gdb/xml-tdesc.c

   1 /* XML target description support for GDB.
   2
   3    Copyright (C) 2006, 2008-2012 Free Software Foundation, Inc.
   4
   5    Contributed by CodeSourcery.
   6
   7    This file is part of GDB.
   8
   9    This program is free software; you can redistribute it and/or modify
  10    it under the terms of the GNU General Public License as published by
  11    the Free Software Foundation; either version 3 of the License, or
  12    (at your option) any later version.
  13
  14    This program is distributed in the hope that it will be useful,
  15    but WITHOUT ANY WARRANTY; without even the implied warranty of
  16    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17    GNU General Public License for more details.
  18
  19    You should have received a copy of the GNU General Public License
  20    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  21
  22 #include "defs.h"
  23 #include "target.h"
  24 #include "target-descriptions.h"
  25 #include "xml-support.h"
  26 #include "xml-tdesc.h"
  27 #include "osabi.h"
  28
  29 #include "filenames.h"
  30
  31 #include "gdb_assert.h"
  32
  33 #if !defined(HAVE_LIBEXPAT)
  34
  35 /* Parse DOCUMENT into a target description.  Or don't, since we don't have
  36    an XML parser.  */
  37
  38 static struct target_desc *
  39 tdesc_parse_xml (const char *document, xml_fetch_another fetcher,
  40                  void *fetcher_baton)
  41 {
  42   static int have_warned;
  43
  44   if (!have_warned)
  45     {
  46       have_warned = 1;
  47       warning (_("Can not parse XML target description; XML support was "
  48                  "disabled at compile time"));
  49     }
  50
  51   return NULL;
  52 }
  53
  54 #else /* HAVE_LIBEXPAT */
  55
  56 /* A record of every XML description we have parsed.  We never discard
  57    old descriptions, because we never discard gdbarches.  As long as we
  58    have a gdbarch referencing this description, we want to have a copy
  59    of it here, so that if we parse the same XML document again we can
  60    return the same "struct target_desc *"; if they are not singletons,
  61    then we will create unnecessary duplicate gdbarches.  See
  62    gdbarch_list_lookup_by_info.  */
  63
  64 struct tdesc_xml_cache
  65 {
  66   const char *xml_document;
  67   struct target_desc *tdesc;
  68 };
  69 typedef struct tdesc_xml_cache tdesc_xml_cache_s;
  70 DEF_VEC_O(tdesc_xml_cache_s);
  71
  72 static VEC(tdesc_xml_cache_s) *xml_cache;
  73
  74 /* Callback data for target description parsing.  */
  75
  76 struct tdesc_parsing_data
  77 {
  78   /* The target description we are building.  */
  79   struct target_desc *tdesc;
  80
  81   /* The target feature we are currently parsing, or last parsed.  */
  82   struct tdesc_feature *current_feature;
  83
  84   /* The register number to use for the next register we see, if
  85      it does not have its own.  This starts at zero.  */
  86   int next_regnum;
  87
  88   /* The struct or union we are currently parsing, or last parsed.  */
  89   struct tdesc_type *current_type;
  90
  91   /* The byte size of the current struct type, if specified.  Zero
  92      if not specified.  */
  93   int current_type_size;
  94
  95   /* Whether the current type is a flags type.  */
  96   int current_type_is_flags;
  97 };
  98
  99 /* Handle the end of an <architecture> element and its value.  */
 100
 101 static void
 102 tdesc_end_arch (struct gdb_xml_parser *parser,
 103                 const struct gdb_xml_element *element,
 104                 void *user_data, const char *body_text)
 105 {
 106   struct tdesc_parsing_data *data = user_data;
 107   const struct bfd_arch_info *arch;
 108
 109   arch = bfd_scan_arch (body_text);
 110   if (arch == NULL)
 111     gdb_xml_error (parser, _("Target description specified unknown "
 112                              "architecture \"%s\""), body_text);
