diff options
Diffstat (limited to 'gcc/ada/checks.ads')
| -rw-r--r-- | gcc/ada/checks.ads | 526 |
1 files changed, 526 insertions, 0 deletions
diff --git a/gcc/ada/checks.ads b/gcc/ada/checks.ads new file mode 100644 index 0000000..d265ae8 --- /dev/null +++ b/gcc/ada/checks.ads @@ -0,0 +1,526 @@ +------------------------------------------------------------------------------ +-- -- +-- GNAT COMPILER COMPONENTS -- +-- -- +-- C H E C K S -- +-- -- +-- S p e c -- +-- -- +-- $Revision: 1.55 $ +-- -- +-- Copyright (C) 1992-2001 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 2, 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 COPYING. If not, write -- +-- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, -- +-- MA 02111-1307, USA. -- +-- -- +-- GNAT was originally developed by the GNAT team at New York University. -- +-- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). -- +-- -- +------------------------------------------------------------------------------ + +-- Package containing routines used to deal with runtime checks. These +-- routines are used both by the semantics and by the expander. In some +-- cases, checks are enabled simply by setting flags for gigi, and in +-- other cases the code for the check is expanded. + +-- The approach used for range and length checks, in regards to suppressed +-- checks, is to attempt to detect at compilation time that a constraint +-- error will occur. If this is detected a warning or error is issued and the +-- offending expression or statement replaced with a constraint error node. +-- This always occurs whether checks are suppressed or not. Dynamic range +-- checks are, of course, not inserted if checks are suppressed. + +with Types; use Types; +with Uintp; use Uintp; + +package Checks is + + procedure Initialize; + -- Called for each new main source program, to initialize internal + -- variables used in the package body of the Checks unit. + + function Access_Checks_Suppressed (E : Entity_Id) return Boolean; + function Accessibility_Checks_Suppressed (E : Entity_Id) return Boolean; + function Discriminant_Checks_Suppressed (E : Entity_Id) return Boolean; + function Division_Checks_Suppressed (E : Entity_Id) return Boolean; + function Elaboration_Checks_Suppressed (E : Entity_Id) return Boolean; + function Index_Checks_Suppressed (E : Entity_Id) return Boolean; + function Length_Checks_Suppressed (E : Entity_Id) return Boolean; + function Overflow_Checks_Suppressed (E : Entity_Id) return Boolean; + function Range_Checks_Suppressed (E : Entity_Id) return Boolean; + function Storage_Checks_Suppressed (E : Entity_Id) return Boolean; + function Tag_Checks_Suppressed (E : Entity_Id) return Boolean; + -- These functions check to see if the named check is suppressed, + -- either by an active scope suppress setting, or because the check + -- has been specifically suppressed for the given entity. If no entity + -- is relevant for the current check, then Empty is used as an argument. + -- Note: the reason we insist on specifying Empty is to force the + -- caller to think about whether there is any relevant entity that + -- should be checked. + + -- General note on following checks. These checks are always active if + -- Expander_Active and not Inside_A_Generic. They are inactive and have + -- no effect Inside_A_Generic. In the case where not Expander_Active + -- and not Inside_A_Generic, most of them are inactive, but some of them + -- operate anyway since they may generate useful compile time warnings. + + procedure Apply_Access_Check (N : Node_Id); + -- Determines whether an expression node should be flagged as needing + -- a runtime access check. If the node requires such a check, the + -- Do_Access_Check flag is turned on. + + procedure Apply_Accessibility_Check (N : Node_Id; Typ : Entity_Id); + -- Given a name N denoting an access parameter, emits a run-time + -- accessibility check (if necessary), checking that the level of + -- the object denoted by the access parameter is not deeper than the + -- level of the type Typ. Program_Error is raised if the check fails. + + procedure Apply_Array_Size_Check (N : Node_Id; Typ : Entity_Id); + -- N is the node for an object declaration that declares an object of + -- array type Typ. This routine generates, if necessary, a check that + -- the size of the array is not too large, raising Storage_Error if so. + + procedure Apply_Arithmetic_Overflow_Check (N : Node_Id); + -- Given a binary arithmetic operator (+ - *) expand a software integer + -- overflow check using range checks on a larger checking type or a call + -- to an appropriate runtime routine. This is used for all three operators + -- for the signed integer case, and for +/- in the fixed-point case. The + -- check is expanded only if Software_Overflow_Checking is enabled and + -- Do_Overflow_Check is set on node N. Note that divide is handled + -- separately using Apply_Arithmetic_Divide_Overflow_Check. + + procedure Apply_Constraint_Check + (N : Node_Id; + Typ : Entity_Id; + No_Sliding : Boolean := False); + -- Top-level