gdb/python/py-prettyprint.c

   1 /* Python pretty-printing
   2
   3    Copyright (C) 2008-2016 Free Software Foundation, Inc.
   4
   5    This file is part of GDB.
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 3 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  19
  20 #include "defs.h"
  21 #include "objfiles.h"
  22 #include "symtab.h"
  23 #include "language.h"
  24 #include "valprint.h"
  25 #include "extension-priv.h"
  26 #include "python.h"
  27 #include "python-internal.h"
  28
  29 /* Return type of print_string_repr.  */
  30
  31 enum string_repr_result
  32   {
  33     /* The string method returned None.  */
  34     string_repr_none,
  35     /* The string method had an error.  */
  36     string_repr_error,
  37     /* Everything ok.  */
  38     string_repr_ok
  39   };
  40
  41 /* Helper function for find_pretty_printer which iterates over a list,
  42    calls each function and inspects output.  This will return a
  43    printer object if one recognizes VALUE.  If no printer is found, it
  44    will return None.  On error, it will set the Python error and
  45    return NULL.  */
  46
  47 static PyObject *
  48 search_pp_list (PyObject *list, PyObject *value)
  49 {
  50   Py_ssize_t pp_list_size, list_index;
  51   PyObject *function, *printer = NULL;
  52
  53   pp_list_size = PyList_Size (list);
  54   for (list_index = 0; list_index < pp_list_size; list_index++)
  55     {
  56       function = PyList_GetItem (list, list_index);
  57       if (! function)
  58         return NULL;
  59
  60       /* Skip if disabled.  */
  61       if (PyObject_HasAttr (function, gdbpy_enabled_cst))
  62         {
  63           PyObject *attr = PyObject_GetAttr (function, gdbpy_enabled_cst);
  64           int cmp;
  65
  66           if (!attr)
  67             return NULL;
  68           cmp = PyObject_IsTrue (attr);
  69           Py_DECREF (attr);
  70           if (cmp == -1)
  71             return NULL;
  72
  73           if (!cmp)
  74             continue;
  75         }
  76
  77       printer = PyObject_CallFunctionObjArgs (function, value, NULL);
  78       if (! printer)
  79         return NULL;
  80       else if (printer != Py_None)
  81         return printer;
  82
  83       Py_DECREF (printer);
  84     }
  85
  86   Py_RETURN_NONE;
  87 }
  88
  89 /* Subroutine of find_pretty_printer to simplify it.
  90    Look for a pretty-printer to print VALUE in all objfiles.
  91    The result is NULL if there's an error and the search should be terminated.
  92    The result is Py_None, suitably inc-ref'd, if no pretty-printer was found.
  93    Otherwise the result is the pretty-printer function, suitably inc-ref'd.  */
  94
  95 static PyObject *
  96 find_pretty_printer_from_objfiles (PyObject *value)
  97 {
  98   PyObject *pp_list;
  99   PyObject *function;
 100   struct objfile *obj;
 101
 102   ALL_OBJFILES (obj)
 103   {
 104     PyObject *objf = objfile_to_objfile_object (obj);
 105     if (!objf)
 106       {
 107         /* Ignore the error and continue.  */
 108         PyErr_Clear ();
 109         continue;
 110       }
 111
 112     pp_list = objfpy_get_printers (objf, NULL);
 113     function = search_pp_list (pp_list, value);
 114     Py_XDECREF (pp_list);
 115
 116     /* If there is an error in any objfile list, abort the search and exit.  */
 117     if (! function)
 118       return NULL;
 119
 120     if (function != Py_None)
 121       return function;
 122
 123     Py_DECREF (function);
 124   }
 125
 126   Py_RETURN_NONE;
 127 }
 128
 129 /* Subroutine of find_pretty_printer to simplify it.
