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
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
|
D B U G
C Program Debugging Package
by
Fred Fish
- 1 -
DBUG User Manual October 29, 1986
INTRODUCTION
Almost every program development environment worthy of
the name provides some sort of debugging facility. Usually
this takes the form of a program which is capable of
controlling execution of other programs and examining the
internal state of other executing programs. These types of
programs will be referred to as external debuggers since the
debugger is not part of the executing program. Examples of
this type of debugger include the adb and sdb debuggers
provided with the UNIX1 operating system.
One of the problems associated with developing programs
in an environment with good external debuggers is that
developed programs tend to have little or no internal
instrumentation. This is usually not a problem for the
developer since he is, or at least should be, intimately
familiar with the internal organization, data structures,
and control flow of the program being debugged. It is a
serious problem for maintenance programmers, who are
unlikely to have such familiarity with the program being
maintained, modified, or ported to another environment. It
is also a problem, even for the developer, when the program
is moved to an environment with a primitive or unfamiliar
debugger, or even no debugger.
On the other hand, dbug is an example of an internal
debugger. Because it requires internal instrumentation of a
program, and its usage does not depend on any special
capabilities of the execution environment, it is always
available and will execute in any environment that the
program itself will execute in. In addition, since it is a
complete package with a specific user interface, all
programs which use it will be provided with similar
debugging capabilities. This is in sharp contrast to other
forms of internal instrumentation where each developer has
their own, usually less capable, form of internal debugger.
In summary, because dbug is an internal debugger it provides
consistency across operating environments, and because it is
available to all developers it provides consistency across
all programs in the same environment.
The dbug package imposes only a slight speed penalty on
executing programs, typically much less than 10 percent, and
a modest size penalty, typically 10 to 20 percent. By
defining a specific C preprocessor symbol both of these can
be reduced to zero with no changes required to the source
____________________
1. UNIX is a trademark of AT&T Bell Laboratories.
- 2 -
DBUG User Manual October 29, 1986
code.
The following list is a quick summary of the
capabilities of the dbug package. Each capability can be
individually enabled or disabled at the time a program is
invoked by specifying the appropriate command line
arguments.
o Execution trace showing function level control
flow in a semi-graphically manner using
indentation to indicate nesting depth.
o Output the values of all, or any subset of, key
internal variables.
o Limit actions to a specific set of named
functions.
o Limit function trace to a specified nesting depth.
o Label each output line with source file name and
line number.
o Label each output line with name of current
process.
o Push or pop internal debugging state to allow
execution with built in debugging defaults.
o Redirect the debug output stream to standard
output (stdout) or a named file. The default
output stream is standard error (stderr). The
redirection mechanism is completely independent of
normal command line redirection to avoid output
conflicts.
- 3 -
DBUG User Manual October 29, 1986
PRIMITIVE DEBUGGING TECHNIQUES
Internal instrumentation is already a familiar concept
to most programmers, since it is usually the first debugging
technique learned. Typically, "print statements" are
inserted in the source code at interesting points, the code
is recompiled and executed, and the resulting output is
examined in an attempt to determine where the problem is.
The procedure is iterative, with each iteration yielding
more and more output, and hopefully the source of the
problem is discovered before the output becomes too large to
deal with or previously inserted statements need to be
removed. Figure 1 is an example of this type of primitive
debugging technique.
#include <stdio.h>
main (argc, argv)
int argc;
char *argv[];
{
printf ("argv[0] = %d\n", argv[0]);
/*
* Rest of program
*/
printf ("== done ==\n");
}
Figure 1
Primitive Debugging Technique
Eventually, and usually after at least several
iterations, the problem will be found and corrected. At
this point, the newly inserted print statements must be
dealt with. One obvious solution is to simply delete them
all. Beginners usually do this a few times until they have
to repeat the entire process every time a new bug pops up.
The second most obvious solution is to somehow disable the
output, either through the source code comment facility,
creation of a debug variable to be switched on or off, or by
using the C preprocessor. Figure 2 is an example of all
three techniques.