procedure, calls all the others depending on the class of Typ. + -- Checks that expression N verifies the constraint of type Typ. No_Sliding + -- is only relevant for constrained array types, id set to true, it + -- checks that indexes are in range. + + procedure Apply_Discriminant_Check + (N : Node_Id; + Typ : Entity_Id; + Lhs : Node_Id := Empty); + -- Given an expression N of a discriminated type, or of an access type + -- whose designated type is a discriminanted type, generates a check to + -- ensure that the expression can be converted to the subtype given as + -- the second parameter. Lhs is empty except in the case of assignments, + -- where the target object may be needed to determine the subtype to + -- check against (such as the cases of unconstrained formal parameters + -- and unconstrained aliased objects). For the case of unconstrained + -- formals, the check is peformed only if the corresponding actual is + -- constrained, i.e., whether Lhs'Constrained is True. + + function Build_Discriminant_Checks + (N : Node_Id; + T_Typ : Entity_Id) + return Node_Id; + -- Subsidiary routine for Apply_Discriminant_Check. Builds the expression + -- that compares discriminants of the expression with discriminants of the + -- type. Also used directly for membership tests (see Exp_Ch4.Expand_N_In). + + procedure Apply_Divide_Check (N : Node_Id); + -- The node kind is N_Op_Divide, N_Op_Mod, or N_Op_Rem. An appropriate + -- check is generated to ensure that the right operand is non-zero. In + -- the divide case, we also check that we do not have the annoying case + -- of the largest negative number divided by minus one. + + procedure Apply_Type_Conversion_Checks (N : Node_Id); + -- N is an N_Type_Conversion node. A type conversion actually involves + -- two sorts of checks. The first check is the checks that ensures that + -- the operand in the type conversion fits onto the base type of the + -- subtype it is being converted to (see RM 4.6 (28)-(50)). The second + -- check is there to ensure that once the operand has been converted to + -- a value of the target type, this converted value meets the + -- constraints imposed by the target subtype (see RM 4.6 (51)). + + procedure Apply_Universal_Integer_Attribute_Checks (N : Node_Id); + -- The argument N is an attribute reference node intended for processing + -- by gigi. The attribute is one that returns a universal integer, but + -- the attribute reference node is currently typed with the expected + -- result type. This routine deals with range and overflow checks needed + -- to make sure that the universal result is in range. + + procedure Determine_Range + (N : Node_Id; + OK : out Boolean; + Lo : out Uint; + Hi : out Uint); + -- N is a node for a subexpression. If N is of a discrete type with + -- no error indications, and no other peculiarities (e.g. missing + -- type fields), then OK is True on return, and Lo and Hi are set + -- to a conservative estimate of the possible range of values of N. + -- Thus if OK is True on return, the value of the subexpression N is + -- known to like in the range Lo .. Hi (inclusive). If the expression + -- is not of a discrete type, or some kind of error condition is + -- detected, then OK is False on exit, and Lo/Hi are set to No_Uint. + -- Thus the significance of OK being False on return is that no + -- useful information is available on the range of the expression. + + ----------------------------- + -- Length and Range Checks -- + ----------------------------- + + -- In the following procedures, there are three arguments which have + -- a common meaning as follows: + + -- Expr The expression to be checked. If a check is required, + -- the appropriate flag will be placed on this node. Whether + -- this node is further examined depends on the setting of + -- the parameter Source_Typ, as described below. + + -- Target_Typ The target type on which the check is to be based. For + -- example, if we have a scalar range check, then the check + -- is that we are in range of this type. + + -- Source_Typ Normally Empty, but can be set to a type, in which case + -- this type is used for the check, see below. + + -- The checks operate in one of two modes: + + -- If Source_Typ is Empty, then the node Expr is examined, at the + -- very least to get the source subtype. In addition for some of + -- the checks, the actual form of the node may be examined. For + -- example, a node of type Integer whose actual form is an Integer + -- conversion from a type with range 0 .. 3 can be determined to + -- have a value in the range 0 .. 