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------------------------------------------------------------------------------
-- --
-- GNAT COMPILER COMPONENTS --
-- --
-- S T R U B --
-- --
-- S p e c --
-- --
-- Copyright (C) 2021-2023, 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. 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 COPYING3. If not, go to --
-- http://www.gnu.org/licenses for a complete copy of the license. --
-- --
-- GNAT was originally developed by the GNAT team at New York University. --
-- Extensive contributions were provided by Ada Core Technologies Inc. --
-- --
------------------------------------------------------------------------------
-- Package containing utility procedures related to Stack Scrubbing
with Types; use Types;
package Strub is
type Strub_Mode is
(Disabled, -- Subprogram cannot be called from strub contexts
At_Calls, -- Subprogram strubbed by caller
Internal, -- Subprogram strubbed by wrapper
Callable, -- Subprogram safe to call despite no strub
Unspecified, -- Subprogram or data without strub annotation
Enabled, -- Data (variable or constant) that enables strub
Not_Applicable); -- Entities that are not strub-capable
-- This is the type that expresses decoded strub annotations
-- We compare strub modes in the following circumstances:
-- * subprogram definition vs specification
-- * overriding vs overridden dispatch subprograms
-- * implementation vs interface dispatch subprogram
-- * renaming vs renamed subprogram
-- * type resolution
-- * explicit conversions
-- Explicit conversions can convert between strub modes other than
-- at-calls (see Compatible_Strub_Modes), but for the other cases
-- above, we insist on identity of the strub modes (see
-- Check_Same_Strub_Mode). Anything else would be
-- troublesome.
-- E.g., overriding a callable subprogram with a strub-disabled
-- implementation would enable a subprogram that's unsafe to call
-- in strub contexts to be called through a dispatching
-- interface. An explicitly strub-disabled subprogram shall not be
-- called from strub contexts, and a callable overriding
-- subprogram would still seem not-callable, so accepting
-- different modes would be surprising.
-- We could relax the requirement for overriders from equality to
-- compatibility, with the understanding that the dispatching ABI
-- is what prevails. For renaming, however, if we don't require
-- equality, it would have to encompass an implicit conversion.
procedure Check_Same_Strub_Mode
(Dest, Src : Entity_Id;
Report : Boolean := True);
-- Check whether Dest and Src are subprograms or subprogram types
-- annotated (or not) with the same strub mode. If Report is
-- requested, and the strub modes are not equivalent, an error
-- message is issued. Unspecified and Internal are considered
-- equivalent, because Internal is an internal implementation
-- detail. Unspecified decays to Disabled or Callable depending on
-- -fstrub=(strict|relaxed), but this procedure does not take this
-- decay into account, which avoids turning strub-equivalent
-- declarations into incompatible ones at command-line changes.
function Compatible_Strub_Modes
(Dest, Src : Entity_Id) return Boolean;
-- Return True if Dest and Src are subprograms or subprogram types
-- annotated (or not) with ABI-compatible strub modes. At-calls is
-- incompatible to other strub modes, because the back end
-- internally modifies the signature of such subprograms, adding
-- hidden parameters. Calling a subprogram through an
-- access-to-subprogram object converted between strub-at-calls
-- and other strub modes should be deemed equivalent to
-- dereferencing an uninitialized access-to-data object, though
-- one-way conversions might seem to work in some circumstances.
--
-- Unspecified, Disabled, Internal and Callable
-- (access-to-)subprograms, on the other hand, can be safely but
-- explicitly converted to each other, because these strub modes
-- do not require signature changes; so it is possible to alter
-- the caller-side stack scrubbing semantics of the call (e.g. to
-- call a subprogram that isn't strub-callable from within a strub
-- context, or to prevent it from being called through an access
-- object) without any incompatibilities.
procedure Copy_Strub_Mode (Dest, Src : Entity_Id);
-- Copy the strub mode from Src to Dest, subprograms or subprogram
-- types. Dest is required to not have a strub mode already set.
function Explicit_Strub_Mode (Id : Entity_Id) return Strub_Mode;
-- Return the strub mode associated with Id, that should refer to
-- a subprogram, a data object, or a type.
function Strub_Pragma_P (Item : Node_Id) return Boolean;
-- Return True iff Item is a strub annotation, specifically, one
-- introduced by pragma Machine_Attribute (Entity, "strub"[, "mode"]).
end Strub;
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