summaryrefslogtreecommitdiffstats
path: root/contrib/gcc/doc/gcov.1
blob: ac3b0c4765a5a016b82a21e01d3fa6d0247eeeea (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
.\" Automatically generated by Pod::Man v1.37, Pod::Parser v1.14
.\"
.\" Standard preamble:
.\" ========================================================================
.de Sh \" Subsection heading
.br
.if t .Sp
.ne 5
.PP
\fB\\$1\fR
.PP
..
.de Sp \" Vertical space (when we can't use .PP)
.if t .sp .5v
.if n .sp
..
.de Vb \" Begin verbatim text
.ft CW
.nf
.ne \\$1
..
.de Ve \" End verbatim text
.ft R
.fi
..
.\" Set up some character translations and predefined strings.  \*(-- will
.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left
.\" double quote, and \*(R" will give a right double quote.  | will give a
.\" real vertical bar.  \*(C+ will give a nicer C++.  Capital omega is used to
.\" do unbreakable dashes and therefore won't be available.  \*(C` and \*(C'
.\" expand to `' in nroff, nothing in troff, for use with C<>.
.tr \(*W-|\(bv\*(Tr
.ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p'
.ie n \{\
.    ds -- \(*W-
.    ds PI pi
.    if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
.    if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\"  diablo 12 pitch
.    ds L" ""
.    ds R" ""
.    ds C` ""
.    ds C' ""
'br\}
.el\{\
.    ds -- \|\(em\|
.    ds PI \(*p
.    ds L" ``
.    ds R" ''
'br\}
.\"
.\" If the F register is turned on, we'll generate index entries on stderr for
.\" titles (.TH), headers (.SH), subsections (.Sh), items (.Ip), and index
.\" entries marked with X<> in POD.  Of course, you'll have to process the
.\" output yourself in some meaningful fashion.
.if \nF \{\
.    de IX
.    tm Index:\\$1\t\\n%\t"\\$2"
..
.    nr % 0
.    rr F
.\}
.\"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.hy 0
.if n .na
.\"
.\" Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2).
.\" Fear.  Run.  Save yourself.  No user-serviceable parts.
.    \" fudge factors for nroff and troff
.if n \{\
.    ds #H 0
.    ds #V .8m
.    ds #F .3m
.    ds #[ \f1
.    ds #] \fP
.\}
.if t \{\
.    ds #H ((1u-(\\\\n(.fu%2u))*.13m)
.    ds #V .6m
.    ds #F 0
.    ds #[ \&
.    ds #] \&
.\}
.    \" simple accents for nroff and troff
.if n \{\
.    ds ' \&
.    ds ` \&
.    ds ^ \&
.    ds , \&
.    ds ~ ~
.    ds /
.\}
.if t \{\
.    ds ' \\k:\h'-(\\n(.wu*8/10-\*(#H)'\'\h"|\\n:u"
.    ds ` \\k:\h'-(\\n(.wu*8/10-\*(#H)'\`\h'|\\n:u'
.    ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'^\h'|\\n:u'
.    ds , \\k:\h'-(\\n(.wu*8/10)',\h'|\\n:u'
.    ds ~ \\k:\h'-(\\n(.wu-\*(#H-.1m)'~\h'|\\n:u'
.    ds / \\k:\h'-(\\n(.wu*8/10-\*(#H)'\z\(sl\h'|\\n:u'
.\}
.    \" troff and (daisy-wheel) nroff accents
.ds : \\k:\h'-(\\n(.wu*8/10-\*(#H+.1m+\*(#F)'\v'-\*(#V'\z.\h'.2m+\*(#F'.\h'|\\n:u'\v'\*(#V'
.ds 8 \h'\*(#H'\(*b\h'-\*(#H'
.ds o \\k:\h'-(\\n(.wu+\w'\(de'u-\*(#H)/2u'\v'-.3n'\*(#[\z\(de\v'.3n'\h'|\\n:u'\*(#]
.ds d- \h'\*(#H'\(pd\h'-\w'~'u'\v'-.25m'\f2\(hy\fP\v'.25m'\h'-\*(#H'
.ds D- D\\k:\h'-\w'D'u'\v'-.11m'\z\(hy\v'.11m'\h'|\\n:u'
.ds th \*(#[\v'.3m'\s+1I\s-1\v'-.3m'\h'-(\w'I'u*2/3)'\s-1o\s+1\*(#]
.ds Th \*(#[\s+2I\s-2\h'-\w'I'u*3/5'\v'-.3m'o\v'.3m'\*(#]
.ds ae a\h'-(\w'a'u*4/10)'e
.ds Ae A\h'-(\w'A'u*4/10)'E
.    \" corrections for vroff
.if v .ds ~ \\k:\h'-(\\n(.wu*9/10-\*(#H)'\s-2\u~\d\s+2\h'|\\n:u'
.if v .ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'\v'-.4m'^\v'.4m'\h'|\\n:u'
.    \" for low resolution devices (crt and lpr)
.if \n(.H>23 .if \n(.V>19 \
\{\
.    ds : e
.    ds 8 ss
