1GCOV(1)                               GNU                              GCOV(1)
2
3
4

NAME

6       gcov - coverage testing tool
7

SYNOPSIS

9       gcov [-v|--version] [-h|--help]
10            [-a|--all-blocks]
11            [-b|--branch-probabilities]
12            [-c|--branch-counts]
13            [-d|--display-progress]
14            [-f|--function-summaries]
15            [-i|--intermediate-format]
16            [-l|--long-file-names]
17            [-m|--demangled-names]
18            [-n|--no-output]
19            [-o|--object-directory directory|file]
20            [-p|--preserve-paths]
21            [-r|--relative-only]
22            [-s|--source-prefix directory]
23            [-u|--unconditional-branches]
24            [-x|--hash-filenames]
25            files
26

DESCRIPTION

28       gcov is a test coverage program.  Use it in concert with GCC to analyze
29       your programs to help create more efficient, faster running code and to
30       discover untested parts of your program.  You can use gcov as a
31       profiling tool to help discover where your optimization efforts will
32       best affect your code.  You can also use gcov along with the other
33       profiling tool, gprof, to assess which parts of your code use the
34       greatest amount of computing time.
35
36       Profiling tools help you analyze your code's performance.  Using a
37       profiler such as gcov or gprof, you can find out some basic performance
38       statistics, such as:
39
40       *   how often each line of code executes
41
42       *   what lines of code are actually executed
43
44       *   how much computing time each section of code uses
45
46       Once you know these things about how your code works when compiled, you
47       can look at each module to see which modules should be optimized.  gcov
48       helps you determine where to work on optimization.
49
50       Software developers also use coverage testing in concert with
51       testsuites, to make sure software is actually good enough for a
52       release.  Testsuites can verify that a program works as expected; a
53       coverage program tests to see how much of the program is exercised by
54       the testsuite.  Developers can then determine what kinds of test cases
55       need to be added to the testsuites to create both better testing and a
56       better final product.
57
58       You should compile your code without optimization if you plan to use
59       gcov because the optimization, by combining some lines of code into one
60       function, may not give you as much information as you need to look for
61       `hot spots' where the code is using a great deal of computer time.
62       Likewise, because gcov accumulates statistics by line (at the lowest
63       resolution), it works best with a programming style that places only
64       one statement on each line.  If you use complicated macros that expand
65       to loops or to other control structures, the statistics are less
66       helpful---they only report on the line where the macro call appears.
67       If your complex macros behave like functions, you can replace them with
68       inline functions to solve this problem.
69
70       gcov creates a logfile called sourcefile.gcov which indicates how many
71       times each line of a source file sourcefile.c has executed.  You can
72       use these logfiles along with gprof to aid in fine-tuning the
73       performance of your programs.  gprof gives timing information you can
74       use along with the information you get from gcov.
75
76       gcov works only on code compiled with GCC.  It is not compatible with
77       any other profiling or test coverage mechanism.
78

