summaryrefslogtreecommitdiff
path: root/doc/user/troubleshoot.xml
blob: 428aa692a4f9a877e17c4ba8d83d0f62a631988e (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
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
<!--

  Copyright (c) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 The SCons Foundation

  Permission is hereby granted, free of charge, to any person obtaining
  a copy of this software and associated documentation files (the
  "Software"), to deal in the Software without restriction, including
  without limitation the rights to use, copy, modify, merge, publish,
  distribute, sublicense, and/or sell copies of the Software, and to
  permit persons to whom the Software is furnished to do so, subject to
  the following conditions:

  The above copyright notice and this permission notice shall be included
  in all copies or substantial portions of the Software.

  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY
  KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
  WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

-->

  <para>

  The experience of configuring any
  software build tool to build a large code base
  usually, at some point,
  involves trying to figure out why
  the tool is behaving a certain way,
  and how to get it to behave the way you want.
  &SCons; is no different.
  This appendix contains a number of
  different ways in which you can
  get some additional insight into &SCons;' behavior.

  </para>

  <para>

  Note that we're always interested in trying to
  improve how you can troubleshoot configuration problems.
  If you run into a problem that has
  you scratching your head,
  and which there just doesn't seem to be a good way to debug,
  odds are pretty good that someone else will run into
  the same problem, too.
  If so, please let the SCons development team know
  (preferably by filing a bug report
  or feature request at our project pages at tigris.org)
  so that we can use your feedback
  to try to come up with a better way to help you,
  and others, get the necessary insight into &SCons; behavior
  to help identify and fix configuration issues.

  </para>

  <section>
  <title>Why is That Target Being Rebuilt?  the &debug-explain; Option</title>

    <para>

    Let's look at a simple example of
    a misconfigured build
    that causes a target to be rebuilt
    every time &SCons; is run:

    </para>

    <programlisting>
      # Intentionally misspell the output file name in the
      # command used to create the file:
      Command('file.out', 'file.in', 'cp $SOURCE file.oout')
    </programlisting>

    <para>

    (Note to Windows users:  The POSIX &cp; command
    copies the first file named on the command line
    to the second file.
    In our example, it copies the &file_in; file
    to the &file_out; file.)

    </para>

    <para>

    Now if we run &SCons; multiple times on this example,
    we see that it re-runs the &cp;
    command every time:

    </para>

    <screen>
      % <userinput>scons -Q</userinput>
      cp file.in file.oout
      % <userinput>scons -Q</userinput>
      cp file.in file.oout
      % <userinput>scons -Q</userinput>
      cp file.in file.oout
    </screen>

    <para>

    In this example,
    the underlying cause is obvious:
    we've intentionally misspelled the output file name
    in the &cp; command,
    so the command doesn't actually
    build the &file_out; file that we've told &SCons; to expect.
    But if the problem weren't obvious,
    it would be helpful
    to specify the &debug-explain; option
    on the command line
    to have &SCons; tell us very specifically
    why it's decided to rebuild the target:

    </para>

    <screen>
      % <userinput>scons -Q --debug=explain</userinput>
      scons: building `file.out' because it doesn't exist
      cp file.in file.oout
    </screen>

    <para>

    If this had been a more complicated example
    involving a lot of build output,
    having &SCons; tell us that
    it's trying to rebuild the target file
    because it doesn't exist
    would be an important clue
    that something was wrong with
    the command that we invoked to build it.

    </para>

    <para>

    The &debug-explain; option also comes in handy
    to help figure out what input file changed.
    Given a simple configuration that builds
    a program from three source files,
    changing one of the source files
    and rebuilding with the &debug-explain;
    option shows very specifically
    why &SCons; rebuilds the files that it does:

    </para>

    

    <screen>
      % <userinput>scons -Q</userinput>
      cc -o file1.o -c file1.c
      cc -o file2.o -c file2.c
      cc -o file3.o -c file3.c
      cc -o prog file1.o file2.o file3.o
      % <userinput>edit file2.c</userinput>
          [CHANGE THE CONTENTS OF file2.c]
      % <userinput>scons -Q --debug=explain</userinput>
      scons: rebuilding `file2.o' because `file2.c' changed
      cc -o file2.o -c file2.c
      scons: rebuilding `prog' because `file2.o' changed
      cc -o prog file1.o file2.o file3.o
    </screen>

    <para>

    This becomes even more helpful
    in identifying when a file is rebuilt
    due to a change in an implicit dependency,
    such as an incuded <filename>.h</filename> file.
    If the <filename>file1.c</filename>
    and <filename>file3.c</filename> files
    in our example
    both included a &hello_h; file,
    then changing that included file
    and re-running &SCons; with the &debug-explain; option
    will pinpoint that it's the change to the included file
    that starts the chain of rebuilds:

    </para>

    

    <screen>
      % <userinput>scons -Q</userinput>
      cc -o file1.o -c -I. file1.c
      cc -o file2.o -c -I. file2.c
      cc -o file3.o -c -I. file3.c
      cc -o prog file1.o file2.o file3.o
      % <userinput>edit hello.h</userinput>
          [CHANGE THE CONTENTS OF hello.h]
      % <userinput>scons -Q --debug=explain</userinput>
      scons: rebuilding `file1.o' because `hello.h' changed
      cc -o file1.o -c -I. file1.c
      scons: rebuilding `file3.o' because `hello.h' changed
      cc -o file3.o -c -I. file3.c
      scons: rebuilding `prog' because:
                 `file1.o' changed
                 `file3.o' changed
      cc -o prog file1.o file2.o file3.o
    </screen>

    <para>

    (Note that the &debug-explain; option will only tell you
    why &SCons; decided to rebuild necessary targets.
    It does not tell you what files it examined
    when deciding <emphasis>not</emphasis>
    to rebuild a target file,
    which is often a more valuable question to answer.)