 113   set_tdesc_architecture (data->tdesc, arch);
 114 }
 115
 116 /* Handle the end of an <osabi> element and its value.  */
 117
 118 static void
 119 tdesc_end_osabi (struct gdb_xml_parser *parser,
 120                  const struct gdb_xml_element *element,
 121                  void *user_data, const char *body_text)
 122 {
 123   struct tdesc_parsing_data *data = user_data;
 124   enum gdb_osabi osabi;
 125
 126   osabi = osabi_from_tdesc_string (body_text);
 127   if (osabi == GDB_OSABI_UNKNOWN)
 128     warning (_("Target description specified unknown osabi \"%s\""),
 129              body_text);
 130   else
 131     set_tdesc_osabi (data->tdesc, osabi);
 132 }
 133
 134 /* Handle the end of a <compatible> element and its value.  */
 135
 136 static void
 137 tdesc_end_compatible (struct gdb_xml_parser *parser,
 138                       const struct gdb_xml_element *element,
 139                       void *user_data, const char *body_text)
 140 {
 141   struct tdesc_parsing_data *data = user_data;
 142   const struct bfd_arch_info *arch;
 143
 144   arch = bfd_scan_arch (body_text);
 145   tdesc_add_compatible (data->tdesc, arch);
 146 }
 147
 148 /* Handle the start of a <target> element.  */
 149
 150 static void
 151 tdesc_start_target (struct gdb_xml_parser *parser,
 152                     const struct gdb_xml_element *element,
 153                     void *user_data, VEC(gdb_xml_value_s) *attributes)
 154 {
 155   char *version = xml_find_attribute (attributes, "version")->value;
 156
 157   if (strcmp (version, "1.0") != 0)
 158     gdb_xml_error (parser,
 159                    _("Target description has unsupported version \"%s\""),
 160                    version);
 161 }
 162
 163 /* Handle the start of a <feature> element.  */
 164
 165 static void
 166 tdesc_start_feature (struct gdb_xml_parser *parser,
 167                      const struct gdb_xml_element *element,
 168                      void *user_data, VEC(gdb_xml_value_s) *attributes)
 169 {
 170   struct tdesc_parsing_data *data = user_data;
 171   char *name = xml_find_attribute (attributes, "name")->value;
 172
 173   data->current_feature = tdesc_create_feature (data->tdesc, name);
 174 }
 175
 176 /* Handle the start of a <reg> element.  Fill in the optional
 177    attributes and attach it to the containing feature.  */
 178
 179 static void
 180 tdesc_start_reg (struct gdb_xml_parser *parser,
 181                  const struct gdb_xml_element *element,
 182                  void *user_data, VEC(gdb_xml_value_s) *attributes)
 183 {
 184   struct tdesc_parsing_data *data = user_data;
 185   struct gdb_xml_value *attrs = VEC_address (gdb_xml_value_s, attributes);
 186   int ix = 0, length;
 187   char *name, *group, *type;
 188   int bitsize, regnum, save_restore;
 189
 190   length = VEC_length (gdb_xml_value_s, attributes);
 191
 192   name = attrs[ix++].value;
 193   bitsize = * (ULONGEST *) attrs[ix++].value;
 194
 195   if (ix < length && strcmp (attrs[ix].name, "regnum") == 0)
 196     regnum = * (ULONGEST *) attrs[ix++].value;
 197   else
 198     regnum = data->next_regnum;
 199
 200   if (ix < length && strcmp (attrs[ix].name, "type") == 0)
 201     type = attrs[ix++].value;
 202   else
 203     type = "int";
 204
 205   if (ix < length && strcmp (attrs[ix].name, "group") == 0)
 206     group = attrs[ix++].value;
 207   else
 208     group = NULL;
 209
 210   if (ix < length && strcmp (attrs[ix].name, "save-restore") == 0)
 211     save_restore = * (ULONGEST *) attrs[ix++].value;
 212   else
 213     save_restore = 1;
 214
 215   if (strcmp (type, "int") != 0
 216       && strcmp (type, "float") != 0
 217       && tdesc_named_type (data->current_feature, type) == NULL)
 218     gdb_xml_error (parser, _("Register \"%s\" has unknown type \"%s\""),
 219                    name, type);
 220
