jhswartz / xfbl

Bootloader (in 512 bytes) for Linux/x86 on a Floppy

xfbl 0.1


INTRODUCTION

    xfbl is a small bootloader for Linux/x86 on a floppy disk.


DISK LAYOUT

    LBA    Component

     0     boot
     1     cmdline
     2     kernel
    ...    initramfs
    ...    free space


BOOT OVERVIEW

    Enable the A20 line via BIOS or i8042.
    Enter unreal mode.
    Load the kernel command line from LBA 1 to 0x7e00.
    Fetch what should be kernel setup code starting at LBA 2.
    Check if what should be the kernel header appears to be valid.
    Tell the kernel about the environment and command line.
    Load the rest of the kernel at 0x00100000.
    Load the initramfs at the address described in "config.s".
    Start Linux.


USAGE

    Create the symbolic link, "ext/kernel".
    Create the symbolic link, "ext/initramfs".
    Populate "ext/cmdline".


INITRAMFS

    By default, the load address and size of initramfs are calculated
    prior to assembly by the script, "misc/generate-config".

    If you would prefer to define these variables manually, create
    "src/config.s" and define the variables INITRAMFS_ADDRESS and
    INITRAMFS_SIZE with your desired values. Then adjust the Makefile
    to avoid regeneration of "src/config.s".


FLOPPY DISTRIBUTION

    For a 1.44MB distribution:
        make dist

    For a 2.88MB distribution:
        make SIZE=2880k dist


ISO9660 DISTRIBUTION

    Populate the "iso" directory with your desired image content, or
    replace the directory with a symbolic link to suitable directory
    elsewhere.

    For a bootable ISO9660 image based on a 1.44MB distribution:
        make iso

    For a bootable ISO9660 image based on a 2.88MB distribution:
        make SIZE=2880k iso


OUTPUT

    Character   Explanation

        .       Sector Read OK
        ?       Sector Read Retry
        3       Sector Read Failed
        2       Old Protocol Version
        1       Bad Kernel Magic


SUGGESTED READING

    The Linux/x86 Boot Protocol