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@c Copyright (C) 1996, 1997, 1999, 2000, 2001,
2
@c 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
3
@c This is part of the GCC manual.
4
@c For copying conditions, see the file gcc.texi.
5
 
6
@ignore
7
@c man begin COPYRIGHT
8
Copyright @copyright{} 1996, 1997, 1999, 2000, 2001, 2002, 2003, 2004, 2005
9
Free Software Foundation, Inc.
10
 
11
Permission is granted to copy, distribute and/or modify this document
12
under the terms of the GNU Free Documentation License, Version 1.2 or
13
any later version published by the Free Software Foundation; with the
14
Invariant Sections being ``GNU General Public License'' and ``Funding
15
Free Software'', the Front-Cover texts being (a) (see below), and with
16
the Back-Cover Texts being (b) (see below).  A copy of the license is
17
included in the gfdl(7) man page.
18
 
19
(a) The FSF's Front-Cover Text is:
20
 
21
     A GNU Manual
22
 
23
(b) The FSF's Back-Cover Text is:
24
 
25
     You have freedom to copy and modify this GNU Manual, like GNU
26
     software.  Copies published by the Free Software Foundation raise
27
     funds for GNU development.
28
@c man end
29
@c Set file name and title for the man page.
30
@setfilename gcov
31
@settitle coverage testing tool
32
@end ignore
33
 
34
@node Gcov
35
@chapter @command{gcov}---a Test Coverage Program
36
 
37
@command{gcov} is a tool you can use in conjunction with GCC to
38
test code coverage in your programs.
39
 
40
@menu
41
* Gcov Intro::                  Introduction to gcov.
42
* Invoking Gcov::               How to use gcov.
43
* Gcov and Optimization::       Using gcov with GCC optimization.
44
* Gcov Data Files::             The files used by gcov.
45
* Cross-profiling::             Data file relocation.
46
@end menu
47
 
48
@node Gcov Intro
49
@section Introduction to @command{gcov}
50
@c man begin DESCRIPTION
51
 
52
@command{gcov} is a test coverage program.  Use it in concert with GCC
53
to analyze your programs to help create more efficient, faster running
54
code and to discover untested parts of your program.  You can use
55
@command{gcov} as a profiling tool to help discover where your
56
optimization efforts will best affect your code.  You can also use
57
@command{gcov} along with the other profiling tool, @command{gprof}, to
58
assess which parts of your code use the greatest amount of computing
59
time.
60
 
61
Profiling tools help you analyze your code's performance.  Using a
62
profiler such as @command{gcov} or @command{gprof}, you can find out some
63
basic performance statistics, such as:
64
 
65
@itemize @bullet
66
@item
67
how often each line of code executes
68
 
69
@item
70
what lines of code are actually executed
71
 
72
@item
73
how much computing time each section of code uses
74
@end itemize
75
 
76
Once you know these things about how your code works when compiled, you
77
can look at each module to see which modules should be optimized.
78
@command{gcov} helps you determine where to work on optimization.
79
 
80
Software developers also use coverage testing in concert with
81
testsuites, to make sure software is actually good enough for a release.
82
Testsuites can verify that a program works as expected; a coverage
83
program tests to see how much of the program is exercised by the
84
testsuite.  Developers can then determine what kinds of test cases need
85
to be added to the testsuites to create both better testing and a better
86
final product.
87
 
88
You should compile your code without optimization if you plan to use
89
@command{gcov} because the optimization, by combining some lines of code
90
into one function, may not give you as much information as you need to
91
look for `hot spots' where the code is using a great deal of computer
92
time.  Likewise, because @command{gcov} accumulates statistics by line (at
93
the lowest resolution), it works best with a programming style that
94
places only one statement on each line.  If you use complicated macros
95
that expand to loops or to other control structures, the statistics are
96
less helpful---they only report on the line where the macro call
97
appears.  If your complex macros behave like functions, you can replace
98
them with inline functions to solve this problem.
99
 
100
@command{gcov} creates a logfile called @file{@var{sourcefile}.gcov} which
101
indicates how many times each line of a source file @file{@var{sourcefile}.c}
102
has executed.  You can use these logfiles along with @command{gprof} to aid
103
in fine-tuning the performance of your programs.  @command{gprof} gives
104
timing information you can use along with the information you get from
105
@command{gcov}.
106
 
107
@command{gcov} works only on code compiled with GCC@.  It is not
108
compatible with any other profiling or test coverage mechanism.
109
 
110
@c man end
111
 
112
@node Invoking Gcov
113
@section Invoking @command{gcov}
114
 
115
@smallexample
116
gcov @r{[}@var{options}@r{]} @var{sourcefile}
117
@end smallexample
118
 
