gcc/ada/tracebak.c

   1 /****************************************************************************
   2  *                                                                          *
   3  *                         GNAT RUN-TIME COMPONENTS                         *
   4  *                                                                          *
   5  *                            T R A C E B A C K                             *
   6  *                                                                          *
   7  *                          C Implementation File                           *
   8  *                                                                          *
   9  *            Copyright (C) 2000-2020, 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 3,  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.                                     *
  17  *                                                                          *
  18  * As a special exception under Section 7 of GPL version 3, you are granted *
  19  * additional permissions described in the GCC Runtime Library Exception,   *
  20  * version 3.1, as published by the Free Software Foundation.               *
  21  *                                                                          *
  22  * You should have received a copy of the GNU General Public License and    *
  23  * a copy of the GCC Runtime Library Exception along with this program;     *
  24  * see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    *
  25  * <http://www.gnu.org/licenses/>.                                          *
  26  *                                                                          *
  27  * GNAT was originally developed  by the GNAT team at  New York University. *
  28  * Extensive contributions were provided by Ada Core Technologies Inc.      *
  29  *                                                                          *
  30  ****************************************************************************/
  31
  32 /* This file contains low level support for stack unwinding using GCC intrinsic
  33    functions.
  34    It has been tested on the following configurations:
  35    PowerPC/AiX
  36    PowerPC/Darwin
  37    PowerPC/VxWorks
  38    PowerPC/LynxOS-178
  39    SPARC/Solaris
  40    i386/GNU/Linux
  41    i386/Solaris
  42    i386/NT
  43    i386/OS2
  44    i386/LynxOS
  45    Alpha/VxWorks
  46    Alpha/VMS
  47 */
  48
  49 #ifdef __cplusplus
  50 extern "C" {
  51 #endif
  52
  53 #ifdef IN_RTS
  54 #define POSIX
  55 #include "runtime.h"
  56 #include <stddef.h>
  57 #else
  58 #include "config.h"
  59 #include "system.h"
  60 /* We don't want fancy_abort here.  */
  61 #undef abort
  62 #endif
  63
  64 extern int __gnat_backtrace (void **, int, void *, void *, int);
  65
  66 /* The point is to provide an implementation of the __gnat_backtrace function
  67    above, called by the default implementation of the System.Traceback package.
  68
  69    We first have a series of target specific implementations, each included
  70    from a separate C file for readability purposes.
  71
  72    Then come two flavors of a generic implementation: one relying on static
  73    assumptions about the frame layout, and the other one using the GCC EH
  74    infrastructure.  The former uses a whole set of macros and structures which
  75    may be tailored on a per target basis, and is activated as soon as
  76    USE_GENERIC_UNWINDER is defined.  The latter uses a small subset of the
  77    macro definitions and is activated when USE_GCC_UNWINDER is defined. It is
  78    only available post GCC 3.3.
