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(gcc-295.info)Invoking Gcov

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Invoking gcov
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     gcov [-b] [-v] [-n] [-l] [-f] [-o directory] SOURCEFILE

`-b'
     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.

`-v'
     Display the `gcov' version number (on the standard error stream).

`-n'
     Do not create the `gcov' output file.

`-l'
     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.

`-f'
     Output summaries for each function in addition to the file level
     summary.

`-o'
     The directory where the object files live.  Gcov will search for
     `.bb', `.bbg', and `.da' files in this directory.

   When using `gcov', you must first compile your program with two
special GNU CC 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 source code 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 source 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
      87.50% of 8 source lines executed in file tmp.c
     Creating tmp.c.gcov.

   The file `tmp.c.gcov' contains output from `gcov'.  Here is a sample:

                     main()
                     {
                1      int i, total;
     
                1      total = 0;
     
               11      for (i = 0; i < 10; i++)
               10        total += i;
     
                1      if (total != 45)
           ######        printf ("Failure\n");
                       else
                1        printf ("Success\n");
                1    }

   When you use the `-b' option, your output looks like this:

     $ gcov -b tmp.c
      87.50% of 8 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:

                     main()
                     {
                1      int i, total;
     
                1      total = 0;
     
               11      for (i = 0; i < 10; i++)
     branch 0 taken = 91%
     branch 1 taken = 100%
     branch 2 taken = 100%
               10        total += i;
     
                1      if (total != 45)
     branch 0 taken = 100%
           ######        printf ("Failure\n");
     call 0 never executed
     branch 1 never executed
                       else
                1        printf ("Success\n");
     call 0 returns = 100%
                1    }

   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 everytime 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.