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[gcc.git] / gcc / ada / rtsfind.adb

------------------------------------------------------------------------------
--                                                                          --
--                         GNAT COMPILER COMPONENTS                         --
--                                                                          --
--                              R T S F I N D                               --
--                                                                          --
--                                 B o d y                                  --
--                                                                          --
--          Copyright (C) 1992-2003, Free Software Foundation, Inc.         --
--                                                                          --
-- GNAT is free software;  you can  redistribute it  and/or modify it under --
-- terms of the  GNU General Public License as published  by the Free Soft- --
-- ware  Foundation;  either version 2,  or (at your option) any later ver- --
-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
-- for  more details.  You should have  received  a copy of the GNU General --
-- Public License  distributed with GNAT;  see file COPYING.  If not, write --
-- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
-- MA 02111-1307, USA.                                                      --
--                                                                          --
-- GNAT was originally developed  by the GNAT team at  New York University. --
-- Extensive contributions were provided by Ada Core Technologies Inc.      --
--                                                                          --
------------------------------------------------------------------------------

with Atree;    use Atree;
with Casing;   use Casing;
with Csets;    use Csets;
with Debug;    use Debug;
with Einfo;    use Einfo;
with Elists;   use Elists;
with Errout;   use Errout;
with Fname;    use Fname;
with Fname.UF; use Fname.UF;
with Lib;      use Lib;
with Lib.Load; use Lib.Load;
with Namet;    use Namet;
with Nlists;   use Nlists;
with Nmake;    use Nmake;
with Output;   use Output;
with Opt;      use Opt;
with Sem;      use Sem;
with Sem_Ch7;  use Sem_Ch7;
with Sem_Util; use Sem_Util;
with Sinfo;    use Sinfo;
with Stand;    use Stand;
with Snames;   use Snames;
with Tbuild;   use Tbuild;
with Uname;    use Uname;

package body Rtsfind is

   RTE_Available_Call : Boolean := False;
   --  Set True during call to RTE from RTE_Available. Tells RTE to set
   --  RTE_Is_Available to False rather than generating an error message.

   RTE_Is_Available : Boolean;
   --  Set True by RTE_Available on entry. When RTE_Available_Call is set
   --  True, set False if RTE would otherwise generate an error message.

   ----------------
   -- Unit table --
   ----------------

   --  The unit table has one entry for each unit included in the definition
   --  of the type RTU_Id in the spec. The table entries are initialized in
   --  Initialize to set the Entity field to Empty, indicating that the
   --  corresponding unit has not yet been loaded. The fields are set when
   --  a unit is loaded to contain the defining entity for the unit, the
   --  unit name, and the unit number.

   type RT_Unit_Table_Record is record
      Entity : Entity_Id;
      Uname  : Unit_Name_Type;
      Unum   : Unit_Number_Type;
      Withed : Boolean;
   end record;

   RT_Unit_Table : array (RTU_Id) of RT_Unit_Table_Record;

   --------------------------
   -- Runtime Entity Table --
   --------------------------

   --  There is one entry in the runtime entity table for each entity that is
   --  included in the definition of the RE_Id type in the spec. The entries
   --  are set by Initialize_Rtsfind to contain Empty, indicating that the
   --  entity has not yet been located. Once the entity is located for the
   --  first time, its ID is stored in this array, so that subsequent calls
   --  for the same entity can be satisfied immediately.

   RE_Table : array (RE_Id) of Entity_Id;

   --------------------------
   -- Generation of WITH's --
   --------------------------

   --  When a unit is implicitly loaded as a result of a call to RTE, it
   --  is necessary to create an implicit WITH to ensure that the object
   --  is correctly loaded by the binder. Such WITH statements are only
   --  required when the request is from the extended main unit (if a
   --  client needs a WITH, that will be taken care of when the client
   --  is compiled).

   --  We always attach the WITH to the main unit. This is not perfectly
   --  accurate in terms of elaboration requirements, but it is close
   --  enough, since the units that are accessed using rtsfind do not
   --  have delicate elaboration requirements.

   --  The flag Withed in the unit table record is initially set to False.
   --  It is set True if a WITH has been generated for the main unit for
   --  the corresponding unit.