OPTIONS

80       -a
81       --all-blocks
82           Write individual execution counts for every basic block.  Normally
83           gcov outputs execution counts only for the main blocks of a line.
84           With this option you can determine if blocks within a single line
85           are not being executed.
86
87       -b
88       --branch-probabilities
89           Write branch frequencies to the output file, and write branch
90           summary info to the standard output.  This option allows you to see
91           how often each branch in your program was taken.  Unconditional
92           branches will not be shown, unless the -u option is given.
93
94       -c
95       --branch-counts
96           Write branch frequencies as the number of branches taken, rather
97           than the percentage of branches taken.
98
99       -d
100       --display-progress
101           Display the progress on the standard output.
102
103       -f
104       --function-summaries
105           Output summaries for each function in addition to the file level
106           summary.
107
108       -h
109       --help
110           Display help about using gcov (on the standard output), and exit
111           without doing any further processing.
112
113       -i
114       --intermediate-format
115           Output gcov file in an easy-to-parse intermediate text format that
116           can be used by lcov or other tools. The output is a single .gcov
117           file per .gcda file. No source code is required.
118
119           The format of the intermediate .gcov file is plain text with one
120           entry per line
121
122                   file:<source_file_name>
123                   function:<line_number>,<execution_count>,<function_name>
124                   lcount:<line number>,<execution_count>
125                   branch:<line_number>,<branch_coverage_type>
126
127                   Where the <branch_coverage_type> is
128                      notexec (Branch not executed)
129                      taken (Branch executed and taken)
130                      nottaken (Branch executed, but not taken)
131
132                   There can be multiple <file> entries in an intermediate gcov
133                   file. All entries following a <file> pertain to that source file
134                   until the next <file> entry.
135
136           Here is a sample when -i is used in conjunction with -b option:
137
138                   file:array.cc
139                   function:11,1,_Z3sumRKSt6vectorIPiSaIS0_EE
140                   function:22,1,main
141                   lcount:11,1
142                   lcount:12,1
143                   lcount:14,1
144                   branch:14,taken
145                   lcount:26,1
146                   branch:28,nottaken
147
148       -l
149       --long-file-names
150           Create long file names for included source files.  For example, if
151           the header file x.h contains code, and was included in the file
152           a.c, then running gcov on the file a.c will produce an output file
153           called a.c##x.h.gcov instead of x.h.gcov.  This can be useful if
154           x.h is included in multiple source files and you want to see the
155           individual contributions.  If you use the -p option, both the
156           including and included file names will be complete path names.
157
158       -m
159       --demangled-names
160           Display demangled function names in output. The default is to show
161           mangled function names.
162
163       -n
164       --no-output
165           Do not create the gcov output file.
166
167       -o directory|file
168       --object-directory directory
169       --object-file file
170           Specify either the directory containing the gcov data files, or the
171           object path name.  The .gcno, and .gcda data files are searched for
172           using this option.  If a directory is specified, the data files are
173           in that directory and named after the input file name, without its
174           extension.  If a file is specified here, the data files are named
175           after that file, without its extension.
176
177       -p
178       --preserve-paths
179           Preserve complete path information in the names of generated .gcov
180           files.  Without this option, just the filename component is used.
181           With this option, all directories are used, with / characters
182           translated to # characters, . directory components removed and
183           unremoveable ..  components renamed to ^.  This is useful if
184           sourcefiles are in several different directories.
185
186       -r
187       --relative-only
188           Only output information about source files with a relative pathname
189           (after source prefix elision).  Absolute paths are usually system
190           header files and coverage of any inline functions therein is
191           normally uninteresting.
192
193       -s directory
194       --source-prefix directory
195           A prefix for source file names to remove when generating the output
196           coverage files.  This option is useful when building in a separate
197           directory, and the pathname to the source directory is not wanted
198           when determining the output file names.  Note that this prefix
199           detection is applied before determining whether the source file is
200           absolute.
201
202       -u
203       --unconditional-branches
204           When branch probabilities are given, include those of unconditional
205           branches.  Unconditional branches are normally not interesting.