  79
  80    Finally, there is a default dummy implementation, necessary to make the
  81    linker happy on platforms where the feature is not supported, but where the
  82    function is still referenced by the default System.Traceback.  */
  83
  84 #define Lock_Task system__soft_links__lock_task
  85 extern void (*Lock_Task) (void);
  86
  87 #define Unlock_Task system__soft_links__unlock_task
  88 extern void (*Unlock_Task) (void);
  89
  90 /*-------------------------------------*
  91  *-- Target specific implementations --*
  92  *-------------------------------------*/
  93
  94 #if defined (_WIN64) && defined (__SEH__)
  95
  96 #include <windows.h>
  97
  98 #define IS_BAD_PTR(ptr) (IsBadCodePtr((FARPROC)ptr))
  99
 100 int
 101 __gnat_backtrace (void **array,
 102                   int size,
 103                   void *exclude_min,
 104                   void *exclude_max,
 105                   int skip_frames)
 106 {
 107   CONTEXT context;
 108   UNWIND_HISTORY_TABLE history;
 109   int i;
 110
 111   /* Get the context.  */
 112   RtlCaptureContext (&context);
 113
 114   /* Setup unwind history table (a cached to speed-up unwinding).  */
 115   memset (&history, 0, sizeof (history));
 116
 117   i = 0;
 118   while (1)
 119     {
 120       PRUNTIME_FUNCTION RuntimeFunction;
 121       KNONVOLATILE_CONTEXT_POINTERS NvContext;
 122       ULONG64 ImageBase;
 123       VOID *HandlerData;
 124       ULONG64 EstablisherFrame;
 125
 126       /* Get function metadata.  */
 127       RuntimeFunction = RtlLookupFunctionEntry
 128         (context.Rip, &ImageBase, &history);
 129
 130       if (!RuntimeFunction)
 131         {
 132           /* In case of failure, assume this is a leaf function.  */
 133           context.Rip = *(ULONG64 *) context.Rsp;
 134           context.Rsp += 8;
 135         }
 136       else
 137         {
 138           /* If the last unwinding step failed somehow, stop here.  */
 139           if (IS_BAD_PTR(context.Rip))
 140             break;
 141
 142           /* Unwind.  */
 143           memset (&NvContext, 0, sizeof (KNONVOLATILE_CONTEXT_POINTERS));
 144           RtlVirtualUnwind (0, ImageBase, context.Rip, RuntimeFunction,
 145                             &context, &HandlerData, &EstablisherFrame,
 146                             &NvContext);
 147         }
 148
 149       /* 0 means bottom of the stack.  */
 150       if (context.Rip == 0)
 151         break;
 152
 153       /* Skip frames.  */
 154       if (skip_frames > 1)
 155         {
 156           skip_frames--;
 157           continue;
 158         }
 159       /* Excluded frames.  */
 160       if ((void *)context.Rip >= exclude_min
 161           && (void *)context.Rip <= exclude_max)
 162         continue;
 163
 164       array[i++] = (void *)(context.Rip - 2);
 165       if (i >= size)
 166         break;
 167     }
 168   return i;
 169 }
 170 #else
 171
 172 /* No target specific implementation.  */
 173
 174 /*----------------------------------------------------------------*
 175  *-- Target specific definitions for the generic implementation --*
 176  *----------------------------------------------------------------*/
 177
 178 /* The stack layout is specified by the target ABI. The "generic" scheme is
 179    based on the following assumption:
 180
 181      The stack layout from some frame pointer is such that the information
 182      required to compute the backtrace is available at static offsets.
 183
 184    For a given frame, the information we are interested in is the saved return
 185    address (somewhere after the call instruction in the caller) and a pointer
 186    to the caller's frame. The former is the base of the call chain information
 187    we store in the tracebacks array. The latter allows us to loop over the
 188    successive frames in the chain.
 189
 190    To initiate the process, we retrieve an initial frame address using the
 191    appropriate GCC builtin (__builtin_frame_address).
 192
 193    This scheme is unfortunately not applicable on every target because the
 194    stack layout is not necessarily regular (static) enough. On targets where
 195    this scheme applies, the implementation relies on the following items:
 196
 197    o struct layout, describing the expected stack data layout relevant to the
 198      information we are interested in,
 199
 200    o FRAME_OFFSET, the offset, from a given frame address or frame pointer
 201      value, at which this layout will be found,
 202
 203    o FRAME_LEVEL, controls how many frames up we get at to start with,
 204      from the initial frame pointer we compute by way of the GCC builtin,
 205
 206      0 is most often the appropriate value. 1 may be necessary on targets
 207      where return addresses are saved by a function in it's caller's frame
 208      (e.g. PPC).
 209
 210    o PC_ADJUST, to account for the difference between a call point (address
 211      of a call instruction), which is what we want in the output array, and
 212      the associated return address, which is what we retrieve from the stack.
 213
 214    o STOP_FRAME, to decide whether we reached the top of the call chain, and
 215      thus if the process shall stop.
