summaryrefslogtreecommitdiff
path: root/SConstruct
blob: d84b91284bde04fc5d52cf90121378465edf2ca7 (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
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
# -*- mode:python -*-

# Copyright (c) 2013, 2015-2019 ARM Limited
# All rights reserved.
#
# The license below extends only to copyright in the software and shall
# not be construed as granting a license to any other intellectual
# property including but not limited to intellectual property relating
# to a hardware implementation of the functionality of the software
# licensed hereunder.  You may use the software subject to the license
# terms below provided that you ensure that this notice is replicated
# unmodified and in its entirety in all distributions of the software,
# modified or unmodified, in source code or in binary form.
#
# Copyright (c) 2011 Advanced Micro Devices, Inc.
# Copyright (c) 2009 The Hewlett-Packard Development Company
# Copyright (c) 2004-2005 The Regents of The University of Michigan
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are
# met: redistributions of source code must retain the above copyright
# notice, this list of conditions and the following disclaimer;
# redistributions in binary form must reproduce the above copyright
# notice, this list of conditions and the following disclaimer in the
# documentation and/or other materials provided with the distribution;
# neither the name of the copyright holders nor the names of its
# contributors may be used to endorse or promote products derived from
# this software without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#
# Authors: Steve Reinhardt
#          Nathan Binkert

###################################################
#
# SCons top-level build description (SConstruct) file.
#
# While in this directory ('gem5'), just type 'scons' to build the default
# configuration (see below), or type 'scons build/<CONFIG>/<binary>'
# to build some other configuration (e.g., 'build/ALPHA/gem5.opt' for
# the optimized full-system version).
#
# You can build gem5 in a different directory as long as there is a
# 'build/<CONFIG>' somewhere along the target path.  The build system
# expects that all configs under the same build directory are being
# built for the same host system.
#
# Examples:
#
#   The following two commands are equivalent.  The '-u' option tells
#   scons to search up the directory tree for this SConstruct file.
#   % cd <path-to-src>/gem5 ; scons build/ALPHA/gem5.debug
#   % cd <path-to-src>/gem5/build/ALPHA; scons -u gem5.debug
#
#   The following two commands are equivalent and demonstrate building
#   in a directory outside of the source tree.  The '-C' option tells
#   scons to chdir to the specified directory to find this SConstruct
#   file.
#   % cd <path-to-src>/gem5 ; scons /local/foo/build/ALPHA/gem5.debug
#   % cd /local/foo/build/ALPHA; scons -C <path-to-src>/gem5 gem5.debug
#
# You can use 'scons -H' to print scons options.  If you're in this
# 'gem5' directory (or use -u or -C to tell scons where to find this
# file), you can use 'scons -h' to print all the gem5-specific build
# options as well.
#
###################################################

from __future__ import print_function

# Global Python includes
import itertools
import os
import re
import shutil
import subprocess
import sys

from os import mkdir, environ
from os.path import abspath, basename, dirname, expanduser, normpath
from os.path import exists,  isdir, isfile
from os.path import join as joinpath, split as splitpath
from re import match

# SCons includes
import SCons
import SCons.Node
import SCons.Node.FS

from m5.util import compareVersions, readCommand

help_texts = {
    "options" : "",
    "global_vars" : "",
    "local_vars" : ""
}

Export("help_texts")


# There's a bug in scons in that (1) by default, the help texts from
# AddOption() are supposed to be displayed when you type 'scons -h'
# and (2) you can override the help displayed by 'scons -h' using the
# Help() function, but these two features are incompatible: once
# you've overridden the help text using Help(), there's no way to get
# at the help texts from AddOptions.  See:
#     http://scons.tigris.org/issues/show_bug.cgi?id=2356
#     http://scons.tigris.org/issues/show_bug.cgi?id=2611
# This hack lets us extract the help text from AddOptions and
# re-inject it via Help().  Ideally someday this bug will be fixed and
# we can just use AddOption directly.
def AddLocalOption(*args, **kwargs):
    col_width = 30

    help = "  " + ", ".join(args)
    if "help" in kwargs:
        length = len(help)
        if length >= col_width:
            help += "\n" + " " * col_width
        else:
            help += " " * (col_width - length)
        help += kwargs["help"]
    help_texts["options"] += help + "\n"

    AddOption(*args, **kwargs)

AddLocalOption('--colors', dest='use_colors', action='store_true',
               help="Add color to abbreviated scons output")
AddLocalOption('--no-colors', dest='use_colors', action='store_false',
               help="Don't add color to abbreviated scons output")
AddLocalOption('--with-cxx-config', dest='with_cxx_config',
               action='store_true',
               help="Build with support for C++-based configuration")
AddLocalOption('--default', dest='default', type='string', action='store',
               help='Override which build_opts file to use for defaults')
AddLocalOption('--ignore-style', dest='ignore_style', action='store_true',
               help='Disable style checking hooks')
AddLocalOption('--gold-linker', dest='gold_linker', action='store_true',
               help='Use the gold linker')
AddLocalOption('--no-lto', dest='no_lto', action='store_true',
               help='Disable Link-Time Optimization for fast')
AddLocalOption('--force-lto', dest='force_lto', action='store_true',
               help='Use Link-Time Optimization instead of partial linking' +
                    ' when the compiler doesn\'t support using them together.')
AddLocalOption('--update-ref', dest='update_ref', action='store_true',
               help='Update test reference outputs')
AddLocalOption('--verbose', dest='verbose', action='store_true',
               help='Print full tool command lines')
AddLocalOption('--without-python', dest='without_python',
               action='store_true',
               help='Build without Python configuration support')
AddLocalOption('--without-tcmalloc', dest='without_tcmalloc',
               action='store_true',
               help='Disable linking against tcmalloc')
AddLocalOption('--with-ubsan', dest='with_ubsan', action='store_true',
               help='Build with Undefined Behavior Sanitizer if available')
AddLocalOption('--with-asan', dest='with_asan', action='store_true',
               help='Build with Address Sanitizer if available')

from gem5_scons import Transform, error, warning

if GetOption('no_lto') and GetOption('force_lto'):
    error('--no-lto and --force-lto are mutually exclusive')

