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.\" ========================================================================

.\"

.IX Title "GCOV 1"

.TH GCOV 1 "2004-11-05" "gcc-3.4.3" "GNU"

.SH "NAME"

gcov \- coverage testing tool

.SH "SYNOPSIS"

.IX Header "SYNOPSIS"

gcov [\fB\-v\fR|\fB\-\-version\fR] [\fB\-h\fR|\fB\-\-help\fR]

     [\fB\-a\fR|\fB\-\-all\-blocks\fR]

     [\fB\-b\fR|\fB\-\-branch\-probabilities\fR]

     [\fB\-c\fR|\fB\-\-branch\-counts\fR]

     [\fB\-n\fR|\fB\-\-no\-output\fR]

     [\fB\-l\fR|\fB\-\-long\-file\-names\fR]

     [\fB\-p\fR|\fB\-\-preserve\-paths\fR]

     [\fB\-f\fR|\fB\-\-function\-summaries\fR]

     [\fB\-o\fR|\fB\-\-object\-directory\fR \fIdirectory|file\fR] \fIsourcefile\fR

     [\fB\-u\fR|\fB\-\-unconditional\-branches\fR]

.SH "DESCRIPTION"

.IX Header "DESCRIPTION"

\&\fBgcov\fR is a test coverage program.  Use it in concert with \s-1GCC\s0

to analyze your programs to help create more efficient, faster running

code and to discover untested parts of your program.  You can use

\&\fBgcov\fR as a profiling tool to help discover where your

optimization efforts will best affect your code.  You can also use

\&\fBgcov\fR along with the other profiling tool, \fBgprof\fR, to

assess which parts of your code use the greatest amount of computing

time.

.PP

Profiling tools help you analyze your code's performance.  Using a

profiler such as \fBgcov\fR or \fBgprof\fR, you can find out some

basic performance statistics, such as:

.IP "\(bu" 4

how often each line of code executes

.IP "\(bu" 4

what lines of code are actually executed

.IP "\(bu" 4

how much computing time each section of code uses

.PP

Once you know these things about how your code works when compiled, you

can look at each module to see which modules should be optimized.

\&\fBgcov\fR helps you determine where to work on optimization.

.PP

Software developers also use coverage testing in concert with

testsuites, to make sure software is actually good enough for a release.

Testsuites can verify that a program works as expected; a coverage

program tests to see how much of the program is exercised by the

testsuite.  Developers can then determine what kinds of test cases need

to be added to the testsuites to create both better testing and a better

final product.

.PP

You should compile your code without optimization if you plan to use

\&\fBgcov\fR because the optimization, by combining some lines of code

into one function, may not give you as much information as you need to

look for `hot spots' where the code is using a great deal of computer

time.  Likewise, because \fBgcov\fR accumulates statistics by line (at

the lowest resolution), it works best with a programming style that

places only one statement on each line.  If you use complicated macros

that expand to loops or to other control structures, the statistics are

less helpful\-\-\-they only report on the line where the macro call

appears.  If your complex macros behave like functions, you can replace

them with inline functions to solve this problem.

.PP

\&\fBgcov\fR creates a logfile called \fI\fIsourcefile\fI.gcov\fR which

indicates how many times each line of a source file \fI\fIsourcefile\fI.c\fR

has executed.  You can use these logfiles along with \fBgprof\fR to aid

in fine-tuning the performance of your programs.  \fBgprof\fR gives

timing information you can use along with the information you get from

\&\fBgcov\fR.

.PP

\&\fBgcov\fR works only on code compiled with \s-1GCC\s0.  It is not

compatible with any other profiling or test coverage mechanism.

.SH "OPTIONS"

.IX Header "OPTIONS"

.IP "\fB\-h\fR" 4

.IX Item "-h"

.PD 0

.IP "\fB\-\-help\fR" 4

.IX Item "--help"

.PD

Display help about using \fBgcov\fR (on the standard output), and

exit without doing any further processing.

.IP "\fB\-v\fR" 4

.IX Item "-v"

.PD 0

.IP "\fB\-\-version\fR" 4

.IX Item "--version"

.PD

Display the \fBgcov\fR version number (on the standard output),

and exit without doing any further processing.

