gcc/ada/sem_elab.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT COMPILER COMPONENTS                         --
   4 --                                                                          --
   5 --                             S E M _ E L A B                              --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 --          Copyright (C) 1997-2012, Free Software Foundation, Inc.         --
  10 --                                                                          --
  11 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  12 -- terms of the  GNU General Public License as published  by the Free Soft- --
  13 -- ware  Foundation;  either version 3,  or (at your option) any later ver- --
  14 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  15 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  16 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  17 -- for  more details.  You should have  received  a copy of the GNU General --
  18 -- Public License  distributed with GNAT; see file COPYING3.  If not, go to --
  19 -- http://www.gnu.org/licenses for a complete copy of the license.          --
  20 --                                                                          --
  21 -- GNAT was originally developed  by the GNAT team at  New York University. --
  22 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  23 --                                                                          --
  24 ------------------------------------------------------------------------------
  25
  26 --  This package contains the routines used to deal with issuing warnings
  27 --  for cases of calls that may require warnings about possible access
  28 --  before elaboration.
  29
  30 with Types; use Types;
  31
  32 package Sem_Elab is
  33
  34    -----------------------------
  35    -- Description of Approach --
  36    -----------------------------
  37
  38    --  Every non-static call that is encountered by Sem_Res results in
  39    --  a call to Check_Elab_Call, with N being the call node, and Outer
  40    --  set to its default value of True.
  41
  42    --  The goal of Check_Elab_Call is to determine whether or not the
  43    --  call in question can generate an access before elaboration
  44    --  error (raising Program_Error) either by directly calling a
  45    --  subprogram whose body has not yet been elaborated, or indirectly,
  46    --  by calling a subprogram whose body has been elaborated, but which
  47    --  contains a call to such a subprogram.
  48
  49    --  The only calls that we need to look at at the outer level are
  50    --  calls that occur in elaboration code. There are two cases. The
  51    --  call can be at the outer level of elaboration code, or it can
  52    --  be within another unit, e.g. the elaboration code of a subprogram.
  53
  54    --  In the case of an elaboration call at the outer level, we must
  55    --  trace all calls to outer level routines either within the current
  56    --  unit or to other units that are with'ed. For calls within the
  57    --  current unit, we can determine if the body has been elaborated
  58    --  or not, and if it has not, then a warning is generated.
  59
  60    --  Note that there are two subcases. If the original call directly
  61    --  calls a subprogram whose body has not been elaborated, then we
  62    --  know that an ABE will take place, and we replace the call by
  63    --  a raise of Program_Error. If the call is indirect, then we don't
  64    --  know that the PE will be raised, since the call might be guarded
  65    --  by a conditional. In this case we set Do_Elab_Check on the call
  66    --  so that a dynamic check is generated, and output a warning.
  67
  68    --  For calls to a subprogram in a with'ed unit, we require that
  69    --  a pragma Elaborate_All or pragma Elaborate be present, or that
  70    --  the referenced unit have a pragma Preelaborate, pragma Pure, or
  71    --  pragma Elaborate_Body. If none of these conditions is met, then
  72    --  a warning is generated that a pragma Elaborate_All may be needed.
  73
  74    --  For the case of an elaboration call at some inner level, we are
  75    --  interested in tracing only calls to subprograms at the same level,
  76    --  i.e. those that can be called during elaboration. Any calls to
  77    --  outer level routines cannot cause ABE's as a result of the original
  78    --  call (there might be an outer level call to the subprogram from
  79    --  outside that causes the ABE, but that gets analyzed separately).
  80
  81    --  Note that we never trace calls to inner level subprograms, since
  82    --  these cannot result in ABE's unless there is an elaboration problem
  83    --  at a lower level, which will be separately detected.