119
@command{gcov} accepts the following options:
120
 
121
@ignore
122
@c man begin SYNOPSIS
123
gcov [@option{-v}|@option{--version}] [@option{-h}|@option{--help}]
124
     [@option{-a}|@option{--all-blocks}]
125
     [@option{-b}|@option{--branch-probabilities}]
126
     [@option{-c}|@option{--branch-counts}]
127
     [@option{-n}|@option{--no-output}]
128
     [@option{-l}|@option{--long-file-names}]
129
     [@option{-p}|@option{--preserve-paths}]
130
     [@option{-f}|@option{--function-summaries}]
131
     [@option{-o}|@option{--object-directory} @var{directory|file}] @var{sourcefile}
132
     [@option{-u}|@option{--unconditional-branches}]
133
@c man end
134
@c man begin SEEALSO
135
gpl(7), gfdl(7), fsf-funding(7), gcc(1) and the Info entry for @file{gcc}.
136
@c man end
137
@end ignore
138
 
139
@c man begin OPTIONS
140
@table @gcctabopt
141
@item -h
142
@itemx --help
143
Display help about using @command{gcov} (on the standard output), and
144
exit without doing any further processing.
145
 
146
@item -v
147
@itemx --version
148
Display the @command{gcov} version number (on the standard output),
149
and exit without doing any further processing.
150
 
151
@item -a
152
@itemx --all-blocks
153
Write individual execution counts for every basic block.  Normally gcov
154
outputs execution counts only for the main blocks of a line.  With this
155
option you can determine if blocks within a single line are not being
156
executed.
157
 
158
@item -b
159
@itemx --branch-probabilities
160
Write branch frequencies to the output file, and write branch summary
161
info to the standard output.  This option allows you to see how often
162
each branch in your program was taken.  Unconditional branches will not
163
be shown, unless the @option{-u} option is given.
164
 
165
@item -c
166
@itemx --branch-counts
167
Write branch frequencies as the number of branches taken, rather than
168
the percentage of branches taken.
169
 
170
@item -n
171
@itemx --no-output
172
Do not create the @command{gcov} output file.
173
 
174
@item -l
175
@itemx --long-file-names
176
Create long file names for included source files.  For example, if the
177
header file @file{x.h} contains code, and was included in the file
178
@file{a.c}, then running @command{gcov} on the file @file{a.c} will produce
179
an output file called @file{a.c##x.h.gcov} instead of @file{x.h.gcov}.
180
This can be useful if @file{x.h} is included in multiple source
181
files.  If you use the @samp{-p} option, both the including and
182
included file names will be complete path names.
183
 
184
@item -p
185
@itemx --preserve-paths
186
Preserve complete path information in the names of generated
187
@file{.gcov} files.  Without this option, just the filename component is
188
used.  With this option, all directories are used, with @samp{/} characters
189
translated to @samp{#} characters, @file{.} directory components
190
removed and @file{..}
191
components renamed to @samp{^}.  This is useful if sourcefiles are in several
192
different directories.  It also affects the @samp{-l} option.
193
 
194
@item -f
195
@itemx --function-summaries
196
Output summaries for each function in addition to the file level summary.
197
 
198
@item -o @var{directory|file}
199
@itemx --object-directory @var{directory}
200
@itemx --object-file @var{file}
201
Specify either the directory containing the gcov data files, or the
202
object path name.  The @file{.gcno}, and
203
@file{.gcda} data files are searched for using this option.  If a directory
204
is specified, the data files are in that directory and named after the
205
source file name, without its extension.  If a file is specified here,
206
the data files are named after that file, without its extension.  If this
207
option is not supplied, it defaults to the current directory.
208
 
209
@item -u
210
@itemx --unconditional-branches
211
When branch probabilities are given, include those of unconditional branches.
212
Unconditional branches are normally not interesting.
213
 
214
@end table
215
 
216
@command{gcov} should be run with the current directory the same as that
217
when you invoked the compiler.  Otherwise it will not be able to locate
218
the source files.  @command{gcov} produces files called
219
@file{@var{mangledname}.gcov} in the current directory.  These contain
220
the coverage information of the source file they correspond to.
221
One @file{.gcov} file is produced for each source file containing code,
222
which was compiled to produce the data files.  The @var{mangledname} part
223
of the output file name is usually simply the source file name, but can
224
be something more complicated if the @samp{-l} or @samp{-p} options are
225
given.  Refer to those options for details.
226
 
227
The @file{.gcov} files contain the @samp{:} separated fields along with
228
program source code.  The format is
229
 
230
@smallexample
231
@var{execution_count}:@var{line_number}:@var{source line text}
232
@end smallexample
233
 
