gcov
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 ana-
lyze 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 perfor-
mance 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
program 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-
mance 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 sum-
mary 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 com-
plete 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, with-
out 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 able to locate the
source files. gcov produces files called mangledname.gcov in the cur-
rent 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
<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 val-
ues 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.
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 exe-
cution 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 exe-
cution 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 con-
tains 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 con-
structs. 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 indi-
cating 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 exe-
cuted 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 optimiza-
tion:
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 func-
tion. 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 cov-
erage 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.
gcc-3.4.6 2008-07-24 GCOV(1)
