Conor's techie blog

Converting i386 to x86-64 assembler

2007-02-21T16:49:00.000Z

One Linux topic there really is a limited amount of information about on the web is converting i386 assembly into x86-64. At a surface level there's not huge differences, x86-64 has an extra 8 general purpose registers, so less has to be put on the stack (& of course all registers are now 64 bit).

As a rule of thumb the x86-64 equivalent GPR registers all start with an r for addressing them in 64 bit mode (this is required for certain operations such as stack manipulation). Then the normal instructions are used, except that they are postfixed with a q (quad word) instead of l (long) for manipulating them. i.e.

movl (%ebx), %eax becomes movq (%rbp), %rax

What can be a subtle annoyance is that syscall numbers & the registers for passing arguments to the Linux kernel have all changed in x86-64. The register associations can be viewed in /usr/src/linux/arch/x86_64/kernel/entry.S & the mapping to syscalls on your system can be found in /usr/include/asm-x86_64/unistd.h

This article (http://www.milw0rm.com/papers/110) contains a nice summary of what has changed & is more accessible then the information on the x86-64.org web site (http://www.x86-64.org/)

For instance to perform the open system call, in i386 we have:

movl $5, %eax
movl 8(%ebp), %ebx # assuming we want the second memory location on the stack
movl $0, %ecx
movl $0644, %edx
int $0x80

In x86-64 this becomes (note the change in registers, & sycall no. from 5 to 2)

movl $2, %eax
movq 16(%rbp), %rdi
movl $0, %esi
movl $0644, %edx
int $0x80

We could safely replace all instances of movl with movq providing we were using GPR's 64 bit counterparts (%rax, ...), however, this is clearly unnecessary as 32 bit is clearly adequate for storing the remaining arguments.

Also, any operations working on the stack need to be performed using 64 bit addressing, hence the 8 byte offsets used for accessing variables on it (of course using popq would take this into account automatically).

Free drivers on Linux

2007-01-31T09:24:00.000Z

There's been a significant development in the LKML this week, with the announcement that the Linux community is offering to develop drivers for free for any unsupported hardware on Linux.

A nice text about CPU architecture

2007-01-14T16:10:00.000Z

One of the topics that I've been spending more time trying to develop my knowledge of lately is coding in assembly & the underlying CPU ISA for different platforms. Robert Love recently blogged about a book on the subject (Inside the Machine) that I decided to purchase a copy of & I have to say I'm very impressed by it. The author, Jon Stokes has written an excellent text (which starts off as entry level, moving on to advanced concepts, although it won't teach you assembly) about the design & operation of CPUs & how some of the largest manufacturers (Intel & Motorola/IBM) have architectured their CPUs over the past couple of decades.

What I really like about the book is that its not just another textbook about computer hardware, its a very readable text, which doesn't cross that common boundary between a regular read & the sort of book you have to study line by line to grasp the concepts its trying to explain. Its full of lovely diagrams, with points explained well & then when they come back up later they are reemphasised so you don't feel your being tested on remembering every single concept outlined in the book at an earlier stage.

An obvious criticism of the book would be why doesn't it cover some of the other architectures such as SPARC & AMD's x86/64 ports (although apparently there's a lack of detailed architectural documentation on AMD). However, with the knowledge gained from this book it certainly makes something like the OpenSPARC project more accessible to the masses. Besides I'd rather have a concise book which I can sit down & read cover to cover anyday over a "definitive" reference that contains everything I'll ever need to know, but I don't have the time to read.

My resolution - to update this blog more...

2007-01-03T20:16:00.000Z

I'm not normally one of those people who bothers with New Years resolutions, however, this year I did decide I'd like to start blogging a bit more regularly. Mainly about Unix/Linux, but I find its difficult to be inspired to write something from time to time.

Last year during one of these moments of inspiration I managed to get an article published which was a first. The article in question was about wireless in Linux using NDiswrapper which was a feature story in the April 2006 issue of Linux Magazine (which is the best techie Linux magazine out there), "Look, Ma, No Wires!", but
since then I haven't had the time to write about anything else.

I did randomly get asked to appear on Newsnight to talk briefly about BitTorrent though which was an interesting experience. The response to the overall piece in the community was even more interesting - Slashdot: A Bit of BitTorrent Bother. I have no regrets on the piece, I agree with much of the criticism of the report (I've using BT for 4 years), but at the end of the day all they (the BBC) wanted to show in the end was me demonstrating how easily torrents can be encypted. Unless you're the producer of a piece, you don't really have much say in how you're portrayed, unfortunately.

There's a couple of topics I feel I could write a decent amount about, which I have had to spend some time looking at - core file creation & kernel panics in Linux versus Solaris; & I/O buffer caching thresholds in Linux/Solaris. Whether I get much written remains to be seen - especially as I'm doing this years Étape du Tour...

Either way, I intend to make 2007 the year I start writing more about Unix & hopefully there could start being some useful information on this blog, that someone out there starts to find useful & insightful.

Fixing a broken laptop & replacing those obscure parts

2007-01-03T19:43:00.000Z

Recently I discovered my laptop stopped working, it had been a month or so since I last powered it up as I had been playing around lately with Minix in VMWare on my work laptop, so playing with Gentoo on my other laptop had regrettably taken a back seat. How I regret my neglect now.

The thing that really annoyed me about the problem was that it was a laptop & I couldn't simply pull open the case to the laptop & put in some spares from other machines I have lying about to find out where the problem lay - no manufacturer would ever dream of making a laptop that friendly :(, so I had to try & reason logically what could be wrong. Given that it simply would not turn on the problem had to lie between the power supply & the power button itself. The fact that the transformer on the power supply still glowed a healthy green indicated it wasn't going to be something as simple as the power supply being broken (plus I could detect current going through it using a volt meter).

