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Add a subsection on the bootloaders

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git-svn-id: svn://svn.openwrt.org/openwrt/trunk@6032 3c298f89-4303-0410-b956-a3cf2f4a3e73
This commit is contained in:
florian 2007-01-08 10:13:55 +00:00
parent 38deb63022
commit 82287902c7
1 changed files with 65 additions and 13 deletions
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docs/adding.tex
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@ -30,14 +30,19 @@ fingerprinting, we will show here an example using \textbf{nmap}:
\begin{Verbatim}
nmap -P0 -O <IP address>
Not shown: 1694 closed ports
PORT STATE SERVICE
631/tcp open ipp
1033/tcp open netinfo
6000/tcp open X11
Device type: general purpose
Running: Apple Mac OS X 10.4.X
OS details: Apple Mac OS X 10.4.8 (Tiger)
Starting Nmap 4.20 ( http://insecure.org ) at 2007-01-08 11:05 CET
Interesting ports on 192.168.2.1:
Not shown: 1693 closed ports
PORT STATE SERVICE
22/tcp open ssh
23/tcp open telnet
53/tcp open domain
80/tcp open http
MAC Address: 00:13:xx:xx:xx:xx (Cisco-Linksys)
Device type: broadband router
Running: Linksys embedded
OS details: Linksys WRT54GS v4 running OpenWrt w/Linux kernel 2.4.30
Network Distance: 1 hop
\end{Verbatim}
nmap is able to report whether your device uses a Linux TCP/IP stack, and if so,
@ -50,7 +55,16 @@ on the device, and which version of the service is being used:
\begin{verbatim}
nmap -P0 -sV <IP address>
Starting Nmap 4.20 ( http://insecure.org ) at 2007-01-08 11:06 CET
Interesting ports on 192.168.2.1:
Not shown: 1693 closed ports
PORT STATE SERVICE VERSION
22/tcp open ssh Dropbear sshd 0.48 (protocol 2.0)
23/tcp open telnet Busybox telnetd
53/tcp open domain ISC Bind dnsmasq-2.35
80/tcp open http OpenWrt BusyBox httpd
MAC Address: 00:13:xx:xx:xx:xx (Cisco-Linksys)
Service Info: Device: WAP
\end{verbatim}
The web server version, if identified, can be determining in knowing the Operating
@ -147,9 +161,11 @@ CD-ROM the open source software used to build or modify the firmware.
In conformance to the GPL license, you have to release the following sources:
- complete toolchain that made the kernel and applications be compiled (gcc, binutils, libc)
- tools to build a custom firmware (mksquashfs, mkcramfs ...)
- kernel sources with patches to make it run on this specific hardware, this does not include binary drivers
\begin{itemize}
\item complete toolchain that made the kernel and applications be compiled (gcc, binutils, libc)
\item tools to build a custom firmware (mksquashfs, mkcramfs ...)
\item kernel sources with patches to make it run on this specific hardware, this does not include binary drivers
\end{itemize}
Thank you very much in advance for your answer.
@ -201,7 +217,7 @@ VERSION = 2
PATCHLEVEL = x
SUBLEVEL = y
EXTRAVERSION = z
NAME=Avast! A bilge rat!
NAME=A fancy name
\end{verbatim}
So now, you know that you have to download a standard kernel tarball at
@ -235,6 +251,42 @@ code that has been added to make the binary driver work with the Linux kernel.
This code might not be useful if you plan on writing from scratch drivers for
this hardware.
\subsubsection{Using the device bootloader}
The bootloader is the first program that is started right after your device has
been powered on. This program, can be more or less sophisticated, some do let you
do network booting, USB mass storage booting ... The bootloader is device and
architeture specific, some bootloaders were designed to be universal such as
RedBoot or U-Boot so that you can meet those loaders on totally different
platforms and expect to work the same way.
If your device runs a proprietary operating system, you are very likely to deal
with a proprietary boot loader as well. This may not always be a limitation,
some proprietary bootloaders can even have source code available (i.e : Broadcom CFE).
According to the bootloader features, hacking on th device will be more or less
easier. It is very probable that the bootloader, even exotic and rare, has a
documentation somewhere over the Internet. In order to know what will be possible
with your bootloader and the way you are going to hack the device, look over the
following features :
\begin{itemize}
\item does the bootloader allow net booting via bootp/DHCP/NFS or tftp
\item does the bootloader accept loading ELF binaries ?
\item does the bootloader have a kernel/firmware size limitation ?
\item does the bootloader expect a firmware format to be loaded with ?
\item are the loaded files executed from RAM or flash ?
\end{itemize}
Net booting is something very convenient, because you will only have to set up network
booting servers on your development station, and keep the original firmware on the device
till you are sure you can replace it. This also prevents your device from being flashed,
and potentially bricked every time you want to test a modification on the kernel/filesystem.
If your device needs to be flashed every time you load a firmware, the bootlader might
only accept a specific firmware format to be loaded, so that you will have to
understand the firmware format as well.
\subsubsection{Making binary drivers work}
As we have explained before, manufacturers do release binary drivers in their GPL