m68k: fix exception stack frame for 68000

68000 CPUs do not save format in the exception stack frame.
This patch adds feature checking to prevent format saving for 68000.
m68k_ret() already includes this modification, this patch fixes
the exception processing function too.

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20180413133041.29509.59064.stgit@pasha-VirtualBox>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

target/m68k/op_helper.c

@@ -287,22 +287,25 @@ static inline void do_stack_frame(CPUM68KState *env, uint32_t *sp,
                                   uint16_t format, uint16_t sr,
                                   uint32_t addr, uint32_t retaddr)
 {
-    CPUState *cs = CPU(m68k_env_get_cpu(env));
-    switch (format) {
-    case 4:
-        *sp -= 4;
-        cpu_stl_kernel(env, *sp, env->pc);
-        *sp -= 4;
-        cpu_stl_kernel(env, *sp, addr);
-        break;
-    case 3:
-    case 2:
-        *sp -= 4;
-        cpu_stl_kernel(env, *sp, addr);
-        break;
+    if (m68k_feature(env, M68K_FEATURE_QUAD_MULDIV)) {
+        /*  all except 68000 */
+        CPUState *cs = CPU(m68k_env_get_cpu(env));
+        switch (format) {
+        case 4:
+            *sp -= 4;
+            cpu_stl_kernel(env, *sp, env->pc);
+            *sp -= 4;
+            cpu_stl_kernel(env, *sp, addr);
+            break;
+        case 3:
+        case 2:
+            *sp -= 4;
+            cpu_stl_kernel(env, *sp, addr);
+            break;
+        }
+        *sp -= 2;
+        cpu_stw_kernel(env, *sp, (format << 12) + (cs->exception_index << 2));
     }
-    *sp -= 2;
-    cpu_stw_kernel(env, *sp, (format << 12) + (cs->exception_index << 2));
     *sp -= 4;
     cpu_stl_kernel(env, *sp, retaddr);
     *sp -= 2;