   -----------------------
   -- Local Subprograms --
   -----------------------

   procedure Entity_Not_Defined (Id : RE_Id);
   --  Outputs error messages for an entity that is not defined in the
   --  run-time library (the form of the error message is tailored for
   --  no run time/configurable run time mode as required).

   procedure Load_Fail (S : String; U_Id : RTU_Id; Id : RE_Id);
   --  Internal procedure called if we can't sucessfully locate or
   --  process a run-time unit. The parameters give information about
   --  the error message to be given. S is a reason for failing to
   --  compile the file and U_Id is the unit id. RE_Id is the RE_Id
   --  originally passed to RTE. The message in S is one of the
   --  following:
   --
   --     "not found"
   --     "had parser errors"
   --     "had semantic errors"
   --
   --  The "not found" case is treated specially in that it is considered
   --  a normal situation in configurable run-time mode (and the message in
   --  this case is suppressed unless we are operating in All_Errors_Mode).

   function Get_Unit_Name (U_Id : RTU_Id) return Unit_Name_Type;
   --  Retrieves the Unit Name given a unit id represented by its
   --  enumaration value in RTU_Id.

   procedure Load_RTU
     (U_Id        : RTU_Id;
      Id          : RE_Id   := RE_Null;
      Use_Setting : Boolean := False);
   --  Load the unit whose Id is given if not already loaded. The unit is
   --  loaded, analyzed, and added to the WITH list, and the entry in
   --  RT_Unit_Table is updated to reflect the load. The second parameter
   --  indicates the initial setting for the Is_Potentially_Use_Visible
   --  flag of the entity for the loaded unit (if it is indeed loaded).
   --  A value of False means nothing special need be done. A value of
   --  True indicates that this flag must be set to True. It is needed
   --  only in the Text_IO_Kludge procedure, which may materialize an
   --  entity of Text_IO (or Wide_Text_IO) that was previously unknown.
   --  Id is the RE_Id value of the entity which was originally requested.
   --  Id is used only for error message detail, and if it is RE_Null, then
   --  the attempt to output the entity name is ignored.

   procedure Output_Entity_Name (Id : RE_Id; Msg : String);
   --  Output continuation error message giving qualified name of entity
   --  corresponding to Id, appending the string given by Msg. This call
   --  is only effective in All_Errors mode.

   function RE_Chars (E : RE_Id) return Name_Id;
   --  Given a RE_Id value returns the Chars of the corresponding entity.

   procedure RTE_Error_Msg (Msg : String);
   --  Generates a message by calling Error_Msg_N specifying Current_Error_Node
   --  as the node location using the given Msg text. Special processing in the
   --  case where RTE_Available_Call is set. In this case, no message is output
   --  and instead RTE_Is_Available is set to False. Note that this can only be
   --  used if you are sure that the message comes directly or indirectly from
   --  a call to the RTE function.

   -------------------
   -- Get_Unit_Name --
   -------------------

   function Get_Unit_Name (U_Id : RTU_Id) return Unit_Name_Type is
      Uname_Chars : constant String := RTU_Id'Image (U_Id);

   begin
      Name_Len := Uname_Chars'Length;
      Name_Buffer (1 .. Name_Len) := Uname_Chars;
      Set_Casing (All_Lower_Case);

      if U_Id in Ada_Child then
         Name_Buffer (4) := '.';

         if U_Id in Ada_Calendar_Child then
            Name_Buffer (13) := '.';

         elsif U_Id in Ada_Finalization_Child then
            Name_Buffer (17) := '.';

         elsif U_Id in Ada_Interrupts_Child then
            Name_Buffer (15) := '.';

         elsif U_Id in Ada_Real_Time_Child then
            Name_Buffer (14) := '.';

         elsif U_Id in Ada_Streams_Child then
            Name_Buffer (12) := '.';

         elsif U_Id in Ada_Text_IO_Child then
            Name_Buffer (12) := '.';

         elsif U_Id in Ada_Wide_Text_IO_Child then
            Name_Buffer (17) := '.';
         end if;

      elsif U_Id in Interfaces_Child then
         Name_Buffer (11) := '.';

      elsif U_Id in System_Child then
         Name_Buffer (7) := '.';

         if U_Id in System_Tasking_Child then
            Name_Buffer (15) := '.';
         end if;

         if U_Id in System_Tasking_Restricted_Child then
            Name_Buffer (26) := '.';
         end if;

         if U_Id in System_Tasking_Protected_Objects_Child then
            Name_Buffer (33) := '.';
         end if;

         if U_Id in System_Tasking_Async_Delays_Child then
            Name_Buffer (28) := '.';
         end if;
      end if;

      --  Add %s at end for spec

      Name_Buffer (Name_Len + 1) := '%';
      Name_Buffer (Name_Len + 2) := 's';
      Name_Len := Name_Len + 2;

      return Name_Find;
   end Get_Unit_Name;

   ----------------
   -- Initialize --
   ----------------

   procedure Initialize is
   begin
      --  Initialize the unit table

      for J in RTU_Id loop
         RT_Unit_Table (J).Entity := Empty;
      end loop;

      for J in RE_Id loop
         RE_Table (J) := Empty;
      end loop;
   end Initialize;

