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132 .\" ========================================================================
135 .TH GCOV 1 "2009-07-22" "gcc-4.4.1" "GNU"
136 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
137 .\" way too many mistakes in technical documents.
141 gcov \- coverage testing tool
143 .IX Header "SYNOPSIS"
144 gcov [\fB\-v\fR|\fB\-\-version\fR] [\fB\-h\fR|\fB\-\-help\fR]
145 [\fB\-a\fR|\fB\-\-all\-blocks\fR]
146 [\fB\-b\fR|\fB\-\-branch\-probabilities\fR]
147 [\fB\-c\fR|\fB\-\-branch\-counts\fR]
148 [\fB\-n\fR|\fB\-\-no\-output\fR]
149 [\fB\-l\fR|\fB\-\-long\-file\-names\fR]
150 [\fB\-p\fR|\fB\-\-preserve\-paths\fR]
151 [\fB\-f\fR|\fB\-\-function\-summaries\fR]
152 [\fB\-o\fR|\fB\-\-object\-directory\fR \fIdirectory|file\fR] \fIsourcefiles\fR
153 [\fB\-u\fR|\fB\-\-unconditional\-branches\fR]
155 .IX Header "DESCRIPTION"
156 \&\fBgcov\fR is a test coverage program. Use it in concert with \s-1GCC\s0
157 to analyze your programs to help create more efficient, faster running
158 code and to discover untested parts of your program. You can use
159 \&\fBgcov\fR as a profiling tool to help discover where your
160 optimization efforts will best affect your code. You can also use
161 \&\fBgcov\fR along with the other profiling tool, \fBgprof\fR, to
162 assess which parts of your code use the greatest amount of computing
165 Profiling tools help you analyze your code's performance. Using a
166 profiler such as \fBgcov\fR or \fBgprof\fR, you can find out some
167 basic performance statistics, such as:
169 how often each line of code executes
171 what lines of code are actually executed
173 how much computing time each section of code uses
175 Once you know these things about how your code works when compiled, you
176 can look at each module to see which modules should be optimized.
177 \&\fBgcov\fR helps you determine where to work on optimization.
179 Software developers also use coverage testing in concert with
180 testsuites, to make sure software is actually good enough for a release.
181 Testsuites can verify that a program works as expected; a coverage
182 program tests to see how much of the program is exercised by the
183 testsuite. Developers can then determine what kinds of test cases need
184 to be added to the testsuites to create both better testing and a better
187 You should compile your code without optimization if you plan to use
188 \&\fBgcov\fR because the optimization, by combining some lines of code
189 into one function, may not give you as much information as you need to
190 look for `hot spots' where the code is using a great deal of computer
191 time. Likewise, because \fBgcov\fR accumulates statistics by line (at
192 the lowest resolution), it works best with a programming style that
193 places only one statement on each line. If you use complicated macros
194 that expand to loops or to other control structures, the statistics are
195 less helpful\-\-\-they only report on the line where the macro call
196 appears. If your complex macros behave like functions, you can replace
197 them with inline functions to solve this problem.
199 \&\fBgcov\fR creates a logfile called \fI\fIsourcefile\fI.gcov\fR which
200 indicates how many times each line of a source file \fI\fIsourcefile\fI.c\fR
201 has executed. You can use these logfiles along with \fBgprof\fR to aid
202 in fine-tuning the performance of your programs. \fBgprof\fR gives
203 timing information you can use along with the information you get from
206 \&\fBgcov\fR works only on code compiled with \s-1GCC\s0. It is not
207 compatible with any other profiling or test coverage mechanism.
213 .IP "\fB\-\-help\fR" 4
216 Display help about using \fBgcov\fR (on the standard output), and
217 exit without doing any further processing.
221 .IP "\fB\-\-version\fR" 4
224 Display the \fBgcov\fR version number (on the standard output),
225 and exit without doing any further processing.
229 .IP "\fB\-\-all\-blocks\fR" 4
230 .IX Item "--all-blocks"
232 Write individual execution counts for every basic block. Normally gcov
233 outputs execution counts only for the main blocks of a line. With this
234 option you can determine if blocks within a single line are not being
239 .IP "\fB\-\-branch\-probabilities\fR" 4
240 .IX Item "--branch-probabilities"
242 Write branch frequencies to the output file, and write branch summary
243 info to the standard output. This option allows you to see how often
244 each branch in your program was taken. Unconditional branches will not
245 be shown, unless the \fB\-u\fR option is given.
249 .IP "\fB\-\-branch\-counts\fR" 4
250 .IX Item "--branch-counts"
252 Write branch frequencies as the number of branches taken, rather than
253 the percentage of branches taken.
257 .IP "\fB\-\-no\-output\fR" 4
258 .IX Item "--no-output"
260 Do not create the \fBgcov\fR output file.
264 .IP "\fB\-\-long\-file\-names\fR" 4
265 .IX Item "--long-file-names"
267 Create long file names for included source files. For example, if the
268 header file \fIx.h\fR contains code, and was included in the file
269 \&\fIa.c\fR, then running \fBgcov\fR on the file \fIa.c\fR will produce
270 an output file called \fIa.c##x.h.gcov\fR instead of \fIx.h.gcov\fR.
271 This can be useful if \fIx.h\fR is included in multiple source
272 files. If you use the \fB\-p\fR option, both the including and
273 included file names will be complete path names.
277 .IP "\fB\-\-preserve\-paths\fR" 4
278 .IX Item "--preserve-paths"
280 Preserve complete path information in the names of generated
281 \&\fI.gcov\fR files. Without this option, just the filename component is
282 used. With this option, all directories are used, with \fB/\fR characters
283 translated to \fB#\fR characters, \fI.\fR directory components
285 components renamed to \fB^\fR. This is useful if sourcefiles are in several
286 different directories. It also affects the \fB\-l\fR option.
290 .IP "\fB\-\-function\-summaries\fR" 4
291 .IX Item "--function-summaries"
293 Output summaries for each function in addition to the file level summary.
294 .IP "\fB\-o\fR \fIdirectory|file\fR" 4
295 .IX Item "-o directory|file"
297 .IP "\fB\-\-object\-directory\fR \fIdirectory\fR" 4
298 .IX Item "--object-directory directory"
299 .IP "\fB\-\-object\-file\fR \fIfile\fR" 4
300 .IX Item "--object-file file"
302 Specify either the directory containing the gcov data files, or the
303 object path name. The \fI.gcno\fR, and
304 \&\fI.gcda\fR data files are searched for using this option. If a directory
305 is specified, the data files are in that directory and named after the
306 source file name, without its extension. If a file is specified here,
307 the data files are named after that file, without its extension. If this
308 option is not supplied, it defaults to the current directory.
312 .IP "\fB\-\-unconditional\-branches\fR" 4
313 .IX Item "--unconditional-branches"
315 When branch probabilities are given, include those of unconditional branches.
316 Unconditional branches are normally not interesting.
318 \&\fBgcov\fR should be run with the current directory the same as that
319 when you invoked the compiler. Otherwise it will not be able to locate
320 the source files. \fBgcov\fR produces files called
321 \&\fI\fImangledname\fI.gcov\fR in the current directory. These contain
322 the coverage information of the source file they correspond to.
323 One \fI.gcov\fR file is produced for each source file containing code,
324 which was compiled to produce the data files. The \fImangledname\fR part
325 of the output file name is usually simply the source file name, but can
326 be something more complicated if the \fB\-l\fR or \fB\-p\fR options are
327 given. Refer to those options for details.
329 The \fI.gcov\fR files contain the \fB:\fR separated fields along with
330 program source code. The format is
333 \& <execution_count>:<line_number>:<source line text>
336 Additional block information may succeed each line, when requested by
337 command line option. The \fIexecution_count\fR is \fB\-\fR for lines
338 containing no code and \fB#####\fR for lines which were never executed.
339 Some lines of information at the start have \fIline_number\fR of zero.
341 The preamble lines are of the form
344 \& \-:0:<tag>:<value>
347 The ordering and number of these preamble lines will be augmented as
348 \&\fBgcov\fR development progresses \-\-\- do not rely on them remaining
349 unchanged. Use \fItag\fR to locate a particular preamble line.
351 The additional block information is of the form
354 \& <tag> <information>
357 The \fIinformation\fR is human readable, but designed to be simple
358 enough for machine parsing too.
360 When printing percentages, 0% and 100% are only printed when the values
361 are \fIexactly\fR 0% and 100% respectively. Other values which would
362 conventionally be rounded to 0% or 100% are instead printed as the
363 nearest non-boundary value.
365 When using \fBgcov\fR, you must first compile your program with two
366 special \s-1GCC\s0 options: \fB\-fprofile\-arcs \-ftest\-coverage\fR.
367 This tells the compiler to generate additional information needed by
368 gcov (basically a flow graph of the program) and also includes
369 additional code in the object files for generating the extra profiling
370 information needed by gcov. These additional files are placed in the
371 directory where the object file is located.
