does Barebox bootloader works on cortex m4? I want to boot uCLinux on the stm32f4 but I don't have enough knowledge about Barebox. is it possible to port Barebox for cortex m4? if yes, how?

The short answer is no. but the barebox community is working on it to bring barebox to cortex m devices too. I suggest you to use u-boot for now because it supports many cortex m socs (m3, m4 and m7).

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you can easily port barebox for any cortex m mcu. you can use u-boot drivers to port them to barebox.

you must have a deep knowledge about linux/u-boot driver model.