 130    Look for a pretty-printer to print VALUE in the current program space.
 131    The result is NULL if there's an error and the search should be terminated.
 132    The result is Py_None, suitably inc-ref'd, if no pretty-printer was found.
 133    Otherwise the result is the pretty-printer function, suitably inc-ref'd.  */
 134
 135 static PyObject *
 136 find_pretty_printer_from_progspace (PyObject *value)
 137 {
 138   PyObject *pp_list;
 139   PyObject *function;
 140   PyObject *obj = pspace_to_pspace_object (current_program_space);
 141
 142   if (!obj)
 143     return NULL;
 144   pp_list = pspy_get_printers (obj, NULL);
 145   function = search_pp_list (pp_list, value);
 146   Py_XDECREF (pp_list);
 147   return function;
 148 }
 149
 150 /* Subroutine of find_pretty_printer to simplify it.
 151    Look for a pretty-printer to print VALUE in the gdb module.
 152    The result is NULL if there's an error and the search should be terminated.
 153    The result is Py_None, suitably inc-ref'd, if no pretty-printer was found.
 154    Otherwise the result is the pretty-printer function, suitably inc-ref'd.  */
 155
 156 static PyObject *
 157 find_pretty_printer_from_gdb (PyObject *value)
 158 {
 159   PyObject *pp_list;
 160   PyObject *function;
 161
 162   /* Fetch the global pretty printer list.  */
 163   if (gdb_python_module == NULL
 164       || ! PyObject_HasAttrString (gdb_python_module, "pretty_printers"))
 165     Py_RETURN_NONE;
 166   pp_list = PyObject_GetAttrString (gdb_python_module, "pretty_printers");
 167   if (pp_list == NULL || ! PyList_Check (pp_list))
 168     {
 169       Py_XDECREF (pp_list);
 170       Py_RETURN_NONE;
 171     }
 172
 173   function = search_pp_list (pp_list, value);
 174   Py_XDECREF (pp_list);
 175   return function;
 176 }
 177
 178 /* Find the pretty-printing constructor function for VALUE.  If no
 179    pretty-printer exists, return None.  If one exists, return a new
 180    reference.  On error, set the Python error and return NULL.  */
 181
 182 static PyObject *
 183 find_pretty_printer (PyObject *value)
 184 {
 185   PyObject *function;
 186
 187   /* Look at the pretty-printer list for each objfile
 188      in the current program-space.  */
 189   function = find_pretty_printer_from_objfiles (value);
 190   if (function == NULL || function != Py_None)
 191     return function;
 192   Py_DECREF (function);
 193
 194   /* Look at the pretty-printer list for the current program-space.  */
 195   function = find_pretty_printer_from_progspace (value);
 196   if (function == NULL || function != Py_None)
 197     return function;
 198   Py_DECREF (function);
 199
 200   /* Look at the pretty-printer list in the gdb module.  */
 201   function = find_pretty_printer_from_gdb (value);
 202   return function;
 203 }
 204
 205 /* Pretty-print a single value, via the printer object PRINTER.
 206    If the function returns a string, a PyObject containing the string
 207    is returned.  If the function returns Py_NONE that means the pretty
 208    printer returned the Python None as a value.  Otherwise, if the
 209    function returns a value,  *OUT_VALUE is set to the value, and NULL
 210    is returned.  On error, *OUT_VALUE is set to NULL, NULL is
 211    returned, with a python exception set.  */
 212
 213 static PyObject *
 214 pretty_print_one_value (PyObject *printer, struct value **out_value)
 215 {
 216   PyObject *result = NULL;
 217
 218   *out_value = NULL;
 219   TRY
 220     {
 221       result = PyObject_CallMethodObjArgs (printer, gdbpy_to_string_cst, NULL);
 222       if (result)
 223         {
 224           if (! gdbpy_is_string (result) && ! gdbpy_is_lazy_string (result)
 225               && result != Py_None)
 226             {
 227               *out_value = convert_value_from_python (result);
 228               if (PyErr_Occurred ())
 229                 *out_value = NULL;
 230               Py_DECREF (result);
 231               result = NULL;
 232             }
 233         }
 234     }
 235   CATCH (except, RETURN_MASK_ALL)
 236     {
 237     }
 238   END_CATCH
 239
 240   return result;
 241 }