########################################################################
#
# Set up the main build environment.
#
########################################################################

main = Environment()

from gem5_scons.util import get_termcap
termcap = get_termcap()

main_dict_keys = main.Dictionary().keys()

# Check that we have a C/C++ compiler
if not ('CC' in main_dict_keys and 'CXX' in main_dict_keys):
    error("No C++ compiler installed (package g++ on Ubuntu and RedHat)")

###################################################
#
# Figure out which configurations to set up based on the path(s) of
# the target(s).
#
###################################################

# Find default configuration & binary.
Default(environ.get('M5_DEFAULT_BINARY', 'build/ALPHA/gem5.debug'))

# helper function: find last occurrence of element in list
def rfind(l, elt, offs = -1):
    for i in range(len(l)+offs, 0, -1):
        if l[i] == elt:
            return i
    raise ValueError("element not found")

# Take a list of paths (or SCons Nodes) and return a list with all
# paths made absolute and ~-expanded.  Paths will be interpreted
# relative to the launch directory unless a different root is provided
def makePathListAbsolute(path_list, root=GetLaunchDir()):
    return [abspath(joinpath(root, expanduser(str(p))))
            for p in path_list]

def find_first_prog(prog_names):
    """Find the absolute path to the first existing binary in prog_names"""

    if not isinstance(prog_names, (list, tuple)):
        prog_names = [ prog_names ]

    for p in prog_names:
        p = main.WhereIs(p)
        if p is not None:
            return p

    return None

# Each target must have 'build' in the interior of the path; the
# directory below this will determine the build parameters.  For
# example, for target 'foo/bar/build/ALPHA_SE/arch/alpha/blah.do' we
# recognize that ALPHA_SE specifies the configuration because it
# follow 'build' in the build path.

# The funky assignment to "[:]" is needed to replace the list contents
# in place rather than reassign the symbol to a new list, which
# doesn't work (obviously!).
BUILD_TARGETS[:] = makePathListAbsolute(BUILD_TARGETS)

# Generate a list of the unique build roots and configs that the
# collected targets reference.
variant_paths = []
build_root = None
for t in BUILD_TARGETS:
    path_dirs = t.split('/')
    try:
        build_top = rfind(path_dirs, 'build', -2)
    except:
        error("No non-leaf 'build' dir found on target path.", t)
    this_build_root = joinpath('/',*path_dirs[:build_top+1])
    if not build_root:
        build_root = this_build_root
    else:
        if this_build_root != build_root:
            error("build targets not under same build root\n"
                  "  %s\n  %s" % (build_root, this_build_root))
    variant_path = joinpath('/',*path_dirs[:build_top+2])
    if variant_path not in variant_paths:
        variant_paths.append(variant_path)

# Make sure build_root exists (might not if this is the first build there)
if not isdir(build_root):
    mkdir(build_root)
main['BUILDROOT'] = build_root

Export('main')

main.SConsignFile(joinpath(build_root, "sconsign"))

# Default duplicate option is to use hard links, but this messes up
# when you use emacs to edit a file in the target dir, as emacs moves
# file to file~ then copies to file, breaking the link.  Symbolic
# (soft) links work better.
main.SetOption('duplicate', 'soft-copy')

#
# Set up global sticky variables... these are common to an entire build
# tree (not specific to a particular build like ALPHA_SE)
#

global_vars_file = joinpath(build_root, 'variables.global')

global_vars = Variables(global_vars_file, args=ARGUMENTS)

global_vars.AddVariables(
    ('CC', 'C compiler', environ.get('CC', main['CC'])),
    ('CXX', 'C++ compiler', environ.get('CXX', main['CXX'])),
    ('CCFLAGS_EXTRA', 'Extra C and C++ compiler flags', ''),
    ('LDFLAGS_EXTRA', 'Extra linker flags', ''),
    ('PYTHON_CONFIG', 'Python config binary to use',
     [ 'python2.7-config', 'python-config' ]),
    ('PROTOC', 'protoc tool', environ.get('PROTOC', 'protoc')),
    ('BATCH', 'Use batch pool for build and tests', False),
    ('BATCH_CMD', 'Batch pool submission command name', 'qdo'),
    ('M5_BUILD_CACHE', 'Cache built objects in this directory', False),
    ('EXTRAS', 'Add extra directories to the compilation', '')
    )

# Update main environment with values from ARGUMENTS & global_vars_file
global_vars.Update(main)
help_texts["global_vars"] += global_vars.GenerateHelpText(main)

# Save sticky variable settings back to current variables file
global_vars.Save(global_vars_file, main)

# Parse EXTRAS variable to build list of all directories where we're
# look for sources etc.  This list is exported as extras_dir_list.
base_dir = main.srcdir.abspath
if main['EXTRAS']:
    extras_dir_list = makePathListAbsolute(main['EXTRAS'].split(':'))
else:
    extras_dir_list = []

Export('base_dir')
Export('extras_dir_list')

# the ext directory should be on the #includes path
main.Append(CPPPATH=[Dir('ext')])

# Add shared top-level headers
main.Prepend(CPPPATH=Dir('include'))

if GetOption('verbose'):
    def MakeAction(action, string, *args, **kwargs):
        return Action(action, *args, **kwargs)
else:
    MakeAction = Action
    main['CCCOMSTR']        = Transform("CC")
    main['CXXCOMSTR']       = Transform("CXX")
    main['ASCOMSTR']        = Transform("AS")
    main['ARCOMSTR']        = Transform("AR", 0)
    main['LINKCOMSTR']      = Transform("LINK", 0)
    main['SHLINKCOMSTR']    = Transform("SHLINK", 0)
    main['RANLIBCOMSTR']    = Transform("RANLIB", 0)
    main['M4COMSTR']        = Transform("M4")
    main['SHCCCOMSTR']      = Transform("SHCC")
    main['SHCXXCOMSTR']     = Transform("SHCXX")
Export('MakeAction')

# Initialize the Link-Time Optimization (LTO) flags
main['LTO_CCFLAGS'] = []
main['LTO_LDFLAGS'] = []

# According to the readme, tcmalloc works best if the compiler doesn't
# assume that we're using the builtin malloc and friends. These flags
# are compiler-specific, so we need to set them after we detect which
# compiler we're using.
main['TCMALLOC_CCFLAGS'] = []

CXX_version = readCommand([main['CXX'],'--version'], exception=False)
CXX_V = readCommand([main['CXX'],'-V'], exception=False)

main['GCC'] = CXX_version and CXX_version.find('g++') >= 0
main['CLANG'] = CXX_version and CXX_version.find('clang') >= 0
if main['GCC'] + main['CLANG'] > 1:
    error('Two compilers enabled at once?')

