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OpenSolaris 2009.06 - man page for gcov (opensolaris section 1)

GCOV(1) 				       GNU					  GCOV(1)

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] sourcefile
	    [-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:

       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.

       -a
       --all-blocks
	   Write individual execution counts for every basic block. Normally gcov outputs execu-
	   tion 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 uses 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 sev-
	   eral 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 counts 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 com-
       piler. 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 compli-
       cated 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 for-
       mat 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.

       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: -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 object file is located.

       Running the program will cause profile output to be generated.  For each source file com-
       piled 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)
	       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\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)
	       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\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 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 .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 pro-
       gram 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 func-
       tion, 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
       Copyright (c) 1996, 1997, 1999, 2000, 2001, 2002, 2003 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.

ATTRIBUTES
       See attributes(5) for descriptions of the following attributes:

       +--------------------+-----------------+
       |  ATTRIBUTE TYPE    | ATTRIBUTE VALUE |
       +--------------------+-----------------+
       |Availability	    | SUNWgcc	      |
       +--------------------+-----------------+
       |Interface Stability | External	      |
       +--------------------+-----------------+
NOTES
       Source for gcc is available on http://opensolaris.org.

gcc-3.4.3				    2004-11-05					  GCOV(1)


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