   ------------
   -- Is_RTE --
   ------------

   function Is_RTE (Ent : Entity_Id; E : RE_Id) return Boolean is
      E_Unit_Name   : Unit_Name_Type;
      Ent_Unit_Name : Unit_Name_Type;

      S  : Entity_Id;
      E1 : Entity_Id;
      E2 : Entity_Id;

   begin
      if No (Ent) then
         return False;

      --  If E has already a corresponding entity, check it directly,
      --  going to full views if they exist to deal with the incomplete
      --  and private type cases properly.

      elsif Present (RE_Table (E)) then
         E1 := Ent;

         if Is_Type (E1) and then Present (Full_View (E1)) then
            E1 := Full_View (E1);
         end if;

         E2 := RE_Table (E);

         if Is_Type (E2) and then Present (Full_View (E2)) then
            E2 := Full_View (E2);
         end if;

         return E1 = E2;
      end if;

      --  If the unit containing E is not loaded, we already know that
      --  the entity we have cannot have come from this unit.

      E_Unit_Name := Get_Unit_Name (RE_Unit_Table (E));

      if not Is_Loaded (E_Unit_Name) then
         return False;
      end if;

      --  Here the unit containing the entity is loaded. We have not made
      --  an explicit call to RTE to get the entity in question, but we may
      --  have obtained a reference to it indirectly from some other entity
      --  in the same unit, or some other unit that references it.

      --  Get the defining unit of the entity

      S := Scope (Ent);

      if Ekind (S) /= E_Package then
         return False;
      end if;

      Ent_Unit_Name := Get_Unit_Name (Unit_Declaration_Node (S));

      --  If the defining unit of the entity we are testing is not the
      --  unit containing E, then they cannot possibly match.

      if Ent_Unit_Name /= E_Unit_Name then
         return False;
      end if;

      --  If the units match, then compare the names (remember that no
      --  overloading is permitted in entities fetched using Rtsfind).

      if RE_Chars (E) = Chars (Ent) then
         RE_Table (E) := Ent;

         --  If front-end inlining is enabled, we may be within a body that
         --  contains inlined functions, which has not been retrieved through
         --  rtsfind, and therefore is not yet recorded in the RT_Unit_Table.
         --  Add the unit information now, it must be fully available.

         declare
            U : RT_Unit_Table_Record
                  renames  RT_Unit_Table (RE_Unit_Table (E));
         begin
            if No (U.Entity) then
               U.Entity := S;
               U.Uname  := E_Unit_Name;
               U.Unum   := Get_Source_Unit (S);
            end if;
         end;

         return True;
      else
         return False;
      end if;
   end Is_RTE;

   ------------
   -- Is_RTU --
   ------------

   function Is_RTU (Ent : Entity_Id;  U : RTU_Id) return Boolean is
      E : constant Entity_Id := RT_Unit_Table (U).Entity;
   begin
      return Present (E) and then E = Ent;
   end Is_RTU;

   ----------------------------
   -- Is_Text_IO_Kludge_Unit --
   ----------------------------

   function Is_Text_IO_Kludge_Unit (Nam : Node_Id) return Boolean is
      Prf : Node_Id;
      Sel : Node_Id;

   begin
      if Nkind (Nam) /= N_Expanded_Name then
         return False;
      end if;

      Prf := Prefix (Nam);
      Sel := Selector_Name (Nam);

      if Nkind (Sel) /= N_Expanded_Name
        or else Nkind (Prf) /= N_Identifier
        or else Chars (Prf) /= Name_Ada
      then
         return False;
      end if;

      Prf := Prefix (Sel);
      Sel := Selector_Name (Sel);

      return
        Nkind (Prf) = N_Identifier
          and then
        (Chars (Prf) = Name_Text_IO or else Chars (Prf) = Name_Wide_Text_IO)
          and then
        Nkind (Sel) = N_Identifier
          and then
        Chars (Sel) in Text_IO_Package_Name;
   end Is_Text_IO_Kludge_Unit;

   ------------------------
   -- Entity_Not_Defined --
   ------------------------

   procedure Entity_Not_Defined (Id : RE_Id) is
   begin
      if No_Run_Time_Mode then
         RTE_Error_Msg ("|construct not allowed in no run time mode");
      elsif Configurable_Run_Time_Mode then
         RTE_Error_Msg ("|construct not allowed in this configuration>");
      else
         RTE_Error_Msg ("run-time configuration error");
      end if;

      Output_Entity_Name (Id, "not defined");
   end Entity_Not_Defined;

