[PATCH v2 1/2] x86: x86_emulate: address violations of MISRA C Rule 19.1

[<victorm.lira@xxxxxxx>]

From: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>

Rule 19.1 states: "An object shall not be assigned or copied
to an overlapping object". In the function like macro "get_rep_prefix",
one member of a union is assigned the value of another member. Reading from one
member and writing to the other violates the rule, while not causing Undefined
Behavior due to their relative sizes. Instead, use casts combined with exactly
overlapping accesses to address violations.

No functional change.

Signed-off-by: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
Signed-off-by: Federico Serafini <federico.serafini@xxxxxxxxxxx>
Signed-off-by: Victor Lira <victorm.lira@xxxxxxx>
---
Changes in v2:
- Use casts combined with exactly overlapping accesses to address
  violations
- fix commit message
---
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: Anthony PERARD <anthony.perard@xxxxxxxxxx>
Cc: Michal Orzel <michal.orzel@xxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Julien Grall <julien@xxxxxxx>
Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
Cc: Federico Serafini <federico.serafini@xxxxxxxxxxx>
Cc: Bertrand Marquis <bertrand.marquis@xxxxxxx>
---
 xen/arch/x86/x86_emulate/x86_emulate.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c 
b/xen/arch/x86/x86_emulate/x86_emulate.c
index 8e14ebb35b..d678855238 100644
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -527,8 +527,8 @@ static inline void put_loop_count(
         if ( !amd_like(ctxt) && mode_64bit() && ad_bytes == 4 )         \
         {                                                               \
             _regs.r(cx) = 0;                                            \
-            if ( extend_si ) _regs.r(si) = _regs.esi;                   \
-            if ( extend_di ) _regs.r(di) = _regs.edi;                   \
+            if ( extend_si ) _regs.r(si) = (uint32_t)_regs.r(si);        \
+            if ( extend_di ) _regs.r(di) = (uint32_t)_regs.r(di);        \
         }                                                               \
         goto complete_insn;                                             \
     }                                                                   \
@@ -2029,7 +2029,7 @@ x86_emulate(
         switch ( op_bytes )
         {
         case 2: _regs.ax = (int8_t)_regs.ax; break; /* cbw */
-        case 4: _regs.r(ax) = (uint32_t)(int16_t)_regs.ax; break; /* cwde */
+        case 4: _regs.r(ax) = (uint32_t)(int16_t)_regs.r(ax); break; /* cwde */
         case 8: _regs.r(ax) = (int32_t)_regs.r(ax); break; /* cdqe */
         }
         break;
--
2.25.1