GCOV(1)                              GNU                             GCOV(1)

NAME         top

       gcov - coverage testing tool

SYNOPSIS         top

       gcov [-v|--version] [-h|--help]
            [-o|--object-directory directory|file]
            [-s|--source-prefix directory]

DESCRIPTION         top

       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         top

           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.

           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

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

           Display the progress on the standard output.

           Output summaries for each function in addition to the file level

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

           Output gcov file in an easy-to-parse intermediate text format
           that can be used by lcov or other tools. The output is a single
           .gcov file per .gcda file. No source code is required.

           The format of the intermediate .gcov file is plain text with one
           entry per line

                   lcount:<line number>,<execution_count>

                   Where the <branch_coverage_type> is
                      notexec (Branch not executed)
                      taken (Branch executed and taken)
                      nottaken (Branch executed, but not taken)

                   There can be multiple <file> entries in an intermediate gcov
                   file. All entries following a <file> pertain to that source file
                   until the next <file> entry.

           Here is a sample when -i is used in conjunction with -b option:


           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 and you
           want to see the individual contributions.  If you use the -p
           option, both the including and included file names will be
           complete path names.

           Display demangled function names in output. The default is to
           show mangled function names.

           Do not create the gcov output file.

       -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 input file
           name, without its extension.  If a file is specified here, the
           data files are named after that file, without its extension.

           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 unremoveable ..  components renamed to ^.  This is
           useful if sourcefiles are in several different directories.

           Only output information about source files with a relative
           pathname (after source prefix elision).  Absolute paths are
           usually system header files and coverage of any inline functions
           therein is normally uninteresting.

       -s directory
       --source-prefix directory
           A prefix for source file names to remove when generating the
           output coverage files.  This option is useful when building in a
           separate directory, and the pathname to the source directory is
           not wanted when determining the output file names.  Note that
           this prefix detection is applied before determining whether the
           source file is absolute.

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

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

           Print verbose informations related to basic blocks and arcs.

           By default, gcov uses the full pathname of the source files to to
           create an output filename.  This can lead to long filenames that
           can overflow filesystem limits.  This option creates names of the
           form source-file##md5.gcov, where the source-file component is
           the final filename part and the md5 component is calculated from
           the full mangled name that would have been used otherwise.

       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 (or header) 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.

       If you invoke gcov with multiple input files, the contributions from
       each input file are summed.  Typically you would invoke it with the
       same list of files as the final link of your executable.

       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.  Unexecuted lines are marked ##### or ====, depending on
       whether they are reachable by non-exceptional paths or only
       exceptional paths such as C++ exception handlers, respectively. Given
       -a option, unexecuted blocks are marked $$$$$ or %%%%%, depending on
       whether a basic block is reachable via non-exceptional or exceptional

       Note that GCC can completely remove the bodies of functions that are
       not needed -- for instance if they are inlined everywhere.  Such
       functions are marked with -, which can be confusing.  Use the
       -fkeep-inline-functions and -fkeep-static-functions options to retain
       these functions and allow gcov to properly show their

       Some lines of information at the start have line_number of zero.
       These preamble lines are of the form


       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
               File 'tmp.c'
               Lines executed:90.00% of 10
               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
               File 'tmp.c'
               Lines executed:90.00% of 10
               Branches executed:80.00% of 5
               Taken at least once:80.00% of 5
               Calls executed:50.00% of 2
               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;
                 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

                     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

       Long-running applications can use the "__gcov_reset" and
       "__gcov_dump" facilities to restrict profile collection to the
       program region of interest. Calling "__gcov_reset(void)" will clear
       all profile counters to zero, and calling "__gcov_dump(void)" will
       cause the profile information collected at that point to be dumped to
       .gcda output files.  Instrumented applications use a static
       destructor with priority 99 to invoke the "__gcov_dump" function.
       Thus "__gcov_dump" is executed after all user defined static
       destructors, as well as handlers registered with "atexit".

SEE ALSO         top

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

COPYRIGHT         top

       Copyright (c) 1996-2017 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 1.3 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.

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gcc-7.3.0                        2018-01-25                          GCOV(1)