373 Running the program will cause profile output to be generated. For each
374 source file compiled with \fB\-fprofile\-arcs\fR, an accompanying
375 \&\fI.gcda\fR file will be placed in the object file directory.
377 Running \fBgcov\fR with your program's source file names as arguments
378 will now produce a listing of the code along with frequency of execution
379 for each line. For example, if your program is called \fItmp.c\fR, this
380 is what you see when you use the basic \fBgcov\fR facility:
383 \& $ gcc \-fprofile\-arcs \-ftest\-coverage tmp.c
386 \& 90.00% of 10 source lines executed in file tmp.c
387 \& Creating tmp.c.gcov.
390 The file \fItmp.c.gcov\fR contains output from \fBgcov\fR.
394 \& \-: 0:Source:tmp.c
395 \& \-: 0:Graph:tmp.gcno
396 \& \-: 0:Data:tmp.gcda
399 \& \-: 1:#include <stdio.h>
401 \& \-: 3:int main (void)
403 \& 1: 5: int i, total;
407 \& 11: 9: for (i = 0; i < 10; i++)
408 \& 10: 10: total += i;
410 \& 1: 12: if (total != 45)
411 \& #####: 13: printf ("Failure\en");
413 \& 1: 15: printf ("Success\en");
418 When you use the \fB\-a\fR option, you will get individual block
419 counts, and the output looks like this:
422 \& \-: 0:Source:tmp.c
423 \& \-: 0:Graph:tmp.gcno
424 \& \-: 0:Data:tmp.gcda
427 \& \-: 1:#include <stdio.h>
429 \& \-: 3:int main (void)
432 \& 1: 5: int i, total;
436 \& 11: 9: for (i = 0; i < 10; i++)
438 \& 10: 10: total += i;
441 \& 1: 12: if (total != 45)
443 \& #####: 13: printf ("Failure\en");
444 \& $$$$$: 13\-block 0
446 \& 1: 15: printf ("Success\en");
453 In this mode, each basic block is only shown on one line \*(-- the last
454 line of the block. A multi-line block will only contribute to the
455 execution count of that last line, and other lines will not be shown
456 to contain code, unless previous blocks end on those lines.
457 The total execution count of a line is shown and subsequent lines show
458 the execution counts for individual blocks that end on that line. After each
459 block, the branch and call counts of the block will be shown, if the
460 \&\fB\-b\fR option is given.
462 Because of the way \s-1GCC\s0 instruments calls, a call count can be shown
463 after a line with no individual blocks.
464 As you can see, line 13 contains a basic block that was not executed.
466 When you use the \fB\-b\fR option, your output looks like this:
470 \& 90.00% of 10 source lines executed in file tmp.c
471 \& 80.00% of 5 branches executed in file tmp.c
472 \& 80.00% of 5 branches taken at least once in file tmp.c
473 \& 50.00% of 2 calls executed in file tmp.c
474 \& Creating tmp.c.gcov.
477 Here is a sample of a resulting \fItmp.c.gcov\fR file:
480 \& \-: 0:Source:tmp.c
481 \& \-: 0:Graph:tmp.gcno
482 \& \-: 0:Data:tmp.gcda
485 \& \-: 1:#include <stdio.h>
487 \& \-: 3:int main (void)
488 \& function main called 1 returned 1 blocks executed 75%
490 \& 1: 5: int i, total;
494 \& 11: 9: for (i = 0; i < 10; i++)
495 \& branch 0 taken 91% (fallthrough)
497 \& 10: 10: total += i;
499 \& 1: 12: if (total != 45)
500 \& branch 0 taken 0% (fallthrough)
501 \& branch 1 taken 100%
502 \& #####: 13: printf ("Failure\en");
503 \& call 0 never executed
505 \& 1: 15: printf ("Success\en");
506 \& call 0 called 1 returned 100%
511 For each function, a line is printed showing how many times the function
512 is called, how many times it returns and what percentage of the
513 function's blocks were executed.
515 For each basic block, a line is printed after the last line of the basic
516 block describing the branch or call that ends the basic block. There can
517 be multiple branches and calls listed for a single source line if there
518 are multiple basic blocks that end on that line. In this case, the
519 branches and calls are each given a number. There is no simple way to map
520 these branches and calls back to source constructs. In general, though,
521 the lowest numbered branch or call will correspond to the leftmost construct
524 For a branch, if it was executed at least once, then a percentage
525 indicating the number of times the branch was taken divided by the
526 number of times the branch was executed will be printed. Otherwise, the
527 message \*(L"never executed\*(R" is printed.