3. + + -- If Source_Typ is given, then nothing can be assumed about the + -- Expr, and indeed its contents are not examined. In this case the + -- check is based on the assumption that Expr can be an arbitrary + -- value of the given Source_Typ. + + -- Currently, the only case in which a Source_Typ is explicitly supplied + -- is for the case of Out and In_Out parameters, where, for the conversion + -- on return (the Out direction), the types must be reversed. This is + -- handled by the caller. + + procedure Apply_Length_Check + (Ck_Node : Node_Id; + Target_Typ : Entity_Id; + Source_Typ : Entity_Id := Empty); + -- This procedure builds a sequence of declarations to do a length check + -- that checks if the lengths of the two arrays Target_Typ and source type + -- are the same. The resulting actions are inserted at Node using a call + -- to Insert_Actions. + -- + -- For access types, the Directly_Designated_Type is retrieved and + -- processing continues as enumerated above, with a guard against + -- null values. + -- + -- Note: calls to Apply_Length_Check currently never supply an explicit + -- Source_Typ parameter, but Apply_Length_Check takes this parameter and + -- processes it as described above for consistency with the other routines + -- in this section. + + procedure Apply_Range_Check + (Ck_Node : Node_Id; + Target_Typ : Entity_Id; + Source_Typ : Entity_Id := Empty); + -- For an Node of kind N_Range, constructs a range check action that + -- tests first that the range is not null and then that the range + -- is contained in the Target_Typ range. + -- + -- For scalar types, constructs a range check action that first tests that + -- the expression is contained in the Target_Typ range. The difference + -- between this and Apply_Scalar_Range_Check is that the latter generates + -- the actual checking code in gigi against the Etype of the expression. + -- + -- For constrained array types, construct series of range check actions + -- to check that each Expr range is properly contained in the range of + -- Target_Typ. + -- + -- For a type conversion to an unconstrained array type, constructs + -- a range check action to check that the bounds of the source type + -- are within the constraints imposed by the Target_Typ. + -- + -- For access types, the Directly_Designated_Type is retrieved and + -- processing continues as enumerated above, with a guard against + -- null values. + -- + -- The source type is used by type conversions to unconstrained array + -- types to retrieve the corresponding bounds. + + procedure Apply_Static_Length_Check + (Expr : Node_Id; + Target_Typ : Entity_Id; + Source_Typ : Entity_Id := Empty); + -- Tries to determine statically whether the two array types source type + -- and Target_Typ have the same length. If it can be determined at compile + -- time that they do not, then an N_Raise_Constraint_Error node replaces + -- Expr, and a warning message is issued. + + procedure Apply_Scalar_Range_Check + (Expr : Node_Id; + Target_Typ : Entity_Id; + Source_Typ : Entity_Id := Empty; + Fixed_Int : Boolean := False); + -- For scalar types, determines whether an expression node should be + -- flagged as needing a runtime range check. If the node requires such + -- a check, the Do_Range_Check flag is turned on. The Fixed_Int flag + -- if set causes any fixed-point values to be treated as though they + -- were discrete values (i.e. the underlying integer value is used). + + type Check_Result is private; + -- Type used to return result of Range_Check call, for later use in + -- call to Insert_Range_Checks procedure. + + procedure Append_Range_Checks + (Checks : Check_Result; + Stmts : List_Id; + Suppress_Typ : Entity_Id; + Static_Sloc : Source_Ptr; + Flag_Node : Node_Id); + -- Called to append range checks as returned by a call to Range_Check. + -- Stmts is a list to which either the dynamic check is appended or + -- the raise Constraint_Error statement is appended (for static checks). + -- Static_Sloc is the Sloc at which the raise CE node points, + -- Flag_Node is used as the node at which to set the Has_Dynamic_Check + -- flag. Checks_On is a boolean value that says if range and index checking + -- is on or not. + + procedure Enable_Range_Check (N : Node_Id); + pragma Inline (Enable_Range_Check); + -- Set Do_Range_Check flag in node N to True unless Kill_Range_Check flag + -- is set in N (the purpose of the latter flag is precisely to prevent + -- Do_Range_Check from being set). + + procedure Insert_Range_Checks + (Checks : Check_Result; + Node : Node_Id; + Suppress_Typ : Entity_Id; + Static_Sloc : Source_Ptr := No_Location; + Flag_Node : Node_Id := Empty; + Do_Before : Boolean := False); + -- Called to insert range checks as returned by a call to Range_Check. + -- Node is the node after which either the dynamic check is inserted or + -- the raise Constraint_Error statement is inserted (for static checks). + -- Suppress_Typ is the type to check to determine if checks are suppressed. + -- Static_Sloc, if passed, is the Sloc at which the raise CE node points, + -- otherwise Sloc (Node) is used. The Has_Dynamic_Check flag is normally + -- set at Node. If Flag_Node is present, then this is used instead as the + -- node at which to set the Has_Dynamic_Check flag. Normally the check is + -- inserted after, if Do_Before is True, the check is inserted before + -- Node. + + function Range_Check + (Ck_Node : Node_Id; + Target_Typ : Entity_Id; + Source_Typ : Entity_Id := Empty; + Warn_Node : Node_Id := Empty) + return Check_Result; + -- Like Apply_Range_Check, except it does