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129 .\" ========================================================================
132 .TH GCOV 1 "2006-03-06" "gcc-3.4.6" "GNU"
134 gcov \- coverage testing tool
136 .IX Header "SYNOPSIS"
137 gcov [\fB\-v\fR|\fB\-\-version\fR] [\fB\-h\fR|\fB\-\-help\fR]
138 [\fB\-a\fR|\fB\-\-all\-blocks\fR]
139 [\fB\-b\fR|\fB\-\-branch\-probabilities\fR]
140 [\fB\-c\fR|\fB\-\-branch\-counts\fR]
141 [\fB\-n\fR|\fB\-\-no\-output\fR]
142 [\fB\-l\fR|\fB\-\-long\-file\-names\fR]
143 [\fB\-p\fR|\fB\-\-preserve\-paths\fR]
144 [\fB\-f\fR|\fB\-\-function\-summaries\fR]
145 [\fB\-o\fR|\fB\-\-object\-directory\fR \fIdirectory|file\fR] \fIsourcefile\fR
146 [\fB\-u\fR|\fB\-\-unconditional\-branches\fR]
148 .IX Header "DESCRIPTION"
149 \&\fBgcov\fR is a test coverage program. Use it in concert with \s-1GCC\s0
150 to analyze your programs to help create more efficient, faster running
151 code and to discover untested parts of your program. You can use
152 \&\fBgcov\fR as a profiling tool to help discover where your
153 optimization efforts will best affect your code. You can also use
154 \&\fBgcov\fR along with the other profiling tool, \fBgprof\fR, to
155 assess which parts of your code use the greatest amount of computing
158 Profiling tools help you analyze your code's performance. Using a
159 profiler such as \fBgcov\fR or \fBgprof\fR, you can find out some
160 basic performance statistics, such as:
162 how often each line of code executes
164 what lines of code are actually executed
166 how much computing time each section of code uses
168 Once you know these things about how your code works when compiled, you
169 can look at each module to see which modules should be optimized.
170 \&\fBgcov\fR helps you determine where to work on optimization.
172 Software developers also use coverage testing in concert with
173 testsuites, to make sure software is actually good enough for a release.
174 Testsuites can verify that a program works as expected; a coverage
175 program tests to see how much of the program is exercised by the
176 testsuite. Developers can then determine what kinds of test cases need
177 to be added to the testsuites to create both better testing and a better
180 You should compile your code without optimization if you plan to use
181 \&\fBgcov\fR because the optimization, by combining some lines of code
182 into one function, may not give you as much information as you need to
183 look for `hot spots' where the code is using a great deal of computer
184 time. Likewise, because \fBgcov\fR accumulates statistics by line (at
185 the lowest resolution), it works best with a programming style that
186 places only one statement on each line. If you use complicated macros
187 that expand to loops or to other control structures, the statistics are
188 less helpful\-\-\-they only report on the line where the macro call
189 appears. If your complex macros behave like functions, you can replace
190 them with inline functions to solve this problem.
192 \&\fBgcov\fR creates a logfile called \fI\fIsourcefile\fI.gcov\fR which
193 indicates how many times each line of a source file \fI\fIsourcefile\fI.c\fR
194 has executed. You can use these logfiles along with \fBgprof\fR to aid
195 in fine-tuning the performance of your programs. \fBgprof\fR gives
196 timing information you can use along with the information you get from
199 \&\fBgcov\fR works only on code compiled with \s-1GCC\s0. It is not
200 compatible with any other profiling or test coverage mechanism.
206 .IP "\fB\-\-help\fR" 4
209 Display help about using \fBgcov\fR (on the standard output), and
210 exit without doing any further processing.
214 .IP "\fB\-\-version\fR" 4
217 Display the \fBgcov\fR version number (on the standard output),
218 and exit without doing any further processing.
222 .IP "\fB\-\-all\-blocks\fR" 4
223 .IX Item "--all-blocks"
225 Write individual execution counts for every basic block. Normally gcov
226 outputs execution counts only for the main blocks of a line. With this
227 option you can determine if blocks within a single line are not being
232 .IP "\fB\-\-branch\-probabilities\fR" 4
233 .IX Item "--branch-probabilities"
235 Write branch frequencies to the output file, and write branch summary
236 info to the standard output. This option allows you to see how often
237 each branch in your program was taken. Unconditional branches will not
238 be shown, unless the \fB\-u\fR option is given.
