454 lines
16 KiB
Groff
454 lines
16 KiB
Groff
.\" Automatically generated by Pod::Man version 1.15
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.\" Wed Feb 5 03:13:55 2003
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.\" ======================================================================
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.\" ======================================================================
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.\"
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.IX Title "GCOV 1"
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.TH GCOV 1 "gcc-3.2.2" "2003-02-05" "GNU"
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.UC
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.SH "NAME"
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gcov \- coverage testing tool
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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gcov [\fB\-v\fR|\fB\*(--version\fR] [\fB\-h\fR|\fB\*(--help\fR]
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[\fB\-b\fR|\fB\*(--branch-probabilities\fR] [\fB\-c\fR|\fB\*(--branch-counts\fR]
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[\fB\-n\fR|\fB\*(--no-output\fR] [\fB\-l\fR|\fB\*(--long-file-names\fR]
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[\fB\-f\fR|\fB\*(--function-summaries\fR]
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[\fB\-o\fR|\fB\*(--object-directory\fR \fIdirectory\fR] \fIsourcefile\fR
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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\&\fBgcov\fR is a test coverage program. Use it in concert with \s-1GCC\s0
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to analyze your programs to help create more efficient, faster
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running code. You can use \fBgcov\fR as a profiling tool to help
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discover where your optimization efforts will best affect your code. You
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can also use \fBgcov\fR along with the other profiling tool,
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\&\fBgprof\fR, to assess which parts of your code use the greatest amount
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of computing time.
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.PP
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Profiling tools help you analyze your code's performance. Using a
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profiler such as \fBgcov\fR or \fBgprof\fR, you can find out some
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basic performance statistics, such as:
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.Ip "\(bu" 4
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how often each line of code executes
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.Ip "\(bu" 4
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what lines of code are actually executed
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.Ip "\(bu" 4
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how much computing time each section of code uses
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.PP
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Once you know these things about how your code works when compiled, you
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can look at each module to see which modules should be optimized.
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\&\fBgcov\fR helps you determine where to work on optimization.
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.PP
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Software developers also use coverage testing in concert with
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testsuites, to make sure software is actually good enough for a release.
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Testsuites can verify that a program works as expected; a coverage
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program tests to see how much of the program is exercised by the
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testsuite. Developers can then determine what kinds of test cases need
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to be added to the testsuites to create both better testing and a better
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final product.
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.PP
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You should compile your code without optimization if you plan to use
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\&\fBgcov\fR because the optimization, by combining some lines of code
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into one function, may not give you as much information as you need to
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look for `hot spots' where the code is using a great deal of computer
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time. Likewise, because \fBgcov\fR accumulates statistics by line (at
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the lowest resolution), it works best with a programming style that
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places only one statement on each line. If you use complicated macros
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that expand to loops or to other control structures, the statistics are
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less helpful\-\-\-they only report on the line where the macro call
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appears. If your complex macros behave like functions, you can replace
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them with inline functions to solve this problem.
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.PP
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\&\fBgcov\fR creates a logfile called \fI\fIsourcefile\fI.gcov\fR which
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indicates how many times each line of a source file \fI\fIsourcefile\fI.c\fR
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has executed. You can use these logfiles along with \fBgprof\fR to aid
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in fine-tuning the performance of your programs. \fBgprof\fR gives
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timing information you can use along with the information you get from
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\&\fBgcov\fR.
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.PP
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\&\fBgcov\fR works only on code compiled with \s-1GCC\s0. It is not
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compatible with any other profiling or test coverage mechanism.
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.SH "OPTIONS"
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.IX Header "OPTIONS"
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.Ip "\fB\-h\fR" 4
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.IX Item "-h"
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.PD 0
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.Ip "\fB\*(--help\fR" 4
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.IX Item "help"
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.PD
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Display help about using \fBgcov\fR (on the standard output), and
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exit without doing any further processing.
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.Ip "\fB\-v\fR" 4
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.IX Item "-v"
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.PD 0
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.Ip "\fB\*(--version\fR" 4
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.IX Item "version"
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.PD
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Display the \fBgcov\fR version number (on the standard output),
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and exit without doing any further processing.
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.Ip "\fB\-b\fR" 4
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.IX Item "-b"
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.PD 0
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.Ip "\fB\*(--branch-probabilities\fR" 4
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.IX Item "branch-probabilities"
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.PD
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Write branch frequencies to the output file, and write branch summary
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info to the standard output. This option allows you to see how often
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each branch in your program was taken.
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.Ip "\fB\-c\fR" 4
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.IX Item "-c"
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.PD 0
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.Ip "\fB\*(--branch-counts\fR" 4
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.IX Item "branch-counts"
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.PD
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Write branch frequencies as the number of branches taken, rather than
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the percentage of branches taken.
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.Ip "\fB\-n\fR" 4
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.IX Item "-n"
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.PD 0
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.Ip "\fB\*(--no-output\fR" 4
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.IX Item "no-output"
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.PD
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Do not create the \fBgcov\fR output file.
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.Ip "\fB\-l\fR" 4
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.IX Item "-l"
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.PD 0
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.Ip "\fB\*(--long-file-names\fR" 4
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.IX Item "long-file-names"
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.PD
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Create long file names for included source files. For example, if the
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header file \fIx.h\fR contains code, and was included in the file
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\&\fIa.c\fR, then running \fBgcov\fR on the file \fIa.c\fR will produce
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an output file called \fIa.c.x.h.gcov\fR instead of \fIx.h.gcov\fR.
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This can be useful if \fIx.h\fR is included in multiple source files.
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.Ip "\fB\-f\fR" 4
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.IX Item "-f"
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.PD 0
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.Ip "\fB\*(--function-summaries\fR" 4
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.IX Item "function-summaries"
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.PD
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Output summaries for each function in addition to the file level summary.
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.Ip "\fB\-o\fR \fIdirectory\fR" 4
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.IX Item "-o directory"
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.PD 0
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.Ip "\fB\*(--object-directory\fR \fIdirectory\fR" 4
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.IX Item "object-directory directory"
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.PD
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The directory where the object files live. Gcov will search for \fI.bb\fR,
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\&\fI.bbg\fR, and \fI.da\fR files in this directory.
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.PP
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When using \fBgcov\fR, you must first compile your program with two
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special \s-1GCC\s0 options: \fB\-fprofile-arcs \-ftest-coverage\fR.
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This tells the compiler to generate additional information needed by
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gcov (basically a flow graph of the program) and also includes
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additional code in the object files for generating the extra profiling
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information needed by gcov. These additional files are placed in the
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directory where the source code is located.
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.PP
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Running the program will cause profile output to be generated. For each
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source file compiled with \fB\-fprofile-arcs\fR, an accompanying \fI.da\fR
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file will be placed in the source directory.
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.PP
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Running \fBgcov\fR with your program's source file names as arguments
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will now produce a listing of the code along with frequency of execution
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for each line. For example, if your program is called \fItmp.c\fR, this
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is what you see when you use the basic \fBgcov\fR facility:
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.PP
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.Vb 5
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\& $ gcc -fprofile-arcs -ftest-coverage tmp.c
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\& $ a.out
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\& $ gcov tmp.c
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\& 87.50% of 8 source lines executed in file tmp.c
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\& Creating tmp.c.gcov.
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.Ve
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The file \fItmp.c.gcov\fR contains output from \fBgcov\fR.
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Here is a sample:
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.PP
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.Vb 3
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\& main()
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\& {
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\& 1 int i, total;
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.Ve
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.Vb 1
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\& 1 total = 0;
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.Ve
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.Vb 2
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\& 11 for (i = 0; i < 10; i++)
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\& 10 total += i;
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.Ve
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.Vb 5
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\& 1 if (total != 45)
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\& ###### printf ("Failure\en");
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\& else
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\& 1 printf ("Success\en");
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\& 1 }
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.Ve
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When you use the \fB\-b\fR option, your output looks like this:
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.PP
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.Vb 6
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\& $ gcov -b tmp.c
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\& 87.50% of 8 source lines executed in file tmp.c
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\& 80.00% of 5 branches executed in file tmp.c
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\& 80.00% of 5 branches taken at least once in file tmp.c
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\& 50.00% of 2 calls executed in file tmp.c
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\& Creating tmp.c.gcov.
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.Ve
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Here is a sample of a resulting \fItmp.c.gcov\fR file:
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.PP
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.Vb 3
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\& main()
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\& {
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\& 1 int i, total;
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.Ve
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.Vb 1
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\& 1 total = 0;
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.Ve
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.Vb 5
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\& 11 for (i = 0; i < 10; i++)
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\& branch 0 taken = 91%
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\& branch 1 taken = 100%
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\& branch 2 taken = 100%
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\& 10 total += i;
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.Ve
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.Vb 9
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\& 1 if (total != 45)
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\& branch 0 taken = 100%
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\& ###### printf ("Failure\en");
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\& call 0 never executed
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\& branch 1 never executed
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\& else
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\& 1 printf ("Success\en");
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\& call 0 returns = 100%
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\& 1 }
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.Ve
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For each basic block, a line is printed after the last line of the basic
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block describing the branch or call that ends the basic block. There can
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be multiple branches and calls listed for a single source line if there
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are multiple basic blocks that end on that line. In this case, the
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branches and calls are each given a number. There is no simple way to map
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these branches and calls back to source constructs. In general, though,
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the lowest numbered branch or call will correspond to the leftmost construct
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on the source line.
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.PP
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For a branch, if it was executed at least once, then a percentage
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indicating the number of times the branch was taken divided by the
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number of times the branch was executed will be printed. Otherwise, the
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message ``never executed'' is printed.
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.PP
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For a call, if it was executed at least once, then a percentage
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indicating the number of times the call returned divided by the number
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of times the call was executed will be printed. This will usually be
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100%, but may be less for functions call \f(CW\*(C`exit\*(C'\fR or \f(CW\*(C`longjmp\*(C'\fR,
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and thus may not return every time they are called.
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.PP
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The execution counts are cumulative. If the example program were
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executed again without removing the \fI.da\fR file, the count for the
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number of times each line in the source was executed would be added to
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the results of the previous \fIrun\fR\|(s). This is potentially useful in
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several ways. For example, it could be used to accumulate data over a
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number of program runs as part of a test verification suite, or to
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provide more accurate long-term information over a large number of
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program runs.
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.PP
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The data in the \fI.da\fR files is saved immediately before the program
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exits. For each source file compiled with \fB\-fprofile-arcs\fR, the profiling
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code first attempts to read in an existing \fI.da\fR file; if the file
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doesn't match the executable (differing number of basic block counts) it
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will ignore the contents of the file. It then adds in the new execution
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counts and finally writes the data to the file.
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.Sh "Using \fBgcov\fP with \s-1GCC\s0 Optimization"
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.IX Subsection "Using gcov with GCC Optimization"
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If you plan to use \fBgcov\fR to help optimize your code, you must
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first compile your program with two special \s-1GCC\s0 options:
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\&\fB\-fprofile-arcs \-ftest-coverage\fR. Aside from that, you can use any
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other \s-1GCC\s0 options; but if you want to prove that every single line
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in your program was executed, you should not compile with optimization
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at the same time. On some machines the optimizer can eliminate some
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simple code lines by combining them with other lines. For example, code
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like this:
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.PP
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.Vb 4
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\& if (a != b)
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\& c = 1;
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\& else
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\& c = 0;
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.Ve
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can be compiled into one instruction on some machines. In this case,
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there is no way for \fBgcov\fR to calculate separate execution counts
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for each line because there isn't separate code for each line. Hence
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the \fBgcov\fR output looks like this if you compiled the program with
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optimization:
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.PP
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.Vb 4
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\& 100 if (a != b)
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\& 100 c = 1;
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\& 100 else
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\& 100 c = 0;
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.Ve
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The output shows that this block of code, combined by optimization,
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executed 100 times. In one sense this result is correct, because there
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was only one instruction representing all four of these lines. However,
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the output does not indicate how many times the result was 0 and how
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many times the result was 1.
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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\&\fIgpl\fR\|(7), \fIgfdl\fR\|(7), \fIfsf-funding\fR\|(7), \fIgcc\fR\|(1) and the Info entry for \fIgcc\fR.
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.SH "COPYRIGHT"
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.IX Header "COPYRIGHT"
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Copyright (c) 1996, 1997, 1999, 2000, 2001 Free Software Foundation, Inc.
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.PP
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the \s-1GNU\s0 Free Documentation License, Version 1.1 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being ``\s-1GNU\s0 General Public License'' and ``Funding
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Free Software'', the Front-Cover texts being (a) (see below), and with
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the Back-Cover Texts being (b) (see below). A copy of the license is
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included in the \fIgfdl\fR\|(7) man page.
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.PP
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(a) The \s-1FSF\s0's Front-Cover Text is:
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.PP
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.Vb 1
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\& A GNU Manual
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.Ve
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(b) The \s-1FSF\s0's Back-Cover Text is:
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.PP
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.Vb 3
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\& You have freedom to copy and modify this GNU Manual, like GNU
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\& software. Copies published by the Free Software Foundation raise
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\& funds for GNU development.
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.Ve
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