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NAME

       gcov - coverage testing tool

SYNOPSIS

       gcov [-v|--version] [-h|--help]
            [-a|--all-blocks]
            [-b|--branch-probabilities]
            [-c|--branch-counts]
            [-n|--no-output]
            [-l|--long-file-names]
            [-p|--preserve-paths]
            [-f|--function-summaries]
            [-o|--object-directory directory|file] sourcefiles
            [-u|--unconditional-branches]

DESCRIPTION

       gcov is a test coverage program.  Use it in concert with GCC to analyze
       your programs to help create more efficient, faster running code and to
       discover untested parts of your program.  You can use gcov as a
       profiling tool to help discover where your optimization efforts will
       best affect your code.  You can also use gcov along with the other
       profiling tool, gprof, to assess which parts of your code use the
       greatest amount of computing time.

       Profiling tools help you analyze your code’s performance.  Using a
       profiler such as gcov or gprof, you can find out some basic performance
       statistics, such as:

       ·   how often each line of code executes

       ·   what lines of code are actually executed

       ·   how much computing time each section of code uses

       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.  gcov
       helps you determine where to work on optimization.

       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.

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

       gcov creates a logfile called sourcefile.gcov which indicates how many
       times each line of a source file sourcefile.c has executed.  You can
       use these logfiles along with gprof to aid in fine-tuning the
       performance of your programs.  gprof gives timing information you can
       use along with the information you get from gcov.

       gcov works only on code compiled with GCC.  It is not compatible with
       any other profiling or test coverage mechanism.

OPTIONS

       -h
       --help
           Display help about using gcov (on the standard output), and exit
           without doing any further processing.

       -v
       --version
           Display the gcov version number (on the standard output), and exit
           without doing any further processing.

       -a
       --all-blocks
           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.

       -b
       --branch-probabilities
           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 -u option is given.

       -c
       --branch-counts
           Write branch frequencies as the number of branches taken, rather
           than the percentage of branches taken.

       -n
       --no-output
           Do not create the gcov output file.

       -l
       --long-file-names
           Create long file names for included source files.  For example, if
           the header file x.h contains code, and was included in the file
           a.c, then running gcov on the file a.c will produce an output file
           called a.c##x.h.gcov instead of x.h.gcov.  This can be useful if
           x.h is included in multiple source files.  If you use the -p
           option, both the including and included file names will be complete
           path names.

       -p
       --preserve-paths
           Preserve complete path information in the names of generated .gcov
           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 -l option.

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

       -o directory|file
       --object-directory directory
       --object-file file
           Specify either the directory containing the gcov data files, or the
           object path name.  The .gcno, and .gcda 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.

       -u
       --unconditional-branches
           When branch probabilities are given, include those of unconditional
           branches.  Unconditional branches are normally not interesting.

       gcov 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.  gcov produces files called mangledname.gcov in the
       current directory.  These contain the coverage information of the
       source file they correspond to.  One .gcov file is produced for each
       source file containing code, which was compiled to produce the data
       files.  The mangledname part of the output file name is usually simply
       the source file name, but can be something more complicated if the -l
       or -p options are given.  Refer to those options for details.

       The .gcov files contain the : separated fields along with program
       source code.  The format is

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

       Additional block information may succeed each line, when requested by
       command line option.  The execution_count is - for lines containing no
       code and ##### for lines which were never executed.  Some lines of
       information at the start have line_number of zero.

       The preamble lines are of the form

               -:0:<tag>:<value>

       The ordering and number of these preamble lines will be augmented as
       gcov development progresses --- do not rely on them remaining
       unchanged.  Use tag to locate a particular preamble line.

       The additional block information is of the form

               <tag> <information>

       The information is human readable, but designed to be simple enough for
       machine parsing too.

       When printing percentages, 0% and 100% are only printed when the values
       are exactly 0% and 100% respectively.  Other values which would
       conventionally be rounded to 0% or 100% are instead printed as the
       nearest non-boundary value.

       When using gcov, you must first compile your program with two special
       GCC options: -fprofile-arcs -ftest-coverage.  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.

       Running the program will cause profile output to be generated.  For
       each source file compiled with -fprofile-arcs, an accompanying .gcda
       file will be placed in the object file directory.