234
Additional block information may succeed each line, when requested by
235
command line option.  The @var{execution_count} is @samp{-} for lines
236
containing no code and @samp{#####} for lines which were never executed.
237
Some lines of information at the start have @var{line_number} of zero.
238
 
239
The preamble lines are of the form
240
 
241
@smallexample
242
-:0:@var{tag}:@var{value}
243
@end smallexample
244
 
245
The ordering and number of these preamble lines will be augmented as
246
@command{gcov} development progresses --- do not rely on them remaining
247
unchanged.  Use @var{tag} to locate a particular preamble line.
248
 
249
The additional block information is of the form
250
 
251
@smallexample
252
@var{tag} @var{information}
253
@end smallexample
254
 
255
The @var{information} is human readable, but designed to be simple
256
enough for machine parsing too.
257
 
258
When printing percentages, 0% and 100% are only printed when the values
259
are @emph{exactly} 0% and 100% respectively.  Other values which would
260
conventionally be rounded to 0% or 100% are instead printed as the
261
nearest non-boundary value.
262
 
263
When using @command{gcov}, you must first compile your program with two
264
special GCC options: @samp{-fprofile-arcs -ftest-coverage}.
265
This tells the compiler to generate additional information needed by
266
gcov (basically a flow graph of the program) and also includes
267
additional code in the object files for generating the extra profiling
268
information needed by gcov.  These additional files are placed in the
269
directory where the object file is located.
270
 
271
Running the program will cause profile output to be generated.  For each
272
source file compiled with @option{-fprofile-arcs}, an accompanying
273
@file{.gcda} file will be placed in the object file directory.
274
 
275
Running @command{gcov} with your program's source file names as arguments
276
will now produce a listing of the code along with frequency of execution
277
for each line.  For example, if your program is called @file{tmp.c}, this
278
is what you see when you use the basic @command{gcov} facility:
279
 
280
@smallexample
281
$ gcc -fprofile-arcs -ftest-coverage tmp.c
282
$ a.out
283
$ gcov tmp.c
284
90.00% of 10 source lines executed in file tmp.c
285
Creating tmp.c.gcov.
286
@end smallexample
287
 
288
The file @file{tmp.c.gcov} contains output from @command{gcov}.
289
Here is a sample:
290
 
291
@smallexample
292
        -:    0:Source:tmp.c
293
        -:    0:Graph:tmp.gcno
294
        -:    0:Data:tmp.gcda
295
        -:    0:Runs:1
296
        -:    0:Programs:1
297
        -:    1:#include <stdio.h>
298
        -:    2:
299
        -:    3:int main (void)
300
        1:    4:@{
301
        1:    5:  int i, total;
302
        -:    6:
303
        1:    7:  total = 0;
304
        -:    8:
305
       11:    9:  for (i = 0; i < 10; i++)
306
       10:   10:    total += i;
307
        -:   11:
308
        1:   12:  if (total != 45)
309
    #####:   13:    printf ("Failure\n");
310
        -:   14:  else
311
        1:   15:    printf ("Success\n");
312
        1:   16:  return 0;
313
        -:   17:@}
314
@end smallexample
315
 
316
When you use the @option{-a} option, you will get individual block
317
counts, and the output looks like this:
318
 
319
@smallexample
320
        -:    0:Source:tmp.c
321
        -:    0:Graph:tmp.gcno
322
        -:    0:Data:tmp.gcda
323
        -:    0:Runs:1
324
        -:    0:Programs:1
325
        -:    1:#include <stdio.h>
326
        -:    2:
327
        -:    3:int main (void)
328
        1:    4:@{
329
        1:    4-block  0
330
        1:    5:  int i, total;
331
        -:    6:
332
        1:    7:  total = 0;
333
        -:    8:
334
       11:    9:  for (i = 0; i < 10; i++)
335
       11:    9-block  0
336
       10:   10:    total += i;
337
       10:   10-block  0
338
        -:   11:
339
        1:   12:  if (total != 45)
340
        1:   12-block  0
341
    #####:   13:    printf ("Failure\n");
342
    $$$$$:   13-block  0
343
        -:   14:  else
344
        1:   15:    printf ("Success\n");
345
        1:   15-block  0
346
        1:   16:  return 0;
347
        1:   16-block  0
348
        -:   17:@}
349
@end smallexample
350
 