 216
 217            :
 218            :                   stack
 219            |             +----------------+
 220            |   +-------->|       :        |
 221            |   |         | (FRAME_OFFSET) |
 222            |   |         |       :        |  (PC_ADJUST)
 223            |   |  layout:| return_address ----------------+
 224            |   |         |     ....       |               |
 225            +---------------  next_frame   |               |
 226                |         |     ....       |               |
 227                |         |                |               |
 228                |         +----------------+               |  +-----+
 229                |         |       :        |<- Base fp     |  |  :  |
 230                |         | (FRAME_OFFSET) | (FRAME_LEVEL) |  |  :  |
 231                |         |       :        |               +--->    | [1]
 232                |  layout:| return_address -------------------->    | [0]
 233                |         |       ...      |  (PC_ADJUST)     +-----+
 234                +----------   next_frame   |                 traceback[]
 235                          |       ...      |
 236                          |                |
 237                          +----------------+
 238
 239    o BASE_SKIP,
 240
 241    Since we inherently deal with return addresses, there is an implicit shift
 242    by at least one for the initial point we are able to observe in the chain.
 243
 244    On some targets (e.g. sparc-solaris), the first return address we can
 245    easily get without special code is even our caller's return address, so
 246    there is a initial shift of two.
 247
 248    BASE_SKIP represents this initial shift, which is the minimal "skip_frames"
 249    value we support. We could add special code for the skip_frames < BASE_SKIP
 250    cases. This is not done currently because there is virtually no situation
 251    in which this would be useful.
 252
 253    Finally, to account for some ABI specificities, a target may (but does
 254    not have to) define:
 255
 256    o FORCE_CALL, to force a call to a dummy function at the very beginning
 257      of the computation. See the PPC AIX target for an example where this
 258      is useful.
 259
 260    o FETCH_UP_FRAME, to force an invocation of __builtin_frame_address with a
 261      positive argument right after a possibly forced call even if FRAME_LEVEL
 262      is 0. See the SPARC Solaris case for an example where this is useful.
 263
 264   */
 265
 266 /*------------------- Darwin 8 (OSX 10.4) or newer ----------------------*/
 267 #if defined (__APPLE__) \
 268     && defined (__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__) \
 269     && __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ >= 1040
 270
 271 #define USE_GCC_UNWINDER
 272
 273 #if defined (__i386__) || defined (__x86_64__)
 274 #define PC_ADJUST -2
 275 #elif defined (__ppc__) || defined (__ppc64__)
 276 #define PC_ADJUST -4
 277 #elif defined (__arm__)
 278 #define PC_ADJUST -2
 279 #elif defined (__arm64__)
 280 #define PC_ADJUST -4
 281 #else
 282 #error Unhandled darwin architecture.
 283 #endif
 284
 285 /*---------------------------- x86 *BSD --------------------------------*/
 286
 287 #elif defined (__i386__) &&   \
 288     ( defined (__NetBSD__) || defined (__FreeBSD__) || defined (__OpenBSD__) )
 289
 290 #define USE_GCC_UNWINDER
 291 /* The generic unwinder is not used for this target because the default
 292    implementation doesn't unwind on the BSD platforms.  AMD64 targets use the
 293    gcc unwinder for all platforms, so let's keep i386 consistent with that.
