Found on debian stable.

../target/s390x/tcg/translate.c: In function ‘get_mem_index’:
../target/s390x/tcg/translate.c:398:1: error: control reaches end of non-void function [-Werror=return-type]
  398 | }
---
 target/s390x/tcg/translate.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/target/s390x/tcg/translate.c b/target/s390x/tcg/translate.c
index c81e035dea4..bcfff40b255 100644
--- a/target/s390x/tcg/translate.c
+++ b/target/s390x/tcg/translate.c
@@ -392,7 +392,6 @@ static int get_mem_index(DisasContext *s)
         return MMU_HOME_IDX;
     default:
         g_assert_not_reached();
-        break;
     }
 #endif
 }
-- 
2.39.2