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------------------------------------------------------------------------------ -- -- -- GNAT COMPILER COMPONENTS -- -- -- -- S E M _ A T T R -- -- -- -- S p e c -- -- -- -- Copyright (C) 1992-2011, 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. -- -- -- -- You should have received a copy of the GNU General Public License along -- -- with this program; see file COPYING3. If not see -- -- <http://www.gnu.org/licenses/>. -- -- -- -- GNAT was originally developed by the GNAT team at New York University. -- -- Extensive contributions were provided by Ada Core Technologies Inc. -- -- -- ------------------------------------------------------------------------------ -- Attribute handling is isolated in a separate package to ease the addition -- of implementation defined attributes. Logically this processing belongs -- in chapter 4. See Sem_Ch4 for a description of the relation of the -- Analyze and Resolve routines for expression components. -- This spec also documents all GNAT implementation defined pragmas with Exp_Tss; use Exp_Tss; with Namet; use Namet; with Snames; use Snames; with Types; use Types; package Sem_Attr is ----------------------------------------- -- Implementation Dependent Attributes -- ----------------------------------------- -- This section describes the implementation dependent attributes -- provided in GNAT, as well as constructing an array of flags -- indicating which attributes these are. Attribute_Impl_Def : Attribute_Class_Array := Attribute_Class_Array'( ------------------ -- Abort_Signal -- ------------------ Attribute_Abort_Signal => True, -- Standard'Abort_Signal (Standard is the only allowed prefix) provides -- the entity for the special exception used to signal task abort or -- asynchronous transfer of control. Normally this attribute should only -- be used in the tasking runtime (it is highly peculiar, and completely -- outside the normal semantics of Ada, for a user program to intercept -- the abort exception). ------------------ -- Address_Size -- ------------------ Attribute_Address_Size => True, -- Standard'Address_Size (Standard is the only allowed prefix) is -- a static constant giving the number of bits in an Address. It -- is used primarily for constructing the definition of Memory_Size -- in package Standard, but may be freely used in user programs. -- This is a static attribute. --------------- -- Asm_Input -- --------------- Attribute_Asm_Input => True, -- Used only in conjunction with the Asm subprograms in package -- Machine_Code to construct machine instructions. See documentation -- in package Machine_Code in file s-maccod.ads. ---------------- -- Asm_Output -- ---------------- Attribute_Asm_Output => True, -- Used only in conjunction with the Asm subprograms in package -- Machine_Code to construct machine instructions. See documentation -- in package Machine_Code in file s-maccod.ads. --------------- -- AST_Entry -- --------------- Attribute_AST_Entry => True, -- E'Ast_Entry, where E is a task entry, yields a value of the -- predefined type System.DEC.AST_Handler, that enables the given -- entry to be called when an AST occurs. If the name to which the -- attribute applies has not been specified with the pragma AST_Entry, -- the attribute returns the value No_Ast_Handler, and no AST occurs. -- If the entry is for a task that is not callable (T'Callable False), -- the exception program error is raised. If an AST occurs for an -- entry of a task that is terminated, the program is erroneous. -- -- The attribute AST_Entry is supported only in OpenVMS versions -- of GNAT. It will be rejected as illegal in other GNAT versions. --------- -- Bit -- --------- Attribute_Bit => True, -- Obj'Bit, where Obj is any object, yields the bit offset within the -- storage unit (byte) that contains the first bit of storage allocated -- for the object. The attribute value is of type Universal_Integer, -- and is always a non-negative number not exceeding the value of -- System.Storage_Unit. -- -- For an object that is a variable or a constant allocated in a -- register, the value is zero. (The use of this attribute does not -- force the allocation of a variable to memory). -- -- For an object that is a formal parameter, this attribute applies to -- either the matching actual parameter or to a copy of the matching -- actual parameter. -- -- For an access object the value is zero. Note that Obj.all'Bit is -- subject to an Access_Check for the designated object. Similarly -- for a record component X.C'Bit is subject to a discriminant check -- and X(I).Bit and X(I1..I2)'Bit are