(gcc.info) Invoking Gcov

 
 Invoking gcov
 =============
 
      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.
Info Catalog
(gcc.info) Gcov Intro
(gcc.info) Gcov
(gcc.info) Gcov and Optimization
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