gcc/ada/s-traceb-hpux.adb

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT COMPILER COMPONENTS                         --
   4 --                                                                          --
   5 --                     S Y S T E M . T R A C E B A C K                      --
   6 --                             (HP/UX Version)                              --
   7 --                                                                          --
   8 --                                 B o d y                                  --
   9 --                                                                          --
  10 --                     Copyright (C) 1999-2006, AdaCore                     --
  11 --            Copyright (C) 2008, Free Software Foundation, Inc.            --
  12 --                                                                          --
  13 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  14 -- terms of the  GNU General Public License as published  by the Free Soft- --
  15 -- ware  Foundation;  either version 2,  or (at your option) any later ver- --
  16 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  17 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  18 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  19 -- for  more details.  You should have  received  a copy of the GNU General --
  20 -- Public License  distributed with GNAT;  see file COPYING.  If not, write --
  21 -- to  the  Free Software Foundation,  51  Franklin  Street,  Fifth  Floor, --
  22 -- Boston, MA 02110-1301, USA.                                              --
  23 --                                                                          --
  24 -- As a special exception,  if other files  instantiate  generics from this --
  25 -- unit, or you link  this unit with other files  to produce an executable, --
  26 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  27 -- covered  by the  GNU  General  Public  License.  This exception does not --
  28 -- however invalidate  any other reasons why  the executable file  might be --
  29 -- covered by the  GNU Public License.                                      --
  30 --                                                                          --
  31 -- GNAT was originally developed  by the GNAT team at  New York University. --
  32 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  33 --                                                                          --
  34 ------------------------------------------------------------------------------
  35
  36 with Ada.Unchecked_Conversion;
  37
  38 package body System.Traceback is
  39
  40    --  This package implements the backtracing facility by way of a dedicated
  41    --  HP library for stack unwinding described in the "Runtime Architecture
  42    --  Document".
  43
  44    pragma Linker_Options ("/usr/lib/libcl.a");
  45
  46    --  The library basically offers services to fetch information about a
  47    --  "previous" frame based on information about a "current" one.
  48
  49    type Current_Frame_Descriptor is record
  50       cur_fsz : Address;  --  Frame size of current routine.
  51       cur_sp  : Address;  --  The current value of stack pointer.
  52       cur_rls : Address;  --  PC-space of the caller.
  53       cur_rlo : Address;  --  PC-offset of the caller.
  54       cur_dp  : Address;  --  Data Pointer of the current routine.
  55       top_rp  : Address;  --  Initial value of RP.
  56       top_mrp : Address;  --  Initial value of MRP.
  57       top_sr0 : Address;  --  Initial value of sr0.
  58       top_sr4 : Address;  --  Initial value of sr4.
  59       top_r3  : Address;  --  Initial value of gr3.
  60       cur_r19 : Address;  --  GR19 value of the calling routine.
  61       top_r4  : Address;  --  Initial value of gr4.
  62       dummy   : Address;  --  Reserved.
  63       out_rlo : Address;  --  PC-offset of the caller after get_previous.
  64    end record;
  65
  66    type Previous_Frame_Descriptor is record
  67       prev_fsz : Address;  --  frame size of calling routine.
  68       prev_sp  : Address;  --  SP of calling routine.
  69       prev_rls : Address;  --  PC_space of calling routine's caller.
  70       prev_rlo : Address;  --  PC_offset of calling routine's caller.
  71       prev_dp  : Address;  --  DP of calling routine.
  72       udescr0  : Address;  --  low word of calling routine's unwind desc.
  73       udescr1  : Address;  --  high word of calling routine's unwind desc.
  74       ustart   : Address;  --  start of the unwind region.
  75       uend     : Address;  --  end of the unwind region.
  76       uw_index : Address;  --  index into the unwind table.
  77       prev_r19 : Address;  --  GR19 value of the caller's caller.
  78       top_r3   : Address;  --  Caller's initial gr3.
  79       top_r4   : Address;  --  Caller's initial gr4.
  80    end record;
  81
  82    --  Provide useful shortcuts for the names
  83
  84    subtype CFD is Current_Frame_Descriptor;
  85    subtype PFD is Previous_Frame_Descriptor;
  86
  87    --  Frames with dynamic stack allocation are handled using the associated
  88    --  frame pointer, but HP compilers and GCC setup this pointer differently.
