summaryrefslogtreecommitdiff
path: root/buildtools/wafsamba/symbols.py
blob: 13d84b9a41201d438647925c32031064b00c6c01 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
# a waf tool to extract symbols from object files or libraries
# using nm, producing a set of exposed defined/undefined symbols

import Utils, Build, subprocess, Logs, re
from samba_wildcard import fake_build_environment
from samba_utils import *

# these are the data structures used in symbols.py:
#
# bld.env.symbol_map : dictionary mapping public symbol names to list of
#                      subsystem names where that symbol exists
#
# t.in_library       : list of libraries that t is in
#
# bld.env.public_symbols: set of public symbols for each subsystem
# bld.env.used_symbols  : set of used symbols for each subsystem
#
# bld.env.syslib_symbols: dictionary mapping system library name to set of symbols
#                         for that library
# bld.env.library_dict  : dictionary mapping built library paths to subsystem names
#
# LOCAL_CACHE(bld, 'TARGET_TYPE') : dictionary mapping subsystem name to target type


def symbols_extract(bld, objfiles, dynamic=False):
    '''extract symbols from objfile, returning a dictionary containing
       the set of undefined and public symbols for each file'''

    ret = {}

    # see if we can get some results from the nm cache
    if not bld.env.nm_cache:
        bld.env.nm_cache = {}

    objfiles = set(objfiles).copy()

    remaining = set()
    for obj in objfiles:
        if obj in bld.env.nm_cache:
            ret[obj] = bld.env.nm_cache[obj].copy()
        else:
            remaining.add(obj)
    objfiles = remaining

    if len(objfiles) == 0:
        return ret

    cmd = ["nm"]
    if dynamic:
        # needed for some .so files
        cmd.append("-D")
    cmd.extend(list(objfiles))

    nmpipe = subprocess.Popen(cmd, stdout=subprocess.PIPE).stdout
    if len(objfiles) == 1:
        filename = list(objfiles)[0]
        ret[filename] = { "PUBLIC": set(), "UNDEFINED" : set()}

    for line in nmpipe:
        line = line.strip()
        if line.endswith(':'):
            filename = line[:-1]
            ret[filename] = { "PUBLIC": set(), "UNDEFINED" : set() }
            continue
        cols = line.split(" ")
        if cols == ['']:
            continue
        # see if the line starts with an address
        if len(cols) == 3:
            symbol_type = cols[1]
            symbol = cols[2]
        else:
            symbol_type = cols[0]
            symbol = cols[1]
        if symbol_type in "BDGTRVWSi":
            # its a public symbol
            ret[filename]["PUBLIC"].add(symbol)
        elif symbol_type in "U":
            ret[filename]["UNDEFINED"].add(symbol)

    # add to the cache
    for obj in objfiles:
        if obj in ret:
            bld.env.nm_cache[obj] = ret[obj].copy()
        else:
            bld.env.nm_cache[obj] = { "PUBLIC": set(), "UNDEFINED" : set() }

    return ret


def real_name(name):
    if name.find(".objlist") != -1:
        name = name[:-8]
    return name


def find_ldd_path(bld, libname, binary):
    '''find the path to the syslib we will link against'''
    ret = None
    if not bld.env.syslib_paths:
        bld.env.syslib_paths = {}
    if libname in bld.env.syslib_paths:
        return bld.env.syslib_paths[libname]

    lddpipe = subprocess.Popen(['ldd', binary], stdout=subprocess.PIPE).stdout
    for line in lddpipe:
        line = line.strip()
        cols = line.split(" ")
        if len(cols) < 3 or cols[1] != "=>":
            continue
        if cols[0].startswith("libc."):
            # save this one too
            bld.env.libc_path = cols[2]
        if cols[0].startswith(libname):
            ret = cols[2]
    bld.env.syslib_paths[libname] = ret
    return ret


# some regular expressions for parsing readelf output
re_sharedlib = re.compile('Shared library: \[(.*)\]')
re_rpath     = re.compile('Library rpath: \[(.*)\]')

def get_libs(bld, binname):
    '''find the list of linked libraries for any binary or library
    binname is the path to the binary/library on disk

    We do this using readelf instead of ldd as we need to avoid recursing
    into system libraries
    '''

