[8/9] xen: add deviations for Rule 11.8

Commit Message

Simone Ballarin Dec. 14, 2023, 12:07 p.m. UTC

From: Maria Celeste Cesario <[e-mail]>

The xen sources contain violations of MISRA C:2012 Rule 11.8 whose
headline states:
"A conversion shall not remove any const, volatile or _Atomic qualification
from the type pointed to by a pointer".

Deviate use of macro container_of.
Deviate use of function ERR_CAST.

Signed-off-by: Maria Celeste Cesario  <[e-mail]>
Signed-off-by: Simone Ballarin  <[e-mail]>
---
container_of: Fixing this violation would require the declaration of a new
 macro taking advantage of the return value of the ternary operator ?: :
 its return value preserves qualifiers present on both expression, hence
 returning void* or qualified void* depending on pointer type, like in this macro:
 '#define same_constness_void_ptr(ptr) ((typeof((false ? (void*) 1 : (ptr)))) (ptr))'
 The result could then be used with a Generic to avoid the cast.
---
 automation/eclair_analysis/ECLAIR/deviations.ecl | 12 ++++++++++++
 docs/misra/deviations.rst                        | 13 +++++++++++++
 2 files changed, 25 insertions(+)

Comments

Jan Beulich Dec. 14, 2023, 12:46 p.m. UTC | #1

On 14.12.2023 13:07, Simone Ballarin wrote:
> --- a/automation/eclair_analysis/ECLAIR/deviations.ecl
> +++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
> @@ -292,6 +292,18 @@ constant expressions are required.\""
>  # Series 11
>  #
>  
> +-doc_begin="Violations caused by container_of are due to pointer arithmetic operations
> +with the provided offset. The resulting pointer is then immediately cast back to its
> +original type, which preserves the qualifier. This use can be deemed as safe.
> +Fixing this violation would require to increase code complexity and lower readability."
> +-config=MC3R1.R11.8,reports+={safe,"any_area(any_loc(any_exp(macro(^container_of$))))"}
> +-doc_end
> +
> +-doc_begin="This function is made to explicitly cast an error-valued pointer to a void
> +pointer type to make it clear that's what's going on, so the violation is deliberate."
> +-config=MC3R1.R11.8,reports+={deliberate,"all_area(context(^ERR_CAST\\(.*$))"}
> +-doc_end

While the wording is okay here, ...

> --- a/docs/misra/deviations.rst
> +++ b/docs/misra/deviations.rst
> @@ -248,6 +248,19 @@ Deviations related to MISRA C:2012 Rules:
>         If no bits are set, 0 is returned.
>       - Tagged as `safe` for ECLAIR.
>  
> +   * - R11.8
> +     - Violations caused by container_of are due to pointer arithmetic operations
> +       with the provided offset. The resulting pointer is then immediately cast back to its
> +       original type, which preserves the qualifier. This use can be deemed as safe.
> +       Fixing this violation would require to increase code complexity and lower readability.
> +     - Tagged as `safe` for ECLAIR.
> +    
> +   * - R11.8
> +     - This function is made to explicitly cast an error-valued pointer to a
> +       void pointer type to make it clear that's what's going on, so the
> +       violation is deliberate.
> +     - Tagged ad `deliberate` for ECLAIR.

... "This function" here is entirely unclear. However, seeing ERR_CAST() has
no users, wouldn't we be better off simply removing it? (Otherwise, nit:
"Tagged as ...".)

Jan

Patch

diff --git a/automation/eclair_analysis/ECLAIR/deviations.ecl b/automation/eclair_analysis/ECLAIR/deviations.ecl
index 683f2bbfe8..d3e32a6ac8 100644
--- a/automation/eclair_analysis/ECLAIR/deviations.ecl
+++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
@@ -292,6 +292,18 @@  constant expressions are required.\""
 # Series 11
 #
 
+-doc_begin="Violations caused by container_of are due to pointer arithmetic operations
+with the provided offset. The resulting pointer is then immediately cast back to its
+original type, which preserves the qualifier. This use can be deemed as safe.
+Fixing this violation would require to increase code complexity and lower readability."
+-config=MC3R1.R11.8,reports+={safe,"any_area(any_loc(any_exp(macro(^container_of$))))"}
+-doc_end
+
+-doc_begin="This function is made to explicitly cast an error-valued pointer to a void
+pointer type to make it clear that's what's going on, so the violation is deliberate."
+-config=MC3R1.R11.8,reports+={deliberate,"all_area(context(^ERR_CAST\\(.*$))"}
+-doc_end
+
 -doc_begin="This construct is used to check if the type is scalar, and for this purpose the use of 0 as a null pointer constant is deliberate."
 -config=MC3R1.R11.9,reports+={deliberate, "any_area(any_loc(any_exp(macro(^__ACCESS_ONCE$))))"
 }
diff --git a/docs/misra/deviations.rst b/docs/misra/deviations.rst
index eda3c8100c..98733d636d 100644
--- a/docs/misra/deviations.rst
+++ b/docs/misra/deviations.rst
@@ -248,6 +248,19 @@  Deviations related to MISRA C:2012 Rules:
        If no bits are set, 0 is returned.
      - Tagged as `safe` for ECLAIR.
 
+   * - R11.8
+     - Violations caused by container_of are due to pointer arithmetic operations
+       with the provided offset. The resulting pointer is then immediately cast back to its
+       original type, which preserves the qualifier. This use can be deemed as safe.
+       Fixing this violation would require to increase code complexity and lower readability.
+     - Tagged as `safe` for ECLAIR.
+    
+   * - R11.8
+     - This function is made to explicitly cast an error-valued pointer to a
+       void pointer type to make it clear that's what's going on, so the
+       violation is deliberate.
+     - Tagged ad `deliberate` for ECLAIR.
+
    * - R11.9
      - __ACCESS_ONCE uses an integer, which happens to be zero, as a
        compile time check. The typecheck uses a cast. The usage of zero or other