  89    --  HP compilers set it to point at the top (highest address) of the static
  90    --  part of the frame, whereas GCC sets it to point at the bottom of this
  91    --  region. We have to fake the unwinder to compensate for this difference,
  92    --  for which we'll need to access some subprograms unwind descriptors.
  93
  94    type Bits_2_Value is mod 2 ** 2;
  95    for Bits_2_Value'Size use 2;
  96
  97    type Bits_4_Value  is mod 2 ** 4;
  98    for Bits_4_Value'Size use 4;
  99
 100    type Bits_5_Value  is mod 2 ** 5;
 101    for Bits_5_Value'Size use 5;
 102
 103    type Bits_27_Value is mod 2 ** 27;
 104    for Bits_27_Value'Size use 27;
 105
 106    type Unwind_Descriptor is record
 107       cannot_unwind         : Boolean;
 108       mcode                 : Boolean;
 109       mcode_save_restore    : Boolean;
 110       region_desc           : Bits_2_Value;
 111       reserved0             : Boolean;
 112       entry_sr              : Boolean;
 113       entry_fr              : Bits_4_Value;
 114       entry_gr              : Bits_5_Value;
 115
 116       args_stored           : Boolean;
 117       variable_frame        : Boolean;
 118       separate_package_body : Boolean;
 119       frame_extension_mcode : Boolean;
 120
 121       stack_overflow_check  : Boolean;
 122       two_steps_sp_adjust   : Boolean;
 123       sr4_export            : Boolean;
 124       cxx_info              : Boolean;
 125
 126       cxx_try_catch         : Boolean;
 127       sched_entry_seq       : Boolean;
 128       reserved1             : Boolean;
 129       save_sp               : Boolean;
 130
 131       save_rp               : Boolean;
 132       save_mrp              : Boolean;
 133       save_r19              : Boolean;
 134       cleanups              : Boolean;
 135
 136       hpe_interrupt_marker  : Boolean;
 137       hpux_interrupt_marker : Boolean;
 138       large_frame           : Boolean;
 139       alloca_frame          : Boolean;
 140
 141       reserved2             : Boolean;
 142       frame_size            : Bits_27_Value;
 143    end record;
 144
 145    for Unwind_Descriptor'Size use 64;
 146
 147    for Unwind_Descriptor use record
 148       cannot_unwind         at 0 range 0 .. 0;
 149       mcode                 at 0 range 1 .. 1;
 150       mcode_save_restore    at 0 range 2 .. 2;
 151       region_desc           at 0 range 3 .. 4;
 152       reserved0             at 0 range 5 .. 5;
 153       entry_sr              at 0 range 6 .. 6;
 154       entry_fr              at 0 range 7 .. 10;
 155
 156       entry_gr              at 1 range 3 .. 7;
 157
 158       args_stored           at 2 range 0 .. 0;
 159       variable_frame        at 2 range 1 .. 1;
 160       separate_package_body at 2 range 2 .. 2;
 161       frame_extension_mcode at 2 range 3 .. 3;
 162       stack_overflow_check  at 2 range 4 .. 4;
 163       two_steps_sp_adjust   at 2 range 5 .. 5;
 164       sr4_export            at 2 range 6 .. 6;
 165       cxx_info              at 2 range 7 .. 7;
 166
 167       cxx_try_catch         at 3 range 0 .. 0;
 168       sched_entry_seq       at 3 range 1 .. 1;
 169       reserved1             at 3 range 2 .. 2;
 170       save_sp               at 3 range 3 .. 3;
 171       save_rp               at 3 range 4 .. 4;
 172       save_mrp              at 3 range 5 .. 5;
 173       save_r19              at 3 range 6 .. 6;
 174       cleanups              at 3 range 7 .. 7;
 175
 176       hpe_interrupt_marker  at 4 range 0 .. 0;
 177       hpux_interrupt_marker at 4 range 1 .. 1;
 178       large_frame           at 4 range 2 .. 2;
 179       alloca_frame          at 4 range 3 .. 3;
 180
 181       reserved2             at 4 range 4 .. 4;
 182       frame_size            at 4 range 5 .. 31;
 183    end record;
 184
 185    subtype UWD is Unwind_Descriptor;
 186    type UWD_Ptr is access all UWD;
 187
 188    function To_UWD_Access is new Ada.Unchecked_Conversion (Address, UWD_Ptr);
 189
 190    --  The descriptor associated with a given code location is retrieved
 191    --  using functions imported from the HP library, requiring the definition
 192    --  of additional structures.