not modify anything. Instead + -- it returns an encapsulated result of the check operations for later + -- use in a call to Insert_Range_Checks. If Warn_Node is non-empty, its + -- Sloc is used, in the static case, for the generated warning or error. + -- Additionally, it is used rather than Expr (or Low/High_Bound of Expr) + -- in constructing the check. + + ----------------------- + -- Validity Checking -- + ----------------------- + + -- In (RM 13.9.1(9-11)) we have the following rules on invalid values + + -- 9 If the representation of a scalar object does not represent a + -- value of the object's subtype (perhaps because the object was not + -- initialized), the object is said to have an invalid representation. + -- It is a bounded error to evaluate the value of such an object. If + -- the error is detected, either Constraint_Error or Program_Error is + -- raised. Otherwise, execution continues using the invalid + -- representation. The rules of the language outside this subclause + -- assume that all objects have valid representations. The semantics + -- of operations on invalid representations are as follows: + -- + -- 10 If the representation of the object represents a value of the + -- object's type, the value of the type is used. + -- + -- 11 If the representation of the object does not represent a value + -- of the object's type, the semantics of operations on such + -- representations is implementation-defined, but does not by + -- itself lead to erroneous or unpredictable execution, or to + -- other objects becoming abnormal. + + -- We quote the rules in full here since they are quite delicate. Most + -- of the time, we can just compute away with wrong values, and get a + -- possibly wrong result, which is well within the range of allowed + -- implementation defined behavior. The two tricky cases are subscripted + -- array assignments, where we don't want to do wild stores, and case + -- statements where we don't want to do wild jumps. + + -- In GNAT, we control validity checking with a switch -gnatV that + -- can take three parameters, n/d/f for None/Default/Full. These + -- modes have the following meanings: + + -- None (no validity checking) + + -- In this mode, there is no specific checking for invalid values + -- and the code generator assumes that all stored values are always + -- within the bounds of the object subtype. The consequences are as + -- follows: + + -- For case statements, an out of range invalid value will cause + -- Constraint_Error to be raised, or an arbitrary one of the case + -- alternatives will be executed. Wild jumps cannot result even + -- in this mode, since we always do a range check + + -- For subscripted array assignments, wild stores will result in + -- the expected manner when addresses are calculated using values + -- of subscripts that are out of range. + + -- It could perhaps be argued that this mode is still conformant with + -- the letter of the RM, since implementation defined is a rather + -- broad category, but certainly it is not in the spirit of the + -- RM requirement, since wild stores certainly seem to be a case of + -- erroneous behavior. + + -- Default (default standard RM-compatible validity checking) + + -- In this mode, which is the default, minimal validity checking is + -- performed to ensure no erroneous behavior as follows: + + -- For case statements, an out of range invalid value will cause + -- Constraint_Error to be raised. + + -- For subscripted array assignments, invalid out of range + -- subscript values will cause Constraint_Error to be raised. + + -- Full (Full validity checking) + + -- In this mode, the protections guaranteed by the standard mode are + -- in place, and the following additional checks are made: + + -- For every assignment, the right side is checked for validity + + -- For every call, IN and IN OUT parameters are checked for validity + + -- For every subscripted array reference, both for stores and loads, + -- all subscripts are checked for validity. + + -- These checks are not required by the RM, but will in practice + -- improve the detection of uninitialized variables, particularly + -- if used in conjunction with pragma Normalize_Scalars. + + -- In the above description, we talk about performing validity checks, + -- but we don't actually generate a check in a case where the compiler + -- can be sure that the value is valid. Note that this assurance must + -- be achieved without assuming that any uninitialized value lies within + -- the range of its type. The following are cases in which values are + -- known to be valid. The flag Is_Known_Valid is used to keep track of + -- some of these cases. + + -- If all possible stored values are valid, then any uninitialized + -- value must be valid. + + -- Literals, including enumeration literals, are clearly always valid. + + -- Constants are always assumed valid, with a validity check being + -- performed on the initializing value where necessary to ensure that + -- this is the case. + + -- For variables, the status is set to known valid