[xen master] xen/gnttab: address a violation of MISRA C Rule 13.6

[patchbot@xxxxxxx]

commit a0094dc136c35e8602f5a01a34904e4e5e2e6b19
Author:     Federico Serafini <federico.serafini@xxxxxxxxxxx>
AuthorDate: Mon Sep 30 14:49:16 2024 +0200
Commit:     Stefano Stabellini <stefano.stabellini@xxxxxxx>
CommitDate: Fri Oct 4 14:24:05 2024 -0700

    xen/gnttab: address a violation of MISRA C Rule 13.6
    
    guest_handle_ok()'s expansion contains a sizeof() involving its
    first argument guest_handle_cast().
    The expansion of the latter, in turn, contains a variable
    initialization.
    
    Since MISRA considers the initialization (even of a local variable)
    a side effect, the chain of expansions mentioned above violates
    MISRA C:2012 Rule 13.6 (The operand of the `sizeof' operator shall not
    contain any expression which has potential side effect).
    
    Refactor the code to address the rule violation.
    
    Suggested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Signed-off-by: Federico Serafini <federico.serafini@xxxxxxxxxxx>
    Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
---
 xen/common/compat/grant_table.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/xen/common/compat/grant_table.c b/xen/common/compat/grant_table.c
index 5ad0debf96..bbb717bf64 100644
--- a/xen/common/compat/grant_table.c
+++ b/xen/common/compat/grant_table.c
@@ -78,12 +78,15 @@ int compat_grant_table_op(
         cmd_op = cmd;
     switch ( cmd_op )
     {
-#define CASE(name) \
-    case GNTTABOP_##name: \
-        if ( unlikely(!guest_handle_okay(guest_handle_cast(uop, \
-                                                           
gnttab_##name##_compat_t), \
-                                         count)) ) \
-            rc = -EFAULT; \
+#define CASE(name)                                                  \
+    case GNTTABOP_ ## name:                                         \
+    {                                                               \
+        XEN_GUEST_HANDLE_PARAM(gnttab_ ## name ## _compat_t) h =    \
+            guest_handle_cast(uop, gnttab_ ## name ## _compat_t);   \
+                                                                    \
+        if ( unlikely(!guest_handle_okay(h, count)) )               \
+            rc = -EFAULT;                                           \
+    }                                                               \
         break
 
 #ifndef CHECK_gnttab_map_grant_ref
--
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