gcc/ada/a-except.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT RUN-TIME COMPONENTS                         --
   4 --                                                                          --
   5 --                       A D A . E X C E P T I O N S                        --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 --          Copyright (C) 1992-2005, Free Software Foundation, Inc.         --
  10 --                                                                          --
  11 -- This specification is derived from the Ada Reference Manual for use with --
  12 -- GNAT. The copyright notice above, and the license provisions that follow --
  13 -- apply solely to the  contents of the part following the private keyword. --
  14 --                                                                          --
  15 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  16 -- terms of the  GNU General Public License as published  by the Free Soft- --
  17 -- ware  Foundation;  either version 2,  or (at your option) any later ver- --
  18 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  19 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  20 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  21 -- for  more details.  You should have  received  a copy of the GNU General --
  22 -- Public License  distributed with GNAT;  see file COPYING.  If not, write --
  23 -- to  the  Free Software Foundation,  51  Franklin  Street,  Fifth  Floor, --
  24 -- Boston, MA 02110-1301, USA.                                              --
  25 --                                                                          --
  26 -- As a special exception,  if other files  instantiate  generics from this --
  27 -- unit, or you link  this unit with other files  to produce an executable, --
  28 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  29 -- covered  by the  GNU  General  Public  License.  This exception does not --
  30 -- however invalidate  any other reasons why  the executable file  might be --
  31 -- covered by the  GNU Public License.                                      --
  32 --                                                                          --
  33 -- GNAT was originally developed  by the GNAT team at  New York University. --
  34 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  35 --                                                                          --
  36 ------------------------------------------------------------------------------
  37
  38 --  This version of Ada.Exceptions is a full Ada 95 version, but lacks the
  39 --  additional definitions of Exception_Name returning Wide_[Wide_]String.
  40 --  It is used for building the compiler and the basic tools, since these
  41 --  builds may be done with bootstrap compilers that cannot handle these
  42 --  additions. The full version of Ada.Exceptions can be found in the files
  43 --  a-except-2005.ads/adb, and is used for all other builds where full Ada
  44 --  2005 functionality is required. in particular, it is used for building
  45 --  run times on all targets.
  46
  47 pragma Polling (Off);
  48 --  We must turn polling off for this unit, because otherwise we get
  49 --  elaboration circularities with ourself.
  50
  51 with System;
  52 with System.Parameters;
  53 with System.Standard_Library;
  54 with System.Traceback_Entries;
  55
  56 package Ada.Exceptions is
  57    pragma Warnings (Off);
  58    pragma Preelaborate_05;
  59    pragma Warnings (On);
  60    --  In accordance with Ada 2005 AI-362. The warnings pragmas are so that we
  61    --  can compile this using older compiler versions, which will ignore the
  62    --  pragma, which is fine for the bootstrap.
  63
  64    type Exception_Id is private;
  65    Null_Id : constant Exception_Id;
  66
  67    type Exception_Occurrence is limited private;
  68    type Exception_Occurrence_Access is access all Exception_Occurrence;
  69
  70    Null_Occurrence : constant Exception_Occurrence;
  71
  72    function Exception_Name (X : Exception_Occurrence) return String;
  73    --  Same as Exception_Name (Exception_Identity (X))
  74
  75    function Exception_Name (Id : Exception_Id) return String;
  76
  77    procedure Raise_Exception (E : Exception_Id; Message : String := "");
  78    --  Note: it would be really nice to give a pragma No_Return for this
  79    --  procedure, but it would be wrong, since Raise_Exception does return
  80    --  if given the null exception. However we do special case the name in
  81    --  the test in the compiler for issuing a warning for a missing return
  82    --  after this call. Program_Error seems reasonable enough in such a case.
  83    --  See also the routine Raise_Exception_Always in the private part.
  84
  85    function Exception_Message (X : Exception_Occurrence) return String;
  86
  87    procedure Reraise_Occurrence (X : Exception_Occurrence);
  88    --  Note: it would be really nice to give a pragma No_Return for this
  89    --  procedure, but it would be wrong, since Reraise_Occurrence does return
  90    --  if the argument is the null exception occurrence. See also procedure
  91    --  Reraise_Occurrence_Always in the private part of this package.
  92
  93    function Exception_Identity (X : Exception_Occurrence) return Exception_Id;
  94
  95    function Exception_Information (X : Exception_Occurrence) return String;
  96    --  The format of the exception information is as follows:
  97    --
  98    --    exception name (as in Exception_Name)
  99    --    message (or a null line if no message)
 100    --    PID=nnnn
 101    --    0xyyyyyyyy 0xyyyyyyyy ...
 102    --
 103    --  The lines are separated by a ASCII.LF character
 104    --  The nnnn is the partition Id given as decimal digits.
 105    --  The 0x... line represents traceback program counter locations,
 106    --  in order with the first one being the exception location.