 242
 243 /* Return the display hint for the object printer, PRINTER.  Return
 244    NULL if there is no display_hint method, or if the method did not
 245    return a string.  On error, print stack trace and return NULL.  On
 246    success, return an xmalloc()d string.  */
 247 char *
 248 gdbpy_get_display_hint (PyObject *printer)
 249 {
 250   PyObject *hint;
 251   char *result = NULL;
 252
 253   if (! PyObject_HasAttr (printer, gdbpy_display_hint_cst))
 254     return NULL;
 255
 256   hint = PyObject_CallMethodObjArgs (printer, gdbpy_display_hint_cst, NULL);
 257   if (hint)
 258     {
 259       if (gdbpy_is_string (hint))
 260         {
 261           result = python_string_to_host_string (hint);
 262           if (result == NULL)
 263             gdbpy_print_stack ();
 264         }
 265       Py_DECREF (hint);
 266     }
 267   else
 268     gdbpy_print_stack ();
 269
 270   return result;
 271 }
 272
 273 /* A wrapper for gdbpy_print_stack that ignores MemoryError.  */
 274
 275 static void
 276 print_stack_unless_memory_error (struct ui_file *stream)
 277 {
 278   if (PyErr_ExceptionMatches (gdbpy_gdb_memory_error))
 279     {
 280       struct cleanup *cleanup;
 281       PyObject *type, *value, *trace;
 282       char *msg;
 283
 284       PyErr_Fetch (&type, &value, &trace);
 285       cleanup = make_cleanup_py_decref (type);
 286       make_cleanup_py_decref (value);
 287       make_cleanup_py_decref (trace);
 288
 289       msg = gdbpy_exception_to_string (type, value);
 290       make_cleanup (xfree, msg);
 291
 292       if (msg == NULL || *msg == '\0')
 293         fprintf_filtered (stream, _("<error reading variable>"));
 294       else
 295         fprintf_filtered (stream, _("<error reading variable: %s>"), msg);
 296
 297       do_cleanups (cleanup);
 298     }
 299   else
 300     gdbpy_print_stack ();
 301 }
 302
 303 /* Helper for gdbpy_apply_val_pretty_printer which calls to_string and
 304    formats the result.  */
 305
 306 static enum string_repr_result
 307 print_string_repr (PyObject *printer, const char *hint,
 308                    struct ui_file *stream, int recurse,
 309                    const struct value_print_options *options,
 310                    const struct language_defn *language,
 311                    struct gdbarch *gdbarch)
 312 {
 313   struct value *replacement = NULL;
 314   PyObject *py_str = NULL;
 315   enum string_repr_result result = string_repr_ok;
 316
 317   py_str = pretty_print_one_value (printer, &replacement);
 318   if (py_str)
 319     {
 320       struct cleanup *cleanup = make_cleanup_py_decref (py_str);
 321
 322       if (py_str == Py_None)
 323         result = string_repr_none;
 324       else if (gdbpy_is_lazy_string (py_str))
 325         {
 326           CORE_ADDR addr;
 327           long length;
 328           struct type *type;
 329           char *encoding = NULL;
 330           struct value_print_options local_opts = *options;
 331
 332           make_cleanup (free_current_contents, &encoding);
 333           gdbpy_extract_lazy_string (py_str, &addr, &type,
 334                                      &length, &encoding);
 335
 336           local_opts.addressprint = 0;
 337           val_print_string (type, encoding, addr, (int) length,
 338                             stream, &local_opts);
 339         }
 340       else
 341         {
 342           PyObject *string;
 343
 344           string = python_string_to_target_python_string (py_str);
 345           if (string)
 346             {
 347               char *output;
 348               long length;
 349               struct type *type;
 350
 351               make_cleanup_py_decref (string);
 352 #ifdef IS_PY3K
 353               output = PyBytes_AS_STRING (string);
 354               length = PyBytes_GET_SIZE (string);
 355 #else
 356               output = PyString_AsString (string);
 357               length = PyString_Size (string);
 358 #endif
 359               type = builtin_type (gdbarch)->builtin_char;
 360
 361               if (hint && !strcmp (hint, "string"))
 362                 LA_PRINT_STRING (stream, type, (gdb_byte *) output,
