buildtools/wafsamba/symbols.py

   1 # a waf tool to extract symbols from object files or libraries
   2 # using nm, producing a set of exposed defined/undefined symbols
   3
   4 import Utils, Build, subprocess, Logs, re
   5 from samba_wildcard import fake_build_environment
   6 from samba_utils import *
   7
   8 # these are the data structures used in symbols.py:
   9 #
  10 # bld.env.symbol_map : dictionary mapping public symbol names to list of
  11 #                      subsystem names where that symbol exists
  12 #
  13 # t.in_library       : list of libraries that t is in
  14 #
  15 # bld.env.public_symbols: set of public symbols for each subsystem
  16 # bld.env.used_symbols  : set of used symbols for each subsystem
  17 #
  18 # bld.env.syslib_symbols: dictionary mapping system library name to set of symbols
  19 #                         for that library
  20 # bld.env.library_dict  : dictionary mapping built library paths to subsystem names
  21 #
  22 # LOCAL_CACHE(bld, 'TARGET_TYPE') : dictionary mapping subsystem name to target type
  23
  24
  25 def symbols_extract(bld, objfiles, dynamic=False):
  26     '''extract symbols from objfile, returning a dictionary containing
  27        the set of undefined and public symbols for each file'''
  28
  29     ret = {}
  30
  31     # see if we can get some results from the nm cache
  32     if not bld.env.nm_cache:
  33         bld.env.nm_cache = {}
  34
  35     objfiles = set(objfiles).copy()
  36
  37     remaining = set()
  38     for obj in objfiles:
  39         if obj in bld.env.nm_cache:
  40             ret[obj] = bld.env.nm_cache[obj].copy()
  41         else:
  42             remaining.add(obj)
  43     objfiles = remaining
  44
  45     if len(objfiles) == 0:
  46         return ret
  47
  48     cmd = ["nm"]
  49     if dynamic:
  50         # needed for some .so files
  51         cmd.append("-D")
  52     cmd.extend(list(objfiles))
  53
  54     nmpipe = subprocess.Popen(cmd, stdout=subprocess.PIPE).stdout
  55     if len(objfiles) == 1:
  56         filename = list(objfiles)[0]
  57         ret[filename] = { "PUBLIC": set(), "UNDEFINED" : set()}
  58
  59     for line in nmpipe:
  60         line = line.strip()
  61         if line.endswith(':'):
  62             filename = line[:-1]
  63             ret[filename] = { "PUBLIC": set(), "UNDEFINED" : set() }
  64             continue
  65         cols = line.split(" ")
  66         if cols == ['']:
  67             continue
  68         # see if the line starts with an address
  69         if len(cols) == 3:
  70             symbol_type = cols[1]
  71             symbol = cols[2]
  72         else:
  73             symbol_type = cols[0]
  74             symbol = cols[1]
  75         if symbol_type in "BDGTRVWSi":
  76             # its a public symbol
  77             ret[filename]["PUBLIC"].add(symbol)
  78         elif symbol_type in "U":
  79             ret[filename]["UNDEFINED"].add(symbol)
  80
  81     # add to the cache
  82     for obj in objfiles:
  83         if obj in ret:
  84             bld.env.nm_cache[obj] = ret[obj].copy()
  85         else:
  86             bld.env.nm_cache[obj] = { "PUBLIC": set(), "UNDEFINED" : set() }
  87
  88     return ret
  89
  90
  91 def real_name(name):
  92     if name.find(".objlist") != -1:
  93         name = name[:-8]
  94     return name
  95
  96
  97 def find_ldd_path(bld, libname, binary):
  98     '''find the path to the syslib we will link against'''
  99     ret = None
 100     if not bld.env.syslib_paths:
 101         bld.env.syslib_paths = {}
 102     if libname in bld.env.syslib_paths:
 103         return bld.env.syslib_paths[libname]
 104
 105     lddpipe = subprocess.Popen(['ldd', binary], stdout=subprocess.PIPE).stdout
 106     for line in lddpipe:
 107         line = line.strip()
 108         cols = line.split(" ")
 109         if len(cols) < 3 or cols[1] != "=>":
 110             continue
 111         if cols[0].startswith("libc."):
 112             # save this one too
 113             bld.env.libc_path = cols[2]
 114         if cols[0].startswith(libname):
 115             ret = cols[2]
 116     bld.env.syslib_paths[libname] = ret
