File : s-mastop.ads
------------------------------------------------------------------------------
-- --
-- GNAT COMPILER COMPONENTS --
-- --
5 -- SYSTEM.MACHINE_STATE_OPERATIONS --
-- --
-- S p e c --
-- --
-- $Revision: 1.5 $
10 -- --
-- Copyright (C) 1999-2001 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- --
15 -- 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 --
20 -- 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. --
-- --
-- As a special exception, if other files instantiate generics from this --
25 -- unit, or you link this unit with other files to produce an executable, --
-- this unit does not by itself cause the resulting executable to be --
-- covered by the GNU General Public License. This exception does not --
-- however invalidate any other reasons why the executable file might be --
-- covered by the GNU Public License. --
30 -- --
-- 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). --
-- --
------------------------------------------------------------------------------
35
pragma Polling (Off);
-- We must turn polling off for this unit, because otherwise we get
-- elaboration circularities with System.Exception_Tables.
40 with System.Storage_Elements;
with System.Exceptions;
package System.Machine_State_Operations is
45 subtype Code_Loc is System.Address;
-- Code location used in building exception tables and for call
-- addresses when propagating an exception (also traceback table)
-- Values of this type are created by using Label'Address or
-- extracted from machine states using Get_Code_Loc.
50
type Machine_State is new System.Address;
-- The table based exception handling approach (see a-except.adb) isolates
-- the target dependent aspects using an abstract data type interface
-- to the type Machine_State, which is represented as a System.Address
55 -- value (presumably implemented as a pointer to an appropriate record
-- structure).
function Machine_State_Length return System.Storage_Elements.Storage_Offset;
-- Function to determine the length of the Storage_Array needed to hold
60 -- a machine state. The machine state will always be maximally aligned.
-- The value returned is a constant that will be used to allocate space
-- for a machine state value.
function Allocate_Machine_State return Machine_State;
65 -- Allocate the required space for a Machine_State
procedure Free_Machine_State (M : in out Machine_State);
-- Free the dynamic memory taken by Machine_State
70 -- The initial value of type Machine_State is created by the low level
-- routine that actually raises an exception using the special builtin
-- _builtin_machine_state. This value will typically encode the value
-- of the program counter, and relevant registers. The following
-- operations are defined on Machine_State values:
75
function Get_Code_Loc (M : Machine_State) return Code_Loc;
-- This function extracts the program counter value from a machine
-- state, which the caller uses for searching the exception tables,
-- and also for recording entries in the traceback table. The call
80 -- returns a value of Null_Loc if the machine state represents the
-- outer level, or some other frame for which no information can be
-- provided.
procedure Pop_Frame
85 (M : Machine_State;
Info : System.Exceptions.Subprogram_Info_Type);
-- This procedure pops the machine state M so that it represents the
-- call point, as though the current subprogram had returned. It
-- changes only the value referenced by M, and does not affect
90 -- the current stack environment.
--
-- The Info parameter represents information generated by the backend
-- (see description of Subprogram_Info node in sinfo.ads). This
-- information is stored as static data during compilation. The
95 -- caller then passes this information to Pop_Frame, which will
-- use it to determine what must be changed in the machine state
-- (e.g. which save-over-call registers must be restored, and from
-- where on the stack frame they must be restored).
--
100 -- A value of No_Info for Info means either that the backend provided
-- no information for current frame, or that the current frame is an
-- other language frame for which no information exists, or that this
-- is an outer level subprogram. In any case, Pop_Frame sets the code
-- location to Null_Address when it pops past such a frame, and this
105 -- is taken as an indication that the exception is unhandled.
-- Note: at the current time, Info, if present is always a copy of
-- the entry point of the procedure, as found by searching the
-- subprogram table. For the case where a procedure is indeed in
110 -- the table (either it is an Ada procedure, or a foreign procedure
-- which is registered using pragma Propagate_Exceptions), then the
-- entry point information will indeed be correct. It may well be
-- possible for Pop_Frame to avoid using the Info parameter (for
-- example if it consults auxiliary Dwarf tables to do its job).
115 -- This is desirable if it can be done, because it means that it
-- will work fine to propagate exceptions through unregistered
-- foreign procedures. What will happen is that the search in the
-- Ada subprogram table will find a junk entry. Even if this junk
-- entry has an exception table, none of them will apply to the
120 -- current location, so they will be ignored, and then Pop_Frame
-- will be called to pop the frame. The Info parameter for this
-- call will be junk, but if it is not used that does not matter.
-- Note that the address recorded in the traceback table is of
-- the exception location, so the traceback will be correct even
125 -- in this case.
procedure Enter_Handler
(M : Machine_State;
Handler : System.Exceptions.Handler_Loc);
130 -- When Propagate_Handler locates an applicable exception handler, it
-- calls Enter_Handler, passing it two parameters. The first is the
-- machine state that corresponds to what is required for entry to
-- the handler, as computed by repeated Pop_Frame calls to reach the
-- handler to be entered. The second is the code location for the
135 -- handler itself which is the address of the label at the start of
-- the handler code.
--
-- Note: The machine state M is likely stored on the part of the
-- stack that will be popped by the call, so care must be taken
140 -- not to pop the stack until the Machine_State is entirely read.
-- The value passed as Handler was obtained from elaboration of
-- an N_Handler_Loc node by the backend.
function Fetch_Code (Loc : Code_Loc) return Code_Loc;
145 -- Some architectures (notably VMS) use a descriptor to describe
-- a subprogram address. This function computes the actual starting
-- address of the code from Loc.
-- Do not add pragma Inline, see 9116-002.
-- ??? This function will go away when 'Code_Address is fixed on VMS.
150
procedure Set_Machine_State (M : Machine_State);
-- This routine sets M from the current machine state. It is called
-- when an exception is initially signalled to initialize the state.
155 procedure Set_Signal_Machine_State
(M : Machine_State;
Context : System.Address);
-- This routine sets M from the machine state that corresponds to the
-- point in the code where a signal was raised. The parameter Context
160 -- is a pointer to a structure created by the operating system when a
-- signal is raised, and made available to the signal handler. The
-- format of this context block, and the manner in which it is made
-- available to the handler, are implementation dependent.
165 end System.Machine_State_Operations;