volk CMakeLists.txt uses CMAKE_INSTALL_LIBDIR without including the 'GNUInstallDirs' module

[fventuri]

I am running Linux Fedora Core here, where for 64bit libraries LIBDIR is expected have the suffix '64' (i.e. /usr/local/lib64).
I noticed today that instead volk installed the shared library and the cmake config files under /usr/local/lib.

I then looked at the volk configuration for cmake (CMakeLists.txt), and I saw that there's code there to decide between lib vs lib64 (https://github.com/gnuradio/volk/blob/main/CMakeLists.txt#L205-L210), however that codes uses the variable CMAKE_INSTALL_LIBDIR.
According to the cmake documentation (https://cmake.org/cmake/help/latest/module/GNUInstallDirs.html) that variable is defined in the GNUInstallDirs module, but I don't see that cmake module included anywhere, and indeed when I added a message() statement to print the value of CMAKE_INSTALL_LIBDIR right before the check above, the value turned out to be empty.

Thanks,
Franco

[jdemel]

I would expect that

volk/CMakeLists.txt

Lines 199 to 201 in f2fb33c

	if (${CMAKE_INSTALL_LIBDIR} MATCHES lib64)
	set(LIB_SUFFIX 64)
	endif()

needs an update here.

e.g. we could use something like:

include(GNUInstallDirs)

How does that affect custom install prefixes? e.g. a conda prefix might not differentiate between the different suffixes.
What happens if this CMake module is used on Windows? I saw a comment regarding homebrew.

[fventuri]

@jdemel - instead of including the module GNUInstallDirs, another option could be to follow the approach used by GNU Radio, where it looks like they have a special case for the RedHat/Slackware family of distributions (which Fedora is part of): https://github.com/gnuradio/gnuradio/blob/main/cmake/Modules/GrPlatform.cmake#L38-L49

In that case you'll also need the code above that, where they set the variables 'REDHAT' and 'SLACKWARE'.

Franco

[jdemel]

I would really prefer to use GNUInstallDirs here. Trying to fix this like GR does, has the potential to open a can of worms.

How would this go along with a conda environment? conda envs seem to use suffix-less folders. How should CMake be configured in these cases?

[fventuri]

The other day I thought about asking @willcode about this issue, since I think he runs Fedora Core too, so he might already have figured out a way to deal with the 'lib64' suffix in Volk.

As per conda my go-to person is @ryanvolz ,since he knows it inside and out, and he might have a recommendation about using GNUInstallDirs.

Franco

[ryanvolz]

I've had to override LIB_SUFFIX for a long time for Conda to get the correct behavior, since all of that logic implicitly assumes that the installation environment is on the build machine. Without looking at the history, I assume that LIB_SUFFIX is from a time before GNUInstallDirs existed, and if that code is being updated it would be best to do away with LIB_SUFFIX entirely and use the CMAKE_INSTALL_LIBDIR that comes from including GNUInstallDirs. I still might have to override that in a conda recipe, but at least that's a standard CMake thing that's needed for a lot of projects and not a GR-and-friends thing.

So bottom line, include GNUInstallDirs to fix the immediate problem, and if you want to completely modernize then ditch LIB_SUFFIX entirely. Packagers will be able to adapt regardless (if they are aware of any changes).

[jdemel]

GNUInstallDirs seems to be the way to go. From the docs:

CMAKE_INSTALL_LIBDIR

object code libraries (lib or lib64)

On Debian, this may be lib/<multiarch-tuple> when [CMAKE_INSTALL_PREFIX](https://cmake.org/cmake/help/latest/variable/CMAKE_INSTALL_PREFIX.html#variable:CMAKE_INSTALL_PREFIX) is /usr.

I wanted to write about what to do in detail but decided a PR with the necessary changes is actually the faster way. Thus see #742