 221   tdesc_create_reg (data->current_feature, name, regnum, save_restore, group,
 222                     bitsize, type);
 223
 224   data->next_regnum = regnum + 1;
 225 }
 226
 227 /* Handle the start of a <union> element.  Initialize the type and
 228    record it with the current feature.  */
 229
 230 static void
 231 tdesc_start_union (struct gdb_xml_parser *parser,
 232                    const struct gdb_xml_element *element,
 233                    void *user_data, VEC(gdb_xml_value_s) *attributes)
 234 {
 235   struct tdesc_parsing_data *data = user_data;
 236   char *id = xml_find_attribute (attributes, "id")->value;
 237
 238   data->current_type = tdesc_create_union (data->current_feature, id);
 239   data->current_type_size = 0;
 240   data->current_type_is_flags = 0;
 241 }
 242
 243 /* Handle the start of a <struct> element.  Initialize the type and
 244    record it with the current feature.  */
 245
 246 static void
 247 tdesc_start_struct (struct gdb_xml_parser *parser,
 248                    const struct gdb_xml_element *element,
 249                    void *user_data, VEC(gdb_xml_value_s) *attributes)
 250 {
 251   struct tdesc_parsing_data *data = user_data;
 252   char *id = xml_find_attribute (attributes, "id")->value;
 253   struct tdesc_type *type;
 254   struct gdb_xml_value *attr;
 255
 256   type = tdesc_create_struct (data->current_feature, id);
 257   data->current_type = type;
 258   data->current_type_size = 0;
 259   data->current_type_is_flags = 0;
 260
 261   attr = xml_find_attribute (attributes, "size");
 262   if (attr != NULL)
 263     {
 264       int size = (int) * (ULONGEST *) attr->value;
 265
 266       tdesc_set_struct_size (type, size);
 267       data->current_type_size = size;
 268     }
 269 }
 270
 271 static void
 272 tdesc_start_flags (struct gdb_xml_parser *parser,
 273                    const struct gdb_xml_element *element,
 274                    void *user_data, VEC(gdb_xml_value_s) *attributes)
 275 {
 276   struct tdesc_parsing_data *data = user_data;
 277   char *id = xml_find_attribute (attributes, "id")->value;
 278   int length = (int) * (ULONGEST *)
 279     xml_find_attribute (attributes, "size")->value;
 280   struct tdesc_type *type;
 281
 282   type = tdesc_create_flags (data->current_feature, id, length);
 283
 284   data->current_type = type;
 285   data->current_type_size = 0;
 286   data->current_type_is_flags = 1;
 287 }
 288
 289 /* Handle the start of a <field> element.  Attach the field to the
 290    current struct or union.  */
 291
 292 static void
 293 tdesc_start_field (struct gdb_xml_parser *parser,
 294                    const struct gdb_xml_element *element,
 295                    void *user_data, VEC(gdb_xml_value_s) *attributes)
 296 {
 297   struct tdesc_parsing_data *data = user_data;
 298   struct gdb_xml_value *attr;
 299   struct tdesc_type *field_type;
 300   char *field_name, *field_type_id;
 301   int start, end;
 302
 303   field_name = xml_find_attribute (attributes, "name")->value;
 304
 305   attr = xml_find_attribute (attributes, "type");
 306   if (attr != NULL)
 307     field_type_id = attr->value;
 308   else
 309     field_type_id = NULL;
 310
 311   attr = xml_find_attribute (attributes, "start");
 312   if (attr != NULL)
 313     start = * (ULONGEST *) attr->value;
 314   else
 315     start = -1;
 316
 317   attr = xml_find_attribute (attributes, "end");
 318   if (attr != NULL)
 319     end = * (ULONGEST *) attr->value;
 320   else
 321     end = -1;
 322
 323   if (field_type_id != NULL)
 324     {
 325       if (data->current_type_is_flags)
 326         gdb_xml_error (parser, _("Cannot add typed field \"%s\" to flags"),
 327                        field_name);
 328       if (data->current_type_size != 0)
 329         gdb_xml_error (parser,
 330                        _("Explicitly sized type can not "
 331                          "contain non-bitfield \"%s\""),
