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