subject to index checks. -- -- This attribute is designed to be compatible with the DEC Ada -- definition and implementation of the Bit attribute. ------------------ -- Code_Address -- ------------------ Attribute_Code_Address => True, -- The reference subp'Code_Address, where subp is a subprogram entity, -- gives the address of the first generated instruction for the sub- -- program. This is often, but not always the same as the 'Address -- value, which is the address to be used in a call. The differences -- occur in the case of a nested procedure (where Address yields the -- address of the trampoline code used to load the static link), and on -- some systems which use procedure descriptors (in which case Address -- yields the address of the descriptor). ----------------------- -- Default_Bit_Order -- ----------------------- Attribute_Default_Bit_Order => True, -- Standard'Default_Bit_Order (Standard is the only permissible prefix), -- provides the value System.Default_Bit_Order as a Pos value (0 for -- High_Order_First, 1 for Low_Order_First). This is used to construct -- the definition of Default_Bit_Order in package System. This is a -- static attribute. --------------- -- Elab_Body -- --------------- Attribute_Elab_Body => True, -- This attribute can only be applied to a program unit name. It returns -- the entity for the corresponding elaboration procedure for elabor- -- ating the body of the referenced unit. This is used in the main -- generated elaboration procedure by the binder, and is not normally -- used in any other context, but there may be specialized situations in -- which it is useful to be able to call this elaboration procedure from -- Ada code, e.g. if it is necessary to do selective reelaboration to -- fix some error. -------------------- -- Elab_Subp_Body -- -------------------- Attribute_Elab_Subp_Body => True, -- This attribute can only be applied to a library level subprogram -- name and is only relevant in CodePeer mode. It returns the entity -- for the corresponding elaboration procedure for elaborating the body -- of the referenced subprogram unit. This is used in the main generated -- elaboration procedure by the binder in CodePeer mode only. --------------- -- Elab_Spec -- --------------- Attribute_Elab_Spec => True, -- This attribute can only be applied to a program unit name. It -- returns the entity for the corresponding elaboration procedure -- for elaborating the spec of the referenced unit. This is used -- in the main generated elaboration procedure by the binder, and -- is not normally used in any other context, but there may be -- specialized situations in which it is useful to be able to -- call this elaboration procedure from Ada code, e.g. if it -- is necessary to do selective reelaboration to fix some error. ---------------- -- Elaborated -- ---------------- Attribute_Elaborated => True, -- Lunit'Elaborated, where Lunit is a library unit, yields a boolean -- value indicating whether or not the body of the designated library -- unit has been elaborated yet. -------------- -- Enum_Rep -- -------------- Attribute_Enum_Rep => True, -- For every enumeration subtype S, S'Enum_Rep denotes a function -- with the following specification: -- -- function S'Enum_Rep (Arg : S'Base) return universal_integer; -- -- The function returns the representation value for the given -- enumeration value. This will be equal to the 'Pos value in the -- absence of an enumeration representation clause. This is a static -- attribute (i.e. the result is static if the argument is static). -------------- -- Enum_Val -- -------------- Attribute_Enum_Val => True, -- For every enumeration subtype S, S'Enum_Val denotes a function -- with the following specification: -- -- function S'Enum_Val (Arg : universal_integer) return S'Base; -- -- This function performs the inverse transformation to Enum_Rep. Given -- a representation value for the type, it returns the corresponding -- enumeration value. Constraint_Error is raised if no value of the -- enumeration type corresponds to the given integer value. ----------------- -- Fixed_Value -- ----------------- Attribute_Fixed_Value => True, -- For every fixed-point type S, S'Fixed_Value denotes a function -- with the following specification: -- -- function S'Fixed_Value (Arg : universal_integer) return S; -- -- The value returned is the fixed-point value V such that -- -- V = Arg * S'Small -- -- The effect is thus equivalent to first converting the argument to -- the integer type used to represent S, and then doing an unchecked -- conversion to the fixed-point type. This attribute is primarily -- intended