 117     return ret
 118
 119
 120 # some regular expressions for parsing readelf output
 121 re_sharedlib = re.compile('Shared library: \[(.*)\]')
 122 re_rpath     = re.compile('Library rpath: \[(.*)\]')
 123
 124 def get_libs(bld, binname):
 125     '''find the list of linked libraries for any binary or library
 126     binname is the path to the binary/library on disk
 127
 128     We do this using readelf instead of ldd as we need to avoid recursing
 129     into system libraries
 130     '''
 131
 132     # see if we can get the result from the ldd cache
 133     if not bld.env.lib_cache:
 134         bld.env.lib_cache = {}
 135     if binname in bld.env.lib_cache:
 136         return bld.env.lib_cache[binname].copy()
 137
 138     rpath = []
 139     libs = set()
 140
 141     elfpipe = subprocess.Popen(['readelf', '--dynamic', binname], stdout=subprocess.PIPE).stdout
 142     for line in elfpipe:
 143         m = re_sharedlib.search(line)
 144         if m:
 145             libs.add(m.group(1))
 146         m = re_rpath.search(line)
 147         if m:
 148             rpath.extend(m.group(1).split(":"))
 149
 150     ret = set()
 151     for lib in libs:
 152         found = False
 153         for r in rpath:
 154             path = os.path.join(r, lib)
 155             if os.path.exists(path):
 156                 ret.add(os.path.realpath(path))
 157                 found = True
 158                 break
 159         if not found:
 160             # we didn't find this lib using rpath. It is probably a system
 161             # library, so to find the path to it we either need to use ldd
 162             # or we need to start parsing /etc/ld.so.conf* ourselves. We'll
 163             # use ldd for now, even though it is slow
 164             path = find_ldd_path(bld, lib, binname)
 165             if path:
 166                 ret.add(os.path.realpath(path))
 167
 168     bld.env.lib_cache[binname] = ret.copy()
 169
 170     return ret
 171
 172
 173 def get_libs_recursive(bld, binname, seen):
 174     '''find the recursive list of linked libraries for any binary or library
 175     binname is the path to the binary/library on disk. seen is a set used
 176     to prevent loops
 177     '''
 178     if binname in seen:
 179         return set()
 180     ret = get_libs(bld, binname)
 181     seen.add(binname)
 182     for lib in ret:
 183         # we don't want to recurse into system libraries. If a system
 184         # library that we use (eg. libcups) happens to use another library
 185         # (such as libkrb5) which contains common symbols with our own
 186         # libraries, then that is not an error
 187         if lib in bld.env.library_dict:
 188             ret = ret.union(get_libs_recursive(bld, lib, seen))
 189     return ret
 190
 191
 192
 193 def find_syslib_path(bld, libname, deps):
 194     '''find the path to the syslib we will link against'''
 195     # the strategy is to use the targets that depend on the library, and run ldd
 196     # on it to find the real location of the library that is used
 197
 198     linkpath = deps[0].link_task.outputs[0].abspath(bld.env)
 199
 200     if libname == "python":
 201         libname += bld.env.PYTHON_VERSION
 202
 203     return find_ldd_path(bld, "lib%s" % libname.lower(), linkpath)
 204
 205
 206 def build_symbol_sets(bld, tgt_list):
 207     '''build the public_symbols and undefined_symbols attributes for each target'''
 208
 209     if bld.env.public_symbols:
 210         return
 211
 212     objlist = []  # list of object file
 213     objmap = {}   # map from object filename to target (subsystem) name
 214
 215     for t in tgt_list:
 216         t.public_symbols = set()
 217         t.undefined_symbols = set()
 218         t.used_symbols = set()
 219         for tsk in getattr(t, 'compiled_tasks', []):
 220             for output in tsk.outputs:
 221                 objpath = output.abspath(bld.env)
 222                 objlist.append(objpath)
 223                 objmap[objpath] = t
 224
 225     symbols = symbols_extract(bld, objlist)
 226     for obj in objlist:
 227         t = objmap[obj]
