gcov (1)





NAME

       gcov - coverage testing tool


SYNOPSIS

       gcov [-v|--version] [-h|--help]
            [-b|--branch-probabilities] [-c|--branch-counts]
            [-n|--no-output] [-l|--long-file-names]
            [-f|--function-summaries]
            [-o|--object-directory directory] sourcefile


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.  You
       can use gcov as a profiling tool to help discover where your optimiza-
       tion 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 pro-
       filer 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 test-
       suites, to make sure software is actually good enough for a release.
       Testsuites can verify that a program works as expected; a coverage pro-
       gram tests to see how much of the program is exercised by the test-
       suite.  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 help-
       ful---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 perfor-
           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.

       -b
       --branch-probabilities
           Write branch frequencies to the output file, and write branch sum-
           mary info to the standard output.  This option allows you to see
           how often each branch in your program was taken.

       -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.

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

       -o directory
       --object-directory directory
           The directory where the object files live.  Gcov will search for
           .bb, .bbg, and .da files in this directory.

       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 source
       code is located.

       Running the program will cause profile output to be generated.  For
       each source file compiled with -fprofile-arcs, an accompanying .da file
       will be placed in the source 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:
                               main()
                               {
                          1      int i, total;

                          1      total = 0;

                         11      for (i = 0; i < 10; i++)
                         10        total += i;

                          1      if (total != 45)
                     ######        printf ("Failure\n");
                                 else
                          1        printf ("Success\n");
                          1    }

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

               $ gcov -b tmp.c
                87.50% of 8 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:

                               main()
                               {
                          1      int i, total;

                          1      total = 0;

                         11      for (i = 0; i < 10; i++)
               branch 0 taken = 91%
               branch 1 taken = 100%
               branch 2 taken = 100%
                         10        total += i;

                          1      if (total != 45)
               branch 0 taken = 100%
                     ######        printf ("Failure\n");
               call 0 never executed
               branch 1 never executed
                                 else
                          1        printf ("Success\n");
               call 0 returns = 100%
                          1    }

       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 sim-
       ple 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.

       may not return every time they are called.

       The execution counts are cumulative.  If the example program were exe-
       cuted again without removing the .da 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 .da files is saved immediately before the program
       exits.  For each source file compiled with -fprofile-arcs, the profil-
       ing code first attempts to read in an existing .da 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 exe-
       cution 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 com-
       pile 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 optimiza-
       tion:

                     100  if (a != b)
                     100    c = 1;
                     100  else
                     100    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.  How-
       ever, the output does not indicate how many times the result was 0 and
       how many times the result was 1.


SEE ALSO

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


COPYRIGHT

       Copyright (c) 1996, 1997, 1999, 2000, 2001 Free Software Foundation,
       Inc.


            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.

gcc-3.2.2                         2003-02-25                           gcov(1)