 193
 194    type Unwind_Table_Region is record
 195       Table_Start : Address;
 196       Table_End   : Address;
 197    end record;
 198    --  An Unwind Table region, which is a memory area containing Unwind
 199    --  Descriptors.
 200
 201    subtype UWT is Unwind_Table_Region;
 202
 203    --  The subprograms imported below are provided by the HP library
 204
 205    function U_get_unwind_table return UWT;
 206    pragma Import (C, U_get_unwind_table, "U_get_unwind_table");
 207    --  Get the unwind table region associated with the current executable.
 208    --  This function is actually documented as having an argument, but which
 209    --  is only used for the MPE/iX targets.
 210
 211    function U_get_shLib_unwind_table (r19 : Address) return UWT;
 212    pragma Import (C, U_get_shLib_unwind_table, "U_get_shLib_unw_tbl");
 213    --  Return the unwind table region associated with a possible shared
 214    --  library, as determined by the provided r19 value.
 215
 216    function U_get_shLib_text_addr (r19 : Address) return Address;
 217    pragma Import (C, U_get_shLib_text_addr, "U_get_shLib_text_addr");
 218    --  Return the address at which the code for a shared library begins, or
 219    --  -1 if the value provided for r19 does not identify shared library code.
 220
 221    function U_get_unwind_entry
 222      (Pc          : Address;
 223       Space       : Address;
 224       Table_Start : Address;
 225       Table_End   : Address) return Address;
 226    pragma Import (C, U_get_unwind_entry, "U_get_unwind_entry");
 227    --  Given the bounds of an unwind table, return the address of the
 228    --  unwind descriptor associated with a code location/space. In the case
 229    --  of shared library code, the offset from the beginning of the library
 230    --  is expected as Pc.
 231
 232    procedure U_init_frame_record (Frame : not null access CFD);
 233    pragma Import (C, U_init_frame_record, "U_init_frame_record");
 234
 235    procedure U_prep_frame_rec_for_unwind (Frame : not null access CFD);
 236    pragma Import (C, U_prep_frame_rec_for_unwind,
 237                     "U_prep_frame_rec_for_unwind");
 238
 239    --  Fetch the description data of the frame in which these two procedures
 240    --  are called.
 241
 242    function U_get_u_rlo
 243      (Cur : not null access CFD; Prev : not null access PFD) return Integer;
 244    pragma Import (C, U_get_u_rlo, "U_IS_STUB_OR_CALLX");
 245    --  From a complete current frame with a return location possibly located
 246    --  into a linker generated stub, and basic information about the previous
 247    --  frame, place the first non stub return location into the current frame.
 248    --  Return -1 if something went wrong during the computation.
 249
 250    function U_is_shared_pc (rlo : Address; r19 : Address) return Address;
 251    pragma Import (C, U_is_shared_pc, "U_is_shared_pc");
 252    --  Return 0 if the provided return location does not correspond to code
 253    --  in a shared library, or something non null otherwise.
 254
 255    function U_get_previous_frame_x
 256      (current_frame  : not null access CFD;
 257       previous_frame : not null access PFD;
 258       previous_size  : Integer) return Integer;
 259    pragma Import (C, U_get_previous_frame_x, "U_get_previous_frame_x");
 260    --  Fetch the data describing the "previous" frame relatively to the
 261    --  "current" one. "previous_size" should be the size of the "previous"
 262    --  frame descriptor provided.
 263    --
 264    --  The library provides a simpler interface without the size parameter
 265    --  but it is not usable when frames with dynamically allocated space are
 266    --  on the way.