- 4 -
DBUG User Manual October 29, 1986
#include <stdio.h>
int debug = 0;
main (argc, argv)
int argc;
char *argv[];
{
/* printf ("argv = %x\n", argv) */
if (debug) printf ("argv[0] = %d\n", argv[0]);
/*
* Rest of program
*/
#ifdef DEBUG
printf ("== done ==\n");
#endif
}
Figure 2
Debug Disable Techniques
Each technique has its advantages and disadvantages
with respect to dynamic vs static activation, source code
overhead, recompilation requirements, ease of use, program
readability, etc. Overuse of the preprocessor solution
quickly leads to problems with source code readability and
maintainability when multiple #ifdef symbols are to be
defined or undefined based on specific types of debug
desired. The source code can be made slightly more readable
by suitable indentation of the #ifdef arguments to match the
indentation of the code, but not all C preprocessors allow
this. The only requirement for the standard UNIX C
preprocessor is for the '#' character to appear in the first
column, but even this seems like an arbitrary and
unreasonable restriction. Figure 3 is an example of this
usage.
- 5 -
DBUG User Manual October 29, 1986
#include <stdio.h>
main (argc, argv)
int argc;
char *argv[];
{
# ifdef DEBUG
printf ("argv[0] = %d\n", argv[0]);
# endif
/*
* Rest of program
*/
# ifdef DEBUG
printf ("== done ==\n");
# endif
}
Figure 3
More Readable Preprocessor Usage
- 6 -
DBUG User Manual October 29, 1986
FUNCTION TRACE EXAMPLE
We will start off learning about the capabilities of
the dbug package by using a simple minded program which
computes the factorial of a number. In order to better
demonstrate the function trace mechanism, this program is
implemented recursively. Figure 4 is the main function for
this factorial program.
#include <stdio.h>
/* User programs should use <local/dbug.h> */
#include "dbug.h"
int main (argc, argv)
int argc;
char *argv[];
{
register int result, ix;
extern int factorial (), atoi ();
DBUG_ENTER ("main");
DBUG_PROCESS (argv[0]);
for (ix = 1; ix < argc && argv[ix][0] == '-'; ix++) {
switch (argv[ix][1]) {
case '#':
DBUG_PUSH (&(argv[ix][2]));
break;
}
}
for (; ix < argc; ix++) {
DBUG_PRINT ("args", ("argv[%d] = %s", ix, argv[ix]));
result = factorial (atoi (argv[ix]));
printf ("%d\n", result);
}
DBUG_RETURN (0);
}
Figure 4
Factorial Program Mainline
The main function is responsible for processing any
command line option arguments and then computing and
printing the factorial of each non-option argument.
First of all, notice that all of the debugger functions
are implemented via preprocessor macros. This does not
- 7 -
DBUG User Manual October 29, 1986
detract from the readability of the code and makes disabling
all debug compilation trivial (a single preprocessor symbol,
DBUG_OFF, forces the macro expansions to be null).
Also notice the inclusion of the header file dbug.h
from the local header file directory. (The version included
here is the test version in the dbug source distribution
directory). This file contains all the definitions for the
debugger macros, which all have the form DBUG_XX...XX.
The DBUG_ENTER macro informs that debugger that we have
entered the function named main. It must be the very first
"executable" line in a function, after all declarations and
before any other executable line. The DBUG_PROCESS macro is
generally used only once per program to inform the debugger
what name the program was invoked with. The DBUG_PUSH macro
modifies the current debugger state by saving the previous
state and setting a new state based on the control string
passed as its argument. The DBUG_PRINT macro is used to
print the values of each argument for which a factorial is
to be computed. The DBUG_RETURN macro tells the debugger
that the end of the current function has been reached and
returns a value to the calling function. All of these
macros will be fully explained in subsequent sections.
To use the debugger, the factorial program is invoked
with a command line of the form:
factorial -#d:t 1 2 3
The main function recognizes the "-#d:t" string as a
debugger control string, and passes the debugger arguments
("d:t") to the dbug runtime support routines via the
DBUG_PUSH macro. This particular string enables output from
the DBUG_PRINT macro with the 'd' flag and enables function
tracing with the 't' flag. The factorial function is then
called three times, with the arguments "1", "2", and "3".
Note that the DBUG_PRINT takes exactly two arguments, with
the second argument (a format string and list of printable
values) enclosed in parenthesis.
Debug control strings consist of a header, the "-#",
followed by a colon separated list of debugger arguments.
Each debugger argument is a single character flag followed
by an optional comma separated list of arguments specific to
the given flag. Some examples are:
-#d:t:o
-#d,in,out:f,main:F:L
Note that previously enabled debugger actions can be
disabled by the control string "-#".
- 8 -
DBUG User Manual October 29, 1986
The definition of the factorial function, symbolized as
"N!", is given by:
N! = N * N-1 * ... 2 * 1
Figure 5 is the factorial function which implements this
algorithm recursively. Note that this is not necessarily
the best way to do factorials and error conditions are
ignored completely.
#include <stdio.h>
/* User programs should use <local/dbug.h> */
#include "dbug.h"
int factorial (value)
register int value;
{
DBUG_ENTER ("factorial");
DBUG_PRINT ("find", ("find %d factorial", value));
if (value > 1) {
value *= factorial (value - 1);
}
DBUG_PRINT ("result", ("result is %d", value));
DBUG_RETURN (value);
}
Figure 5
Factorial Function
One advantage (some may not consider it so) to using
the dbug package is that it strongly encourages fully
structured coding with only one entry and one exit point in
each function. Multiple exit points, such as early returns
to escape a loop, may be used, but each such point requires
the use of an appropriate DBUG_RETURN or DBUG_VOID_RETURN
macro.
To build the factorial program on a UNIX system,
compile and link with the command:
cc -o factorial main.c factorial.c -ldbug
The "-ldbug" argument tells the loader to link in the
runtime support modules for the dbug package. Executing the
factorial program with a command of the form:
- 9 -
DBUG User Manual October 29, 1986
factorial 1 2 3 4 5
generates the output shown in figure 6.
1
2
6
24
120
Figure 6
factorial 1 2 3 4 5
Function level tracing is enabled by passing the
debugger the 't' flag in the debug control string. Figure 7
is the output resulting from the command
"factorial -#t:o 3 2".
| >factorial
| | >factorial
| | <factorial
| <factorial
2
| >factorial
| | >factorial
| | | >factorial
| | | <factorial
| | <factorial
| <factorial
6
<main
Figure 7
factorial -#t:o 3 2
Each entry to or return from a function is indicated by
'>' for the entry point and '<' for the exit point,
connected by vertical bars to allow matching points to be
easily found when separated by large distances.
This trace output indicates that there was an initial
- 10 -
DBUG User Manual October 29, 1986
call to factorial from main (to compute 2!), followed by a
single recursive call to factorial to compute 1!. The main
program then output the result for 2! and called the
factorial function again with the second argument, 3.
Factorial called itself recursively to compute 2! and 1!,
then returned control to main, which output the value for 3!
and exited.
Note that there is no matching entry point "main>" for
the return point "<main" because at the time the DBUG_ENTER
macro was reached in main, tracing was not enabled yet. It
was only after the macro DBUG_PUSH was executing that
tracing became enabled. This implies that the argument list
should be processed as early as possible since all code
preceding the first call to DBUG_PUSH is essentially
invisible to dbug (this can be worked around by inserting a
temporary DBUG_PUSH(argv[1]) immediately after the
DBUG_ENTER("main") macro.
One last note, the trace output normally comes out on
the standard error. Since the factorial program prints its
result on the standard output, there is the possibility of
the output on the terminal being scrambled if the two
streams are not synchronized. Thus the debugger is told to
write its output on the standard output instead, via the 'o'
flag character. Note that no 'o' implies the default
(standard error), a 'o' with no arguments means standard
output, and a 'o' with an argument means used the named
file. I.E, "factorial -#t:o,logfile 3 2" would write the
trace output in "logfile". Because of UNIX implementation
details, programs usually run faster when writing to stdout
rather than stderr, though this is not a prime consideration
in this example.
