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 os, re, subprocess
   5 from waflib import Utils, Build, Options, Logs, Errors
   6 from waflib.Logs import debug
   7 from samba_utils import TO_LIST, LOCAL_CACHE, get_tgt_list
   8
   9 # these are the data structures used in symbols.py:
  10 #
  11 # bld.env.symbol_map : dictionary mapping public symbol names to list of
  12 #                      subsystem names where that symbol exists
  13 #
  14 # t.in_library       : list of libraries that t is in
  15 #
  16 # bld.env.public_symbols: set of public symbols for each subsystem
  17 # bld.env.used_symbols  : set of used symbols for each subsystem
  18 #
  19 # bld.env.syslib_symbols: dictionary mapping system library name to set of symbols
  20 #                         for that library
  21 # bld.env.library_dict  : dictionary mapping built library paths to subsystem names
  22 #
  23 # LOCAL_CACHE(bld, 'TARGET_TYPE') : dictionary mapping subsystem name to target type
  24
  25
  26 def symbols_extract(bld, objfiles, dynamic=False):
  27     '''extract symbols from objfile, returning a dictionary containing
  28        the set of undefined and public symbols for each file'''
  29
  30     ret = {}
  31
  32     # see if we can get some results from the nm cache
  33     if not bld.env.nm_cache:
  34         bld.env.nm_cache = {}
  35
  36     objfiles = set(objfiles).copy()
  37
  38     remaining = set()
  39     for obj in objfiles:
  40         if obj in bld.env.nm_cache:
  41             ret[obj] = bld.env.nm_cache[obj].copy()
  42         else:
  43             remaining.add(obj)
  44     objfiles = remaining
  45
  46     if len(objfiles) == 0:
  47         return ret
  48
  49     cmd = ["nm"]
  50     if dynamic:
  51         # needed for some .so files
  52         cmd.append("-D")
  53     cmd.extend(list(objfiles))
  54
  55     nmpipe = subprocess.Popen(cmd, stdout=subprocess.PIPE).stdout
  56     if len(objfiles) == 1:
  57         filename = list(objfiles)[0]
  58         ret[filename] = { "PUBLIC": set(), "UNDEFINED" : set()}
  59
  60     for line in nmpipe:
  61         line = line.strip()
  62         if line.endswith(b':'):
  63             filename = line[:-1]
  64             ret[filename] = { "PUBLIC": set(), "UNDEFINED" : set() }
  65             continue
  66         cols = line.split(b" ")
  67         if cols == [b'']:
  68             continue
  69         # see if the line starts with an address
  70         if len(cols) == 3:
  71             symbol_type = cols[1]
  72             symbol = cols[2]
  73         else:
  74             symbol_type = cols[0]
  75             symbol = cols[1]
  76         if symbol_type in b"BDGTRVWSi":
  77             # its a public symbol
  78             ret[filename]["PUBLIC"].add(symbol)
  79         elif symbol_type in b"U":
  80             ret[filename]["UNDEFINED"].add(symbol)
  81
  82     # add to the cache
  83     for obj in objfiles:
  84         if obj in ret:
  85             bld.env.nm_cache[obj] = ret[obj].copy()
  86         else:
  87             bld.env.nm_cache[obj] = { "PUBLIC": set(), "UNDEFINED" : set() }
  88
  89     return ret
  90
  91
  92 def real_name(name):
  93     if name.find(".objlist") != -1:
  94         name = name[:-8]
  95     return name
  96
  97
  98 def find_ldd_path(bld, libname, binary):
  99     '''find the path to the syslib we will link against'''
 100     ret = None
 101     if not bld.env.syslib_paths:
 102         bld.env.syslib_paths = {}
 103     if libname in bld.env.syslib_paths:
 104         return bld.env.syslib_paths[libname]
 105
 106     lddpipe = subprocess.Popen(['ldd', binary], stdout=subprocess.PIPE).stdout
 107     for line in lddpipe:
 108         line = line.strip()
 109         cols = line.split(b" ")
 110         if len(cols) < 3 or cols[1] != b"=>":
 111             continue
 112         if cols[0].startswith(b"libc."):
 113             # save this one too
 114             bld.env.libc_path = cols[2]
 115         if cols[0].startswith(libname):
 116             ret = cols[2]
 117     bld.env.syslib_paths[libname] = ret
 118     return ret
 119
 120
 121 # some regular expressions for parsing readelf output