 363                                  length, NULL, 0, options);
 364               else
 365                 fputs_filtered (output, stream);
 366             }
 367           else
 368             {
 369               result = string_repr_error;
 370               print_stack_unless_memory_error (stream);
 371             }
 372         }
 373
 374       do_cleanups (cleanup);
 375     }
 376   else if (replacement)
 377     {
 378       struct value_print_options opts = *options;
 379
 380       opts.addressprint = 0;
 381       common_val_print (replacement, stream, recurse, &opts, language);
 382     }
 383   else
 384     {
 385       result = string_repr_error;
 386       print_stack_unless_memory_error (stream);
 387     }
 388
 389   return result;
 390 }
 391
 392 #ifndef IS_PY3K
 393 static void
 394 py_restore_tstate (void *p)
 395 {
 396   PyFrameObject *frame = (PyFrameObject *) p;
 397   PyThreadState *tstate = PyThreadState_GET ();
 398
 399   tstate->frame = frame;
 400 }
 401
 402 /* Create a dummy PyFrameObject, needed to work around
 403    a Python-2.4 bug with generators.  */
 404 static PyObject *
 405 push_dummy_python_frame (void)
 406 {
 407   PyObject *empty_string, *null_tuple, *globals;
 408   PyCodeObject *code;
 409   PyFrameObject *frame;
 410   PyThreadState *tstate;
 411
 412   empty_string = PyString_FromString ("");
 413   if (!empty_string)
 414     return NULL;
 415
 416   null_tuple = PyTuple_New (0);
 417   if (!null_tuple)
 418     {
 419       Py_DECREF (empty_string);
 420       return NULL;
 421     }
 422
 423   code = PyCode_New (0,                 /* argcount */
 424                      0,                 /* nlocals */
 425                      0,                 /* stacksize */
 426                      0,                 /* flags */
 427                      empty_string,      /* code */
 428                      null_tuple,        /* consts */
 429                      null_tuple,        /* names */
 430                      null_tuple,        /* varnames */
 431 #if PYTHON_API_VERSION >= 1010
 432                      null_tuple,        /* freevars */
 433                      null_tuple,        /* cellvars */
 434 #endif
 435                      empty_string,      /* filename */
 436                      empty_string,      /* name */
 437                      1,                 /* firstlineno */
 438                      empty_string       /* lnotab */
 439                     );
 440
 441   Py_DECREF (empty_string);
 442   Py_DECREF (null_tuple);
 443
 444   if (!code)
 445     return NULL;
 446
 447   globals = PyDict_New ();
 448   if (!globals)
 449     {
 450       Py_DECREF (code);
 451       return NULL;
 452     }
 453
 454   tstate = PyThreadState_GET ();
 455
 456   frame = PyFrame_New (tstate, code, globals, NULL);
 457
 458   Py_DECREF (globals);
 459   Py_DECREF (code);
 460
 461   if (!frame)
 462     return NULL;
 463
 464   tstate->frame = frame;
 465   make_cleanup (py_restore_tstate, frame->f_back);
 466   return (PyObject *) frame;
 467 }
 468 #endif
 469
 470 /* Helper for gdbpy_apply_val_pretty_printer that formats children of the
 471    printer, if any exist.  If is_py_none is true, then nothing has
 472    been printed by to_string, and format output accordingly. */
 473 static void
 474 print_children (PyObject *printer, const char *hint,
 475                 struct ui_file *stream, int recurse,
 476                 const struct value_print_options *options,
 477                 const struct language_defn *language,
 478                 int is_py_none)
 479 {
 480   int is_map, is_array, done_flag, pretty;
 481   unsigned int i;
 482   PyObject *children, *iter;
 483 #ifndef IS_PY3K
 484   PyObject *frame;
 485 #endif
 486   struct cleanup *cleanups;
 487
 488   if (! PyObject_HasAttr (printer, gdbpy_children_cst))
 489     return;
 490
 491   /* If we are printing a map or an array, we want some special
 492      formatting.  */
 493   is_map = hint && ! strcmp (hint, "map");
 494   is_array = hint && ! strcmp (hint, "array");
 495
 496   children = PyObject_CallMethodObjArgs (printer, gdbpy_children_cst,
