| ------------------------------------------------------------------------------ |
| -- -- |
| -- GNAT COMPILER COMPONENTS -- |
| -- -- |
| -- SYSTEM.MACHINE_STATE_OPERATIONS -- |
| -- -- |
| -- S p e c -- |
| -- -- |
| -- $Revision: 1.4 $ |
| -- -- |
| -- 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; |