    </para>

  </section>

  <section>
  <title>What's in That Construction Environment?  the &Dump; Method</title>

    <para>

    When you create a construction environment,
    &SCons; populates it
    with construction variables that are set up
    for various compilers, linkers and utilities
    that it finds on your system.
    Although this is usually helpful and what you want,
    it might be frustrating if &SCons;
    doesn't set certain variables that you
    expect to be set.
    In situations like this,
    it's sometimes helpful to use the
    construction environment &Dump; method
    to print all or some of
    the construction variables.
    Note that the &Dump; method
    <emphasis>returns</emphasis>
    the representation of the variables
    in the environment
    for you to print (or otherwise manipulate):

    </para>

    <programlisting>
         env = Environment()
         print env.Dump()
    </programlisting>

    <para>

    On a POSIX system with gcc installed,
    this might generate:

    </para>

    <screen>
      % <userinput>scons</userinput>
      scons: Reading SConscript files ...
      { 'BUILDERS': {'_InternalInstall': &lt;function InstallBuilderWrapper at 0x700000&gt;, '_InternalInstallAs': &lt;function InstallAsBuilderWrapper at 0x700000&gt;},
        'CONFIGUREDIR': '#/.sconf_temp',
        'CONFIGURELOG': '#/config.log',
        'CPPSUFFIXES': [ '.c',
                         '.C',
                         '.cxx',
                         '.cpp',
                         '.c++',
                         '.cc',
                         '.h',
                         '.H',
                         '.hxx',
                         '.hpp',
                         '.hh',
                         '.F',
                         '.fpp',
                         '.FPP',
                         '.m',
                         '.mm',
                         '.S',
                         '.spp',
                         '.SPP'],
        'DSUFFIXES': ['.d'],
        'Dir': &lt;SCons.Defaults.Variable_Method_Caller instance at 0x700000&gt;,
        'Dirs': &lt;SCons.Defaults.Variable_Method_Caller instance at 0x700000&gt;,
        'ENV': {'PATH': '/usr/local/bin:/opt/bin:/bin:/usr/bin'},
        'ESCAPE': &lt;function escape at 0x700000&gt;,
        'File': &lt;SCons.Defaults.Variable_Method_Caller instance at 0x700000&gt;,
        'HOST_ARCH': None,
        'HOST_OS': None,
        'IDLSUFFIXES': ['.idl', '.IDL'],
        'INSTALL': &lt;function copyFunc at 0x700000&gt;,
        'LIBPREFIX': 'lib',
        'LIBPREFIXES': ['$LIBPREFIX'],
        'LIBSUFFIX': '.a',
        'LIBSUFFIXES': ['$LIBSUFFIX', '$SHLIBSUFFIX'],
        'MAXLINELENGTH': 128072,
        'OBJPREFIX': '',
        'OBJSUFFIX': '.o',
        'PLATFORM': 'posix',
        'PROGPREFIX': '',
        'PROGSUFFIX': '',
        'PSPAWN': &lt;function piped_env_spawn at 0x700000&gt;,
        'RDirs': &lt;SCons.Defaults.Variable_Method_Caller instance at 0x700000&gt;,
        'SCANNERS': [],
        'SHELL': 'sh',
        'SHLIBPREFIX': '$LIBPREFIX',
        'SHLIBSUFFIX': '.so',
        'SHOBJPREFIX': '$OBJPREFIX',
        'SHOBJSUFFIX': '$OBJSUFFIX',
        'SPAWN': &lt;function spawnvpe_spawn at 0x700000&gt;,
        'TARGET_ARCH': None,
        'TARGET_OS': None,
        'TEMPFILE': &lt;class SCons.Platform.TempFileMunge at 0x700000&gt;,
        'TEMPFILEPREFIX': '@',
        'TOOLS': ['install', 'install'],
        '_CPPDEFFLAGS': '${_defines(CPPDEFPREFIX, CPPDEFINES, CPPDEFSUFFIX, __env__)}',
        '_CPPINCFLAGS': '$( ${_concat(INCPREFIX, CPPPATH, INCSUFFIX, __env__, RDirs, TARGET, SOURCE)} $)',
        '_LIBDIRFLAGS': '$( ${_concat(LIBDIRPREFIX, LIBPATH, LIBDIRSUFFIX, __env__, RDirs, TARGET, SOURCE)} $)',
        '_LIBFLAGS': '${_concat(LIBLINKPREFIX, LIBS, LIBLINKSUFFIX, __env__)}',
        '__RPATH': '$_RPATH',
        '_concat': &lt;function _concat at 0x700000&gt;,
        '_defines': &lt;function _defines at 0x700000&gt;,
        '_stripixes': &lt;function _stripixes at 0x700000&gt;}
      scons: done reading SConscript files.
      scons: Building targets ...
      scons: `.' is up to date.
      scons: done building targets.
    </screen>