.    ds o a
.    ds d- d\h'-1'\(ga
.    ds D- D\h'-1'\(hy
.    ds th \o'bp'
.    ds Th \o'LP'
.    ds ae ae
.    ds Ae AE
.\}
.rm #[ #] #H #V #F C
.\" ========================================================================
.\"
.IX Title "GCOV 1"
.TH GCOV 1 "2007-07-19" "gcc-4.2.1" "GNU"
.SH "NAME"
gcov \- coverage testing tool
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
gcov [\fB\-v\fR|\fB\-\-version\fR] [\fB\-h\fR|\fB\-\-help\fR]
     [\fB\-a\fR|\fB\-\-all\-blocks\fR]
     [\fB\-b\fR|\fB\-\-branch\-probabilities\fR]
     [\fB\-c\fR|\fB\-\-branch\-counts\fR]
     [\fB\-n\fR|\fB\-\-no\-output\fR]
     [\fB\-l\fR|\fB\-\-long\-file\-names\fR]
     [\fB\-p\fR|\fB\-\-preserve\-paths\fR]
     [\fB\-f\fR|\fB\-\-function\-summaries\fR]
     [\fB\-o\fR|\fB\-\-object\-directory\fR \fIdirectory|file\fR] \fIsourcefile\fR
     [\fB\-u\fR|\fB\-\-unconditional\-branches\fR]
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fBgcov\fR is a test coverage program.  Use it in concert with \s-1GCC\s0
to analyze your programs to help create more efficient, faster running
code and to discover untested parts of your program.  You can use
\&\fBgcov\fR as a profiling tool to help discover where your
optimization efforts will best affect your code.  You can also use
\&\fBgcov\fR along with the other profiling tool, \fBgprof\fR, to
assess which parts of your code use the greatest amount of computing
time.
.PP
Profiling tools help you analyze your code's performance.  Using a
profiler such as \fBgcov\fR or \fBgprof\fR, you can find out some
basic performance statistics, such as:
.IP "\(bu" 4
how often each line of code executes
.IP "\(bu" 4
what lines of code are actually executed
.IP "\(bu" 4
how much computing time each section of code uses
.PP
Once you know these things about how your code works when compiled, you
can look at each module to see which modules should be optimized.
\&\fBgcov\fR helps you determine where to work on optimization.
.PP
Software developers also use coverage testing in concert with
testsuites, to make sure software is actually good enough for a release.
Testsuites can verify that a program works as expected; a coverage
program tests to see how much of the program is exercised by the
testsuite.  Developers can then determine what kinds of test cases need
to be added to the testsuites to create both better testing and a better
final product.
.PP
You should compile your code without optimization if you plan to use
\&\fBgcov\fR because the optimization, by combining some lines of code
into one function, may not give you as much information as you need to
look for `hot spots' where the code is using a great deal of computer
time.  Likewise, because \fBgcov\fR accumulates statistics by line (at
the lowest resolution), it works best with a programming style that
places only one statement on each line.  If you use complicated macros
that expand to loops or to other control structures, the statistics are
less helpful\-\-\-they only report on the line where the macro call
appears.  If your complex macros behave like functions, you can replace
them with inline functions to solve this problem.
.PP
\&\fBgcov\fR creates a logfile called \fI\fIsourcefile\fI.gcov\fR which
indicates how many times each line of a source file \fI\fIsourcefile\fI.c\fR
has executed.  You can use these logfiles along with \fBgprof\fR to aid
in fine-tuning the performance of your programs.  \fBgprof\fR gives
timing information you can use along with the information you get from
\&\fBgcov\fR.
