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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | SEE ALSO | COPYRIGHT | COLOPHON |
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GCOV(1) GNU GCOV(1)
gcov - coverage testing tool
gcov [-v|--version] [-h|--help]
[-a|--all-blocks]
[-b|--branch-probabilities]
[-c|--branch-counts]
[-d|--display-progress]
[-f|--function-summaries]
[-i|--json-format]
[-j|--human-readable]
[-k|--use-colors]
[-l|--long-file-names]
[-m|--demangled-names]
[-n|--no-output]
[-o|--object-directory directory|file]
[-p|--preserve-paths]
[-q|--use-hotness-colors]
[-r|--relative-only]
[-s|--source-prefix directory]
[-t|--stdout]
[-u|--unconditional-branches]
[-x|--hash-filenames]
files
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 gcov as a profiling tool to help discover where your
optimization efforts will best affect your code. You can also
use gcov along with the other profiling tool, 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 gcov or gprof, you can find out some basic
performance statistics, such as:
* how often each line of code executes
* what lines of code are actually executed
* how much computing time each section of code uses
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. 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 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 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.
gcov creates a logfile called sourcefile.gcov which indicates how
many times each line of a source file sourcefile.c has executed.
You can use these logfiles along with gprof to aid in fine-tuning
the performance of your programs. gprof gives timing information
you can use along with the information you get from gcov.
gcov works only on code compiled with GCC. It is not compatible
with any other profiling or test coverage mechanism.
-a
--all-blocks
Write individual execution counts for every basic block.
Normally gcov outputs execution counts only for the main
blocks of a line. With this option you can determine if
blocks within a single line are not being executed.
-b
--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.
Unconditional branches will not be shown, unless the -u
option is given.
-c
--branch-counts
Write branch frequencies as the number of branches taken,
rather than the percentage of branches taken.
-d
--display-progress
Display the progress on the standard output.
-f
--function-summaries
Output summaries for each function in addition to the file
level summary.
-h
--help
Display help about using gcov (on the standard output), and
exit without doing any further processing.
-i
--json-format
Output gcov file in an easy-to-parse JSON intermediate format
which does not require source code for generation. The JSON
file is compressed with gzip compression algorithm and the
files have .gcov.json.gz extension.
Structure of the JSON is following:
{
"current_working_directory": <current_working_directory>,
"data_file": <data_file>,
"format_version": <format_version>,
"gcc_version": <gcc_version>
"files": [<file>]
}
Fields of the root element have following semantics:
* current_working_directory: working directory where a
compilation unit was compiled
* data_file: name of the data file (GCDA)
* format_version: semantic version of the format
* gcc_version: version of the GCC compiler
Each file has the following form:
{
"file": <file_name>,
"functions": [<function>],
"lines": [<line>]
}
Fields of the file element have following semantics:
* file_name: name of the source file
Each function has the following form:
{
"blocks": <blocks>,
"blocks_executed": <blocks_executed>,
"demangled_name": "<demangled_name>,
"end_column": <end_column>,
"end_line": <end_line>,
"execution_count": <execution_count>,
"name": <name>,
"start_column": <start_column>
"start_line": <start_line>
}
Fields of the function element have following semantics:
* blocks: number of blocks that are in the function
* blocks_executed: number of executed blocks of the
function
* demangled_name: demangled name of the function
* end_column: column in the source file where the function
ends
* end_line: line in the source file where the function ends
* execution_count: number of executions of the function
* name: name of the function
* start_column: column in the source file where the
function begins
* start_line: line in the source file where the function
begins
Note that line numbers and column numbers number from 1. In
the current implementation, start_line and start_column do
not include any template parameters and the leading return
type but that this is likely to be fixed in the future.
Each line has the following form:
{
"branches": [<branch>],
"count": <count>,
"line_number": <line_number>,
"unexecuted_block": <unexecuted_block>
"function_name": <function_name>,
}
Branches are present only with -b option. Fields of the line
element have following semantics:
* count: number of executions of the line
* line_number: line number
* unexecuted_block: flag whether the line contains an
unexecuted block (not all statements on the line are
executed)
* function_name: a name of a function this line belongs to
(for a line with an inlined statements can be not set)
Each branch has the following form:
{
"count": <count>,
"fallthrough": <fallthrough>,
"throw": <throw>
}
Fields of the branch element have following semantics:
* count: number of executions of the branch
* fallthrough: true when the branch is a fall through
branch
* throw: true when the branch is an exceptional branch
-j
--human-readable
Write counts in human readable format (like 24.6k).
-k
--use-colors
Use colors for lines of code that have zero coverage. We use
red color for non-exceptional lines and cyan for exceptional.
Same colors are used for basic blocks with -a option.
-l
--long-file-names
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 and you want to see the individual
contributions. If you use the -p option, both the including
and included file names will be complete path names.