    <para>

    On a Windows system with Visual C++
    the output might look like:

    </para>

    <screen>
      C:\><userinput>scons</userinput>
      scons: Reading SConscript files ...
      { 'BUILDERS': {'_InternalInstall': &lt;function InstallBuilderWrapper at 0x700000&gt;, 'Object': &lt;SCons.Builder.CompositeBuilder instance at 0x700000&gt;, 'PCH': &lt;SCons.Builder.BuilderBase instance at 0x700000&gt;, 'RES': &lt;SCons.Builder.BuilderBase instance at 0x700000&gt;, 'SharedObject': &lt;SCons.Builder.CompositeBuilder instance at 0x700000&gt;, 'StaticObject': &lt;SCons.Builder.CompositeBuilder instance at 0x700000&gt;, '_InternalInstallAs': &lt;function InstallAsBuilderWrapper at 0x700000&gt;},
        'CC': 'cl',
        'CCCOM': &lt;SCons.Action.FunctionAction instance at 0x700000&gt;,
        'CCFLAGS': ['/nologo'],
        'CCPCHFLAGS': ['${(PCH and "/Yu%s /Fp%s"%(PCHSTOP or "",File(PCH))) or ""}'],
        'CCPDBFLAGS': ['${(PDB and "/Z7") or ""}'],
        'CFILESUFFIX': '.c',
        'CFLAGS': [],
        'CONFIGUREDIR': '#/.sconf_temp',
        'CONFIGURELOG': '#/config.log',
        'CPPDEFPREFIX': '/D',
        'CPPDEFSUFFIX': '',
        'CPPSUFFIXES': [ '.c',
                         '.C',
                         '.cxx',
                         '.cpp',
                         '.c++',
                         '.cc',
                         '.h',
                         '.H',
                         '.hxx',
                         '.hpp',
                         '.hh',
                         '.F',
                         '.fpp',
                         '.FPP',
                         '.m',
                         '.mm',
                         '.S',
                         '.spp',
                         '.SPP'],
        'CXX': '$CC',
        'CXXCOM': '$CXX $_MSVC_OUTPUT_FLAG /c $CHANGED_SOURCES $CXXFLAGS $CCFLAGS $_CCCOMCOM',
        'CXXFILESUFFIX': '.cc',
        'CXXFLAGS': ['$(', '/TP', '$)'],
        'DSUFFIXES': ['.d'],
        'Dir': &lt;SCons.Defaults.Variable_Method_Caller instance at 0x700000&gt;,
        'Dirs': &lt;SCons.Defaults.Variable_Method_Caller instance at 0x700000&gt;,
        'ENV': { 'PATH': 'C:\\WINDOWS\\System32',
                 'PATHEXT': '.COM;.EXE;.BAT;.CMD',
                 'SystemRoot': 'C:\\WINDOWS'},
        'ESCAPE': &lt;function escape at 0x700000&gt;,
        'File': &lt;SCons.Defaults.Variable_Method_Caller instance at 0x700000&gt;,
        'HOST_ARCH': '',
        'HOST_OS': 'win32',
        'IDLSUFFIXES': ['.idl', '.IDL'],
        'INCPREFIX': '/I',
        'INCSUFFIX': '',
        'INSTALL': &lt;function copyFunc at 0x700000&gt;,
        'LIBPREFIX': '',
        'LIBPREFIXES': ['$LIBPREFIX'],
        'LIBSUFFIX': '.lib',
        'LIBSUFFIXES': ['$LIBSUFFIX'],
        'MAXLINELENGTH': 2048,
        'MSVC_SETUP_RUN': True,
        'OBJPREFIX': '',
        'OBJSUFFIX': '.obj',
        'PCHCOM': '$CXX /Fo${TARGETS[1]} $CXXFLAGS $CCFLAGS $CPPFLAGS $_CPPDEFFLAGS $_CPPINCFLAGS /c $SOURCES /Yc$PCHSTOP /Fp${TARGETS[0]} $CCPDBFLAGS $PCHPDBFLAGS',
        'PCHPDBFLAGS': ['${(PDB and "/Yd") or ""}'],
        'PLATFORM': 'win32',
        'PROGPREFIX': '',
        'PROGSUFFIX': '.exe',
        'PSPAWN': &lt;function piped_spawn at 0x700000&gt;,
        'RC': 'rc',
        'RCCOM': &lt;SCons.Action.FunctionAction instance at 0x700000&gt;,
        'RCFLAGS': [],
        'RCSUFFIXES': ['.rc', '.rc2'],
        'RDirs': &lt;SCons.Defaults.Variable_Method_Caller instance at 0x700000&gt;,
        'SCANNERS': [],
        'SHCC': '$CC',
        'SHCCCOM': &lt;SCons.Action.FunctionAction instance at 0x700000&gt;,
        'SHCCFLAGS': ['$CCFLAGS'],
        'SHCFLAGS': ['$CFLAGS'],
        'SHCXX': '$CXX',
        'SHCXXCOM': '$SHCXX $_MSVC_OUTPUT_FLAG /c $CHANGED_SOURCES $SHCXXFLAGS $SHCCFLAGS $_CCCOMCOM',
        'SHCXXFLAGS': ['$CXXFLAGS'],
        'SHELL': None,
        'SHLIBPREFIX': '',
        'SHLIBSUFFIX': '.dll',
        'SHOBJPREFIX': '$OBJPREFIX',
        'SHOBJSUFFIX': '$OBJSUFFIX',
        'SPAWN': &lt;function spawn at 0x700000&gt;,
        'STATIC_AND_SHARED_OBJECTS_ARE_THE_SAME': 1,
        'TARGET_ARCH': '',
        'TARGET_OS': 'win32',
        'TEMPFILE': &lt;class SCons.Platform.TempFileMunge at 0x700000&gt;,
        'TEMPFILEPREFIX': '@',
        'TOOLS': ['msvc', 'install', 'install'],
        '_CCCOMCOM': '$CPPFLAGS $_CPPDEFFLAGS $_CPPINCFLAGS $CCPCHFLAGS $CCPDBFLAGS',
        '_CPPDEFFLAGS': '${_defines(CPPDEFPREFIX, CPPDEFINES, CPPDEFSUFFIX, __env__)}',
        '_CPPINCFLAGS': '$( ${_concat(INCPREFIX, CPPPATH, INCSUFFIX, __env__, RDirs, TARGET, SOURCE)} $)',
        '_LIBDIRFLAGS': '$( ${_concat(LIBDIRPREFIX, LIBPATH, LIBDIRSUFFIX, __env__, RDirs, TARGET, SOURCE)} $)',
        '_LIBFLAGS': '${_concat(LIBLINKPREFIX, LIBS, LIBLINKSUFFIX, __env__)}',
        '_MSVC_OUTPUT_FLAG': &lt;function msvc_output_flag at 0x700000&gt;,
        '_concat': &lt;function _concat at 0x700000&gt;,
        '_defines': &lt;function _defines at 0x700000&gt;,
        '_stripixes': &lt;function _stripixes at 0x700000&gt;}
      scons: done reading SConscript files.
      scons: Building targets ...
      scons: `.' is up to date.
      scons: done building targets.
    </screen>