       Running gcov 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 tmp.c, this is what
       you see when you use the basic gcov facility:

               $ 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.

       The file tmp.c.gcov contains output from gcov.  Here is a sample:

                       -:    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)
                       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\n");
                       -:   14:  else
                       1:   15:    printf ("Success\n");
                       1:   16:  return 0;
                       -:   17:}

       When you use the -a option, you will get individual block counts, and
       the output looks like this:

                       -:    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)
                       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\n");
                   $$$$$:   13-block  0
                       -:   14:  else
                       1:   15:    printf ("Success\n");
                       1:   15-block  0
                       1:   16:  return 0;
                       1:   16-block  0
                       -:   17:}

       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 -b option is given.

       Because of the way GCC 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.

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

               $ 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.

       Here is a sample of a resulting tmp.c.gcov file:

                       -:    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\n");
               call    0 never executed
                       -:   14:  else
                       1:   15:    printf ("Success\n");
               call    0 called 1 returned 100%
                       1:   16:  return 0;
                       -:   17:}

       For each function, a line is printed showing how many times the
       function is called, how many times it returns and what percentage of
       the function’s blocks were executed.

       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.

       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.

       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 that call "exit" or "longjmp", and
       thus may not return every time they are called.

       The execution counts are cumulative.  If the example program were
       executed again without removing the .gcda 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.

       The data in the .gcda files is saved immediately before the program
       exits.  For each source file compiled with -fprofile-arcs, the
       profiling code first attempts to read in an existing .gcda 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.

       Using gcov with GCC Optimization

       If you plan to use gcov to help optimize your code, you must first
       compile your program with two special GCC options: -fprofile-arcs
       -ftest-coverage.  Aside from that, you can use any other GCC 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 simple code lines by
       combining them with other lines.  For example, code like this:

               if (a != b)
                 c = 1;
               else
                 c = 0;

       can be compiled into one instruction on some machines.  In this case,
       there is no way for gcov to calculate separate execution counts for
       each line because there isn’t separate code for each line.  Hence the
       gcov output looks like this if you compiled the program with
       optimization:

                     100:   12:if (a != b)
                     100:   13:  c = 1;
                     100:   14:else
                     100:   15:  c = 0;

       The output shows that this block of code, combined by optimization,
       executed 100 times.  In one sense this result is correct, because there
       was only one instruction representing all four of these lines.
       However, the output does not indicate how many times the result was 0
       and how many times the result was 1.

       Inlineable functions can create unexpected line counts.  Line counts
       are shown for the source code of the inlineable function, but what is
       shown depends on where the function is inlined, or if it is not inlined
       at all.

       If the function is not inlined, the compiler must emit an out of line
       copy of the function, in any object file that needs it.  If fileA.o and
       fileB.o both contain out of line bodies of a particular inlineable
       function, they will also both contain coverage counts for that
       function.  When fileA.o and fileB.o are linked together, the linker
       will, on many systems, select one of those out of line bodies for all
       calls to that function, and remove or ignore the other.  Unfortunately,
       it will not remove the coverage counters for the unused function body.
       Hence when instrumented, all but one use of that function will show
       zero counts.

       If the function is inlined in several places, the block structure in
       each location might not be the same.  For instance, a condition might
       now be calculable at compile time in some instances.  Because the
       coverage of all the uses of the inline function will be shown for the
       same source lines, the line counts themselves might seem inconsistent.

SEE ALSO

       gpl(7), gfdl(7), fsf-funding(7), gcc(1) and the Info entry for gcc.

COPYRIGHT

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       2008  Free Software Foundation, Inc.

       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.2 or
       any later version published by the Free Software Foundation; with the
       Invariant Sections being "GNU General Public License" and "Funding Free
       Software", the Front-Cover texts being (a) (see below), and with the
       Back-Cover Texts being (b) (see below).  A copy of the license is
       included in the gfdl(7) man page.

       (a) The FSF’s Front-Cover Text is:

            A GNU Manual

       (b) The FSF’s Back-Cover Text is:

            You have freedom to copy and modify this GNU Manual, like GNU
            software.  Copies published by the Free Software Foundation raise
            funds for GNU development.