.IP "\fB\-a\fR" 4

.IX Item "-a"

.PD 0

.IP "\fB\-\-all\-blocks\fR" 4

.IX Item "--all-blocks"

.PD

Write individual execution counts for every basic block. Normally gcov

outputs execution counts only for the main blocks of a line. With this

option you can determine if blocks within a single line are not being

executed.

.IP "\fB\-b\fR" 4

.IX Item "-b"

.PD 0

.IP "\fB\-\-branch\-probabilities\fR" 4

.IX Item "--branch-probabilities"

.PD

Write branch frequencies to the output file, and write branch summary

info to the standard output.  This option allows you to see how often

each branch in your program was taken. Unconditional branches will not

be shown, unless the \fB\-u\fR option is given.

.IP "\fB\-c\fR" 4

.IX Item "-c"

.PD 0

.IP "\fB\-\-branch\-counts\fR" 4

.IX Item "--branch-counts"

.PD

Write branch frequencies as the number of branches taken, rather than

the percentage of branches taken.

.IP "\fB\-n\fR" 4

.IX Item "-n"

.PD 0

.IP "\fB\-\-no\-output\fR" 4

.IX Item "--no-output"

.PD

Do not create the \fBgcov\fR output file.

.IP "\fB\-l\fR" 4

.IX Item "-l"

.PD 0

.IP "\fB\-\-long\-file\-names\fR" 4

.IX Item "--long-file-names"

.PD

Create long file names for included source files.  For example, if the

header file \fIx.h\fR contains code, and was included in the file

\&\fIa.c\fR, then running \fBgcov\fR on the file \fIa.c\fR will produce

an output file called \fIa.c##x.h.gcov\fR instead of \fIx.h.gcov\fR.

This can be useful if \fIx.h\fR is included in multiple source

files. If you uses the \fB\-p\fR option, both the including and

included file names will be complete path names.

.IP "\fB\-p\fR" 4

.IX Item "-p"

.PD 0

.IP "\fB\-\-preserve\-paths\fR" 4

.IX Item "--preserve-paths"

.PD

Preserve complete path information in the names of generated

\&\fI.gcov\fR files. Without this option, just the filename component is

used. With this option, all directories are used, with '/' characters

translated to '#' characters, '.' directory components removed and '..'

components renamed to '^'. This is useful if sourcefiles are in several

different directories. It also affects the \fB\-l\fR option.

.IP "\fB\-f\fR" 4

.IX Item "-f"

.PD 0

.IP "\fB\-\-function\-summaries\fR" 4

.IX Item "--function-summaries"

.PD

Output summaries for each function in addition to the file level summary.

.IP "\fB\-o\fR \fIdirectory|file\fR" 4

.IX Item "-o directory|file"

.PD 0

.IP "\fB\-\-object\-directory\fR \fIdirectory\fR" 4

.IX Item "--object-directory directory"

.IP "\fB\-\-object\-file\fR \fIfile\fR" 4

.IX Item "--object-file file"

.PD

Specify either the directory containing the gcov data files, or the

object path name. The \fI.gcno\fR, and

\&\fI.gcda\fR data files are searched for using this option. If a directory

is specified, the data files are in that directory and named after the

source file name, without its extension. If a file is specified here,

the data files are named after that file, without its extension. If this

option is not supplied, it defaults to the current directory.

.IP "\fB\-u\fR" 4

.IX Item "-u"

.PD 0

.IP "\fB\-\-unconditional\-branches\fR" 4

.IX Item "--unconditional-branches"

.PD

When branch counts are given, include those of unconditional branches.

Unconditional branches are normally not interesting.

.PP

\&\fBgcov\fR should be run with the current directory the same as that

when you invoked the compiler. Otherwise it will not be able to locate

the source files. \fBgcov\fR produces files called

\&\fI\fImangledname\fI.gcov\fR in the current directory. These contain

the coverage information of the source file they correspond to.

One \fI.gcov\fR file is produced for each source file containing code,

which was compiled to produce the data files. The \fImangledname\fR part

of the output file name is usually simply the source file name, but can

be something more complicated if the \fB\-l\fR or \fB\-p\fR options are

given. Refer to those options for details.

