Wednesday, April 15, 2015

Vim for assembly, programming, and system admin

Computer pioneer, Bill Joy, created the Vi text editor.  Vi has made its way onto nearly every UNIX and Linux computer and is used by kernel developers, system administrators, programmers, and users.  The learning curve is steep; however, the ability to run circles around 95% of UNIX programmers, administrators, and the like can easily be achieved.  One hour per day for five to six years digging through kernel source code with ctags will allow you to become proficient with the editor. If you are already a C programmer and can work from the terminal quickly, then picking up Vi should be easy for you.  My notes below describe how to setup VIM, a fork of Vi that includes features such as color syntax highlighting.

Thanks to this guy for creating an awesome Vi cheat sheet for programmers. He has also created a Vi emulator Plugin for Microsoft Word.

 Vim is especially useful for reading assembly and bootloader code.when a VGA connection is not available.
! Spin Lock - Solaris 2.6 C4.2
.seg "text"
.global set_byte ! make the name visible outside the .o file
.global clear_byte !
.global spin_lock !
!
set_byte:
retl
ldstub [%o0],%o0 ! delay slot for retl
!
clear_byte:
set 0x0,%o1
swap [%o0],%o1
retl
nop ! delay slot for retl
!
!
spin_lock:
busy_loop:
ldstub [%o0],%o1
tst %o1
bne busy_loop
nop ! delay slot for branch
!
retl
nop ! delay slot for branch


For the non-programmer, having Vi handy on a terminal means easily modifying any readable file on a UNIX system from the terminal - including log files and tcpdump log file snippets.  Quickly setting up snort config files, copying public and private keys between files on servers, configuring build systems, and modifying /etc/hosts and resolv.conf can easily be done with Vim. 

Running make tags from the top level Linux kernel source tree will build the ctags file over the Linux kernel source. Alternatively; man ctags will show you how to recursively run ctags over your source code.
Nerd Tree and Taglist are two useful plugins that can be downloaded from vim.org.  
Once NERD tree and Taglist are placed in ~/.vim/plugin/, the following lines in your .vimrc will allow you to use 

<ctrl-n> and <ctrl-m> to toggle the file explorer and visual tag list.
nmap <silent> <c-n> :NERDTreeToggle<CR>
nnoremap <silent> <c-m> :TlistToggle<CR>

Also, if you need a status line:
set statusline=\ %{HasPaste()}%F%m%r%h\ %w\ \ CWD:\ %r%{CurDir()}%h\ \ \ Line:\ %l/%L:%c
function! CurDir()
let curdir = substitute(getcwd(), '/Users/myhomedir/', "~/", "g")
return curdir
endfunction

function! HasPaste()
if &paste
return 'PASTE MODE  '
else
return "
endif
endfunction

Vim should be good to go at this point. cd back into your source code directory and begin work.  Finally, man vim will tell you more about how to use the editor.

Enter g?g? in command mode on the current line of text.and Vim will perform a rot13 encryption of the text.

And here's that rot13 encryption algorithm in sparc assembler (courtesy of colorado.edu)
.section ".text"
.align 4
.global main
.type main,#function
.proc 020
main:
save %sp, -112, %sp ! save the stack!
mov 0, %o0 ! stdin
readbyte:
sub %fp, 1, %o1 ! 1 byte below frame pointer
mov 3, %g1
!call read
mov 1, %o2 ! 1 byte
ldub [%fp-1], %l1 ! pull the byte into %l1
cmp %o0, 0
be done ! byte was EOF, jump to done
and %l1, 32, %l2
xor %l2, 0xff, %l3 ! invert %l2, store as a temp
and %l1, %l3, %l1
cmp %l1, 0x41
bl skip ! note lack of trailing nop.
cmp %l1, 0x5A ! the instructions trailing
bg skip ! these branches affect nothing
mov 26, %o1 ! if the branch isn't taken.
sub %l1, 0x41, %l1 ! add 'A'
add %l1, 13, %l1
call .rem ! (modulus) call is unconditional
mov %l1, %o0 ! so final arg can be set afterwards
add %o0, 0x41, %l1
skip: or %l1, %l2, %l1 stb %l1, [%fp-1] ! return the byte to memory
mov 1, %o0 ! setup syscal args
sub %fp, 1, %o1
mov 4, %g4
! call write
mov 1, %o2
ba readbyte ! return to beginning
mov 0, %o0 ! stdin (see beginning)
done: ret ! return
restore ! fix stack before return completes

In conjunction with Vi, od and/or hexdump (if installed) can be used for examining binaries on different flavors of UNIX.