 294 */
 295
 296 #define PC_ADJUST -2
 297 /* The minimum size of call instructions on this architecture is 2 bytes */
 298
 299 /*---------------------- ARM VxWorks ------------------------------------*/
 300 #elif (defined (ARMEL) && defined (__vxworks))
 301
 302 #include "vxWorks.h"
 303 #include "version.h"
 304
 305 #define USE_GCC_UNWINDER
 306 #define PC_ADJUST -2
 307
 308 #if ((_WRS_VXWORKS_MAJOR >= 7) && (_VX_CPU != ARMARCH8A))
 309 #define USING_ARM_UNWINDING 1
 310 #endif
 311
 312 /*---------------------- PPC AIX/PPC Lynx 178/Older Darwin --------------*/
 313 #elif ((defined (_POWER) && defined (_AIX)) || \
 314        (defined (__powerpc__) && defined (__Lynx__) && !defined(__ELF__)) || \
 315        (defined (__ppc__) && defined (__APPLE__)))
 316
 317 #define USE_GENERIC_UNWINDER
 318
 319 struct layout
 320 {
 321   struct layout *next;
 322   void *pad;
 323   void *return_address;
 324 };
 325
 326 #define FRAME_OFFSET(FP) 0
 327 #define PC_ADJUST -4
 328
 329 /* Eventhough the base PPC ABI states that a toplevel frame entry
 330    should to feature a null backchain, AIX might expose a null return
 331    address instead.  */
 332
 333 /* Then LynxOS-178 features yet another variation, with return_address
 334    == &<entrypoint>, with two possible entry points (one for the main
 335    process and one for threads). Beware that &bla returns the address
 336    of a descriptor when "bla" is a function.  Getting the code address
 337    requires an extra dereference.  */
 338
 339 #if defined (__Lynx__)
 340 extern void __start();  /* process entry point.  */
 341 extern void __runnit(); /* thread entry point.  */
 342 #define EXTRA_STOP_CONDITION(CURRENT)                 \
 343   ((CURRENT)->return_address == *(void**)&__start     \
 344    || (CURRENT)->return_address == *(void**)&__runnit)
 345 #else
 346 #define EXTRA_STOP_CONDITION(CURRENT) (0)
 347 #endif
 348
 349 #define STOP_FRAME(CURRENT, TOP_STACK) \
 350   (((void *) (CURRENT) < (TOP_STACK)) \
 351    || (CURRENT)->return_address == NULL \
 352    || EXTRA_STOP_CONDITION(CURRENT))
 353
 354 /* The PPC ABI has an interesting specificity: the return address saved by a
 355    function is located in it's caller's frame, and the save operation only
 356    takes place if the function performs a call.
 357
 358    To have __gnat_backtrace retrieve its own return address, we then
 359    define ... */
 360
 361 #define FORCE_CALL 1
 362 #define FRAME_LEVEL 1
 363
 364 #define BASE_SKIP 1
 365
 366 /*----------- PPC ELF (GNU/Linux & VxWorks & Lynx178e) -------------------*/
 367
 368 #elif (defined (_ARCH_PPC) && defined (__vxworks)) ||  \
 369   (defined (__powerpc__) && defined (__Lynx__) && defined(__ELF__)) || \
 370   (defined (__linux__) && defined (__powerpc__))
 371
 372 #if defined (_ARCH_PPC64) && !defined (__USING_SJLJ_EXCEPTIONS__)
 373 #define USE_GCC_UNWINDER
 374 #else
 375 #define USE_GENERIC_UNWINDER
 376 #endif
 377
 378 struct layout
 379 {
 380   struct layout *next;
 381   void *return_address;
 382 };
 383
 384 #define FORCE_CALL 1
 385 #define FRAME_LEVEL 1
 386 /* See the PPC AIX case for an explanation of these values.  */
 387
 388 #define FRAME_OFFSET(FP) 0
 389 #define PC_ADJUST -4
 390
 391 /* According to the base PPC ABI, a toplevel frame entry should feature
 392    a null backchain.  What happens at signal handler frontiers isn't so
 393    well specified, so we add a safety guard on top.  */
 394
 395 #define STOP_FRAME(CURRENT, TOP_STACK) \
 396  ((CURRENT)->next == 0 || ((long)(CURRENT)->next % __alignof__(void*)) != 0)