.PP
\&\fBgcov\fR works only on code compiled with \s-1GCC\s0.  It is not
compatible with any other profiling or test coverage mechanism.
.SH "OPTIONS"
.IX Header "OPTIONS"
.IP "\fB\-h\fR" 4
.IX Item "-h"
.PD 0
.IP "\fB\-\-help\fR" 4
.IX Item "--help"
.PD
Display help about using \fBgcov\fR (on the standard output), and
exit without doing any further processing.
.IP "\fB\-v\fR" 4
.IX Item "-v"
.PD 0
.IP "\fB\-\-version\fR" 4
.IX Item "--version"
.PD
Display the \fBgcov\fR version number (on the standard output),
and exit without doing any further processing.
.IP "\fB\-a\fR" 4
.IX Item "-a"
.PD 0
.IP "\fB\-\-all\-blocks\fR" 4
.IX Item "--all-blocks"
.PD
Write individual execution counts for every basic block.  Normally gcov
outputs execution counts only for the main blocks of a line.  With this
option you can determine if blocks within a single line are not being
executed.
.IP "\fB\-b\fR" 4
.IX Item "-b"
.PD 0
.IP "\fB\-\-branch\-probabilities\fR" 4
.IX Item "--branch-probabilities"
.PD
Write branch frequencies to the output file, and write branch summary
info to the standard output.  This option allows you to see how often
each branch in your program was taken.  Unconditional branches will not
be shown, unless the \fB\-u\fR option is given.
.IP "\fB\-c\fR" 4
.IX Item "-c"
.PD 0
.IP "\fB\-\-branch\-counts\fR" 4
.IX Item "--branch-counts"
.PD
Write branch frequencies as the number of branches taken, rather than
the percentage of branches taken.
.IP "\fB\-n\fR" 4
.IX Item "-n"
.PD 0
.IP "\fB\-\-no\-output\fR" 4
.IX Item "--no-output"
.PD
Do not create the \fBgcov\fR output file.
.IP "\fB\-l\fR" 4
.IX Item "-l"
.PD 0
.IP "\fB\-\-long\-file\-names\fR" 4
.IX Item "--long-file-names"
.PD
Create long file names for included source files.  For example, if the
header file \fIx.h\fR contains code, and was included in the file
\&\fIa.c\fR, then running \fBgcov\fR on the file \fIa.c\fR will produce
an output file called \fIa.c##x.h.gcov\fR instead of \fIx.h.gcov\fR.
This can be useful if \fIx.h\fR is included in multiple source
files.  If you use the \fB\-p\fR option, both the including and
included file names will be complete path names.
.IP "\fB\-p\fR" 4
.IX Item "-p"
.PD 0
.IP "\fB\-\-preserve\-paths\fR" 4
.IX Item "--preserve-paths"
.PD
Preserve complete path information in the names of generated
\&\fI.gcov\fR files.  Without this option, just the filename component is
used.  With this option, all directories are used, with \fB/\fR characters
translated to \fB#\fR characters, \fI.\fR directory components
removed and \fI..\fR
components renamed to \fB^\fR.  This is useful if sourcefiles are in several
different directories.  It also affects the \fB\-l\fR option.
.IP "\fB\-f\fR" 4
.IX Item "-f"
.PD 0
.IP "\fB\-\-function\-summaries\fR" 4
.IX Item "--function-summaries"
.PD
Output summaries for each function in addition to the file level summary.
.IP "\fB\-o\fR \fIdirectory|file\fR" 4
.IX Item "-o directory|file"
.PD 0
.IP "\fB\-\-object\-directory\fR \fIdirectory\fR" 4
.IX Item "--object-directory directory"
.IP "\fB\-\-object\-file\fR \fIfile\fR" 4
.IX Item "--object-file file"
.PD
Specify either the directory containing the gcov data files, or the
object path name.  The \fI.gcno\fR, and
\&\fI.gcda\fR data files are searched for using this option.  If a directory
is specified, the data files are in that directory and named after the
source file name, without its extension.  If a file is specified here,
the data files are named after that file, without its extension.  If this
option is not supplied, it defaults to the current directory.