    <para>

    The construction environments in these examples have
    actually been restricted to just gcc and Visual C++,
    respectively.
    In a real-life situation,
    the construction environments will
    likely contain a great many more variables.
    Also note that we've massaged the example output above
    to make the memory address of all objects a constant 0x700000.
    In reality, you would see a different hexadecimal
    number for each object.

    </para>

    <para>

    To make it easier to see just what you're
    interested in,
    the &Dump; method allows you to
    specify a specific constrcution variable
    that you want to disply.
    For example,
    it's not unusual to want to verify
    the external environment used to execute build commands,
    to make sure that the PATH and other
    environment variables are set up the way they should be.
    You can do this as follows:

    </para>

    <programlisting>
         env = Environment()
         print env.Dump('ENV')
    </programlisting>

    <para>

    Which might display the following when executed on a POSIX system:

    </para>

    <screen>
      % <userinput>scons</userinput>
      scons: Reading SConscript files ...
      {'PATH': '/usr/local/bin:/opt/bin:/bin:/usr/bin'}
      scons: done reading SConscript files.
      scons: Building targets ...
      scons: `.' is up to date.
      scons: done building targets.
    </screen>

    <para>

    And the following when executed on a Windows system:

    </para>

    <screen>
      C:\><userinput>scons</userinput>
      scons: Reading SConscript files ...
      { 'PATH': 'C:\\WINDOWS\\System32',
        'PATHEXT': '.COM;.EXE;.BAT;.CMD',
        'SystemRoot': 'C:\\WINDOWS'}
      scons: done reading SConscript files.
      scons: Building targets ...
      scons: `.' is up to date.
      scons: done building targets.
    </screen>

  </section>

  <section>

  <title>What Dependencies Does &SCons; Know About?  the &tree; Option</title>

    <para>

    Sometimes the best way to try to figure out what
    &SCons; is doing is simply to take a look at the
    dependency graph that it constructs
    based on your &SConscript; files.
    The <literal>--tree</literal> option
    will display all or part of the
    &SCons; dependency graph in an
    "ASCII art" graphical format
    that shows the dependency hierarchy.

    </para>

    <para>

    For example, given the following input &SConstruct; file:

    </para>

    <programlisting>
         env = Environment(CPPPATH = ['.'])
         env.Program('prog', ['f1.c', 'f2.c', 'f3.c'])
    </programlisting>

    <para>

    Running &SCons; with the <literal>--tree=all</literal>
    option yields:

    </para>

    <screen>
      % <userinput>scons -Q --tree=all</userinput>
      cc -o f1.o -c -I. f1.c
      cc -o f2.o -c -I. f2.c
      cc -o f3.o -c -I. f3.c
      cc -o prog f1.o f2.o f3.o
      +-.
        +-SConstruct
        +-f1.c
        +-f1.o
        | +-f1.c
        | +-inc.h
        +-f2.c
        +-f2.o
        | +-f2.c
        | +-inc.h
        +-f3.c
        +-f3.o
        | +-f3.c
        | +-inc.h
        +-inc.h
        +-prog
          +-f1.o
          | +-f1.c
          | +-inc.h
          +-f2.o
          | +-f2.c
          | +-inc.h
          +-f3.o
            +-f3.c
            +-inc.h
    </screen>

    <para>

    The tree will also be printed when the
    <literal>-n</literal> (no execute) option is used,
    which allows you to examine the dependency graph
    for a configuration without actually
    rebuilding anything in the tree.