    # see if we can get the result from the ldd cache
    if not bld.env.lib_cache:
        bld.env.lib_cache = {}
    if binname in bld.env.lib_cache:
        return bld.env.lib_cache[binname].copy()

    rpath = []
    libs = set()

    elfpipe = subprocess.Popen(['readelf', '--dynamic', binname], stdout=subprocess.PIPE).stdout
    for line in elfpipe:
        m = re_sharedlib.search(line)
        if m:
            libs.add(m.group(1))
        m = re_rpath.search(line)
        if m:
            rpath.extend(m.group(1).split(":"))

    ret = set()
    for lib in libs:
        found = False
        for r in rpath:
            path = os.path.join(r, lib)
            if os.path.exists(path):
                ret.add(os.path.realpath(path))
                found = True
                break
        if not found:
            # we didn't find this lib using rpath. It is probably a system
            # library, so to find the path to it we either need to use ldd
            # or we need to start parsing /etc/ld.so.conf* ourselves. We'll
            # use ldd for now, even though it is slow
            path = find_ldd_path(bld, lib, binname)
            if path:
                ret.add(os.path.realpath(path))

    bld.env.lib_cache[binname] = ret.copy()

    return ret


def get_libs_recursive(bld, binname, seen):
    '''find the recursive list of linked libraries for any binary or library
    binname is the path to the binary/library on disk. seen is a set used
    to prevent loops
    '''
    if binname in seen:
        return set()
    ret = get_libs(bld, binname)
    seen.add(binname)
    for lib in ret:
        # we don't want to recurse into system libraries. If a system
        # library that we use (eg. libcups) happens to use another library
        # (such as libkrb5) which contains common symbols with our own
        # libraries, then that is not an error
        if lib in bld.env.library_dict:
            ret = ret.union(get_libs_recursive(bld, lib, seen))
    return ret



def find_syslib_path(bld, libname, deps):
    '''find the path to the syslib we will link against'''
    # the strategy is to use the targets that depend on the library, and run ldd
    # on it to find the real location of the library that is used

    linkpath = deps[0].link_task.outputs[0].abspath(bld.env)

    if libname == "python":
        libname += bld.env.PYTHON_VERSION

    return find_ldd_path(bld, "lib%s" % libname.lower(), linkpath)


def build_symbol_sets(bld, tgt_list):
    '''build the public_symbols and undefined_symbols attributes for each target'''

    if bld.env.public_symbols:
        return

    objlist = []  # list of object file
    objmap = {}   # map from object filename to target (subsystem) name

    for t in tgt_list:
        t.public_symbols = set()
        t.undefined_symbols = set()
        t.used_symbols = set()
        for tsk in getattr(t, 'compiled_tasks', []):
            for output in tsk.outputs:
                objpath = output.abspath(bld.env)
                objlist.append(objpath)
                objmap[objpath] = t

    symbols = symbols_extract(bld, objlist)
    for obj in objlist:
        t = objmap[obj]
        t.public_symbols = t.public_symbols.union(symbols[obj]["PUBLIC"])
        t.undefined_symbols = t.undefined_symbols.union(symbols[obj]["UNDEFINED"])
        t.used_symbols = t.used_symbols.union(symbols[obj]["UNDEFINED"])

    t.undefined_symbols = t.undefined_symbols.difference(t.public_symbols)

    # and the reverse map of public symbols to subsystem name
    bld.env.symbol_map = {}

    for t in tgt_list:
        for s in t.public_symbols:
            if not s in bld.env.symbol_map:
                bld.env.symbol_map[s] = []
            bld.env.symbol_map[s].append(real_name(t.sname))

    targets = LOCAL_CACHE(bld, 'TARGET_TYPE')

    bld.env.public_symbols = {}
    for t in tgt_list:
        name = real_name(t.sname)
        if name in bld.env.public_symbols:
            bld.env.public_symbols[name] = bld.env.public_symbols[name].union(t.public_symbols)
        else:
            bld.env.public_symbols[name] = t.public_symbols
        if t.samba_type == 'LIBRARY':
            for dep in t.add_objects:
                t2 = bld.name_to_obj(dep, bld.env)
                bld.ASSERT(t2 is not None, "Library '%s' has unknown dependency '%s'" % (name, dep))
                bld.env.public_symbols[name] = bld.env.public_symbols[name].union(t2.public_symbols)

    bld.env.used_symbols = {}
    for t in tgt_list:
        name = real_name(t.sname)
        if name in bld.env.used_symbols:
            bld.env.used_symbols[name] = bld.env.used_symbols[name].union(t.used_symbols)
        else:
            bld.env.used_symbols[name] = t.used_symbols
        if t.samba_type == 'LIBRARY':
            for dep in t.add_objects:
                t2 = bld.name_to_obj(dep, bld.env)
                bld.ASSERT(t2 is not None, "Library '%s' has unknown dependency '%s'" % (name, dep))
                bld.env.used_symbols[name] = bld.env.used_symbols[name].union(t2.used_symbols)


