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  • README file for the LTP GCOV extension (LCOV) -
  • Last changes: 2022-10-04


LCOV is an extension of GCOV, a GNU tool which provides information about what parts of a program are actually executed (i.e. "covered") while running a particular test case. The extension consists of a set of Perl scripts which build on the textual GCOV output to implement the following enhanced functionality:

* HTML based output: coverage rates are additionally indicated using bar
  graphs and specific colors.

* Support for large projects: overview pages allow quick browsing of
  coverage data by providing either a hierarchical directory structure
  view or a three-level detail view: directory, file and source code view.

LCOV was initially designed to support Linux kernel coverage measurements, but works as well for coverage measurements on standard user space applications.

LCOV has recently been enhanced to support differential coverage, as well as date- and owner-binning. See or for a detailed explanation of the concepts and several possible use models. A video presentation of the basic ideas can be found at

In addition, several other features and capabilities have been added. See section 5, below, for a brief description - and also see the man pages and the test cases.

Further README contents

  1. Included files

  2. Installing LCOV

  3. Dependencies

  4. An example of how to access kernel coverage data

  5. An example of how to access coverage data for a user space program

  6. New features (compared to lcov 1.16).

  7. Questions and Comments

  8. Important files

README - This README file CHANGES - List of changes between releases bin/lcov - Tool for capturing LCOV coverage data bin/genhtml - Tool for creating HTML output from LCOV data bin/gendesc - Tool for creating description files as used by genhtml bin/geninfo - Internal tool (creates LCOV data files) bin/genpng - Internal tool (creates png overviews of source files) bin/ - Internal tool (takes care of un-/installing) man - Directory containing man pages for included tools example - Directory containing an example to demonstrate LCOV lcovrc - LCOV configuration file Makefile - Makefile providing 'install' and 'uninstall' targets

  1. Installing LCOV

The LCOV package is available as either RPM or tarball from:

To install the tarball, unpack it to a directory and run:

make install

Use Git for the most recent (but possibly unstable) version:

git clone

Change to the resulting lcov directory and type:

make install

The default install location is /usr/local. Note that you may need to have superuser permissions to write into system directories.

To install in a different location - for example, your home directory, run:

make PREFIX=$HOME/my_lcov install

  1. Dependencies:

The lcov module is implemented primarily in Perl - and requires both a moderately up-to-date Perl installation and multiple Perl packages.

These perl packages include:

  • Capture::Tiny
  • DateTime
  • DateTime::Format::W3CDTF
  • Devel::Cover
  • Digest::MD5
  • File::Spec
  • at least one flavor of JSON module. In order of performance/preference:
    • JSON::XS
    • Cpanel::JSON::XS
    • JSON::PP
    • JSON
  • Memory::Process
  • Time::HiRes

If your system is missing any of these, then you may be able to install them via:

$ perl -MCPAN -e 'install "packageName"'

You will very likely need superuser access to be able to install Perl modules.

Some of the applications provided with the lcov module are written in Python - and may require additional Python packages. In particular, 'xlsxwriter' is required in order to generate any of the spreadsheet reports.

  1. An example of how to access Linux kernel coverage data

Requirements: Follow the Linux kernel coverage setup instructions at:

As root, do the following:

a) Resetting counters

 lcov --zerocounters

b) Capturing the current coverage state to a file

 lcov --capture --output-file

c) Getting HTML output


Point the web browser of your choice to the resulting index.html file.

  1. An example of how to access coverage data for a user space program

Requirements: compile the program in question using GCC with the options -fprofile-arcs and -ftest-coverage. During linking, make sure to specify -lgcov or -coverage.

Assuming the compile directory is called "appdir", do the following:

a) Resetting counters

 lcov --directory appdir --zerocounters

b) Capturing the current coverage state to a file

 lcov --directory appdir --capture --output-file

 Note that this step only works after the application has
 been started and stopped at least once. Otherwise lcov will
 abort with an error mentioning that there are no data/.gcda files.

c) Getting HTML output


d) Generating a differential coverage report

 See the examples in .../tests/gendiffcov.

Point the web browser of your choice to the resulting index.html file.

Please note that independently of where the application is installed or from which directory it is run, the --directory statement needs to point to the directory in which the application was compiled.