 497                                          NULL);
 498   if (! children)
 499     {
 500       print_stack_unless_memory_error (stream);
 501       return;
 502     }
 503
 504   cleanups = make_cleanup_py_decref (children);
 505
 506   iter = PyObject_GetIter (children);
 507   if (!iter)
 508     {
 509       print_stack_unless_memory_error (stream);
 510       goto done;
 511     }
 512   make_cleanup_py_decref (iter);
 513
 514   /* Use the prettyformat_arrays option if we are printing an array,
 515      and the pretty option otherwise.  */
 516   if (is_array)
 517     pretty = options->prettyformat_arrays;
 518   else
 519     {
 520       if (options->prettyformat == Val_prettyformat)
 521         pretty = 1;
 522       else
 523         pretty = options->prettyformat_structs;
 524     }
 525
 526   /* Manufacture a dummy Python frame to work around Python 2.4 bug,
 527      where it insists on having a non-NULL tstate->frame when
 528      a generator is called.  */
 529 #ifndef IS_PY3K
 530   frame = push_dummy_python_frame ();
 531   if (!frame)
 532     {
 533       gdbpy_print_stack ();
 534       goto done;
 535     }
 536   make_cleanup_py_decref (frame);
 537 #endif
 538
 539   done_flag = 0;
 540   for (i = 0; i < options->print_max; ++i)
 541     {
 542       PyObject *py_v, *item = PyIter_Next (iter);
 543       const char *name;
 544       struct cleanup *inner_cleanup;
 545
 546       if (! item)
 547         {
 548           if (PyErr_Occurred ())
 549             print_stack_unless_memory_error (stream);
 550           /* Set a flag so we can know whether we printed all the
 551              available elements.  */
 552           else
 553             done_flag = 1;
 554           break;
 555         }
 556
 557       if (! PyTuple_Check (item) || PyTuple_Size (item) != 2)
 558         {
 559           PyErr_SetString (PyExc_TypeError,
 560                            _("Result of children iterator not a tuple"
 561                              " of two elements."));
 562           gdbpy_print_stack ();
 563           Py_DECREF (item);
 564           continue;
 565         }
 566       if (! PyArg_ParseTuple (item, "sO", &name, &py_v))
 567         {
 568           /* The user won't necessarily get a stack trace here, so provide
 569              more context.  */
 570           if (gdbpy_print_python_errors_p ())
 571             fprintf_unfiltered (gdb_stderr,
 572                                 _("Bad result from children iterator.\n"));
 573           gdbpy_print_stack ();
 574           Py_DECREF (item);
 575           continue;
 576         }
 577       inner_cleanup = make_cleanup_py_decref (item);
 578
 579       /* Print initial "{".  For other elements, there are three
 580          cases:
 581          1. Maps.  Print a "," after each value element.
 582          2. Arrays.  Always print a ",".
 583          3. Other.  Always print a ",".  */
 584       if (i == 0)
 585         {
 586          if (is_py_none)
 587            fputs_filtered ("{", stream);
 588          else
 589            fputs_filtered (" = {", stream);
 590        }
 591
 592       else if (! is_map || i % 2 == 0)
 593         fputs_filtered (pretty ? "," : ", ", stream);
 594
 595       /* In summary mode, we just want to print "= {...}" if there is
 596          a value.  */
 597       if (options->summary)
 598         {
 599           /* This increment tricks the post-loop logic to print what
 600              we want.  */
 601           ++i;
 602           /* Likewise.  */
 603           pretty = 0;
 604           break;
 605         }
 606
 607       if (! is_map || i % 2 == 0)
 608         {
 609           if (pretty)
 610             {
 611               fputs_filtered ("\n", stream);
 612               print_spaces_filtered (2 + 2 * recurse, stream);
 613             }
 614           else
 615             wrap_here (n_spaces (2 + 2 *recurse));
 616         }
 617
 618       if (is_map && i % 2 == 0)
 619         fputs_filtered ("[", stream);
 620       else if (is_array)
 621         {
 622           /* We print the index, not whatever the child method
