|
111
|
1 ------------------------------------------------------------------------------
|
|
|
2 -- --
|
|
|
3 -- GNAT COMPILER COMPONENTS --
|
|
|
4 -- --
|
|
|
5 -- S E M _ M E C H --
|
|
|
6 -- --
|
|
|
7 -- S p e c --
|
|
|
8 -- --
|
|
|
9 -- Copyright (C) 1996-2014, 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 routine used to establish calling mechanisms
|
|
|
27 -- The reason we separate this off into its own package is that it is
|
|
|
28 -- entirely possible that it may need some target specific specialization.
|
|
|
29
|
|
|
30 with Types; use Types;
|
|
|
31
|
|
|
32 package Sem_Mech is
|
|
|
33
|
|
|
34 -------------------------------------------------
|
|
|
35 -- Definitions for Parameter Mechanism Control --
|
|
|
36 -------------------------------------------------
|
|
|
37
|
|
|
38 -- For parameters passed to subprograms, and for function return values,
|
|
|
39 -- a passing mechanism is defined. The entity attribute Mechanism returns
|
|
|
40 -- an indication of the mechanism, and Set_Mechanism can be used to set
|
|
|
41 -- the mechanism. At the program level, there are three ways to explicitly
|
|
|
42 -- set the mechanism:
|
|
|
43
|
|
|
44 -- An Import_xxx or Export_xxx pragma (where xxx is Function, Procedure,
|
|
|
45 -- or Valued_Procedure) can explicitly set the mechanism for either a
|
|
|
46 -- parameter or a function return value. A mechanism explicitly set by
|
|
|
47 -- such a pragma overrides the effect of C_Pass_By_Copy described below.
|
|
|
48
|
|
|
49 -- If convention C_Pass_By_Copy is set for a record, and the record type
|
|
|
50 -- is used as the formal type of a subprogram with a foreign convention,
|
|
|
51 -- then the mechanism is set to By_Copy.
|
|
|
52
|
|
|
53 -- If a pragma C_Pass_By_Copy applies, and a record type has Convention
|
|
|
54 -- C, and the record type is used as the formal type of a subprogram
|
|
|
55 -- with a foreign convention, then the mechanism is set to use By_Copy
|
|
|
56 -- if the size of the record is sufficiently small (as determined by
|
|
|
57 -- the value of the parameter to pragma C_Pass_By_Copy).
|
|
|
58
|
|
|
59 -- The subtype Mechanism_Type (declared in Types) is used to describe
|
|
|
60 -- the mechanism to be used. The following special values of this type
|
|
|
61 -- specify the mechanism, as follows.
|
|
|
62
|
|
|
63 Default_Mechanism : constant Mechanism_Type := 0;
|
|
|
64 -- The default setting indicates that the backend will choose the proper
|
|
|
65 -- default mechanism. This depends on the convention of the subprogram
|
|
|
66 -- involved, and is generally target dependent. In the compiler, the
|
|
|
67 -- backend chooses the mechanism in this case in accordance with any
|
|
|
68 -- requirements imposed by the ABI. Note that Default is never used for
|
|
|
69 -- record types on foreign convention subprograms, since By_Reference
|
|
|
70 -- is forced for such types unless one of the above described approaches
|
|
|
71 -- is used to explicitly force By_Copy.
|
|
|
72
|
|
|
73 By_Copy : constant Mechanism_Type := -1;
|
|
|
74 -- Passing by copy is forced. The exact meaning of By_Copy (e.g. whether
|
|
|
75 -- at a low level the value is passed in registers, or the value is copied
|
|
|
76 -- and a pointer is passed), is determined by the backend in accordance
|
|
|
77 -- with requirements imposed by the ABI. Note that in the extended import
|
|
|
78 -- and export pragma mechanisms, this is called Value, rather than Copy.
|
|
|
79
|
|
|
80 By_Reference : constant Mechanism_Type := -2;
|
|
|
81 -- Passing by reference is forced. This is always equivalent to passing
|
|
|
82 -- a simple pointer in the case of subprograms with a foreign convention.