206
207       -v
208       --version
209           Display the gcov version number (on the standard output), and exit
210           without doing any further processing.
211
212       -w
213       --verbose
214           Print verbose informations related to basic blocks and arcs.
215
216       -x
217       --hash-filenames
218           By default, gcov uses the full pathname of the source files to to
219           create an output filename.  This can lead to long filenames that
220           can overflow filesystem limits.  This option creates names of the
221           form source-file##md5.gcov, where the source-file component is the
222           final filename part and the md5 component is calculated from the
223           full mangled name that would have been used otherwise.
224
225       gcov should be run with the current directory the same as that when you
226       invoked the compiler.  Otherwise it will not be able to locate the
227       source files.  gcov produces files called mangledname.gcov in the
228       current directory.  These contain the coverage information of the
229       source file they correspond to.  One .gcov file is produced for each
230       source (or header) file containing code, which was compiled to produce
231       the data files.  The mangledname part of the output file name is
232       usually simply the source file name, but can be something more
233       complicated if the -l or -p options are given.  Refer to those options
234       for details.
235
236       If you invoke gcov with multiple input files, the contributions from
237       each input file are summed.  Typically you would invoke it with the
238       same list of files as the final link of your executable.
239
240       The .gcov files contain the : separated fields along with program
241       source code.  The format is
242
243               <execution_count>:<line_number>:<source line text>
244
245       Additional block information may succeed each line, when requested by
246       command line option.  The execution_count is - for lines containing no
247       code.  Unexecuted lines are marked ##### or =====, depending on whether
248       they are reachable by non-exceptional paths or only exceptional paths
249       such as C++ exception handlers, respectively. Given -a option,
250       unexecuted blocks are marked $$$$$ or %%%%%, depending on whether a
251       basic block is reachable via non-exceptional or exceptional paths.
252
253       Note that GCC can completely remove the bodies of functions that are
254       not needed -- for instance if they are inlined everywhere.  Such
255       functions are marked with -, which can be confusing.  Use the
256       -fkeep-inline-functions and -fkeep-static-functions options to retain
257       these functions and allow gcov to properly show their execution_count.
258
259       Some lines of information at the start have line_number of zero.  These
260       preamble lines are of the form
261
262               -:0:<tag>:<value>
263
264       The ordering and number of these preamble lines will be augmented as
265       gcov development progresses --- do not rely on them remaining
266       unchanged.  Use tag to locate a particular preamble line.
267
268       The additional block information is of the form
269
270               <tag> <information>
271
272       The information is human readable, but designed to be simple enough for
273       machine parsing too.
274
275       When printing percentages, 0% and 100% are only printed when the values
276       are exactly 0% and 100% respectively.  Other values which would
277       conventionally be rounded to 0% or 100% are instead printed as the
278       nearest non-boundary value.
279
280       When using gcov, you must first compile your program with two special
281       GCC options: -fprofile-arcs -ftest-coverage.  This tells the compiler
282       to generate additional information needed by gcov (basically a flow
283       graph of the program) and also includes additional code in the object
284       files for generating the extra profiling information needed by gcov.
285       These additional files are placed in the directory where the object
286       file is located.
287
288       Running the program will cause profile output to be generated.  For
289       each source file compiled with -fprofile-arcs, an accompanying .gcda
290       file will be placed in the object file directory.
291
292       Running gcov with your program's source file names as arguments will
293       now produce a listing of the code along with frequency of execution for
294       each line.  For example, if your program is called tmp.c, this is what
295       you see when you use the basic gcov facility:
296
297               $ gcc -fprofile-arcs -ftest-coverage tmp.c
298               $ a.out
299               $ gcov tmp.c
300               File 'tmp.c'
301               Lines executed:90.00% of 10
302               Creating 'tmp.c.gcov'
303
304       The file tmp.c.gcov contains output from gcov.  Here is a sample:
305
306                       -:    0:Source:tmp.c
307                       -:    0:Graph:tmp.gcno
308                       -:    0:Data:tmp.gcda
309                       -:    0:Runs:1
310                       -:    0:Programs:1
311                       -:    1:#include <stdio.h>
312                       -:    2:
313                       -:    3:int main (void)
314                       1:    4:{
315                       1:    5:  int i, total;
316                       -:    6:
317                       1:    7:  total = 0;
318                       -:    8:
