+++ /dev/null
-------------------------------------------------------------------------------
--- --
--- GNAT COMPILER COMPONENTS --
--- --
--- SYSTEM.MACHINE_STATE_OPERATIONS --
--- --
--- S p e c --
--- --
--- $Revision: 1.1 $
--- --
--- Copyright (C) 1999-2001 Ada Core Technologies, 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. --
--- --
--- As a special exception, if other files instantiate generics from this --
--- 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. --
--- --
--- 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). --
--- --
-------------------------------------------------------------------------------
-
-pragma Polling (Off);
--- We must turn polling off for this unit, because otherwise we get
--- elaboration circularities with System.Exception_Tables.
-
-with System.Storage_Elements;
-with System.Exceptions;
-
-package System.Machine_State_Operations is
-
- 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.
-
- 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
- -- 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
- -- 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;
- -- 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
-
- -- 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:
-
- 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
- -- 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
- (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
- -- 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
- -- 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).
- --
- -- 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
- -- 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
- -- 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).
- -- 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
- -- 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
- -- in this case.
-
- procedure Enter_Handler
- (M : Machine_State;
- Handler : System.Exceptions.Handler_Loc);
- -- 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
- -- 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
- -- 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;
- -- 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.
-
- 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.
-
- 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
- -- 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.
-
-end System.Machine_State_Operations;
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