misra: allow discarding 'noreturn' during conversions

The conversion from a function pointer with the 'noreturn' attribute
('void noreturn (*)(...)') to a function pointer type ('void (*)(...)'
causes type incompatibility according to MISRA C Rule 11.1, which
forbids conversions between incompatible function pointer types.

The violation occurs at the call site:
    smp_call_function(halt_this_cpu, NULL, 0);
where 'halt_this_cpu' with type 'void noreturn (*)(void *)' is passed to
'smp_call_function' expecting function pointer of type 'void (*)(void *)'.

The 'noreturn' attribute does not change the function calling convention
or parameter handling at runtime, making the conversion safe.

For now, configure Eclair to just treat implicit conversions that lose
the "noreturn" attribute on a function 'void (*)(void*)' as safe.

Signed-off-by: Dmytro Prokopchuk <dmytro_prokopchuk1@epam.com>
Acked-by: Jan Beulich <jbeulich@suse.com> # docs
Reviewed-by: Nicola Vetrini <nicola.vetrini@bugseng.com> # ECLAIR

automation/eclair_analysis/ECLAIR/deviations.ecl

@@ -372,6 +372,13 @@ constant expressions are required.\""
 }
 -doc_end
 
+-doc_begin="The conversion from 'void noreturn (*)(void *)' to 'void (*)(void *)' is safe
+because the semantics of the 'noreturn' attribute do not alter the calling convention or behavior of the resulting code."
+-config=MC3A2.R11.1,casts+={safe,
+  "kind(bitcast)&&to(type(pointer(inner(return(builtin(void))&&all_param(1, pointer(builtin(void)))))))&&from(expr(skip(!syntactic(),
+   ref(property(noreturn)))))"} 
+-doc_end
+
 -doc_begin="The conversion from a pointer to an incomplete type to unsigned long does not lose any information, provided that the target type has enough bits to store it."
 -config=MC3A2.R11.2,casts+={safe,
   "from(type(any()))

docs/misra/deviations.rst

@@ -353,6 +353,13 @@ Deviations related to MISRA C:2012 Rules:
        semantics that do not lead to unexpected behaviour.
      - 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.
+     - Tagged as `safe` for ECLAIR.
+
    * - R11.2
      - The conversion from a pointer to an incomplete type to unsigned long
        does not lose any information, provided that the target type has enough

docs/misra/rules.rst

@@ -409,11 +409,12 @@ maintainers if you want to suggest a change.
 
    * - `Rule 11.1 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_11_01.c>`_
      - Required
-     - Conversions shall not be performed between a pointer to a
-       function and any other type
+     - Conversions shall not be performed between a pointer to a function
+       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.
+       type has enough bits to hold the entire value. Conversions to bool
+       and void* are permitted. Conversions from 'void noreturn (*)(...)'
+       to 'void (*)(...)' are permitted.
 
    * - `Rule 11.2 <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_11_02.c>`_
      - Required