Invoking gcov#
gcov [options] files
gcov accepts the following options:
Options#
- -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
-uoption 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.
- -j, --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.gzextension.Structure of the JSON is following:
{ "current_working_directory": "foo/bar", "data_file": "a.out", "format_version": "1", "gcc_version": "11.1.1 20210510" "files": ["$file"] }
Fields of the root element have following semantics:
current_working_directory: working directory where a compilation unit was compileddata_file: name of the data file (GCDA)format_version: semantic version of the formatgcc_version: version of the GCC compiler
Each
filehas the following form:{ "file": "a.c", "functions": ["$function"], "lines": ["$line"] }
Fields of the
fileelement have following semantics:file_name: name of the source file
Each
functionhas the following form:{ "blocks": 2, "blocks_executed": 2, "demangled_name": "foo", "end_column": 1, "end_line": 4, "execution_count": 1, "name": "foo", "start_column": 5, "start_line": 1 }
Fields of the
functionelement have following semantics:blocks: number of blocks that are in the functionblocks_executed: number of executed blocks of the functiondemangled_name: demangled name of the functionend_column: column in the source file where the function endsend_line: line in the source file where the function endsexecution_count: number of executions of the functionname: name of the functionstart_column: column in the source file where the function beginsstart_line: line in the source file where the function begins
Note that line numbers and column numbers number from 1. In the current implementation,
start_lineandstart_columndo not include any template parameters and the leading return type but that this is likely to be fixed in the future.Each
linehas the following form:{ "branches": ["$branch"], "count": 2, "line_number": 15, "unexecuted_block": false, "function_name": "foo", }
Branches are present only with
-boption. Fields of thelineelement have following semantics:count: number of executions of the lineline_number: line numberunexecuted_block: flag whether the line contains an unexecuted block (not all statements on the line are executed)function_name: a name of a function thislinebelongs to (for a line with an inlined statements can be not set)
Each
branchhas the following form:{ "count": 11, "fallthrough": true, "throw": false }
Fields of the
branchelement have following semantics:count: number of executions of the branchfallthrough: true when the branch is a fall through branchthrow: true when the branch is an exceptional branch
- -H, --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
-aoption.
- -l, --long-file-names#
Create long file names for included source files. For example, if the header file
x.hcontains code, and was included in the filea.c, then running gcov on the filea.cwill produce an output file calleda.c##x.h.gcovinstead ofx.h.gcov. This can be useful ifx.his included in multiple source files and you want to see the individual contributions. If you use the-poption, 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.gcdadata 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
.gcovfiles. 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 formsource-file##md5.gcov, where thesource-filecomponent is the final filename part and themd5component is calculated from the full mangled name that would have been used otherwise. The option is an alternative to the--preserve-pathson 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 -c
$ g++ --coverage tmp.o
$ 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.