242 .IP "\fB\-\-branch\-counts\fR" 4
243 .IX Item "--branch-counts"
245 Write branch frequencies as the number of branches taken, rather than
246 the percentage of branches taken.
250 .IP "\fB\-\-no\-output\fR" 4
251 .IX Item "--no-output"
253 Do not create the \fBgcov\fR output file.
257 .IP "\fB\-\-long\-file\-names\fR" 4
258 .IX Item "--long-file-names"
260 Create long file names for included source files. For example, if the
261 header file \fIx.h\fR contains code, and was included in the file
262 \&\fIa.c\fR, then running \fBgcov\fR on the file \fIa.c\fR will produce
263 an output file called \fIa.c##x.h.gcov\fR instead of \fIx.h.gcov\fR.
264 This can be useful if \fIx.h\fR is included in multiple source
265 files. If you uses the \fB\-p\fR option, both the including and
266 included file names will be complete path names.
270 .IP "\fB\-\-preserve\-paths\fR" 4
271 .IX Item "--preserve-paths"
273 Preserve complete path information in the names of generated
274 \&\fI.gcov\fR files. Without this option, just the filename component is
275 used. With this option, all directories are used, with '/' characters
276 translated to '#' characters, '.' directory components removed and '..'
277 components renamed to '^'. This is useful if sourcefiles are in several
278 different directories. It also affects the \fB\-l\fR option.
282 .IP "\fB\-\-function\-summaries\fR" 4
283 .IX Item "--function-summaries"
285 Output summaries for each function in addition to the file level summary.
286 .IP "\fB\-o\fR \fIdirectory|file\fR" 4
287 .IX Item "-o directory|file"
289 .IP "\fB\-\-object\-directory\fR \fIdirectory\fR" 4
290 .IX Item "--object-directory directory"
291 .IP "\fB\-\-object\-file\fR \fIfile\fR" 4
292 .IX Item "--object-file file"
294 Specify either the directory containing the gcov data files, or the
295 object path name. The \fI.gcno\fR, and
296 \&\fI.gcda\fR data files are searched for using this option. If a directory
297 is specified, the data files are in that directory and named after the
298 source file name, without its extension. If a file is specified here,
299 the data files are named after that file, without its extension. If this
300 option is not supplied, it defaults to the current directory.
304 .IP "\fB\-\-unconditional\-branches\fR" 4
305 .IX Item "--unconditional-branches"
307 When branch counts are given, include those of unconditional branches.
308 Unconditional branches are normally not interesting.
310 \&\fBgcov\fR should be run with the current directory the same as that
311 when you invoked the compiler. Otherwise it will not be able to locate
312 the source files. \fBgcov\fR produces files called
313 \&\fI\fImangledname\fI.gcov\fR in the current directory. These contain
314 the coverage information of the source file they correspond to.
315 One \fI.gcov\fR file is produced for each source file containing code,
316 which was compiled to produce the data files. The \fImangledname\fR part
317 of the output file name is usually simply the source file name, but can
318 be something more complicated if the \fB\-l\fR or \fB\-p\fR options are
319 given. Refer to those options for details.
321 The \fI.gcov\fR files contain the ':' separated fields along with
322 program source code. The format is
325 \& <execution_count>:<line_number>:<source line text>
328 Additional block information may succeed each line, when requested by
329 command line option. The \fIexecution_count\fR is \fB\-\fR for lines
330 containing no code and \fB#####\fR for lines which were never
331 executed. Some lines of information at the start have \fIline_number\fR
334 When printing percentages, 0% and 100% are only printed when the values
335 are \fIexactly\fR 0% and 100% respectively. Other values which would
336 conventionally be rounded to 0% or 100% are instead printed as the
337 nearest non-boundary value.
339 When using \fBgcov\fR, you must first compile your program with two
340 special \s-1GCC\s0 options: \fB\-fprofile\-arcs \-ftest\-coverage\fR.
341 This tells the compiler to generate additional information needed by
342 gcov (basically a flow graph of the program) and also includes
343 additional code in the object files for generating the extra profiling
344 information needed by gcov. These additional files are placed in the
345 directory where the object file is located.
347 Running the program will cause profile output to be generated. For each
348 source file compiled with \fB\-fprofile\-arcs\fR, an accompanying
349 \&\fI.gcda\fR file will be placed in the object file directory.