def build_library_dict(bld, tgt_list):
    '''build the library_dict dictionary'''

    if bld.env.library_dict:
        return

    bld.env.library_dict = {}

    for t in tgt_list:
        if t.samba_type in [ 'LIBRARY', 'PYTHON' ]:
            linkpath = os.path.realpath(t.link_task.outputs[0].abspath(bld.env))
            bld.env.library_dict[linkpath] = t.sname


def build_syslib_sets(bld, tgt_list):
    '''build the public_symbols for all syslibs'''

    if bld.env.syslib_symbols:
        return

    # work out what syslibs we depend on, and what targets those are used in
    syslibs = {}
    objmap = {}
    for t in tgt_list:
        if getattr(t, 'uselib', []) and t.samba_type in [ 'LIBRARY', 'BINARY', 'PYTHON' ]:
            for lib in t.uselib:
                if lib in ['PYEMBED', 'PYEXT']:
                    lib = "python"
                if not lib in syslibs:
                    syslibs[lib] = []
                syslibs[lib].append(t)

    # work out the paths to each syslib
    syslib_paths = []
    for lib in syslibs:
        path = find_syslib_path(bld, lib, syslibs[lib])
        if path is None:
            Logs.warn("Unable to find syslib path for %s" % lib)
        if path is not None:
            syslib_paths.append(path)
            objmap[path] = lib.lower()

    # add in libc
    syslib_paths.append(bld.env.libc_path)
    objmap[bld.env.libc_path] = 'c'

    symbols = symbols_extract(bld, syslib_paths, dynamic=True)

    # keep a map of syslib names to public symbols
    bld.env.syslib_symbols = {}
    for lib in symbols:
        bld.env.syslib_symbols[lib] = symbols[lib]["PUBLIC"]

    # add to the map of symbols to dependencies
    for lib in symbols:
        for sym in symbols[lib]["PUBLIC"]:
            if not sym in bld.env.symbol_map:
                bld.env.symbol_map[sym] = []
            bld.env.symbol_map[sym].append(objmap[lib])

    # keep the libc symbols as well, as these are useful for some of the
    # sanity checks
    bld.env.libc_symbols = symbols[bld.env.libc_path]["PUBLIC"]

    # add to the combined map of dependency name to public_symbols
    for lib in bld.env.syslib_symbols:
        bld.env.public_symbols[objmap[lib]] = bld.env.syslib_symbols[lib]


def build_autodeps(bld, t):
    '''build the set of dependencies for a target'''
    deps = set()
    name = real_name(t.sname)

    targets    = LOCAL_CACHE(bld, 'TARGET_TYPE')

    for sym in t.undefined_symbols:
        if sym in t.public_symbols:
            continue
        if sym in bld.env.symbol_map:
            depname = bld.env.symbol_map[sym]
            if depname == [ name ]:
                # self dependencies aren't interesting
                continue
            if t.in_library == depname:
                # no need to depend on the library we are part of
                continue
            if depname[0] in ['c', 'python']:
                # these don't go into autodeps
                continue
            if targets[depname[0]] in [ 'SYSLIB' ]:
                deps.add(depname[0])
                continue
            t2 = bld.name_to_obj(depname[0], bld.env)
            if len(t2.in_library) != 1:
                deps.add(depname[0])
                continue
            if t2.in_library == t.in_library:
                # if we're part of the same library, we don't need to autodep
                continue
            deps.add(t2.in_library[0])
    t.autodeps = deps


def build_library_names(bld, tgt_list):
    '''add a in_library attribute to all targets that are part of a library'''

    if bld.env.done_build_library_names:
        return

    for t in tgt_list:
        t.in_library = []

    for t in tgt_list:
        if t.samba_type in [ 'LIBRARY' ]:
            for obj in t.samba_deps_extended:
                t2 = bld.name_to_obj(obj, bld.env)
                if t2 and t2.samba_type in [ 'SUBSYSTEM', 'ASN1' ]:
                    if not t.sname in t2.in_library:
                        t2.in_library.append(t.sname)
    bld.env.done_build_library_names = True


def check_library_deps(bld, t):
    '''check that all the autodeps that have mutual dependency of this
    target are in the same library as the target'''

    name = real_name(t.sname)

    if len(t.in_library) > 1:
        Logs.warn("WARNING: Target '%s' in multiple libraries: %s" % (t.sname, t.in_library))

    for dep in t.autodeps:
        t2 = bld.name_to_obj(dep, bld.env)
        if t2 is None:
            continue
        for dep2 in t2.autodeps:
            if dep2 == name and t.in_library != t2.in_library:
                Logs.warn("WARNING: mutual dependency %s <=> %s" % (name, real_name(t2.sname)))
                Logs.warn("Libraries should match. %s != %s" % (t.in_library, t2.in_library))
                # raise Utils.WafError("illegal mutual dependency")


def check_syslib_collisions(bld, tgt_list):
    '''check if a target has any symbol collisions with a syslib