319                      11:    9:  for (i = 0; i < 10; i++)
320                      10:   10:    total += i;
321                       -:   11:
322                       1:   12:  if (total != 45)
323                   #####:   13:    printf ("Failure\n");
324                       -:   14:  else
325                       1:   15:    printf ("Success\n");
326                       1:   16:  return 0;
327                       -:   17:}
328
329       When you use the -a option, you will get individual block counts, and
330       the output looks like this:
331
332                       -:    0:Source:tmp.c
333                       -:    0:Graph:tmp.gcno
334                       -:    0:Data:tmp.gcda
335                       -:    0:Runs:1
336                       -:    0:Programs:1
337                       -:    1:#include <stdio.h>
338                       -:    2:
339                       -:    3:int main (void)
340                       1:    4:{
341                       1:    4-block  0
342                       1:    5:  int i, total;
343                       -:    6:
344                       1:    7:  total = 0;
345                       -:    8:
346                      11:    9:  for (i = 0; i < 10; i++)
347                      11:    9-block  0
348                      10:   10:    total += i;
349                      10:   10-block  0
350                       -:   11:
351                       1:   12:  if (total != 45)
352                       1:   12-block  0
353                   #####:   13:    printf ("Failure\n");
354                   $$$$$:   13-block  0
355                       -:   14:  else
356                       1:   15:    printf ("Success\n");
357                       1:   15-block  0
358                       1:   16:  return 0;
359                       1:   16-block  0
360                       -:   17:}
361
362       In this mode, each basic block is only shown on one line -- the last
363       line of the block.  A multi-line block will only contribute to the
364       execution count of that last line, and other lines will not be shown to
365       contain code, unless previous blocks end on those lines.  The total
366       execution count of a line is shown and subsequent lines show the
367       execution counts for individual blocks that end on that line.  After
368       each block, the branch and call counts of the block will be shown, if
369       the -b option is given.
370
371       Because of the way GCC instruments calls, a call count can be shown
372       after a line with no individual blocks.  As you can see, line 13
373       contains a basic block that was not executed.
374
375       When you use the -b option, your output looks like this:
376
377               $ gcov -b tmp.c
378               File 'tmp.c'
379               Lines executed:90.00% of 10
380               Branches executed:80.00% of 5
381               Taken at least once:80.00% of 5
382               Calls executed:50.00% of 2
383               Creating 'tmp.c.gcov'
384
385       Here is a sample of a resulting tmp.c.gcov file:
386
387                       -:    0:Source:tmp.c
388                       -:    0:Graph:tmp.gcno
389                       -:    0:Data:tmp.gcda
390                       -:    0:Runs:1
391                       -:    0:Programs:1
392                       -:    1:#include <stdio.h>
393                       -:    2:
394                       -:    3:int main (void)
395               function main called 1 returned 1 blocks executed 75%
396                       1:    4:{
397                       1:    5:  int i, total;
398                       -:    6:
399                       1:    7:  total = 0;
400                       -:    8:
401                      11:    9:  for (i = 0; i < 10; i++)
402               branch  0 taken 91% (fallthrough)
403               branch  1 taken 9%
404                      10:   10:    total += i;
405                       -:   11:
406                       1:   12:  if (total != 45)
407               branch  0 taken 0% (fallthrough)
408               branch  1 taken 100%
409                   #####:   13:    printf ("Failure\n");
410               call    0 never executed
411                       -:   14:  else
412                       1:   15:    printf ("Success\n");
413               call    0 called 1 returned 100%
414                       1:   16:  return 0;
415                       -:   17:}
416
417       For each function, a line is printed showing how many times the
418       function is called, how many times it returns and what percentage of
419       the function's blocks were executed.
420
421       For each basic block, a line is printed after the last line of the
422       basic block describing the branch or call that ends the basic block.
423       There can be multiple branches and calls listed for a single source
424       line if there are multiple basic blocks that end on that line.  In this
425       case, the branches and calls are each given a number.  There is no
426       simple way to map these branches and calls back to source constructs.
427       In general, though, the lowest numbered branch or call will correspond
428       to the leftmost construct on the source line.
429
430       For a branch, if it was executed at least once, then a percentage
431       indicating the number of times the branch was taken divided by the
432       number of times the branch was executed will be printed.  Otherwise,
433       the message "never executed" is printed.
434
435       For a call, if it was executed at least once, then a percentage
436       indicating the number of times the call returned divided by the number