    </para>

    <para>

    The <literal>--tree</literal> option only prints
    the dependency graph for the specified targets
    (or the default target(s) if none are specified on the command line).
    So if you specify a target like <filename>f2.o</filename>
    on the command line,
    the <literal>--tree</literal> option will only
    print the dependency graph for that file:

    </para>

    <screen>
      % <userinput>scons -Q --tree=all f2.o</userinput>
      cc -o f2.o -c -I. f2.c
      +-f2.o
        +-f2.c
        +-inc.h
    </screen>

    <para>

    This is, of course, useful for
    restricting the output from a very large
    build configuration to just a
    portion in which you're interested.
    Multiple targets are fine,
    in which case a tree will be printed
    for each specified target:

    </para>

    <screen>
      % <userinput>scons -Q --tree=all f1.o f3.o</userinput>
      cc -o f1.o -c -I. f1.c
      +-f1.o
        +-f1.c
        +-inc.h
      cc -o f3.o -c -I. f3.c
      +-f3.o
        +-f3.c
        +-inc.h
    </screen>

    <para>

    The <literal>status</literal> argument may be used
    to tell &SCons; to print status information about
    each file in the dependency graph:

    </para>

    <screen>
      % <userinput>scons -Q --tree=status</userinput>
      cc -o f1.o -c -I. f1.c
      cc -o f2.o -c -I. f2.c
      cc -o f3.o -c -I. f3.c
      cc -o prog f1.o f2.o f3.o
       E         = exists
        R        = exists in repository only
         b       = implicit builder
         B       = explicit builder
          S      = side effect
           P     = precious
            A    = always build
             C   = current
              N  = no clean
               H = no cache
      
      [E b      ]+-.
      [E     C  ]  +-SConstruct
      [E     C  ]  +-f1.c
      [E B   C  ]  +-f1.o
      [E     C  ]  | +-f1.c
      [E     C  ]  | +-inc.h
      [E     C  ]  +-f2.c
      [E B   C  ]  +-f2.o
      [E     C  ]  | +-f2.c
      [E     C  ]  | +-inc.h
      [E     C  ]  +-f3.c
      [E B   C  ]  +-f3.o
      [E     C  ]  | +-f3.c
      [E     C  ]  | +-inc.h
      [E     C  ]  +-inc.h
      [E B   C  ]  +-prog
      [E B   C  ]    +-f1.o
      [E     C  ]    | +-f1.c
      [E     C  ]    | +-inc.h
      [E B   C  ]    +-f2.o
      [E     C  ]    | +-f2.c
      [E     C  ]    | +-inc.h
      [E B   C  ]    +-f3.o
      [E     C  ]      +-f3.c
      [E     C  ]      +-inc.h
    </screen>

    <para>

    Note that <literal>--tree=all,status</literal> is equivalent;
    the <literal>all</literal>
    is assumed if only <literal>status</literal> is present.
    As an alternative to <literal>all</literal>,
    you can specify <literal>--tree=derived</literal>
    to have &SCons; only print derived targets
    in the tree output,
    skipping source files
    (like <filename>.c</filename> and <filename>.h</filename> files):

    </para>

    <screen>
      % <userinput>scons -Q --tree=derived</userinput>
      cc -o f1.o -c -I. f1.c
      cc -o f2.o -c -I. f2.c
      cc -o f3.o -c -I. f3.c
      cc -o prog f1.o f2.o f3.o
      +-.
        +-f1.o
        +-f2.o
        +-f3.o
        +-prog
          +-f1.o
          +-f2.o
          +-f3.o
    </screen>

    <para>

    You can use the <literal>status</literal>
    modifier with <literal>derived</literal> as well:

    </para>

    <screen>
      % <userinput>scons -Q --tree=derived,status</userinput>
      cc -o f1.o -c -I. f1.c
      cc -o f2.o -c -I. f2.c
      cc -o f3.o -c -I. f3.c
      cc -o prog f1.o f2.o f3.o
       E         = exists
        R        = exists in repository only
         b       = implicit builder
         B       = explicit builder
          S      = side effect
           P     = precious
            A    = always build
             C   = current
              N  = no clean
               H = no cache
      
      [E b      ]+-.
      [E B   C  ]  +-f1.o
      [E B   C  ]  +-f2.o
      [E B   C  ]  +-f3.o
      [E B   C  ]  +-prog
      [E B   C  ]    +-f1.o
      [E B   C  ]    +-f2.o
      [E B   C  ]    +-f3.o
    </screen>

    <para>

    Note that the order of the <literal>--tree=</literal>
    arguments doesn't matter;
    <literal>--tree=status,derived</literal> is
    completely equivalent.

