Trouble with installing a patched vanilla upstream kernel

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Hi, I’ve been following this guide to build and install a custom kernel. I’m specifically targeting Fedora with the Asahi kernel.

I’m running into some weird issues and I don’t know what all is going wrong. But here’s what I’ve been doing (let me know if I’m missing anything important):

  1. I clone the Fedora Asahi kernel.
  2. I copy the config file from /boot/config-6.6.3-411.asahi.fc39.aarch64+16k to ./.config
  3. I modify the Makefile and set EXTRAVERSION = -custom.
  4. I run make oldconfig.
  5. I run make Image (I saw online that bzImage is changed for arm64).
  6. I run make -j4 (I saw online that make modules is redundant now). I should have a linux image built.
  7. I then run sudo make modules_install. It seems to have worked as now there’s a folder /lib/modules/6.6.3-custom
  8. I run sudo make install. It seems to have worked as now there’s a file /boot/vmlinuz-6.6.3-custom.

Now when I reboot my machine and run uname -r it prints out 6.6.3-custom. So I think that means it worked right? Or were there extra steps I needed to do? I thought I would have to modify some bootloader files but does sudo make install take care of that?

Well I try to do it all again with a patched version of the kernel. I clone kernel-asahi, but this time I modify the source files. I again modify the Makefile but this time set EXTRAVERSION = -modified. I run all the same commands as before, but when I reboot, uname -r still prints 6.6.3-custom instead of 6.6.3-modified. Why didn’t my patched kernel get booted up correctly?

I think I’m making some sort of mistake in the process, but I’m not sure what’s missing as I’m following that guide pretty closely…

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Added kernel, kernel-install

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Did you build create the -modified versions?
Check the files in your build tree to see what you have.

Also did you keep all the output from all the makes?
When I do this sort of thing I keep logs of all output so I can go back and see what was done.
Can you compare your custom build vs. your modified build?

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Did you clean out the old compilation files before recompiling the newer kernel.
make clean should remove all the previous object files and allow a new full compile with the new settings. Without that it will not recompile and link already existing object files.

This is a part of the way make works.

1 Like
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The -custom and -modified versions were created from 2 different git clone instances, so there was nothing to clean.

I did some digging and it looks like make install isn’t updating the BOOT_IMAGE parameter in the /proc/cmdline file

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/proc/cmdline is a read-only copy of the kernel command line at boot.
Its not an input.

What is the booting your system? grub? You need to change that boot managers config.

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How do I update grub to use my custom kernel? Do I just use sudo grubby --set-default? Or are there extra steps? Do I need to call grub2-mkconfig as well?

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Research grub bls (boot loader spec) and create a bls file for grub pointing to your kernel. I do not know the details off the top of my head but know it is well documented so you should be able to get this working.

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Running sudo grubby --set-default with my -custom kernel as input, and then calling grub2-mkconfig seems to have worked. I don’t know if that’s the “right” way to do it, but at least now uname -r returns the name of my -custom kernel. Is that sufficient proof or could it be a red herring?

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That just picks which one of the installed kernels to boot.
It does not add a newly built kernel to grub.