 397
 398 #define BASE_SKIP 1
 399
 400 /*-------------------------- SPARC Solaris -----------------------------*/
 401
 402 #elif defined (__sun__) && defined (__sparc__)
 403
 404 #define USE_GENERIC_UNWINDER
 405
 406 /* These definitions are inspired from the Appendix D (Software
 407    Considerations) of the SPARC V8 architecture manual.  */
 408
 409 struct layout
 410 {
 411   struct layout *next;
 412   void *return_address;
 413 };
 414
 415 #ifdef __arch64__
 416 #define STACK_BIAS 2047 /* V9 ABI */
 417 #else
 418 #define STACK_BIAS 0    /* V8 ABI */
 419 #endif
 420
 421 #define FRAME_LEVEL 0
 422 #define FRAME_OFFSET(FP) (14 * sizeof (void*) + (FP ? STACK_BIAS : 0))
 423 #define PC_ADJUST 0
 424 #define STOP_FRAME(CURRENT, TOP_STACK) \
 425   ((CURRENT)->return_address == 0|| (CURRENT)->next == 0 \
 426    || (void *) (CURRENT) < (TOP_STACK))
 427
 428 /* The SPARC register windows need to be flushed before we may access them
 429    from the stack. This is achieved by way of builtin_frame_address only
 430    when the "count" argument is positive, so force at least one such call.  */
 431 #define FETCH_UP_FRAME_ADDRESS
 432
 433 #define BASE_SKIP 2
 434 /* From the frame pointer of frame N, we are accessing the flushed register
 435    window of frame N-1 (positive offset from fp), in which we retrieve the
 436    saved return address. We then end up with our caller's return address.  */
 437
 438 /*---------------------------- x86 & x86_64 ---------------------------------*/
 439
 440 #elif defined (__i386__) || defined (__x86_64__)
 441
 442 #if defined (__WIN32)
 443 #include <windows.h>
 444 #define IS_BAD_PTR(ptr) (IsBadCodePtr((FARPROC)ptr))
 445 #elif defined (__sun__)
 446 #define IS_BAD_PTR(ptr) ((unsigned long)ptr == -1UL)
 447 #else
 448 #define IS_BAD_PTR(ptr) 0
 449 #endif
 450
 451 /* Use the dwarf2 unwinder when we expect to have dwarf2 tables at
 452    hand. Backtraces will reliably stop on frames missing such tables,
 453    but our only alternative is the generic unwinder which requires
 454    compilation forcing a frame pointer to be reliable.  */
 455
 456 #if (defined (__x86_64__) || defined (__linux__)) && !defined (__USING_SJLJ_EXCEPTIONS__)
 457 #define USE_GCC_UNWINDER
 458 #else
 459 #define USE_GENERIC_UNWINDER
 460 #endif
 461
 462 struct layout
 463 {
 464   struct layout *next;
 465   void *return_address;
 466 };
 467
 468 #define FRAME_LEVEL 1
 469 /* builtin_frame_address (1) is expected to work on this family of targets,
 470    and (0) might return the soft stack pointer, which does not designate a
 471    location where a backchain and a return address might be found.  */
 472
 473 #define FRAME_OFFSET(FP) 0
 474 #define PC_ADJUST -2
 475 #define STOP_FRAME(CURRENT, TOP_STACK) \
 476   (IS_BAD_PTR((long)(CURRENT)) \
 477    || (void *) (CURRENT) < (TOP_STACK) \
 478    || IS_BAD_PTR((long)(CURRENT)->return_address) \
 479    || (CURRENT)->return_address == 0 \
 480    || (void *) ((CURRENT)->next) < (TOP_STACK)  \
 481    || EXTRA_STOP_CONDITION(CURRENT))
 482
 483 #define BASE_SKIP (1+FRAME_LEVEL)
 484
 485 /* On i386 architecture we check that at the call point we really have a call
 486    insn. Possible call instructions are:
 487
 488    call  addr16        E8 xx xx xx xx
 489    call  reg           FF Dx
 490    call  off(reg)      FF xx xx
 491    lcall addr seg      9A xx xx xx xx xx xx
 492
 493    This check will not catch all cases but it will increase the backtrace
 494    reliability on this architecture.