.IP "\fB\-u\fR" 4
.IX Item "-u"
.PD 0
.IP "\fB\-\-unconditional\-branches\fR" 4
.IX Item "--unconditional-branches"
.PD
When branch probabilities are given, include those of unconditional branches.
Unconditional branches are normally not interesting.
.PP
\&\fBgcov\fR should be run with the current directory the same as that
when you invoked the compiler.  Otherwise it will not be able to locate
the source files.  \fBgcov\fR produces files called
\&\fI\fImangledname\fI.gcov\fR in the current directory.  These contain
the coverage information of the source file they correspond to.
One \fI.gcov\fR file is produced for each source file containing code,
which was compiled to produce the data files.  The \fImangledname\fR part
of the output file name is usually simply the source file name, but can
be something more complicated if the \fB\-l\fR or \fB\-p\fR options are
given.  Refer to those options for details.
.PP
The \fI.gcov\fR files contain the \fB:\fR separated fields along with
program source code.  The format is
.PP
.Vb 1
\&        <execution_count>:<line_number>:<source line text>
.Ve
.PP
Additional block information may succeed each line, when requested by
command line option.  The \fIexecution_count\fR is \fB\-\fR for lines
containing no code and \fB#####\fR for lines which were never executed.
Some lines of information at the start have \fIline_number\fR of zero.
.PP
The preamble lines are of the form
.PP
.Vb 1
\&        -:0:<tag>:<value>
.Ve
.PP
The ordering and number of these preamble lines will be augmented as
\&\fBgcov\fR development progresses \-\-\- do not rely on them remaining
unchanged.  Use \fItag\fR to locate a particular preamble line.
.PP
The additional block information is of the form
.PP
.Vb 1
\&        <tag> <information>
.Ve
.PP
The \fIinformation\fR is human readable, but designed to be simple
enough for machine parsing too.
.PP
When printing percentages, 0% and 100% are only printed when the values
are \fIexactly\fR 0% and 100% respectively.  Other values which would
conventionally be rounded to 0% or 100% are instead printed as the
nearest non-boundary value.
.PP
When using \fBgcov\fR, you must first compile your program with two
special \s-1GCC\s0 options: \fB\-fprofile\-arcs \-ftest\-coverage\fR.
This tells the compiler to generate additional information needed by
gcov (basically a flow graph of the program) and also includes
additional code in the object files for generating the extra profiling
information needed by gcov.  These additional files are placed in the
directory where the object file is located.
.PP
Running the program will cause profile output to be generated.  For each
source file compiled with \fB\-fprofile\-arcs\fR, an accompanying
\&\fI.gcda\fR file will be placed in the object file directory.
.PP
Running \fBgcov\fR with your program's source file names as arguments
will now produce a listing of the code along with frequency of execution
for each line.  For example, if your program is called \fItmp.c\fR, this
is what you see when you use the basic \fBgcov\fR facility:
.PP
.Vb 5
\&        $ gcc -fprofile-arcs -ftest-coverage tmp.c
\&        $ a.out
\&        $ gcov tmp.c
\&        90.00% of 10 source lines executed in file tmp.c
\&        Creating tmp.c.gcov.
.Ve
.PP
The file \fItmp.c.gcov\fR contains output from \fBgcov\fR.
Here is a sample:
.PP
.Vb 22
\&                -:    0:Source:tmp.c
\&                -:    0:Graph:tmp.gcno
\&                -:    0:Data:tmp.gcda
\&                -:    0:Runs:1
\&                -:    0:Programs:1
\&                -:    1:#include <stdio.h>
\&                -:    2:
\&                -:    3:int main (void)
\&                1:    4:{
\&                1:    5:  int i, total;
\&                -:    6:
\&                1:    7:  total = 0;
\&                -:    8:
\&               11:    9:  for (i = 0; i < 10; i++)
\&               10:   10:    total += i;
\&                -:   11:
\&                1:   12:  if (total != 45)
\&            #####:   13:    printf ("Failure\en");
\&                -:   14:  else
\&                1:   15:    printf ("Success\en");
\&                1:   16:  return 0;
\&                -:   17:}
.Ve
.PP
When you use the \fB\-a\fR option, you will get individual block
counts, and the output looks like this:
.PP
.Vb 29
\&                -:    0:Source:tmp.c
\&                -:    0:Graph:tmp.gcno
\&                -:    0:Data:tmp.gcda
\&                -:    0:Runs:1
\&                -:    0:Programs:1
\&                -:    1:#include <stdio.h>
\&                -:    2:
\&                -:    3:int main (void)
\&                1:    4:{
\&                1:    4-block  0
\&                1:    5:  int i, total;
\&                -:    6:
\&                1:    7:  total = 0;
\&                -:    8:
\&               11:    9:  for (i = 0; i < 10; i++)
\&               11:    9-block  0
\&               10:   10:    total += i;
\&               10:   10-block  0
\&                -:   11:
\&                1:   12:  if (total != 45)
\&                1:   12-block  0
\&            #####:   13:    printf ("Failure\en");
\&            $$$$$:   13-block  0
\&                -:   14:  else
\&                1:   15:    printf ("Success\en");
\&                1:   15-block  0
\&                1:   16:  return 0;
\&                1:   16-block  0
\&                -:   17:}
.Ve
.PP
In this mode, each basic block is only shown on one line \*(-- the last
line of the block.  A multi-line block will only contribute to the
execution count of that last line, and other lines will not be shown
to contain code, unless previous blocks end on those lines.
