[Ada] Buffer reading overflow in dispatch table initialization

For tagged types not defined at library level that derive from library
level tagged types the compiler may generate code to initialize their
dispatch table of predefined primitives copying from the parent type
data stored in memory after the dispatch table of the parent; that is,
at runtime the initialization of dispatch tables overflows reading the
parent dispatch table.

This problem does not affect the execution of the program since the
target dispatch table always has enough space to store the extra data,
and after such copy the compiler generates code to complete the
initialization of the dispatch table.

The following test must compile and execute without errors.

package pkg_a is
   type Root is tagged null record;
end pkg_a;

with pkg_a;
procedure main is
   type Derived is new pkg_a.Root with null record;  -- Test
begin
   null;
end main;

Command: gnatmake -q main -fsanitize=address; ./main

2019-08-19  Javier Miranda  <miranda@adacore.com>

gcc/ada/

	PR ada/65696
	* exp_atag.ads, exp_atag.adb (Build_Inherit_Predefined_Prims):
	Adding formal to specify how many predefined primitives are
	inherited from the parent type.
	* exp_disp.adb (Number_Of_Predefined_Prims): New subprogram.
	(Make_Secondary_DT): Compute the number of predefined primitives
	of all tagged types (including tagged types not defined at
	library level).  Previously we unconditionally relied on the
	Max_Predef_Prims constant value when building the dispatch
	tables of tagged types not defined at library level (thus
	consuming more memory for their dispatch tables than required).
	(Make_DT): Compute the number of predefined primitives that must
	be inherited from their parent type when building the dispatch
	tables of tagged types not defined at library level. Previously
	we unconditionally relied on the Max_Predef_Prims constant value
	when building the dispatch tables of tagged types not defined at
	library level (thus copying more data than required from the
	parent type).

From-SVN: r274654

gcc/ada/ChangeLog

+2019-08-19  Javier Miranda  <miranda@adacore.com>
+
+	PR ada/65696
+	* exp_atag.ads, exp_atag.adb (Build_Inherit_Predefined_Prims):
+	Adding formal to specify how many predefined primitives are
+	inherited from the parent type.
+	* exp_disp.adb (Number_Of_Predefined_Prims): New subprogram.
+	(Make_Secondary_DT): Compute the number of predefined primitives
+	of all tagged types (including tagged types not defined at
+	library level).  Previously we unconditionally relied on the
+	Max_Predef_Prims constant value when building the dispatch
+	tables of tagged types not defined at library level (thus
+	consuming more memory for their dispatch tables than required).
+	(Make_DT): Compute the number of predefined primitives that must
+	be inherited from their parent type when building the dispatch
+	tables of tagged types not defined at library level. Previously
+	we unconditionally relied on the Max_Predef_Prims constant value
+	when building the dispatch tables of tagged types not defined at
+	library level (thus copying more data than required from the
+	parent type).
+
 2019-08-19  Bob Duff  <duff@adacore.com>
 
 	* sem_ch13.adb (Record_Hole_Check): Procedure to check for holes

gcc/ada/exp_atag.adb

@@ -744,7 +744,8 @@ package body Exp_Atag is
    function Build_Inherit_Predefined_Prims
      (Loc              : Source_Ptr;
       Old_Tag_Node     : Node_Id;
-      New_Tag_Node : Node_Id) return Node_Id
+      New_Tag_Node     : Node_Id;
+      Num_Predef_Prims : Int) return Node_Id
    is
    begin
       return
@@ -759,7 +760,7 @@ package body Exp_Atag is
                         New_Tag_Node)))),
               Discrete_Range => Make_Range (Loc,
                 Make_Integer_Literal (Loc, Uint_1),
-                New_Occurrence_Of (RTE (RE_Max_Predef_Prims), Loc))),
+                Make_Integer_Literal (Loc, Num_Predef_Prims))),
 
           Expression =>
             Make_Slice (Loc,
@@ -772,7 +773,7 @@ package body Exp_Atag is
               Discrete_Range =>
                 Make_Range (Loc,
                   Make_Integer_Literal (Loc, 1),
-                  New_Occurrence_Of (RTE (RE_Max_Predef_Prims), Loc))));
+                  Make_Integer_Literal (Loc, Num_Predef_Prims))));
    end Build_Inherit_Predefined_Prims;
 