351 Running \fBgcov\fR with your program's source file names as arguments
352 will now produce a listing of the code along with frequency of execution
353 for each line. For example, if your program is called \fItmp.c\fR, this
354 is what you see when you use the basic \fBgcov\fR facility:
357 \& $ gcc -fprofile-arcs -ftest-coverage tmp.c
360 \& 90.00% of 10 source lines executed in file tmp.c
361 \& Creating tmp.c.gcov.
364 The file \fItmp.c.gcov\fR contains output from \fBgcov\fR.
369 \& -: 0:Graph:tmp.gcno
370 \& -: 0:Data:tmp.gcda
373 \& -: 1:#include <stdio.h>
375 \& -: 3:int main (void)
376 \& function main called 1 returned 1 blocks executed 75%
378 \& 1: 5: int i, total;
382 \& 11: 9: for (i = 0; i < 10; i++)
383 \& 10: 10: total += i;
385 \& 1: 12: if (total != 45)
386 \& #####: 13: printf ("Failure\en");
388 \& 1: 15: printf ("Success\en");
393 When you use the \fB\-a\fR option, you will get individual block
394 counts, and the output looks like this:
398 \& -: 0:Graph:tmp.gcno
399 \& -: 0:Data:tmp.gcda
402 \& -: 1:#include <stdio.h>
404 \& -: 3:int main (void)
405 \& function main called 1 returned 1 blocks executed 75%
408 \& 1: 5: int i, total;
412 \& 11: 9: for (i = 0; i < 10; i++)
414 \& 10: 10: total += i;
417 \& 1: 12: if (total != 45)
419 \& #####: 13: printf ("Failure\en");
422 \& 1: 15: printf ("Success\en");
429 In this mode, each basic block is only shown on one line \*(-- the last
430 line of the block. A multi-line block will only contribute to the
431 execution count of that last line, and other lines will not be shown
432 to contain code, unless previous blocks end on those lines.
433 The total execution count of a line is shown and subsequent lines show
434 the execution counts for individual blocks that end on that line. After each
435 block, the branch and call counts of the block will be shown, if the
436 \&\fB\-b\fR option is given.
438 Because of the way \s-1GCC\s0 instruments calls, a call count can be shown
439 after a line with no individual blocks.
440 As you can see, line 13 contains a basic block that was not executed.
442 When you use the \fB\-b\fR option, your output looks like this:
446 \& 90.00% of 10 source lines executed in file tmp.c
447 \& 80.00% of 5 branches executed in file tmp.c
448 \& 80.00% of 5 branches taken at least once in file tmp.c
449 \& 50.00% of 2 calls executed in file tmp.c
450 \& Creating tmp.c.gcov.
453 Here is a sample of a resulting \fItmp.c.gcov\fR file:
457 \& -: 0:Graph:tmp.gcno
458 \& -: 0:Data:tmp.gcda
461 \& -: 1:#include <stdio.h>
463 \& -: 3:int main (void)
464 \& function main called 1 returned 1 blocks executed 75%
466 \& 1: 5: int i, total;
470 \& 11: 9: for (i = 0; i < 10; i++)
471 \& branch 0 taken 91% (fallthrough)
473 \& 10: 10: total += i;
475 \& 1: 12: if (total != 45)
476 \& branch 0 taken 0% (fallthrough)
477 \& branch 1 taken 100%
478 \& #####: 13: printf ("Failure\en");
479 \& call 0 never executed
481 \& 1: 15: printf ("Success\en");
482 \& call 0 called 1 returned 100%
487 For each basic block, a line is printed after the last line of the basic
488 block describing the branch or call that ends the basic block. There can
489 be multiple branches and calls listed for a single source line if there
490 are multiple basic blocks that end on that line. In this case, the
491 branches and calls are each given a number. There is no simple way to map
492 these branches and calls back to source constructs. In general, though,
493 the lowest numbered branch or call will correspond to the leftmost construct
496 For a branch, if it was executed at least once, then a percentage
497 indicating the number of times the branch was taken divided by the
498 number of times the branch was executed will be printed. Otherwise, the
499 message ``never executed'' is printed.