 495 */
 496
 497 #define VALID_STACK_FRAME(ptr) \
 498    (!IS_BAD_PTR(ptr) \
 499     && (((*((ptr) - 3) & 0xff) == 0xe8) \
 500         || ((*((ptr) - 5) & 0xff) == 0x9a) \
 501         || ((*((ptr) - 1) & 0xff) == 0xff) \
 502         || (((*(ptr) & 0xd0ff) == 0xd0ff))))
 503
 504 #if defined (__vxworks) && defined (__RTP__)
 505
 506 /* For VxWorks following backchains past the "main" frame gets us into the
 507    kernel space, where it can't be dereferenced. So lets stop at the main
 508    symbol.  */
 509 extern void main();
 510
 511 static int
 512 is_return_from(void *symbol_addr, void *ret_addr)
 513 {
 514   int ret = 0;
 515   char *ptr = (char *)ret_addr;
 516
 517   if ((*(ptr - 5) & 0xff) == 0xe8)
 518     {
 519       /* call addr16  E8 xx xx xx xx  */
 520       int32_t offset = *(int32_t *)(ptr - 4);
 521       ret = (ptr + offset) == symbol_addr;
 522     }
 523
 524   /* Others not implemented yet...  But it is very likely that call addr16
 525      is used here.  */
 526   return ret;
 527 }
 528
 529 #define EXTRA_STOP_CONDITION(CURRENT) \
 530   (is_return_from(&main, (CURRENT)->return_address))
 531 #else /* not (defined (__vxworks) && defined (__RTP__)) */
 532 #define EXTRA_STOP_CONDITION(CURRENT) (0)
 533 #endif /* not (defined (__vxworks) && defined (__RTP__)) */
 534
 535 /*----------------------------- qnx ----------------------------------*/
 536
 537 #elif defined (__QNX__)
 538
 539 #define USE_GCC_UNWINDER
 540
 541 #if defined (__aarch64__)
 542 #define PC_ADJUST -4
 543 #else
 544 #error Unhandled QNX architecture.
 545 #endif
 546
 547 /*------------------- aarch64-linux ----------------------------------*/
 548
 549 #elif (defined (__aarch64__) && defined (__linux__))
 550
 551 #define USE_GCC_UNWINDER
 552 #define PC_ADJUST -4
 553
 554 /*----------------------------- ia64 ---------------------------------*/
 555
 556 #elif defined (__ia64__) && (defined (__linux__) || defined (__hpux__))
 557
 558 #define USE_GCC_UNWINDER
 559 /* Use _Unwind_Backtrace driven exceptions on ia64 HP-UX and ia64
 560    GNU/Linux, where _Unwind_Backtrace is provided by the system unwind
 561    library. On HP-UX 11.23 this requires patch PHSS_33352, which adds
 562    _Unwind_Backtrace to the system unwind library. */
 563
 564 #define PC_ADJUST -4
 565
 566
 567 #endif
 568
 569 /*---------------------------------------------------------------------*
 570  *--      The post GCC 3.3 infrastructure based implementation       --*
 571  *---------------------------------------------------------------------*/
 572
 573 #if defined (USE_GCC_UNWINDER) && (__GNUC__ * 10 + __GNUC_MINOR__ > 33)
 574
 575 /* Conditioning the inclusion on the GCC version is useful to avoid bootstrap
 576    path problems, since the included file refers to post 3.3 functions in
 577    libgcc, and the stage1 compiler is unlikely to be linked against a post 3.3
 578    library.  It actually disables the support for backtraces in this compiler
 579    for targets defining USE_GCC_UNWINDER, which is OK since we don't use the
 580    traceback capability in the compiler anyway.
