The 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