The sources for this loader can be found in directory
linux/arch/alpha/boot
of the Linux kernel source distribution. It loads the Linux kernel by
reading START_SIZE bytes starting at disk offset
BOOT_SIZE+512 (also in bytes). The constants
START_SIZE and BOOT_SIZE are defined in
linux/include/asm-alpha/system.h. START_SIZE
must be at least as big as the kernel image (i.e., the size of the
.text, .data, and .bss segments). Similarly,
BOOT_SIZE must be at least as big as the image of the raw
bootstrap loader. Both constants should be an integer multiple of the
sector size, which is 512 bytes. The default values are currently
2MB for START_SIZE and 16KB for BOOT_SIZE.
Note that if you want to boot from a 1.44MB floppy disk, you have to
reduce START_SIZE to 1400KB and make sure that the kernel
you want to boot is no bigger than that.
To build a raw loader, simply type make rawboot in
/usr/src/linux. This should produce the following files in
arch/alpha/boot:
tools/lxboot:The first sector on the disk. It contains the offset and size of the next file in the format described above.
tools/bootlx:The raw boot loader that will load the file below.
vmlinux.nh:The raw kernel image consisting of
the .text, .data, and .bss segments of the
object file in /usr/src/linux/vmlinux. The
extension .nh indicates that this file has no object-file
header.
The concatenation of these three files should be written to the
disk from which you want to boot. For example, to boot from a floppy,
insert an empty floppy disk in, say, /dev/fd0 and then type:
cat tools/lxboot tools/bootlx vmlinux >/dev/fd0
You can then shutdown the system and boot from the floppy by
issuing the command boot dva0.