[PATCH v4] misra: allow discarding 'noreturn' during conversions

[Dmytro Prokopchuk1 <dmytro_prokopchuk1@xxxxxxxx>]

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.

Configure ECLAIR to treat implicit conversions that lose the "noreturn"
attribute on a function 'void (*)(void*)' as safe.

Signed-off-by: Dmytro Prokopchuk <dmytro_prokopchuk1@xxxxxxxx>
---
Changes in v4:
- removed words "function pointer" in subject (to fit in 50 chars)
- wrote deviation description more generic
- adjusted commit message
- adjusted of line capacity

Link to v3:
https://lists.xenproject.org/archives/html/xen-devel/2025-08/msg00009.html
---
 automation/eclair_analysis/ECLAIR/deviations.ecl | 7 +++++++
 docs/misra/deviations.rst                        | 7 +++++++
 docs/misra/rules.rst                             | 9 +++++----
 3 files changed, 19 insertions(+), 4 deletions(-)

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..38b536dfe4 100644
--- a/docs/misra/deviations.rst
+++ b/docs/misra/deviations.rst
@@ -342,6 +342,13 @@ 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
diff --git a/docs/misra/rules.rst b/docs/misra/rules.rst
index 3e014a6298..2b6f30e56d 100644
--- a/docs/misra/rules.rst
+++ b/docs/misra/rules.rst
@@ -400,11 +400,12 @@ 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
-- 
2.43.0