 107
 108    --  Note on ordering: the compiler uses the Save_Occurrence procedure, but
 109    --  not the function from Rtsfind, so it is important that the procedure
 110    --  come first, since Rtsfind finds the first matching entity.
 111
 112    procedure Save_Occurrence
 113      (Target : out Exception_Occurrence;
 114       Source : Exception_Occurrence);
 115
 116    function Save_Occurrence
 117      (Source : Exception_Occurrence)
 118       return   Exception_Occurrence_Access;
 119
 120 private
 121    package SSL renames System.Standard_Library;
 122    package SP renames System.Parameters;
 123
 124    subtype EOA is Exception_Occurrence_Access;
 125
 126    Exception_Msg_Max_Length : constant := SP.Default_Exception_Msg_Max_Length;
 127
 128    ------------------
 129    -- Exception_Id --
 130    ------------------
 131
 132    subtype Code_Loc is System.Address;
 133    --  Code location used in building exception tables and for call addresses
 134    --  when propagating an exception. Values of this type are created by using
 135    --  Label'Address or extracted from machine states using Get_Code_Loc.
 136
 137    Null_Loc : constant Code_Loc := System.Null_Address;
 138    --  Null code location, used to flag outer level frame
 139
 140    type Exception_Id is new SSL.Exception_Data_Ptr;
 141
 142    function EId_To_String (X : Exception_Id) return String;
 143    function String_To_EId (S : String) return Exception_Id;
 144    pragma Stream_Convert (Exception_Id, String_To_EId, EId_To_String);
 145    --  Functions for implementing Exception_Id stream attributes
 146
 147    Null_Id : constant Exception_Id := null;
 148
 149    -------------------------
 150    -- Private Subprograms --
 151    -------------------------
 152
 153    function Current_Target_Exception return Exception_Occurrence;
 154    pragma Export
 155      (Ada, Current_Target_Exception,
 156       "__gnat_current_target_exception");
 157    --  This routine should return the current raised exception on targets
 158    --  which have built-in exception handling such as the Java Virtual
 159    --  Machine. For other targets this routine is simply ignored. Currently,
 160    --  only JGNAT uses this. See 4jexcept.ads for details. The pragma Export
 161    --  allows this routine to be accessed elsewhere in the run-time, even
 162    --  though it is in the private part of this package (it is not allowed
 163    --  to be in the visible part, since this is set by the reference manual).
 164
 165    function Exception_Name_Simple (X : Exception_Occurrence) return String;
 166    --  Like Exception_Name, but returns the simple non-qualified name of the
 167    --  exception. This is used to implement the Exception_Name function in
 168    --  Current_Exceptions (the DEC compatible unit). It is called from the
 169    --  compiler generated code (using Rtsfind, which does not respect the
 170    --  private barrier, so we can place this function in the private part
 171    --  where the compiler can find it, but the spec is unchanged.)
 172
 173    procedure Raise_Exception_Always (E : Exception_Id; Message : String := "");
 174    pragma No_Return (Raise_Exception_Always);
 175    pragma Export (Ada, Raise_Exception_Always, "__gnat_raise_exception");
 176    --  This differs from Raise_Exception only in that the caller has determined
 177    --  that for sure the parameter E is not null, and that therefore the call
 178    --  to this procedure cannot return. The expander converts Raise_Exception
 179    --  calls to Raise_Exception_Always if it can determine this is the case.
 180    --  The Export allows this routine to be accessed from Pure units.
 181
 182    procedure Raise_From_Signal_Handler
 183      (E : Exception_Id;
 184       M : System.Address);
 185    pragma Export
 186      (Ada, Raise_From_Signal_Handler,
 187            "ada__exceptions__raise_from_signal_handler");
 188    pragma No_Return (Raise_From_Signal_Handler);
 189    --  This routine is used to raise an exception from a signal handler. The
 190    --  signal handler has already stored the machine state (i.e. the state that
 191    --  corresponds to the location at which the signal was raised). E is the
 192    --  Exception_Id specifying what exception is being raised, and M is a
 193    --  pointer to a null-terminated string which is the message to be raised.
 194    --  Note that this routine never returns, so it is permissible to simply
 195    --  jump to this routine, rather than call it. This may be appropriate for
 196    --  systems where the right way to get out of signal handler is to alter the
 197    --  PC value in the machine state or in some other way ask the operating
 198    --  system to return here rather than to the original location.
 199
 200    procedure Reraise_Occurrence_Always (X : Exception_Occurrence);
 201    pragma No_Return (Reraise_Occurrence_Always);
 202    --  This differs from Raise_Occurrence only in that the caller guarantees
 203    --  that for sure the parameter X is not the null occurrence, and that
 204    --  therefore this procedure cannot return. The expander uses this routine
 205    --  in the translation of a raise statement with no parameter (reraise).