529 For a call, if it was executed at least once, then a percentage
530 indicating the number of times the call returned divided by the number
531 of times the call was executed will be printed. This will usually be
532 100%, but may be less for functions that call \f(CW\*(C`exit\*(C'\fR or \f(CW\*(C`longjmp\*(C'\fR,
533 and thus may not return every time they are called.
535 The execution counts are cumulative. If the example program were
536 executed again without removing the \fI.gcda\fR file, the count for the
537 number of times each line in the source was executed would be added to
538 the results of the previous run(s). This is potentially useful in
539 several ways. For example, it could be used to accumulate data over a
540 number of program runs as part of a test verification suite, or to
541 provide more accurate long-term information over a large number of
544 The data in the \fI.gcda\fR files is saved immediately before the program
545 exits. For each source file compiled with \fB\-fprofile\-arcs\fR, the
546 profiling code first attempts to read in an existing \fI.gcda\fR file; if
547 the file doesn't match the executable (differing number of basic block
548 counts) it will ignore the contents of the file. It then adds in the
549 new execution counts and finally writes the data to the file.
550 .Sh "Using \fBgcov\fP with \s-1GCC\s0 Optimization"
551 .IX Subsection "Using gcov with GCC Optimization"
552 If you plan to use \fBgcov\fR to help optimize your code, you must
553 first compile your program with two special \s-1GCC\s0 options:
554 \&\fB\-fprofile\-arcs \-ftest\-coverage\fR. Aside from that, you can use any
555 other \s-1GCC\s0 options; but if you want to prove that every single line
556 in your program was executed, you should not compile with optimization
557 at the same time. On some machines the optimizer can eliminate some
558 simple code lines by combining them with other lines. For example, code
568 can be compiled into one instruction on some machines. In this case,
569 there is no way for \fBgcov\fR to calculate separate execution counts
570 for each line because there isn't separate code for each line. Hence
571 the \fBgcov\fR output looks like this if you compiled the program with
575 \& 100: 12:if (a != b)
581 The output shows that this block of code, combined by optimization,
582 executed 100 times. In one sense this result is correct, because there
583 was only one instruction representing all four of these lines. However,
584 the output does not indicate how many times the result was 0 and how
585 many times the result was 1.
587 Inlineable functions can create unexpected line counts. Line counts are
588 shown for the source code of the inlineable function, but what is shown
589 depends on where the function is inlined, or if it is not inlined at all.
591 If the function is not inlined, the compiler must emit an out of line
592 copy of the function, in any object file that needs it. If
593 \&\fIfileA.o\fR and \fIfileB.o\fR both contain out of line bodies of a
594 particular inlineable function, they will also both contain coverage
595 counts for that function. When \fIfileA.o\fR and \fIfileB.o\fR are
596 linked together, the linker will, on many systems, select one of those
597 out of line bodies for all calls to that function, and remove or ignore
598 the other. Unfortunately, it will not remove the coverage counters for
599 the unused function body. Hence when instrumented, all but one use of
600 that function will show zero counts.
602 If the function is inlined in several places, the block structure in
603 each location might not be the same. For instance, a condition might
604 now be calculable at compile time in some instances. Because the
605 coverage of all the uses of the inline function will be shown for the
606 same source lines, the line counts themselves might seem inconsistent.
608 .IX Header "SEE ALSO"
609 \&\fIgpl\fR\|(7), \fIgfdl\fR\|(7), \fIfsf\-funding\fR\|(7), \fIgcc\fR\|(1) and the Info entry for \fIgcc\fR.
611 .IX Header "COPYRIGHT"
612 Copyright (c) 1996, 1997, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
613 2008 Free Software Foundation, Inc.
615 Permission is granted to copy, distribute and/or modify this document
616 under the terms of the \s-1GNU\s0 Free Documentation License, Version 1.2 or
617 any later version published by the Free Software Foundation; with the
618 Invariant Sections being \*(L"\s-1GNU\s0 General Public License\*(R" and \*(L"Funding
619 Free Software\*(R", the Front-Cover texts being (a) (see below), and with
620 the Back-Cover Texts being (b) (see below). A copy of the license is
621 included in the \fIgfdl\fR\|(7) man page.
623 (a) The \s-1FSF\s0's Front-Cover Text is:
629 (b) The \s-1FSF\s0's Back-Cover Text is:
632 \& You have freedom to copy and modify this GNU Manual, like GNU
633 \& software. Copies published by the Free Software Foundation raise
634 \& funds for GNU development.
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