1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT COMPILER COMPONENTS                         --
4--                                                                          --
5--                      SYSTEM.MACHINE_STATE_OPERATIONS                     --
6--                                                                          --
7--                                 S p e c                                  --
8--                                                                          --
9--          Copyright (C) 1999-2001 Free Software Foundation, Inc.          --
10--                                                                          --
11-- GNAT is free software;  you can  redistribute it  and/or modify it under --
12-- terms of the  GNU General Public License as published  by the Free Soft- --
13-- ware  Foundation;  either version 2,  or (at your option) any later ver- --
14-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
15-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
16-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
17-- for  more details.  You should have  received  a copy of the GNU General --
18-- Public License  distributed with GNAT;  see file COPYING.  If not, write --
19-- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
20-- MA 02111-1307, USA.                                                      --
21--                                                                          --
22-- As a special exception,  if other files  instantiate  generics from this --
23-- unit, or you link  this unit with other files  to produce an executable, --
24-- this  unit  does not  by itself cause  the resulting  executable  to  be --
25-- covered  by the  GNU  General  Public  License.  This exception does not --
26-- however invalidate  any other reasons why  the executable file  might be --
27-- covered by the  GNU Public License.                                      --
28--                                                                          --
29-- GNAT was originally developed  by the GNAT team at  New York University. --
30-- Extensive contributions were provided by Ada Core Technologies Inc.      --
31--                                                                          --
32------------------------------------------------------------------------------
33
34pragma Polling (Off);
35--  We must turn polling off for this unit, because otherwise we get
36--  elaboration circularities with System.Exception_Tables.
37
38with System.Storage_Elements;
39with System.Exceptions;
40
41package System.Machine_State_Operations is
42
43   subtype Code_Loc is System.Address;
44   --  Code location used in building exception tables and for call
45   --  addresses when propagating an exception (also traceback table)
46   --  Values of this type are created by using Label'Address or
47   --  extracted from machine states using Get_Code_Loc.
48
49   type Machine_State is new System.Address;
50   --  The table based exception handling approach (see a-except.adb) isolates
51   --  the target dependent aspects using an abstract data type interface
52   --  to the type Machine_State, which is represented as a System.Address
53   --  value (presumably implemented as a pointer to an appropriate record
54   --  structure).
55
56   function Machine_State_Length return System.Storage_Elements.Storage_Offset;
57   --  Function to determine the length of the Storage_Array needed to hold
58   --  a machine state. The machine state will always be maximally aligned.
59   --  The value returned is a constant that will be used to allocate space
60   --  for a machine state value.
61
62   function Allocate_Machine_State return Machine_State;
63   --  Allocate the required space for a Machine_State
64
65   procedure Free_Machine_State (M : in out Machine_State);
66   --  Free the dynamic memory taken by Machine_State
67
68   --  The initial value of type Machine_State is created by the low level
69   --  routine that actually raises an exception using the special builtin
70   --  _builtin_machine_state. This value will typically encode the value
71   --  of the program counter, and relevant registers. The following
72   --  operations are defined on Machine_State values:
73
74   function Get_Code_Loc (M : Machine_State) return Code_Loc;
75   --  This function extracts the program counter value from a machine
76   --  state, which the caller uses for searching the exception tables,
77   --  and also for recording entries in the traceback table. The call
78   --  returns a value of Null_Loc if the machine state represents the
79   --  outer level, or some other frame for which no information can be
80   --  provided.
81
82   procedure Pop_Frame
83     (M    : Machine_State;
84      Info : System.Exceptions.Subprogram_Info_Type);
85   --  This procedure pops the machine state M so that it represents the
86   --  call point, as though the current subprogram had returned. It
87   --  changes only the value referenced by M, and does not affect
88   --  the current stack environment.
89   --
90   --  The Info parameter represents information generated by the backend
91   --  (see description of Subprogram_Info node in sinfo.ads). This
92   --  information is stored as static data during compilation. The
93   --  caller then passes this information to Pop_Frame, which will
94   --  use it to determine what must be changed in the machine state
95   --  (e.g. which save-over-call registers must be restored, and from
96   --  where on the stack frame they must be restored).
97   --
98   --  A value of No_Info for Info means either that the backend provided
99   --  no information for current frame, or that the current frame is an
100   --  other language frame for which no information exists, or that this
101   --  is an outer level subprogram. In any case, Pop_Frame sets the code
102   --  location to Null_Address when it pops past such a frame, and this
103   --  is taken as an indication that the exception is unhandled.
104
105   --  Note: at the current time, Info, if present is always a copy of
106   --  the entry point of the procedure, as found by searching the
107   --  subprogram table. For the case where a procedure is indeed in
108   --  the table (either it is an Ada procedure, or a foreign procedure
109   --  which is registered using pragma Propagate_Exceptions), then the
110   --  entry point information will indeed be correct. It may well be
111   --  possible for Pop_Frame to avoid using the Info parameter (for
112   --  example if it consults auxiliary Dwarf tables to do its job).
113   --  This is desirable if it can be done, because it means that it
114   --  will work fine to propagate exceptions through unregistered
115   --  foreign procedures. What will happen is that the search in the
116   --  Ada subprogram table will find a junk entry. Even if this junk
117   --  entry has an exception table, none of them will apply to the
118   --  current location, so they will be ignored, and then Pop_Frame
119   --  will be called to pop the frame. The Info parameter for this
120   --  call will be junk, but if it is not used that does not matter.
121   --  Note that the address recorded in the traceback table is of
122   --  the exception location, so the traceback will be correct even
123   --  in this case.
124
125   procedure Enter_Handler
126     (M       : Machine_State;
127      Handler : System.Exceptions.Handler_Loc);
128   --  When Propagate_Handler locates an applicable exception handler, it
129   --  calls Enter_Handler, passing it two parameters. The first is the
130   --  machine state that corresponds to what is required for entry to
131   --  the handler, as computed by repeated Pop_Frame calls to reach the
132   --  handler to be entered. The second is the code location for the
133   --  handler itself which is the address of the label at the start of
134   --  the handler code.
135   --
136   --  Note: The machine state M is likely stored on the part of the
137   --  stack that will be popped by the call, so care must be taken
138   --  not to pop the stack until the Machine_State is entirely read.
139   --  The value passed as Handler was obtained from elaboration of
140   --  an N_Handler_Loc node by the backend.
141
142   function Fetch_Code (Loc : Code_Loc) return Code_Loc;
143   --  Some architectures (notably VMS) use a descriptor to describe
144   --  a subprogram address. This function computes the actual starting
145   --  address of the code from Loc.
146   --  Do not add pragma Inline, see 9116-002.
147   --  ??? This function will go away when 'Code_Address is fixed on VMS.
148
149   procedure Set_Machine_State (M : Machine_State);
150   --  This routine sets M from the current machine state. It is called
151   --  when an exception is initially signalled to initialize the state.
152
153   procedure Set_Signal_Machine_State
154     (M       : Machine_State;
155      Context : System.Address);
156   --  This routine sets M from the machine state that corresponds to the
157   --  point in the code where a signal was raised. The parameter Context
158   --  is a pointer to a structure created by the operating system when a
159   --  signal is raised, and made available to the signal handler. The
160   --  format of this context block, and the manner in which it is made
161   --  available to the handler, are implementation dependent.
162
163end System.Machine_State_Operations;
164