 206
 207    procedure Reraise_Occurrence_No_Defer (X : Exception_Occurrence);
 208    pragma No_Return (Reraise_Occurrence_No_Defer);
 209    --  Exactly like Reraise_Occurrence, except that abort is not deferred
 210    --  before the call and the parameter X is known not to be the null
 211    --  occurrence. This is used in generated code when it is known that
 212    --  abort is already deferred.
 213
 214    -----------------------
 215    -- Polling Interface --
 216    -----------------------
 217
 218    --  The GNAT compiler has an option to generate polling calls to the Poll
 219    --  routine in this package. Specifying the -gnatP option for a compilation
 220    --  causes a call to Ada.Exceptions.Poll to be generated on every subprogram
 221    --  entry and on every iteration of a loop, thus avoiding the possibility of
 222    --  a case of unbounded time between calls.
 223
 224    --  This polling interface may be used for instrumentation or debugging
 225    --  purposes (e.g. implementing watchpoints in software or in the debugger).
 226
 227    --  In the GNAT technology itself, this interface is used to implement
 228    --  immediate aynschronous transfer of control and immediate abort on
 229    --  targets which do not provide for one thread interrupting another.
 230
 231    --  Note: this used to be in a separate unit called System.Poll, but that
 232    --  caused horrible circular elaboration problems between System.Poll and
 233    --  Ada.Exceptions. One way of solving such circularities is unification!
 234
 235    procedure Poll;
 236    --  Check for asynchronous abort. Note that we do not inline the body.
 237    --  This makes the interface more useful for debugging purposes.
 238
 239    --------------------------
 240    -- Exception_Occurrence --
 241    --------------------------
 242
 243    package TBE renames System.Traceback_Entries;
 244
 245    Max_Tracebacks : constant := 50;
 246    --  Maximum number of trace backs stored in exception occurrence
 247
 248    type Tracebacks_Array is array (1 .. Max_Tracebacks) of TBE.Traceback_Entry;
 249    --  Traceback array stored in exception occurrence
 250
 251    type Exception_Occurrence is record
 252       Id : Exception_Id;
 253       --  Exception_Identity for this exception occurrence
 254       --  WARNING System.System.Finalization_Implementation.Finalize_List
 255       --  relies on the fact that this field is always first in the exception
 256       --  occurrence
 257
 258       Msg_Length : Natural := 0;
 259       --  Length of message (zero = no message)
 260
 261       Msg : String (1 .. Exception_Msg_Max_Length);
 262       --  Characters of message
 263
 264       Cleanup_Flag : Boolean := False;
 265       --  The cleanup flag is normally False, it is set True for an exception
 266       --  occurrence passed to a cleanup routine, and will still be set True
 267       --  when the cleanup routine does a Reraise_Occurrence call using this
 268       --  exception occurrence. This is used to avoid recording a bogus trace
 269       --  back entry from this reraise call.
 270
 271       Exception_Raised : Boolean := False;
 272       --  Set to true to indicate that this exception occurrence has actually
 273       --  been raised. When an exception occurrence is first created, this is
 274       --  set to False, then when it is processed by Raise_Current_Exception,
 275       --  it is set to True. If Raise_Current_Exception is used to raise an
 276       --  exception for which this flag is already True, then it knows that
 277       --  it is dealing with the reraise case (which is useful to distinguish
 278       --  for exception tracing purposes).
 279
 280       Pid : Natural := 0;
 281       --  Partition_Id for partition raising exception
 282
 283       Num_Tracebacks : Natural range 0 .. Max_Tracebacks := 0;
 284       --  Number of traceback entries stored
 285
 286       Tracebacks : Tracebacks_Array;
 287       --  Stored tracebacks (in Tracebacks (1 .. Num_Tracebacks))
 288
 289       Private_Data : System.Address := System.Null_Address;
 290       --  Field used by low level exception mechanism to store specific data.
 291       --  Currently used by the GCC exception mechanism to store a pointer to
 292       --  a GNAT_GCC_Exception.
 293    end record;
 294
 295    function "=" (Left, Right : Exception_Occurrence) return Boolean
 296      is abstract;
 297    --  Don't allow comparison on exception occurrences, we should not need
 298    --  this, and it would not work right, because of the Msg and Tracebacks
 299    --  fields which have unused entries not copied by Save_Occurrence.
 300
 301    function EO_To_String (X : Exception_Occurrence) return String;
 302    function String_To_EO (S : String) return Exception_Occurrence;
 303    pragma Stream_Convert (Exception_Occurrence, String_To_EO, EO_To_String);
 304    --  Functions for implementing Exception_Occurrence stream attributes
 305
 306    Null_Occurrence : constant Exception_Occurrence := (
 307      Id               => null,
 308      Msg_Length       => 0,
 309      Msg              => (others => ' '),
 310      Cleanup_Flag     => False,
 311      Exception_Raised => False,
 312      Pid              => 0,
 313      Num_Tracebacks   => 0,
 314      Tracebacks       => (others => TBE.Null_TB_Entry),
 315      Private_Data     => System.Null_Address);
 316
 317 end Ada.Exceptions;