 332                        field_name);
 333
 334       field_type = tdesc_named_type (data->current_feature, field_type_id);
 335       if (field_type == NULL)
 336         gdb_xml_error (parser, _("Field \"%s\" references undefined "
 337                                  "type \"%s\""),
 338                        field_name, field_type_id);
 339
 340       tdesc_add_field (data->current_type, field_name, field_type);
 341     }
 342   else if (start != -1 && end != -1)
 343     {
 344       struct tdesc_type *t = data->current_type;
 345
 346       if (data->current_type_is_flags)
 347         tdesc_add_flag (t, start, field_name);
 348       else
 349         {
 350           if (data->current_type_size == 0)
 351             gdb_xml_error (parser,
 352                            _("Implicitly sized type can "
 353                              "not contain bitfield \"%s\""),
 354                            field_name);
 355
 356           if (end >= 64)
 357             gdb_xml_error (parser,
 358                            _("Bitfield \"%s\" goes past "
 359                              "64 bits (unsupported)"),
 360                            field_name);
 361
 362           /* Assume that the bit numbering in XML is "lsb-zero".  Most
 363              architectures other than PowerPC use this ordering.  In
 364              the future, we can add an XML tag to indicate "msb-zero"
 365              numbering.  */
 366           if (start > end)
 367             gdb_xml_error (parser, _("Bitfield \"%s\" has start after end"),
 368                            field_name);
 369
 370           if (end >= data->current_type_size * TARGET_CHAR_BIT)
 371             gdb_xml_error (parser,
 372                            _("Bitfield \"%s\" does not fit in struct"));
 373
 374           tdesc_add_bitfield (t, field_name, start, end);
 375         }
 376     }
 377   else
 378     gdb_xml_error (parser, _("Field \"%s\" has neither type nor bit position"),
 379                    field_name);
 380 }
 381
 382 /* Handle the start of a <vector> element.  Initialize the type and
 383    record it with the current feature.  */
 384
 385 static void
 386 tdesc_start_vector (struct gdb_xml_parser *parser,
 387                     const struct gdb_xml_element *element,
 388                     void *user_data, VEC(gdb_xml_value_s) *attributes)
 389 {
 390   struct tdesc_parsing_data *data = user_data;
 391   struct gdb_xml_value *attrs = VEC_address (gdb_xml_value_s, attributes);
 392   struct tdesc_type *field_type;
 393   char *id, *field_type_id;
 394   int count;
 395
 396   id = attrs[0].value;
 397   field_type_id = attrs[1].value;
 398   count = * (ULONGEST *) attrs[2].value;
 399
 400   field_type = tdesc_named_type (data->current_feature, field_type_id);
 401   if (field_type == NULL)
 402     gdb_xml_error (parser, _("Vector \"%s\" references undefined type \"%s\""),
 403                    id, field_type_id);
 404
 405   tdesc_create_vector (data->current_feature, id, field_type, count);
 406 }
 407
 408 /* The elements and attributes of an XML target description.  */
 409
 410 static const struct gdb_xml_attribute field_attributes[] = {
 411   { "name", GDB_XML_AF_NONE, NULL, NULL },
 412   { "type", GDB_XML_AF_OPTIONAL, NULL, NULL },
 413   { "start", GDB_XML_AF_OPTIONAL, gdb_xml_parse_attr_ulongest, NULL },
 414   { "end", GDB_XML_AF_OPTIONAL, gdb_xml_parse_attr_ulongest, NULL },
 415   { NULL, GDB_XML_AF_NONE, NULL, NULL }
 416 };
 417
 418 static const struct gdb_xml_element struct_union_children[] = {
 419   { "field", field_attributes, NULL, GDB_XML_EF_REPEATABLE,
 420     tdesc_start_field, NULL },
 421   { NULL, NULL, NULL, GDB_XML_EF_NONE, NULL, NULL }
 422 };
 423
 424 static const struct gdb_xml_attribute reg_attributes[] = {
 425   { "name", GDB_XML_AF_NONE, NULL, NULL },
 426   { "bitsize", GDB_XML_AF_NONE, gdb_xml_parse_attr_ulongest, NULL },
