------------------------------------------------------------------------------ -- -- -- GNAT COMPILER COMPONENTS -- -- -- -- SYSTEM.MACHINE_STATE_OPERATIONS -- -- -- -- S p e c -- -- -- -- 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- -- -- 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. -- -- Extensive contributions were provided by Ada Core Technologies Inc. -- -- -- ------------------------------------------------------------------------------ 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;