   ---------------
   -- Load_Fail --
   ---------------

   procedure Load_Fail (S : String; U_Id : RTU_Id; Id : RE_Id) is
      M : String (1 .. 100);
      P : Natural := 0;

   begin
      --  Output header message

      if Configurable_Run_Time_Mode then
         RTE_Error_Msg ("construct not allowed in configurable run-time mode");
      else
         RTE_Error_Msg ("run-time library configuration error");
      end if;

      --  Output file name and reason string

      if S /= "not found"
        or else not Configurable_Run_Time_Mode
      then
         M (1 .. 6) := "\file ";
         P := 6;

         Get_Name_String
           (Get_File_Name (RT_Unit_Table (U_Id).Uname, Subunit => False));
         M (P + 1 .. P + Name_Len) := Name_Buffer (1 .. Name_Len);
         P := P + Name_Len;

         M (P + 1) := ' ';
         P := P + 1;

         M (P + 1 .. P + S'Length) := S;
         P := P + S'Length;

         RTE_Error_Msg (M (1 .. P));

         --  Output entity name

         Output_Entity_Name (Id, "not available");
      end if;

      raise RE_Not_Available;
   end Load_Fail;

   --------------
   -- Load_RTU --
   --------------

   procedure Load_RTU
     (U_Id        : RTU_Id;
      Id          : RE_Id   := RE_Null;
      Use_Setting : Boolean := False)
   is
      U        : RT_Unit_Table_Record renames RT_Unit_Table (U_Id);
      Priv_Par : constant Elist_Id := New_Elmt_List;
      Lib_Unit : Node_Id;

      procedure Save_Private_Visibility;
      --  If the current unit is the body of child unit or the spec of a
      --  private child unit, the private declarations of the parent (s)
      --  are visible. If the unit to be loaded is another public sibling,
      --  its compilation will affect the visibility of the common ancestors.
      --  Indicate those that must be restored.

      procedure Restore_Private_Visibility;
      --  Restore the visibility of ancestors after compiling RTU.

      --------------------------------
      -- Restore_Private_Visibility --
      --------------------------------

      procedure Restore_Private_Visibility is
         E_Par : Elmt_Id;

      begin
         E_Par := First_Elmt (Priv_Par);

         while Present (E_Par) loop
            if not In_Private_Part (Node (E_Par)) then
               Install_Private_Declarations (Node (E_Par));
            end if;

            Next_Elmt (E_Par);
         end loop;
      end Restore_Private_Visibility;

      -----------------------------
      -- Save_Private_Visibility --
      -----------------------------

      procedure Save_Private_Visibility is
         Par : Entity_Id;

      begin
         Par := Scope (Current_Scope);

         while Present (Par)
           and then Par /= Standard_Standard
         loop
            if Ekind (Par) = E_Package
              and then Is_Compilation_Unit (Par)
              and then In_Private_Part (Par)
            then
               Append_Elmt (Par, Priv_Par);
            end if;

            Par := Scope (Par);
         end loop;
      end Save_Private_Visibility;

   --  Start of processing for Load_RTU

   begin
      --  Nothing to do if unit is already loaded

      if Present (U.Entity) then
         return;
      end if;

      --  Otherwise we need to load the unit, First build unit name
      --  from the enumeration literal name in type RTU_Id.

      U.Uname  := Get_Unit_Name (U_Id);
      U.Withed := False;

      declare
         Loaded : Boolean;
         pragma Warnings (Off, Loaded);

      begin
         Loaded := Is_Loaded (U.Uname);
      end;

      --  Now do the load call, note that setting Error_Node to Empty is
      --  a signal to Load_Unit that we will regard a failure to find the
      --  file as a fatal error, and that it should not output any kind
      --  of diagnostics, since we will take care of it here.

      U.Unum :=
        Load_Unit
          (Load_Name  => U.Uname,
           Required   => False,
           Subunit    => False,
           Error_Node => Empty);

      if U.Unum = No_Unit then
         Load_Fail ("not found", U_Id, Id);

      elsif Fatal_Error (U.Unum) then
         Load_Fail ("had parser errors", U_Id, Id);
      end if;

      --  Make sure that the unit is analyzed

      declare
         Was_Analyzed : constant Boolean :=
                          Analyzed (Cunit (Current_Sem_Unit));

      begin
         --  Pretend that the current unit is analyzed, in case it is System
         --  or some such. This allows us to put some declarations, such as
         --  exceptions and packed arrays of Boolean, into System even though
         --  expanding them requires System...

         --  This is a bit odd but works fine. If the RTS unit does not depend
         --  in any way on the current unit, then it never gets back into the
         --  current unit's tree, and the change we make to the current unit
         --  tree is never noticed by anyone (it is undone in a moment). That
         --  is the normal situation.

