+++ /dev/null
-------------------------------------------------------------------------------
--- --
--- GNAT COMPILER COMPONENTS --
--- --
--- C H E C K S --
--- --
--- S p e c --
--- --
--- $Revision: 1.2.10.1 $
--- --
--- 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. --
--- Extensive contributions were provided by Ada Core Technologies Inc. --
--- --
-------------------------------------------------------------------------------
-
--- 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_Alignment_Check (E : Entity_Id; N : Node_Id);
- -- E is the entity for an object. If there is an address clause for
- -- this entity, and checks are enabled, then this procedure generates
- -- a check that the specified address has an alignment consistent with
- -- the alignment of the object, raising PE if this is not the case. The
- -- resulting check (if one is generated) is inserted before node N.
-
- 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;
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