 228         t.public_symbols = t.public_symbols.union(symbols[obj]["PUBLIC"])
 229         t.undefined_symbols = t.undefined_symbols.union(symbols[obj]["UNDEFINED"])
 230         t.used_symbols = t.used_symbols.union(symbols[obj]["UNDEFINED"])
 231
 232     t.undefined_symbols = t.undefined_symbols.difference(t.public_symbols)
 233
 234     # and the reverse map of public symbols to subsystem name
 235     bld.env.symbol_map = {}
 236
 237     for t in tgt_list:
 238         for s in t.public_symbols:
 239             if not s in bld.env.symbol_map:
 240                 bld.env.symbol_map[s] = []
 241             bld.env.symbol_map[s].append(real_name(t.sname))
 242
 243     targets = LOCAL_CACHE(bld, 'TARGET_TYPE')
 244
 245     bld.env.public_symbols = {}
 246     for t in tgt_list:
 247         name = real_name(t.sname)
 248         if name in bld.env.public_symbols:
 249             bld.env.public_symbols[name] = bld.env.public_symbols[name].union(t.public_symbols)
 250         else:
 251             bld.env.public_symbols[name] = t.public_symbols
 252         if t.samba_type == 'LIBRARY':
 253             for dep in t.add_objects:
 254                 t2 = bld.name_to_obj(dep, bld.env)
 255                 bld.ASSERT(t2 is not None, "Library '%s' has unknown dependency '%s'" % (name, dep))
 256                 bld.env.public_symbols[name] = bld.env.public_symbols[name].union(t2.public_symbols)
 257
 258     bld.env.used_symbols = {}
 259     for t in tgt_list:
 260         name = real_name(t.sname)
 261         if name in bld.env.used_symbols:
 262             bld.env.used_symbols[name] = bld.env.used_symbols[name].union(t.used_symbols)
 263         else:
 264             bld.env.used_symbols[name] = t.used_symbols
 265         if t.samba_type == 'LIBRARY':
 266             for dep in t.add_objects:
 267                 t2 = bld.name_to_obj(dep, bld.env)
 268                 bld.ASSERT(t2 is not None, "Library '%s' has unknown dependency '%s'" % (name, dep))
 269                 bld.env.used_symbols[name] = bld.env.used_symbols[name].union(t2.used_symbols)
 270
 271
 272 def build_library_dict(bld, tgt_list):
 273     '''build the library_dict dictionary'''
 274
 275     if bld.env.library_dict:
 276         return
 277
 278     bld.env.library_dict = {}
 279
 280     for t in tgt_list:
 281         if t.samba_type in [ 'LIBRARY', 'PYTHON' ]:
 282             linkpath = os.path.realpath(t.link_task.outputs[0].abspath(bld.env))
 283             bld.env.library_dict[linkpath] = t.sname
 284
 285
 286 def build_syslib_sets(bld, tgt_list):
 287     '''build the public_symbols for all syslibs'''
 288
 289     if bld.env.syslib_symbols:
 290         return
 291
 292     # work out what syslibs we depend on, and what targets those are used in
 293     syslibs = {}
 294     objmap = {}
 295     for t in tgt_list:
 296         if getattr(t, 'uselib', []) and t.samba_type in [ 'LIBRARY', 'BINARY', 'PYTHON' ]:
 297             for lib in t.uselib:
 298                 if lib in ['PYEMBED', 'PYEXT']:
 299                     lib = "python"
 300                 if not lib in syslibs:
 301                     syslibs[lib] = []
 302                 syslibs[lib].append(t)
 303
 304     # work out the paths to each syslib
 305     syslib_paths = []
 306     for lib in syslibs:
 307         path = find_syslib_path(bld, lib, syslibs[lib])
 308         if path is None:
 309             Logs.warn("Unable to find syslib path for %s" % lib)
 310         if path is not None:
 311             syslib_paths.append(path)
 312             objmap[path] = lib.lower()
 313
 314     # add in libc
 315     syslib_paths.append(bld.env.libc_path)
 316     objmap[bld.env.libc_path] = 'c'
 317
 318     symbols = symbols_extract(bld, syslib_paths, dynamic=True)
 319
 320     # keep a map of syslib names to public symbols
 321     bld.env.syslib_symbols = {}
 322     for lib in symbols:
 323         bld.env.syslib_symbols[lib] = symbols[lib]["PUBLIC"]
 324
 325     # add to the map of symbols to dependencies
 326     for lib in symbols:
 327         for sym in symbols[lib]["PUBLIC"]:
 328             if not sym in bld.env.symbol_map:
 329                 bld.env.symbol_map[sym] = []
