[Ada] Memory corruption when using formal hashed sets or maps

Add a check to avoid causing a buffer overflow when the map is empty

2019-07-11  Claire Dross  <dross@adacore.com>

gcc/ada/

	* libgnat/a-cfhama.adb, libgnat/a-cfhase.adb (Free): Do not
	reset the Has_Element flag if no element is freed.

From-SVN: r273397

gcc/ada/ChangeLog

+2019-07-11  Claire Dross  <dross@adacore.com>
+
+	* libgnat/a-cfhama.adb, libgnat/a-cfhase.adb (Free): Do not
+	reset the Has_Element flag if no element is freed.
+
 2019-07-11  Arnaud Charlet  <charlet@adacore.com>
 
 	* errno.c: Remove obsolete support for MaRTE OS.

gcc/ada/libgnat/a-cfhama.adb

@@ -509,8 +509,11 @@ is
 
    procedure Free (HT : in out Map; X : Count_Type) is
    begin
-      HT.Nodes (X).Has_Element := False;
-      HT_Ops.Free (HT, X);
+      if X /= 0 then
+         pragma Assert (X <= HT.Capacity);
+         HT.Nodes (X).Has_Element := False;
+         HT_Ops.Free (HT, X);
+      end if;
    end Free;
 
    ----------------------

gcc/ada/libgnat/a-cfhase.adb

@@ -760,8 +760,11 @@ is
 
    procedure Free (HT : in out Set; X : Count_Type) is
    begin
-      HT.Nodes (X).Has_Element := False;
-      HT_Ops.Free (HT, X);
+      if X /= 0 then
+         pragma Assert (X <= HT.Capacity);
+         HT.Nodes (X).Has_Element := False;
+         HT_Ops.Free (HT, X);
+      end if;
    end Free;
 
    ----------------------