Import gcc-4.4.1
[dragonfly.git] / contrib / gcc-4.4 / gcc / doc / gcov.1
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131.rm #[ #] #H #V #F C
132.\" ========================================================================
133.\"
134.IX Title "GCOV 1"
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.
138.if n .ad l
139.nh
140.SH "NAME"
141gcov \- coverage testing tool
142.SH "SYNOPSIS"
143.IX Header "SYNOPSIS"
144gcov [\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]
154.SH "DESCRIPTION"
155.IX Header "DESCRIPTION"
156\&\fBgcov\fR is a test coverage program. Use it in concert with \s-1GCC\s0
157to analyze your programs to help create more efficient, faster running
158code and to discover untested parts of your program. You can use
159\&\fBgcov\fR as a profiling tool to help discover where your
160optimization efforts will best affect your code. You can also use
161\&\fBgcov\fR along with the other profiling tool, \fBgprof\fR, to
162assess which parts of your code use the greatest amount of computing
163time.
164.PP
165Profiling tools help you analyze your code's performance. Using a
166profiler such as \fBgcov\fR or \fBgprof\fR, you can find out some
167basic performance statistics, such as:
168.IP "\(bu" 4
169how often each line of code executes
170.IP "\(bu" 4
171what lines of code are actually executed
172.IP "\(bu" 4
173how much computing time each section of code uses
174.PP
175Once you know these things about how your code works when compiled, you
176can look at each module to see which modules should be optimized.
177\&\fBgcov\fR helps you determine where to work on optimization.
178.PP
179Software developers also use coverage testing in concert with
180testsuites, to make sure software is actually good enough for a release.
181Testsuites can verify that a program works as expected; a coverage
182program tests to see how much of the program is exercised by the
183testsuite. Developers can then determine what kinds of test cases need
184to be added to the testsuites to create both better testing and a better
185final product.
186.PP
187You should compile your code without optimization if you plan to use
188\&\fBgcov\fR because the optimization, by combining some lines of code
189into one function, may not give you as much information as you need to
190look for `hot spots' where the code is using a great deal of computer
191time. Likewise, because \fBgcov\fR accumulates statistics by line (at
192the lowest resolution), it works best with a programming style that
193places only one statement on each line. If you use complicated macros
194that expand to loops or to other control structures, the statistics are
195less helpful\-\-\-they only report on the line where the macro call
196appears. If your complex macros behave like functions, you can replace
197them with inline functions to solve this problem.
198.PP
199\&\fBgcov\fR creates a logfile called \fI\fIsourcefile\fI.gcov\fR which
200indicates how many times each line of a source file \fI\fIsourcefile\fI.c\fR
201has executed. You can use these logfiles along with \fBgprof\fR to aid
202in fine-tuning the performance of your programs. \fBgprof\fR gives
203timing information you can use along with the information you get from
204\&\fBgcov\fR.
205.PP
206\&\fBgcov\fR works only on code compiled with \s-1GCC\s0. It is not
207compatible with any other profiling or test coverage mechanism.
208.SH "OPTIONS"
209.IX Header "OPTIONS"
210.IP "\fB\-h\fR" 4
211.IX Item "-h"
212.PD 0
213.IP "\fB\-\-help\fR" 4
214.IX Item "--help"
215.PD
216Display help about using \fBgcov\fR (on the standard output), and
217exit without doing any further processing.
218.IP "\fB\-v\fR" 4
219.IX Item "-v"
220.PD 0
221.IP "\fB\-\-version\fR" 4
222.IX Item "--version"
223.PD
224Display the \fBgcov\fR version number (on the standard output),
225and exit without doing any further processing.
226.IP "\fB\-a\fR" 4
227.IX Item "-a"
228.PD 0
229.IP "\fB\-\-all\-blocks\fR" 4
230.IX Item "--all-blocks"
231.PD
232Write individual execution counts for every basic block. Normally gcov
233outputs execution counts only for the main blocks of a line. With this
234option you can determine if blocks within a single line are not being
235executed.
236.IP "\fB\-b\fR" 4
237.IX Item "-b"
238.PD 0
239.IP "\fB\-\-branch\-probabilities\fR" 4
240.IX Item "--branch-probabilities"
241.PD
242Write branch frequencies to the output file, and write branch summary
243info to the standard output. This option allows you to see how often
244each branch in your program was taken. Unconditional branches will not
245be shown, unless the \fB\-u\fR option is given.
246.IP "\fB\-c\fR" 4
247.IX Item "-c"
248.PD 0
249.IP "\fB\-\-branch\-counts\fR" 4
250.IX Item "--branch-counts"
251.PD
252Write branch frequencies as the number of branches taken, rather than
253the percentage of branches taken.