- 11 -
DBUG User Manual October 29, 1986
USE OF DBUG_PRINT MACRO
The mechanism used to produce "printf" style output is
the DBUG_PRINT macro.
To allow selection of output from specific macros, the
first argument to every DBUG_PRINT macro is a dbug keyword.
When this keyword appears in the argument list of the 'd'
flag in a debug control string, as in
"-#d,keyword1,keyword2,...:t", output from the corresponding
macro is enabled. The default when there is no 'd' flag in
the control string is to enable output from all DBUG_PRINT
macros.
Typically, a program will be run once, with no keywords
specified, to determine what keywords are significant for
the current problem (the keywords are printed in the macro
output line). Then the program will be run again, with the
desired keywords, to examine only specific areas of
interest.
The second argument to a DBUG_PRINT macro is a standard
printf style format string and one or more arguments to
print, all enclosed in parenthesis so that they collectively
become a single macro argument. This is how variable
numbers of printf arguments are supported. Also note that
no explicit newline is required at the end of the format
string. As a matter of style, two or three small DBUG_PRINT
macros are preferable to a single macro with a huge format
string. Figure 8 shows the output for default tracing and
debug.
- 12 -
DBUG User Manual October 29, 1986
| args: argv[2] = 3
| >factorial
| | find: find 3 factorial
| | >factorial
| | | find: find 2 factorial
| | | >factorial
| | | | find: find 1 factorial
| | | | result: result is 1
| | | <factorial
| | | result: result is 2
| | <factorial
| | result: result is 6
| <factorial
6
<main
Figure 8
factorial -#d:t:o 3
The output from the DBUG_PRINT macro is indented to
match the trace output for the function in which the macro
occurs. When debugging is enabled, but not trace, the
output starts at the left margin, without indentation.
To demonstrate selection of specific macros for output,
figure 9 shows the result when the factorial program is
invoked with the debug control string "-#d,result:o".
factorial: result: result is 1
factorial: result: result is 2
factorial: result: result is 6
factorial: result: result is 24
24
Figure 9
factorial -#d,result:o 4
It is sometimes desirable to restrict debugging and
trace actions to a specific function or list of functions.
This is accomplished with the 'f' flag character in the
debug control string. Figure 10 is the output of the
factorial program when run with the control string
"-#d:f,factorial:F:L:o". The 'F' flag enables printing of
- 13 -
DBUG User Manual October 29, 1986
the source file name and the 'L' flag enables printing of
the source file line number.
factorial.c: 9: factorial: find: find 3 factorial
factorial.c: 9: factorial: find: find 2 factorial
factorial.c: 9: factorial: find: find 1 factorial
factorial.c: 13: factorial: result: result is 1
factorial.c: 13: factorial: result: result is 2
factorial.c: 13: factorial: result: result is 6
6
Figure 10
factorial -#d:f,factorial:F:L:o 3
The output in figure 10 shows that the "find" macro is
in file "factorial.c" at source line 8 and the "result"
macro is in the same file at source line 12.
- 14 -
DBUG User Manual October 29, 1986
SUMMARY OF MACROS
This section summarizes the usage of all currently
defined macros in the dbug package. The macros definitions
are found in the user include file dbug.h from the standard
include directory.
DBUG_ENTER Used to tell the runtime support module
the name of the function being entered.
The argument must be of type "pointer to
character". The DBUG_ENTER macro must
precede all executable lines in the
function just entered, and must come
after all local declarations. Each
DBUG_ENTER macro must have a matching
DBUG_RETURN or DBUG_VOID_RETURN macro at
the function exit points. DBUG_ENTER
macros used without a matching
DBUG_RETURN or DBUG_VOID_RETURN macro
will cause warning messages from the
dbug package runtime support module.
