Can I use a custom kernel with prebuilt ROM release?

gregthemadmonk

Hello!

I've compiled a custom Linux kernel according to https://grapheneos.org/build#kernel . Is it possible for me to use it without compiling the whole GrapheneOS ROM? I don't have enough hard drive space (or time xD) to compile entire Android right now

I've tried just replacing .img files in the unpacked zip with .img files from my out/muzel/dist and running flash-all.sh after that, but it just bootloops.

I'm sorry if this isn't an appropriate place to ask things like that, but being the only custom ROM and having the only instruction I found on compiling your own kernel for Pixel 10 series, it seemed like a good idea to ask here.

gregthemadmonk

I was building the wrong version... I checked out 2026020600 and flashing it with fastboot worked perfectly fine

gregthemadmonk

The 2026021200 update seems to have broken this. I received an update, re-downloaded a clean kernel_pixel_muzel repo from a 2026021200 branch, and now flashing the output images from kernel build results in the bootloop. The bootloop occurs before I even get the chance to flash vendor_dlkm and system_dlkm, after flashing boot, dtbo and vendor_kernel_boot and during fastboot flash fastboot.

Were there some new hardening changes that began preventing custom kernel builds (even from unmodified source code) from booting?

gregthemadmonk

fastboot flash fastboot

of course I mean fastboot reboot fastboot 🤦

gregthemadmonk

Still broken as of 2026030200. rm -rfed the kernel repo, did a clean

git clone https://gitlab.com/grapheneos/kernel_pixel_muzel.git -b 2026030200 --recurse-submodules --depth=1 --shallow-submodules
cd kernel_pixel_muzel
./build_muzel.sh --lto=full --repo_manifest="$(realpath .)":"$(realpath aosp_manifest.xml)"

Then flashed boot.img, dtbo.img and vendor_kernel_boot.img from out/muzel/dist and got a bootloop on fastboot reboot fastboot (before even getting to flash system_dlkm and vendor_dlkm).

Is this even supposed to work in the first place?

Johnnyloans

Best of luck mate. I think almost no one on the forum does this. Hopefully it works out (:

gregthemadmonk

Johnnyloans :( I guess might as well just buy a cheap 1TB drive and try my luck with recompiling the whole OS...

Imagine if this also doesn't work though and I was just doing something wrong xD

traveller

If I understand correctly, all components (.img files) need to be re-signed with the same key or something? When I was building GOS, I had to run m, not just m <component>, otherwise I kept getting boot loops with a "corrupted build" message on the phone screen.

gregthemadmonk I guess might as well just buy a cheap 1TB drive and try my luck with recompiling the whole OS...
Imagine if this also doesn't work though and I was just doing something wrong xD

Some people use online/cloud services for building AOSP, can be cheaper (and much faster too) for running such experiment.

Johnnyloans

gregthemadmonk

Perhaps relevant?
2 comments, same thread:

https://discuss.grapheneos.org/d/31546-pixel-10-frankel-kernel-build/2

https://discuss.grapheneos.org/d/31546-pixel-10-frankel-kernel-build/5

gregthemadmonk

Johnnyloans yes, it is! Applying

diff --git a/arch/arm64/configs/gki_defconfig b/arch/arm64/configs/gki_defconfig
index 2efefe74f..11e2f983a 100644
--- a/arch/arm64/configs/gki_defconfig
+++ b/arch/arm64/configs/gki_defconfig
@@ -101,7 +101,7 @@ CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT=y
 CONFIG_MODULES=y
 CONFIG_MODULE_UNLOAD=y
 CONFIG_MODULE_SCMVERSION=y
-CONFIG_MODULE_SIG_FORCE=y
+CONFIG_MODULE_SIG_PROTECT=y
 CONFIG_MODULE_SIG_SHA256=y
 CONFIG_MODPROBE_PATH="/system/bin/modprobe"
 CONFIG_BLK_DEV_ZONED=y

and performing fastboot oem disable-verification before flashing in the bootloader I was actually able to successfully boot the system! I think I saw this flag in the diff between versions somewhere but among other changes didn't think to try it... Thank you! I think it's safe to say that this is

SOLVED

at least for now...

P.S.

traveller I've also rented a server for a day to try building GrapheneOS with kernel artifacts from source, but couldn't get it to produce final images

$ script/finalize.sh
cp: cannot stat '/home/greg/pixel/kernel/grapheneos/2026030200/out/target/product/mustang/obj/PACKAGING/target_files_intermediates/mustang-target_files.zip': No such file or directory

but this is out of the scope for this discussion. Maybe there is a way to flash artifacts as-is, without producing the image but I don't really have time for this right now... maybe later today. I'd actually love to play around with modifying the system just for the sake of it.

P.P.S. BTW, the repeated kernel build actually takes longer on a server since most of the time is spent in a non-parallelizeable linking of the kernel rather than compiling a lot of files and the server's CPU freq is lower than my PC's. lol. I imagine it would still be quite the opposite for the whole Android, but I've read it's pretty good at not doing full rebuilds once the first one is done. Probably will end up buying a cheap SSD for this - would cost less than a server, and without time restrictions xD

traveller

gregthemadmonk

honestly never tried building it on cloud, just heard AOSP devs are doing that and it takes them several (something like 2-3) hours. On my laptop the full Graphene build takes around 10 hours, which is painful. I do a rebase to the newer tags, and sometimes to make it build I need to delete the build directory, and the whole process repeats over again.

Just wondering what are you doing with the kernel, any interesting modifications, or just building it for educational purposes?

gregthemadmonk

traveller AOSP devs are doing that and it takes them several (something like 2-3) hours

I left it overnight so don't know how long exactly it took... but probably something like that too...

traveller Just wondering what are you doing with the kernel, any interesting modifications, or just building it for educational purposes?

Just playing around enabling flags, mostly just for the sake of it. It's my first Pixel phone and the excitement of being able to just enable stuff didn't wear off yet :)

The things that I've enabled that are actually useful are SYSV_IPC (for software compatibility in chroot) and BINFMT (for box64) - I'm trying to replace the laptop completely with my phone for working away from home. I know rooting etc. goes against what GrapheneOS stands for, but it seems like the only available base to start with (for Pixel 10 Pro XL).

Also it would be nice (when I get more drive space) to dig a little into the desktop mode code, since atm it doesn't work properly with my 1920x1200 dock display (Android thinks it's a 1920x1080 and the picture is stretched a little - nothing critical, but an annoyance nontheless). Also I'm still looking (although not particularly thoroughly) into making the flashlight toggle by long power button press when the screen is off - I really miss this feature from custom ROMs on my older phones.

traveller do a rebase to the newer tags

Oh, do you have some cool features you've made for yourself? Or are you also doing it for education/fun?

traveller

gregthemadmonk Or are you also doing it for education/fun?

Same reason, mostly for education, happy that I can tinker with the parts of the operating system (and there is no extremely annoying certificates/provisioning profiles hassle, like they have on iOS even for personal apps).