[PATCH] misra: add deviation of Rule 2.1 for BUG() macro

[Dmytro Prokopchuk1 <dmytro_prokopchuk1@xxxxxxxx>]

MISRA C Rule 2.1 states: "A project shall not contain unreachable code".
Functions that are non-returning and are not explicitly annotated with
the 'noreturn' attribute are considered a violation of this rule.

In certain cases, some functions might be non-returning in specific build
configurations due to call to '__builtin_unreachable()' in the expansion
of the macro 'BUG()':
 - functions 'gicv3_do_LPI()' and 'gicv3_its_setup_collection()' when the
config CONFIG_HAS_ITS is not defined, it is intentionally used to catch
and prevent any unintended execution of code that should only run when
ITS is available;
 - function 'prepare_acpi()' when the config CONFIG_ACPI is not defined,
to trigger an error if ACPI-related features are used incorrectly.

To account for that in specific builds, update the ECLAIR configuration
to deviate these violations. Update deviations.rst file accordingly.
No functional changes.

Signed-off-by: Dmytro Prokopchuk <dmytro_prokopchuk1@xxxxxxxx>
---
Test CI pipeline:
https://gitlab.com/xen-project/people/dimaprkp4k/xen/-/pipelines/2000738682
---
 automation/eclair_analysis/ECLAIR/deviations.ecl | 11 +++++++++++
 docs/misra/deviations.rst                        | 13 +++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/automation/eclair_analysis/ECLAIR/deviations.ecl 
b/automation/eclair_analysis/ECLAIR/deviations.ecl
index 7f3fd35a33..336aec58c2 100644
--- a/automation/eclair_analysis/ECLAIR/deviations.ecl
+++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
@@ -41,6 +41,17 @@ not executable, and therefore it is safe for them to be 
unreachable."
 
-call_properties+={"name(__builtin_unreachable)&&stmt(begin(any_exp(macro(name(ASSERT_UNREACHABLE)))))",
 {"noreturn(false)"}}
 -doc_end
 
+-doc_begin="The 'BUG()' macro is intentionally used in the 'prepare_acpi()' 
function in specific build configuration
+(when the config CONFIG_ACPI is not defined) to trigger an error if 
ACPI-related features are used incorrectly."
+-config=MC3A2.R2.1,reports+={deliberate, 
"any_area(any_loc(file(^xen/arch/arm/include/asm/domain_build\\.h$))&&context(name(prepare_acpi)))"}
+-doc_end
+
+-doc_begin="The 'BUG()' macro is intentionally used in 'gicv3_do_LPI'() and 
'gicv3_its_setup_collection()' functions
+in specific build configuration (when the config CONFIG_HAS_ITS is not 
defined) to catch and prevent any unintended
+execution of code that should only run when ITS is available."
+-config=MC3A2.R2.1,reports+={deliberate, 
"any_area(any_loc(file(^xen/arch/arm/include/asm/gic_v3_its\\.h$))&&context(name(gicv3_do_LPI||gicv3_its_setup_collection)))"}
+-doc_end
+
 -doc_begin="Proving compliance with respect to Rule 2.2 is generally 
impossible:
 see https://arxiv.org/abs/2212.13933 for details. Moreover, peer review gives 
us
 confidence that no evidence of errors in the program's logic has been missed 
due
diff --git a/docs/misra/deviations.rst b/docs/misra/deviations.rst
index 2119066531..96eb202502 100644
--- a/docs/misra/deviations.rst
+++ b/docs/misra/deviations.rst
@@ -97,6 +97,19 @@ Deviations related to MISRA C:2012 Rules:
        Xen expects developers to ensure code remains safe and reliable in 
builds,
        even when debug-only assertions like `ASSERT_UNREACHABLE() are removed.
 
+   * - R2.1
+     - The 'BUG()' macro is intentionally used in the 'prepare_acpi()' function
+       in specific build configuration (when the config CONFIG_ACPI is not
+       defined) to trigger an error if ACPI-related features are used 
incorrectly.
+     - Tagged as `deliberate` for ECLAIR.
+
+   * - R2.1
+     - The 'BUG()' macro is intentionally used in 'gicv3_do_LPI'() and
+       'gicv3_its_setup_collection()' functions in specific build configuration
+       (when the config CONFIG_HAS_ITS is not defined) to catch and prevent any
+       unintended execution of code that should only run when ITS is available.
+     - Tagged as `deliberate` for ECLAIR.
+
    * - R2.2
      - Proving compliance with respect to Rule 2.2 is generally impossible:
        see `<https://arxiv.org/abs/2212.13933>`_ for details. Moreover, peer
-- 
2.43.0