ggccoovv 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
ggccoovv as a profiling tool to help discover where your
optimization efforts will best affect your code. You can also use
ggccoovv along with the other profiling tool, ggpprrooff, 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 ggccoovv or ggpprrooff, 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.
ggccoovv 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
ggccoovv 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 ggccoovv 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.
ggccoovv creates a logfile called _s_o_u_r_c_e_f_i_l_e_._g_c_o_v which
indicates how many times each line of a source file _s_o_u_r_c_e_f_i_l_e_._c
has executed. You can use these logfiles along with ggpprrooff to aid
in fine-tuning the performance of your programs. ggpprrooff gives
timing information you can use along with the information you get from
ggccoovv.
ggccoovv works only on code compiled with GCC. It is not
compatible with any other profiling or test coverage mechanism.
OPTIONS
--hh
----hheellpp
Display help about using ggccoovv (on the standard output), and
exit without doing any further processing.
--vv
----vveerrssiioonn
Display the ggccoovv version number (on the standard output),
and exit without doing any further processing.
--aa
----aallll--bblloocckkss
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.
--bb
----bbrraanncchh--pprroobbaabbiilliittiieess
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 --uu option is given.
--cc
----bbrraanncchh--ccoouunnttss
Write branch frequencies as the number of branches taken, rather than
the percentage of branches taken.
--nn
----nnoo--oouuttppuutt
Do not create the ggccoovv output file.
--ll
----lloonngg--ffiillee--nnaammeess
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 ggccoovv on the file _a_._c will produce
an output file called _a_._c_#_#_x_._h_._g_c_o_v instead of _x_._h_._g_c_o_v.
This can be useful if _x_._h is included in multiple source
files. If you use the --pp option, both the including and
included file names will be complete path names.
--pp
----pprreesseerrvvee--ppaatthhss
Preserve complete path information in the names of generated
_._g_c_o_v 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 --ll option.
--ff
----ffuunnccttiioonn--ssuummmmaarriieess
Output summaries for each function in addition to the file level summary.
----oobbjjeecctt--ffiillee _f_i_l_e
Specify either the directory containing the gcov data files, or the
object path name. The _._g_c_n_o, and
_._g_c_d_a 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.
--uu
----uunnccoonnddiittiioonnaall--bbrraanncchheess
When branch probabilities are given, include those of unconditional branches.
Unconditional branches are normally not interesting.
ggccoovv 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. ggccoovv produces files called
_m_a_n_g_l_e_d_n_a_m_e_._g_c_o_v in the current directory. These contain
the coverage information of the source file they correspond to.
One _._g_c_o_v file is produced for each source file containing code,
which was compiled to produce the data files. The _m_a_n_g_l_e_d_n_a_m_e part
of the output file name is usually simply the source file name, but can
be something more complicated if the --ll or --pp options are
given. Refer to those options for details.
The _._g_c_o_v 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 _e_x_e_c_u_t_i_o_n___c_o_u_n_t is -- for lines
containing no code and ########## for lines which were never executed.
Some lines of information at the start have _l_i_n_e___n_u_m_b_e_r of zero.
The preamble lines are of the form
-:0::
The ordering and number of these preamble lines will be augmented as
ggccoovv development progresses --- do not rely on them remaining
unchanged. Use _t_a_g to locate a particular preamble line.
The additional block information is of the form
The _i_n_f_o_r_m_a_t_i_o_n 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 _e_x_a_c_t_l_y 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 ggccoovv, you must first compile your program with two
special GCC options: --ffpprrooffiillee--aarrccss --fftteesstt--ccoovveerraaggee.
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 --ffpprrooffiillee--aarrccss, an accompanying
_._g_c_d_a file will be placed in the object file directory.
Running ggccoovv 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 _t_m_p_._c, this
is what you see when you use the basic ggccoovv facility:
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
--bb 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 --bb 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 _t_m_p_._c_._g_c_o_v 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 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 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 _._g_c_d_a 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 _._g_c_d_a files is saved immediately before the program
exits. For each source file compiled with --ffpprrooffiillee--aarrccss, the
profiling code first attempts to read in an existing _._g_c_d_a 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.
If you plan to use ggccoovv to help optimize your code, you must
first compile your program with two special GCC options:
--ffpprrooffiillee--aarrccss --fftteesstt--ccoovveerraaggee. 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 ggccoovv to calculate separate execution counts
for each line because there isn't separate code for each line. Hence
the ggccoovv 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
_f_i_l_e_A_._o and _f_i_l_e_B_._o both contain out of line bodies of a
particular inlineable function, they will also both contain coverage
counts for that function. When _f_i_l_e_A_._o and _f_i_l_e_B_._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
_g_p_l(7), _g_f_d_l(7), _f_s_f_-_f_u_n_d_i_n_g(7), _g_c_c(1) and the Info entry for _g_c_c.
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any later version published by the Free Software Foundation; with the
Invariant Sections being "GNU General Public License" and "Funding
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the Back-Cover Texts being (b) (see below). A copy of the license is
included in the _g_f_d_l(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
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funds for GNU development.