    -------------------------

gcc/ada/exp_atag.ads

@@ -111,7 +111,8 @@ package Exp_Atag is
    function Build_Inherit_Predefined_Prims
      (Loc              : Source_Ptr;
       Old_Tag_Node     : Node_Id;
-      New_Tag_Node : Node_Id) return Node_Id;
+      New_Tag_Node     : Node_Id;
+      Num_Predef_Prims : Int) return Node_Id;
    --  Build code that inherits the predefined primitives of the parent.
    --
    --  Generates: Predefined_DT (New_T).D (All_Predefined_Prims) :=

gcc/ada/exp_disp.adb

@@ -3817,6 +3817,9 @@ package body Exp_Disp is
       --  this secondary dispatch table by Make_Tags when its unique external
       --  name was generated.
 
+      function Number_Of_Predefined_Prims (Typ : Entity_Id) return Nat;
+      --  Returns the number of predefined primitives of Typ
+
       ------------------------------
       -- Check_Premature_Freezing --
       ------------------------------
@@ -3970,12 +3973,10 @@ package body Exp_Disp is
          DT_Constr_List     : List_Id;
          DT_Aggr_List       : List_Id;
          Empty_DT           : Boolean := False;
-         Nb_Predef_Prims    : Nat := 0;
          Nb_Prim            : Nat;
          New_Node           : Node_Id;
          OSD                : Entity_Id;
          OSD_Aggr_List      : List_Id;
-         Pos                : Nat;
          Prim               : Entity_Id;
          Prim_Elmt          : Elmt_Id;
          Prim_Ops_Aggr_List : List_Id;
@@ -4022,38 +4023,12 @@ package body Exp_Disp is
          --                     predef-prim-op-thunk-n'address);
          --   for Predef_Prims'Alignment use Address'Alignment
 
-         --  Stage 1: Calculate the number of predefined primitives
-
-         if not Building_Static_DT (Typ) then
-            Nb_Predef_Prims := Max_Predef_Prims;
-         else
-            Prim_Elmt := First_Elmt (Primitive_Operations (Typ));
-            while Present (Prim_Elmt) loop
-               Prim := Node (Prim_Elmt);
-
-               if Is_Predefined_Dispatching_Operation (Prim)
-                 and then not Is_Abstract_Subprogram (Prim)
-               then
-                  Pos := UI_To_Int (DT_Position (Prim));
-
-                  if Pos > Nb_Predef_Prims then
-                     Nb_Predef_Prims := Pos;
-                  end if;
-               end if;
-
-               Next_Elmt (Prim_Elmt);
-            end loop;
-         end if;
-
-         if Generate_SCIL then
-            Nb_Predef_Prims := 0;
-         end if;
-
-         --  Stage 2: Create the thunks associated with the predefined
-         --  primitives and save their entity to fill the aggregate.
+         --  Create the thunks associated with the predefined primitives and
+         --  save their entity to fill the aggregate.
 
          declare
-            Prim_Table : array (Nat range 1 .. Nb_Predef_Prims) of Entity_Id;
+            Nb_P_Prims : constant Nat := Number_Of_Predefined_Prims (Typ);
+            Prim_Table : array (Nat range 1 .. Nb_P_Prims) of Entity_Id;
             Decl       : Node_Id;
             Thunk_Id   : Entity_Id;
             Thunk_Code : Node_Id;
@@ -4525,6 +4500,44 @@ package body Exp_Disp is
          Append_Elmt (Iface_DT, DT_Decl);
       end Make_Secondary_DT;
 
+      --------------------------------
+      -- Number_Of_Predefined_Prims --
+      --------------------------------
+
+      function Number_Of_Predefined_Prims (Typ : Entity_Id) return Nat is
+         Nb_Predef_Prims : Nat := 0;
+
+      begin
+         if not Generate_SCIL then
+            declare
+               Prim      : Entity_Id;
+               Prim_Elmt : Elmt_Id;
+               Pos       : Nat;
+
+            begin
+               Prim_Elmt := First_Elmt (Primitive_Operations (Typ));
+               while Present (Prim_Elmt) loop
+                  Prim := Node (Prim_Elmt);
+
+                  if Is_Predefined_Dispatching_Operation (Prim)
+                    and then not Is_Abstract_Subprogram (Prim)
+                  then
+                     Pos := UI_To_Int (DT_Position (Prim));
+
+                     if Pos > Nb_Predef_Prims then
+                        Nb_Predef_Prims := Pos;
+                     end if;
+                  end if;
+
+                  Next_Elmt (Prim_Elmt);
+               end loop;
+            end;
+         end if;
+
+         pragma Assert (Nb_Predef_Prims <= Max_Predef_Prims);
+         return Nb_Predef_Prims;
+      end Number_Of_Predefined_Prims;
+
       --  Local variables
 
       Elab_Code : constant List_Id := New_List;
@@ -4584,7 +4597,6 @@ package body Exp_Disp is
       I_Depth            : Nat := 0;
       Iface_Table_Node   : Node_Id;
       Name_ITable        : Name_Id;
-      Nb_Predef_Prims    : Nat := 0;
       Nb_Prim            : Nat := 0;
       New_Node           : Node_Id;
       Num_Ifaces         : Nat := 0;
@@ -5924,40 +5936,13 @@ package body Exp_Disp is
 
       else
          declare
-            Pos : Nat;
-
-         begin
-            if not Building_Static_DT (Typ) then
-               Nb_Predef_Prims := Max_Predef_Prims;
-
-            else
-               Prim_Elmt := First_Elmt (Primitive_Operations (Typ));
-               while Present (Prim_Elmt) loop
-                  Prim := Node (Prim_Elmt);
-
-                  if Is_Predefined_Dispatching_Operation (Prim)
-                    and then not Is_Abstract_Subprogram (Prim)
-                  then
-                     Pos := UI_To_Int (DT_Position (Prim));
-
-                     if Pos > Nb_Predef_Prims then
-                        Nb_Predef_Prims := Pos;
-                     end if;
-                  end if;
-
-                  Next_Elmt (Prim_Elmt);
-               end loop;
-            end if;
-
-            declare
-               Prim_Table : array
-                              (Nat range 1 .. Nb_Predef_Prims) of Entity_Id;
+            Nb_P_Prims : constant Nat := Number_Of_Predefined_Prims (Typ);
+            Prim_Table : array (Nat range 1 .. Nb_P_Prims) of Entity_Id;
             Decl       : Node_Id;
             E          : Entity_Id;
 
          begin
             Prim_Ops_Aggr_List := New_List;
-
             Prim_Table := (others => Empty);
 
             if Building_Static_DT (Typ) then
@@ -5968,6 +5953,7 @@ package body Exp_Disp is
                   if Is_Predefined_Dispatching_Operation (Prim)
                     and then not Is_Abstract_Subprogram (Prim)
                     and then not Is_Eliminated (Prim)
+                    and then not Generate_SCIL
                     and then not Present (Prim_Table
                                            (UI_To_Int (DT_Position (Prim))))
                   then
@@ -6030,7 +6016,6 @@ package body Exp_Disp is
                       New_Occurrence_Of (RTE (RE_Integer_Address), Loc),
                     Attribute_Name => Name_Alignment)));
          end;
-         end;
 
          --  Stage 1: Initialize the discriminant and the record components
 
@@ -6301,7 +6286,9 @@ package body Exp_Disp is
                           (Node
                             (Next_Elmt
                               (First_Elmt
-                                (Access_Disp_Table (Typ)))), Loc)));
+                                (Access_Disp_Table (Typ)))), Loc),
+                      Num_Predef_Prims =>
+                        Number_Of_Predefined_Prims (Parent_Typ)));
 
                   if Nb_Prims /= 0 then
                      Append_To (Elab_Code,
@@ -6390,7 +6377,10 @@ package body Exp_Disp is
                                           Unchecked_Convert_To (RTE (RE_Tag),
                                             New_Occurrence_Of
                                               (Node (Next_Elmt (Sec_DT_Typ)),
-                                               Loc))));
+                                               Loc)),
+                                        Num_Predef_Prims =>
+                                          Number_Of_Predefined_Prims
+                                            (Parent_Typ)));
 
                                     if Num_Prims /= 0 then
                                        Append_To (Elab_Code,
@@ -6436,7 +6426,10 @@ package body Exp_Disp is
                                           Unchecked_Convert_To (RTE (RE_Tag),
                                             New_Occurrence_Of
                                               (Node (Next_Elmt (Sec_DT_Typ)),
-                                               Loc))));
+                                               Loc)),
+                                        Num_Predef_Prims =>
+                                          Number_Of_Predefined_Prims
+                                            (Parent_Typ)));
 
                                     if Num_Prims /= 0 then
                                        Append_To (Elab_Code,