------------------------------------------------------------------------------ -- -- -- GNAT COMPILER COMPONENTS -- -- -- -- S E M _ E L A B -- -- -- -- S p e c -- -- -- -- Copyright (C) 1997-2017, 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 3, 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 COPYING3. If not, go to -- -- http://www.gnu.org/licenses for a complete copy of the license. -- -- -- -- GNAT was originally developed by the GNAT team at New York University. -- -- Extensive contributions were provided by Ada Core Technologies Inc. -- -- -- ------------------------------------------------------------------------------ -- This package contains the routines used to deal with issuing warnings -- for cases of calls that may require warnings about possible access -- before elaboration. with Types; use Types; package Sem_Elab is ----------------------------- -- Description of Approach -- ----------------------------- -- Every non-static call that is encountered by Sem_Res results in a call -- to Check_Elab_Call, with N being the call node, and Outer set to its -- default value of True. In addition X'Access is treated like a call -- for the access-to-procedure case, and in SPARK mode only we also -- check variable references. -- The goal of Check_Elab_Call is to determine whether or not the reference -- in question can generate an access before elaboration error (raising -- Program_Error) either by directly calling a subprogram whose body -- has not yet been elaborated, or indirectly, by calling a subprogram -- whose body has been elaborated, but which contains a call to such a -- subprogram. -- In addition, in SPARK mode, we are checking for a variable reference in -- another package, which requires an explicit Elaborate_All pragma. -- The only references that we need to look at the outer level are -- references that occur in elaboration code. There are two cases. The -- reference can be at the outer level of elaboration code, or it can -- be within another unit, e.g. the elaboration code of a subprogram. -- In the case of an elaboration call at the outer level, we must trace -- all calls to outer level routines either within the current unit or to -- other units that are with'ed. For calls within the current unit, we can -- determine if the body has been elaborated or not, and if it has not, -- then a warning is generated. -- Note that there are two subcases. If the original call directly calls a -- subprogram whose body has not been elaborated, then we know that an ABE -- will take place, and we replace the call by a raise of Program_Error. -- If the call is indirect, then we don't know that the PE will be raised, -- since the call might be guarded by a conditional. In this case we set -- Do_Elab_Check on the call so that a dynamic check is generated, and -- output a warning. -- For calls to a subprogram in a with'ed unit or a 'Access or variable -- refernece (SPARK mode case), we require that a pragma Elaborate_All -- or pragma Elaborate be present, or that the referenced unit have a -- pragma Preelaborate, pragma Pure, or pragma Elaborate_Body. If none -- of these conditions is met, then a warning is generated that a pragma -- Elaborate_All may be needed (error in the SPARK case), or an implicit -- pragma is generated. -- For the case of an elaboration call at some inner level, we are -- interested in tracing only calls to subprograms at the same level, -- i.e. those that can be called during elaboration. Any calls to -- outer level routines cannot cause ABE's as a result of the original -- call (there might be an outer level call to the subprogram from -- outside that causes the ABE, but that gets analyzed separately). -- Note that we never trace calls to inner level subprograms, since -- these cannot result in ABE's unless there is an elaboration problem -- at a lower level, which will be separately detected. -- Note on pragma Elaborate. The checking here assumes that a pragma -- Elaborate on a with'ed unit guarantees that subprograms within the -- unit can be called without causing an ABE. This is not in fact the -- case since pragma Elaborate does not guarantee the transitive -- coverage guaranteed by Elaborate_All. However, we decide to trust -- the user in this case. -------------------------------------- -- Instantiation Elaboration Errors -- -------------------------------------- -- A special case arises when an instantiation appears in a context -- that is known to be before the body is elaborated, e.g. -- generic package x is ... -- ... -- package xx is new x; -- ... -- package body x is ... -- In this situation it is certain that an elaboration error will -- occur, and an unconditional raise Program_Error statement is -- inserted before the instantiation, and a warning generated. -- The problem is that in this case we have no place to put the -- body of the instantiation. We can't put it in the normal place, -- because it is too early, and will cause errors to occur as a -- result of referencing entities before they are declared. -- Our approach in this case is simply to avoid creating the body -- of the instantiation in such a case. The instantiation spec is -- modified to include dummy bodies for all subprograms, so that -- the resulting code does not contain subprogram specs with no -- corresponding bodies. procedure Check_Elab_Call (N : Node_Id; Outer_Scope : Entity_Id := Empty; In_Init_Proc : Boolean := False); -- Check a call for possible elaboration problems. The node N is either an -- N_Function_Call or N_Procedure_Call_Statement node or an access -- attribute reference whose prefix is a subprogram. -- -- If SPARK_Mode is On, then N can also be a variable reference, since -- SPARK requires the use of Elaborate_All for references to variables -- in other packages. -- The Outer_Scope argument indicates whether this is an outer level -- call from Sem_Res (Outer_Scope set to Empty), or an internal recursive -- call (Outer_Scope set to entity of outermost call, see body). The flag -- In_Init_Proc should be set whenever the current context is a type -- init proc. -- Note: this might better be called Check_Elab_Reference (to recognize -- the SPARK case), but we prefer to keep the original name, since this -- is primarily used for checking for calls that could generate an ABE). procedure Check_Elab_Calls; -- Not all the processing for Check_Elab_Call can be done at the time -- of calls to Check_Elab_Call. This is because for internal calls, we -- need to wait to complete the check until all generic bodies have been -- instantiated. The Check_Elab_Calls procedure cleans up these waiting -- checks. It is called once after the completion of instantiation. procedure Check_Elab_Assign (N : Node_Id); -- N is either the left side of an assignment, or a procedure argument for -- a mode OUT or IN OUT formal. This procedure checks for a possible case -- of access to an entity from elaboration code before the entity has been -- initialized, and issues appropriate warnings. procedure Check_Elab_Instantiation (N : Node_Id; Outer_Scope : Entity_Id := Empty); -- Check an instantiation for possible elaboration problems. N is an -- instantiation node (N_Package_Instantiation, N_Function_Instantiation, -- or N_Procedure_Instantiation), and Outer_Scope indicates if this is -- an outer level call from Sem_Ch12 (Outer_Scope set to Empty), or an -- internal recursive call (Outer_Scope set to scope of outermost call, -- see body for further details). The returned value is relevant only -- for an outer level call, and is set to False if an elaboration error -- is bound to occur on the instantiation, and True otherwise. This is -- used by the caller to signal that the body of the instance should -- not be generated (see detailed description in body). procedure Check_Task_Activation (N : Node_Id); -- At the point at which tasks are activated in a package body, check -- that the bodies of the tasks are elaborated. end Sem_Elab;