 122 re_sharedlib = re.compile(b'Shared library: \[(.*)\]')
 123 # output from readelf could be `Library rpath` or `Libray runpath`
 124 re_rpath     = re.compile(b'Library (rpath|runpath): \[(.*)\]')
 125
 126 def get_libs(bld, binname):
 127     '''find the list of linked libraries for any binary or library
 128     binname is the path to the binary/library on disk
 129
 130     We do this using readelf instead of ldd as we need to avoid recursing
 131     into system libraries
 132     '''
 133
 134     # see if we can get the result from the ldd cache
 135     if not bld.env.lib_cache:
 136         bld.env.lib_cache = {}
 137     if binname in bld.env.lib_cache:
 138         return bld.env.lib_cache[binname].copy()
 139
 140     rpath = []
 141     libs = set()
 142
 143     elfpipe = subprocess.Popen(['readelf', '--dynamic', binname], stdout=subprocess.PIPE).stdout
 144     for line in elfpipe:
 145         m = re_sharedlib.search(line)
 146         if m:
 147             libs.add(m.group(1))
 148         m = re_rpath.search(line)
 149         if m:
 150             # output from Popen is always bytestr even in py3
 151             rpath.extend(m.group(2).split(b":"))
 152
 153     ret = set()
 154     for lib in libs:
 155         found = False
 156         for r in rpath:
 157             path = os.path.join(r, lib)
 158             if os.path.exists(path):
 159                 ret.add(os.path.realpath(path))
 160                 found = True
 161                 break
 162         if not found:
 163             # we didn't find this lib using rpath. It is probably a system
 164             # library, so to find the path to it we either need to use ldd
 165             # or we need to start parsing /etc/ld.so.conf* ourselves. We'll
 166             # use ldd for now, even though it is slow
 167             path = find_ldd_path(bld, lib, binname)
 168             if path:
 169                 ret.add(os.path.realpath(path))
 170
 171     bld.env.lib_cache[binname] = ret.copy()
 172
 173     return ret
 174
 175
 176 def get_libs_recursive(bld, binname, seen):
 177     '''find the recursive list of linked libraries for any binary or library
 178     binname is the path to the binary/library on disk. seen is a set used
 179     to prevent loops
 180     '''
 181     if binname in seen:
 182         return set()
 183     ret = get_libs(bld, binname)
 184     seen.add(binname)
 185     for lib in ret:
 186         # we don't want to recurse into system libraries. If a system
 187         # library that we use (eg. libcups) happens to use another library
 188         # (such as libkrb5) which contains common symbols with our own
 189         # libraries, then that is not an error
 190         if lib in bld.env.library_dict:
 191             ret = ret.union(get_libs_recursive(bld, lib, seen))
 192     return ret
 193
 194
 195
 196 def find_syslib_path(bld, libname, deps):
 197     '''find the path to the syslib we will link against'''
 198     # the strategy is to use the targets that depend on the library, and run ldd
 199     # on it to find the real location of the library that is used
 200
 201     linkpath = deps[0].link_task.outputs[0].abspath(bld.env)
 202
 203     if libname == "python":
 204         libname += bld.env.PYTHON_VERSION
 205
 206     return find_ldd_path(bld, "lib%s" % libname.lower(), linkpath)
 207
 208
 209 def build_symbol_sets(bld, tgt_list):
 210     '''build the public_symbols and undefined_symbols attributes for each target'''
 211
 212     if bld.env.public_symbols:
 213         return
 214
 215     objlist = []  # list of object file
 216     objmap = {}   # map from object filename to target (subsystem) name
 217
 218     for t in tgt_list:
 219         t.public_symbols = set()
 220         t.undefined_symbols = set()
 221         t.used_symbols = set()
 222         for tsk in getattr(t, 'compiled_tasks', []):
 223             for output in tsk.outputs:
 224                 objpath = output.abspath(bld.env)
 225                 objlist.append(objpath)
 226                 objmap[objpath] = t
 227
 228     symbols = symbols_extract(bld, objlist)
 229     for obj in objlist:
 230         t = objmap[obj]
