164 lines
9.1 KiB
Ada
164 lines
9.1 KiB
Ada
------------------------------------------------------------------------------
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-- --
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-- GNAT COMPILER COMPONENTS --
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-- --
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-- SYSTEM.MACHINE_STATE_OPERATIONS --
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-- --
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-- S p e c --
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-- --
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-- Copyright (C) 1999-2001 Free Software Foundation, Inc. --
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-- --
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-- GNAT is free software; you can redistribute it and/or modify it under --
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-- terms of the GNU General Public License as published by the Free Soft- --
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-- ware Foundation; either version 2, or (at your option) any later ver- --
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-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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-- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
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-- for more details. You should have received a copy of the GNU General --
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-- Public License distributed with GNAT; see file COPYING. If not, write --
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-- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
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-- MA 02111-1307, USA. --
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-- --
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-- As a special exception, if other files instantiate generics from this --
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-- unit, or you link this unit with other files to produce an executable, --
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-- this unit does not by itself cause the resulting executable to be --
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-- covered by the GNU General Public License. This exception does not --
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-- however invalidate any other reasons why the executable file might be --
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-- covered by the GNU Public License. --
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-- --
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-- GNAT was originally developed by the GNAT team at New York University. --
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-- Extensive contributions were provided by Ada Core Technologies Inc. --
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-- --
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------------------------------------------------------------------------------
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pragma Polling (Off);
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-- We must turn polling off for this unit, because otherwise we get
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-- elaboration circularities with System.Exception_Tables.
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with System.Storage_Elements;
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with System.Exceptions;
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package System.Machine_State_Operations is
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subtype Code_Loc is System.Address;
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-- Code location used in building exception tables and for call
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-- addresses when propagating an exception (also traceback table)
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-- Values of this type are created by using Label'Address or
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-- extracted from machine states using Get_Code_Loc.
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type Machine_State is new System.Address;
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-- The table based exception handling approach (see a-except.adb) isolates
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-- the target dependent aspects using an abstract data type interface
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-- to the type Machine_State, which is represented as a System.Address
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-- value (presumably implemented as a pointer to an appropriate record
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-- structure).
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function Machine_State_Length return System.Storage_Elements.Storage_Offset;
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-- Function to determine the length of the Storage_Array needed to hold
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-- a machine state. The machine state will always be maximally aligned.
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-- The value returned is a constant that will be used to allocate space
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-- for a machine state value.
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function Allocate_Machine_State return Machine_State;
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-- Allocate the required space for a Machine_State
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procedure Free_Machine_State (M : in out Machine_State);
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-- Free the dynamic memory taken by Machine_State
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-- The initial value of type Machine_State is created by the low level
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-- routine that actually raises an exception using the special builtin
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-- _builtin_machine_state. This value will typically encode the value
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-- of the program counter, and relevant registers. The following
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-- operations are defined on Machine_State values:
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function Get_Code_Loc (M : Machine_State) return Code_Loc;
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-- This function extracts the program counter value from a machine
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-- state, which the caller uses for searching the exception tables,
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-- and also for recording entries in the traceback table. The call
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-- returns a value of Null_Loc if the machine state represents the
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-- outer level, or some other frame for which no information can be
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-- provided.
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procedure Pop_Frame
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(M : Machine_State;
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Info : System.Exceptions.Subprogram_Info_Type);
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-- This procedure pops the machine state M so that it represents the
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-- call point, as though the current subprogram had returned. It
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-- changes only the value referenced by M, and does not affect
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-- the current stack environment.
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--
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-- The Info parameter represents information generated by the backend
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-- (see description of Subprogram_Info node in sinfo.ads). This
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-- information is stored as static data during compilation. The
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-- caller then passes this information to Pop_Frame, which will
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-- use it to determine what must be changed in the machine state
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-- (e.g. which save-over-call registers must be restored, and from
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-- where on the stack frame they must be restored).
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--
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-- A value of No_Info for Info means either that the backend provided
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-- no information for current frame, or that the current frame is an
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-- other language frame for which no information exists, or that this
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-- is an outer level subprogram. In any case, Pop_Frame sets the code
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-- location to Null_Address when it pops past such a frame, and this
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-- is taken as an indication that the exception is unhandled.
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-- Note: at the current time, Info, if present is always a copy of
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-- the entry point of the procedure, as found by searching the
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-- subprogram table. For the case where a procedure is indeed in
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-- the table (either it is an Ada procedure, or a foreign procedure
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-- which is registered using pragma Propagate_Exceptions), then the
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-- entry point information will indeed be correct. It may well be
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-- possible for Pop_Frame to avoid using the Info parameter (for
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-- example if it consults auxiliary Dwarf tables to do its job).
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-- This is desirable if it can be done, because it means that it
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-- will work fine to propagate exceptions through unregistered
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-- foreign procedures. What will happen is that the search in the
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-- Ada subprogram table will find a junk entry. Even if this junk
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-- entry has an exception table, none of them will apply to the
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-- current location, so they will be ignored, and then Pop_Frame
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-- will be called to pop the frame. The Info parameter for this
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-- call will be junk, but if it is not used that does not matter.
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-- Note that the address recorded in the traceback table is of
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-- the exception location, so the traceback will be correct even
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-- in this case.
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procedure Enter_Handler
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(M : Machine_State;
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Handler : System.Exceptions.Handler_Loc);
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-- When Propagate_Handler locates an applicable exception handler, it
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-- calls Enter_Handler, passing it two parameters. The first is the
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-- machine state that corresponds to what is required for entry to
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-- the handler, as computed by repeated Pop_Frame calls to reach the
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-- handler to be entered. The second is the code location for the
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-- handler itself which is the address of the label at the start of
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-- the handler code.
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--
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-- Note: The machine state M is likely stored on the part of the
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-- stack that will be popped by the call, so care must be taken
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-- not to pop the stack until the Machine_State is entirely read.
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-- The value passed as Handler was obtained from elaboration of
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-- an N_Handler_Loc node by the backend.
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function Fetch_Code (Loc : Code_Loc) return Code_Loc;
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-- Some architectures (notably VMS) use a descriptor to describe
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-- a subprogram address. This function computes the actual starting
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-- address of the code from Loc.
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-- Do not add pragma Inline, see 9116-002.
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-- ??? This function will go away when 'Code_Address is fixed on VMS.
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procedure Set_Machine_State (M : Machine_State);
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-- This routine sets M from the current machine state. It is called
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-- when an exception is initially signalled to initialize the state.
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procedure Set_Signal_Machine_State
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(M : Machine_State;
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Context : System.Address);
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-- This routine sets M from the machine state that corresponds to the
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-- point in the code where a signal was raised. The parameter Context
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-- is a pointer to a structure created by the operating system when a
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-- signal is raised, and made available to the signal handler. The
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-- format of this context block, and the manner in which it is made
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-- available to the handler, are implementation dependent.
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end System.Machine_State_Operations;
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