 623              returned as the name.  */
 624           if (options->print_array_indexes)
 625             fprintf_filtered (stream, "[%d] = ", i);
 626         }
 627       else if (! is_map)
 628         {
 629           fputs_filtered (name, stream);
 630           fputs_filtered (" = ", stream);
 631         }
 632
 633       if (gdbpy_is_lazy_string (py_v))
 634         {
 635           CORE_ADDR addr;
 636           struct type *type;
 637           long length;
 638           char *encoding = NULL;
 639           struct value_print_options local_opts = *options;
 640
 641           make_cleanup (free_current_contents, &encoding);
 642           gdbpy_extract_lazy_string (py_v, &addr, &type, &length, &encoding);
 643
 644           local_opts.addressprint = 0;
 645           val_print_string (type, encoding, addr, (int) length, stream,
 646                             &local_opts);
 647         }
 648       else if (gdbpy_is_string (py_v))
 649         {
 650           char *output;
 651
 652           output = python_string_to_host_string (py_v);
 653           if (!output)
 654             gdbpy_print_stack ();
 655           else
 656             {
 657               fputs_filtered (output, stream);
 658               xfree (output);
 659             }
 660         }
 661       else
 662         {
 663           struct value *value = convert_value_from_python (py_v);
 664
 665           if (value == NULL)
 666             {
 667               gdbpy_print_stack ();
 668               error (_("Error while executing Python code."));
 669             }
 670           else
 671             common_val_print (value, stream, recurse + 1, options, language);
 672         }
 673
 674       if (is_map && i % 2 == 0)
 675         fputs_filtered ("] = ", stream);
 676
 677       do_cleanups (inner_cleanup);
 678     }
 679
 680   if (i)
 681     {
 682       if (!done_flag)
 683         {
 684           if (pretty)
 685             {
 686               fputs_filtered ("\n", stream);
 687               print_spaces_filtered (2 + 2 * recurse, stream);
 688             }
 689           fputs_filtered ("...", stream);
 690         }
 691       if (pretty)
 692         {
 693           fputs_filtered ("\n", stream);
 694           print_spaces_filtered (2 * recurse, stream);
 695         }
 696       fputs_filtered ("}", stream);
 697     }
 698
 699  done:
 700   do_cleanups (cleanups);
 701 }
 702
 703 enum ext_lang_rc
 704 gdbpy_apply_val_pretty_printer (const struct extension_language_defn *extlang,
 705                                 struct type *type, const gdb_byte *valaddr,
 706                                 LONGEST embedded_offset, CORE_ADDR address,
 707                                 struct ui_file *stream, int recurse,
 708                                 const struct value *val,
 709                                 const struct value_print_options *options,
 710                                 const struct language_defn *language)
 711 {
 712   struct gdbarch *gdbarch = get_type_arch (type);
 713   PyObject *printer = NULL;
 714   PyObject *val_obj = NULL;
 715   struct value *value;
 716   char *hint = NULL;
 717   struct cleanup *cleanups;
 718   enum ext_lang_rc result = EXT_LANG_RC_NOP;
 719   enum string_repr_result print_result;
 720
 721   /* No pretty-printer support for unavailable values.  */
 722   if (!value_bytes_available (val, embedded_offset, TYPE_LENGTH (type)))
 723     return EXT_LANG_RC_NOP;
 724
 725   if (!gdb_python_initialized)
 726     return EXT_LANG_RC_NOP;
 727
 728   cleanups = ensure_python_env (gdbarch, language);
 729
 730   /* Instantiate the printer.  */
 731   if (valaddr)
 732     valaddr += embedded_offset;
 733   value = value_from_contents_and_address (type, valaddr,
 734                                            address + embedded_offset);
 735
 736   set_value_component_location (value, val);
 737   /* set_value_component_location resets the address, so we may
 738      need to set it again.  */
 739   if (VALUE_LVAL (value) != lval_internalvar
 740       && VALUE_LVAL (value) != lval_internalvar_component