# Set up default C++ compiler flags
if main['GCC'] or main['CLANG']:
    # As gcc and clang share many flags, do the common parts here
    main.Append(CCFLAGS=['-pipe'])
    main.Append(CCFLAGS=['-fno-strict-aliasing'])
    # Enable -Wall and -Wextra and then disable the few warnings that
    # we consistently violate
    main.Append(CCFLAGS=['-Wall', '-Wundef', '-Wextra',
                         '-Wno-sign-compare', '-Wno-unused-parameter'])
    # We always compile using C++11
    main.Append(CXXFLAGS=['-std=c++11'])
    if sys.platform.startswith('freebsd'):
        main.Append(CCFLAGS=['-I/usr/local/include'])
        main.Append(CXXFLAGS=['-I/usr/local/include'])

    main.Append(LINKFLAGS='-Wl,--as-needed')
    main['FILTER_PSHLINKFLAGS'] = lambda x: str(x).replace(' -shared', '')
    main['PSHLINKFLAGS'] = main.subst('${FILTER_PSHLINKFLAGS(SHLINKFLAGS)}')
    if GetOption('gold_linker'):
        main.Append(LINKFLAGS='-fuse-ld=gold')
    main['PLINKFLAGS'] = main.subst('${LINKFLAGS}')
    shared_partial_flags = ['-r', '-nostdlib']
    main.Append(PSHLINKFLAGS=shared_partial_flags)
    main.Append(PLINKFLAGS=shared_partial_flags)

    # Treat warnings as errors but white list some warnings that we
    # want to allow (e.g., deprecation warnings).
    main.Append(CCFLAGS=['-Werror',
                         '-Wno-error=deprecated-declarations',
                         '-Wno-error=deprecated',
                        ])
else:
    error('\n'.join(
          "Don't know what compiler options to use for your compiler.",
          "compiler: " + main['CXX'],
          "version: " + CXX_version.replace('\n', '<nl>') if
                CXX_version else 'COMMAND NOT FOUND!',
          "If you're trying to use a compiler other than GCC",
          "or clang, there appears to be something wrong with your",
          "environment.",
          "",
          "If you are trying to use a compiler other than those listed",
          "above you will need to ease fix SConstruct and ",
          "src/SConscript to support that compiler."))

if main['GCC']:
    # Check for a supported version of gcc. >= 4.8 is chosen for its
    # level of c++11 support. See
    # http://gcc.gnu.org/projects/cxx0x.html for details.
    gcc_version = readCommand([main['CXX'], '-dumpversion'], exception=False)
    if compareVersions(gcc_version, "4.8") < 0:
        error('gcc version 4.8 or newer required.\n'
              'Installed version:', gcc_version)
        Exit(1)

    main['GCC_VERSION'] = gcc_version

    if compareVersions(gcc_version, '4.9') >= 0:
        # Incremental linking with LTO is currently broken in gcc versions
        # 4.9 and above. A version where everything works completely hasn't
        # yet been identified.
        #
        # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67548
        main['BROKEN_INCREMENTAL_LTO'] = True
    if compareVersions(gcc_version, '6.0') >= 0:
        # gcc versions 6.0 and greater accept an -flinker-output flag which
        # selects what type of output the linker should generate. This is
        # necessary for incremental lto to work, but is also broken in
        # current versions of gcc. It may not be necessary in future
        # versions. We add it here since it might be, and as a reminder that
        # it exists. It's excluded if lto is being forced.
        #
        # https://gcc.gnu.org/gcc-6/changes.html
        # https://gcc.gnu.org/ml/gcc-patches/2015-11/msg03161.html
        # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69866
        if not GetOption('force_lto'):
            main.Append(PSHLINKFLAGS='-flinker-output=rel')
            main.Append(PLINKFLAGS='-flinker-output=rel')

    disable_lto = GetOption('no_lto')
    if not disable_lto and main.get('BROKEN_INCREMENTAL_LTO', False) and \
            not GetOption('force_lto'):
        warning('Warning: Your compiler doesn\'t support incremental linking '
                'and lto at the same time, so lto is being disabled. To force '
                'lto on anyway, use the --force-lto option. That will disable '
                'partial linking.')
        disable_lto = True

    # Add the appropriate Link-Time Optimization (LTO) flags
    # unless LTO is explicitly turned off. Note that these flags
    # are only used by the fast target.
    if not disable_lto:
        # Pass the LTO flag when compiling to produce GIMPLE
        # output, we merely create the flags here and only append
        # them later
        main['LTO_CCFLAGS'] = ['-flto=%d' % GetOption('num_jobs')]

        # Use the same amount of jobs for LTO as we are running
        # scons with
        main['LTO_LDFLAGS'] = ['-flto=%d' % GetOption('num_jobs')]

    main.Append(TCMALLOC_CCFLAGS=['-fno-builtin-malloc', '-fno-builtin-calloc',
                                  '-fno-builtin-realloc', '-fno-builtin-free'])

elif main['CLANG']:
    # Check for a supported version of clang, >= 3.1 is needed to
    # support similar features as gcc 4.8. See
    # http://clang.llvm.org/cxx_status.html for details
    clang_version_re = re.compile(".* version (\d+\.\d+)")
    clang_version_match = clang_version_re.search(CXX_version)
    if (clang_version_match):
        clang_version = clang_version_match.groups()[0]
        if compareVersions(clang_version, "3.1") < 0:
            error('clang version 3.1 or newer required.\n'
                  'Installed version:', clang_version)
    else:
        error('Unable to determine clang version.')

    # clang has a few additional warnings that we disable, extraneous
    # parantheses are allowed due to Ruby's printing of the AST,
    # finally self assignments are allowed as the generated CPU code
    # is relying on this
    main.Append(CCFLAGS=['-Wno-parentheses',
                         '-Wno-self-assign',
                         # Some versions of libstdc++ (4.8?) seem to
                         # use struct hash and class hash
                         # interchangeably.
                         '-Wno-mismatched-tags',
                         ])

    main.Append(TCMALLOC_CCFLAGS=['-fno-builtin'])

    # On Mac OS X/Darwin we need to also use libc++ (part of XCode) as
    # opposed to libstdc++, as the later is dated.
    if sys.platform == "darwin":
        main.Append(CXXFLAGS=['-stdlib=libc++'])
        main.Append(LIBS=['c++'])

    # On FreeBSD we need libthr.
    if sys.platform.startswith('freebsd'):
        main.Append(LIBS=['thr'])

# Add sanitizers flags
sanitizers=[]
if GetOption('with_ubsan'):
    # Only gcc >= 4.9 supports UBSan, so check both the version
    # and the command-line option before adding the compiler and
    # linker flags.
    if not main['GCC'] or compareVersions(main['GCC_VERSION'], '4.9') >= 0:
        sanitizers.append('undefined')
if GetOption('with_asan'):
    # Available for gcc >= 4.8 or llvm >= 3.1 both a requirement
    # by the build system
    sanitizers.append('address')
if sanitizers:
    sanitizers = ','.join(sanitizers)
    if main['GCC'] or main['CLANG']:
        main.Append(CCFLAGS=['-fsanitize=%s' % sanitizers,
                             '-fno-omit-frame-pointer'],
                    LINKFLAGS='-fsanitize=%s' % sanitizers)
    else:
        warning("Don't know how to enable %s sanitizer(s) for your "
                "compiler." % sanitizers)

# Set up common yacc/bison flags (needed for Ruby)
main['YACCFLAGS'] = '-d'
main['YACCHXXFILESUFFIX'] = '.hh'

# Do this after we save setting back, or else we'll tack on an
# extra 'qdo' every time we run scons.
if main['BATCH']:
    main['CC']     = main['BATCH_CMD'] + ' ' + main['CC']
    main['CXX']    = main['BATCH_CMD'] + ' ' + main['CXX']
    main['AS']     = main['BATCH_CMD'] + ' ' + main['AS']
    main['AR']     = main['BATCH_CMD'] + ' ' + main['AR']
    main['RANLIB'] = main['BATCH_CMD'] + ' ' + main['RANLIB']

if sys.platform == 'cygwin':
    # cygwin has some header file issues...
    main.Append(CCFLAGS=["-Wno-uninitialized"])


have_pkg_config = readCommand(['pkg-config', '--version'], exception='')

# Check for the protobuf compiler
try:
    main['HAVE_PROTOC'] = True
    protoc_version = readCommand([main['PROTOC'], '--version']).split()

    # First two words should be "libprotoc x.y.z"
    if len(protoc_version) < 2 or protoc_version[0] != 'libprotoc':
        warning('Protocol buffer compiler (protoc) not found.\n'
                'Please install protobuf-compiler for tracing support.')
        main['HAVE_PROTOC'] = False
    else:
        # Based on the availability of the compress stream wrappers,
        # require 2.1.0
        min_protoc_version = '2.1.0'
        if compareVersions(protoc_version[1], min_protoc_version) < 0:
            warning('protoc version', min_protoc_version,
                    'or newer required.\n'
                    'Installed version:', protoc_version[1])
            main['HAVE_PROTOC'] = False
        else:
            # Attempt to determine the appropriate include path and
            # library path using pkg-config, that means we also need to
            # check for pkg-config. Note that it is possible to use
            # protobuf without the involvement of pkg-config. Later on we
            # check go a library config check and at that point the test
            # will fail if libprotobuf cannot be found.
            if have_pkg_config:
                try:
                    # Attempt to establish what linking flags to add for
                    # protobuf
                    # using pkg-config
                    main.ParseConfig(
                            'pkg-config --cflags --libs-only-L protobuf')
                except:
                    warning('pkg-config could not get protobuf flags.')
except Exception as e:
    warning('While checking protoc version:', str(e))
    main['HAVE_PROTOC'] = False

# Check for 'timeout' from GNU coreutils. If present, regressions will
# be run with a time limit. We require version 8.13 since we rely on
# support for the '--foreground' option.
if sys.platform.startswith('freebsd'):
    timeout_lines = readCommand(['gtimeout', '--version'],
                                exception='').splitlines()
else:
    timeout_lines = readCommand(['timeout', '--version'],
                                exception='').splitlines()
# Get the first line and tokenize it
timeout_version = timeout_lines[0].split() if timeout_lines else []
main['TIMEOUT'] =  timeout_version and \
    compareVersions(timeout_version[-1], '8.13') >= 0

# Add a custom Check function to test for structure members.
def CheckMember(context, include, decl, member, include_quotes="<>"):
    context.Message("Checking for member %s in %s..." %
                    (member, decl))
    text = """
#include %(header)s
int main(){
  %(decl)s test;
  (void)test.%(member)s;
  return 0;
};
""" % { "header" : include_quotes[0] + include + include_quotes[1],
        "decl" : decl,
        "member" : member,
        }

    ret = context.TryCompile(text, extension=".cc")
    context.Result(ret)
    return ret

# Platform-specific configuration.  Note again that we assume that all
# builds under a given build root run on the same host platform.
conf = Configure(main,
                 conf_dir = joinpath(build_root, '.scons_config'),
                 log_file = joinpath(build_root, 'scons_config.log'),
                 custom_tests = {
        'CheckMember' : CheckMember,
        })

