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RedHat 9 (Linux i386) - man page for gcov (redhat section 1)

GCOV(1) 				       GNU					  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 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:

       o   how often each line of code executes

       o   what lines of code are actually executed

       o   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 reso-
       lution), 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.

       -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.

       -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 use-
	   ful 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: -fpro-
       file-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 com-
       piled with -fprofile-arcs, an accompanying .da file will be placed in the source direc-
       tory.

       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
		87.50% of 8 source lines executed in file tmp.c
	       Creating tmp.c.gcov.

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

			       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 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 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 .da file, the count for the number of times each line in the source was exe-
       cuted 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 informa-
       tion 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 profiling code first attempts to read in an exist-
       ing .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 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  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.  However, 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.

       Permission is granted to copy, distribute and/or modify this document under the terms of
       the GNU Free Documentation License, Version 1.1 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.

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


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