 267
 268    ------------------
 269    -- C_Call_Chain --
 270    ------------------
 271
 272    function C_Call_Chain
 273      (Traceback : System.Address;
 274       Max_Len   : Natural) return Natural
 275    is
 276       Val : Natural;
 277
 278    begin
 279       Call_Chain (Traceback, Max_Len, Val);
 280       return Val;
 281    end C_Call_Chain;
 282
 283    ----------------
 284    -- Call_Chain --
 285    ----------------
 286
 287    procedure Call_Chain
 288      (Traceback   : System.Address;
 289       Max_Len     : Natural;
 290       Len         : out Natural;
 291       Exclude_Min : System.Address := System.Null_Address;
 292       Exclude_Max : System.Address := System.Null_Address;
 293       Skip_Frames : Natural := 1)
 294    is
 295       type Tracebacks_Array is array (1 .. Max_Len) of System.Address;
 296       pragma Suppress_Initialization (Tracebacks_Array);
 297
 298       --  The code location returned by the unwinder is a return location but
 299       --  what we need is a call point. Under HP-UX call instructions are 4
 300       --  bytes long and the return point they specify is 4 bytes beyond the
 301       --  next instruction because of the delay slot.
 302
 303       Call_Size  : constant := 4;
 304       DSlot_Size : constant := 4;
 305       Rlo_Offset : constant := Call_Size + DSlot_Size;
 306
 307       --  Moreover, the return point is passed via a register which two least
 308       --  significant bits specify a privilege level that we will have to mask.
 309
 310       Priv_Mask  : constant := 16#00000003#;
 311
 312       Frame       : aliased CFD;
 313       Code        : System.Address;
 314       J           : Natural := 1;
 315       Pop_Success : Boolean;
 316       Trace       : Tracebacks_Array;
 317       for Trace'Address use Traceback;
 318
 319       --  The backtracing process needs a set of subprograms :
 320
 321       function UWD_For_RLO_Of (Frame : not null access CFD) return UWD_Ptr;
 322       --  Return an access to the unwind descriptor for the caller of
 323       --  a given frame, using only the provided return location.
 324
 325       function UWD_For_Caller_Of (Frame : not null access CFD) return UWD_Ptr;
 326       --  Return an access to the unwind descriptor for the user code caller
 327       --  of a given frame, or null if the information is not available.
 328
 329       function Pop_Frame (Frame : not null access CFD) return Boolean;
 330       --  Update the provided machine state structure so that it reflects
 331       --  the state one call frame "above" the initial one.
 332       --
 333       --  Return True if the operation has been successful, False otherwise.
 334       --  Failure typically occurs when the top of the call stack has been
 335       --  reached.
 336
 337       function Prepare_For_Unwind_Of
 338         (Frame : not null access CFD) return Boolean;
 339       --  Perform the necessary adaptations to the machine state before
 340       --  calling the unwinder. Currently used for the specific case of
 341       --  dynamically sized previous frames.
 342       --
 343       --  Return True if everything went fine, or False otherwise.
 344
 345       Program_UWT : constant UWT := U_get_unwind_table;
 346
 347       ---------------
 348       -- Pop_Frame --
 349       ---------------
 350
 351       function Pop_Frame (Frame : not null access CFD) return Boolean is
 352          Up_Frame    : aliased PFD;
 353          State_Ready : Boolean;
 354
 355       begin
 356          --  Check/adapt the state before calling the unwinder and return
 357          --  if anything went wrong.
 358
 359          State_Ready := Prepare_For_Unwind_Of (Frame);
 360
 361          if not State_Ready then
 362             return False;
 363          end if;
 364
 365          --  Now, safely call the unwinder and use the results
 366
 367          if U_get_previous_frame_x (Frame,
 368                                     Up_Frame'Access,
 369                                     Up_Frame'Size) /= 0
 370          then
 371             return False;
 372          end if;
 373
 374          --  In case a stub is on the way, the usual previous return location
 375          --  (the one in prev_rlo) is the one in the stub and the "real" one
 376          --  is placed in the "current" record, so let's take this one into
 377          --  account.