|
|
|
83 -- For unconstrained arrays passed to foreign convention subprograms, the
|
|
|
84 -- address of the first element of the array is passed. For convention
|
|
|
85 -- Ada, the result is logically to pass a reference, but the precise
|
|
|
86 -- mechanism (e.g. to pass bounds of unconstrained types and other needed
|
|
|
87 -- special information) is determined by the backend in accordance with
|
|
|
88 -- requirements imposed by the ABI as interpreted for Ada.
|
|
|
89
|
|
|
90 pragma Assert (Mechanism_Type'First = -2);
|
|
|
91 -- Check definition in types is right!
|
|
|
92
|
|
|
93 -- All the above special values are non-positive. Positive values for
|
|
|
94 -- Mechanism_Type values have a special meaning. They are used only in
|
|
|
95 -- the case of records, as a result of the use of the C_Pass_By_Copy
|
|
|
96 -- pragma, and the meaning is that if the size of the record is known
|
|
|
97 -- at compile time and does not exceed the mechanism type value, then
|
|
|
98 -- By_Copy passing is forced, otherwise By_Reference is forced.
|
|
|
99
|
|
|
100 ----------------------
|
|
|
101 -- Global Variables --
|
|
|
102 ----------------------
|
|
|
103
|
|
|
104 Default_C_Record_Mechanism : Mechanism_Type := By_Reference;
|
|
|
105 -- This value is the default mechanism used for C convention records
|
|
|
106 -- in foreign-convention subprograms if no mechanism is otherwise
|
|
|
107 -- specified. This value is modified appropriately by the occurrence
|
|
|
108 -- of a C_Pass_By_Copy configuration pragma.
|
|
|
109
|
|
|
110 -----------------
|
|
|
111 -- Subprograms --
|
|
|
112 -----------------
|
|
|
113
|
|
|
114 procedure Set_Mechanisms (E : Entity_Id);
|
|
|
115 -- E is a subprogram or subprogram type that has been frozen, so the
|
|
|
116 -- convention of the subprogram and all its formal types and result
|
|
|
117 -- type in the case of a function are established. The function of
|
|
|
118 -- this call is to set mechanism values for formals and for the
|
|
|
119 -- function return if they have not already been explicitly set by
|
|
|
120 -- a use of an extended Import or Export pragma. The idea is to set
|
|
|
121 -- mechanism values wherever the semantics is dictated by either
|
|
|
122 -- requirements or implementation advice in the RM, and to leave
|
|
|
123 -- the mechanism set to Default if there is no requirement, so that
|
|
|
124 -- the back-end is free to choose the most efficient method.
|
|
|
125
|
|
|
126 procedure Set_Mechanism_Value (Ent : Entity_Id; Mech_Name : Node_Id);
|
|
|
127 -- Mech is a parameter passing mechanism (see Import_Function syntax
|
|
|
128 -- for MECHANISM_NAME). This routine checks that the mechanism argument
|
|
|
129 -- has the right form, and if not issues an error message. If the
|
|
|
130 -- argument has the right form then the Mechanism field of Ent is
|
|
|
131 -- set appropriately. It also performs some error checks. Note that
|
|
|
132 -- the mechanism name has not been analyzed (and cannot indeed be
|
|
|
133 -- analyzed, since it is semantic nonsense), so we get it in the
|
|
|
134 -- exact form created by the parser.
|
|
|
135
|
|
|
136 procedure Set_Mechanism_With_Checks
|
|
|
137 (Ent : Entity_Id;
|
|
|
138 Mech : Mechanism_Type;
|
|
|
139 Enod : Node_Id);
|
|
|
140 -- Sets the mechanism of Ent to the given Mech value, after first checking
|
|
|
141 -- that the request makes sense. If it does not make sense, a warning is
|
|
|
142 -- posted on node Enod, and the Mechanism of Ent is unchanged.
|
|
|
143
|
|
|
144 end Sem_Mech;
|
