arm kernel won't boot when compiled with gcc > 9

[Thomas Meyer]

Hi,

currently I do play around a bit with my android phone and I want to
compile the vendor kernel myself, but I did encounter a strange
phenomena.

The vendor kernel is based on 3.18.x and I did apply some patches from
current upstream so it does compile with gcc 9/10.

The kernel compiles successfully, but it the boot hangs for unknown
reasons.

gcc 4.9.2 -> compiles and boots
gcc 7.5.0 -> compiles and boots
gcc 8.4.0 -> compiles and boots
gcc 9.2.1 -> compiles but doesn't boot (this is the arm cross compiler
from fedora 32)
gcc 9.3.0 -> compiles but doesn't boot
gcc 10.2.0 -> compiles but doesn't boot.

as I have no UART and no fbcon or any other debugging capability, can
somebody in this mailing list think of something obviously that I may
miss or encounter in my endeavour?

PS: code is here: https://github.com/thomasmey/linux/commits/motorola-msm-potter-v3.18.x

with kind regards
thomas