for use in implementation of the input-output functions for -- fixed-point values. ----------------------- -- Has_Discriminants -- ----------------------- Attribute_Has_Discriminants => True, -- Gtyp'Has_Discriminants, where Gtyp is a generic formal type, yields -- a Boolean value indicating whether or not the actual instantiation -- type has discriminants. --------- -- Img -- --------- Attribute_Img => True, -- The 'Img function is defined for any prefix, P, that denotes an -- object of scalar type T. P'Img is equivalent to T'Image (P). This -- is convenient for debugging. For example: -- -- Put_Line ("X = " & X'Img); -- -- has the same meaning as the more verbose: -- -- Put_Line ("X = " & Temperature_Type'Image (X)); -- -- where Temperature_Type is the subtype of the object X. ------------------- -- Integer_Value -- ------------------- Attribute_Integer_Value => True, -- For every integer type S, S'Integer_Value denotes a function -- with the following specification: -- -- function S'Integer_Value (Arg : universal_fixed) return S; -- -- The value returned is the integer value V, such that -- -- Arg = V * fixed-type'Small -- -- The effect is thus equivalent to first doing an unchecked convert -- from the fixed-point type to its corresponding implementation type, -- and then converting the result to the target integer type. This -- attribute is primarily intended for use in implementation of the -- standard input-output functions for fixed-point values. Attribute_Invalid_Value => True, -- For every scalar type, S'Invalid_Value designates an undefined value -- of the type. If possible this value is an invalid value, and in fact -- is identical to the value that would be set if Initialize_Scalars -- mode were in effect (including the behavior of its value on -- environment variables or binder switches). The intended use is -- to set a value where initialization is required (e.g. as a result of -- the coding standards in use), but logically no initialization is -- needed, and the value should never be accessed. ------------------ -- Machine_Size -- ------------------ Attribute_Machine_Size => True, -- This attribute is identical to the Object_Size attribute. It is -- provided for compatibility with the DEC attribute of this name. ----------------------- -- Maximum_Alignment -- ----------------------- Attribute_Maximum_Alignment => True, -- Standard'Maximum_Alignment (Standard is the only permissible prefix) -- provides the maximum useful alignment value for the target. This -- is a static value that can be used to specify the alignment for an -- object, guaranteeing that it is properly aligned in all cases. The -- time this is useful is when an external object is imported and its -- alignment requirements are unknown. This is a static attribute. -------------------- -- Mechanism_Code -- -------------------- Attribute_Mechanism_Code => True, -- function'Mechanism_Code yields an integer code for the mechanism -- used for the result of function, and subprogram'Mechanism_Code (n) -- yields the mechanism used for formal parameter number n (a static -- integer value, 1 = first parameter). The code returned is: -- -- 1 = by copy (value) -- 2 = by reference -- 3 = by descriptor (default descriptor type) -- 4 = by descriptor (UBS unaligned bit string) -- 5 = by descriptor (UBSB aligned bit string with arbitrary bounds) -- 6 = by descriptor (UBA unaligned bit array) -- 7 = by descriptor (S string, also scalar access type parameter) -- 8 = by descriptor (SB string with arbitrary bounds) -- 9 = by descriptor (A contiguous array) -- 10 = by descriptor (NCA non-contiguous array) -------------------- -- Null_Parameter -- -------------------- Attribute_Null_Parameter => True, -- A reference T'Null_Parameter denotes an (imaginary) object of type or -- subtype T allocated at (machine) address zero. The attribute is -- allowed only as the default expression of a formal parameter, or as -- an actual expression of a subprogram call. In either case, the -- subprogram must be imported. -- -- The identity of the object is represented by the address zero in the -- argument list, independent of the passing mechanism (explicit or -- default). -- -- The reason that this capability is needed is that for a record or -- other composite object passed by reference, there is no other way of -- specifying that a zero address should be passed. ----------------- -- Object_Size -- ----------------- Attribute_Object_Size => True, -- Type'Object_Size is the same as Type'Size for all types except -- fixed-point types and discrete types. For fixed-point types and -- discrete types, this attribute