Circular buffer on flash

As is commonly known, many STM32 MCUs, including the STM32F103 used on the Blue Pill boards, contains more non-volatile flash storage than is advertised by ST. On my own Green Pill board a STM32F103C8 MCU is used. This MCU has got - according to ST, 64kB of flash, but in reality it is identical to the STM32F103CB and it does have 128kB of flash. This is documented in quite some detail here.