+The :program:`llvm-cov` tool reads code coverage data files and displays the
+coverage information for a specified source file. It is compatible with the
+``gcov`` tool from version 4.2 of ``GCC`` and may also be compatible with
+some later versions of ``gcov``.
+
+To use llvm-cov, you must first build an instrumented version of your
+application that collects coverage data as it runs. Compile with the
+``-fprofile-arcs`` and ``-ftest-coverage`` options to add the
+instrumentation. (Alternatively, you can use the ``--coverage`` option, which
+includes both of those other options.) You should compile with debugging
+information (``-g``) and without optimization (``-O0``); otherwise, the
+coverage data cannot be accurately mapped back to the source code.
+
+At the time you compile the instrumented code, a ``.gcno`` data file will be
+generated for each object file. These ``.gcno`` files contain half of the
+coverage data. The other half of the data comes from ``.gcda`` files that are
+generated when you run the instrumented program, with a separate ``.gcda``
+file for each object file. Each time you run the program, the execution counts
+are summed into any existing ``.gcda`` files, so be sure to remove any old
+files if you do not want their contents to be included.
+
+By default, the ``.gcda`` files are written into the same directory as the
+object files, but you can override that by setting the ``GCOV_PREFIX`` and
+``GCOV_PREFIX_STRIP`` environment variables. The ``GCOV_PREFIX_STRIP``
+variable specifies a number of directory components to be removed from the
+start of the absolute path to the object file directory. After stripping those
+directories, the prefix from the ``GCOV_PREFIX`` variable is added. These
+environment variables allow you to run the instrumented program on a machine
+where the original object file directories are not accessible, but you will
+then need to copy the ``.gcda`` files back to the object file directories
+where llvm-cov expects to find them.
+
+Once you have generated the coverage data files, run llvm-cov for each main
+source file where you want to examine the coverage results. This should be run
+from the same directory where you previously ran the compiler. The results for
+the specified source file are written to a file named by appending a ``.gcov``
+suffix. A separate output file is also created for each file included by the
+main source file, also with a ``.gcov`` suffix added.
+
+The basic content of an llvm-cov output file is a copy of the source file with
+an execution count and line number prepended to every line. The execution
+count is shown as ``-`` if a line does not contain any executable code. If
+a line contains code but that code was never executed, the count is displayed
+as ``#####``.
+