 378
 379          Frame.out_rlo := Frame.cur_rlo;
 380
 381          Frame.cur_fsz := Up_Frame.prev_fsz;
 382          Frame.cur_sp  := Up_Frame.prev_sp;
 383          Frame.cur_rls := Up_Frame.prev_rls;
 384          Frame.cur_rlo := Up_Frame.prev_rlo;
 385          Frame.cur_dp  := Up_Frame.prev_dp;
 386          Frame.cur_r19 := Up_Frame.prev_r19;
 387          Frame.top_r3  := Up_Frame.top_r3;
 388          Frame.top_r4  := Up_Frame.top_r4;
 389
 390          return True;
 391       end Pop_Frame;
 392
 393       ---------------------------------
 394       -- Prepare_State_For_Unwind_Of --
 395       ---------------------------------
 396
 397       function Prepare_For_Unwind_Of
 398         (Frame : not null access CFD) return Boolean
 399       is
 400          Caller_UWD    : UWD_Ptr;
 401          FP_Adjustment : Integer;
 402
 403       begin
 404          --  No need to bother doing anything if the stack is already fully
 405          --  unwound.
 406
 407          if Frame.cur_rlo = 0 then
 408             return False;
 409          end if;
 410
 411          --  When ALLOCA_FRAME is set in an unwind descriptor, the unwinder
 412          --  uses the value provided in current.top_r3 or current.top_r4 as
 413          --  a frame pointer to compute the size of the frame. What decides
 414          --  between r3 or r4 is the unwind descriptor LARGE_FRAME bit, with
 415          --  r4 chosen if the bit is set.
 416
 417          --  The size computed by the unwinder is STATIC_PART + (SP - FP),
 418          --  which is correct with HP's frame pointer convention, but not
 419          --  with GCC's one since we end up with the static part accounted
 420          --  for twice.
 421
 422          --  We have to compute r4 when it is required because the unwinder
 423          --  has looked for it at a place where it was not if we went through
 424          --  GCC frames.
 425
 426          --  The size of the static part of a frame can be found in the
 427          --  associated unwind descriptor.
 428
 429          Caller_UWD := UWD_For_Caller_Of (Frame);
 430
 431          --  If we cannot get it, we are unable to compute the potentially
 432          --  necessary adjustments. We'd better not try to go on then.
 433
 434          if Caller_UWD = null then
 435             return False;
 436          end if;
 437
 438          --  If the caller frame is a GCC one, r3 is its frame pointer and
 439          --  points to the bottom of the frame. The value to provide for r4
 440          --  can then be computed directly from the one of r3, compensating
 441          --  for the static part of the frame.
 442
 443          --  If the caller frame is an HP one, r3 is used to locate the
 444          --  previous frame marker, that is it also points to the bottom of
 445          --  the frame (this is why r3 cannot be used as the frame pointer in
 446          --  the HP sense for large frames). The value to provide for r4 can
 447          --  then also be computed from the one of r3 with the compensation
 448          --  for the static part of the frame.
 449
 450          FP_Adjustment := Integer (Caller_UWD.frame_size * 8);
 451          Frame.top_r4  := Address (Integer (Frame.top_r3) + FP_Adjustment);
 452
 453          return True;
 454       end Prepare_For_Unwind_Of;
 455
 456       -----------------------
 457       -- UWD_For_Caller_Of --
 458       -----------------------
 459
 460       function UWD_For_Caller_Of (Frame : not null access CFD) return UWD_Ptr
 461       is
 462          UWD_Access : UWD_Ptr;
 463
 464       begin
 465          --  First try the most direct path, using the return location data
 466          --  associated with the frame.
 467
 468          UWD_Access := UWD_For_RLO_Of (Frame);
 469
 470          if UWD_Access /= null then
 471             return UWD_Access;
 472          end if;
 473
 474          --  If we did not get a result, we might face an in-stub return
 475          --  address. In this case U_get_previous_frame can tell us what the
 476          --  first not-in-stub return point is. We cannot call it directly,
 477          --  though, because we haven't computed the potentially necessary
 478          --  frame pointer adjustments, which might lead to SEGV in some
 479          --  circumstances. Instead, we directly call the libcl routine which
 480          --  is called by U_get_previous_frame and which only requires few
 481          --  information. Take care, however, that the information is provided
 482          --  in the "current" argument, so we need to work on a copy to avoid
 483          --  disturbing our caller.