# Check if we should compile a 64 bit binary on Mac OS X/Darwin
try:
    import platform
    uname = platform.uname()
    if uname[0] == 'Darwin' and compareVersions(uname[2], '9.0.0') >= 0:
        if int(readCommand('sysctl -n hw.cpu64bit_capable')[0]):
            main.Append(CCFLAGS=['-arch', 'x86_64'])
            main.Append(CFLAGS=['-arch', 'x86_64'])
            main.Append(LINKFLAGS=['-arch', 'x86_64'])
            main.Append(ASFLAGS=['-arch', 'x86_64'])
except:
    pass

# Recent versions of scons substitute a "Null" object for Configure()
# when configuration isn't necessary, e.g., if the "--help" option is
# present.  Unfortuantely this Null object always returns false,
# breaking all our configuration checks.  We replace it with our own
# more optimistic null object that returns True instead.
if not conf:
    def NullCheck(*args, **kwargs):
        return True

    class NullConf:
        def __init__(self, env):
            self.env = env
        def Finish(self):
            return self.env
        def __getattr__(self, mname):
            return NullCheck

    conf = NullConf(main)

# Cache build files in the supplied directory.
if main['M5_BUILD_CACHE']:
    print('Using build cache located at', main['M5_BUILD_CACHE'])
    CacheDir(main['M5_BUILD_CACHE'])

main['USE_PYTHON'] = not GetOption('without_python')
if main['USE_PYTHON']:
    # Find Python include and library directories for embedding the
    # interpreter. We rely on python-config to resolve the appropriate
    # includes and linker flags. ParseConfig does not seem to understand
    # the more exotic linker flags such as -Xlinker and -export-dynamic so
    # we add them explicitly below. If you want to link in an alternate
    # version of python, see above for instructions on how to invoke
    # scons with the appropriate PATH set.

    python_config = find_first_prog(main['PYTHON_CONFIG'])
    if python_config is None:
        error("Can't find a suitable python-config, tried %s" % \
              main['PYTHON_CONFIG'])

    print("Info: Using Python config: %s" % (python_config, ))
    py_includes = readCommand([python_config, '--includes'],
                              exception='').split()
    py_includes = filter(lambda s: match(r'.*\/include\/.*',s), py_includes)
    # Strip the -I from the include folders before adding them to the
    # CPPPATH
    py_includes = map(lambda s: s[2:] if s.startswith('-I') else s, py_includes)
    main.Append(CPPPATH=py_includes)

    # Read the linker flags and split them into libraries and other link
    # flags. The libraries are added later through the call the CheckLib.
    py_ld_flags = readCommand([python_config, '--ldflags'],
        exception='').split()
    py_libs = []
    for lib in py_ld_flags:
         if not lib.startswith('-l'):
             main.Append(LINKFLAGS=[lib])
         else:
             lib = lib[2:]
             if lib not in py_libs:
                 py_libs.append(lib)

    # verify that this stuff works
    if not conf.CheckHeader('Python.h', '<>'):
        error("Check failed for Python.h header in",
                ' '.join(py_includes), "\n"
              "Two possible reasons:\n"
              "1. Python headers are not installed (You can install the "
              "package python-dev on Ubuntu and RedHat)\n"
              "2. SCons is using a wrong C compiler. This can happen if "
              "CC has the wrong value.\n"
              "CC = %s" % main['CC'])

    for lib in py_libs:
        if not conf.CheckLib(lib):
            error("Can't find library %s required by python." % lib)

# On Solaris you need to use libsocket for socket ops
if not conf.CheckLibWithHeader(None, 'sys/socket.h', 'C++', 'accept(0,0,0);'):
   if not conf.CheckLibWithHeader('socket', 'sys/socket.h',
                                  'C++', 'accept(0,0,0);'):
       error("Can't find library with socket calls (e.g. accept()).")

# Check for zlib.  If the check passes, libz will be automatically
# added to the LIBS environment variable.
if not conf.CheckLibWithHeader('z', 'zlib.h', 'C++','zlibVersion();'):
    error('Did not find needed zlib compression library '
          'and/or zlib.h header file.\n'
          'Please install zlib and try again.')

# If we have the protobuf compiler, also make sure we have the
# development libraries. If the check passes, libprotobuf will be
# automatically added to the LIBS environment variable. After
# this, we can use the HAVE_PROTOBUF flag to determine if we have
# got both protoc and libprotobuf available.
main['HAVE_PROTOBUF'] = main['HAVE_PROTOC'] and \
    conf.CheckLibWithHeader('protobuf', 'google/protobuf/message.h',
                            'C++', 'GOOGLE_PROTOBUF_VERIFY_VERSION;')

# Valgrind gets much less confused if you tell it when you're using
# alternative stacks.
main['HAVE_VALGRIND'] = conf.CheckCHeader('valgrind/valgrind.h')

# If we have the compiler but not the library, print another warning.
if main['HAVE_PROTOC'] and not main['HAVE_PROTOBUF']:
    warning('Did not find protocol buffer library and/or headers.\n'
            'Please install libprotobuf-dev for tracing support.')

# Check for librt.
have_posix_clock = \
    conf.CheckLibWithHeader(None, 'time.h', 'C',
                            'clock_nanosleep(0,0,NULL,NULL);') or \
    conf.CheckLibWithHeader('rt', 'time.h', 'C',
                            'clock_nanosleep(0,0,NULL,NULL);')

have_posix_timers = \
    conf.CheckLibWithHeader([None, 'rt'], [ 'time.h', 'signal.h' ], 'C',
                            'timer_create(CLOCK_MONOTONIC, NULL, NULL);')

if not GetOption('without_tcmalloc'):
    if conf.CheckLib('tcmalloc'):
        main.Append(CCFLAGS=main['TCMALLOC_CCFLAGS'])
    elif conf.CheckLib('tcmalloc_minimal'):
        main.Append(CCFLAGS=main['TCMALLOC_CCFLAGS'])
    else:
        warning("You can get a 12% performance improvement by "
                "installing tcmalloc (libgoogle-perftools-dev package "
                "on Ubuntu or RedHat).")