.PP

The \fI.gcov\fR files contain the ':' separated fields along with

program source code. The format is

.PP

.Vb 1

\&        <execution_count>:<line_number>:<source line text>

.Ve

.PP

Additional block information may succeed each line, when requested by

command line option. The \fIexecution_count\fR is \fB\-\fR for lines

containing no code and \fB#####\fR for lines which were never

executed. Some lines of information at the start have \fIline_number\fR

of zero.

.PP

When printing percentages, 0% and 100% are only printed when the values

are \fIexactly\fR 0% and 100% respectively. Other values which would

conventionally be rounded to 0% or 100% are instead printed as the

nearest non-boundary value.

.PP

When using \fBgcov\fR, you must first compile your program with two

special \s-1GCC\s0 options: \fB\-fprofile\-arcs \-ftest\-coverage\fR.

This tells the compiler to generate additional information needed by

gcov (basically a flow graph of the program) and also includes

additional code in the object files for generating the extra profiling

information needed by gcov.  These additional files are placed in the

directory where the object file is located.

.PP

Running the program will cause profile output to be generated.  For each

source file compiled with \fB\-fprofile\-arcs\fR, an accompanying

\&\fI.gcda\fR file will be placed in the object file directory.

.PP

Running \fBgcov\fR with your program's source file names as arguments

will now produce a listing of the code along with frequency of execution

for each line.  For example, if your program is called \fItmp.c\fR, this

is what you see when you use the basic \fBgcov\fR facility:

.PP

.Vb 5

\&        $ gcc -fprofile-arcs -ftest-coverage tmp.c

\&        $ a.out

\&        $ gcov tmp.c

\&        90.00% of 10 source lines executed in file tmp.c

\&        Creating tmp.c.gcov.

.Ve

.PP

The file \fItmp.c.gcov\fR contains output from \fBgcov\fR.

Here is a sample:

.PP

.Vb 23

\&                -:    0:Source:tmp.c

\&                -:    0:Graph:tmp.gcno

\&                -:    0:Data:tmp.gcda

\&                -:    0:Runs:1

\&                -:    0:Programs:1

\&                -:    1:#include <stdio.h>

\&                -:    2:

\&                -:    3:int main (void)

\&        function main called 1 returned 1 blocks executed 75%

\&                1:    4:{

\&                1:    5:  int i, total;

\&                -:    6:

\&                1:    7:  total = 0;

\&                -:    8:

\&               11:    9:  for (i = 0; i < 10; i++)

\&               10:   10:    total += i;

\&                -:   11:

\&                1:   12:  if (total != 45)

\&            #####:   13:    printf ("Failure\en");

\&                -:   14:  else

\&                1:   15:    printf ("Success\en");

\&                1:   16:  return 0;

\&                -:   17:}

.Ve

.PP

When you use the \fB\-a\fR option, you will get individual block

counts, and the output looks like this:

.PP

.Vb 30

\&                -:    0:Source:tmp.c

\&                -:    0:Graph:tmp.gcno

\&                -:    0:Data:tmp.gcda

\&                -:    0:Runs:1

\&                -:    0:Programs:1

\&                -:    1:#include <stdio.h>

\&                -:    2:

\&                -:    3:int main (void)

\&        function main called 1 returned 1 blocks executed 75%

\&                1:    4:{

\&                1:    4-block  0

\&                1:    5:  int i, total;

\&                -:    6:

\&                1:    7:  total = 0;

\&                -:    8:

\&               11:    9:  for (i = 0; i < 10; i++)

\&               11:    9-block  0

\&               10:   10:    total += i;

\&               10:   10-block  0

\&                -:   11:

\&                1:   12:  if (total != 45)

\&                1:   12-block  0

\&            #####:   13:    printf ("Failure\en");

\&            $$$$$:   13-block  0

\&                -:   14:  else

\&                1:   15:    printf ("Success\en");

\&                1:   15-block  0

\&                1:   16:  return 0;

\&                1:   16-block  0

\&                -:   17:}

.Ve

.PP

In this mode, each basic block is only shown on one line \*(-- the last

line of the block. A multi-line block will only contribute to the

execution count of that last line, and other lines will not be shown

to contain code, unless previous blocks end on those lines.

