@c Copyright (C) 1996, 1997, 1999, 2000, 2001, @c 2002, 2003 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, 2002, 2003 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 1.2 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 and to discover untested parts of your program. 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{-p}|@option{--preserve-paths}] [@option{-f}|@option{--function-summaries}] [@option{-o}|@option{--object-directory} @var{directory|file}] @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 -p @itemx --preserve-paths Preserve complete path information in the names of generated @file{.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 @samp{-l} option. @item -f @itemx --function-summaries Output summaries for each function in addition to the file level summary. @item -o @var{directory|file} @itemx --object-directory @var{directory} @itemx --object-file @var{file} Specify either the directory containing the gcov data files, or the object path name. The @file{.bb}, @file{.bbg}, and @file{.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. @end table 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 @file{@var{mangledname}.gcov} in the current directory. These contain the coverage information of the source file they correspond to. One @file{.gcov} file is produced for each source file containing code, which was compiled to produce the data files. The @file{.gcov} files contain the ':' separated fields along with program source code. The format is @smallexample @var{execution_count}:@var{line_number}:@var{source line text} @end smallexample Additional block information may succeed each line, when requested by command line option. The @var{execution_count} is @samp{-} for lines containing no code and @samp{#####} for lines which were never executed. Some lines of information at the start have @var{line_number} of zero. When printing percentages, 0% and 100% are only printed when the values are @emph{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 @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 object file 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 object file 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 90.00% of 10 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 -: 0:Source:tmp.c -: 0:Object:tmp.bb -: 1:#include -: 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:@} @end smallexample @need 450 When you use the @option{-b} option, your output looks like this: @smallexample $ 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. @end smallexample Here is a sample of a resulting @file{tmp.c.gcov} file: @smallexample -: 0:Source:tmp.c -: 0:Object:tmp.bb -: 1:#include -: 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:@} @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: 12:if (a != b) 100: 13: c = 1; 100: 14:else 100: 15: 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 name of function #0 checksum of function #0 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 function name is stored as a @minus{}1 (4 bytes), the length (4 bytes), the name itself (padded to 4-byte boundary) followed by a @minus{}1 (4 bytes). The flags are defined as follows: @itemize @item bit0 On function spanning tree @item bit1 Is a fake edge @item bit2 Is the fall through edge from one block to its immediate successor. @item bit3-bit31 For future expansion @end itemize 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 object file name by substituting a @file{.da} suffix. The @file{.da} consists of one or more blocks with the following structure: @smallexample "magic" number @minus{}123 (4-byte number) number of functions (4-byte number) length of the "extension block" in bytes extension block (variable length) name of function #0 (the same format as in .bbg file) checksum of function #0 number of instrumented arcs (4-byte number) count of arc #0 (8-byte number) count of arc #1 (8-byte number) @dots{} count of arc #M_0 (8-byte number) name of function #1 (the same format as in .bbg file) checksum of function #1 @dots{} @end smallexample Multiple program runs might merge data into a single block, or might append a new block. The current structure of the extension block is as follows: @smallexample number of instrumented arcs in whole program (4-byte number) sum all of instrumented arcs in whole program (8-byte number) maximal value of counter in whole program (8-byte number) number of instrumented arcs in the object file (4-byte number) sum all of instrumented arcs in the object file (8-byte number) maximal value of counter in the object file (8-byte number) @end smallexample 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.