254.IP "\fB\-n\fR" 4
255.IX Item "-n"
256.PD 0
257.IP "\fB\-\-no\-output\fR" 4
258.IX Item "--no-output"
259.PD
260Do not create the \fBgcov\fR output file.
261.IP "\fB\-l\fR" 4
262.IX Item "-l"
263.PD 0
264.IP "\fB\-\-long\-file\-names\fR" 4
265.IX Item "--long-file-names"
266.PD
267Create long file names for included source files. For example, if the
268header 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
270an output file called \fIa.c##x.h.gcov\fR instead of \fIx.h.gcov\fR.
271This can be useful if \fIx.h\fR is included in multiple source
272files. If you use the \fB\-p\fR option, both the including and
273included file names will be complete path names.
274.IP "\fB\-p\fR" 4
275.IX Item "-p"
276.PD 0
277.IP "\fB\-\-preserve\-paths\fR" 4
278.IX Item "--preserve-paths"
279.PD
280Preserve complete path information in the names of generated
281\&\fI.gcov\fR files. Without this option, just the filename component is
282used. With this option, all directories are used, with \fB/\fR characters
283translated to \fB#\fR characters, \fI.\fR directory components
284removed and \fI..\fR
285components renamed to \fB^\fR. This is useful if sourcefiles are in several
286different directories. It also affects the \fB\-l\fR option.
287.IP "\fB\-f\fR" 4
288.IX Item "-f"
289.PD 0
290.IP "\fB\-\-function\-summaries\fR" 4
291.IX Item "--function-summaries"
292.PD
293Output 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"
296.PD 0
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"
301.PD
302Specify either the directory containing the gcov data files, or the
303object path name. The \fI.gcno\fR, and
304\&\fI.gcda\fR data files are searched for using this option. If a directory
305is specified, the data files are in that directory and named after the
306source file name, without its extension. If a file is specified here,
307the data files are named after that file, without its extension. If this
308option is not supplied, it defaults to the current directory.
309.IP "\fB\-u\fR" 4
310.IX Item "-u"
311.PD 0
312.IP "\fB\-\-unconditional\-branches\fR" 4
313.IX Item "--unconditional-branches"
314.PD
315When branch probabilities are given, include those of unconditional branches.
316Unconditional branches are normally not interesting.
317.PP
318\&\fBgcov\fR should be run with the current directory the same as that
319when you invoked the compiler. Otherwise it will not be able to locate
320the source files. \fBgcov\fR produces files called
321\&\fI\fImangledname\fI.gcov\fR in the current directory. These contain
322the coverage information of the source file they correspond to.
323One \fI.gcov\fR file is produced for each source file containing code,
324which was compiled to produce the data files. The \fImangledname\fR part
325of the output file name is usually simply the source file name, but can
326be something more complicated if the \fB\-l\fR or \fB\-p\fR options are
327given. Refer to those options for details.
328.PP
329The \fI.gcov\fR files contain the \fB:\fR separated fields along with
330program source code. The format is
331.PP
332.Vb 1
333\& <execution_count>:<line_number>:<source line text>
334.Ve
335.PP
336Additional block information may succeed each line, when requested by
337command line option. The \fIexecution_count\fR is \fB\-\fR for lines
338containing no code and \fB#####\fR for lines which were never executed.
339Some lines of information at the start have \fIline_number\fR of zero.
340.PP
341The preamble lines are of the form
342.PP
343.Vb 1
344\& \-:0:<tag>:<value>
345.Ve
346.PP
347The ordering and number of these preamble lines will be augmented as
348\&\fBgcov\fR development progresses \-\-\- do not rely on them remaining
349unchanged. Use \fItag\fR to locate a particular preamble line.
350.PP
351The additional block information is of the form
352.PP
353.Vb 1
354\& <tag> <information>
355.Ve
356.PP
357The \fIinformation\fR is human readable, but designed to be simple
358enough for machine parsing too.
359.PP
360When printing percentages, 0% and 100% are only printed when the values
361are \fIexactly\fR 0% and 100% respectively. Other values which would
362conventionally be rounded to 0% or 100% are instead printed as the
363nearest non-boundary value.
364.PP
365When using \fBgcov\fR, you must first compile your program with two
366special \s-1GCC\s0 options: \fB\-fprofile\-arcs \-ftest\-coverage\fR.
367This tells the compiler to generate additional information needed by
368gcov (basically a flow graph of the program) and also includes
369additional code in the object files for generating the extra profiling
370information needed by gcov. These additional files are placed in the
371directory where the object file is located.
372.PP
373Running the program will cause profile output to be generated. For each
374source file compiled with \fB\-fprofile\-arcs\fR, an accompanying
375\&\fI.gcda\fR file will be placed in the object file directory.