 231         t.public_symbols = t.public_symbols.union(symbols[obj]["PUBLIC"])
 232         t.undefined_symbols = t.undefined_symbols.union(symbols[obj]["UNDEFINED"])
 233         t.used_symbols = t.used_symbols.union(symbols[obj]["UNDEFINED"])
 234
 235     t.undefined_symbols = t.undefined_symbols.difference(t.public_symbols)
 236
 237     # and the reverse map of public symbols to subsystem name
 238     bld.env.symbol_map = {}
 239
 240     for t in tgt_list:
 241         for s in t.public_symbols:
 242             if not s in bld.env.symbol_map:
 243                 bld.env.symbol_map[s] = []
 244             bld.env.symbol_map[s].append(real_name(t.sname))
 245
 246     targets = LOCAL_CACHE(bld, 'TARGET_TYPE')
 247
 248     bld.env.public_symbols = {}
 249     for t in tgt_list:
 250         name = real_name(t.sname)
 251         if name in bld.env.public_symbols:
 252             bld.env.public_symbols[name] = bld.env.public_symbols[name].union(t.public_symbols)
 253         else:
 254             bld.env.public_symbols[name] = t.public_symbols
 255         if t.samba_type == 'LIBRARY':
 256             for dep in t.add_objects:
 257                 t2 = bld.get_tgen_by_name(dep)
 258                 bld.ASSERT(t2 is not None, "Library '%s' has unknown dependency '%s'" % (name, dep))
 259                 bld.env.public_symbols[name] = bld.env.public_symbols[name].union(t2.public_symbols)
 260
 261     bld.env.used_symbols = {}
 262     for t in tgt_list:
 263         name = real_name(t.sname)
 264         if name in bld.env.used_symbols:
 265             bld.env.used_symbols[name] = bld.env.used_symbols[name].union(t.used_symbols)
 266         else:
 267             bld.env.used_symbols[name] = t.used_symbols
 268         if t.samba_type == 'LIBRARY':
 269             for dep in t.add_objects:
 270                 t2 = bld.get_tgen_by_name(dep)
 271                 bld.ASSERT(t2 is not None, "Library '%s' has unknown dependency '%s'" % (name, dep))
 272                 bld.env.used_symbols[name] = bld.env.used_symbols[name].union(t2.used_symbols)
 273
 274
 275 def build_library_dict(bld, tgt_list):
 276     '''build the library_dict dictionary'''
 277
 278     if bld.env.library_dict:
 279         return
 280
 281     bld.env.library_dict = {}
 282
 283     for t in tgt_list:
 284         if t.samba_type in [ 'LIBRARY', 'PYTHON' ]:
 285             linkpath = os.path.realpath(t.link_task.outputs[0].abspath(bld.env))
 286             bld.env.library_dict[linkpath] = t.sname
 287
 288
 289 def build_syslib_sets(bld, tgt_list):
 290     '''build the public_symbols for all syslibs'''
 291
 292     if bld.env.syslib_symbols:
 293         return
 294
 295     # work out what syslibs we depend on, and what targets those are used in
 296     syslibs = {}
 297     objmap = {}
 298     for t in tgt_list:
 299         if getattr(t, 'uselib', []) and t.samba_type in [ 'LIBRARY', 'BINARY', 'PYTHON' ]:
 300             for lib in t.uselib:
 301                 if lib in ['PYEMBED', 'PYEXT']:
 302                     lib = "python"
 303                 if not lib in syslibs:
 304                     syslibs[lib] = []
 305                 syslibs[lib].append(t)
 306
 307     # work out the paths to each syslib
 308     syslib_paths = []
 309     for lib in syslibs:
 310         path = find_syslib_path(bld, lib, syslibs[lib])
 311         if path is None:
 312             Logs.warn("Unable to find syslib path for %s" % lib)
 313         if path is not None:
 314             syslib_paths.append(path)
 315             objmap[path] = lib.lower()
 316
 317     # add in libc
 318     syslib_paths.append(bld.env.libc_path)
 319     objmap[bld.env.libc_path] = 'c'
 320
 321     symbols = symbols_extract(bld, syslib_paths, dynamic=True)
 322
 323     # keep a map of syslib names to public symbols
 324     bld.env.syslib_symbols = {}
 325     for lib in symbols:
 326         bld.env.syslib_symbols[lib] = symbols[lib]["PUBLIC"]
 327
 328     # add to the map of symbols to dependencies
 329     for lib in symbols:
 330         for sym in symbols[lib]["PUBLIC"]:
 331             if not sym in bld.env.symbol_map:
 332                 bld.env.symbol_map[sym] = []