         --  If the RTS Unit *does* depend on the current unit, for instance,
         --  when you are compiling System, then you had better have finished
         --  analyzing the part of System that is depended on before you try
         --  to load the RTS Unit. This means having the System ordered in an
         --  appropriate manner.

         Set_Analyzed (Cunit (Current_Sem_Unit), True);

         if not Analyzed (Cunit (U.Unum)) then

            Save_Private_Visibility;
            Semantics (Cunit (U.Unum));
            Restore_Private_Visibility;

            if Fatal_Error (U.Unum) then
               Load_Fail ("had semantic errors", U_Id, Id);
            end if;
         end if;

         --  Undo the pretence

         Set_Analyzed (Cunit (Current_Sem_Unit), Was_Analyzed);
      end;

      Lib_Unit := Unit (Cunit (U.Unum));
      U.Entity := Defining_Entity (Lib_Unit);

      if Use_Setting then
         Set_Is_Potentially_Use_Visible (U.Entity, True);
      end if;
   end Load_RTU;

   -----------------------
   -- Output_Entity_Name --
   ------------------------

   procedure Output_Entity_Name (Id : RE_Id; Msg : String) is
      M : String (1 .. 2048);
      P : Natural := 0;
      --  M (1 .. P) is current message to be output

      RE_Image : constant String := RE_Id'Image (Id);

   begin
      if Id = RE_Null or else not All_Errors_Mode then
         return;
      end if;

      M (1 .. 9) := "\entity """;
      P := 9;

      --  Add unit name to message, excluding %s or %b at end

      Get_Name_String (Get_Unit_Name (RE_Unit_Table (Id)));
      Name_Len := Name_Len - 2;
      Set_Casing (Mixed_Case);
      M (P + 1 .. P + Name_Len) := Name_Buffer (1 .. Name_Len);
      P := P + Name_Len;

      --  Add a qualifying period

      M (P + 1) := '.';
      P := P + 1;

      --  Add entity name and closing quote to message

      Name_Len := RE_Image'Length - 3;
      Name_Buffer (1 .. Name_Len) := RE_Image (4 .. RE_Image'Length);
      Set_Casing (Mixed_Case);
      M (P + 1 .. P + Name_Len) := Name_Buffer (1 .. Name_Len);
      P := P + Name_Len;
      M (P + 1) := '"';
      P := P + 1;

      --  Add message

      M (P + 1) := ' ';
      P := P + 1;
      M (P + 1 .. P + Msg'Length) := Msg;
      P := P + Msg'Length;

      --  Output message at current error node location

      RTE_Error_Msg (M (1 .. P));
   end Output_Entity_Name;

   --------------
   -- RE_Chars --
   --------------

   function RE_Chars (E : RE_Id) return Name_Id is
      RE_Name_Chars : constant String := RE_Id'Image (E);

   begin
      --  Copy name skipping initial RE_ or RO_XX characters

      if RE_Name_Chars (1 .. 2) = "RE" then
         for J in 4 .. RE_Name_Chars'Last loop
            Name_Buffer (J - 3) := Fold_Lower (RE_Name_Chars (J));
         end loop;

         Name_Len := RE_Name_Chars'Length - 3;

      else
         for J in 7 .. RE_Name_Chars'Last loop
            Name_Buffer (J - 6) := Fold_Lower (RE_Name_Chars (J));
         end loop;

         Name_Len := RE_Name_Chars'Length - 6;
      end if;

      return Name_Find;
   end RE_Chars;

   ---------
   -- RTE --
   ---------

   function RTE (E : RE_Id) return Entity_Id is
      U_Id : constant RTU_Id := RE_Unit_Table (E);
      U    : RT_Unit_Table_Record renames RT_Unit_Table (U_Id);

      Lib_Unit : Node_Id;
      Pkg_Ent  : Entity_Id;
      Ename    : Name_Id;

      --  The following flag is used to disable front-end inlining when RTE
      --  is invoked. This prevents the analysis of other runtime bodies when
      --  a particular spec is loaded through Rtsfind. This is both efficient,
      --  and it prevents spurious visibility conflicts between use-visible
      --  user entities, and entities in run-time packages.

      --  In configurable run-time mode, subprograms marked Inlined_Always must
      --  be inlined, so in the case we retain the Front_End_Inlining mode.