351
In this mode, each basic block is only shown on one line -- the last
352
line of the block.  A multi-line block will only contribute to the
353
execution count of that last line, and other lines will not be shown
354
to contain code, unless previous blocks end on those lines.
355
The total execution count of a line is shown and subsequent lines show
356
the execution counts for individual blocks that end on that line.  After each
357
block, the branch and call counts of the block will be shown, if the
358
@option{-b} option is given.
359
 
360
Because of the way GCC instruments calls, a call count can be shown
361
after a line with no individual blocks.
362
As you can see, line 13 contains a basic block that was not executed.
363
 
364
@need 450
365
When you use the @option{-b} option, your output looks like this:
366
 
367
@smallexample
368
$ gcov -b tmp.c
369
90.00% of 10 source lines executed in file tmp.c
370
80.00% of 5 branches executed in file tmp.c
371
80.00% of 5 branches taken at least once in file tmp.c
372
50.00% of 2 calls executed in file tmp.c
373
Creating tmp.c.gcov.
374
@end smallexample
375
 
376
Here is a sample of a resulting @file{tmp.c.gcov} file:
377
 
378
@smallexample
379
        -:    0:Source:tmp.c
380
        -:    0:Graph:tmp.gcno
381
        -:    0:Data:tmp.gcda
382
        -:    0:Runs:1
383
        -:    0:Programs:1
384
        -:    1:#include <stdio.h>
385
        -:    2:
386
        -:    3:int main (void)
387
function main called 1 returned 1 blocks executed 75%
388
        1:    4:@{
389
        1:    5:  int i, total;
390
        -:    6:
391
        1:    7:  total = 0;
392
        -:    8:
393
       11:    9:  for (i = 0; i < 10; i++)
394
branch  0 taken 91% (fallthrough)
395
branch  1 taken 9%
396
       10:   10:    total += i;
397
        -:   11:
398
        1:   12:  if (total != 45)
399
branch  0 taken 0% (fallthrough)
400
branch  1 taken 100%
401
    #####:   13:    printf ("Failure\n");
402
call    0 never executed
403
        -:   14:  else
404
        1:   15:    printf ("Success\n");
405
call    0 called 1 returned 100%
406
        1:   16:  return 0;
407
        -:   17:@}
408
@end smallexample
409
 
410
For each function, a line is printed showing how many times the function
411
is called, how many times it returns and what percentage of the
412
function's blocks were executed.
413
 
414
For each basic block, a line is printed after the last line of the basic
415
block describing the branch or call that ends the basic block.  There can
416
be multiple branches and calls listed for a single source line if there
417
are multiple basic blocks that end on that line.  In this case, the
418
branches and calls are each given a number.  There is no simple way to map
419
these branches and calls back to source constructs.  In general, though,
420
the lowest numbered branch or call will correspond to the leftmost construct
421
on the source line.
422
 
423
For a branch, if it was executed at least once, then a percentage
424
indicating the number of times the branch was taken divided by the
425
number of times the branch was executed will be printed.  Otherwise, the
426
message ``never executed'' is printed.
427
 
428
For a call, if it was executed at least once, then a percentage
429
indicating the number of times the call returned divided by the number
430
of times the call was executed will be printed.  This will usually be
431
100%, but may be less for functions that call @code{exit} or @code{longjmp},
432
and thus may not return every time they are called.
433
 
434
The execution counts are cumulative.  If the example program were
435
executed again without removing the @file{.gcda} file, the count for the
436
number of times each line in the source was executed would be added to
437
the results of the previous run(s).  This is potentially useful in
438
several ways.  For example, it could be used to accumulate data over a
439
number of program runs as part of a test verification suite, or to
440
provide more accurate long-term information over a large number of
441
program runs.
442
 
443
The data in the @file{.gcda} files is saved immediately before the program
444
exits.  For each source file compiled with @option{-fprofile-arcs}, the
445
profiling code first attempts to read in an existing @file{.gcda} file; if
446
the file doesn't match the executable (differing number of basic block
447
counts) it will ignore the contents of the file.  It then adds in the
448
new execution counts and finally writes the data to the file.
449
 
450
@node Gcov and Optimization
451
@section Using @command{gcov} with GCC Optimization
452
 
453
If you plan to use @command{gcov} to help optimize your code, you must
454
first compile your program with two special GCC options:
455
@samp{-fprofile-arcs -ftest-coverage}.  Aside from that, you can use any
456
other GCC options; but if you want to prove that every single line
457
in your program was executed, you should not compile with optimization
458
at the same time.  On some machines the optimizer can eliminate some
459
simple code lines by combining them with other lines.  For example, code
460
like this:
461
 
462
@smallexample
463
if (a != b)
464
  c = 1;
465
else
466
  c = 0;
467
@end smallexample
468
 