 333             bld.env.symbol_map[sym].append(objmap[lib])
 334
 335     # keep the libc symbols as well, as these are useful for some of the
 336     # sanity checks
 337     bld.env.libc_symbols = symbols[bld.env.libc_path]["PUBLIC"]
 338
 339     # add to the combined map of dependency name to public_symbols
 340     for lib in bld.env.syslib_symbols:
 341         bld.env.public_symbols[objmap[lib]] = bld.env.syslib_symbols[lib]
 342
 343
 344 def build_autodeps(bld, t):
 345     '''build the set of dependencies for a target'''
 346     deps = set()
 347     name = real_name(t.sname)
 348
 349     targets    = LOCAL_CACHE(bld, 'TARGET_TYPE')
 350
 351     for sym in t.undefined_symbols:
 352         if sym in t.public_symbols:
 353             continue
 354         if sym in bld.env.symbol_map:
 355             depname = bld.env.symbol_map[sym]
 356             if depname == [ name ]:
 357                 # self dependencies aren't interesting
 358                 continue
 359             if t.in_library == depname:
 360                 # no need to depend on the library we are part of
 361                 continue
 362             if depname[0] in ['c', 'python']:
 363                 # these don't go into autodeps
 364                 continue
 365             if targets[depname[0]] in [ 'SYSLIB' ]:
 366                 deps.add(depname[0])
 367                 continue
 368             t2 = bld.get_tgen_by_name(depname[0])
 369             if len(t2.in_library) != 1:
 370                 deps.add(depname[0])
 371                 continue
 372             if t2.in_library == t.in_library:
 373                 # if we're part of the same library, we don't need to autodep
 374                 continue
 375             deps.add(t2.in_library[0])
 376     t.autodeps = deps
 377
 378
 379 def build_library_names(bld, tgt_list):
 380     '''add a in_library attribute to all targets that are part of a library'''
 381
 382     if bld.env.done_build_library_names:
 383         return
 384
 385     for t in tgt_list:
 386         t.in_library = []
 387
 388     for t in tgt_list:
 389         if t.samba_type in [ 'LIBRARY' ]:
 390             for obj in t.samba_deps_extended:
 391                 t2 = bld.get_tgen_by_name(obj)
 392                 if t2 and t2.samba_type in [ 'SUBSYSTEM', 'ASN1' ]:
 393                     if not t.sname in t2.in_library:
 394                         t2.in_library.append(t.sname)
 395     bld.env.done_build_library_names = True
 396
 397
 398 def check_library_deps(bld, t):
 399     '''check that all the autodeps that have mutual dependency of this
 400     target are in the same library as the target'''
 401
 402     name = real_name(t.sname)
 403
 404     if len(t.in_library) > 1:
 405         Logs.warn("WARNING: Target '%s' in multiple libraries: %s" % (t.sname, t.in_library))
 406
 407     for dep in t.autodeps:
 408         t2 = bld.get_tgen_by_name(dep)
 409         if t2 is None:
 410             continue
 411         for dep2 in t2.autodeps:
 412             if dep2 == name and t.in_library != t2.in_library:
 413                 Logs.warn("WARNING: mutual dependency %s <=> %s" % (name, real_name(t2.sname)))
 414                 Logs.warn("Libraries should match. %s != %s" % (t.in_library, t2.in_library))
 415                 # raise Errors.WafError("illegal mutual dependency")
 416
 417
 418 def check_syslib_collisions(bld, tgt_list):
 419     '''check if a target has any symbol collisions with a syslib
 420
 421     We do not want any code in Samba to use a symbol name from a
 422     system library. The chance of that causing problems is just too
 423     high. Note that libreplace uses a rep_XX approach of renaming
 424     symbols via macros
 425     '''
 426
 427     has_error = False
 428     for t in tgt_list:
 429         for lib in bld.env.syslib_symbols:
 430             common = t.public_symbols.intersection(bld.env.syslib_symbols[lib])
 431             if common:
 432                 Logs.error("ERROR: Target '%s' has symbols '%s' which is also in syslib '%s'" % (t.sname, common, lib))
 433                 has_error = True
 434     if has_error:
 435         raise Errors.WafError("symbols in common with system libraries")
 436
 437
 438 def check_dependencies(bld, t):
 439     '''check for depenencies that should be changed'''
 440
 441     if bld.get_tgen_by_name(t.sname + ".objlist"):
 442         return
 443
 444     targets = LOCAL_CACHE(bld, 'TARGET_TYPE')
 445
 446     remaining = t.undefined_symbols.copy()
 447     remaining = remaining.difference(t.public_symbols)
 448
 449     sname = real_name(t.sname)
 450
 451     deps = set(t.samba_deps)
 452     for d in t.samba_deps:
 453         if targets[d] in [ 'EMPTY', 'DISABLED', 'SYSLIB', 'GENERATOR' ]:
 454             continue
 455         bld.ASSERT(d in bld.env.public_symbols, "Failed to find symbol list for dependency '%s'" % d)
 456         diff = remaining.intersection(bld.env.public_symbols[d])
 457         if not diff and targets[sname] != 'LIBRARY':
 458             Logs.info("Target '%s' has no dependency on %s" % (sname, d))
 459         else:
 460             remaining = remaining.difference(diff)
 461
 462     t.unsatisfied_symbols = set()
 463     needed = {}
 464     for sym in remaining:
 465         if sym in bld.env.symbol_map:
 466             dep = bld.env.symbol_map[sym]
 467             if not dep[0] in needed:
 468                 needed[dep[0]] = set()
 469             needed[dep[0]].add(sym)
 470         else:
 471             t.unsatisfied_symbols.add(sym)
 472
 473     for dep in needed:
 474         Logs.info("Target '%s' should add dep '%s' for symbols %s" % (sname, dep, " ".join(needed[dep])))
 475
 476
 477
 478 def check_syslib_dependencies(bld, t):
 479     '''check for syslib depenencies'''
 480
 481     if bld.get_tgen_by_name(t.sname + ".objlist"):
 482         return
 483
 484     sname = real_name(t.sname)
 485
 486     remaining = set()
 487
 488     features = TO_LIST(t.features)
 489     if 'pyembed' in features or 'pyext' in features:
 490         if 'python' in bld.env.public_symbols:
 491             t.unsatisfied_symbols = t.unsatisfied_symbols.difference(bld.env.public_symbols['python'])
 492
 493     needed = {}
 494     for sym in t.unsatisfied_symbols:
 495         if sym in bld.env.symbol_map:
 496             dep = bld.env.symbol_map[sym][0]
 497             if dep == 'c':
 498                 continue
 499             if not dep in needed:
 500                 needed[dep] = set()
 501             needed[dep].add(sym)
 502         else:
 503             remaining.add(sym)
 504
 505     for dep in needed:
 506         Logs.info("Target '%s' should add syslib dep '%s' for symbols %s" % (sname, dep, " ".join(needed[dep])))
 507
 508     if remaining:
 509         debug("deps: Target '%s' has unsatisfied symbols: %s" % (sname, " ".join(remaining)))
 510
 511
 512
 513 def symbols_symbolcheck(task):
 514     '''check the internal dependency lists'''
 515     bld = task.env.bld
 516     tgt_list = get_tgt_list(bld)
 517
 518     build_symbol_sets(bld, tgt_list)
 519     build_library_names(bld, tgt_list)
 520
 521     for t in tgt_list:
 522         t.autodeps = set()
 523         if getattr(t, 'source', ''):
 524             build_autodeps(bld, t)
 525
 526     for t in tgt_list:
 527         check_dependencies(bld, t)
 528
 529     for t in tgt_list:
 530         check_library_deps(bld, t)
 531
 532 def symbols_syslibcheck(task):
 533     '''check the syslib dependencies'''
 534     bld = task.env.bld
 535     tgt_list = get_tgt_list(bld)
 536
 537     build_syslib_sets(bld, tgt_list)
 538     check_syslib_collisions(bld, tgt_list)
 539
 540     for t in tgt_list:
 541         check_syslib_dependencies(bld, t)
 542
 543
 544 def symbols_whyneeded(task):
 545     """check why 'target' needs to link to 'subsystem'"""
 546     bld = task.env.bld
 547     tgt_list = get_tgt_list(bld)
 548
 549     why = Options.options.WHYNEEDED.split(":")
 550     if len(why) != 2:
 551         raise Errors.WafError("usage: WHYNEEDED=TARGET:DEPENDENCY")
 552     target = why[0]
 553     subsystem = why[1]
 554
 555     build_symbol_sets(bld, tgt_list)
 556     build_library_names(bld, tgt_list)
 557     build_syslib_sets(bld, tgt_list)
 558
 559     Logs.info("Checking why %s needs to link to %s" % (target, subsystem))
