gcov [options] sourcefile
gcov accepts the following options:
-h
--help
gcov (on the standard output), and
exit without doing any further processing.
-v
--version
gcov version number (on the standard output),
and exit without doing any further processing.
-b
--branch-probabilities
-c
--branch-counts
-n
--no-output
gcov output file.
-l
--long-file-names
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
.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
-o directory|file--object-directory directory--object-file file.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, 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.
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 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 .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 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 .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 -fprofile-arcs, the
profiling code first attempts to read in an existing .da 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.