. Code left in place
+       is a tolerated violation of Rule 2.1.
      - Tagged as `safe` for ECLAIR.
 
    * - R11.2

docs/misra/rules.rst

@@ -435,9 +435,11 @@ maintainers if you want to suggest a change.
        and any other type
      - All conversions to integer types are permitted if the destination
        type has enough bits to hold the entire value. Conversions to bool
-       and void* are permitted. Conversions from 'void noreturn (*)(...)'
-       to 'void (*)(...)' are permitted. Conversions from [unsigned] long
-       or '(void *)' to a function pointer are permitted.
+       and '(void *)' are permitted. Conversions from a noreturn function
+       pointer to a function pointer with noreturn omitted but an otherwise
+       compatible signature are permitted.
+       Conversions from [unsigned] long or '(void *)' to a function pointer
+       are permitted.
        Example::
 
            unsigned long func_addr = (unsigned long)&some_function;