README

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- README file for the LTP GCOV extension (LCOV) -
- Last changes: 2024-11-20
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Description
-----------
  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 a hierarchical directory structure
      view, a flat list of all source files in the project,  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 supports differential coverage, as well   as date- and owner-binning.
  See:
      https://arxiv.org/abs/2008.07947
   or
      https://ieeexplore.ieee.org/document/9438597
  for a detailed explanation of the concepts and several possible use models.

  A video presentation of the basic ideas can be found at
      http://doi.org/10.5281/zenodo.4653252

  In addition, several other features and capabilities have been added.  See
  section 6, 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 in lcov 2.0
  7. Questions and Comments
  8. Filing a new issue



1. 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/perl2lcov      - Tool to translate Perl Devel::Cover data to lcov format
  bin/llvm2lcov      - Tool to translate LLVM 'llvm-cov' JSON data to LCOV format
  bin/py2lcov        - Tool to translate Python Coverage.py to lcov format
  bin/xml2lcov       - Tool to translate Cobertura-like XML coverage data
                       to lcov format
  bin/geninfo        - Internal tool (creates LCOV data files)
  bin/genpng         - Internal tool (creates png overviews of source files)
  lcovrc             - LCOV configuration file
  man                - Directory containing man pages for included tools
  example            - Directory containing an example to demonstrate LCOV
  tests              - Directory containing lcov regression tests
  Makefile           - Makefile providing 'install' and 'uninstall' targets


2. Installing LCOV
------------------
The LCOV package is available as either RPM or tarball from:

  https://github.com/linux-test-project/lcov/releases

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 https://github.com/linux-test-project/lcov.git

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

your PREFIX should be an absolute path.

To run the LCOV regression test suite on your installation:

  $ cp -r $LCOV_HOME/share/test path/to/myTestDir
  $ cd path/to/myTestDir
  $ make [COVERAGE=1]

If desired, you can collect coverage data for the LCOV module by setting
the COVERAGE makefile variable.
Note that the Devel::Cover package must be installed if COVERAGE is enabled
or if you want to use the perl2lcov utility.
To view the collected coverage information, point your browser to
.../lcov_coverage/index.html after running the tests.

Note that the testcases are primarily intended to test LCOV functionality
and not to be easily readable tutorial examples.

3. 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
  - 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
 - Module::Load::Conditional
 - Scalar::Util
 - 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.

To measure Python code coverage, users will need Python packages:

  - Coverage.py

In addition, contributors will need:

  - perltidy

Your platform may support other mechanisms to install and/or update
required packages.



4. An example of how to access Linux kernel coverage data
---------------------------------------------------------
Requirements: Follow the Linux kernel coverage setup instructions at:

  https://docs.kernel.org/dev-tools/gcov.html

As root, do the following:

  a) Resetting counters

     lcov --zerocounters

  b) Capturing the current coverage state to a file

     lcov --capture --output-file kernel.info

  c) Getting HTML output

     genhtml kernel.info

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


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

 a) Capture current coverage state to a file:

   i) C/C++ code:

      Compile your program using the '--coverage' GCC or LLVM
      option. During linking, make sure to specify '--coverage':

        $ gcc -o myTest --coverage simple.c
          OR
        $ gcc -c file1.c file2.c ... --coverage
        $ gcc -o myOtherTest --coverage file1.o file2.o ....

       Run your testcase at least once:

        $ path/to/my/testcase/myTest

       Capture the current coverage state to a file:

         $ lcov --directory path/to/my/testcase --capture --output-file app.info

       If you want to collect Modified Condition / Decision Coverage (MD/DC)
       date, then:
         - you must use gcc/14.2 or newer
         - your compile- and link command line must include flag
           '-fcondition-coverage'
         - your lcov and genhtml command line must include flag
           '--mcdc-coverage'
       See the '--mcdc-coverage' section in the lcov and geninfo man pages.

       Note that runtime coverage data exists only after the application has
       been started and stopped at least once. Otherwise, no data will be found
       and lcov will abort with an error mentioning that there are no
       data/.gcda files.

       The coverage runtime emits data (the .gcda files) in an atexit
       callback.  If your application exits abnormally or crashes before
       the callback is executed, then no coverage data will be available.

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

      See 'man lcov' for more information - especially if your build/test
      environment is not trivial.

   ii) Python code:

     - install the Coverage.py module

     - execute your testcase to produce python coverage data:

         $ COVERAGE_FILE=./pycov.dat coverage run --append --branch \
             myPythonScript [my script args]

     - translate Python coverage data to LCOV format:

         $ py2lcov -o pycov.info [py2lcov_options] pycov.dat [x.dat]+

     See 'py2lcov --help' and the Coverage.py documentation for more
     information.

   iii) Perl code:

     - install the Devel::Cover module

     - execute your testcase to produce perl coverage data:

         $ perl -MDevel::Cover=-db,perlcov_db,-coverage,statement,branch,condition,subroutine,-silent,1 myPerlTest.pl [my script args]

     - translate Perl coverage data to LCOV format:

         $ perl2lcov --output perlcov.info perlcov_db [perl2lcov options]

     See 'perl2lcov --help' and the Devel::Cover documentation for more
     information.

   iv) XML data (for example, generated by Cobertura):

     - translate XM coverage data to LCOV format:

         $ xml2lcov --output myData.info coverage.xml [xml2lcov options]

     See 'xml2lcov --help' and the Cobertura documentation for more
     information.

 b) Generate an HTML coverage report:

    Generate an HTML report, combining all of your LCOV data files:

      $ genhtml -o html_report app.info pycov.info perlcov.info

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

    See 'man genhtml' for more details.

 c) Generate a differential coverage report:

    See the example in .../example (run "make test_differential")
    as well as the examples in .../tests/gendiffcov.