 581
 582    The condition is expressed the way above because we cannot reliably rely on
 583    any other macro from the base compiler when compiling stage1.  */
 584
 585 #ifdef USING_ARM_UNWINDING
 586 /* This value is not part of the enumerated reason codes defined in unwind.h
 587    for ARM style unwinding, but is used in the included "C" code, so we
 588    define it to a reasonable value to avoid a compilation error.  */
 589 #define _URC_NORMAL_STOP 0
 590 #endif
 591
 592 /* This is an implementation of the __gnat_backtrace routine using the
 593    underlying GCC unwinding support associated with the exception handling
 594    infrastructure.  This will only work for ZCX based applications.  */
 595
 596 #include <unwind.h>
 597
 598 /* The implementation boils down to a call to _Unwind_Backtrace with a
 599    tailored callback and carried-on data structure to keep track of the
 600    input parameters we got as well as of the basic processing state.  */
 601
 602 /******************
 603  * trace_callback *
 604  ******************/
 605
 606 #if !defined (__USING_SJLJ_EXCEPTIONS__)
 607
 608 typedef struct {
 609   void ** traceback;
 610   int max_len;
 611   void * exclude_min;
 612   void * exclude_max;
 613   int  n_frames_to_skip;
 614   int  n_frames_skipped;
 615   int  n_entries_filled;
 616 } uw_data_t;
 617
 618 #if defined (__ia64__) && defined (__hpux__)
 619 #include <uwx.h>
 620 #endif
 621
 622 static _Unwind_Reason_Code
 623 trace_callback (struct _Unwind_Context * uw_context, uw_data_t * uw_data)
 624 {
 625   char * pc;
 626
 627 #if defined (__ia64__) && defined (__hpux__) && defined (USE_LIBUNWIND_EXCEPTIONS)
 628   /* Work around problem with _Unwind_GetIP on ia64 HP-UX. */
 629   uwx_get_reg ((struct uwx_env *) uw_context, UWX_REG_IP, (uint64_t *) &pc);
 630 #else
 631   pc = (char *) _Unwind_GetIP (uw_context);
 632 #endif
 633
 634   if (uw_data->n_frames_skipped < uw_data->n_frames_to_skip)
 635     {
 636       uw_data->n_frames_skipped ++;
 637       return _URC_NO_REASON;
 638     }
 639
 640   if (uw_data->n_entries_filled >= uw_data->max_len)
 641     return _URC_NORMAL_STOP;
 642
 643   if (pc < (char *)uw_data->exclude_min || pc > (char *)uw_data->exclude_max)
 644     uw_data->traceback [uw_data->n_entries_filled ++] = pc + PC_ADJUST;
 645
 646   return _URC_NO_REASON;
 647 }
 648
 649 #endif
 650
 651 /********************
 652  * __gnat_backtrace *
 653  ********************/
 654
 655 int
 656 __gnat_backtrace (void ** traceback __attribute__((unused)),
 657                   int max_len __attribute__((unused)),
 658                   void * exclude_min __attribute__((unused)),
 659                   void * exclude_max __attribute__((unused)),
 660                   int skip_frames __attribute__((unused)))
 661 {
 662 #if defined (__USING_SJLJ_EXCEPTIONS__)
 663   /* We have no unwind material (tables) at hand with sjlj eh, and no
 664      way to retrieve complete and accurate call chain information from
 665      the context stack we maintain.  */
 666   return 0;
 667 #else
 668   uw_data_t uw_data;
 669   /* State carried over during the whole unwinding process.  */
 670
 671   uw_data.traceback   = traceback;
 672   uw_data.max_len     = max_len;
 673   uw_data.exclude_min = exclude_min;
 674   uw_data.exclude_max = exclude_max;
 675
 676   uw_data.n_frames_to_skip = skip_frames;
 677
 678   uw_data.n_frames_skipped = 0;
 679   uw_data.n_entries_filled = 0;
 680
 681   _Unwind_Backtrace ((_Unwind_Trace_Fn)trace_callback, &uw_data);
 682
 683   return uw_data.n_entries_filled;
