(gcc.info.gz) Invoking Gcov
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9.2 Invoking `gcov'
===================
gcov [OPTIONS] SOURCEFILES
`gcov' accepts the following 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. 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 `..' 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 probabilities 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
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
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.
The 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.
Info Catalog
(gcc.info.gz) Gcov Intro
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(gcc.info.gz) Gcov and Optimization
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