# Detect back trace implementations. The last implementation in the
# list will be used by default.
backtrace_impls = [ "none" ]

backtrace_checker = 'char temp;' + \
    ' backtrace_symbols_fd((void*)&temp, 0, 0);'
if conf.CheckLibWithHeader(None, 'execinfo.h', 'C', backtrace_checker):
    backtrace_impls.append("glibc")
elif conf.CheckLibWithHeader('execinfo', 'execinfo.h', 'C',
                             backtrace_checker):
    # NetBSD and FreeBSD need libexecinfo.
    backtrace_impls.append("glibc")
    main.Append(LIBS=['execinfo'])

if backtrace_impls[-1] == "none":
    default_backtrace_impl = "none"
    warning("No suitable back trace implementation found.")

if not have_posix_clock:
    warning("Can't find library for POSIX clocks.")

# Check for <fenv.h> (C99 FP environment control)
have_fenv = conf.CheckHeader('fenv.h', '<>')
if not have_fenv:
    warning("Header file <fenv.h> not found.\n"
            "This host has no IEEE FP rounding mode control.")

# Check for <png.h> (libpng library needed if wanting to dump
# frame buffer image in png format)
have_png = conf.CheckHeader('png.h', '<>')
if not have_png:
    warning("Header file <png.h> not found.\n"
            "This host has no libpng library.\n"
            "Disabling support for PNG framebuffers.")

# Check if we should enable KVM-based hardware virtualization. The API
# we rely on exists since version 2.6.36 of the kernel, but somehow
# the KVM_API_VERSION does not reflect the change. We test for one of
# the types as a fall back.
have_kvm = conf.CheckHeader('linux/kvm.h', '<>')
if not have_kvm:
    print("Info: Compatible header file <linux/kvm.h> not found, "
          "disabling KVM support.")

# Check if the TUN/TAP driver is available.
have_tuntap = conf.CheckHeader('linux/if_tun.h', '<>')
if not have_tuntap:
    print("Info: Compatible header file <linux/if_tun.h> not found.")

# x86 needs support for xsave. We test for the structure here since we
# won't be able to run new tests by the time we know which ISA we're
# targeting.
have_kvm_xsave = conf.CheckTypeSize('struct kvm_xsave',
                                    '#include <linux/kvm.h>') != 0

# Check if the requested target ISA is compatible with the host
def is_isa_kvm_compatible(isa):
    try:
        import platform
        host_isa = platform.machine()
    except:
        warning("Failed to determine host ISA.")
        return False

    if not have_posix_timers:
        warning("Can not enable KVM, host seems to lack support "
                "for POSIX timers")
        return False

    if isa == "arm":
        return host_isa in ( "armv7l", "aarch64" )
    elif isa == "x86":
        if host_isa != "x86_64":
            return False

        if not have_kvm_xsave:
            warning("KVM on x86 requires xsave support in kernel headers.")
            return False

        return True
    else:
        return False


# Check if the exclude_host attribute is available. We want this to
# get accurate instruction counts in KVM.
main['HAVE_PERF_ATTR_EXCLUDE_HOST'] = conf.CheckMember(
    'linux/perf_event.h', 'struct perf_event_attr', 'exclude_host')

def check_hdf5():
    return \
        conf.CheckLibWithHeader('hdf5', 'hdf5.h', 'C',
                                'H5Fcreate("", 0, 0, 0);') and \
        conf.CheckLibWithHeader('hdf5_cpp', 'H5Cpp.h', 'C++',
                                'H5::H5File("", 0);')

def check_hdf5_pkg(name):
    print("Checking for %s using pkg-config..." % name, end="")
    if not have_pkg_config:
        print(" pkg-config not found")
        return False

    try:
        main.ParseConfig('pkg-config --cflags-only-I --libs-only-L %s' % name)
        print(" yes")
        return True
    except:
        print(" no")
        return False

# Check if there is a pkg-config configuration for hdf5. If we find
# it, setup the environment to enable linking and header inclusion. We
# don't actually try to include any headers or link with hdf5 at this
# stage.
if not check_hdf5_pkg('hdf5-serial'):
    check_hdf5_pkg('hdf5')

# Check if the HDF5 libraries can be found. This check respects the
# include path and library path provided by pkg-config. We perform
# this check even if there isn't a pkg-config configuration for hdf5
# since some installations don't use pkg-config.
have_hdf5 = check_hdf5()
if not have_hdf5:
    print("Warning: Couldn't find any HDF5 C++ libraries. Disabling")
    print("         HDF5 support.")

######################################################################
#
# Finish the configuration
#
main = conf.Finish()

######################################################################
#
# Collect all non-global variables
#

# Define the universe of supported ISAs
all_isa_list = [ ]
all_gpu_isa_list = [ ]
Export('all_isa_list')
Export('all_gpu_isa_list')

class CpuModel(object):
    '''The CpuModel class encapsulates everything the ISA parser needs to
    know about a particular CPU model.'''

    # Dict of available CPU model objects.  Accessible as CpuModel.dict.
    dict = {}

    # Constructor.  Automatically adds models to CpuModel.dict.
    def __init__(self, name, default=False):
        self.name = name           # name of model

        # This cpu is enabled by default
        self.default = default

        # Add self to dict
        if name in CpuModel.dict:
            raise AttributeError("CpuModel '%s' already registered" % name)
        CpuModel.dict[name] = self

Export('CpuModel')

# Sticky variables get saved in the variables file so they persist from
# one invocation to the next (unless overridden, in which case the new
# value becomes sticky).
sticky_vars = Variables(args=ARGUMENTS)
Export('sticky_vars')

# Sticky variables that should be exported
export_vars = []
Export('export_vars')

# For Ruby
all_protocols = []
Export('all_protocols')
protocol_dirs = []
Export('protocol_dirs')
slicc_includes = []
Export('slicc_includes')