    </para>

    <para>

    The default behavior of the <literal>--tree</literal> option
    is to repeat all of the dependencies each time the library dependency
    (or any other dependency file) is encountered in the tree.
    If certain target files share other target files,
    such as two programs that use the same library:

    </para>

    <programlisting>
         env = Environment(CPPPATH = ['.'],
                           LIBS = ['foo'],
                           LIBPATH = ['.'])
         env.Library('foo', ['f1.c', 'f2.c', 'f3.c'])
         env.Program('prog1.c')
         env.Program('prog2.c')
    </programlisting>

    <para>

    Then there can be a <emphasis>lot</emphasis> of repetition in the
    <literal>--tree=</literal> output:

    </para>

    <screen>
      % <userinput>scons -Q --tree=all</userinput>
      cc -o f1.o -c -I. f1.c
      cc -o f2.o -c -I. f2.c
      cc -o f3.o -c -I. f3.c
      ar rc libfoo.a f1.o f2.o f3.o
      ranlib libfoo.a
      cc -o prog1.o -c -I. prog1.c
      cc -o prog1 prog1.o -L. -lfoo
      cc -o prog2.o -c -I. prog2.c
      cc -o prog2 prog2.o -L. -lfoo
      +-.
        +-SConstruct
        +-f1.c
        +-f1.o
        | +-f1.c
        | +-inc.h
        +-f2.c
        +-f2.o
        | +-f2.c
        | +-inc.h
        +-f3.c
        +-f3.o
        | +-f3.c
        | +-inc.h
        +-inc.h
        +-libfoo.a
        | +-f1.o
        | | +-f1.c
        | | +-inc.h
        | +-f2.o
        | | +-f2.c
        | | +-inc.h
        | +-f3.o
        |   +-f3.c
        |   +-inc.h
        +-prog1
        | +-prog1.o
        | | +-prog1.c
        | | +-inc.h
        | +-libfoo.a
        |   +-f1.o
        |   | +-f1.c
        |   | +-inc.h
        |   +-f2.o
        |   | +-f2.c
        |   | +-inc.h
        |   +-f3.o
        |     +-f3.c
        |     +-inc.h
        +-prog1.c
        +-prog1.o
        | +-prog1.c
        | +-inc.h
        +-prog2
        | +-prog2.o
        | | +-prog2.c
        | | +-inc.h
        | +-libfoo.a
        |   +-f1.o
        |   | +-f1.c
        |   | +-inc.h
        |   +-f2.o
        |   | +-f2.c
        |   | +-inc.h
        |   +-f3.o
        |     +-f3.c
        |     +-inc.h
        +-prog2.c
        +-prog2.o
          +-prog2.c
          +-inc.h
    </screen>

    <para>

    In a large configuration with many internal libraries
    and include files,
    this can very quickly lead to huge output trees.
    To help make this more manageable,
    a <literal>prune</literal> modifier may
    be added to the option list,
    in which case &SCons;
    will print the name of a target that has
    already been visited during the tree-printing
    in <literal>[square brackets]</literal>
    as an indication that the dependencies
    of the target file may be found
    by looking farther up the tree:

    </para>

    <screen>
      % <userinput>scons -Q --tree=prune</userinput>
      cc -o f1.o -c -I. f1.c
      cc -o f2.o -c -I. f2.c
      cc -o f3.o -c -I. f3.c
      ar rc libfoo.a f1.o f2.o f3.o
      ranlib libfoo.a
      cc -o prog1.o -c -I. prog1.c
      cc -o prog1 prog1.o -L. -lfoo
      cc -o prog2.o -c -I. prog2.c
      cc -o prog2 prog2.o -L. -lfoo
      +-.
        +-SConstruct
        +-f1.c
        +-f1.o
        | +-f1.c
        | +-inc.h
        +-f2.c
        +-f2.o
        | +-f2.c
        | +-inc.h
        +-f3.c
        +-f3.o
        | +-f3.c
        | +-inc.h
        +-inc.h
        +-libfoo.a
        | +-[f1.o]
        | +-[f2.o]
        | +-[f3.o]
        +-prog1
        | +-prog1.o
        | | +-prog1.c
        | | +-inc.h
        | +-[libfoo.a]
        +-prog1.c
        +-[prog1.o]
        +-prog2
        | +-prog2.o
        | | +-prog2.c
        | | +-inc.h
        | +-[libfoo.a]
        +-prog2.c
        +-[prog2.o]
    </screen>

    <para>

    Like the <literal>status</literal> keyword,
    the <literal>prune</literal> argument by itself
    is equivalent to <literal>--tree=all,prune</literal>.

    </para>

  </section>

  <section>

  <title>How is &SCons; Constructing the Command Lines It Executes?  the &debug-presub; Option</title>

    <para>

    Sometimes it's useful to look at the
    pre-substitution string
    that &SCons; uses to generate
    the command lines it executes.
    This can be done with the &debug-presub; option:

    </para>

    

    <!--

    Have to capture output here, otherwise the - -debug=presub output
    shows the Python functions from the sconsdoc.py execution wrapper
    used to generate this manual, not the underlying command-line strings.