 560     if not target in bld.env.used_symbols:
 561         Logs.warn("unable to find target '%s' in used_symbols dict" % target)
 562         return
 563     if not subsystem in bld.env.public_symbols:
 564         Logs.warn("unable to find subsystem '%s' in public_symbols dict" % subsystem)
 565         return
 566     overlap = bld.env.used_symbols[target].intersection(bld.env.public_symbols[subsystem])
 567     if not overlap:
 568         Logs.info("target '%s' doesn't use any public symbols from '%s'" % (target, subsystem))
 569     else:
 570         Logs.info("target '%s' uses symbols %s from '%s'" % (target, overlap, subsystem))
 571
 572
 573 def report_duplicate(bld, binname, sym, libs, fail_on_error):
 574     '''report duplicated symbols'''
 575     if sym in ['_init', '_fini', '_edata', '_end', '__bss_start']:
 576         return
 577     libnames = []
 578     for lib in libs:
 579         if lib in bld.env.library_dict:
 580             libnames.append(bld.env.library_dict[lib])
 581         else:
 582             libnames.append(lib)
 583     if fail_on_error:
 584         raise Errors.WafError("%s: Symbol %s linked in multiple libraries %s" % (binname, sym, libnames))
 585     else:
 586         print("%s: Symbol %s linked in multiple libraries %s" % (binname, sym, libnames))
 587
 588
 589 def symbols_dupcheck_binary(bld, binname, fail_on_error):
 590     '''check for duplicated symbols in one binary'''
 591
 592     libs = get_libs_recursive(bld, binname, set())
 593     symlist = symbols_extract(bld, libs, dynamic=True)
 594
 595     symmap = {}
 596     for libpath in symlist:
 597         for sym in symlist[libpath]['PUBLIC']:
 598             if sym == '_GLOBAL_OFFSET_TABLE_':
 599                 continue
 600             if not sym in symmap:
 601                 symmap[sym] = set()
 602             symmap[sym].add(libpath)
 603     for sym in symmap:
 604         if len(symmap[sym]) > 1:
 605             for libpath in symmap[sym]:
 606                 if libpath in bld.env.library_dict:
 607                     report_duplicate(bld, binname, sym, symmap[sym], fail_on_error)
 608                     break
 609
 610 def symbols_dupcheck(task, fail_on_error=False):
 611     '''check for symbols defined in two different subsystems'''
 612     bld = task.env.bld
 613     tgt_list = get_tgt_list(bld)
 614
 615     targets = LOCAL_CACHE(bld, 'TARGET_TYPE')
 616
 617     build_library_dict(bld, tgt_list)
 618     for t in tgt_list:
 619         if t.samba_type == 'BINARY':
 620             binname = os.path.relpath(t.link_task.outputs[0].abspath(bld.env), os.getcwd())
 621             symbols_dupcheck_binary(bld, binname, fail_on_error)
 622
 623
 624 def symbols_dupcheck_fatal(task):
 625     '''check for symbols defined in two different subsystems (and fail if duplicates are found)'''
 626     symbols_dupcheck(task, fail_on_error=True)
 627
 628
 629 def SYMBOL_CHECK(bld):
 630     '''check our dependency lists'''
 631     if Options.options.SYMBOLCHECK:
 632         bld.SET_BUILD_GROUP('symbolcheck')
 633         task = bld(rule=symbols_symbolcheck, always=True, name='symbol checking')
 634         task.env.bld = bld
 635
 636         bld.SET_BUILD_GROUP('syslibcheck')
 637         task = bld(rule=symbols_syslibcheck, always=True, name='syslib checking')
 638         task.env.bld = bld
 639
 640         bld.SET_BUILD_GROUP('syslibcheck')
 641         task = bld(rule=symbols_dupcheck, always=True, name='symbol duplicate checking')
 642         task.env.bld = bld
 643
 644     if Options.options.WHYNEEDED:
 645         bld.SET_BUILD_GROUP('syslibcheck')
 646         task = bld(rule=symbols_whyneeded, always=True, name='check why a dependency is needed')
 647         task.env.bld = bld
 648
 649
 650 Build.BuildContext.SYMBOL_CHECK = SYMBOL_CHECK
 651
 652 def DUP_SYMBOL_CHECK(bld):
 653     if Options.options.DUP_SYMBOLCHECK and bld.env.DEVELOPER:
 654         '''check for duplicate symbols'''
 655         bld.SET_BUILD_GROUP('syslibcheck')
 656         task = bld(rule=symbols_dupcheck_fatal, always=True, name='symbol duplicate checking')
 657         task.env.bld = bld
 658
 659 Build.BuildContext.DUP_SYMBOL_CHECK = DUP_SYMBOL_CHECK