NAME
gcov - coverage testing tool
SYNOPSIS
gcov [
-v|
--version] [
-h|
--help]
[
-a|
--all-blocks]
[
-b|
--branch-probabilities]
[
-c|
--branch-counts]
[
-d|
--display-progress]
[
-f|
--function-summaries]
[
-i|
--intermediate-format]
[
-l|
--long-file-names]
[
-m|
--demangled-names]
[
-n|
--no-output]
[
-o|
--object-directory directory|file]
[
-p|
--preserve-paths]
[
-r|
--relative-only]
[
-s|
--source-prefix directory]
[
-u|
--unconditional-branches]
files
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:
- *
- 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 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 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.
- -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 and you want to see the individual contributions. If you use
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 unremoveable .. components renamed to
^. This is useful if sourcefiles are in several different
directories.
- -r
- --relative-only
- Only output information about source files with a relative
pathname (after source prefix elision). Absolute paths are usually system
header files and coverage of any inline functions therein is normally
uninteresting.
- -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 input file name,
without its extension. If a file is specified here, the data files are
named after that file, without its extension.
- -s directory
- --source-prefix directory
- A prefix for source file names to remove when generating
the output coverage files. This option is useful when building in a
separate directory, and the pathname to the source directory is not wanted
when determining the output file names. Note that this prefix detection is
applied before determining whether the source file is absolute.
- -u
- --unconditional-branches
- When branch probabilities are given, include those of
unconditional branches. Unconditional branches are normally not
interesting.
- -d
- --display-progress
- Display the progress on the standard output.
- -i
- --intermediate-format
- Output gcov file in an easy-to-parse intermediate text
format that can be used by lcov or other tools. The output is a
single .gcov file per .gcda file. No source code is
required.
The format of the intermediate .gcov file is plain text with one
entry per line
file:<source_file_name>
function:<line_number>,<execution_count>,<function_name>
lcount:<line number>,<execution_count>
branch:<line_number>,<branch_coverage_type>
Where the <branch_coverage_type> is
notexec (Branch not executed)
taken (Branch executed and taken)
nottaken (Branch executed, but not taken)
There can be multiple <file> entries in an intermediate gcov
file. All entries following a <file> pertain to that source file
until the next <file> entry.
Here is a sample when -i is used in conjunction with -b
option:
file:array.cc
function:11,1,_Z3sumRKSt6vectorIPiSaIS0_EE
function:22,1,main
lcount:11,1
lcount:12,1
lcount:14,1
branch:14,taken
lcount:26,1
branch:28,nottaken
- -m
- --demangled-names
- Display demangled function names in output. The default is
to show mangled function names.
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 (or
header) 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.
If you invoke
gcov with multiple input files, the contributions from each
input file are summed. Typically you would invoke it with the same list of
files as the final link of your executable.
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. Unexecuted lines are marked
##### or
====, depending on
whether they are reachable by non-exceptional paths or only exceptional paths
such as C++ exception handlers, respectively.
Some lines of information at the start have
line_number of zero. These
preamble lines are of the form
-:0:<tag>:<value>
The ordering and number of these preamble lines will be augmented as
gcov
development progresses --- do not rely on them remaining unchanged. Use
tag to locate a particular preamble line.
The additional block information is of the form
<tag> <information>
The
information is human readable, but designed to be simple enough for
machine parsing too.
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.
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)
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)
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 function, a line is printed showing how many times the function is
called, how many times it returns and what percentage of the function's blocks
were executed.
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 that 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:
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.
Long-running applications can use the "_gcov_reset" and
"_gcov_dump" facilities to restrict profile collection to the
program region of interest. Calling "_gcov_reset(void)" will clear
all profile counters to zero, and calling "_gcov_dump(void)" will
cause the profile information collected at that point to be dumped to
.gcda output files.
SEE ALSO
gpl(7),
gfdl(7),
fsf-funding(7),
gcc(1) and the Info
entry for
gcc.
COPYRIGHT
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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.
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A GNU Manual
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