  84
  85    --  Note on pragma Elaborate. The checking here assumes that a pragma
  86    --  Elaborate on a with'ed unit guarantees that subprograms within the
  87    --  unit can be called without causing an ABE. This is not in fact the
  88    --  case since pragma Elaborate does not guarantee the transitive
  89    --  coverage guaranteed by Elaborate_All. However, we leave this issue
  90    --  up to the binder, which has generates warnings if there are possible
  91    --  problems in the use of pragma Elaborate.
  92
  93    --------------------------------------
  94    -- Instantiation Elaboration Errors --
  95    --------------------------------------
  96
  97    --  A special case arises when an instantiation appears in a context
  98    --  that is known to be before the body is elaborated, e.g.
  99
 100    --       generic package x is ...
 101    --       ...
 102    --       package xx is new x;
 103    --       ...
 104    --       package body x is ...
 105
 106    --  In this situation it is certain that an elaboration error will
 107    --  occur, and an unconditional raise Program_Error statement is
 108    --  inserted before the instantiation, and a warning generated.
 109
 110    --  The problem is that in this case we have no place to put the
 111    --  body of the instantiation. We can't put it in the normal place,
 112    --  because it is too early, and will cause errors to occur as a
 113    --  result of referencing entities before they are declared.
 114
 115    --  Our approach in this case is simply to avoid creating the body
 116    --  of the instantiation in such a case. The instantiation spec is
 117    --  modified to include dummy bodies for all subprograms, so that
 118    --  the resulting code does not contain subprogram specs with no
 119    --  corresponding bodies.
 120
 121    procedure Check_Elab_Call
 122      (N            : Node_Id;
 123       Outer_Scope  : Entity_Id := Empty;
 124       In_Init_Proc : Boolean   := False);
 125    --  Check a call for possible elaboration problems. The node N is either an
 126    --  N_Function_Call or N_Procedure_Call_Statement node or an access
 127    --  attribute reference whose prefix is a subprogram. The Outer_Scope
 128    --  argument indicates whether this is an outer level call from Sem_Res
 129    --  (Outer_Scope set to Empty), or an internal recursive call (Outer_Scope
 130    --  set to entity of outermost call, see body). Flag In_Init_Proc should be
 131    --  set whenever the current context is a type init proc.
 132
 133    procedure Check_Elab_Calls;
 134    --  Not all the processing for Check_Elab_Call can be done at the time
 135    --  of calls to Check_Elab_Call. This is because for internal calls, we
 136    --  need to wait to complete the check until all generic bodies have been
 137    --  instantiated. The Check_Elab_Calls procedure cleans up these waiting
 138    --  checks. It is called once after the completion of instantiation.
 139
 140    procedure Check_Elab_Assign (N : Node_Id);
 141    --  N is either the left side of an assignment, or a procedure argument for
 142    --  a mode OUT or IN OUT formal. This procedure checks for a possible case
 143    --  of access to an entity from elaboration code before the entity has been
 144    --  initialized, and issues appropriate warnings.
 145
 146    procedure Check_Elab_Instantiation
 147      (N           : Node_Id;
 148       Outer_Scope : Entity_Id := Empty);
 149    --  Check an instantiation for possible elaboration problems. N is an
 150    --  instantiation node (N_Package_Instantiation, N_Function_Instantiation,
 151    --  or N_Procedure_Instantiation), and Outer_Scope indicates if this is
 152    --  an outer level call from Sem_Ch12 (Outer_Scope set to Empty), or an
 153    --  internal recursive call (Outer_Scope set to scope of outermost call,
 154    --  see body for further details). The returned value is relevant only
 155    --  for an outer level call, and is set to False if an elaboration error
 156    --  is bound to occur on the instantiation, and True otherwise. This is
 157    --  used by the caller to signal that the body of the instance should
 158    --  not be generated (see detailed description in body).
 159
 160    procedure Check_Task_Activation (N : Node_Id);
 161    --  at the point at which tasks are activated in a package body, check
 162    --  that the bodies of the tasks are elaborated.
 163
 164 end Sem_Elab;