501 For a call, if it was executed at least once, then a percentage
502 indicating the number of times the call returned divided by the number
503 of times the call was executed will be printed. This will usually be
504 100%, but may be less for functions call \f(CW\*(C`exit\*(C'\fR or \f(CW\*(C`longjmp\*(C'\fR,
505 and thus may not return every time they are called.
507 The execution counts are cumulative. If the example program were
508 executed again without removing the \fI.gcda\fR file, the count for the
509 number of times each line in the source was executed would be added to
510 the results of the previous run(s). This is potentially useful in
511 several ways. For example, it could be used to accumulate data over a
512 number of program runs as part of a test verification suite, or to
513 provide more accurate long-term information over a large number of
516 The data in the \fI.gcda\fR files is saved immediately before the program
517 exits. For each source file compiled with \fB\-fprofile\-arcs\fR, the
518 profiling code first attempts to read in an existing \fI.gcda\fR file; if
519 the file doesn't match the executable (differing number of basic block
520 counts) it will ignore the contents of the file. It then adds in the
521 new execution counts and finally writes the data to the file.
522 .Sh "Using \fBgcov\fP with \s-1GCC\s0 Optimization"
523 .IX Subsection "Using gcov with GCC Optimization"
524 If you plan to use \fBgcov\fR to help optimize your code, you must
525 first compile your program with two special \s-1GCC\s0 options:
526 \&\fB\-fprofile\-arcs \-ftest\-coverage\fR. Aside from that, you can use any
527 other \s-1GCC\s0 options; but if you want to prove that every single line
528 in your program was executed, you should not compile with optimization
529 at the same time. On some machines the optimizer can eliminate some
530 simple code lines by combining them with other lines. For example, code
540 can be compiled into one instruction on some machines. In this case,
541 there is no way for \fBgcov\fR to calculate separate execution counts
542 for each line because there isn't separate code for each line. Hence
543 the \fBgcov\fR output looks like this if you compiled the program with
547 \& 100: 12:if (a != b)
553 The output shows that this block of code, combined by optimization,
554 executed 100 times. In one sense this result is correct, because there
555 was only one instruction representing all four of these lines. However,
556 the output does not indicate how many times the result was 0 and how
557 many times the result was 1.
559 Inlineable functions can create unexpected line counts. Line counts are
560 shown for the source code of the inlineable function, but what is shown
561 depends on where the function is inlined, or if it is not inlined at all.
563 If the function is not inlined, the compiler must emit an out of line
564 copy of the function, in any object file that needs it. If
565 \&\fIfileA.o\fR and \fIfileB.o\fR both contain out of line bodies of a
566 particular inlineable function, they will also both contain coverage
567 counts for that function. When \fIfileA.o\fR and \fIfileB.o\fR are
568 linked together, the linker will, on many systems, select one of those
569 out of line bodies for all calls to that function, and remove or ignore
570 the other. Unfortunately, it will not remove the coverage counters for
571 the unused function body. Hence when instrumented, all but one use of
572 that function will show zero counts.
574 If the function is inlined in several places, the block structure in
575 each location might not be the same. For instance, a condition might
576 now be calculable at compile time in some instances. Because the
577 coverage of all the uses of the inline function will be shown for the
578 same source lines, the line counts themselves might seem inconsistent.
580 .IX Header "SEE ALSO"
581 \&\fIgpl\fR\|(7), \fIgfdl\fR\|(7), \fIfsf\-funding\fR\|(7), \fIgcc\fR\|(1) and the Info entry for \fIgcc\fR.
583 .IX Header "COPYRIGHT"
584 Copyright (c) 1996, 1997, 1999, 2000, 2001, 2002, 2003
585 Free Software Foundation, Inc.
587 Permission is granted to copy, distribute and/or modify this document
588 under the terms of the \s-1GNU\s0 Free Documentation License, Version 1.2 or
589 any later version published by the Free Software Foundation; with the
590 Invariant Sections being ``\s-1GNU\s0 General Public License'' and ``Funding
591 Free Software'', the Front-Cover texts being (a) (see below), and with
592 the Back-Cover Texts being (b) (see below). A copy of the license is
593 included in the \fIgfdl\fR\|(7) man page.
595 (a) The \s-1FSF\s0's Front-Cover Text is:
601 (b) The \s-1FSF\s0's Back-Cover Text is:
604 \& You have freedom to copy and modify this GNU Manual, like GNU
605 \& software. Copies published by the Free Software Foundation raise
606 \& funds for GNU development.
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