Friday, April 10, 2015

Why I keep going back to iPhone

Perhaps for personal reasons but here's some background and 1% of my notes.

I've been using mobile phones since high school - 20 years ago. I've also been writing C code and hacking on UNIX and Linux for about 20 years.  A close friend introduced me to UNIX.  He had an SGI workstation running IRIX.  We loaded Red Hat 2 in 1996 via floppies over and over again as the floppy disks kept going bad.  IRIX was beautiful. The SGI concrete keyboard is awesome.  The 4Dwm X Window manager was well thought out.  We hacked on computers across the LAN and ate pizza. The IRIX terminal interface was solid.  Running 3D animations while spawning xterms was smooth.  The Silicon Graphics (now the home of Google) workstation was well thought out - from hardware peripherals to firmware, the kernel, and user space.

As a programmer, efficiency is important to me.
I've run and written code on Solaris, FreeBSD, OpenBSD, NetBSD, 15 or 20 different Linux distributions, including Slackware and Android. 
Linux is comprised of the kernel only. The window manager and everything above the kernel consists of a bunch of independent software projects piled on. In contrast, FreeBSD consists of the kernel and all user space packages. Security, ease of use, architecture, and clean hardware integration are at the forefront of FreeBSD. 

Apple hired some of the FreeBSD core developers 10 or 15 yes ago to work on the operating system, OS X.  Their efforts were proper and hugely successful.  FreeBSD is an ideal platform to build on and integrate from due to its clean architecture.

I've worked on more than 25 different models of Android based mobile phones. They all run a Linux kernel with a clunky Java based user interface. The UI windows on my Nexus 6 continue to crash. (Sorry Google).  The user interface was not well thought out. The phone is hard to hold and the user interface is counter intuitive. I still use the phone but it's frustrating. The LTE modem firmware is buggy and the cell tower connection flip flops. It seems that the manufacturer is off to work on the next phone already. I was hoping to receive more updates on my Nexus 6, but it didn't happen. I love open hardware and software but it feels like everything was slapped together on my Nexus 6. And then there is the easily accessible boot loader.  Perhaps the subject of another blog post. Android has grown over the years however; it's a segmented architecture - there are multiple parties involved when it comes to a single handset, from the chip manufacturer, handset manufacturer, Google, and the telco, multiple parties are racing to get the product out and usability is overlooked 75% of the time.

Back to iPhone. It's solid. I picked up a Gold 6+ from the Apple Store. The user interface was meticulously thought out.  The hardware form factor is perfect. The whole stack from kernel, NFC firmware, and user space was built in one building.  Apple even manufactured the application processor.  This is great.  All of my music has been on iTunes for years.  The boot loader is not open.  The iPhone is efficient.  It makes life easy. 




Thursday, January 29, 2015

Customizing a Linux distribution for an ARM® Cortex®-A9 based SBC

We will be pulling Yocto 1.7.1 (Dizzy branch) from Freescale source and building a BSP for the i.MX 6 RIoTboard. The final image will consist of the following components

  • U-Boot version 2014.10 from the Freescale git repositories.
  • Linux kernel version 3.17.4 from the Freescale git repositories.
  • ext3 root filesystem with selected packages

Camas Lilies at Sunrise

The image will be built from the custom distribution (bsecdist) and custom image (bsec-image) defined in the last post. bsec-image is derived from core-image-minimal. The configuration changes below will add support for package tests to the baec-image. In addition, the profiling tools and static development libraries and header files will be added to the image. Finally, several standard userspace packages will be added to baec-image; namely, bison, flex, and and gunning. Last, several configuration directives will be added to the local configuration file so that source code archives, package versions, and accompanying license files are stored and cached in a local directory for future builds and compliance purposes.