EX: DBUG_ENTER ("main");
DBUG_RETURN Used at each exit point of a function
containing a DBUG_ENTER macro at the
entry point. The argument is the value
to return. Functions which return no
value (void) should use the
DBUG_VOID_RETURN macro. It is an error
to have a DBUG_RETURN or
DBUG_VOID_RETURN macro in a function
which has no matching DBUG_ENTER macro,
and the compiler will complain if the
macros are actually used (expanded).
EX: DBUG_RETURN (value);
EX: DBUG_VOID_RETURN;
DBUG_PROCESS Used to name the current process being
executed. A typical argument for this
macro is "argv[0]", though it will be
perfectly happy with any other string.
EX: DBUG_PROCESS (argv[0]);
DBUG_PUSH Sets a new debugger state by pushing the
current dbug state onto an internal
stack and setting up the new state using
the debug control string passed as the
macro argument. The most common usage
- 15 -
DBUG User Manual October 29, 1986
is to set the state specified by a debug
control string retrieved from the
argument list. Note that the leading
"-#" in a debug control string specified
as a command line argument must not be
passed as part of the macro argument.
The proper usage is to pass a pointer to
the first character after the "-#"
string.
EX: DBUG_PUSH ((argv[i][2]));
EX: DBUG_PUSH ("d:t");
EX: DBUG_PUSH ("");
DBUG_POP Restores the previous debugger state by
popping the state stack. Attempting to
pop more states than pushed will be
ignored and no warning will be given.
The DBUG_POP macro has no arguments.
EX: DBUG_POP ();
DBUG_FILE The DBUG_FILE macro is used to do
explicit I/O on the debug output stream.
It is used in the same manner as the
symbols "stdout" and "stderr" in the
standard I/O package.
EX: fprintf (DBUG_FILE, "Doing my own
I/O!\n");
DBUG_EXECUTE The DBUG_EXECUTE macro is used to
execute any arbitrary C code. The first
argument is the debug keyword, used to
trigger execution of the code specified
as the second argument. This macro must
be used cautiously because, like the
DBUG_PRINT macro, it is automatically
selected by default whenever the 'd'
flag has no argument list (I.E., a
"-#d:t" control string).
EX: DBUG_EXECUTE ("abort", abort ());
DBUG_N These macros, where N is in the range
2-5, are currently obsolete and will be
removed in a future release. Use the
new DBUG_PRINT macro.
DBUG_PRINT Used to do printing via the "fprintf"
library function on the current debug
stream, DBUG_FILE. The first argument
is a debug keyword, the second is a
format string and the corresponding
- 16 -
DBUG User Manual October 29, 1986
argument list. Note that the format
string and argument list are all one
macro argument and must be enclosed in
parenthesis.
EX: DBUG_PRINT ("eof", ("end of file found"));
EX: DBUG_PRINT ("type", ("type is %x",
type));
EX: DBUG_PRINT ("stp", ("%x -> %s", stp,
stp -> name));
DBUG_SETJMP Used in place of the setjmp() function
to first save the current debugger state
and then execute the standard setjmp
call. This allows to the debugger to
restore it's state when the DBUG_LONGJMP
macro is used to invoke the standard
longjmp() call. Currently all instances
of DBUG_SETJMP must occur within the
same function and at the same function
nesting level.
EX: DBUG_SETJMP (env);
DBUG_LONGJMP Used in place of the longjmp() function
to first restore the previous debugger
state at the time of the last
DBUG_SETJMP and then execute the
standard longjmp() call. Note that
currently all DBUG_LONGJMP macros
restore the state at the time of the
last DBUG_SETJMP. It would be possible
to maintain separate DBUG_SETJMP and
DBUG_LONGJMP pairs by having the
debugger runtime support module use the
first argument to differentiate the
pairs.