# Walk the tree and execute all SConsopts scripts that wil add to the
# above variables
if GetOption('verbose'):
    print("Reading SConsopts")
for bdir in [ base_dir ] + extras_dir_list:
    if not isdir(bdir):
        error("Directory '%s' does not exist." % bdir)
    for root, dirs, files in os.walk(bdir):
        if 'SConsopts' in files:
            if GetOption('verbose'):
                print("Reading", joinpath(root, 'SConsopts'))
            SConscript(joinpath(root, 'SConsopts'))

all_isa_list.sort()
all_gpu_isa_list.sort()

sticky_vars.AddVariables(
    EnumVariable('TARGET_ISA', 'Target ISA', 'alpha', all_isa_list),
    EnumVariable('TARGET_GPU_ISA', 'Target GPU ISA', 'hsail', all_gpu_isa_list),
    ListVariable('CPU_MODELS', 'CPU models',
                 sorted(n for n,m in CpuModel.dict.iteritems() if m.default),
                 sorted(CpuModel.dict.keys())),
    BoolVariable('EFENCE', 'Link with Electric Fence malloc debugger',
                 False),
    BoolVariable('SS_COMPATIBLE_FP',
                 'Make floating-point results compatible with SimpleScalar',
                 False),
    BoolVariable('USE_SSE2',
                 'Compile for SSE2 (-msse2) to get IEEE FP on x86 hosts',
                 False),
    BoolVariable('USE_POSIX_CLOCK', 'Use POSIX Clocks', have_posix_clock),
    BoolVariable('USE_FENV', 'Use <fenv.h> IEEE mode control', have_fenv),
    BoolVariable('USE_PNG',  'Enable support for PNG images', have_png),
    BoolVariable('CP_ANNOTATE', 'Enable critical path annotation capability',
                 False),
    BoolVariable('USE_KVM', 'Enable hardware virtualized (KVM) CPU models',
                 have_kvm),
    BoolVariable('USE_TUNTAP',
                 'Enable using a tap device to bridge to the host network',
                 have_tuntap),
    BoolVariable('BUILD_GPU', 'Build the compute-GPU model', False),
    EnumVariable('PROTOCOL', 'Coherence protocol for Ruby', 'None',
                  all_protocols),
    EnumVariable('BACKTRACE_IMPL', 'Post-mortem dump implementation',
                 backtrace_impls[-1], backtrace_impls),
    ('NUMBER_BITS_PER_SET', 'Max elements in set (default 64)',
                 64),
    BoolVariable('USE_HDF5', 'Enable the HDF5 support', have_hdf5),
    )

# These variables get exported to #defines in config/*.hh (see src/SConscript).
export_vars += ['USE_FENV', 'SS_COMPATIBLE_FP', 'TARGET_ISA', 'TARGET_GPU_ISA',
                'CP_ANNOTATE', 'USE_POSIX_CLOCK', 'USE_KVM', 'USE_TUNTAP',
                'PROTOCOL', 'HAVE_PROTOBUF', 'HAVE_VALGRIND',
                'HAVE_PERF_ATTR_EXCLUDE_HOST', 'USE_PNG',
                'NUMBER_BITS_PER_SET', 'USE_HDF5']

###################################################
#
# Define a SCons builder for configuration flag headers.
#
###################################################

# This function generates a config header file that #defines the
# variable symbol to the current variable setting (0 or 1).  The source
# operands are the name of the variable and a Value node containing the
# value of the variable.
def build_config_file(target, source, env):
    (variable, value) = [s.get_contents() for s in source]
    f = file(str(target[0]), 'w')
    print('#define', variable, value, file=f)
    f.close()
    return None

# Combine the two functions into a scons Action object.
config_action = MakeAction(build_config_file, Transform("CONFIG H", 2))

# The emitter munges the source & target node lists to reflect what
# we're really doing.
def config_emitter(target, source, env):
    # extract variable name from Builder arg
    variable = str(target[0])
    # True target is config header file
    target = joinpath('config', variable.lower() + '.hh')
    val = env[variable]
    if isinstance(val, bool):
        # Force value to 0/1
        val = int(val)
    elif isinstance(val, str):
        val = '"' + val + '"'

    # Sources are variable name & value (packaged in SCons Value nodes)
    return ([target], [Value(variable), Value(val)])

config_builder = Builder(emitter = config_emitter, action = config_action)

main.Append(BUILDERS = { 'ConfigFile' : config_builder })

###################################################
#
# Builders for static and shared partially linked object files.
#
###################################################

partial_static_builder = Builder(action=SCons.Defaults.LinkAction,
                                 src_suffix='$OBJSUFFIX',
                                 src_builder=['StaticObject', 'Object'],
                                 LINKFLAGS='$PLINKFLAGS',
                                 LIBS='')

def partial_shared_emitter(target, source, env):
    for tgt in target:
        tgt.attributes.shared = 1
    return (target, source)
partial_shared_builder = Builder(action=SCons.Defaults.ShLinkAction,
                                 emitter=partial_shared_emitter,
                                 src_suffix='$SHOBJSUFFIX',
                                 src_builder='SharedObject',
                                 SHLINKFLAGS='$PSHLINKFLAGS',
                                 LIBS='')

main.Append(BUILDERS = { 'PartialShared' : partial_shared_builder,
                         'PartialStatic' : partial_static_builder })

def add_local_rpath(env, *targets):
    '''Set up an RPATH for a library which lives in the build directory.

    The construction environment variable BIN_RPATH_PREFIX should be set to
    the relative path of the build directory starting from the location of the
    binary.'''
    for target in targets:
        target = env.Entry(target)
        if not isinstance(target, SCons.Node.FS.Dir):
            target = target.dir
        relpath = os.path.relpath(target.abspath, env['BUILDDIR'])
        components = [
            '\\$$ORIGIN',
            '${BIN_RPATH_PREFIX}',
            relpath
        ]
        env.Append(RPATH=[env.Literal(os.path.join(*components))])

if sys.platform != "darwin":
    main.Append(LINKFLAGS=Split('-z origin'))

main.AddMethod(add_local_rpath, 'AddLocalRPATH')

# builds in ext are shared across all configs in the build root.
ext_dir = abspath(joinpath(str(main.root), 'ext'))
ext_build_dirs = []
for root, dirs, files in os.walk(ext_dir):
    if 'SConscript' in files:
        build_dir = os.path.relpath(root, ext_dir)
        ext_build_dirs.append(build_dir)
        main.SConscript(joinpath(root, 'SConscript'),
                        variant_dir=joinpath(build_root, build_dir))

gdb_xml_dir = joinpath(ext_dir, 'gdb-xml')
Export('gdb_xml_dir')

main.Prepend(CPPPATH=Dir('ext/pybind11/include/'))

