3.1.3 The address fields of Multiboot header

All of the address fields enabled by flag bit 16 are physical addresses. The meaning of each is as follows:

header_addr

Contains the address corresponding to the beginning of the Multiboot header — the physical memory location at which the magic value is supposed to be loaded. This field serves to synchronize the mapping between OS image offsets and physical memory addresses.

load_addr

Contains the physical address of the beginning of the text segment. The offset in the OS image file at which to start loading is defined by the offset at which the header was found, minus (header_addr - load_addr). load_addr must be less than or equal to header_addr.

load_end_addr

Contains the physical address of the end of the data segment. (load_end_addr - load_addr) specifies how much data to load. This implies that the text and data segments must be consecutive in the OS image; this is true for existing a.out executable formats. If this field is zero, the boot loader assumes that the text and data segments occupy the whole OS image file.

bss_end_addr

Contains the physical address of the end of the bss segment. The boot loader initializes this area to zero, and reserves the memory it occupies to avoid placing boot modules and other data relevant to the operating system in that area. If this field is zero, the boot loader assumes that no bss segment is present.

entry_addr

The physical address to which the boot loader should jump in order to start running the operating system.