target/arm: Diagnose too few registers in list for LDM/STM

This has been a TODO item for quite a while.  The minimum bit
count for A32 and T16 is 1, and for T32 is 2.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20190904193059.26202-31-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

target/arm/translate.c

@@ -9846,7 +9846,7 @@ static void op_addr_block_post(DisasContext *s, arg_ldst_block *a,
     }
 }
 
-static bool op_stm(DisasContext *s, arg_ldst_block *a)
+static bool op_stm(DisasContext *s, arg_ldst_block *a, int min_n)
 {
     int i, j, n, list, mem_idx;
     bool user = a->u;
@@ -9863,7 +9863,10 @@ static bool op_stm(DisasContext *s, arg_ldst_block *a)
 
     list = a->list;
     n = ctpop16(list);
-    /* TODO: test invalid n == 0 case */
+    if (n < min_n) {
+        unallocated_encoding(s);
+        return true;
+    }
 
     addr = op_addr_block_pre(s, a, n);
     mem_idx = get_mem_index(s);
@@ -9896,7 +9899,8 @@ static bool op_stm(DisasContext *s, arg_ldst_block *a)
 
 static bool trans_STM(DisasContext *s, arg_ldst_block *a)
 {
-    return op_stm(s, a);
+    /* BitCount(list) < 1 is UNPREDICTABLE */
+    return op_stm(s, a, 1);
 }
 
 static bool trans_STM_t32(DisasContext *s, arg_ldst_block *a)
@@ -9906,10 +9910,11 @@ static bool trans_STM_t32(DisasContext *s, arg_ldst_block *a)
         unallocated_encoding(s);
         return true;
     }
-    return op_stm(s, a);
+    /* BitCount(list) < 2 is UNPREDICTABLE */
+    return op_stm(s, a, 2);
 }
 
-static bool do_ldm(DisasContext *s, arg_ldst_block *a)
+static bool do_ldm(DisasContext *s, arg_ldst_block *a, int min_n)
 {
     int i, j, n, list, mem_idx;
     bool loaded_base;
@@ -9938,7 +9943,10 @@ static bool do_ldm(DisasContext *s, arg_ldst_block *a)
 
     list = a->list;
     n = ctpop16(list);
-    /* TODO: test invalid n == 0 case */
+    if (n < min_n) {
+        unallocated_encoding(s);
+        return true;
+    }
 
     addr = op_addr_block_pre(s, a, n);
     mem_idx = get_mem_index(s);
@@ -10006,7 +10014,8 @@ static bool trans_LDM_a32(DisasContext *s, arg_ldst_block *a)
         unallocated_encoding(s);
         return true;
     }
-    return do_ldm(s, a);
+    /* BitCount(list) < 1 is UNPREDICTABLE */
+    return do_ldm(s, a, 1);
 }
 
 static bool trans_LDM_t32(DisasContext *s, arg_ldst_block *a)
@@ -10016,7 +10025,8 @@ static bool trans_LDM_t32(DisasContext *s, arg_ldst_block *a)
         unallocated_encoding(s);
         return true;
     }
-    return do_ldm(s, a);
+    /* BitCount(list) < 2 is UNPREDICTABLE */
+    return do_ldm(s, a, 2);
 }
 
 /*