The total execution count of a line is shown and subsequent lines show
the execution counts for individual blocks that end on that line.  After each
block, the branch and call counts of the block will be shown, if the
\&\fB\-b\fR option is given.
.PP
Because of the way \s-1GCC\s0 instruments calls, a call count can be shown
after a line with no individual blocks.
As you can see, line 13 contains a basic block that was not executed.
.PP
When you use the \fB\-b\fR option, your output looks like this:
.PP
.Vb 6
\&        $ gcov -b tmp.c
\&        90.00% of 10 source lines executed in file tmp.c
\&        80.00% of 5 branches executed in file tmp.c
\&        80.00% of 5 branches taken at least once in file tmp.c
\&        50.00% of 2 calls executed in file tmp.c
\&        Creating tmp.c.gcov.
.Ve
.PP
Here is a sample of a resulting \fItmp.c.gcov\fR file:
.PP
.Vb 29
\&                -:    0:Source:tmp.c
\&                -:    0:Graph:tmp.gcno
\&                -:    0:Data:tmp.gcda
\&                -:    0:Runs:1
\&                -:    0:Programs:1
\&                -:    1:#include <stdio.h>
\&                -:    2:
\&                -:    3:int main (void)
\&        function main called 1 returned 1 blocks executed 75%
\&                1:    4:{
\&                1:    5:  int i, total;
\&                -:    6:
\&                1:    7:  total = 0;
\&                -:    8:
\&               11:    9:  for (i = 0; i < 10; i++)
\&        branch  0 taken 91% (fallthrough)
\&        branch  1 taken 9%
\&               10:   10:    total += i;
\&                -:   11:
\&                1:   12:  if (total != 45)
\&        branch  0 taken 0% (fallthrough)
\&        branch  1 taken 100%
\&            #####:   13:    printf ("Failure\en");
\&        call    0 never executed
\&                -:   14:  else
\&                1:   15:    printf ("Success\en");
\&        call    0 called 1 returned 100%
\&                1:   16:  return 0;
\&                -:   17:}
.Ve
.PP
For each function, a line is printed showing how many times the function
is called, how many times it returns and what percentage of the
function's blocks were executed.
.PP
For each basic block, a line is printed after the last line of the basic
block describing the branch or call that ends the basic block.  There can
be multiple branches and calls listed for a single source line if there
are multiple basic blocks that end on that line.  In this case, the
branches and calls are each given a number.  There is no simple way to map
these branches and calls back to source constructs.  In general, though,
the lowest numbered branch or call will correspond to the leftmost construct
on the source line.
.PP
For a branch, if it was executed at least once, then a percentage
indicating the number of times the branch was taken divided by the
number of times the branch was executed will be printed.  Otherwise, the
message \*(L"never executed\*(R" is printed.
.PP
For a call, if it was executed at least once, then a percentage
indicating the number of times the call returned divided by the number
of times the call was executed will be printed.  This will usually be
100%, but may be less for functions that call \f(CW\*(C`exit\*(C'\fR or \f(CW\*(C`longjmp\*(C'\fR,
and thus may not return every time they are called.