 330             bld.env.symbol_map[sym].append(objmap[lib])
 331
 332     # keep the libc symbols as well, as these are useful for some of the
 333     # sanity checks
 334     bld.env.libc_symbols = symbols[bld.env.libc_path]["PUBLIC"]
 335
 336     # add to the combined map of dependency name to public_symbols
 337     for lib in bld.env.syslib_symbols:
 338         bld.env.public_symbols[objmap[lib]] = bld.env.syslib_symbols[lib]
 339
 340
 341 def build_autodeps(bld, t):
 342     '''build the set of dependencies for a target'''
 343     deps = set()
 344     name = real_name(t.sname)
 345
 346     targets    = LOCAL_CACHE(bld, 'TARGET_TYPE')
 347
 348     for sym in t.undefined_symbols:
 349         if sym in t.public_symbols:
 350             continue
 351         if sym in bld.env.symbol_map:
 352             depname = bld.env.symbol_map[sym]
 353             if depname == [ name ]:
 354                 # self dependencies aren't interesting
 355                 continue
 356             if t.in_library == depname:
 357                 # no need to depend on the library we are part of
 358                 continue
 359             if depname[0] in ['c', 'python']:
 360                 # these don't go into autodeps
 361                 continue
 362             if targets[depname[0]] in [ 'SYSLIB' ]:
 363                 deps.add(depname[0])
 364                 continue
 365             t2 = bld.name_to_obj(depname[0], bld.env)
 366             if len(t2.in_library) != 1:
 367                 deps.add(depname[0])
 368                 continue
 369             if t2.in_library == t.in_library:
 370                 # if we're part of the same library, we don't need to autodep
 371                 continue
 372             deps.add(t2.in_library[0])
 373     t.autodeps = deps
 374
 375
 376 def build_library_names(bld, tgt_list):
 377     '''add a in_library attribute to all targets that are part of a library'''
 378
 379     if bld.env.done_build_library_names:
 380         return
 381
 382     for t in tgt_list:
 383         t.in_library = []
 384
 385     for t in tgt_list:
 386         if t.samba_type in [ 'LIBRARY' ]:
 387             for obj in t.samba_deps_extended:
 388                 t2 = bld.name_to_obj(obj, bld.env)
 389                 if t2 and t2.samba_type in [ 'SUBSYSTEM', 'ASN1' ]:
 390                     if not t.sname in t2.in_library:
 391                         t2.in_library.append(t.sname)
 392     bld.env.done_build_library_names = True
 393
 394
 395 def check_library_deps(bld, t):
 396     '''check that all the autodeps that have mutual dependency of this
 397     target are in the same library as the target'''
 398
 399     name = real_name(t.sname)
 400
 401     if len(t.in_library) > 1:
 402         Logs.warn("WARNING: Target '%s' in multiple libraries: %s" % (t.sname, t.in_library))
 403
 404     for dep in t.autodeps:
 405         t2 = bld.name_to_obj(dep, bld.env)
 406         if t2 is None:
 407             continue
 408         for dep2 in t2.autodeps:
 409             if dep2 == name and t.in_library != t2.in_library:
 410                 Logs.warn("WARNING: mutual dependency %s <=> %s" % (name, real_name(t2.sname)))
 411                 Logs.warn("Libraries should match. %s != %s" % (t.in_library, t2.in_library))
 412                 # raise Utils.WafError("illegal mutual dependency")
 413
 414
 415 def check_syslib_collisions(bld, tgt_list):
 416     '''check if a target has any symbol collisions with a syslib
 417
 418     We do not want any code in Samba to use a symbol name from a
 419     system library. The chance of that causing problems is just too
 420     high. Note that libreplace uses a rep_XX approach of renaming
 421     symbols via macros
 422     '''
 423
 424     has_error = False
 425     for t in tgt_list:
 426         for lib in bld.env.syslib_symbols:
 427             common = t.public_symbols.intersection(bld.env.syslib_symbols[lib])
 428             if common:
 429                 Logs.error("ERROR: Target '%s' has symbols '%s' which is also in syslib '%s'" % (t.sname, common, lib))
 430                 has_error = True
 431     if has_error:
