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- README file for the LTP GCOV extension (LCOV) -
- Last changes: 2022-10-04
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Description
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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 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 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. An example of how to access kernel coverage data
4. An example of how to access coverage data for a user space program
5. New features (compared to lcov 1.16).
6. 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/geninfo - Internal tool (creates LCOV data files)
bin/genpng - Internal tool (creates png overviews of source files)
bin/install.sh - 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
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
3. An example of how to access Linux kernel coverage data
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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.
4. 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 app.info
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
genhtml app.info
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.
5. 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 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, --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
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) 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, --hierarchical,
--show-owners, --show-noncode, --show-navigation
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, --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 'spreadsheet.py'
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.
6. 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