mirror of
https://git.FreeBSD.org/src.git
synced 2024-12-17 10:26:15 +00:00
407 lines
16 KiB
Plaintext
407 lines
16 KiB
Plaintext
@c Copyright (C) 1996, 1997, 1999, 2000, 2001 Free Software Foundation, Inc.
|
|
@c This is part of the GCC manual.
|
|
@c For copying conditions, see the file gcc.texi.
|
|
|
|
@ignore
|
|
@c man begin COPYRIGHT
|
|
Copyright @copyright{} 1996, 1997, 1999, 2000, 2001 Free Software Foundation, Inc.
|
|
|
|
Permission is granted to copy, distribute and/or modify this document
|
|
under the terms of the GNU Free Documentation License, Version 1.1 or
|
|
any later version published by the Free Software Foundation; with the
|
|
Invariant Sections being ``GNU General Public License'' and ``Funding
|
|
Free Software'', the Front-Cover texts being (a) (see below), and with
|
|
the Back-Cover Texts being (b) (see below). A copy of the license is
|
|
included in the gfdl(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
|
|
software. Copies published by the Free Software Foundation raise
|
|
funds for GNU development.
|
|
@c man end
|
|
@c Set file name and title for the man page.
|
|
@setfilename gcov
|
|
@settitle coverage testing tool
|
|
@end ignore
|
|
|
|
@node Gcov
|
|
@chapter @command{gcov}: a Test Coverage Program
|
|
|
|
@command{gcov} is a tool you can use in conjunction with GCC to
|
|
test code coverage in your programs.
|
|
|
|
@menu
|
|
* Gcov Intro:: Introduction to gcov.
|
|
* Invoking Gcov:: How to use gcov.
|
|
* Gcov and Optimization:: Using gcov with GCC optimization.
|
|
* Gcov Data Files:: The files used by gcov.
|
|
@end menu
|
|
|
|
@node Gcov Intro
|
|
@section Introduction to @command{gcov}
|
|
@c man begin DESCRIPTION
|
|
|
|
@command{gcov} is a test coverage program. Use it in concert with GCC
|
|
to analyze your programs to help create more efficient, faster
|
|
running code. You can use @command{gcov} as a profiling tool to help
|
|
discover where your optimization efforts will best affect your code. You
|
|
can also use @command{gcov} along with the other profiling tool,
|
|
@command{gprof}, 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 @command{gcov} or @command{gprof}, you can find out some
|
|
basic performance statistics, such as:
|
|
|
|
@itemize @bullet
|
|
@item
|
|
how often each line of code executes
|
|
|
|
@item
|
|
what lines of code are actually executed
|
|
|
|
@item
|
|
how much computing time each section of code uses
|
|
@end itemize
|
|
|
|
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.
|
|
@command{gcov} 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
|
|
@command{gcov} 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 @command{gcov} 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.
|
|
|
|
@command{gcov} creates a logfile called @file{@var{sourcefile}.gcov} which
|
|
indicates how many times each line of a source file @file{@var{sourcefile}.c}
|
|
has executed. You can use these logfiles along with @command{gprof} to aid
|
|
in fine-tuning the performance of your programs. @command{gprof} gives
|
|
timing information you can use along with the information you get from
|
|
@command{gcov}.
|
|
|
|
@command{gcov} works only on code compiled with GCC@. It is not
|
|
compatible with any other profiling or test coverage mechanism.
|
|
|
|
@c man end
|
|
|
|
@node Invoking Gcov
|
|
@section Invoking gcov
|
|
|
|
@smallexample
|
|
gcov @r{[}@var{options}@r{]} @var{sourcefile}
|
|
@end smallexample
|
|
|
|
@command{gcov} accepts the following options:
|
|
|
|
@ignore
|
|
@c man begin SYNOPSIS
|
|
gcov [@option{-v}|@option{--version}] [@option{-h}|@option{--help}]
|
|
[@option{-b}|@option{--branch-probabilities}] [@option{-c}|@option{--branch-counts}]
|
|
[@option{-n}|@option{--no-output}] [@option{-l}|@option{--long-file-names}]
|
|
[@option{-f}|@option{--function-summaries}]
|
|
[@option{-o}|@option{--object-directory} @var{directory}] @var{sourcefile}
|
|
@c man end
|
|
@c man begin SEEALSO
|
|
gpl(7), gfdl(7), fsf-funding(7), gcc(1) and the Info entry for @file{gcc}.