 741       && VALUE_LVAL (value) != lval_computed)
 742     set_value_address (value, address + embedded_offset);
 743
 744   val_obj = value_to_value_object (value);
 745   if (! val_obj)
 746     {
 747       result = EXT_LANG_RC_ERROR;
 748       goto done;
 749     }
 750
 751   /* Find the constructor.  */
 752   printer = find_pretty_printer (val_obj);
 753   Py_DECREF (val_obj);
 754
 755   if (printer == NULL)
 756     {
 757       result = EXT_LANG_RC_ERROR;
 758       goto done;
 759     }
 760
 761   make_cleanup_py_decref (printer);
 762   if (printer == Py_None)
 763     {
 764       result = EXT_LANG_RC_NOP;
 765       goto done;
 766     }
 767
 768   /* If we are printing a map, we want some special formatting.  */
 769   hint = gdbpy_get_display_hint (printer);
 770   make_cleanup (free_current_contents, &hint);
 771
 772   /* Print the section */
 773   print_result = print_string_repr (printer, hint, stream, recurse,
 774                                     options, language, gdbarch);
 775   if (print_result != string_repr_error)
 776     print_children (printer, hint, stream, recurse, options, language,
 777                     print_result == string_repr_none);
 778
 779   result = EXT_LANG_RC_OK;
 780
 781  done:
 782   if (PyErr_Occurred ())
 783     print_stack_unless_memory_error (stream);
 784   do_cleanups (cleanups);
 785   return result;
 786 }
 787
 788
 789 /* Apply a pretty-printer for the varobj code.  PRINTER_OBJ is the
 790    print object.  It must have a 'to_string' method (but this is
 791    checked by varobj, not here) which takes no arguments and
 792    returns a string.  The printer will return a value and in the case
 793    of a Python string being returned, this function will return a
 794    PyObject containing the string.  For any other type, *REPLACEMENT is
 795    set to the replacement value and this function returns NULL.  On
 796    error, *REPLACEMENT is set to NULL and this function also returns
 797    NULL.  */
 798 PyObject *
 799 apply_varobj_pretty_printer (PyObject *printer_obj,
 800                              struct value **replacement,
 801                              struct ui_file *stream)
 802 {
 803   PyObject *py_str = NULL;
 804
 805   *replacement = NULL;
 806   py_str = pretty_print_one_value (printer_obj, replacement);
 807
 808   if (*replacement == NULL && py_str == NULL)
 809     print_stack_unless_memory_error (stream);
 810
 811   return py_str;
 812 }
 813
 814 /* Find a pretty-printer object for the varobj module.  Returns a new
 815    reference to the object if successful; returns NULL if not.  VALUE
 816    is the value for which a printer tests to determine if it
 817    can pretty-print the value.  */
 818 PyObject *
 819 gdbpy_get_varobj_pretty_printer (struct value *value)
 820 {
 821   PyObject *val_obj;
 822   PyObject *pretty_printer = NULL;
 823
 824   TRY
 825     {
 826       value = value_copy (value);
 827     }
 828   CATCH (except, RETURN_MASK_ALL)
 829     {
 830       GDB_PY_HANDLE_EXCEPTION (except);
 831     }
 832   END_CATCH
 833
 834   val_obj = value_to_value_object (value);
 835   if (! val_obj)
 836     return NULL;
 837
 838   pretty_printer = find_pretty_printer (val_obj);
 839   Py_DECREF (val_obj);
 840   return pretty_printer;
 841 }
 842
 843 /* A Python function which wraps find_pretty_printer and instantiates
 844    the resulting class.  This accepts a Value argument and returns a
 845    pretty printer instance, or None.  This function is useful as an
 846    argument to the MI command -var-set-visualizer.  */
 847 PyObject *
 848 gdbpy_default_visualizer (PyObject *self, PyObject *args)
 849 {
 850   PyObject *val_obj;
 851   PyObject *cons;
 852   struct value *value;
 853
 854   if (! PyArg_ParseTuple (args, "O", &val_obj))
 855     return NULL;
 856   value = value_object_to_value (val_obj);
 857   if (! value)
 858     {
 859       PyErr_SetString (PyExc_TypeError,
 860                        _("Argument must be a gdb.Value."));
 861       return NULL;
 862     }
 863
 864   cons = find_pretty_printer (val_obj);
 865   return cons;
 866 }