[PATCH] misra: add deviation for MISRA C Rule 18.3

[Dmytro Prokopchuk1 <dmytro_prokopchuk1@xxxxxxxx>]

MISRA C Rule 18.3 states:"The relational operators >, >=, < and <= shall
not be applied to objects of pointer type except where they point into
the same object."

Comparisons in the 'find_text_region()' function are safe because linker
symbols '_stext' and '_etext' represent fixed virtual addresses within
the same '.text' region, and the function 'addr' argument is explicitly
compared to known valid memory bounds ('text_start' and 'text_end')
derived from these linker symbols:
    if ( (void *)addr >= iter->text_start &&
         (void *)addr <  iter->text_end )

Configure Eclair to suppress violation reports occured in the function
'find_text_region()'. 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/1993673043
---
 automation/eclair_analysis/ECLAIR/deviations.ecl | 6 ++++++
 docs/misra/deviations.rst                        | 8 ++++++++
 2 files changed, 14 insertions(+)

diff --git a/automation/eclair_analysis/ECLAIR/deviations.ecl 
b/automation/eclair_analysis/ECLAIR/deviations.ecl
index 7f3fd35a33..32b596c9da 100644
--- a/automation/eclair_analysis/ECLAIR/deviations.ecl
+++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
@@ -590,6 +590,12 @@ C99 Undefined Behaviour 45: Pointers that do not point 
into, or just beyond, the
 -config=MC3A2.R18.2,reports+={safe, 
"any_area(any_loc(any_exp(macro(^page_to_mfn$))))"}
 -doc_end
 
+-doc_begin="Comparisons in the 'find_text_region()' function are safe because 
linker symbols '_stext' and '_etext' represent fixed
+virtual addresses within the same '.text' region, and the function 'addr' 
argument is explicitly compared to known valid memory
+bounds ('text_start' and 'text_end') derived from these linker symbols."
+-config=MC3A2.R18.3,reports+={safe, 
"any_area(any_loc(file(^xen/common/virtual_region\\.c$))&&context(name(find_text_region)))"}
+-doc_end
+
 -doc_begin="Flexible array members are deliberately used and XEN developers 
are aware of the dangers related to them:
 unexpected result when the structure is given as argument to a sizeof() 
operator and the truncation in assignment between structures."
 -config=MC3A2.R18.7,reports+={deliberate, "any()"}
diff --git a/docs/misra/deviations.rst b/docs/misra/deviations.rst
index 2119066531..a726fb22a8 100644
--- a/docs/misra/deviations.rst
+++ b/docs/misra/deviations.rst
@@ -586,6 +586,14 @@ Deviations related to MISRA C:2012 Rules:
        are safe.
      - Tagged as `safe` for ECLAIR.
 
+   * - R18.3
+     - Comparisons in the 'find_text_region()' function are safe because
+       linker symbols '_stext' and '_etext' represent fixed virtual
+       addresses within the same '.text' region, and the function 'addr'
+       argument is explicitly compared to known valid memory bounds
+       ('text_start' and 'text_end') derived from these linker symbols.
+     - Tagged as `safe` for ECLAIR.
+
    * - R20.4
      - The override of the keyword \"inline\" in xen/compiler.h is present so
        that section contents checks pass when the compiler chooses not to
-- 
2.43.0