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$Id: README,v 1.1 2002/11/25 02:07:53 rminnich Exp $
A project to combine coreboot and BOCHS BIOS to add support
for booting legacy applications, such as Microsoft Windows.
Boot Overvew:
ADLO requires an boot loader with ELF support.
In our case it is either coreboot or EtherBOOT.
Sample execution paths:
coreboot -> ADLO -> LILO -> LINUX
coreboot -> EtherBOOT -> ADLO -> LILO -> LINUX
Then it can start any real mode application.
In our case it could be LILO or GRUB, but
choices are not limited to this.
ADLO overview:
-Elf header
-mainteance routines
-bochs bios
-vga bios
Elf header
hand crafted binary. Currently there are 3 diff binaries
for three different sizes of payload (65kb,113kb,129kb).
they are catted at beginning of file
mainteance routines
this is the loader.s file which gets compiled into loader.o binary
it is catted 2nd right after elf header and it is where
control is being transfered when the elf is executed.
it consist of :
select device to boot
set memory for Int15/EAX=E820
enable LBA
copy coreboot table [TODO]
-shadow :
bochs @ 0xF00000
video bios (binary only) @ 0xC00000
from Real to Protected Mode
jmp to the bios at 0xFFFF:0x0000
we must have bios payload always at 1kb
offset from start of ELF payload so loader.o
must be always 1024 bytes.
we have taken the boch's project and just extracted
its bios from it only. it took us (so far) only
minor modifications in order to make it work.
basically it is the following directory in the
bochs sources
of all files there the rombios.c is the key file.
Most of the times our patches are against current
version of the rombios.c file. We try to feed back
the patches to bochs maintainers so that's possible
to use the bochs bios as is.
the boch's related stuff are in bochs subdirectory.
building boch's bios is as simple as
cd bochs/bochs-cvs/bochs/bios
the resulting file rombios.bin is our bios image.
At present time, it is recommended to use
dev86-0.16.3 + my patch in order to compile
bochs' bios. The dev86 package can be found
prepatched sources at:
Video BIOS
Video BIOS we use is binary only, so far.
At the present time we are using the original
Video BIOS as supplied from the system.
To get the image simply type:
make makevideobios
The right thing will happen. For refernece the
magic line in the Makefile is:
dd if=/proc/kcore \
of=./video.bios.bin \
bs=1 count=65536 skip=790528
We assume it is located at 0xC00000-0xE00000
and we use 'dd and /proc/kcore to extract it
(obviously it works as root only).
Obviously it needs to be done with original
(as shipped by manufactuer bios) so it should
be done as the first step of the ADLO setup.
The /proc/kcore is in ELF format (linux kernel
2.4.x and later) so if we want to get accurate
image of ram we must skip the ELF header.
The magic command is :
readelf -a /proc/kcore
Program Headers:
Type Offset VirtAddr PhysAddr FileSiz MemSiz
NOTE 0x0007d4 0x00000000 0x00000000 0x005b0 0x00000
LOAD 0x001000 0xc0000000 0x00000000 0xff60000 0xff60000
There we look for the first LOAD section, and see what
is its offset (for us it is 0x1000)
64KiB = 65536
0x0C 00 00 + 0x10 00 = 790528
On technical note in our case video bios
is just 48kb, but for paranoia sake we copy
Environment overview
ADLO is an ELF file and thus can be loaded either directly from 1)
coreboot, or 2) via EtherBOOT, or 3) via EtherBOOT+ AA patch for FS
Both coreboot and ADLO are on the same EEPROM chip. From end-user
viewpoint it is probably the most similar to the bios classic.
(computer boots up and just loads whatever is in MBR).
Set it up in /tftpboot directory on dhcp/tftp server and have it served
from there. (this is how we did the development)
Use AA patch and put it as /kernel file and it will be then loaded by
etherboot from local hard disk.
Before ADLO starts.
ADLO requires an boot loader with ELF support.
In our case it is:
-coreboot and EtherBOOT
-coreboot and EtherBOOT + AA polled I/O patch (w/ FS support).
As little as coreboot only is required to get ADLO
up and running.
For development purposes it is recommended full set of
coreboot + EtherBOOT and boot via DHCP/TFTP.
After ADLO finish.
ADLO will attempt to locate the first hard disk
and read MBR from it and execute.
Then it can start any real mode application.
In our case it could be LILO or GRUB
but choices are not limited to this.
In our case it would cause LILO to load
(fully usable) and from there it was able to
execute simple programs. so far the list
of the program is limited to linux which
runs somewhat. More to come in future.