    <scons_output example="presub">
      <scons_output_command>scons -Q - -debug=presub</scons_output_command>
    </scons_output>

    -->

    <screen>
      % <userinput>scons -Q --debug=presub</userinput>
      Building prog.o with action:
        $CC -o $TARGET -c $CFLAGS $CCFLAGS $_CCOMCOM $SOURCES
      cc -o prog.o -c -I. prog.c
      Building prog with action:
        $SMART_LINKCOM
      cc -o prog prog.o
    </screen>

  </section>

  <section>

  <title>Where is &SCons; Searching for Libraries?  the &debug-findlibs; Option</title>

    <para>

    To get some insight into what library names
    &SCons; is searching for,
    and in which directories it is searching,
    Use the <literal>--debug=findlibs</literal> option.
    Given the following input &SConstruct; file:

    </para>

    <programlisting>
        env = Environment(LIBPATH = ['libs1', 'libs2'])
        env.Program('prog.c', LIBS=['foo', 'bar'])
    </programlisting>

    <para>

    And the libraries <filename>libfoo.a</filename>
    and <filename>libbar.a</filename>
    in <filename>libs1</filename> and <filename>libs2</filename>,
    respectively,
    use of the <literal>--debug=findlibs</literal> option yields:

    </para>

    <screen>
      % <userinput>scons -Q --debug=findlibs</userinput>
        findlibs: looking for 'libfoo.a' in 'libs1' ...
        findlibs: ... FOUND 'libfoo.a' in 'libs1'
        findlibs: looking for 'libfoo.so' in 'libs1' ...
        findlibs: looking for 'libfoo.so' in 'libs2' ...
        findlibs: looking for 'libbar.a' in 'libs1' ...
        findlibs: looking for 'libbar.a' in 'libs2' ...
        findlibs: ... FOUND 'libbar.a' in 'libs2'
        findlibs: looking for 'libbar.so' in 'libs1' ...
        findlibs: looking for 'libbar.so' in 'libs2' ...
      cc -o prog.o -c prog.c
      cc -o prog prog.o -Llibs1 -Llibs2 -lfoo -lbar
    </screen>

  </section>

  <!--

  <section>

  <title>What Implicit Dependencies Did the &SCons; Scanner find?  the &debug-includes; Option</title>

    <para>

    XXX explain the - - debug=includes option

    </para>

    <scons_example name="includes">
      <file name="SConstruct" printme="1">
        env = Environment(CPPPATH = ['inc1', 'inc2'])
        env.Program('prog.c')
      </file>
      <file name="prog.c">
      #include "file1.h"
      #include "file2.h"
      prog.c
      </file>
      <file name="inc1/file1.h">
      inc1/file1.h
      </file>
      <file name="inc2/file2.h">
      inc2/file2.h
      </file>
    </scons_example>

    <scons_output example="includes">
      <scons_output_command>scons -Q - - debug=includes prog</scons_output_command>
    </scons_output>

  </section>

  -->

  <section>

  <title>Where is &SCons; Blowing Up?  the &debug-stacktrace; Option</title>

    <para>

    In general, &SCons; tries to keep its error
    messages short and informative.
    That means we usually try to avoid showing
    the stack traces that are familiar
    to experienced Python programmers,
    since they usually contain much more
    information than is useful to most people.

    </para>

    <para>

    For example, the following &SConstruct; file:

    </para>

    <programlisting>
         Program('prog.c')
    </programlisting>

    <para>

    Generates the following error if the
    <filename>prog.c</filename> file
    does not exist:

    </para>

    <screen>
      % <userinput>scons -Q</userinput>
      scons: *** [prog.o] Source `prog.c' not found, needed by target `prog.o'.
    </screen>

    <para>

    In this case,
    the error is pretty obvious.
    But if it weren't,
    and you wanted to try to get more information
    about the error,
    the &debug-stacktrace; option
    would show you exactly where in the &SCons; source code
    the problem occurs:

    </para>

    <screen>
      % <userinput>scons -Q --debug=stacktrace</userinput>
      scons: *** [prog.o] Source `prog.c' not found, needed by target `prog.o'.
      scons: internal stack trace:
        File "bootstrap/src/engine/SCons/Job.py", line 197, in start
          task.prepare()
        File "bootstrap/src/engine/SCons/Script/Main.py", line 167, in prepare
          return SCons.Taskmaster.OutOfDateTask.prepare(self)
        File "bootstrap/src/engine/SCons/Taskmaster.py", line 190, in prepare
          executor.prepare()
        File "bootstrap/src/engine/SCons/Executor.py", line 397, in prepare
          raise SCons.Errors.StopError, msg % (s, self.batches[0].targets[0])
    </screen>

    <para>

    Of course, if you do need to dive into the &SCons; source code,
    we'd like to know if, or how,
    the error messages or troubleshooting options
    could have been improved to avoid that.
    Not everyone has the necessary time or
    Python skill to dive into the source code,
    and we'd like to improve &SCons;
    for those people as well...

    </para>

  </section>

  <section>

  <title>How is &SCons; Making Its Decisions?  the &taskmastertrace; Option</title>

    <para>

    The internal &SCons; subsystem that handles walking
    the dependency graph
    and controls the decision-making about what to rebuild
    is the <literal>Taskmaster</literal>.
    &SCons; supports a <literal>--taskmastertrace</literal>
    option that tells the Taskmaster to print
    information about the children (dependencies)
    of the various Nodes on its walk down the graph,
    which specific dependent Nodes are being evaluated,
    and in what order.