 432         raise Utils.WafError("symbols in common with system libraries")
 433
 434
 435 def check_dependencies(bld, t):
 436     '''check for depenencies that should be changed'''
 437
 438     if bld.name_to_obj(t.sname + ".objlist", bld.env):
 439         return
 440
 441     targets = LOCAL_CACHE(bld, 'TARGET_TYPE')
 442
 443     remaining = t.undefined_symbols.copy()
 444     remaining = remaining.difference(t.public_symbols)
 445
 446     sname = real_name(t.sname)
 447
 448     deps = set(t.samba_deps)
 449     for d in t.samba_deps:
 450         if targets[d] in [ 'EMPTY', 'DISABLED', 'SYSLIB', 'GENERATOR' ]:
 451             continue
 452         bld.ASSERT(d in bld.env.public_symbols, "Failed to find symbol list for dependency '%s'" % d)
 453         diff = remaining.intersection(bld.env.public_symbols[d])
 454         if not diff and targets[sname] != 'LIBRARY':
 455             Logs.info("Target '%s' has no dependency on %s" % (sname, d))
 456         else:
 457             remaining = remaining.difference(diff)
 458
 459     t.unsatisfied_symbols = set()
 460     needed = {}
 461     for sym in remaining:
 462         if sym in bld.env.symbol_map:
 463             dep = bld.env.symbol_map[sym]
 464             if not dep[0] in needed:
 465                 needed[dep[0]] = set()
 466             needed[dep[0]].add(sym)
 467         else:
 468             t.unsatisfied_symbols.add(sym)
 469
 470     for dep in needed:
 471         Logs.info("Target '%s' should add dep '%s' for symbols %s" % (sname, dep, " ".join(needed[dep])))
 472
 473
 474
 475 def check_syslib_dependencies(bld, t):
 476     '''check for syslib depenencies'''
 477
 478     if bld.name_to_obj(t.sname + ".objlist", bld.env):
 479         return
 480
 481     sname = real_name(t.sname)
 482
 483     remaining = set()
 484
 485     features = TO_LIST(t.features)
 486     if 'pyembed' in features or 'pyext' in features:
 487         if 'python' in bld.env.public_symbols:
 488             t.unsatisfied_symbols = t.unsatisfied_symbols.difference(bld.env.public_symbols['python'])
 489
 490     needed = {}
 491     for sym in t.unsatisfied_symbols:
 492         if sym in bld.env.symbol_map:
 493             dep = bld.env.symbol_map[sym][0]
 494             if dep == 'c':
 495                 continue
 496             if not dep in needed:
 497                 needed[dep] = set()
 498             needed[dep].add(sym)
 499         else:
 500             remaining.add(sym)
 501
 502     for dep in needed:
 503         Logs.info("Target '%s' should add syslib dep '%s' for symbols %s" % (sname, dep, " ".join(needed[dep])))
 504
 505     if remaining:
 506         debug("deps: Target '%s' has unsatisfied symbols: %s" % (sname, " ".join(remaining)))
 507
 508
 509
 510 def symbols_symbolcheck(task):
 511     '''check the internal dependency lists'''
 512     bld = task.env.bld
 513     tgt_list = get_tgt_list(bld)
 514
 515     build_symbol_sets(bld, tgt_list)
 516     build_library_names(bld, tgt_list)
 517
 518     for t in tgt_list:
 519         t.autodeps = set()
 520         if getattr(t, 'source', ''):
 521             build_autodeps(bld, t)
 522
 523     for t in tgt_list:
 524         check_dependencies(bld, t)
 525
 526     for t in tgt_list:
 527         check_library_deps(bld, t)
 528
 529 def symbols_syslibcheck(task):
 530     '''check the syslib dependencies'''
 531     bld = task.env.bld
 532     tgt_list = get_tgt_list(bld)
 533
 534     build_syslib_sets(bld, tgt_list)
 535     check_syslib_collisions(bld, tgt_list)
 536
 537     for t in tgt_list:
 538         check_syslib_dependencies(bld, t)
 539
 540
 541 def symbols_whyneeded(task):
 542     """check why 'target' needs to link to 'subsystem'"""
 543     bld = task.env.bld
 544     tgt_list = get_tgt_list(bld)
 545
 546     why = Options.options.WHYNEEDED.split(":")
 547     if len(why) != 2:
 548         raise Utils.WafError("usage: WHYNEEDED=TARGET:DEPENDENCY")
 549     target = why[0]
 550     subsystem = why[1]
 551
 552     build_symbol_sets(bld, tgt_list)
 553     build_library_names(bld, tgt_list)
 554     build_syslib_sets(bld, tgt_list)
 555