 427   { "regnum", GDB_XML_AF_OPTIONAL, gdb_xml_parse_attr_ulongest, NULL },
 428   { "type", GDB_XML_AF_OPTIONAL, NULL, NULL },
 429   { "group", GDB_XML_AF_OPTIONAL, NULL, NULL },
 430   { "save-restore", GDB_XML_AF_OPTIONAL,
 431     gdb_xml_parse_attr_enum, gdb_xml_enums_boolean },
 432   { NULL, GDB_XML_AF_NONE, NULL, NULL }
 433 };
 434
 435 static const struct gdb_xml_attribute struct_union_attributes[] = {
 436   { "id", GDB_XML_AF_NONE, NULL, NULL },
 437   { "size", GDB_XML_AF_OPTIONAL, gdb_xml_parse_attr_ulongest, NULL},
 438   { NULL, GDB_XML_AF_NONE, NULL, NULL }
 439 };
 440
 441 static const struct gdb_xml_attribute flags_attributes[] = {
 442   { "id", GDB_XML_AF_NONE, NULL, NULL },
 443   { "size", GDB_XML_AF_NONE, gdb_xml_parse_attr_ulongest, NULL},
 444   { NULL, GDB_XML_AF_NONE, NULL, NULL }
 445 };
 446
 447 static const struct gdb_xml_attribute vector_attributes[] = {
 448   { "id", GDB_XML_AF_NONE, NULL, NULL },
 449   { "type", GDB_XML_AF_NONE, NULL, NULL },
 450   { "count", GDB_XML_AF_NONE, gdb_xml_parse_attr_ulongest, NULL },
 451   { NULL, GDB_XML_AF_NONE, NULL, NULL }
 452 };
 453
 454 static const struct gdb_xml_attribute feature_attributes[] = {
 455   { "name", GDB_XML_AF_NONE, NULL, NULL },
 456   { NULL, GDB_XML_AF_NONE, NULL, NULL }
 457 };
 458
 459 static const struct gdb_xml_element feature_children[] = {
 460   { "reg", reg_attributes, NULL,
 461     GDB_XML_EF_OPTIONAL | GDB_XML_EF_REPEATABLE,
 462     tdesc_start_reg, NULL },
 463   { "struct", struct_union_attributes, struct_union_children,
 464     GDB_XML_EF_OPTIONAL | GDB_XML_EF_REPEATABLE,
 465     tdesc_start_struct, NULL },
 466   { "union", struct_union_attributes, struct_union_children,
 467     GDB_XML_EF_OPTIONAL | GDB_XML_EF_REPEATABLE,
 468     tdesc_start_union, NULL },
 469   { "flags", flags_attributes, struct_union_children,
 470     GDB_XML_EF_OPTIONAL | GDB_XML_EF_REPEATABLE,
 471     tdesc_start_flags, NULL },
 472   { "vector", vector_attributes, NULL,
 473     GDB_XML_EF_OPTIONAL | GDB_XML_EF_REPEATABLE,
 474     tdesc_start_vector, NULL },
 475   { NULL, NULL, NULL, GDB_XML_EF_NONE, NULL, NULL }
 476 };
 477
 478 static const struct gdb_xml_attribute target_attributes[] = {
 479   { "version", GDB_XML_AF_NONE, NULL, NULL },
 480   { NULL, GDB_XML_AF_NONE, NULL, NULL }
 481 };
 482
 483 static const struct gdb_xml_element target_children[] = {
 484   { "architecture", NULL, NULL, GDB_XML_EF_OPTIONAL,
 485     NULL, tdesc_end_arch },
 486   { "osabi", NULL, NULL, GDB_XML_EF_OPTIONAL,
 487     NULL, tdesc_end_osabi },
 488   { "compatible", NULL, NULL, GDB_XML_EF_OPTIONAL | GDB_XML_EF_REPEATABLE,
 489     NULL, tdesc_end_compatible },
 490   { "feature", feature_attributes, feature_children,
 491     GDB_XML_EF_OPTIONAL | GDB_XML_EF_REPEATABLE,
 492     tdesc_start_feature, NULL },
 493   { NULL, NULL, NULL, GDB_XML_EF_NONE, NULL, NULL }
 494 };
 495
 496 static const struct gdb_xml_element tdesc_elements[] = {
 497   { "target", target_attributes, target_children, GDB_XML_EF_NONE,
 498     tdesc_start_target, NULL },
 499   { NULL, NULL, NULL, GDB_XML_EF_NONE, NULL, NULL }
 500 };
 501
 502 /* Parse DOCUMENT into a target description and return it.  */
 503
 504 static struct target_desc *
 505 tdesc_parse_xml (const char *document, xml_fetch_another fetcher,
 506                  void *fetcher_baton)
 507 {
 508   struct cleanup *back_to, *result_cleanup;
 509   struct tdesc_parsing_data data;
 510   struct tdesc_xml_cache *cache;
 511   char *expanded_text;
 512   int ix;
 513
 514   /* Expand all XInclude directives.  */
 515   expanded_text = xml_process_xincludes (_("target description"),
 516                                          document, fetcher, fetcher_baton, 0);
 517   if (expanded_text == NULL)
 518     {
 519       warning (_("Could not load XML target description; ignoring"));