 684 #endif
 685 }
 686
 687 /*------------------------------------------------------------------*
 688  *-- The generic implementation based on frame layout assumptions --*
 689  *------------------------------------------------------------------*/
 690
 691 #elif defined (USE_GENERIC_UNWINDER)
 692
 693 #ifndef CURRENT_STACK_FRAME
 694 # define CURRENT_STACK_FRAME  ({ char __csf; &__csf; })
 695 #endif
 696
 697 #ifndef VALID_STACK_FRAME
 698 #define VALID_STACK_FRAME(ptr) 1
 699 #endif
 700
 701 #ifndef MAX
 702 #define MAX(x,y) ((x) > (y) ? (x) : (y))
 703 #endif
 704
 705 #ifndef FORCE_CALL
 706 #define FORCE_CALL 0
 707 #endif
 708
 709 /* Make sure the function is not inlined.  */
 710 static void forced_callee (void) __attribute__ ((noinline));
 711
 712 static void forced_callee (void)
 713 {
 714   /* Make sure the function is not pure.  */
 715   volatile int i __attribute__ ((unused)) = 0;
 716 }
 717
 718 int
 719 __gnat_backtrace (void **array,
 720                   int size,
 721                   void *exclude_min,
 722                   void *exclude_max,
 723                   int skip_frames)
 724 {
 725   struct layout *current;
 726   void *top_frame;
 727   void *top_stack ATTRIBUTE_UNUSED;
 728   int cnt = 0;
 729
 730   if (FORCE_CALL)
 731     forced_callee ();
 732
 733   /* Force a call to builtin_frame_address with a positive argument
 734      if required. This is necessary e.g. on SPARC to have the register
 735      windows flushed before we attempt to access them on the stack.  */
 736 #if defined (FETCH_UP_FRAME_ADDRESS) && (FRAME_LEVEL == 0)
 737   __builtin_frame_address (1);
 738 #endif
 739
 740   top_frame = __builtin_frame_address (FRAME_LEVEL);
 741   top_stack = CURRENT_STACK_FRAME;
 742   current = (struct layout *) ((size_t) top_frame + FRAME_OFFSET (0));
 743
 744   /* Skip the number of calls we have been requested to skip, accounting for
 745      the BASE_SKIP parameter.
 746
 747      FRAME_LEVEL is meaningless for the count adjustment. It impacts where we
 748      start retrieving data from, but how many frames "up" we start at is in
 749      BASE_SKIP by definition.  */
 750
 751   skip_frames = MAX (0, skip_frames - BASE_SKIP);
 752
 753   while (cnt < skip_frames)
 754     {
 755       current = (struct layout *) ((size_t) current->next + FRAME_OFFSET (1));
 756       cnt++;
 757     }
 758
 759   cnt = 0;
 760   while (cnt < size)
 761     {
 762       if (STOP_FRAME (current, top_stack) ||
 763           !VALID_STACK_FRAME(((char *) current->return_address) + PC_ADJUST))
 764         break;
 765
 766       if (current->return_address < exclude_min
 767           || current->return_address > exclude_max)
 768         array[cnt++] = ((char *) current->return_address) + PC_ADJUST;
 769
 770       current = (struct layout *) ((size_t) current->next + FRAME_OFFSET (1));
 771     }
 772
 773   return cnt;
 774 }
 775
 776 #else
 777
 778 /* No target specific implementation and neither USE_GCC_UNWINDER nor
 779    USE_GENERIC_UNWINDER defined.  */
 780
 781 /*------------------------------*
 782  *-- The dummy implementation --*
 783  *------------------------------*/
 784
 785 int
 786 __gnat_backtrace (void **array ATTRIBUTE_UNUSED,
 787                   int size ATTRIBUTE_UNUSED,
 788                   void *exclude_min ATTRIBUTE_UNUSED,
 789                   void *exclude_max ATTRIBUTE_UNUSED,
 790                   int skip_frames ATTRIBUTE_UNUSED)
 791 {
 792   return 0;
 793 }
 794
 795 #endif
 796
 797 #endif
 798
 799 #ifdef __cplusplus
 800 }
 801 #endif