-m
--demangled-names
Display demangled function names in output. The default is to
show mangled function names.
-n
--no-output
Do not create the gcov output file.
-o directory|file
--object-directory directory
--object-file file
Specify either the directory containing the gcov data files,
or the object path name. The .gcno, and .gcda data files are
searched for using this option. If a directory is specified,
the data files are in that directory and named after the
input file name, without its extension. If a file is
specified here, the data files are named after that file,
without its extension.
-p
--preserve-paths
Preserve complete path information in the names of generated
.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 unremoveable .. components
renamed to ^. This is useful if sourcefiles are in several
different directories.
-q
--use-hotness-colors
Emit perf-like colored output for hot lines. Legend of the
color scale is printed at the very beginning of the output
file.
-r
--relative-only
Only output information about source files with a relative
pathname (after source prefix elision). Absolute paths are
usually system header files and coverage of any inline
functions therein is normally uninteresting.
-s directory
--source-prefix directory
A prefix for source file names to remove when generating the
output coverage files. This option is useful when building
in a separate directory, and the pathname to the source
directory is not wanted when determining the output file
names. Note that this prefix detection is applied before
determining whether the source file is absolute.
-t
--stdout
Output to standard output instead of output files.
-u
--unconditional-branches
When branch probabilities are given, include those of
unconditional branches. Unconditional branches are normally
not interesting.
-v
--version
Display the gcov version number (on the standard output), and
exit without doing any further processing.
-w
--verbose
Print verbose informations related to basic blocks and arcs.
-x
--hash-filenames
When using --preserve-paths, gcov uses the full pathname of
the source files to create an output filename. This can lead
to long filenames that can overflow filesystem limits. This
option creates names of the form source-file##md5.gcov, where
the source-file component is the final filename part and the
md5 component is calculated from the full mangled name that
would have been used otherwise. The option is an alternative
to the --preserve-paths on systems which have a filesystem
limit.
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
mangledname.gcov in the current directory. These contain the
coverage information of the source file they correspond to. One
.gcov file is produced for each source (or header) file
containing code, which was compiled to produce the data files.
The mangledname part of the output file name is usually simply
the source file name, but can be something more complicated if
the -l or -p options are given. Refer to those options for
details.
If you invoke gcov with multiple input files, the contributions
from each input file are summed. Typically you would invoke it
with the same list of files as the final link of your executable.
The .gcov files contain the : separated fields along with program
source code. The format is
<execution_count>:<line_number>:<source line text>
Additional block information may succeed each line, when
requested by command line option. The execution_count is - for
lines containing no code. Unexecuted lines are marked ##### or
=====, depending on whether they are reachable by non-exceptional
paths or only exceptional paths such as C++ exception handlers,
respectively. Given the -a option, unexecuted blocks are marked
$$$$$ or %%%%%, depending on whether a basic block is reachable
via non-exceptional or exceptional paths. Executed basic blocks
having a statement with zero execution_count end with * character
and are colored with magenta color with the -k option. This
functionality is not supported in Ada.
Note that GCC can completely remove the bodies of functions that
are not needed -- for instance if they are inlined everywhere.
Such functions are marked with -, which can be confusing. Use
the -fkeep-inline-functions and -fkeep-static-functions options
to retain these functions and allow gcov to properly show their
execution_count.
Some lines of information at the start have line_number of zero.
These preamble lines are of the form
-:0:<tag>:<value>
The ordering and number of these preamble lines will be augmented
as gcov development progresses --- do not rely on them remaining
unchanged. Use tag to locate a particular preamble line.
The additional block information is of the form
<tag> <information>
The information is human readable, but designed to be simple
enough for machine parsing too.