 484
 485          declare
 486             U_Current  : aliased CFD := Frame.all;
 487             U_Previous : aliased PFD;
 488
 489          begin
 490             U_Previous.prev_dp  := U_Current.cur_dp;
 491             U_Previous.prev_rls := U_Current.cur_rls;
 492             U_Previous.prev_sp  := U_Current.cur_sp - U_Current.cur_fsz;
 493
 494             if U_get_u_rlo (U_Current'Access, U_Previous'Access) /= -1 then
 495                UWD_Access := UWD_For_RLO_Of (U_Current'Access);
 496             end if;
 497          end;
 498
 499          return UWD_Access;
 500       end UWD_For_Caller_Of;
 501
 502       --------------------
 503       -- UWD_For_RLO_Of --
 504       --------------------
 505
 506       function UWD_For_RLO_Of (Frame : not null access CFD) return UWD_Ptr
 507       is
 508          UWD_Address : Address;
 509
 510          --  The addresses returned by the library point to full descriptors
 511          --  including the frame information bits but also the applicable PC
 512          --  range. We need to account for this.
 513
 514          Frame_Info_Offset  : constant := 8;
 515
 516       begin
 517          --  First try to locate the descriptor in the program's unwind table
 518
 519          UWD_Address := U_get_unwind_entry (Frame.cur_rlo,
 520                                             Frame.cur_rls,
 521                                             Program_UWT.Table_Start,
 522                                             Program_UWT.Table_End);
 523
 524          --  If we did not get it, we might have a frame from code in a
 525          --  stub or shared library. For code in stub we would have to
 526          --  compute the first non-stub return location but this is not
 527          --  the role of this subprogram, so let's just try to see if we
 528          --  can get a result from the tables in shared libraries.
 529
 530          if UWD_Address = -1
 531            and then U_is_shared_pc (Frame.cur_rlo, Frame.cur_r19) /= 0
 532          then
 533             declare
 534                Shlib_UWT   : constant UWT     :=
 535                                U_get_shLib_unwind_table (Frame.cur_r19);
 536                Shlib_Start : constant Address :=
 537                                U_get_shLib_text_addr (Frame.cur_r19);
 538                Rlo_Offset  : constant Address :=
 539                                Frame.cur_rlo - Shlib_Start;
 540             begin
 541                UWD_Address := U_get_unwind_entry (Rlo_Offset,
 542                                                   Frame.cur_rls,
 543                                                   Shlib_UWT.Table_Start,
 544                                                   Shlib_UWT.Table_End);
 545             end;
 546          end if;
 547
 548          if UWD_Address /= -1 then
 549             return To_UWD_Access (UWD_Address + Frame_Info_Offset);
 550          else
 551             return null;
 552          end if;
 553       end UWD_For_RLO_Of;
 554
 555    --  Start of processing for Call_Chain
 556
 557    begin
 558       --  Fetch the state for this subprogram's frame and pop it so that we
 559       --  start with an initial out_rlo "here".
 560
 561       U_init_frame_record (Frame'Access);
 562       Frame.top_sr0 := 0;
 563       Frame.top_sr4 := 0;
 564
 565       U_prep_frame_rec_for_unwind (Frame'Access);
 566
 567       Pop_Success := Pop_Frame (Frame'Access);
 568
 569       --  Skip the requested number of frames
 570
 571       for I in 1 .. Skip_Frames loop
 572          Pop_Success := Pop_Frame (Frame'Access);
 573       end loop;
 574
 575       --  Loop popping frames and storing locations until either a problem
 576       --  occurs, or the top of the call chain is reached, or the provided
 577       --  array is full.
 578
 579       loop
 580          --  We have to test some conditions against the return location
 581          --  as it is returned, so get it as is first.
 582
 583          Code := Frame.out_rlo;
 584
 585          exit when not Pop_Success or else Code = 0 or else J = Max_Len + 1;
 586
 587          --  Compute the call point from the retrieved return location :
 588          --  Mask the privilege bits and account for the delta between the
 589          --  call site and the return point.
 590
 591          Code := (Code and not Priv_Mask) - Rlo_Offset;
 592
 593          if Code < Exclude_Min or else Code > Exclude_Max then
 594             Trace (J) := Code;
 595             J := J + 1;
 596          end if;
 597
 598          Pop_Success := Pop_Frame (Frame'Access);
 599       end loop;
 600
 601       Len := J - 1;
 602    end Call_Chain;
 603
 604 end System.Traceback;