gives the size used for default -- allocation of objects and components of the size. See section in -- Einfo ("Handling of type'Size values") for further details. ------------------------- -- Passed_By_Reference -- ------------------------- Attribute_Passed_By_Reference => True, -- T'Passed_By_Reference for any subtype T returns a boolean value that -- is true if the type is normally passed by reference and false if the -- type is normally passed by copy in calls. For scalar types, the -- result is always False and is static. For non-scalar types, the -- result is non-static (since it is computed by Gigi). ------------------ -- Range_Length -- ------------------ Attribute_Range_Length => True, -- T'Range_Length for any discrete type T yields the number of values -- represented by the subtype (zero for a null range). The result is -- static for static subtypes. Note that Range_Length applied to the -- index subtype of a one dimensional array always gives the same result -- as Range applied to the array itself. The result is of type universal -- integer. --------- -- Ref -- --------- Attribute_Ref => True, -- System.Address'Ref (Address is the only permissible prefix) is -- equivalent to System'To_Address, provided for compatibility with -- other compilers. ------------------ -- Storage_Unit -- ------------------ Attribute_Storage_Unit => True, -- Standard'Storage_Unit (Standard is the only permissible prefix) -- provides the value System.Storage_Unit, and is intended primarily -- for constructing this definition in package System (see note above -- in Default_Bit_Order description). The is a static attribute. --------------- -- Stub_Type -- --------------- Attribute_Stub_Type => True, -- The GNAT implementation of remote access-to-classwide types is -- organised as described in AARM E.4(20.t): a value of an RACW type -- (designating a remote object) is represented as a normal access -- value, pointing to a "stub" object which in turn contains the -- necessary information to contact the designated remote object. A -- call on any dispatching operation of such a stub object does the -- remote call, if necessary, using the information in the stub object -- to locate the target partition, etc. -- -- For a prefix T that denotes a remote access-to-classwide type, -- T'Stub_Type denotes the type of the corresponding stub objects. -- -- By construction, the layout of T'Stub_Type is identical to that of -- System.Partition_Interface.RACW_Stub_Type (see implementation notes -- in body of Exp_Dist). ----------------- -- Target_Name -- ----------------- Attribute_Target_Name => True, -- Standard'Target_Name yields the string identifying the target for the -- compilation, taken from Sdefault.Target_Name. ---------------- -- To_Address -- ---------------- Attribute_To_Address => True, -- System'To_Address (System is the only permissible prefix) is a -- function that takes any integer value, and converts it into an -- address value. The semantics is to first convert the integer value to -- type Integer_Address according to normal conversion rules, and then -- to convert this to an address using the same semantics as the -- System.Storage_Elements.To_Address function. The important difference -- is that this is a static attribute so it can be used in -- initializations in preelaborate packages. ---------------- -- Type_Class -- ---------------- Attribute_Type_Class => True, -- T'Type_Class for any type or subtype T yields the value of the type -- class for the full type of T. If T is a generic formal type, then the -- value is the value for the corresponding actual subtype. The value of -- this attribute is of type System.Aux_DEC.Type_Class, which has the -- following definition: -- -- type Type_Class is -- (Type_Class_Enumeration, -- Type_Class_Integer, -- Type_Class_Fixed_Point, -- Type_Class_Floating_Point, -- Type_Class_Array, -- Type_Class_Record, -- Type_Class_Access, -- Type_Class_Task, -- Type_Class_Address); -- -- Protected types yield the value Type_Class_Task, which thus applies -- to all concurrent types. This attribute is designed to be compatible -- with the DEC Ada attribute of the same name. -- -- Note: if pragma Extend_System is used to merge the definitions of -- Aux_DEC into System, then the type Type_Class can be referenced -- as an entity within System, as can its enumeration literals. ----------------- -- UET_Address -- ----------------- Attribute_UET_Address => True, -- Unit'UET_Address, where Unit is a program unit, yields the address -- of the unit exception table for the specified unit. This is only -- used in the internal implementation of exception