[PATCH v3] misra: allow discarding 'noreturn' during function pointer conversions

[Dmytro Prokopchuk1 <dmytro_prokopchuk1@xxxxxxxx>]

The conversion from a function pointer with the 'noreturn' attribute
('void noreturn (*)(void *)') to a function pointer type ('void (*)(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 a 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.

Configure ECLAIR to treat implicit conversions that lose the "noreturn"
attribute on a function 'void (*)(void*)' as safe. This is because the
deviation actually just deviates 'void noreturn (*)(void*)' -> 'void 
(*)(void*)'.

Signed-off-by: Dmytro Prokopchuk <dmytro_prokopchuk1@xxxxxxxx>
---
Changes in v3:
- updated commit subject 

Link to v2: 
https://patchew.org/Xen/3b821bc506b04bf7ff8bf5a3712449d45429dc90.1753791398.git.dmytro._5Fprokopchuk1@xxxxxxxx/
---
 automation/eclair_analysis/ECLAIR/deviations.ecl | 7 +++++++
 docs/misra/deviations.rst                        | 6 ++++++
 docs/misra/rules.rst                             | 3 ++-
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/automation/eclair_analysis/ECLAIR/deviations.ecl 
b/automation/eclair_analysis/ECLAIR/deviations.ecl
index 483507e7b9..0e04681c4c 100644
--- a/automation/eclair_analysis/ECLAIR/deviations.ecl
+++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
@@ -367,6 +367,13 @@ 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()))
diff --git a/docs/misra/deviations.rst b/docs/misra/deviations.rst
index e78179fcb8..4e430bb17e 100644
--- a/docs/misra/deviations.rst
+++ b/docs/misra/deviations.rst
@@ -342,6 +342,12 @@ 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 (*)(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.
+     - 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
diff --git a/docs/misra/rules.rst b/docs/misra/rules.rst
index 3e014a6298..82a26162a9 100644
--- a/docs/misra/rules.rst
+++ b/docs/misra/rules.rst
@@ -404,7 +404,8 @@ maintainers if you want to suggest a change.
        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.
+       bool and void* are permitted. Conversions from 'void noreturn (*)(void 
*)'
+       to 'void (*)(void *)' are permitted.
 
    * - `Rule 11.2 
<https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_11_02.c>`_
      - Required
-- 
2.43.0