m68k: Fix regression causing Single-Step via GDB/RSP to not single step

A regression that was introduced, with the refactor to TranslatorOps,
drops two lines that update the PC when single-stepping is being performed.

Fixes: 11ab74b0 ("target/m68k: Convert to TranslatorOps")
Reported-by: NLucien Murray-Pitts <lucienmp_antispam@yahoo.com>
Suggested-by: NLucien Murray-Pitts <lucienmp_antispam@yahoo.com>
Suggested-by: NRichard Henderson <richard.henderson@linaro.org>
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>
Signed-off-by: NLaurent Vivier <laurent@vivier.eu>
Message-Id: <20200116165454.2076265-1-laurent@vivier.eu>
(cherry picked from commit 322f244a)
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>

target/m68k/translate.c

@@ -289,16 +289,21 @@ static void gen_jmp(DisasContext *s, TCGv dest)
     s->base.is_jmp = DISAS_JUMP;
 }
 
-static void gen_exception(DisasContext *s, uint32_t dest, int nr)
+static void gen_raise_exception(int nr)
 {
     TCGv_i32 tmp;
 
-    update_cc_op(s);
-    tcg_gen_movi_i32(QREG_PC, dest);
-
     tmp = tcg_const_i32(nr);
     gen_helper_raise_exception(cpu_env, tmp);
     tcg_temp_free_i32(tmp);
+}
+
+static void gen_exception(DisasContext *s, uint32_t dest, int nr)
+{
+    update_cc_op(s);
+    tcg_gen_movi_i32(QREG_PC, dest);
+
+    gen_raise_exception(nr);
 
     s->base.is_jmp = DISAS_NORETURN;
 }
@@ -6198,29 +6203,36 @@ static void m68k_tr_tb_stop(DisasContextBase *dcbase, CPUState *cpu)
 {
     DisasContext *dc = container_of(dcbase, DisasContext, base);
 
-    if (dc->base.is_jmp == DISAS_NORETURN) {
-        return;
-    }
-    if (dc->base.singlestep_enabled) {
-        gen_helper_raise_exception(cpu_env, tcg_const_i32(EXCP_DEBUG));
-        return;
-    }
-
     switch (dc->base.is_jmp) {
+    case DISAS_NORETURN:
+        break;
     case DISAS_TOO_MANY:
         update_cc_op(dc);
-        gen_jmp_tb(dc, 0, dc->pc);
+        if (dc->base.singlestep_enabled) {
+            tcg_gen_movi_i32(QREG_PC, dc->pc);
+            gen_raise_exception(EXCP_DEBUG);
+        } else {
+            gen_jmp_tb(dc, 0, dc->pc);
+        }
         break;
     case DISAS_JUMP:
         /* We updated CC_OP and PC in gen_jmp/gen_jmp_im.  */
-        tcg_gen_lookup_and_goto_ptr();
+        if (dc->base.singlestep_enabled) {
+            gen_raise_exception(EXCP_DEBUG);
+        } else {
+            tcg_gen_lookup_and_goto_ptr();
+        }
         break;
     case DISAS_EXIT:
         /*
          * We updated CC_OP and PC in gen_exit_tb, but also modified
          * other state that may require returning to the main loop.
          */
-        tcg_gen_exit_tb(NULL, 0);
+        if (dc->base.singlestep_enabled) {
+            gen_raise_exception(EXCP_DEBUG);
+        } else {
+            tcg_gen_exit_tb(NULL, 0);
+        }
         break;
     default:
         g_assert_not_reached();