I know, to some people, this question may seem illogical, but I have tried every possible solution available. I want to flash a 64 bit AOSP phusson's GSI in my Redmi S2, which has stock 32 bit OS, however, the CPU is capable of 64 bit. I tried directly to install 64 bit gsi but it failed and repeatedly booted into fastboot rather than system. Then I read somewhere that it was so because it'd kernel too is 32 bit. I gathered 64 bit source files for my phone, compiled it and tried to flash it but the kernel was looping over and over in bootloader. What should I do to install a 64 bit ROM? (32BU It GSI is working in my phone)
You will need to recompile your entire ROM as 64 bit, then flash the GSI
GSIs will need the vendor and kernel and well everything else to be 64 bit
This is not a task for the faint heart, but I'm sure you can find a guide somewhere. Even so, the source ROM may not have the required 64 bit libraries, so you'll have to include those. Basically the only way to bring 64 bit support is a 64 bit ROM. Not undoablle, but not easy.