Re: [PATCH] CMakeLists.txt: Remove custom `LIB_INSTALL_DIR` handling

[Alan Maguire <alan.maguire@oracle.com>]

On 20/04/2025 07:42, Paul Menzel wrote:
> There is no need to explicitly set `LIB_INSTALL_DIR`, as CMake’s module
> GNUInstallDirs sets it itself from `CMAKE_INSTALL_LIBDIR`, and takes
> care of everything, so the line below is enough.
> 
>     cmake -DLIBBPF_EMBEDDED=OFF -DCMAKE_INSTALL_LIBDIR=lib ..
> 
> Note, it’s common to set it to a relative path, but absolute paths are
> allowed too.
> 
>     cmake -DLIBBPF_EMBEDDED=OFF -DCMAKE_INSTALL_LIBDIR=/opt/usr/lib64 ..
> 
> From the [CMake documentation][1]:
> 
>> CMAKE_INSTALL_<dir>
>>
>> Destination for files of a given type. This value may be passed to the
>> DESTINATION options of install() commands for the corresponding file type.
>> It should be a path relative to the installation prefix so that it can be
>> converted to an absolute path in a relocatable way.
>>
>> While absolute paths are allowed, they are not recommended as they do not
>> work with the cmake --install command's --prefix option, or with the cpack
>> installer generators. In particular, there is no need to make paths
>> absolute by prepending CMAKE_INSTALL_PREFIX; this prefix is used by
>> default if the DESTINATION is a relative path.
> 
> So, remove the custom handling from `CMakeLists.txt`. Also, update
> `README` and mention the option.
> 
> [1]: https://cmake.org/cmake/help/v3.31/module/GNUInstallDirs.html
> 
> Link: https://lore.kernel.org/all/9fb4f7ba-0de1-4f75-9bd2-66212ca8cd86@molgen.mpg.de/
> Fixes: a2abd9482162 ("CMakeList.txt: Respect CMAKE_INSTALL_LIBDIR")
> Signed-off-by: Paul Menzel <pmenzel@molgen.mpg.de>

Sorry Paul, left you hanging here. Above seems reasonable - any issues
with this from anyone (I've cc'ed Ben who made changes in this area before)?

If not I'll apply early next week. Thanks!

Alan

> ---
>  CMakeLists.txt | 5 -----
>  README         | 4 ++++
>  2 files changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/CMakeLists.txt b/CMakeLists.txt
> index eb87300..844ab61 100644
> --- a/CMakeLists.txt
> +++ b/CMakeLists.txt
> @@ -23,7 +23,6 @@ endif()
>  
>  # Use the standard library installation directory
>  include(GNUInstallDirs)
> -set(CMAKE_INSTALL_LIBDIR "lib" CACHE STRING "libdir name")
>  
>  # where to look first for cmake modules,
>  # before ${CMAKE_ROOT}/Modules/ is checked
> @@ -75,10 +74,6 @@ if(NOT LIBBPF_FOUND AND NOT EXISTS "${PROJECT_SOURCE_DIR}/lib/bpf/src/btf.h")
>  	message(FATAL_ERROR "The submodules were not downloaded! GIT_SUBMODULE was turned off or failed. Please update submodules and try again.")
>  endif()
>  
> -if (NOT DEFINED LIB_INSTALL_DIR)
> -    set(LIB_INSTALL_DIR "${EXEC_INSTALL_PREFIX}${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_LIBDIR}")
> -endif()
> -
>  # libbpf uses reallocarray, which is not available in all versions of glibc
>  # libbpf's include/tools/libc_compat.h provides implementation, but needs
>  # COMPACT_NEED_REALLOCARRAY to be set
> diff --git a/README b/README
> index a938266..fb92d68 100644
> --- a/README
> +++ b/README
> @@ -18,6 +18,10 @@ cmake Options:
>      Default is to install to /usr/local, use -DCMAKE_INSTALL_PREFIX=
>      when invoking cmake to specify another install location.
>  
> +  -DCMAKE_INSTALL_LIBDIR
> +    Default is to install to lib or lib64, use -DCMAKE_INSTALL_LIBDIR=
> +    when invoking cmake to specify another install location.
> +
>  You may need to update the libbpf git submodule:
>  
>  git submodule update --init --recursive