    </para>

    <para>

    The <literal>--taskmastertrace</literal> option
    takes as an argument the name of a file in
    which to put the trace output,
    with <filename>-</filename> (a single hyphen)
    indicating that the trace messages
    should be printed to the standard output:

    </para>

    <programlisting>
      env = Environment(CPPPATH = ['.'])
      env.Program('prog.c')
    </programlisting>

    <screen>
      % <userinput>scons -Q --taskmastertrace=- prog</userinput>
      
      Taskmaster: Looking for a node to evaluate
      Taskmaster:     Considering node &lt;no_state   0   'prog'&gt; and its children:
      Taskmaster:        &lt;no_state   0   'prog.o'&gt;
      Taskmaster:      adjusted ref count: &lt;pending    1   'prog'&gt;, child 'prog.o'
      Taskmaster:     Considering node &lt;no_state   0   'prog.o'&gt; and its children:
      Taskmaster:        &lt;no_state   0   'prog.c'&gt;
      Taskmaster:        &lt;no_state   0   'inc.h'&gt;
      Taskmaster:      adjusted ref count: &lt;pending    1   'prog.o'&gt;, child 'prog.c'
      Taskmaster:      adjusted ref count: &lt;pending    2   'prog.o'&gt;, child 'inc.h'
      Taskmaster:     Considering node &lt;no_state   0   'prog.c'&gt; and its children:
      Taskmaster: Evaluating &lt;pending    0   'prog.c'&gt;
      
      Task.make_ready_current(): node &lt;pending    0   'prog.c'&gt;
      Task.prepare():      node &lt;up_to_date 0   'prog.c'&gt;
      Task.executed_with_callbacks(): node &lt;up_to_date 0   'prog.c'&gt;
      Task.postprocess():  node &lt;up_to_date 0   'prog.c'&gt;
      Task.postprocess():  removing &lt;up_to_date 0   'prog.c'&gt;
      Task.postprocess():  adjusted parent ref count &lt;pending    1   'prog.o'&gt;
      
      Taskmaster: Looking for a node to evaluate
      Taskmaster:     Considering node &lt;no_state   0   'inc.h'&gt; and its children:
      Taskmaster: Evaluating &lt;pending    0   'inc.h'&gt;
      
      Task.make_ready_current(): node &lt;pending    0   'inc.h'&gt;
      Task.prepare():      node &lt;up_to_date 0   'inc.h'&gt;
      Task.executed_with_callbacks(): node &lt;up_to_date 0   'inc.h'&gt;
      Task.postprocess():  node &lt;up_to_date 0   'inc.h'&gt;
      Task.postprocess():  removing &lt;up_to_date 0   'inc.h'&gt;
      Task.postprocess():  adjusted parent ref count &lt;pending    0   'prog.o'&gt;
      
      Taskmaster: Looking for a node to evaluate
      Taskmaster:     Considering node &lt;pending    0   'prog.o'&gt; and its children:
      Taskmaster:        &lt;up_to_date 0   'prog.c'&gt;
      Taskmaster:        &lt;up_to_date 0   'inc.h'&gt;
      Taskmaster: Evaluating &lt;pending    0   'prog.o'&gt;
      
      Task.make_ready_current(): node &lt;pending    0   'prog.o'&gt;
      Task.prepare():      node &lt;executing  0   'prog.o'&gt;
      Task.execute():      node &lt;executing  0   'prog.o'&gt;
      cc -o prog.o -c -I. prog.c
      Task.executed_with_callbacks(): node &lt;executing  0   'prog.o'&gt;
      Task.postprocess():  node &lt;executed   0   'prog.o'&gt;
      Task.postprocess():  removing &lt;executed   0   'prog.o'&gt;
      Task.postprocess():  adjusted parent ref count &lt;pending    0   'prog'&gt;
      
      Taskmaster: Looking for a node to evaluate
      Taskmaster:     Considering node &lt;pending    0   'prog'&gt; and its children:
      Taskmaster:        &lt;executed   0   'prog.o'&gt;
      Taskmaster: Evaluating &lt;pending    0   'prog'&gt;
      
      Task.make_ready_current(): node &lt;pending    0   'prog'&gt;
      Task.prepare():      node &lt;executing  0   'prog'&gt;
      Task.execute():      node &lt;executing  0   'prog'&gt;
      cc -o prog prog.o
      Task.executed_with_callbacks(): node &lt;executing  0   'prog'&gt;
      Task.postprocess():  node &lt;executed   0   'prog'&gt;
      
      Taskmaster: Looking for a node to evaluate
      Taskmaster: No candidate anymore.
    </screen>

    <para>

    The <literal>--taskmastertrace</literal> option
    doesn't provide information about the actual
    calculations involved in deciding if a file is up-to-date,
    but it does show all of the dependencies
    it knows about for each Node,
    and the order in which those dependencies are evaluated.
    This can be useful as an alternate way to determine
    whether or not your &SCons; configuration,
    or the implicit dependency scan,
    has actually identified all the correct dependencies
    you want it to.

    </para>

  </section>

  <!--

  <section>

  <title>Where Are My Build Bottlenecks?  the &profile; Option</title>

    <para>

    XXX explain the - - profile= option

    </para>

  </section>

  -->

  <!--

  <section>
  <title>Troubleshooting Shared Caching:  the &cache-debug; Option</title>

    <para>

    XXX describe the - - cache-debug option
    XXX maybe point to the caching.in chapter?

    </para>

  </section>

  -->