ppc: Fix the range check in the LSWI instruction

There are two issues: First, the number of registers that are used has
to be calculated with "(nb + 3) / 4" (i.e. round always up, not down).
Second, the "start <= ra && (start + nr - 32) > ra" condition for the
wrap-around case is wrong: It has to be tested with "||" instead of "&&".
Since we can reuse this check later for the LSWX instruction, let's
place the fixed code into a helper function, too.
Signed-off-by: NThomas Huth <thuth@redhat.com>
Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au>

target-ppc/cpu.h

@@ -2415,6 +2415,16 @@ static inline bool msr_is_64bit(CPUPPCState *env, target_ulong msr)
     return msr & (1ULL << MSR_SF);
 }
 
+/**
+ * Check whether register rx is in the range between start and
+ * start + nregs (as needed by the LSWX and LSWI instructions)
+ */
+static inline bool lsw_reg_in_range(int start, int nregs, int rx)
+{
+    return (start + nregs <= 32 && rx >= start && rx < start + nregs) ||
+           (start + nregs > 32 && (rx >= start || rx < start + nregs - 32));
+}
+
 extern void (*cpu_ppc_hypercall)(PowerPCCPU *);
 
 #include "exec/exec-all.h"

target-ppc/translate.c

@@ -3227,10 +3227,8 @@ static void gen_lswi(DisasContext *ctx)
 
     if (nb == 0)
         nb = 32;
-    nr = nb / 4;
-    if (unlikely(((start + nr) > 32  &&
-                  start <= ra && (start + nr - 32) > ra) ||
-                 ((start + nr) <= 32 && start <= ra && (start + nr) > ra))) {
+    nr = (nb + 3) / 4;
+    if (unlikely(lsw_reg_in_range(start, nr, ra))) {
         gen_inval_exception(ctx, POWERPC_EXCP_INVAL_LSWX);
         return;
     }