Fedora: Building External Kernel Modules (Screenplay)

Prerequisite: Build Entire Kernel

  • A kernel module is built against the kernel it will be loaded into

  • The exact kernel version matters: there is no backward compatibility

  • Kernel module uses symbols from the kernel

    • Core kernel modules

    • The kernel proper itself

This means that, as a prerequisite the entire target kernel needs to be built.

We used to make modules in the past, so Module.symvers was created for the in-tree modules. However, nowadays the build complains,

WARNING: modpost: Symbol info of vmlinux is missing. Unresolved symbol check will be entirely skipped.

See this message for background; to us this means we need to build the entire kernel.

Build Modules

(See here for the whole story.)

$ MODULE_SRC=/home/jfasch/kernel-training/jf-kernel-course/drivers
$ KERNEL_BUILD=/home/jfasch/kernel-training/kernel-exploded-git-tree
$ DEPLOYMENT=/home/jfasch/kernel-training/deployment

$ cd $MODULE_SRC
$ make -C $KERNEL_BUILD M=$(pwd)

Install Modules

You might want to copy the modules into one deployment location, especially if your external modules tree spans subdirectories.

$ make -C $KERNEL_BUILD M=$(pwd) INSTALL_MOD_PATH=$DEPLOYMENT modules_install