.PP
The execution counts are cumulative.  If the example program were
executed again without removing the \fI.gcda\fR file, the count for the
number of times each line in the source was executed would be added to
the results of the previous run(s).  This is potentially useful in
several ways.  For example, it could be used to accumulate data over a
number of program runs as part of a test verification suite, or to
provide more accurate long-term information over a large number of
program runs.
.PP
The data in the \fI.gcda\fR files is saved immediately before the program
exits.  For each source file compiled with \fB\-fprofile\-arcs\fR, the
profiling code first attempts to read in an existing \fI.gcda\fR file; if
the file doesn't match the executable (differing number of basic block
counts) it will ignore the contents of the file.  It then adds in the
new execution counts and finally writes the data to the file.
.Sh "Using \fBgcov\fP with \s-1GCC\s0 Optimization"
.IX Subsection "Using gcov with GCC Optimization"
If you plan to use \fBgcov\fR to help optimize your code, you must
first compile your program with two special \s-1GCC\s0 options:
\&\fB\-fprofile\-arcs \-ftest\-coverage\fR.  Aside from that, you can use any
other \s-1GCC\s0 options; but if you want to prove that every single line
in your program was executed, you should not compile with optimization
at the same time.  On some machines the optimizer can eliminate some
simple code lines by combining them with other lines.  For example, code
like this:
.PP
.Vb 4
\&        if (a != b)
\&          c = 1;
\&        else
\&          c = 0;
.Ve
.PP
can be compiled into one instruction on some machines.  In this case,
there is no way for \fBgcov\fR to calculate separate execution counts
for each line because there isn't separate code for each line.  Hence
the \fBgcov\fR output looks like this if you compiled the program with
optimization:
.PP
.Vb 4
\&              100:   12:if (a != b)
\&              100:   13:  c = 1;
\&              100:   14:else
\&              100:   15:  c = 0;
.Ve
.PP
The output shows that this block of code, combined by optimization,
executed 100 times.  In one sense this result is correct, because there
was only one instruction representing all four of these lines.  However,
the output does not indicate how many times the result was 0 and how
many times the result was 1.
.PP
Inlineable functions can create unexpected line counts.  Line counts are
shown for the source code of the inlineable function, but what is shown
depends on where the function is inlined, or if it is not inlined at all.
.PP
If the function is not inlined, the compiler must emit an out of line
copy of the function, in any object file that needs it.  If
\&\fIfileA.o\fR and \fIfileB.o\fR both contain out of line bodies of a
particular inlineable function, they will also both contain coverage
counts for that function.  When \fIfileA.o\fR and \fIfileB.o\fR are
linked together, the linker will, on many systems, select one of those
out of line bodies for all calls to that function, and remove or ignore
the other.  Unfortunately, it will not remove the coverage counters for
the unused function body.  Hence when instrumented, all but one use of
that function will show zero counts.
.PP
If the function is inlined in several places, the block structure in
each location might not be the same.  For instance, a condition might
now be calculable at compile time in some instances.  Because the
coverage of all the uses of the inline function will be shown for the
same source lines, the line counts themselves might seem inconsistent.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIgpl\fR\|(7), \fIgfdl\fR\|(7), \fIfsf\-funding\fR\|(7), \fIgcc\fR\|(1) and the Info entry for \fIgcc\fR.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright (c) 1996, 1997, 1999, 2000, 2001, 2002, 2003, 2004, 2005
Free Software Foundation, Inc.
.PP
Permission is granted to copy, distribute and/or modify this document
under the terms of the \s-1GNU\s0 Free Documentation License, Version 1.2 or
any later version published by the Free Software Foundation; with the
Invariant Sections being \*(L"\s-1GNU\s0 General Public License\*(R" and \*(L"Funding
Free Software\*(R", the Front-Cover texts being (a) (see below), and with
the Back-Cover Texts being (b) (see below).  A copy of the license is
included in the \fIgfdl\fR\|(7) man page.
.PP
(a) The \s-1FSF\s0's Front-Cover Text is:
.PP
.Vb 1
\&     A GNU Manual
.Ve
.PP
(b) The \s-1FSF\s0's Back-Cover Text is:
.PP
.Vb 3
\&     You have freedom to copy and modify this GNU Manual, like GNU
\&     software.  Copies published by the Free Software Foundation raise
\&     funds for GNU development.
.Ve
OpenPOWER on IntegriCloud