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------------------------------------------------- - README file for the LTP GCOV extension (LCOV) - - Last changes: 2023-05-22 ------------------------------------------------- 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 has recently been enhanced to support 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 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/py2lcov - Tool to translate Python Coverage.py to lcov format bin/geninfo - Internal tool (creates LCOV data files) bin/genpng - Internal tool (creates png overviews of source files) 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 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 To view the collected coverage information, point your browser to .../cover_db/coverage.html after running the tests. Note that the testcases are 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 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. 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. 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, --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, --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. 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 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 support Added 'py2lcov' and 'perl2lcov' scripts. - 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. 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
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