437       of times the call was executed will be printed.  This will usually be
438       100%, but may be less for functions that call "exit" or "longjmp", and
439       thus may not return every time they are called.
440
441       The execution counts are cumulative.  If the example program were
442       executed again without removing the .gcda file, the count for the
443       number of times each line in the source was executed would be added to
444       the results of the previous run(s).  This is potentially useful in
445       several ways.  For example, it could be used to accumulate data over a
446       number of program runs as part of a test verification suite, or to
447       provide more accurate long-term information over a large number of
448       program runs.
449
450       The data in the .gcda files is saved immediately before the program
451       exits.  For each source file compiled with -fprofile-arcs, the
452       profiling code first attempts to read in an existing .gcda file; if the
453       file doesn't match the executable (differing number of basic block
454       counts) it will ignore the contents of the file.  It then adds in the
455       new execution counts and finally writes the data to the file.
456
457   Using gcov with GCC Optimization
458       If you plan to use gcov to help optimize your code, you must first
459       compile your program with two special GCC options: -fprofile-arcs
460       -ftest-coverage.  Aside from that, you can use any other GCC options;
461       but if you want to prove that every single line in your program was
462       executed, you should not compile with optimization at the same time.
463       On some machines the optimizer can eliminate some simple code lines by
464       combining them with other lines.  For example, code like this:
465
466               if (a != b)
467                 c = 1;
468               else
469                 c = 0;
470
471       can be compiled into one instruction on some machines.  In this case,
472       there is no way for gcov to calculate separate execution counts for
473       each line because there isn't separate code for each line.  Hence the
474       gcov output looks like this if you compiled the program with
475       optimization:
476
477                     100:   12:if (a != b)
478                     100:   13:  c = 1;
479                     100:   14:else
480                     100:   15:  c = 0;
481
482       The output shows that this block of code, combined by optimization,
483       executed 100 times.  In one sense this result is correct, because there
484       was only one instruction representing all four of these lines.
485       However, the output does not indicate how many times the result was 0
486       and how many times the result was 1.
487
488       Inlineable functions can create unexpected line counts.  Line counts
489       are shown for the source code of the inlineable function, but what is
490       shown depends on where the function is inlined, or if it is not inlined
491       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 fileA.o and
495       fileB.o both contain out of line bodies of a particular inlineable
496       function, they will also both contain coverage counts for that
497       function.  When fileA.o and fileB.o are linked together, the linker
498       will, on many systems, select one of those out of line bodies for all
499       calls to that function, and remove or ignore the other.  Unfortunately,
500       it will not remove the coverage counters for the unused function body.
501       Hence when instrumented, all but one use of that function will show
502       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       Long-running applications can use the "__gcov_reset" and "__gcov_dump"
511       facilities to restrict profile collection to the program region of
512       interest. Calling "__gcov_reset(void)" will clear all profile counters
513       to zero, and calling "__gcov_dump(void)" will cause the profile
514       information collected at that point to be dumped to .gcda output files.
515       Instrumented applications use a static destructor with priority 99 to
516       invoke the "__gcov_dump" function. Thus "__gcov_dump" is executed after
517       all user defined static destructors, as well as handlers registered
518       with "atexit".  If an executable loads a dynamic shared object via
519       dlopen functionality, -Wl,--dynamic-list-data is needed to dump all
520       profile data.
521

SEE ALSO

523       gpl(7), gfdl(7), fsf-funding(7), gcc(1) and the Info entry for gcc.
524
526       Copyright (c) 1996-2017 Free Software Foundation, Inc.
527
528       Permission is granted to copy, distribute and/or modify this document
529       under the terms of the GNU Free Documentation License, Version 1.3 or
530       any later version published by the Free Software Foundation; with the
531       Invariant Sections being "GNU General Public License" and "Funding Free
532       Software", the Front-Cover texts being (a) (see below), and with the
533       Back-Cover Texts being (b) (see below).  A copy of the license is
534       included in the gfdl(7) man page.
535
536       (a) The FSF's Front-Cover Text is:
537
538            A GNU Manual
539
540       (b) The FSF's Back-Cover Text is:
541
542            You have freedom to copy and modify this GNU Manual, like GNU
543            software.  Copies published by the Free Software Foundation raise
544            funds for GNU development.
545
546
547
548gcc-7.4.0                         2018-12-06                           GCOV(1)
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