if there is an + -- initializing expression. Again a check is made on the initializing + -- value if necessary to ensure that this assumption is valid. The + -- status can change as a result of local assignments to a variable. + -- If a known valid value is unconditionally assigned, then we mark + -- the left side as known valid. If a value is assigned that is not + -- known to be valid, then we mark the left side as invalid. This + -- kind of processing does NOT apply to non-local variables since we + -- are not following the flow graph (more properly the flow of actual + -- processing only corresponds to the flow graph for local assignments). + -- For non-local variables, we preserve the current setting, i.e. a + -- validity check is performed when assigning to a knonwn valid global. + + -- Note: no validity checking is required if range checks are suppressed + -- regardless of the setting of the validity checking mode. + + -- The following procedures are used in handling validity checking + + procedure Apply_Subscript_Validity_Checks (Expr : Node_Id); + -- Expr is the node for an indexed component. If validity checking and + -- range checking are enabled, all subscripts for this indexed component + -- are checked for validity. + + procedure Check_Valid_Lvalue_Subscripts (Expr : Node_Id); + -- Expr is a lvalue, i.e. an expression representing the target of + -- an assignment. This procedure checks for this expression involving + -- an assignment to an array value. We have to be sure that all the + -- subscripts in such a case are valid, since according to the rules + -- in (RM 13.9.1(9-11)) such assignments are not permitted to result + -- in erroneous behavior in the case of invalid subscript values. + + procedure Ensure_Valid (Expr : Node_Id; Holes_OK : Boolean := False); + -- Ensure that Expr represents a valid value of its type. If this type + -- is not a scalar type, then the call has no effect, since validity + -- is only an issue for scalar types. The effect of this call is to + -- check if the value is known valid, if so, nothing needs to be done. + -- If this is not known, then either Expr is set to be range checked, + -- or specific checking code is inserted so that an exception is raised + -- if the value is not valid. + -- + -- The optional argument Holes_OK indicates whether it is necessary to + -- worry about enumeration types with non-standard representations leading + -- to "holes" in the range of possible representations. If Holes_OK is + -- True, then such values are assumed valid (this is used when the caller + -- will make a separate check for this case anyway). If Holes_OK is False, + -- then this case is checked, and code is inserted to ensure that Expr is + -- valid, raising Constraint_Error if the value is not valid. + + function Expr_Known_Valid (Expr : Node_Id) return Boolean; + -- This function tests it the value of Expr is known to be valid in + -- the sense of RM 13.9.1(9-11). In the case of GNAT, it is only + -- discrete types which are a concern, since for non-discrete types + -- we simply continue computation with invalid values, which does + -- not lead to erroneous behavior. Thus Expr_Known_Valid always + -- returns True if the type of Expr is non-discrete. For discrete + -- types the value returned is True only if it can be determined + -- that the value is Valid. Otherwise False is returned. + + procedure Insert_Valid_Check (Expr : Node_Id); + -- Inserts code that will check for the value of Expr being valid, in + -- the sense of the 'Valid attribute returning True. Constraint_Error + -- will be raised if the value is not valid. + +private + + type Check_Result is array (Positive range 1 .. 2) of Node_Id; + -- There are two cases for the result returned by Range_Check: + -- + -- For the static case the result is one or two nodes that should cause + -- a Constraint_Error. Typically these will include Expr itself or the + -- direct descendents of Expr, such as Low/High_Bound (Expr)). It is the + -- responsibility of the caller to rewrite and substitute the nodes with + -- N_Raise_Constraint_Error nodes. + -- + -- For the non-static case a single N_Raise_Constraint_Error node + -- with a non-empty Condition field is returned. + -- + -- Unused entries in Check_Result, if any, are simply set to Empty + -- For external clients, the required processing on this result is + -- achieved using the Insert_Range_Checks routine. + + pragma Inline (Access_Checks_Suppressed); + pragma Inline (Accessibility_Checks_Suppressed); + pragma Inline (Discriminant_Checks_Suppressed); + pragma Inline (Division_Checks_Suppressed); + pragma Inline (Elaboration_Checks_Suppressed); + pragma Inline (Index_Checks_Suppressed); + pragma Inline (Length_Checks_Suppressed); + pragma Inline (Overflow_Checks_Suppressed); + pragma Inline (Range_Checks_Suppressed); + pragma Inline (Storage_Checks_Suppressed); + pragma Inline (Tag_Checks_Suppressed); + + pragma Inline (Apply_Length_Check); + pragma Inline (Apply_Range_Check); + pragma Inline (Apply_Static_Length_Check); +end Checks; |