###################################################
#
# This builder and wrapper method are used to set up a directory with
# switching headers. Those are headers which are in a generic location and
# that include more specific headers from a directory chosen at build time
# based on the current build settings.
#
###################################################

def build_switching_header(target, source, env):
    path = str(target[0])
    subdir = str(source[0])
    dp, fp = os.path.split(path)
    dp = os.path.relpath(os.path.realpath(dp),
                         os.path.realpath(env['BUILDDIR']))
    with open(path, 'w') as hdr:
        print('#include "%s/%s/%s"' % (dp, subdir, fp), file=hdr)

switching_header_action = MakeAction(build_switching_header,
                                     Transform('GENERATE'))

switching_header_builder = Builder(action=switching_header_action,
                                   source_factory=Value,
                                   single_source=True)

main.Append(BUILDERS = { 'SwitchingHeader': switching_header_builder })

def switching_headers(self, headers, source):
    for header in headers:
        self.SwitchingHeader(header, source)

main.AddMethod(switching_headers, 'SwitchingHeaders')

###################################################
#
# Define build environments for selected configurations.
#
###################################################

for variant_path in variant_paths:
    if not GetOption('silent'):
        print("Building in", variant_path)

    # Make a copy of the build-root environment to use for this config.
    env = main.Clone()
    env['BUILDDIR'] = variant_path

    # variant_dir is the tail component of build path, and is used to
    # determine the build parameters (e.g., 'ALPHA_SE')
    (build_root, variant_dir) = splitpath(variant_path)

    # Set env variables according to the build directory config.
    sticky_vars.files = []
    # Variables for $BUILD_ROOT/$VARIANT_DIR are stored in
    # $BUILD_ROOT/variables/$VARIANT_DIR so you can nuke
    # $BUILD_ROOT/$VARIANT_DIR without losing your variables settings.
    current_vars_file = joinpath(build_root, 'variables', variant_dir)
    if isfile(current_vars_file):
        sticky_vars.files.append(current_vars_file)
        if not GetOption('silent'):
            print("Using saved variables file %s" % current_vars_file)
    elif variant_dir in ext_build_dirs:
        # Things in ext are built without a variant directory.
        continue
    else:
        # Build dir-specific variables file doesn't exist.

        # Make sure the directory is there so we can create it later
        opt_dir = dirname(current_vars_file)
        if not isdir(opt_dir):
            mkdir(opt_dir)

        # Get default build variables from source tree.  Variables are
        # normally determined by name of $VARIANT_DIR, but can be
        # overridden by '--default=' arg on command line.
        default = GetOption('default')
        opts_dir = joinpath(main.root.abspath, 'build_opts')
        if default:
            default_vars_files = [joinpath(build_root, 'variables', default),
                                  joinpath(opts_dir, default)]
        else:
            default_vars_files = [joinpath(opts_dir, variant_dir)]
        existing_files = filter(isfile, default_vars_files)
        if existing_files:
            default_vars_file = existing_files[0]
            sticky_vars.files.append(default_vars_file)
            print("Variables file %s not found,\n  using defaults in %s"
                  % (current_vars_file, default_vars_file))
        else:
            error("Cannot find variables file %s or default file(s) %s"
                  % (current_vars_file, ' or '.join(default_vars_files)))
            Exit(1)

    # Apply current variable settings to env
    sticky_vars.Update(env)

    help_texts["local_vars"] += \
        "Build variables for %s:\n" % variant_dir \
                 + sticky_vars.GenerateHelpText(env)

    # Process variable settings.

    if not have_fenv and env['USE_FENV']:
        warning("<fenv.h> not available; forcing USE_FENV to False in",
                variant_dir + ".")
        env['USE_FENV'] = False

    if not env['USE_FENV']:
        warning("No IEEE FP rounding mode control in", variant_dir + ".\n"
                "FP results may deviate slightly from other platforms.")

    if not have_png and env['USE_PNG']:
        warning("<png.h> not available; forcing USE_PNG to False in",
                variant_dir + ".")
        env['USE_PNG'] = False

    if env['USE_PNG']:
        env.Append(LIBS=['png'])

    if env['EFENCE']:
        env.Append(LIBS=['efence'])

    if env['USE_KVM']:
        if not have_kvm:
            warning("Can not enable KVM, host seems to lack KVM support")
            env['USE_KVM'] = False
        elif not is_isa_kvm_compatible(env['TARGET_ISA']):
            print("Info: KVM support disabled due to unsupported host and "
                  "target ISA combination")
            env['USE_KVM'] = False

    if env['USE_TUNTAP']:
        if not have_tuntap:
            warning("Can't connect EtherTap with a tap device.")
            env['USE_TUNTAP'] = False

    if env['BUILD_GPU']:
        env.Append(CPPDEFINES=['BUILD_GPU'])

    # Warn about missing optional functionality
    if env['USE_KVM']:
        if not main['HAVE_PERF_ATTR_EXCLUDE_HOST']:
            warning("perf_event headers lack support for the exclude_host "
                    "attribute. KVM instruction counts will be inaccurate.")

    # Save sticky variable settings back to current variables file
    sticky_vars.Save(current_vars_file, env)

    if env['USE_SSE2']:
        env.Append(CCFLAGS=['-msse2'])

    env.Append(CCFLAGS='$CCFLAGS_EXTRA')
    env.Append(LINKFLAGS='$LDFLAGS_EXTRA')

    # The src/SConscript file sets up the build rules in 'env' according
    # to the configured variables.  It returns a list of environments,
    # one for each variant build (debug, opt, etc.)
    SConscript('src/SConscript', variant_dir = variant_path, exports = 'env')

# base help text
Help('''
Usage: scons [scons options] [build variables] [target(s)]

Extra scons options:
%(options)s

Global build variables:
%(global_vars)s

%(local_vars)s
''' % help_texts)