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) 1997-2015, 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 30with Types; use Types; 31 32package Sem_Elab is 33 34 ----------------------------- 35 -- Description of Approach -- 36 ----------------------------- 37 38 -- Every non-static call that is encountered by Sem_Res results in a call 39 -- to Check_Elab_Call, with N being the call node, and Outer set to its 40 -- default value of True. In addition X'Access is treated like a call 41 -- for the access-to-procedure case, and in SPARK mode only we also 42 -- check variable references. 43 44 -- The goal of Check_Elab_Call is to determine whether or not the reference 45 -- in question can generate an access before elaboration error (raising 46 -- Program_Error) either by directly calling a subprogram whose body 47 -- has not yet been elaborated, or indirectly, by calling a subprogram 48 -- whose body has been elaborated, but which contains a call to such a 49 -- subprogram. 50 51 -- In addition, in SPARK mode, we are checking for a variable reference in 52 -- another package, which requires an explicit Elaborate_All pragma. 53 54 -- The only references that we need to look at the outer level are 55 -- references that occur in elaboration code. There are two cases. The 56 -- reference can be at the outer level of elaboration code, or it can 57 -- be within another unit, e.g. the elaboration code of a subprogram. 58 59 -- In the case of an elaboration call at the outer level, we must trace 60 -- all calls to outer level routines either within the current unit or to 61 -- other units that are with'ed. For calls within the current unit, we can 62 -- determine if the body has been elaborated or not, and if it has not, 63 -- then a warning is generated. 64 65 -- Note that there are two subcases. If the original call directly calls a 66 -- subprogram whose body has not been elaborated, then we know that an ABE 67 -- will take place, and we replace the call by a raise of Program_Error. 68 -- If the call is indirect, then we don't know that the PE will be raised, 69 -- since the call might be guarded by a conditional. In this case we set 70 -- Do_Elab_Check on the call so that a dynamic check is generated, and 71 -- output a warning. 72 73 -- For calls to a subprogram in a with'ed unit or a 'Access or variable 74 -- refernece (SPARK mode case), we require that a pragma Elaborate_All 75 -- or pragma Elaborate be present, or that the referenced unit have a 76 -- pragma Preelaborate, pragma Pure, or pragma Elaborate_Body. If none 77 -- of these conditions is met, then a warning is generated that a pragma 78 -- Elaborate_All may be needed (error in the SPARK case), or an implicit 79 -- pragma is generated. 80 81 -- For the case of an elaboration call at some inner level, we are 82 -- interested in tracing only calls to subprograms at the same level, 83 -- i.e. those that can be called during elaboration. Any calls to 84 -- outer level routines cannot cause ABE's as a result of the original 85 -- call (there might be an outer level call to the subprogram from 86 -- outside that causes the ABE, but that gets analyzed separately). 87 88 -- Note that we never trace calls to inner level subprograms, since 89 -- these cannot result in ABE's unless there is an elaboration problem 90 -- at a lower level, which will be separately detected. 91 92 -- Note on pragma Elaborate. The checking here assumes that a pragma 93 -- Elaborate on a with'ed unit guarantees that subprograms within the 94 -- unit can be called without causing an ABE. This is not in fact the 95 -- case since pragma Elaborate does not guarantee the transitive 96 -- coverage guaranteed by Elaborate_All. However, we decide to trust 97 -- the user in this case. 98 99 -------------------------------------- 100 -- Instantiation Elaboration Errors -- 101 -------------------------------------- 102 103 -- A special case arises when an instantiation appears in a context 104 -- that is known to be before the body is elaborated, e.g. 105 106 -- generic package x is ... 107 -- ... 108 -- package xx is new x; 109 -- ... 110 -- package body x is ... 111 112 -- In this situation it is certain that an elaboration error will 113 -- occur, and an unconditional raise Program_Error statement is 114 -- inserted before the instantiation, and a warning generated. 115 116 -- The problem is that in this case we have no place to put the 117 -- body of the instantiation. We can't put it in the normal place, 118 -- because it is too early, and will cause errors to occur as a 119 -- result of referencing entities before they are declared. 120 121 -- Our approach in this case is simply to avoid creating the body 122 -- of the instantiation in such a case. The instantiation spec is 123 -- modified to include dummy bodies for all subprograms, so that 124 -- the resulting code does not contain subprogram specs with no 125 -- corresponding bodies. 126 127 procedure Check_Elab_Call 128 (N : Node_Id; 129 Outer_Scope : Entity_Id := Empty; 130 In_Init_Proc : Boolean := False); 131 -- Check a call for possible elaboration problems. The node N is either an 132 -- N_Function_Call or N_Procedure_Call_Statement node or an access 133 -- attribute reference whose prefix is a subprogram. 134 -- 135 -- If SPARK_Mode is On, then N can also be a variablr reference, since 136 -- SPARK requires the use of Elaborate_All for references to variables 137 -- in other packages. 138 139 -- The Outer_Scope argument indicates whether this is an outer level 140 -- call from Sem_Res (Outer_Scope set to Empty), or an internal recursive 141 -- call (Outer_Scope set to entity of outermost call, see body). The flag 142 -- In_Init_Proc should be set whenever the current context is a type 143 -- init proc. 144 145 -- Note: this might better be called Check_Elab_Reference (to recognize 146 -- the SPARK case), but we prefer to keep the original name, since this 147 -- is primarily used for checking for calls that could generate an ABE). 148 149 procedure Check_Elab_Calls; 150 -- Not all the processing for Check_Elab_Call can be done at the time 151 -- of calls to Check_Elab_Call. This is because for internal calls, we 152 -- need to wait to complete the check until all generic bodies have been 153 -- instantiated. The Check_Elab_Calls procedure cleans up these waiting 154 -- checks. It is called once after the completion of instantiation. 155 156 procedure Check_Elab_Assign (N : Node_Id); 157 -- N is either the left side of an assignment, or a procedure argument for 158 -- a mode OUT or IN OUT formal. This procedure checks for a possible case 159 -- of access to an entity from elaboration code before the entity has been 160 -- initialized, and issues appropriate warnings. 161 162 procedure Check_Elab_Instantiation 163 (N : Node_Id; 164 Outer_Scope : Entity_Id := Empty); 165 -- Check an instantiation for possible elaboration problems. N is an 166 -- instantiation node (N_Package_Instantiation, N_Function_Instantiation, 167 -- or N_Procedure_Instantiation), and Outer_Scope indicates if this is 168 -- an outer level call from Sem_Ch12 (Outer_Scope set to Empty), or an 169 -- internal recursive call (Outer_Scope set to scope of outermost call, 170 -- see body for further details). The returned value is relevant only 171 -- for an outer level call, and is set to False if an elaboration error 172 -- is bound to occur on the instantiation, and True otherwise. This is 173 -- used by the caller to signal that the body of the instance should 174 -- not be generated (see detailed description in body). 175 176 procedure Check_Task_Activation (N : Node_Id); 177 -- Tt the point at which tasks are activated in a package body, check 178 -- that the bodies of the tasks are elaborated. 179 180end Sem_Elab; 181