      Save_Front_End_Inlining : Boolean;

      function Check_CRT (Eid : Entity_Id) return Entity_Id;
      --  Check entity Eid to ensure that configurable run-time restrictions
      --  are met. May generate an error message and raise RE_Not_Available
      --  if the entity E does not exist (i.e. Eid is Empty)

      procedure Check_RPC;
      --  Reject programs that make use of distribution features not supported
      --  on the current target. On such targets (VMS, Vxworks, others?) we
      --  only provide a minimal body for System.Rpc that only supplies an
      --  implementation of partition_id.

      function Find_Local_Entity (E : RE_Id) return Entity_Id;
      --  This function is used when entity E is in this compilation's main
      --  unit. It gets the value from the already compiled declaration.

      function Make_Unit_Name (N : Node_Id) return Node_Id;
      --  If the unit is a child unit, build fully qualified name for use
      --  in With_Clause.

      ---------------
      -- Check_CRT --
      ---------------

      function Check_CRT (Eid : Entity_Id) return Entity_Id is
      begin
         if No (Eid) then
            Entity_Not_Defined (E);
            raise RE_Not_Available;

         --  Entity is available

         else
            --  If in No_Run_Time mode and entity is not in one of the
            --  specially permitted units, raise the exception.

            if No_Run_Time_Mode
                 and then not OK_No_Run_Time_Unit (U_Id)
            then
               Entity_Not_Defined (E);
               raise RE_Not_Available;
            end if;

            --  Otherwise entity is accessible

            return Eid;
         end if;
      end Check_CRT;

      ---------------
      -- Check_RPC --
      ---------------

      procedure Check_RPC is
         Body_Name    : Unit_Name_Type;
         Unum         : Unit_Number_Type;

      begin
         --  Bypass this check if debug flag -gnatdR set

         if Debug_Flag_RR then
            return;
         end if;

         --  Otherwise we need the check if we are going after one of
         --  the critical entities in System.RPC in stubs mode.

         if (Distribution_Stub_Mode = Generate_Receiver_Stub_Body
                      or else
                        Distribution_Stub_Mode = Generate_Caller_Stub_Body)
           and then (E = RE_Do_Rpc
                       or else E = RE_Do_Apc
                       or else E = RE_Params_Stream_Type
                       or else E = RE_RPC_Receiver)
         then
            --  Load body of System.Rpc, and abort if this is the body that is
            --  provided by GNAT, for which these features are not supported
            --  on current target. We identify the gnat body by the presence
            --  of a local entity called Gnat in the first declaration.

            Lib_Unit := Unit (Cunit (U.Unum));
            Body_Name := Get_Body_Name (Get_Unit_Name (Lib_Unit));
            Unum :=
              Load_Unit
                (Load_Name  => Body_Name,
                 Required   => False,
                 Subunit    => False,
                 Error_Node => Empty,
                 Renamings  => True);

            if Unum /= No_Unit then
               declare
                  Decls : constant List_Id :=
                            Declarations (Unit (Cunit (Unum)));

               begin
                  if Present (Decls)
                    and then Nkind (First (Decls)) = N_Object_Declaration
                    and then
                      Chars (Defining_Identifier (First (Decls))) = Name_Gnat
                  then
                     Set_Standard_Error;
                     Write_Str ("distribution feature not supported");
                     Write_Eol;
                     raise Unrecoverable_Error;
                  end if;
               end;
            end if;
         end if;
      end Check_RPC;

      ------------------------
      -- Find_System_Entity --
      ------------------------

      function Find_Local_Entity (E : RE_Id) return Entity_Id is
         RE_Str : String renames RE_Id'Image (E);
         Ent    : Entity_Id;

         Save_Nam : constant String := Name_Buffer (1 .. Name_Len);
         --  Save name buffer and length over call

      begin
         Name_Len := Natural'Max (0, RE_Str'Length - 3);
         Name_Buffer (1 .. Name_Len) :=
           RE_Str (RE_Str'First + 3 .. RE_Str'Last);

         Ent := Entity_Id (Get_Name_Table_Info (Name_Find));

         Name_Len := Save_Nam'Length;
         Name_Buffer (1 .. Name_Len) := Save_Nam;

         return Ent;
      end Find_Local_Entity;

      --------------------
      -- Make_Unit_Name --
      --------------------

      function Make_Unit_Name (N : Node_Id) return Node_Id is
         Nam  : Node_Id;
         Scop : Entity_Id;

      begin
         Nam  := New_Reference_To (U.Entity, Standard_Location);
         Scop := Scope (U.Entity);

         if Nkind (N) = N_Defining_Program_Unit_Name then
            while Scop /= Standard_Standard loop
               Nam :=
                 Make_Expanded_Name (Standard_Location,
                   Chars  => Chars (U.Entity),
                   Prefix => New_Reference_To (Scop, Standard_Location),
                   Selector_Name => Nam);
               Set_Entity (Nam, U.Entity);

               Scop := Scope (Scop);
            end loop;
         end if;

         return Nam;
      end Make_Unit_Name;

   --  Start of processing for RTE

   begin
      --  Doing a rtsfind in system.ads is special, as we cannot do this
      --  when compiling System itself. So if we are compiling system then
      --  we should already have acquired and processed the declaration
      --  of the entity. The test is to see if this compilation's main unit
      --  is System. If so, return the value from the already compiled
      --  declaration and otherwise do a regular find.