handling. See the -- implementation of unit Ada.Exceptions for details on its use. ------------------------------ -- Universal_Literal_String -- ------------------------------ Attribute_Universal_Literal_String => True, -- The prefix of 'Universal_Literal_String must be a named number. -- The static result is the string consisting of the characters of -- the number as defined in the original source. This allows the -- user program to access the actual text of named numbers without -- intermediate conversions and without the need to enclose the -- strings in quotes (which would preclude their use as numbers). ------------------------- -- Unrestricted_Access -- ------------------------- Attribute_Unrestricted_Access => True, -- The Unrestricted_Access attribute is similar to Access except that -- all accessibility and aliased view checks are omitted. This is very -- much a user-beware attribute. Basically its status is very similar -- to Address, for which it is a desirable replacement where the value -- desired is an access type. In other words, its effect is identical -- to first taking 'Address and then doing an unchecked conversion to -- a desired access type. Note that in GNAT, but not necessarily in -- other implementations, the use of static chains for inner level -- subprograms means that Unrestricted_Access applied to a subprogram -- yields a value that can be called as long as the subprogram is in -- scope (normal Ada 95 accessibility rules restrict this usage). --------------- -- VADS_Size -- --------------- Attribute_VADS_Size => True, -- Typ'VADS_Size yields the Size value typically yielded by some Ada 83 -- compilers. The differences between VADS_Size and Size is that for -- scalar types for which no Size has been specified, VADS_Size yields -- the Object_Size rather than the Value_Size. For example, while -- Natural'Size is typically 31, the value of Natural'VADS_Size is 32. -- For all other types, Size and VADS_Size yield the same value. ---------------- -- Value_Size -- ---------------- Attribute_Value_Size => True, -- Type'Value_Size is the number of bits required to represent value of -- the given subtype. It is the same as Type'Size, but, unlike Size, may -- be set for non-first subtypes. See section in Einfo ("Handling of -- type'Size values") for further details. --------------- -- Word_Size -- --------------- Attribute_Word_Size => True, -- Standard'Word_Size (Standard is the only permissible prefix) -- provides the value System.Word_Size, and is intended primarily -- for constructing this definition in package System (see note above -- in Default_Bit_Order description). This is a static attribute. others => False); ----------------- -- Subprograms -- ----------------- procedure Analyze_Attribute (N : Node_Id); -- Performs bottom up semantic analysis of an attribute. Note that the -- parser has already checked that type returning attributes appear only -- in appropriate contexts (i.e. in subtype marks, or as prefixes for -- other attributes). function Name_Implies_Lvalue_Prefix (Nam : Name_Id) return Boolean; -- Determine whether the name of an attribute reference categorizes its -- prefix as an lvalue. The following attributes fall under this bracket -- by directly or indirectly modifying their prefixes. -- Access -- Address -- Input -- Read -- Unchecked_Access -- Unrestricted_Access procedure Resolve_Attribute (N : Node_Id; Typ : Entity_Id); -- Performs type resolution of attribute. If the attribute yields a -- universal value, mark its type as that of the context. On the other -- hand, if the context itself is universal (as in T'Val (T'Pos (X)), mark -- the type as being the largest type of that class that can be used at -- run-time. This is correct since either the value gets folded (in which -- case it doesn't matter what type of the class we give if, since the -- folding uses universal arithmetic anyway) or it doesn't get folded (in -- which case it is going to be dealt with at runtime, and the largest type -- is right). function Stream_Attribute_Available (Typ : Entity_Id; Nam : TSS_Name_Type; Partial_View : Entity_Id := Empty) return Boolean; -- For a limited type Typ, return True if and only if the given attribute -- is available. For Ada 2005, availability is defined by 13.13.2(36/1). -- For Ada 95, an attribute is considered to be available if it has been -- specified using an attribute definition clause for the type, or for its -- full view, or for an ancestor of either. Parameter Partial_View is used -- only internally, when checking for an attribute definition clause that -- is not visible (Ada 95 only). end Sem_Attr;