Manual Pages for UNIX Operating System command usage for man gcov
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
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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.
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-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 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 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 compiler. Otherwise it will not be
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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
::
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: -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.
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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
-: 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:
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-: 0:Source:tmp.c
-: 0:Graph:tmp.gcno
-: 0:Data:tmp.gcda
-: 0:Runs:1
-: 0:Programs:1
-: 1:#include
-: 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:
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$ 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
-: 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
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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 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:
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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
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
gcc-3.4.3 Last change: 2004-11-05 9
GNU GCOV(1)
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 | developer/gcc-3|
|____________________|__________________|_
| Interface Stability| External |
|____________________|_________________|
NOTES
Source for gcc is available on http://opensolaris.org.