    We do not want any code in Samba to use a symbol name from a
    system library. The chance of that causing problems is just too
    high. Note that libreplace uses a rep_XX approach of renaming
    symbols via macros
    '''

    has_error = False
    for t in tgt_list:
        for lib in bld.env.syslib_symbols:
            common = t.public_symbols.intersection(bld.env.syslib_symbols[lib])
            if common:
                Logs.error("ERROR: Target '%s' has symbols '%s' which is also in syslib '%s'" % (t.sname, common, lib))
                has_error = True
    if has_error:
        raise Utils.WafError("symbols in common with system libraries")


def check_dependencies(bld, t):
    '''check for depenencies that should be changed'''

    if bld.name_to_obj(t.sname + ".objlist", bld.env):
        return

    targets = LOCAL_CACHE(bld, 'TARGET_TYPE')

    remaining = t.undefined_symbols.copy()
    remaining = remaining.difference(t.public_symbols)

    sname = real_name(t.sname)

    deps = set(t.samba_deps)
    for d in t.samba_deps:
        if targets[d] in [ 'EMPTY', 'DISABLED', 'SYSLIB', 'GENERATOR' ]:
            continue
        bld.ASSERT(d in bld.env.public_symbols, "Failed to find symbol list for dependency '%s'" % d)
        diff = remaining.intersection(bld.env.public_symbols[d])
        if not diff and targets[sname] != 'LIBRARY':
            Logs.info("Target '%s' has no dependency on %s" % (sname, d))
        else:
            remaining = remaining.difference(diff)

    t.unsatisfied_symbols = set()
    needed = {}
    for sym in remaining:
        if sym in bld.env.symbol_map:
            dep = bld.env.symbol_map[sym]
            if not dep[0] in needed:
                needed[dep[0]] = set()
            needed[dep[0]].add(sym)
        else:
            t.unsatisfied_symbols.add(sym)

    for dep in needed:
        Logs.info("Target '%s' should add dep '%s' for symbols %s" % (sname, dep, " ".join(needed[dep])))



def check_syslib_dependencies(bld, t):
    '''check for syslib depenencies'''

    if bld.name_to_obj(t.sname + ".objlist", bld.env):
        return

    sname = real_name(t.sname)

    remaining = set()

    features = TO_LIST(t.features)
    if 'pyembed' in features or 'pyext' in features:
        if 'python' in bld.env.public_symbols:
            t.unsatisfied_symbols = t.unsatisfied_symbols.difference(bld.env.public_symbols['python'])

    needed = {}
    for sym in t.unsatisfied_symbols:
        if sym in bld.env.symbol_map:
            dep = bld.env.symbol_map[sym][0]
            if dep == 'c':
                continue
            if not dep in needed:
                needed[dep] = set()
            needed[dep].add(sym)
        else:
            remaining.add(sym)

    for dep in needed:
        Logs.info("Target '%s' should add syslib dep '%s' for symbols %s" % (sname, dep, " ".join(needed[dep])))

    if remaining:
        debug("deps: Target '%s' has unsatisfied symbols: %s" % (sname, " ".join(remaining)))



def symbols_symbolcheck(task):
    '''check the internal dependency lists'''
    bld = task.env.bld
    tgt_list = get_tgt_list(bld)

    build_symbol_sets(bld, tgt_list)
    build_library_names(bld, tgt_list)

    for t in tgt_list:
        t.autodeps = set()
        if getattr(t, 'source', ''):
            build_autodeps(bld, t)

    for t in tgt_list:
        check_dependencies(bld, t)

    for t in tgt_list:
        check_library_deps(bld, t)

def symbols_syslibcheck(task):
    '''check the syslib dependencies'''
    bld = task.env.bld
    tgt_list = get_tgt_list(bld)

    build_syslib_sets(bld, tgt_list)
    check_syslib_collisions(bld, tgt_list)

    for t in tgt_list:
        check_syslib_dependencies(bld, t)


def symbols_whyneeded(task):
    """check why 'target' needs to link to 'subsystem'"""
    bld = task.env.bld
    tgt_list = get_tgt_list(bld)

    why = Options.options.WHYNEEDED.split(":")
    if len(why) != 2:
        raise Utils.WafError("usage: WHYNEEDED=TARGET:DEPENDENCY")
    target = why[0]
    subsystem = why[1]

    build_symbol_sets(bld, tgt_list)
    build_library_names(bld, tgt_list)
    build_syslib_sets(bld, tgt_list)