      --  Not pleasant, but these kinds of annoying recursion when
      --  writing an Ada compiler in Ada have to be broken somewhere!

      if Present (Main_Unit_Entity)
        and then Chars (Main_Unit_Entity) = Name_System
        and then Analyzed (Main_Unit_Entity)
        and then not Is_Child_Unit (Main_Unit_Entity)
      then
         return Check_CRT (Find_Local_Entity (E));
      end if;

      Save_Front_End_Inlining := Front_End_Inlining;
      Front_End_Inlining := Configurable_Run_Time_Mode;

      --  Load unit if unit not previously loaded

      if No (RE_Table (E)) then
         Load_RTU (U_Id, Id => E);
         Lib_Unit := Unit (Cunit (U.Unum));

         --  In the subprogram case, we are all done, the entity we want
         --  is the entity for the subprogram itself. Note that we do not
         --  bother to check that it is the entity that was requested.
         --  the only way that could fail to be the case is if runtime is
         --  hopelessly misconfigured, and it isn't worth testing for this.

         if Nkind (Lib_Unit) = N_Subprogram_Declaration then
            RE_Table (E) := U.Entity;

         --  Otherwise we must have the package case. First check package
         --  entity itself (e.g. RTE_Name for System.Interrupts.Name)

         else
            pragma Assert (Nkind (Lib_Unit) = N_Package_Declaration);
            Ename := RE_Chars (E);

            --  First we search the package entity chain

               Pkg_Ent := First_Entity (U.Entity);
               while Present (Pkg_Ent) loop
                  if Ename = Chars (Pkg_Ent) then
                     RE_Table (E) := Pkg_Ent;
                     Check_RPC;
                     goto Found;
                  end if;

                  Next_Entity (Pkg_Ent);
               end loop;

            --  If we did not find the entity in the package entity chain,
            --  then check if the package entity itself matches. Note that
            --  we do this check after searching the entity chain, since
            --  the rule is that in case of ambiguity, we prefer the entity
            --  defined within the package, rather than the package itself.

            if Ename = Chars (U.Entity) then
               RE_Table (E) := U.Entity;
            end if;

            --  If we didn't find the entity we want, something is wrong.
            --  We just leave RE_Table (E) set to Empty and the appropriate
            --  action will be taken by Check_CRT when we exit.

         end if;
      end if;

      --  See if we have to generate a WITH for this entity. We generate
      --  a WITH if the current unit is part of the extended main code
      --  unit, and if we have not already added the with. The WITH is
      --  added to the appropriate unit (the current one). We do not need
      --  to generate a WITH for an

   <<Found>>
      if (not U.Withed)
        and then
          In_Extended_Main_Code_Unit (Cunit_Entity (Current_Sem_Unit))
        and then not RTE_Available_Call
      then
         U.Withed := True;

         declare
            Withn    : Node_Id;
            Lib_Unit : Node_Id;

         begin
            Lib_Unit := Unit (Cunit (U.Unum));
            Withn :=
              Make_With_Clause (Standard_Location,
                Name =>
                  Make_Unit_Name
                    (Defining_Unit_Name (Specification (Lib_Unit))));
            Set_Library_Unit          (Withn, Cunit (U.Unum));
            Set_Corresponding_Spec    (Withn, U.Entity);
            Set_First_Name            (Withn, True);
            Set_Implicit_With         (Withn, True);

            Mark_Rewrite_Insertion (Withn);
            Append (Withn, Context_Items (Cunit (Current_Sem_Unit)));
         end;
      end if;

      Front_End_Inlining := Save_Front_End_Inlining;
      return Check_CRT (RE_Table (E));
   end RTE;

   -------------------
   -- RTE_Available --
   -------------------

   function RTE_Available (E : RE_Id) return Boolean is
      Dummy : Entity_Id;
      pragma Warnings (Off, Dummy);

      Result : Boolean;

      Save_RTE_Available_Call : constant Boolean := RTE_Available_Call;
      Save_RTE_Is_Available   : constant Boolean := RTE_Is_Available;
      --  These are saved recursively because the call to load a unit
      --  caused by an upper level call may perform a recursive call
      --  to this routine during analysis of the corresponding unit.