The total execution count of a line is shown and subsequent lines show

the execution counts for individual blocks that end on that line. After each

block, the branch and call counts of the block will be shown, if the

\&\fB\-b\fR option is given.

.PP

Because of the way \s-1GCC\s0 instruments calls, a call count can be shown

after a line with no individual blocks.

As you can see, line 13 contains a basic block that was not executed.

.PP

When you use the \fB\-b\fR option, your output looks like this:

.PP

.Vb 6

\&        $ gcov -b tmp.c

\&        90.00% of 10 source lines executed in file tmp.c

\&        80.00% of 5 branches executed in file tmp.c

\&        80.00% of 5 branches taken at least once in file tmp.c

\&        50.00% of 2 calls executed in file tmp.c

\&        Creating tmp.c.gcov.

.Ve

.PP

Here is a sample of a resulting \fItmp.c.gcov\fR file:

.PP

.Vb 29

\&                -:    0:Source:tmp.c

\&                -:    0:Graph:tmp.gcno

\&                -:    0:Data:tmp.gcda

\&                -:    0:Runs:1

\&                -:    0:Programs:1

\&                -:    1:#include <stdio.h>

\&                -:    2:

\&                -:    3:int main (void)

\&        function main called 1 returned 1 blocks executed 75%

\&                1:    4:{

\&                1:    5:  int i, total;

\&                -:    6:

\&                1:    7:  total = 0;

\&                -:    8:

\&               11:    9:  for (i = 0; i < 10; i++)

\&        branch  0 taken 91% (fallthrough)

\&        branch  1 taken 9%

\&               10:   10:    total += i;

\&                -:   11:

\&                1:   12:  if (total != 45)

\&        branch  0 taken 0% (fallthrough)

\&        branch  1 taken 100%

\&            #####:   13:    printf ("Failure\en");

\&        call    0 never executed

\&                -:   14:  else

\&                1:   15:    printf ("Success\en");

\&        call    0 called 1 returned 100%

\&                1:   16:  return 0;

\&                -:   17:}

.Ve

.PP

For each basic block, a line is printed after the last line of the basic

block describing the branch or call that ends the basic block.  There can

be multiple branches and calls listed for a single source line if there

are multiple basic blocks that end on that line.  In this case, the

branches and calls are each given a number.  There is no simple way to map

these branches and calls back to source constructs.  In general, though,

the lowest numbered branch or call will correspond to the leftmost construct

on the source line.

.PP

For a branch, if it was executed at least once, then a percentage

indicating the number of times the branch was taken divided by the

number of times the branch was executed will be printed.  Otherwise, the

message ``never executed'' is printed.

.PP

For a call, if it was executed at least once, then a percentage

indicating the number of times the call returned divided by the number

of times the call was executed will be printed.  This will usually be

100%, but may be less for functions call \f(CW\*(C`exit\*(C'\fR or \f(CW\*(C`longjmp\*(C'\fR,

and thus may not return every time they are called.

.PP

The execution counts are cumulative.  If the example program were

executed again without removing the \fI.gcda\fR file, the count for the

number of times each line in the source was executed would be added to

the results of the previous run(s).  This is potentially useful in

several ways.  For example, it could be used to accumulate data over a

number of program runs as part of a test verification suite, or to

provide more accurate long-term information over a large number of

program runs.

.PP

The data in the \fI.gcda\fR files is saved immediately before the program

exits.  For each source file compiled with \fB\-fprofile\-arcs\fR, the

profiling code first attempts to read in an existing \fI.gcda\fR file; if

the file doesn't match the executable (differing number of basic block

counts) it will ignore the contents of the file.  It then adds in the

new execution counts and finally writes the data to the file.

.Sh "Using \fBgcov\fP with \s-1GCC\s0 Optimization"

.IX Subsection "Using gcov with GCC Optimization"

If you plan to use \fBgcov\fR to help optimize your code, you must

first compile your program with two special \s-1GCC\s0 options:

\&\fB\-fprofile\-arcs \-ftest\-coverage\fR.  Aside from that, you can use any

other \s-1GCC\s0 options; but if you want to prove that every single line

in your program was executed, you should not compile with optimization

at the same time.  On some machines the optimizer can eliminate some