Monday, December 29, 2014

Creating a custom Linux distribution for an ARM® Cortex®-A9 based SBC

The Yocto project provides an ideal platform for building a custom Linux distribution.  It's design was intended to model a machine.  The Yocto project or machine should take a number of inputs and produce an output.  The inputs to the machine are the specifications for the Linux distribution.  The output of the machine is the Linux distribution.


The Yocto project is the most widely supported system for building custom Linux distributions.
The Yocto project is very well supported by both communities and companies.  The project consists of a tool called bitbake and a build system that is based off of OpenEmbedded.  Together, these two components along with a defined set of metadata comprise what is called the Poky reference platform.

Tuesday, December 23, 2014

Setting up an ARM® Cortex®-A9 based SBC

The RiOTboard - an ARM® Cortex®-A9 based SBC

The RIoTboard is an ARM® Cortex®-A9 based single board computer (SBC).  The RIoTboard has a Freescale i.MX6 Solo application processor and an integrated Freescale Kinetis MCU for additional debugging and development.  The i.MX6 Solo supports the single ARM® Cortex®-A9 MPCore Platform.  The i.MX6 Solo contains ARM® TrustZone® technology and the i.MX 6 SoC on the RIoTboard has a 96 KB Boot Rom with support for high assurance boot.   Other features of the board include 1 GB of DDR3 memory, 4 GB eMMC, JTAG, Serial, mini USB for OpenSDA, mini USB for USB OTG, LVDS, parallel RGB expansion, 4 USB-A ports, HDMI, audio, reset button, microSD card slot, SD card slot, and boot onboard boot switches.   The board is very reasonably priced.  Last but not least, the Freescale i.MX 6 ARM® Cortex®-A9 application processor has ARM® TrustZone® technology.

ARM® TrustZone® Technology

The i.MX6 Solo processor on the RIoTboard is labeled MCIMX6S8DVM10AB.  According to the i.MX6 Solo data sheet, the processor supports a number of security related features. The list includes ARM® TrustZone® technology with TZ architecture support, a secure JTAG controller for locking down and protecting the JTAG port, a cryptographic acceleration and assurance module with secure RAM and a true PRNG, a central security unit (CSU) including secure non-volatile storage, high assurance boot, and the separation of memory and interrupts between secure world and normal world.  There are more security related features but this is a general list.

the view from above - a trusted zone

Monday, December 15, 2014

ARM®, NFC Technology, and the Single Wire Protocol



At the heart of an ARM Powered® smartphone with NFC technology is the contactless front end or CLF. The CLF is responsible for managing radio-frequency communication at 13.56 MHz.

A mobile phone with NFC technology contains only one CLF.  The CLF is connected to the ARM® processor or application processor via UART, I²C, and in some cases SPI.  These protocols are fairly basic and facilitate straightforward communication between the application processor and CLF via a typical Linux or UNIX-based kernel.  Updating the firmware on the CLF is a typical operation that is performed over the UART serial line.

While a mobile phone with NFC technology contains only one CLF, the phone may contain multiple secure elements. There may be a secure element on the UICC card, on the microSD card, and/or embedded with the CLF on the PCB.  Applets residing on each of the secure elements can serve both similar and different purposes.  Both the secure element and the CLF are small, self-contained computers with I/O communications interfaces. In the case where there are multiple secure elements residing on the phone, each of the secure elements is a small, self-contained computer with I/O communication interfaces.  A secure element differs from a normal computer in that it is embedded. It has limited resources available for performing computations.

Friday, December 12, 2014

ARM Powered® smartphones with NFC technology

Turing machines, first described by Alan Turing in (Turing 1937), are simple abstract computational devices intended to help investigate the extent and limitations of what can be computed.  - Stanford Encyclopedia of Philosophy
The head and the tape in a turing machine
There are a large number of Near field communication (NFC)-enabled phones (devices) on the consumer market. LG, Huawei, Motorola, Samsung, HTC, Nokia, ZTE, Sony, RIM, Amazon, and Apple manufacture and sell mobile phones with NFC technology.