EX: DBUG_LONGJMP (env,val);
- 17 -
DBUG User Manual October 29, 1986
DEBUG CONTROL STRING
The debug control string is used to set the state of
the debugger via the DBUG_PUSH macro. This section
summarizes the currently available debugger options and the
flag characters which enable or disable them. Argument
lists enclosed in '[' and ']' are optional.
d[,keywords] Enable output from macros with
specified keywords. A null list of
keywords implies that all keywords are
selected.
D[,time] Delay for specified time after each
output line, to let output drain.
Time is given in tenths of a second
(value of 10 is one second). Default
is zero.
f[,functions] Limit debugger actions to the
specified list of functions. A null
list of functions implies that all
functions are selected.
F Mark each debugger output line with
the name of the source file containing
the macro causing the output.
L Mark each debugger output line with
the source file line number of the
macro causing the output.
n Mark each debugger output line with
the current function nesting depth.
N Sequentially number each debugger
output line starting at 1. This is
useful for reference purposes when
debugger output is interspersed with
program output.
o[,file] Redirect the debugger output stream to
the specified file. The default
output stream is stderr. A null
argument list causes output to be
redirected to stdout.
p[,processes] Limit debugger actions to the
specified processes. A null list
implies all processes. This is useful
for processes which run child
processes. Note that each debugger
- 18 -
DBUG User Manual October 29, 1986
output line can be marked with the
name of the current process via the
'P' flag. The process name must match
the argument passed to the
DBUG_PROCESS macro.
P Mark each debugger output line with
the name of the current process. Most
useful when used with a process which
runs child processes that are also
being debugged. Note that the parent
process must arrange for the debugger
control string to be passed to the
child processes.
r Used in conjunction with the DBUG_PUSH
macro to reset the current indentation
level back to zero. Most useful with
DBUG_PUSH macros used to temporarily
alter the debugger state.
t[,N] Enable function control flow tracing.
The maximum nesting depth is specified
by N, and defaults to 200.
- 19 -
DBUG User Manual October 29, 1986
HINTS AND MISCELLANEOUS
One of the most useful capabilities of the dbug package
is to compare the executions of a given program in two
different environments. This is typically done by executing
the program in the environment where it behaves properly and
saving the debugger output in a reference file. The program
is then run with identical inputs in the environment where
it misbehaves and the output is again captured in a
reference file. The two reference files can then be
differentially compared to determine exactly where execution
of the two processes diverges.
A related usage is regression testing where the
execution of a current version is compared against
executions of previous versions. This is most useful when
there are only minor changes.
It is not difficult to modify an existing compiler to
implement some of the functionality of the dbug package
automatically, without source code changes to the program
being debugged. In fact, such changes were implemented in a
version of the Portable C Compiler by the author in less
than a day. However, it is strongly encouraged that all
newly developed code continue to use the debugger macros for
the portability reasons noted earlier. The modified
compiler should be used only for testing existing programs.
- 20 -
DBUG User Manual October 29, 1986
CAVEATS
The dbug package works best with programs which have
"line oriented" output, such as text processors, general
purpose utilities, etc. It can be interfaced with screen
oriented programs such as visual editors by redefining the
appropriate macros to call special functions for displaying
the debugger results. Of course, this caveat is not
applicable if the debugger output is simply dumped into a
file for post-execution examination.
Programs which use memory allocation functions other
than malloc will usually have problems using the standard
dbug package. The most common problem is multiply allocated
memory.
- 21 -
D B U G
C Program Debugging Package
by
Fred Fish
ABSTRACT
This document introduces dbug, a macro based C debugging
package which has proven to be a very flexible and useful
tool for debugging, testing, and porting C programs.
All of the features of the dbug package can be enabled
or disabled dynamically at execution time. This means that
production programs will run normally when debugging is not
enabled, and eliminates the need to maintain two separate
versions of a program.
Many of the things easily accomplished with
conventional debugging tools, such as symbolic debuggers,
are difficult or impossible with this package, and vice
versa. Thus the dbug package should not be thought of as a
replacement or substitute for other debugging tools, but
simply as a useful addition to the program development and
maintenance environment.
- 22 -
|