|
|
@c man end
|
|
@end ignore
|
|
|
|
@c man begin OPTIONS
|
|
@table @gcctabopt
|
|
@item -h
|
|
@itemx --help
|
|
Display help about using @command{gcov} (on the standard output), and
|
|
exit without doing any further processing.
|
|
|
|
@item -v
|
|
@itemx --version
|
|
Display the @command{gcov} version number (on the standard output),
|
|
and exit without doing any further processing.
|
|
|
|
@item -b
|
|
@itemx --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.
|
|
|
|
@item -c
|
|
@itemx --branch-counts
|
|
Write branch frequencies as the number of branches taken, rather than
|
|
the percentage of branches taken.
|
|
|
|
@item -n
|
|
@itemx --no-output
|
|
Do not create the @command{gcov} output file.
|
|
|
|
@item -l
|
|
@itemx --long-file-names
|
|
Create long file names for included source files. For example, if the
|
|
header file @file{x.h} contains code, and was included in the file
|
|
@file{a.c}, then running @command{gcov} on the file @file{a.c} will produce
|
|
an output file called @file{a.c.x.h.gcov} instead of @file{x.h.gcov}.
|
|
This can be useful if @file{x.h} is included in multiple source files.
|
|
|
|
@item -f
|
|
@itemx --function-summaries
|
|
Output summaries for each function in addition to the file level summary.
|
|
|
|
@item -o @var{directory}
|
|
@itemx --object-directory @var{directory}
|
|
The directory where the object files live. Gcov will search for @file{.bb},
|
|
@file{.bbg}, and @file{.da} files in this directory.
|
|
@end table
|
|
|
|
@need 3000
|
|
When using @command{gcov}, you must first compile your program with two
|
|
special GCC options: @samp{-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 @option{-fprofile-arcs}, an accompanying @file{.da}
|
|
file will be placed in the source directory.
|
|
|
|
Running @command{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 @file{tmp.c}, this
|
|
is what you see when you use the basic @command{gcov} facility:
|
|
|
|
@smallexample
|
|
$ 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.
|
|
@end smallexample
|
|
|
|
The file @file{tmp.c.gcov} contains output from @command{gcov}.
|
|
Here is a sample:
|
|
|
|
@smallexample
|
|
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 @}
|
|
@end smallexample
|
|
|
|
@need 450
|
|
When you use the @option{-b} option, your output looks like this:
|
|
|
|
@smallexample
|
|
$ 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.
|
|
@end smallexample
|
|
|
|
Here is a sample of a resulting @file{tmp.c.gcov} file:
|
|
|
|
@smallexample
|
|
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 @}
|
|
@end smallexample
|
|
|
|
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 @code{exit} or @code{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 @file{.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 @file{.da} files is saved immediately before the program
|
|
exits. For each source file compiled with @option{-fprofile-arcs}, the profiling
|
|
code first attempts to read in an existing @file{.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.
|
|
|
|
@node Gcov and Optimization
|
|
@section Using @command{gcov} with GCC Optimization
|
|
|
|
If you plan to use @command{gcov} to help optimize your code, you must
|
|
first compile your program with two special GCC options:
|
|
@samp{-fprofile-arcs -ftest-coverage}. 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:
|
|
|
|
@smallexample
|
|
if (a != b)
|
|
c = 1;
|
|
else
|
|
c = 0;
|
|
@end smallexample
|
|
|
|
@noindent
|
|
can be compiled into one instruction on some machines. In this case,
|
|
there is no way for @command{gcov} to calculate separate execution counts
|
|
for each line because there isn't separate code for each line. Hence
|
|
the @command{gcov} output looks like this if you compiled the program with
|
|
optimization:
|
|
|
|
@smallexample
|
|
100 if (a != b)
|
|
100 c = 1;
|
|
100 else
|
|
100 c = 0;
|
|
@end smallexample
|
|
|
|
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.
|
|
@c man end
|
|
|
|
@node Gcov Data Files
|
|
@section Brief description of @command{gcov} data files
|
|
|
|
@command{gcov} uses three files for doing profiling. The names of these
|
|
files are derived from the original @emph{source} file by substituting
|
|
the file suffix with either @file{.bb}, @file{.bbg}, or @file{.da}. All
|
|
of these files are placed in the same directory as the source file, and
|
|
contain data stored in a platform-independent method.
|
|
|
|
The @file{.bb} and @file{.bbg} files are generated when the source file
|
|
is compiled with the GCC @option{-ftest-coverage} option. The
|
|
@file{.bb} file contains a list of source files (including headers),
|
|
functions within those files, and line numbers corresponding to each
|
|
basic block in the source file.
|
|
|
|
The @file{.bb} file format consists of several lists of 4-byte integers
|
|
which correspond to the line numbers of each basic block in the
|
|
file. Each list is terminated by a line number of 0. A line number of @minus{}1
|
|
is used to designate that the source file name (padded to a 4-byte
|
|
boundary and followed by another @minus{}1) follows. In addition, a line number
|
|
of @minus{}2 is used to designate that the name of a function (also padded to a
|
|
4-byte boundary and followed by a @minus{}2) follows.
|
|
|
|
The @file{.bbg} file is used to reconstruct the program flow graph for
|
|
the source file. It contains a list of the program flow arcs (possible
|
|
branches taken from one basic block to another) for each function which,
|
|
in combination with the @file{.bb} file, enables gcov to reconstruct the
|
|
program flow.
|
|
|
|
In the @file{.bbg} file, the format is:
|
|
@smallexample
|
|
number of basic blocks for function #0 (4-byte number)
|
|
total number of arcs for function #0 (4-byte number)
|
|
count of arcs in basic block #0 (4-byte number)
|
|
destination basic block of arc #0 (4-byte number)
|
|
flag bits (4-byte number)
|
|
destination basic block of arc #1 (4-byte number)
|
|
flag bits (4-byte number)
|
|
@dots{}
|
|
destination basic block of arc #N (4-byte number)
|
|
flag bits (4-byte number)
|
|
count of arcs in basic block #1 (4-byte number)
|
|
destination basic block of arc #0 (4-byte number)
|
|
flag bits (4-byte number)
|
|
@dots{}
|
|
@end smallexample
|
|
|
|
A @minus{}1 (stored as a 4-byte number) is used to separate each function's
|
|
list of basic blocks, and to verify that the file has been read
|
|
correctly.
|
|
|
|
The @file{.da} file is generated when a program containing object files
|
|
built with the GCC @option{-fprofile-arcs} option is executed. A
|
|
separate @file{.da} file is created for each source file compiled with
|
|
this option, and the name of the @file{.da} file is stored as an
|
|
absolute pathname in the resulting object file. This path name is
|
|
derived from the source file name by substituting a @file{.da} suffix.
|
|
|
|
The format of the @file{.da} file is fairly simple. The first 8-byte
|
|
number is the number of counts in the file, followed by the counts
|
|
(stored as 8-byte numbers). Each count corresponds to the number of
|
|
times each arc in the program is executed. The counts are cumulative;
|
|
each time the program is executed, it attempts to combine the existing
|
|
@file{.da} files with the new counts for this invocation of the
|
|
program. It ignores the contents of any @file{.da} files whose number of
|
|
arcs doesn't correspond to the current program, and merely overwrites
|
|
them instead.
|
|
|
|
All three of these files use the functions in @file{gcov-io.h} to store
|
|
integers; the functions in this header provide a machine-independent
|
|
mechanism for storing and retrieving data from a stream.
|
|
|