 556     Logs.info("Checking why %s needs to link to %s" % (target, subsystem))
 557     if not target in bld.env.used_symbols:
 558         Logs.warn("unable to find target '%s' in used_symbols dict" % target)
 559         return
 560     if not subsystem in bld.env.public_symbols:
 561         Logs.warn("unable to find subsystem '%s' in public_symbols dict" % subsystem)
 562         return
 563     overlap = bld.env.used_symbols[target].intersection(bld.env.public_symbols[subsystem])
 564     if not overlap:
 565         Logs.info("target '%s' doesn't use any public symbols from '%s'" % (target, subsystem))
 566     else:
 567         Logs.info("target '%s' uses symbols %s from '%s'" % (target, overlap, subsystem))
 568
 569
 570 def report_duplicate(bld, binname, sym, libs, fail_on_error):
 571     '''report duplicated symbols'''
 572     if sym in ['_init', '_fini']:
 573         return
 574     libnames = []
 575     for lib in libs:
 576         if lib in bld.env.library_dict:
 577             libnames.append(bld.env.library_dict[lib])
 578         else:
 579             libnames.append(lib)
 580     if fail_on_error:
 581         raise Utils.WafError("%s: Symbol %s linked in multiple libraries %s" % (binname, sym, libnames))
 582     else:
 583         print("%s: Symbol %s linked in multiple libraries %s" % (binname, sym, libnames))
 584
 585
 586 def symbols_dupcheck_binary(bld, binname, fail_on_error):
 587     '''check for duplicated symbols in one binary'''
 588
 589     libs = get_libs_recursive(bld, binname, set())
 590     symlist = symbols_extract(bld, libs, dynamic=True)
 591
 592     symmap = {}
 593     for libpath in symlist:
 594         for sym in symlist[libpath]['PUBLIC']:
 595             if not sym in symmap:
 596                 symmap[sym] = set()
 597             symmap[sym].add(libpath)
 598     for sym in symmap:
 599         if len(symmap[sym]) > 1:
 600             for libpath in symmap[sym]:
 601                 if libpath in bld.env.library_dict:
 602                     report_duplicate(bld, binname, sym, symmap[sym], fail_on_error)
 603                     break
 604
 605 def symbols_dupcheck(task, fail_on_error=False):
 606     '''check for symbols defined in two different subsystems'''
 607     bld = task.env.bld
 608     tgt_list = get_tgt_list(bld)
 609
 610     targets = LOCAL_CACHE(bld, 'TARGET_TYPE')
 611
 612     build_library_dict(bld, tgt_list)
 613     for t in tgt_list:
 614         if t.samba_type == 'BINARY':
 615             binname = os_path_relpath(t.link_task.outputs[0].abspath(bld.env), os.getcwd())
 616             symbols_dupcheck_binary(bld, binname, fail_on_error)
 617
 618
 619 def symbols_dupcheck_fatal(task):
 620     '''check for symbols defined in two different subsystems (and fail if duplicates are found)'''
 621     symbols_dupcheck(task, fail_on_error=True)
 622
 623
 624 def SYMBOL_CHECK(bld):
 625     '''check our dependency lists'''
 626     if Options.options.SYMBOLCHECK:
 627         bld.SET_BUILD_GROUP('symbolcheck')
 628         task = bld(rule=symbols_symbolcheck, always=True, name='symbol checking')
 629         task.env.bld = bld
 630
 631         bld.SET_BUILD_GROUP('syslibcheck')
 632         task = bld(rule=symbols_syslibcheck, always=True, name='syslib checking')
 633         task.env.bld = bld
 634
 635         bld.SET_BUILD_GROUP('syslibcheck')
 636         task = bld(rule=symbols_dupcheck, always=True, name='symbol duplicate checking')
 637         task.env.bld = bld
 638
 639     if Options.options.WHYNEEDED:
 640         bld.SET_BUILD_GROUP('syslibcheck')
 641         task = bld(rule=symbols_whyneeded, always=True, name='check why a dependency is needed')
 642         task.env.bld = bld
 643
 644
 645 Build.BuildContext.SYMBOL_CHECK = SYMBOL_CHECK
 646
 647 def DUP_SYMBOL_CHECK(bld):
 648     if Options.options.DUP_SYMBOLCHECK and bld.env.DEVELOPER and not bld.env.BUILD_FARM:
 649         '''check for duplicate symbols'''
 650         bld.SET_BUILD_GROUP('syslibcheck')
 651         task = bld(rule=symbols_dupcheck_fatal, always=True, name='symbol duplicate checking')
 652         task.env.bld = bld
 653
 654 Build.BuildContext.DUP_SYMBOL_CHECK = DUP_SYMBOL_CHECK