 520       return NULL;
 521     }
 522
 523   /* Check for an exact match in the list of descriptions we have
 524      previously parsed.  strcmp is a slightly inefficient way to
 525      do this; an SHA-1 checksum would work as well.  */
 526   for (ix = 0; VEC_iterate (tdesc_xml_cache_s, xml_cache, ix, cache); ix++)
 527     if (strcmp (cache->xml_document, expanded_text) == 0)
 528       {
 529        xfree (expanded_text);
 530        return cache->tdesc;
 531       }
 532
 533   back_to = make_cleanup (null_cleanup, NULL);
 534
 535   memset (&data, 0, sizeof (struct tdesc_parsing_data));
 536   data.tdesc = allocate_target_description ();
 537   result_cleanup = make_cleanup_free_target_description (data.tdesc);
 538   make_cleanup (xfree, expanded_text);
 539
 540   if (gdb_xml_parse_quick (_("target description"), "gdb-target.dtd",
 541                            tdesc_elements, expanded_text, &data) == 0)
 542     {
 543       /* Parsed successfully.  */
 544       struct tdesc_xml_cache new_cache;
 545
 546       new_cache.xml_document = expanded_text;
 547       new_cache.tdesc = data.tdesc;
 548       VEC_safe_push (tdesc_xml_cache_s, xml_cache, &new_cache);
 549       discard_cleanups (result_cleanup);
 550       do_cleanups (back_to);
 551       return data.tdesc;
 552     }
 553   else
 554     {
 555       warning (_("Could not load XML target description; ignoring"));
 556       do_cleanups (back_to);
 557       return NULL;
 558     }
 559 }
 560 #endif /* HAVE_LIBEXPAT */
 561 \f
 562
 563 /* Read an XML target description from FILENAME.  Parse it, and return
 564    the parsed description.  */
 565
 566 const struct target_desc *
 567 file_read_description_xml (const char *filename)
 568 {
 569   struct target_desc *tdesc;
 570   char *tdesc_str;
 571   struct cleanup *back_to;
 572   char *dirname;
 573
 574   tdesc_str = xml_fetch_content_from_file (filename, NULL);
 575   if (tdesc_str == NULL)
 576     {
 577       warning (_("Could not open \"%s\""), filename);
 578       return NULL;
 579     }
 580
 581   back_to = make_cleanup (xfree, tdesc_str);
 582
 583   dirname = ldirname (filename);
 584   if (dirname != NULL)
 585     make_cleanup (xfree, dirname);
 586
 587   tdesc = tdesc_parse_xml (tdesc_str, xml_fetch_content_from_file, dirname);
 588   do_cleanups (back_to);
 589
 590   return tdesc;
 591 }
 592
 593 /* Read a string representation of available features from the target,
 594    using TARGET_OBJECT_AVAILABLE_FEATURES.  The returned string is
 595    malloc allocated and NUL-terminated.  NAME should be a non-NULL
 596    string identifying the XML document we want; the top level document
 597    is "target.xml".  Other calls may be performed for the DTD or
 598    for <xi:include>.  */
 599
 600 static char *
 601 fetch_available_features_from_target (const char *name, void *baton_)
 602 {
 603   struct target_ops *ops = baton_;
 604
 605   /* Read this object as a string.  This ensures that a NUL
 606      terminator is added.  */
 607   return target_read_stralloc (ops,
 608                                TARGET_OBJECT_AVAILABLE_FEATURES,
 609                                name);
 610 }
 611 \f
 612
 613 /* Read an XML target description using OPS.  Parse it, and return the
 614    parsed description.  */
 615
 616 const struct target_desc *
 617 target_read_description_xml (struct target_ops *ops)
 618 {
 619   struct target_desc *tdesc;
 620   char *tdesc_str;
 621   struct cleanup *back_to;
 622
 623   tdesc_str = fetch_available_features_from_target ("target.xml", ops);
 624   if (tdesc_str == NULL)
 625     return NULL;
 626
 627   back_to = make_cleanup (xfree, tdesc_str);
 628   tdesc = tdesc_parse_xml (tdesc_str,
 629                            fetch_available_features_from_target,
 630                            ops);
 631   do_cleanups (back_to);
 632
 633   return tdesc;
 634 }