Compiling kernel module only w/o whole kernel compilation

如何只编译内核的单个模块，然后reload新的模块呢？本文以kvm kernel module为例，阐述下具体的过程。本文转载自: Compiling kernel module only w/o whole kernel compilation

1. Introduction

I was tried to modify a kvm kernel module for my research. Because it was a built-in kernel module, I needed to build all the kernel source code after modifying kvm module which is located in path arch/x86/kvm/ from the linux kernel source root.

The whole kernel compilation was a time consuming job, usually taking over 10 minutes even on my i7 desktop machine. I tried to find a way to compile modules only without the whole kernel compilation. The solution and some troublesomes are described below.

2. Assumption

It is assumed that you have a kernel source code and configured it properly according to your taste. Also, assumed that you had installed the kernel and rebooted with it.

3. Solution

Building only one module is easy. After configuring, build the source as following.

1 2	make M=path/to/module/directory make M=path/to/module/directory modules_install

You can find the path of modules with modinfo command.
In my case, the required module was kvm.ko, and kvm-intel.ko. They were located in arch/x86/kvm.

1 2	make M=arch/x86/kvm make M=arch/x86/kvm modules_install

You can reload the new modules. I removed the kvm-intel module first because it depends on the kvm module.

1	sudo rmmod kvm-intel kvm

And, load the new modules.

1	sudo modprobe kvm-intel

Loading kvm-intel will load kvm automatically.

FYI: the new modules are installed in /lib/modules/`uname -r`/extra directory.

4. Troublesomes

4.1 `modprobe` failure.

1	modprobe: error: could not insert 'kvm': exec format error

The modprobe might fail if the version of a kernel module and that of a kernel are different. You can check the error with dmesg after the modprobe failure.

In my case, I built the kernel without any modification which resulted in the version number of 4.13.0-rc6. When I modified the kvm module and compiled it, the version number was changed to 4.13.0-rc6+.

My solution was building the kernel with some small modifications generating the version number as 4.13.0-rc6+ as a baseline.
The problem solved because the kvm module was also built with the same version number, 4.13.0-rc6+, which did not produce any modprobe error.

4. 2 Location of generated modules

The modules generated with M=path options are installed into /lib/modules/`uname -r`/extra path. The path is different from the originally built one (when compiling the whole kernel) which is /lib/modules/`uname -r`/kernel/arch/x86/kvm in the case of kvm.

If you want to install a new module into the same location of original one, use INSTALL_MOD_DIR option. Example follows.

1	sudo make INSTALL_MOD_DIR=kernel/arch/x86/kvm M=arch/x86/kvm modules_install

如果modprobe中遇到其他问题，请参考commands on Linux kernel modules。

5. Conclusion

make M=arch/x86/kvm
make INSTALL_MOD_DIR=kernel/arch/x86/kvm M=arch/x86/kvm modules_install

rmmod kvm-intel kvm
modprobe kvm-intel

Create a simple shell file under your Linux source code root.

参考资料:

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