For further information on the gcc profiling mechanism, please also consult the gcov man page.

  1. New features (compared to lcov 1.16):

New features and capabilities fall into 6 major categories:

a) Categorization

 This refers primarily to differentical coverage categorization as
 well as date- and owner-binning.  See
 or for a detailed
 description of the concepts.

 Differential categorization and binning are orthogonal in the sense
 that you can generate differential report without binning as well
 as 'vanilla' coverage reports with binning.  See the above papers
 and the genhtml man page for details.

 Related options:
    --baseline-file, --diff-file, --annotate-script, --date-bins,
    --new-file-as-baseline, --elide-path-mismtach

b) Error handling

 A generic - but very simple - error handler has been added to the
 lcov tool suite.  The error handler is used to report exceptions,
 and provides a mechanism for the user to ignore the particular
 message if desired.
 See the genhtml/lcov/geninfo man pages for details.

 Note that some errors are unrecoverable - and cannot be suppressed or

 Related options:  --ignore-error, --keep-going

c) Navigation and display:

 Navigation aids such as hyperlinks to the first uncovered region,
 to the next uncovered region, etc. have been implemented.  Similarly,
 new tables, new columns, and new links between tables enable the
 user to identify the author of particular code (covered or not
 covered), as well as the time period when the code was written.

 Collectively, these features help the user to quickly identify the
 cause of code coverage issues, and to then decide what to do.

 An option to generate a 'hierarchical' coverage report (which follows
 the source code directory structure) or 'flat' (all files in top level
 of two-level report) as well as various other small features (tooltip
 popups, user-specified HTML header, footer, and table labels, etc.) are
 also available.

 See the genhtml man page for some details, as well as the
 'gendiffcov/simple' testcases for some examples.

  Related options:
      --baseline-title, --baseline-date, --current-date, --flat, --hierarchical,
      --show-owners, --show-noncode, --show-navigation, --show-proportion,

d) Data manipulation

 Filters are used to suppress or remove certain coverage artifacts -
 for example, branches generated by the compiler (e.g., for exception
 handling).  These artifacts can overwhelm the user code and obscure
 coverage features that are interesting to the user.

 Other options are used to focus on or to exclude certain sections
 of code, as well as to do regexp replacement of file names.
 (Path munging is useful primarily when the build structure does
 not exactly match the layout in your revision control system; this
 is common in large projects with reusable components.)

 See the lcov/geninfo/genhtml man pages for a detailed description of
 the available filters and manipulation features.

 Related options:
    --include, --exclude, --erase-functions, --omit-lines,
    --substitute, --filter

e) Callbacks/customization

 The user can supply callbacks which are used to:

    i) interface with the revision control system
       Sample scripts:
         - Perforce:  see 'p4diff' and 'p4annotate'
         - Git: see 'gitdiff' and 'gitblame'
    ii) verify that source code versions are compatible, and
        Sample scripts: see 'get_signature', 'getp4version'
    iii) enforce a desired code coverage criteria
         Sample script: criteria

 See the genhtml/lcov/geninfo man pages for details.

 Note that the various sample scripts are found in the source code 'bin'
 directory, but are installed in the $LCOV_HOME/share/lcov/support-scripts
 directory of the release.

 Related options:
   --annotate-script, --criteria-script, --version-script

f) Performance

 lcov/genhtml/geninfo have been refactored to parallelize computation
 across multiple cores, if requested.
 In general, this provides speedup that is nearly linear in the number
 of cores.
 There is also an option to throttle parallelism to not exceed peak
 memory consumption contraints, as well as options to enable simple
 profile data collection - so you can see where time in going and
 thus to hint at potential optimizations.  The ''
 script can be used to view generated profile data..

 See the genhtml/lcov/geninfo man pages for details

 Related options: --parallel, --memory, --profile

In general, the new features and options are implemented uniformly in lcov, genhtml, and geninfo. Most of the features can be enabled/disabled using either command line options or by setting defaults in your 'lcovrc' file. See the lcovrc man page for details.

  1. Questions and comments

See the included man pages for more information on how to use the LCOV tools.

In case of further questions, feel free to open a new issue using the issue tracker on the LCOV code repository site at:

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