Default [Help] Kernel building issue

Hello everyone !

I try to build my own kernel from CM source but i'm facing a strange problem.
I try two different method :

1 / - Clone CM kernel source
- Add fix variant commit
- Unpack ramdisk from CM rom
- Build succed
----> LG Logo for 1 sec then just a black screen.

2/ - Clone savoca kernel source (wich works of course)
- Adapt build script
- Build succed
-----> LG Logo for 1 sec then just a black screen

Here is my configuration :
- Ubuntu 14 64bits
- Toolchain : arm-eabi-4.7 from google / android-arm-eabi-4.7 from linaro


I don't know what to do ...
Maybe it's related to mkbootfs / mkbootimg / dtbTool ?

Thanks for the help !

And sorry for my english (french) !

Have a good day
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Device - LG G2 - D802 //