EFI stub kernel not working after upgrade (4.12.5) [SOLVED]

[Azimoth]

Hi,

I just tried to upgrade from one stable kernel (4.9.34) to another (4.12.5), but the new kernel is stuck at boot.

The problem alreay existed with 4.10.x kernels so I stayed with 4.9 and hoped for this to be solved with the stabilized kernel.

The system:

- Macbook Pro 8,1 (early 2011)
- Sandy Bridge CPU
- LUKS encrypted BTRFS
- the corresponding .config for the 4.12.5 kernel

I setup the system following Sakaki's EFI Guide
Accordingly I use Sakaki's buildkernel command for kernel upgdates.

How it should work:

As usual on a Mac the screen turns white after the start chime.
If it was a pure Apple system the apple logo would appear now, but since I'm using a EFI stub kernel, the screen remains white for about 13-14 seconds until text output starts to fly by, eventually resulting in a password request to decrypt the hard drive. (By default with plymouth)

The symptoms:
The screen simply remains white forever (well, I never waited longer than 2-3 minutes).

Theories:
iamben from the #gentoo IRC suggested there might be something wrong with the framebuffer, yet there was no way to narrow down the problem.
His best guess was to try to disable FB_EFI, which I did, but this did not change anything.

The question: What change from kernel 4.9 to 4.1x might have caused this problem? What do I have to do to fix this?

[Azimoth]

Thanks to the help and patience of Sakaki I found the solution.

The problem was caused by this part of the kernel .config: