Yes, the __sramdata in the declaration is a mistake, the correct target section for that global needs to be .pmusram.data. This used to be in .sram.data once upon a time but then the suspend.c stuff got added and required it to be moved to PMUSRAM. I guess they forgot to update that part in the declaration and since the old GCC seemed to silently prefer the attribute in the definition, nobody noticed. Please apply CJKay's first patch to fix the warning.

You'll probably want to write a function like this: