Unable to reach (null) from global pointer - multiple onchip rams for applications

It looks like the linker is trying to use relarive addressing but your bss and text_data on chip memories are too far away in the address space. I would first try and manually edit the addresses of your onchip memories so that they are contiguous in the memory space, and if this is not enough write a custom link script that declares a single space including all the onchip memories and that maps all the sections (except heap and stack) to that space.