376.PP
377Running \fBgcov\fR with your program's source file names as arguments
378will now produce a listing of the code along with frequency of execution
379for each line. For example, if your program is called \fItmp.c\fR, this
380is what you see when you use the basic \fBgcov\fR facility:
381.PP
382.Vb 5
383\& $ gcc \-fprofile\-arcs \-ftest\-coverage tmp.c
384\& $ a.out
385\& $ gcov tmp.c
386\& 90.00% of 10 source lines executed in file tmp.c
387\& Creating tmp.c.gcov.
388.Ve
389.PP
390The file \fItmp.c.gcov\fR contains output from \fBgcov\fR.
391Here is a sample:
392.PP
393.Vb 10
394\& \-: 0:Source:tmp.c
395\& \-: 0:Graph:tmp.gcno
396\& \-: 0:Data:tmp.gcda
397\& \-: 0:Runs:1
398\& \-: 0:Programs:1
399\& \-: 1:#include <stdio.h>
400\& \-: 2:
401\& \-: 3:int main (void)
402\& 1: 4:{
403\& 1: 5: int i, total;
404\& \-: 6:
405\& 1: 7: total = 0;
406\& \-: 8:
407\& 11: 9: for (i = 0; i < 10; i++)
408\& 10: 10: total += i;
409\& \-: 11:
410\& 1: 12: if (total != 45)
411\& #####: 13: printf ("Failure\en");
412\& \-: 14: else
413\& 1: 15: printf ("Success\en");
414\& 1: 16: return 0;
415\& \-: 17:}
416.Ve
417.PP
418When you use the \fB\-a\fR option, you will get individual block
419counts, and the output looks like this:
420.PP
421.Vb 10
422\& \-: 0:Source:tmp.c
423\& \-: 0:Graph:tmp.gcno
424\& \-: 0:Data:tmp.gcda
425\& \-: 0:Runs:1
426\& \-: 0:Programs:1
427\& \-: 1:#include <stdio.h>
428\& \-: 2:
429\& \-: 3:int main (void)
430\& 1: 4:{
431\& 1: 4\-block 0
432\& 1: 5: int i, total;
433\& \-: 6:
434\& 1: 7: total = 0;
435\& \-: 8:
436\& 11: 9: for (i = 0; i < 10; i++)
437\& 11: 9\-block 0
438\& 10: 10: total += i;
439\& 10: 10\-block 0
440\& \-: 11:
441\& 1: 12: if (total != 45)
442\& 1: 12\-block 0
443\& #####: 13: printf ("Failure\en");
444\& $$$$$: 13\-block 0
445\& \-: 14: else
446\& 1: 15: printf ("Success\en");
447\& 1: 15\-block 0
448\& 1: 16: return 0;
449\& 1: 16\-block 0
450\& \-: 17:}
451.Ve
452.PP
453In this mode, each basic block is only shown on one line \*(-- the last
454line of the block. A multi-line block will only contribute to the
455execution count of that last line, and other lines will not be shown
456to contain code, unless previous blocks end on those lines.
457The total execution count of a line is shown and subsequent lines show
458the execution counts for individual blocks that end on that line. After each
459block, the branch and call counts of the block will be shown, if the
460\&\fB\-b\fR option is given.
461.PP
462Because of the way \s-1GCC\s0 instruments calls, a call count can be shown
463after a line with no individual blocks.
464As you can see, line 13 contains a basic block that was not executed.
465.PP
466When you use the \fB\-b\fR option, your output looks like this:
467.PP
468.Vb 6
469\& $ gcov \-b tmp.c
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.
475.Ve
476.PP
477Here is a sample of a resulting \fItmp.c.gcov\fR file:
478.PP
479.Vb 10
480\& \-: 0:Source:tmp.c
481\& \-: 0:Graph:tmp.gcno
482\& \-: 0:Data:tmp.gcda
483\& \-: 0:Runs:1
484\& \-: 0:Programs:1
485\& \-: 1:#include <stdio.h>
486\& \-: 2:
487\& \-: 3:int main (void)
488\& function main called 1 returned 1 blocks executed 75%
489\& 1: 4:{
490\& 1: 5: int i, total;
491\& \-: 6:
492\& 1: 7: total = 0;
493\& \-: 8:
494\& 11: 9: for (i = 0; i < 10; i++)
495\& branch 0 taken 91% (fallthrough)
496\& branch 1 taken 9%
497\& 10: 10: total += i;
498\& \-: 11:
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
504\& \-: 14: else
505\& 1: 15: printf ("Success\en");
506\& call 0 called 1 returned 100%
507\& 1: 16: return 0;
508\& \-: 17:}
509.Ve
510.PP
511For each function, a line is printed showing how many times the function
512is called, how many times it returns and what percentage of the
513function's blocks were executed.
514.PP
515For each basic block, a line is printed after the last line of the basic
516block describing the branch or call that ends the basic block. There can
517be multiple branches and calls listed for a single source line if there
518are multiple basic blocks that end on that line. In this case, the
519branches and calls are each given a number. There is no simple way to map
520these branches and calls back to source constructs. In general, though,
521the lowest numbered branch or call will correspond to the leftmost construct
522on the source line.
523.PP
524For a branch, if it was executed at least once, then a percentage
525indicating the number of times the branch was taken divided by the
526number of times the branch was executed will be printed. Otherwise, the
527message \*(L"never executed\*(R" is printed.
528.PP
529For a call, if it was executed at least once, then a percentage
530indicating the number of times the call returned divided by the number
531of times the call was executed will be printed. This will usually be
532100%, but may be less for functions that call \f(CW\*(C`exit\*(C'\fR or \f(CW\*(C`longjmp\*(C'\fR,
533and thus may not return every time they are called.
534.PP
535The execution counts are cumulative. If the example program were
536executed again without removing the \fI.gcda\fR file, the count for the
537number of times each line in the source was executed would be added to
538the results of the previous run(s). This is potentially useful in
539several ways. For example, it could be used to accumulate data over a
540number of program runs as part of a test verification suite, or to
541provide more accurate long-term information over a large number of
542program runs.
543.PP
544The data in the \fI.gcda\fR files is saved immediately before the program
545exits. For each source file compiled with \fB\-fprofile\-arcs\fR, the
546profiling code first attempts to read in an existing \fI.gcda\fR file; if
547the file doesn't match the executable (differing number of basic block
548counts) it will ignore the contents of the file. It then adds in the
549new 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"
552If you plan to use \fBgcov\fR to help optimize your code, you must
553first compile your program with two special \s-1GCC\s0 options:
554\&\fB\-fprofile\-arcs \-ftest\-coverage\fR. Aside from that, you can use any
555other \s-1GCC\s0 options; but if you want to prove that every single line
556in your program was executed, you should not compile with optimization
557at the same time. On some machines the optimizer can eliminate some
558simple code lines by combining them with other lines. For example, code
559like this:
560.PP
561.Vb 4
562\& if (a != b)
563\& c = 1;
564\& else
565\& c = 0;
566.Ve
567.PP
568can be compiled into one instruction on some machines. In this case,
569there is no way for \fBgcov\fR to calculate separate execution counts
570for each line because there isn't separate code for each line. Hence
571the \fBgcov\fR output looks like this if you compiled the program with
572optimization:
573.PP
574.Vb 4
575\& 100: 12:if (a != b)
576\& 100: 13: c = 1;
577\& 100: 14:else
578\& 100: 15: c = 0;
579.Ve
580.PP
581The output shows that this block of code, combined by optimization,
582executed 100 times. In one sense this result is correct, because there
583was only one instruction representing all four of these lines. However,
584the output does not indicate how many times the result was 0 and how
585many times the result was 1.
586.PP
587Inlineable functions can create unexpected line counts. Line counts are
588shown for the source code of the inlineable function, but what is shown
589depends on where the function is inlined, or if it is not inlined at all.
590.PP
591If the function is not inlined, the compiler must emit an out of line
592copy 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
594particular inlineable function, they will also both contain coverage
595counts for that function. When \fIfileA.o\fR and \fIfileB.o\fR are
596linked together, the linker will, on many systems, select one of those
597out of line bodies for all calls to that function, and remove or ignore
598the other. Unfortunately, it will not remove the coverage counters for
599the unused function body. Hence when instrumented, all but one use of
600that function will show zero counts.
601.PP
602If the function is inlined in several places, the block structure in
603each location might not be the same. For instance, a condition might
604now be calculable at compile time in some instances. Because the
605coverage of all the uses of the inline function will be shown for the
606same source lines, the line counts themselves might seem inconsistent.
607.SH "SEE ALSO"
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.
610.SH "COPYRIGHT"
611.IX Header "COPYRIGHT"
612Copyright (c) 1996, 1997, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
6132008 Free Software Foundation, Inc.
614.PP
615Permission is granted to copy, distribute and/or modify this document
616under the terms of the \s-1GNU\s0 Free Documentation License, Version 1.2 or
617any later version published by the Free Software Foundation; with the
618Invariant Sections being \*(L"\s-1GNU\s0 General Public License\*(R" and \*(L"Funding
619Free Software\*(R", the Front-Cover texts being (a) (see below), and with
620the Back-Cover Texts being (b) (see below). A copy of the license is
621included in the \fIgfdl\fR\|(7) man page.
622.PP
623(a) The \s-1FSF\s0's Front-Cover Text is:
624.PP
625.Vb 1
626\& A GNU Manual
627.Ve
628.PP
629(b) The \s-1FSF\s0's Back-Cover Text is:
630.PP
631.Vb 3
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.
635.Ve