    Logs.info("Checking why %s needs to link to %s" % (target, subsystem))
    if not target in bld.env.used_symbols:
        Logs.warn("unable to find target '%s' in used_symbols dict" % target)
        return
    if not subsystem in bld.env.public_symbols:
        Logs.warn("unable to find subsystem '%s' in public_symbols dict" % subsystem)
        return
    overlap = bld.env.used_symbols[target].intersection(bld.env.public_symbols[subsystem])
    if not overlap:
        Logs.info("target '%s' doesn't use any public symbols from '%s'" % (target, subsystem))
    else:
        Logs.info("target '%s' uses symbols %s from '%s'" % (target, overlap, subsystem))


def report_duplicate(bld, binname, sym, libs, fail_on_error):
    '''report duplicated symbols'''
    if sym in ['_init', '_fini']:
        return
    libnames = []
    for lib in libs:
        if lib in bld.env.library_dict:
            libnames.append(bld.env.library_dict[lib])
        else:
            libnames.append(lib)
    if fail_on_error:
        raise Utils.WafError("%s: Symbol %s linked in multiple libraries %s" % (binname, sym, libnames))
    else:
        print("%s: Symbol %s linked in multiple libraries %s" % (binname, sym, libnames))


def symbols_dupcheck_binary(bld, binname, fail_on_error):
    '''check for duplicated symbols in one binary'''

    libs = get_libs_recursive(bld, binname, set())
    symlist = symbols_extract(bld, libs, dynamic=True)

    symmap = {}
    for libpath in symlist:
        for sym in symlist[libpath]['PUBLIC']:
            if sym == '_GLOBAL_OFFSET_TABLE_':
                continue
            if not sym in symmap:
                symmap[sym] = set()
            symmap[sym].add(libpath)
    for sym in symmap:
        if len(symmap[sym]) > 1:
            for libpath in symmap[sym]:
                if libpath in bld.env.library_dict:
                    report_duplicate(bld, binname, sym, symmap[sym], fail_on_error)
                    break

def symbols_dupcheck(task, fail_on_error=False):
    '''check for symbols defined in two different subsystems'''
    bld = task.env.bld
    tgt_list = get_tgt_list(bld)

    targets = LOCAL_CACHE(bld, 'TARGET_TYPE')

    build_library_dict(bld, tgt_list)
    for t in tgt_list:
        if t.samba_type == 'BINARY':
            binname = os_path_relpath(t.link_task.outputs[0].abspath(bld.env), os.getcwd())
            symbols_dupcheck_binary(bld, binname, fail_on_error)


def symbols_dupcheck_fatal(task):
    '''check for symbols defined in two different subsystems (and fail if duplicates are found)'''
    symbols_dupcheck(task, fail_on_error=True)


def SYMBOL_CHECK(bld):
    '''check our dependency lists'''
    if Options.options.SYMBOLCHECK:
        bld.SET_BUILD_GROUP('symbolcheck')
        task = bld(rule=symbols_symbolcheck, always=True, name='symbol checking')
        task.env.bld = bld

        bld.SET_BUILD_GROUP('syslibcheck')
        task = bld(rule=symbols_syslibcheck, always=True, name='syslib checking')
        task.env.bld = bld

        bld.SET_BUILD_GROUP('syslibcheck')
        task = bld(rule=symbols_dupcheck, always=True, name='symbol duplicate checking')
        task.env.bld = bld

    if Options.options.WHYNEEDED:
        bld.SET_BUILD_GROUP('syslibcheck')
        task = bld(rule=symbols_whyneeded, always=True, name='check why a dependency is needed')
        task.env.bld = bld


Build.BuildContext.SYMBOL_CHECK = SYMBOL_CHECK

def DUP_SYMBOL_CHECK(bld):
    if Options.options.DUP_SYMBOLCHECK and bld.env.DEVELOPER:
        '''check for duplicate symbols'''
        bld.SET_BUILD_GROUP('syslibcheck')
        task = bld(rule=symbols_dupcheck_fatal, always=True, name='symbol duplicate checking')
        task.env.bld = bld

Build.BuildContext.DUP_SYMBOL_CHECK = DUP_SYMBOL_CHECK