GCOV(1) GNU GCOV(1)NAMEgcov - coverage testing tool
SYNOPSISgcov [-v|--version] [-h|--help]
[-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
DESCRIPTIONgcov is a test coverage program. Use it in concert with
GCC to analyze your programs to help create more effi-
cient, 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 pro-
gram 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. Like-
wise, 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 con-
trol 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 com-
patible with any other profiling or test coverage mecha-
nism.
OPTIONS-h
--help
Display help about using gcov (on the standard out-
put), and exit without doing any further processing.
-v
--version
Display the gcov version number (on the standard out-
put), 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 useful
if x.h is included in multiple source files.
-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 .bb, .bbg, and .da
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.
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 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 .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 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 gen-
erating 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 gener-
ated. For each source file compiled with -fprofile-arcs,
an accompanying .da 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:Object:tmp.bb
-: 1:#include <stdio.h>
-: 2:
-: 3:int main (void)
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;
1: 17:}
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:Object:tmp.bb
-: 1:#include <stdio.h>
-: 2:
-: 3:int main (void)
1: 4:{
1: 5: int i, total;
-: 6:
1: 7: total = 0;
-: 8:
11: 9: for (i = 0; i < 10; i++)
branch 0: taken 90%
branch 1: taken 100%
branch 2: taken 100%
10: 10: total += i;
-: 11:
1: 12: if (total != 45)
branch 0: taken 100%
#####: 13: printf ("Failure\n");
call 0: never executed
branch 1: never executed
-: 14: else
1: 15: printf ("Success\n");
call 0: returns 100%
1: 16: return 0;
1: 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 multi-
ple 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 exe-
cuted will be printed. Otherwise, the message ``never
executed'' is printed.
For a call, if it was executed at least once, then a per-
centage 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 pro-
gram were executed 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 -fpro-
file-arcs, the profiling code first attempts to read in an
existing .da file; if the file doesn't match the exe-
cutable (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 exam-
ple, 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 sepa-
rate 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.
SEE ALSOgpl(7), gfdl(7), fsf-funding(7), gcc(1) and the Info entry
for gcc.
COPYRIGHT
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Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify
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by the Free Software Foundation; with the Invariant Sec-
tions being ``GNU General Public License'' and ``Funding
Free Software'', the Front-Cover texts being (a) (see
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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
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gcc-3.3 2003-05-14 GCOV(1)