6. New features:
----------------

New features and capabilities fall into 7 major categories:

  a) Categorization

     This refers primarily to differential coverage categorization as
     well as date- and owner-binning.  See https://arxiv.org/abs/2008.07947
     or https://ieeexplore.ieee.org/document/9438597 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, --select-script
        --date-bins, --new-file-as-baseline, --elide-path-mismatch

  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.  Note that ignoring certain errors can cause
     subsequent errors and/or can result in inconsistent or confusing
     coverage reports.
     See the genhtml/lcov/geninfo man pages for details.

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

     Related options:
        --ignore-error, --expect-message-count, --keep-going, --msg-log

  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,
          --suppress-aliases

  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 - possibly
     using case-insensitive comparison.
     (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.)

     During coverage data capture, the --build-directory option can be used
     to specify a search path, to find the .gcno (compile-time coverage data)
     file corresponding to a particular .gcda runtime coverage data) file.
     Similarly, the --source-directory pption can be used to specify a
     search path for source files.

     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
        --build-directory --source-directory

  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'
            and 'gitversion'
        iii) enforce a desired code coverage criteria
             Sample script: criteria
        iv) find source files in more complicated environments - where
            simple substitutions become complicated or unweildy.
        v) select a subset of coverage data to display - e.g., to
           use in a code review which wants to concentrate on only
           the changes caused by a particular commit or range of commits.
         vi) keep track of environment and other settings - to aid
            infrastructure debugging in more complicated use cases.

     The callback may be any desired script or executable - but there
     may be performance advantages if it is written as a Perl module.

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

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

     Related options:
       --annotate-script, --criteria-script, --version-script
       --resolve-script, --select-script, --context-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 constraints, as well as options to enable simple
     profile data collection - so you can see where time is going and
     thus to hint at potential optimizations.  The 'spreadsheet.py'
     script can be used to view generated profile data.

     There are several configuration file options which can be used to
     tweak certain parallelization parameters to optimize performance
     for your environment in cases that the default behaviour is suboptimal.
     See the lcovrc man page for more information.

     See the genhtml/lcov/geninfo man pages for details

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

  g) Language/tool support

     Added 'llvm2lcov', 'py2lcov', 'perl2lcov' and 'xml2lcov' scripts.

       - llvm2lcov:

           translates JSON coverage data generated by 'llvm-cov export -format=text ...'
           to lcov format.

           See "llvm2lcov --help" for brief instruction on how to use the
           translator.  Note tha llvm2lcov uses a similar set of command line
           and configuration file options as lcov, genhtml, and geninfo.

       - py2lcov:

           translates python Coverage.py XML data to lcov format.

           See the Coverage.py documentation at https://coverage.readthedocs.io,
           as well as ".../py2lcov --help"

       - perl2lcov

          translates Perl Devel::Cover data to lcov format.

          See the Devel::Cover documentation at
            https://metacpan.org/pod/Devel::Cover
          to find out how to generate coverage data for Perl code.

          See "perl2lcov --help" for brief instructions on how to
          use the translator.
          Note that perl2lcov uses a similar set of command line and
          config file options as lcov, genhtml, and geninfo.

       - xml2lcov

          translates XML coverage data to lcov format.
          The XML data may come from Cobertura or similar tools.

          See "xml2lcov --help" fir brief instructions on how to use
          the translator.
          See the Coburtura documention for directions on how to
          generate XML data.

     Other languages can be integrated using a similar approach.

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.


7. 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:

  https://github.com/linux-test-project/lcov


8. Filing a new issue
---------------------
Before filing a new issue - and if you are using an LCOV release (as opposed
to using a clone of the github repo) - please verify whether the issue is
still present in the LCOV master version.  See section 2, above for
directions on how to clone and install the most up-to-date LCOV version.

If possible, please include a testcase which illustrates the problem
when you file an issue.
Please describe your environment (platform, compiler, perl, and python
versions,  etc.).  Please include a detailed description of the issue:
what you were trying to do (your goal - not the mechanics of your
procedure), what you did (the mechanics of your procedure), the result
you wanted to see vs. what actually happened.
Depending on the issue, your testcase may need to include source code and
compile/link command lines, directions for how to run your example, the
command lines used to capture and generate your lcov reports, etc.
In other cases, the captured '.info' files may be sufficient to reproduce
the issue.
When in doubt: more is better than less.

If you cannot include a testcase - e.g., because you feel that it is
senstitive or proprietary - then your detailed description is even more
important.
Note that, without an example, it may be difficult or impossible to
diagnose or fix the problem.

Bear in mind that you are asking for help from volunteers.   Your
priority might not be their priority. Civility, consideration and politeness
go a long way.

Please check back and to verify the fix and close the issue once it has
been addressed.
Again:  remember that you are asking for help from volunteers.
Make sure that you are doing your part.