• From a remote network host
• From the boot sector of a floppy disk
• From a file on a DOS partition

• The boot image will be located starting at 0x100000.
• The boot directory (64 entries) will be located at offset 0 of the boot image (also 0x100000.
• Entry 0 in the directory must be the directory itself (be_offset = 0, be_type = BE_TYPE_DIRECTORY, be_size = 1, be_vsize = 1)
• Entry 1 in the directory must be the 2nd stage loader (or kernel if the kernel is sufficiently simple). be_offset = 1, be_type = BE_TYPE_BOOTSTRAP
• Once the Image is loaded, control is transferred to boot_dir->bd_entry[1].be_extra1 + 0x101000;
• The bootstrap entry point looks like:
  void _start(uint32 mem, char *params, boot_dir *bd);
  mem = system memory size (in bytes), params = zero terminate parameter string, bd = 0x100000
• The last entry will be of type BE_TYPE_NONE to indicate the end of the directory

typedef struct {
    char          be_name[32];  /* asciiZ   */
    unsigned int  be_offset;    /* 4K pages */
    unsigned int  be_type;      /* BE_*     */
    unsigned int  be_size;      /* 4K pages */
    unsigned int  be_vsize;     /* 4K pages */
    unsigned int  be_extra0;
    unsigned int  be_extra1;
    unsigned int  be_extra2;
    unsigned int  be_extra3;
} boot_entry;

typedef struct {
    boot_entry bd_entry[64];
} boot_dir;

#define BE_TYPE_NONE         0  /* empty entry            */
#define BE_TYPE_DIRECTORY    1  /* directory (entry 0)    */
#define BE_TYPE_BOOTSTRAP    2  /* bootstrap code object  */
#define BE_TYPE_CODE         3  /* executable code object */
#define BE_TYPE_DATA         4  /* raw data object        */
#define BE_TYPE_ELF32        5  /* 32bit ELF object       */

/* for BE_TYPE_CODE / BE_TYPE_BOOTSTRAP */
#define be_code_vaddr be_extra0 /* virtual address (rel offset 0)     */
#define be_code_ventr be_extra1 /* virtual entry point (rel offset 0) */

# Boot Image for stock OpenBLT
#

[bootstrap]
type=boot
file=boot/boot.bin
ventry=128

[kernel]
type=code
file=kernel/kernel.bin

[namer]
type=code
file=srv/namer/namer.bin

[console]
type=code
file=srv/console/console.bin

A mechanism for defining your own types and meanings for the extra[0123] fields will be available soon. The name in the []'s starting the section will be placed in be_name. The first entry should be a bootstrap entry (as the bootloader will transfer control into it whether it is or no.

bootmaker <descr_file> <bootimage_file> [ -floppy ]

The bootmaker util reads the descr_file, writes the bootimage_file, and if the optional -floppy flag is specified, the bootimage_file will be a disk image suitable for rawriting or copying with dd.

boot.com bootfile
Will load the boot image in bootfile to 0x100000 and transfer control to it as described above.

boot.com net=ip=x.y.z.w
Will load the netboot bootstrap out of netboot.bin (this will be bundled in boot.com in the next revision) and start a netboot server, waiting for a unix netboot client to send it a boot image file (see below).