x86/domain: deviate violation of MISRA C Rule 20.12

MISRA C Rule 20.12 states: "A macro parameter used as an operand to
the # or ## operators, which is itself subject to further macro replacement,
shall only be used as an operand to these operators".

In this case, builds where CONFIG_COMPAT=y the fpu_ctxt
macro is used both as a regular macro argument and as an operand for
stringification in the expansion of CHECK_FIELD_.
This is deviated using a SAF-x-safe comment.

No functional change.

Signed-off-by: Nicola Vetrini <nicola.vetrini@bugseng.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

docs/misra/safe.json

@@ -52,6 +52,14 @@
         },
         {
             "id": "SAF-6-safe",
+            "analyser": {
+                "eclair": "MC3R1.R20.12"
+            },
+            "name": "MC3R1.R20.12: use of a macro argument that deliberately violates the Rule",
+            "text": "A macro parameter that is itself a macro is intentionally used within the macro both as a regular parameter and for text replacement."
+        },
+        {
+            "id": "SAF-7-safe",
             "analyser": {},
             "name": "Sentinel",
             "text": "Next ID to be used"

xen/arch/x86/domain.c

@@ -1084,6 +1084,7 @@ void arch_domain_creation_finished(struct domain *d)
 #ifdef CONFIG_COMPAT
 #define xen_vcpu_guest_context vcpu_guest_context
 #define fpu_ctxt fpu_ctxt.x
+/* SAF-6-safe Rule 20.12 expansion of macro fpu_ctxt with CONFIG_COMPAT */
 CHECK_FIELD_(struct, vcpu_guest_context, fpu_ctxt);
 #undef fpu_ctxt
 #undef xen_vcpu_guest_context

xen/arch/x86/domctl.c

@@ -1326,6 +1326,7 @@ long arch_do_domctl(
 #ifdef CONFIG_COMPAT
 #define xen_vcpu_guest_context vcpu_guest_context
 #define fpu_ctxt fpu_ctxt.x
+/* SAF-6-safe Rule 20.12 expansion of macro fpu_ctxt with CONFIG_COMPAT */
 CHECK_FIELD_(struct, vcpu_guest_context, fpu_ctxt);
 #undef fpu_ctxt
 #undef xen_vcpu_guest_context