   begin
      RTE_Available_Call := True;
      RTE_Is_Available := True;
      Dummy := RTE (E);
      Result := RTE_Is_Available;
      RTE_Available_Call := Save_RTE_Available_Call;
      RTE_Is_Available   := Save_RTE_Is_Available;
      return Result;

   exception
      when RE_Not_Available =>
         RTE_Available_Call := Save_RTE_Available_Call;
         RTE_Is_Available   := Save_RTE_Is_Available;
         return False;
   end RTE_Available;

   -------------------
   -- RTE_Error_Msg --
   -------------------

   procedure RTE_Error_Msg (Msg : String) is
   begin
      if RTE_Available_Call then
         RTE_Is_Available := False;
      else
         Error_Msg_N (Msg, Current_Error_Node);

         --  Bump count of violations if we are in configurable run-time
         --  mode and this is not a continuation message.

         if Configurable_Run_Time_Mode and then Msg (1) /= '\' then
            Configurable_Run_Time_Violations :=
              Configurable_Run_Time_Violations + 1;
         end if;
      end if;
   end RTE_Error_Msg;

   --------------------
   -- Text_IO_Kludge --
   --------------------

   procedure Text_IO_Kludge (Nam : Node_Id) is
      Chrs : Name_Id;

      type Name_Map_Type is array (Text_IO_Package_Name) of RTU_Id;

      Name_Map : constant Name_Map_Type := Name_Map_Type'(
        Name_Decimal_IO     => Ada_Text_IO_Decimal_IO,
        Name_Enumeration_IO => Ada_Text_IO_Enumeration_IO,
        Name_Fixed_IO       => Ada_Text_IO_Fixed_IO,
        Name_Float_IO       => Ada_Text_IO_Float_IO,
        Name_Integer_IO     => Ada_Text_IO_Integer_IO,
        Name_Modular_IO     => Ada_Text_IO_Modular_IO);

      Wide_Name_Map : constant Name_Map_Type := Name_Map_Type'(
        Name_Decimal_IO     => Ada_Wide_Text_IO_Decimal_IO,
        Name_Enumeration_IO => Ada_Wide_Text_IO_Enumeration_IO,
        Name_Fixed_IO       => Ada_Wide_Text_IO_Fixed_IO,
        Name_Float_IO       => Ada_Wide_Text_IO_Float_IO,
        Name_Integer_IO     => Ada_Wide_Text_IO_Integer_IO,
        Name_Modular_IO     => Ada_Wide_Text_IO_Modular_IO);

   begin
      --  Nothing to do if name is not identifier or a selected component
      --  whose selector_name is not an identifier.

      if Nkind (Nam) = N_Identifier then
         Chrs := Chars (Nam);

      elsif Nkind (Nam) = N_Selected_Component
        and then Nkind (Selector_Name (Nam)) = N_Identifier
      then
         Chrs := Chars (Selector_Name (Nam));

      else
         return;
      end if;

      --  Nothing to do if name is not one of the Text_IO subpackages
      --  Otherwise look through loaded units, and if we find Text_IO
      --  or Wide_Text_IO already loaded, then load the proper child.

      if Chrs in Text_IO_Package_Name then
         for U in Main_Unit .. Last_Unit loop
            Get_Name_String (Unit_File_Name (U));

            if Name_Len = 12 then

               --  Here is where we do the loads if we find one of the
               --  units Ada.Text_IO or Ada.Wide_Text_IO. An interesting
               --  detail is that these units may already be used (i.e.
               --  their In_Use flags may be set). Normally when the In_Use
               --  flag is set, the Is_Potentially_Use_Visible flag of all
               --  entities in the package is set, but the new entity we
               --  are mysteriously adding was not there to have its flag
               --  set at the time. So that's why we pass the extra parameter
               --  to RTU_Find, to make sure the flag does get set now.
               --  Given that those generic packages are in fact child units,
               --  we must indicate that they are visible.

               if Name_Buffer (1 .. 12) = "a-textio.ads" then
                  Load_RTU
                    (Name_Map (Chrs),
                     Use_Setting => In_Use (Cunit_Entity (U)));
                  Set_Is_Visible_Child_Unit
                    (RT_Unit_Table (Name_Map (Chrs)).Entity);

               elsif Name_Buffer (1 .. 12) = "a-witeio.ads" then
                  Load_RTU
                    (Wide_Name_Map (Chrs),
                     Use_Setting => In_Use (Cunit_Entity (U)));
                  Set_Is_Visible_Child_Unit
                    (RT_Unit_Table (Wide_Name_Map (Chrs)).Entity);
               end if;
            end if;
         end loop;
      end if;
   end Text_IO_Kludge;

end Rtsfind;