/dev/boot
/dev/kexec
/dev/mem

Boot is a write-only file that accepts 4 bytes representing a kernel address, high-order byte first. The system will transfer control to that address, which is assumed to be the start of low-level reboot code. There is no return from the write on success or failure.

Kexec is a write-only file to which an uncompressed kernel image can be written, a chunk at a time. When the file is closed, the system will transfer control to the start of the image, which again is assumed to be low-level reboot code.

Mem copies data to and from kernel memory, taking the current file offset as an address therein.

Boot flushes caches as necessary to ensure that writes to kernel memory through any of these files will be visible when subsequently executed as instructions.