When printing percentages, 0% and 100% are only printed when the
values are 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 gcov, you must first compile your program with a
special GCC option --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 -fprofile-arcs, an
accompanying .gcda file will be placed in the object file
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.cpp, this is what you see when you use the basic gcov
facility:
$ g++ --coverage tmp.cpp
$ a.out
$ gcov tmp.cpp -m
File 'tmp.cpp'
Lines executed:92.86% of 14
Creating 'tmp.cpp.gcov'
The file tmp.cpp.gcov contains output from gcov. Here is a
sample:
-: 0:Source:tmp.cpp
-: 0:Working directory:/home/gcc/testcase
-: 0:Graph:tmp.gcno
-: 0:Data:tmp.gcda
-: 0:Runs:1
-: 0:Programs:1
-: 1:#include <stdio.h>
-: 2:
-: 3:template<class T>
-: 4:class Foo
-: 5:{
-: 6: public:
1*: 7: Foo(): b (1000) {}
------------------
Foo<char>::Foo():
#####: 7: Foo(): b (1000) {}
------------------
Foo<int>::Foo():
1: 7: Foo(): b (1000) {}
------------------
2*: 8: void inc () { b++; }
------------------
Foo<char>::inc():
#####: 8: void inc () { b++; }
------------------
Foo<int>::inc():
2: 8: void inc () { b++; }
------------------
-: 9:
-: 10: private:
-: 11: int b;
-: 12:};
-: 13:
-: 14:template class Foo<int>;
-: 15:template class Foo<char>;
-: 16:
-: 17:int
1: 18:main (void)
-: 19:{
-: 20: int i, total;
1: 21: Foo<int> counter;
-: 22:
1: 23: counter.inc();
1: 24: counter.inc();
1: 25: total = 0;
-: 26:
11: 27: for (i = 0; i < 10; i++)
10: 28: total += i;
-: 29:
1*: 30: int v = total > 100 ? 1 : 2;
-: 31:
1: 32: if (total != 45)
#####: 33: printf ("Failure\n");
-: 34: else
1: 35: printf ("Success\n");
1: 36: return 0;
-: 37:}
Note that line 7 is shown in the report multiple times. First
occurrence presents total number of execution of the line and the
next two belong to instances of class Foo constructors. As you
can also see, line 30 contains some unexecuted basic blocks and
thus execution count has asterisk symbol.
When you use the -a option, you will get individual block counts,
and the output looks like this:
-: 0:Source:tmp.cpp
-: 0:Working directory:/home/gcc/testcase
-: 0:Graph:tmp.gcno
-: 0:Data:tmp.gcda
-: 0:Runs:1
-: 0:Programs:1
-: 1:#include <stdio.h>
-: 2:
-: 3:template<class T>
-: 4:class Foo
-: 5:{
-: 6: public:
1*: 7: Foo(): b (1000) {}
------------------
Foo<char>::Foo():
#####: 7: Foo(): b (1000) {}
------------------
Foo<int>::Foo():
1: 7: Foo(): b (1000) {}
------------------
2*: 8: void inc () { b++; }
------------------
Foo<char>::inc():
#####: 8: void inc () { b++; }
------------------
Foo<int>::inc():
2: 8: void inc () { b++; }
------------------
-: 9:
-: 10: private:
-: 11: int b;
-: 12:};
-: 13:
-: 14:template class Foo<int>;
-: 15:template class Foo<char>;
-: 16:
-: 17:int
1: 18:main (void)
-: 19:{
-: 20: int i, total;
1: 21: Foo<int> counter;
1: 21-block 0
-: 22:
1: 23: counter.inc();
1: 23-block 0
1: 24: counter.inc();
1: 24-block 0
1: 25: total = 0;
-: 26:
11: 27: for (i = 0; i < 10; i++)
1: 27-block 0
11: 27-block 1
10: 28: total += i;
10: 28-block 0
-: 29:
1*: 30: int v = total > 100 ? 1 : 2;
1: 30-block 0
%%%%%: 30-block 1
1: 30-block 2
-: 31:
1: 32: if (total != 45)
1: 32-block 0
#####: 33: printf ("Failure\n");
%%%%%: 33-block 0
-: 34: else
1: 35: printf ("Success\n");
1: 35-block 0
1: 36: return 0;
1: 36-block 0
-: 37:}
In this mode, each basic block is only shown on one line -- the
last line of the block. A multi-line block will only contribute
to the execution count of that last line, and other lines will
not be shown to contain code, unless previous blocks end on those
lines. The total execution count of a line is shown and
subsequent lines show the execution counts for individual blocks
that end on that line. After each block, the branch and call
counts of the block will be shown, if the -b option is given.
Because of the way GCC instruments calls, a call count can be
shown after a line with no individual blocks. As you can see,
line 33 contains a basic block that was not executed.
