[XEN PATCH v2] x86: p2m-pod: address violation of MISRA C Rule 2.1

[Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>]

The label 'out_unmap' is only reachable after ASSERT_UNREACHABLE,
so the code below is only executed upon erroneously reaching that
program point and calling domain_crash, thus resulting in the
for loop after 'out_unmap' to become unreachable in some configurations.

This is a defensive coding measure to have a safe fallback that is
reachable in non-debug builds, and can thus be deviated with a
comment-based deviation.

No functional change.

Signed-off-by: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
---
Changes in v2:
- rebased against current staging
---
 docs/misra/safe.json      | 8 ++++++++
 xen/arch/x86/mm/p2m-pod.c | 1 +
 2 files changed, 9 insertions(+)

diff --git a/docs/misra/safe.json b/docs/misra/safe.json
index 3f18ef401c7d..880aef784ea1 100644
--- a/docs/misra/safe.json
+++ b/docs/misra/safe.json
@@ -68,6 +68,14 @@
         },
         {
             "id": "SAF-8-safe",
+            "analyser": {
+                "eclair": "MC3R1.R2.1"
+            },
+            "name": "MC3R1.R2.1: statement unreachable in some configurations",
+            "text": "Every path that can reach this statement is preceded by 
statements that make it unreachable in certain configurations (e.g. 
ASSERT_UNREACHABLE). This is understood as a means of defensive programming."
+        },
+        {
+            "id": "SAF-9-safe",
             "analyser": {},
             "name": "Sentinel",
             "text": "Next ID to be used"
diff --git a/xen/arch/x86/mm/p2m-pod.c b/xen/arch/x86/mm/p2m-pod.c
index bd84fe9e27ee..736d3ffd1ff6 100644
--- a/xen/arch/x86/mm/p2m-pod.c
+++ b/xen/arch/x86/mm/p2m-pod.c
@@ -1040,6 +1040,7 @@ out_unmap:
      * Something went wrong, probably crashing the domain.  Unmap
      * everything and return.
      */
+    /* SAF-8-safe Rule 2.1: defensive programming */
     for ( i = 0; i < count; i++ )
         if ( map[i] )
             unmap_domain_page(map[i]);
-- 
2.34.1