I wanted to make my OpenWrt firmware (ipq806x) compatible with the official one. And it fails to do so. It's all because in my .config file there is an option CONFIG_KERNEL_KALLSYMS=y, and in the official kernel there is no this option.
Probably guilty of this:
bool "Compile the kernel with symbol table information"
default y if !SMALL_FLASH
This will give you more information in stack traces from kernel oopses.
That is, it can be seen that there is a difference when build one target and build all targets at a time.
Recently there was a similar problem with the build system:
PS. It's too bad that the all official firmwares does not contain a kernel config! This really needs to be fixed!