When you use the -b option, your output looks like this:
-: 0:Source:tmp.cpp
-: 0:Working directory:/home/gcc/testcase
-: 0:Graph:tmp.gcno
-: 0:Data:tmp.gcda
-: 0:Runs:1
-: 0:Programs:1
-: 1:#include <stdio.h>
-: 2:
-: 3:template<class T>
-: 4:class Foo
-: 5:{
-: 6: public:
1*: 7: Foo(): b (1000) {}
------------------
Foo<char>::Foo():
function Foo<char>::Foo() called 0 returned 0% blocks executed 0%
#####: 7: Foo(): b (1000) {}
------------------
Foo<int>::Foo():
function Foo<int>::Foo() called 1 returned 100% blocks executed 100%
1: 7: Foo(): b (1000) {}
------------------
2*: 8: void inc () { b++; }
------------------
Foo<char>::inc():
function Foo<char>::inc() called 0 returned 0% blocks executed 0%
#####: 8: void inc () { b++; }
------------------
Foo<int>::inc():
function Foo<int>::inc() called 2 returned 100% blocks executed 100%
2: 8: void inc () { b++; }
------------------
-: 9:
-: 10: private:
-: 11: int b;
-: 12:};
-: 13:
-: 14:template class Foo<int>;
-: 15:template class Foo<char>;
-: 16:
-: 17:int
function main called 1 returned 100% blocks executed 81%
1: 18:main (void)
-: 19:{
-: 20: int i, total;
1: 21: Foo<int> counter;
call 0 returned 100%
branch 1 taken 100% (fallthrough)
branch 2 taken 0% (throw)
-: 22:
1: 23: counter.inc();
call 0 returned 100%
branch 1 taken 100% (fallthrough)
branch 2 taken 0% (throw)
1: 24: counter.inc();
call 0 returned 100%
branch 1 taken 100% (fallthrough)
branch 2 taken 0% (throw)
1: 25: total = 0;
-: 26:
11: 27: for (i = 0; i < 10; i++)
branch 0 taken 91% (fallthrough)
branch 1 taken 9%
10: 28: total += i;
-: 29:
1*: 30: int v = total > 100 ? 1 : 2;
branch 0 taken 0% (fallthrough)
branch 1 taken 100%
-: 31:
1: 32: if (total != 45)
branch 0 taken 0% (fallthrough)
branch 1 taken 100%
#####: 33: printf ("Failure\n");
call 0 never executed
branch 1 never executed
branch 2 never executed
-: 34: else
1: 35: printf ("Success\n");
call 0 returned 100%
branch 1 taken 100% (fallthrough)
branch 2 taken 0% (throw)
1: 36: return 0;
-: 37:}
For each function, a line is printed showing how many times the
function is called, how many times it returns and what percentage
of the function's blocks were executed.
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 that call "exit"
or "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 .gcda 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 .gcda 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 .gcda 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.
Using gcov with GCC Optimization
If you plan to use gcov to help optimize your code, you must
first compile your program with a special GCC option --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:
if (a != b)
c = 1;
else
c = 0;
can be compiled into one instruction on some machines. In this
case, there is no way for gcov to calculate separate execution
counts for each line because there isn't separate code for each
line. Hence the gcov output looks like this if you compiled the
program with optimization:
100: 12:if (a != b)
100: 13: c = 1;
100: 14:else
100: 15: c = 0;
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.
Inlineable functions can create unexpected line counts. Line
counts are shown for the source code of the inlineable function,
but what is shown depends on where the function is inlined, or if
it is not inlined at all.
If the function is not inlined, the compiler must emit an out of
line copy of the function, in any object file that needs it. If
fileA.o and fileB.o both contain out of line bodies of a
particular inlineable function, they will also both contain
coverage counts for that function. When fileA.o and fileB.o are
linked together, the linker will, on many systems, select one of
those out of line bodies for all calls to that function, and
remove or ignore the other. Unfortunately, it will not remove
the coverage counters for the unused function body. Hence when
instrumented, all but one use of that function will show zero
counts.
If the function is inlined in several places, the block structure
in each location might not be the same. For instance, a
condition might now be calculable at compile time in some
instances. Because the coverage of all the uses of the inline
function will be shown for the same source lines, the line counts
themselves might seem inconsistent.
Long-running applications can use the "__gcov_reset" and
"__gcov_dump" facilities to restrict profile collection to the
program region of interest. Calling "__gcov_reset(void)" will
clear all profile counters to zero, and calling
"__gcov_dump(void)" will cause the profile information collected
at that point to be dumped to .gcda output files. Instrumented
applications use a static destructor with priority 99 to invoke
the "__gcov_dump" function. Thus "__gcov_dump" is executed after
all user defined static destructors, as well as handlers
registered with "atexit". If an executable loads a dynamic
shared object via dlopen functionality, -Wl,--dynamic-list-data
is needed to dump all profile data.
Profiling run-time library reports various errors related to
profile manipulation and profile saving. Errors are printed into
standard error output or GCOV_ERROR_FILE file, if environment
variable is used. In order to terminate immediately after an
errors occurs set GCOV_EXIT_AT_ERROR environment variable. That
can help users to find profile clashing which leads to a
misleading profile.
gpl(7), gfdl(7), fsf-funding(7), gcc(1) and the Info entry for
gcc.
Copyright (c) 1996-2019 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 1.3 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.
This page is part of the gcc (GNU Compiler Collection) project.
Information about the project can be found at
⟨http://gcc.gnu.org/⟩. If you have a bug report for this manual
page, see ⟨http://gcc.gnu.org/bugs/⟩. This page was obtained
from the tarball gcc-9.5.0.tar.xz fetched from
⟨https://ftp.fu-berlin.de/unix/languages/gcc/releases/⟩ on
2024-06-14. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
gcc-9.5.0 2022-05-27 GCOV(1)
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