469
@noindent
470
can be compiled into one instruction on some machines.  In this case,
471
there is no way for @command{gcov} to calculate separate execution counts
472
for each line because there isn't separate code for each line.  Hence
473
the @command{gcov} output looks like this if you compiled the program with
474
optimization:
475
 
476
@smallexample
477
      100:   12:if (a != b)
478
      100:   13:  c = 1;
479
      100:   14:else
480
      100:   15:  c = 0;
481
@end smallexample
482
 
483
The output shows that this block of code, combined by optimization,
484
executed 100 times.  In one sense this result is correct, because there
485
was only one instruction representing all four of these lines.  However,
486
the output does not indicate how many times the result was 0 and how
487
many times the result was 1.
488
 
489
Inlineable functions can create unexpected line counts.  Line counts are
490
shown for the source code of the inlineable function, but what is shown
491
depends on where the function is inlined, or if it is not inlined at all.
492
 
493
If the function is not inlined, the compiler must emit an out of line
494
copy of the function, in any object file that needs it.  If
495
@file{fileA.o} and @file{fileB.o} both contain out of line bodies of a
496
particular inlineable function, they will also both contain coverage
497
counts for that function.  When @file{fileA.o} and @file{fileB.o} are
498
linked together, the linker will, on many systems, select one of those
499
out of line bodies for all calls to that function, and remove or ignore
500
the other.  Unfortunately, it will not remove the coverage counters for
501
the unused function body.  Hence when instrumented, all but one use of
502
that function will show zero counts.
503
 
504
If the function is inlined in several places, the block structure in
505
each location might not be the same.  For instance, a condition might
506
now be calculable at compile time in some instances.  Because the
507
coverage of all the uses of the inline function will be shown for the
508
same source lines, the line counts themselves might seem inconsistent.
509
 
510
@c man end
511
 
512
@node Gcov Data Files
513
@section Brief description of @command{gcov} data files
514
 
515
@command{gcov} uses two files for profiling.  The names of these files
516
are derived from the original @emph{object} file by substituting the
517
file suffix with either @file{.gcno}, or @file{.gcda}.  All of these files
518
are placed in the same directory as the object file, and contain data
519
stored in a platform-independent format.
520
 
521
The @file{.gcno} file is generated when the source file is compiled with
522
the GCC @option{-ftest-coverage} option.  It contains information to
523
reconstruct the basic block graphs and assign source line numbers to
524
blocks.
525
 
526
The @file{.gcda} file is generated when a program containing object files
527
built with the GCC @option{-fprofile-arcs} option is executed.  A
528
separate @file{.gcda} file is created for each object file compiled with
529
this option.  It contains arc transition counts, and some summary
530
information.
531
 
532
The full details of the file format is specified in @file{gcov-io.h},
533
and functions provided in that header file should be used to access the
534
coverage files.
535
 
536
@node Cross-profiling
537
@section Data file relocation to support cross-profiling
538
 
539
Running the program will cause profile output to be generated.  For each
540
source file compiled with @option{-fprofile-arcs}, an accompanying @file{.gcda}
541
file will be placed in the object file directory. That implicitly requires
542
running the program on the same system as it was built or having the same
543
absolute directory structure on the target system. The program will try
544
to create the needed directory structure, if it is not already present.
545
 
546
To support cross-profiling, a program compiled with @option{-fprofile-arcs}
547
can relocate the data files based on two environment variables:
548
 
549
@itemize @bullet
550
@item
551
GCOV_PREFIX contains the prefix to add to the absolute paths
552
in the object file. Prefix must be absolute as well, otherwise its
553
value is ignored. The default is no prefix.
554
 
555
@item
556
GCOV_PREFIX_STRIP indicates the how many initial directory names to strip off
557
the hardwired absolute paths. Default value is 0.
558
 
559
@emph{Note:} GCOV_PREFIX_STRIP has no effect if GCOV_PREFIX is undefined, empty
560
or non-absolute.
561
@end itemize
562
 
563
For example, if the object file @file{/user/build/foo.o} was built with
564
@option{-fprofile-arcs}, the final executable will try to create the data file
565
@file{/user/build/foo.gcda} when running on the target system.  This will
566
fail if the corresponding directory does not exist and it is unable to create
567
it.  This can be overcome by, for example, setting the environment as
568
@samp{GCOV_PREFIX=/target/run} and @samp{GCOV_PREFIX_STRIP=1}.  Such a
569
setting will name the data file @file{/target/run/build/foo.gcda}.
570
 
571
You must move the data files to the expected directory tree in order to
572
use them for profile directed optimizations (@option{--use-profile}), or to
573
use the @command{gcov} tool.

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