Obviously this left me with no choice but to take the laptop apart & hopefully work our what was wrong. Take it apart I did, I had to remove every single component off the laptop (damn you Acer) in order to get underneath the motherboard & discover what was wrong.

Turns out that the pin in the DC socket on the motherboard had broken, how on earth this happened I cannot fathom. But it did leave me scratching my head thinking where I could get it replaced from. Tried the usual suspects - Maplin, Farnell & RS components for an exact match to no avail. Then I googled for a bit & found my saviour www.laptopsockets.co.uk

This site seems to contain all those small & obscure spare parts that you need to fix your laptop & they have the exact DC socket I need. Granted there is a slight premium on the part (which should cost < £1), £15 including P&P, but I'm happy as I can fix my laptop & can be certain its the exact replacement I need.

Plus I feel I'm no longer at the mercy of a laptop manufacturer to fix problems with it, where all you actually need is a random part, & some solder.

Using gdm instead of dtlogin on Nevada

2005-08-15T20:02:00.000+01:00

Having finally got Nevada running on my laptop, to get gdm running instead of the usual standard dtlogin screen, the gdm-login service has to be enabled, which isn't immediately obvious. Laurent Blume cleared this one up.

From the console, disable dtlogin,

/etc/init.d/dtlogin stop
/usr/dt/bin/dtconfig -d
svcadm enable gdm2-login && exit

If you want to be able to shutdown the box from the gdm menu, edit the file
/etc/X11/gdm/gdm.conf first, and uncomment the following lines:

RebootCommand=/sbin/init 6
HaltCommand=/sbin/init 5

Then you can customise your gdm with some of the OpenSolaris images posted on Chandan's blog here

The joys of a new Acer laptop, OpenSolaris & Gentoo

2005-08-11T12:02:00.000+01:00

Its been quite some time since I wrote anything, mainly because I got a new laptop & have been experiencing the joys of trying to get it running OpenSolaris & Gentoo in a dual boot configuration. I was adament that there was going to be no trace of Windows on it, so had to ensure I could get all the multimedia functionality working flawlessly to keep me happy.

The laptop itself is an Acer Aspire 5020 series laptop (5024WLMI to be exact) with a healthly Turion 1.8GHZ, 1GB RAM, 100GB HDD, x700 Radeon & 15.4" TFT. I bought it mainly because it was very similar spec to the Acer Ferrarri 4000, but slightly more affordable. I reasoned that by having a laptop of similar spec, chances are Solaris is going to be fairly well supported.

I had the laptop just in time for OpenSolaris being made available, downloaded Nevada 16, tried to boot the CD & after a minute or so the system would panic & reboot itself.

I then started making posts to comp.unix.solaris to try to resolve the issue, & recieved valuable postings from a variety of Solaris experts including kernel developers. This really made me realise quite how willing really knowledgeable members of the Solaris community are more than happy to assist with people's issues. It also gave me hope that although no-one managed to solve my problem on the comp.unix.solaris newsgroup initially, with the level of input I recieved I was confident it would get solved.

In the following weeks I went on holiday a couple of times, and started concentrating on getting Gentoo up & running, while I posted a bug report, waited for new Nevada releases to appear (approx one every two weeks), and bounced posts between the solarisx86 yahoo group.

This is something I'm going to cover in a lot more detail shortly, the only thing I will say is that I have almost achieved everything I set out to achieve on my laptop back in June.

1st London OpenSolaris User Group meeting

2005-06-13T13:31:00.000+01:00

Following on from Santa Clara & Sydney, the first London OpenSolaris Uuser Group meeting has been announced - next Monday from 18:00 at Sun's Offices in the city, which is handy for me as its about 2 minutes from where I'm working currently. You can read more at Ulf's blog:

http://blogs.sun.com/roller/page/ulf/20050610#uk_s_first_opensolaris_user

Its great that this is finally happening & that I'll finally have an opportunity to meet some of the community in person.

All new Acer Ferrari

2005-06-01T21:33:00.000+01:00

Acer have unveilled the latest in their line of Ferrari laptops, the Ferrari 4000 which I have to say looks pretty damn sweet. Not only is it in a superior (in my opinion) stylish black, but the case is also made from carbon fibre. You can see more pictures here . Can't see it being much below £1400 miniumum though, so I think I better wait. Unless - I can somehow convince my girlfriend it will be more beneficial then a summer break...

South Park

2005-05-05T11:32:00.000+01:00

I've added my South Park image, following in the footsteps of Alan Coopersmith (http://blogs.sun.com/roller/page/alanc/20050501#what_would_you_look_like) & numerous other members of the Sun Community who seem to all be follow suit.

Its been a while...

2005-02-17T07:40:00.000Z

Its been a while since I wrote anything, but its been a while since I had anything interesting to say. It seems one of the journalists at the Enterprise Systems Journal (http://www.esj.com) seems to think otherwise quoting me in my views on Solaris 10 in a recent article entitled "Sun Unveils Updated OS, New Services, Aggressive Chip Strategy" (http://www.esj.com/Enterprise/article.aspx?EditorialsID=1278). Its a big deal to me as its the first time I've had my name appear in a "real" article on the web.

Last time I wrote anything in my Blog I was busy playing with Oracle to take a few exams, I got my 9i OCA & have since decided thats enough Oracle for me for the time being. Not that I have anything against databases, but I find Unix OS's, more specifically Solaris far more interesting. As I probed further into the depths of Oracle administration I came to realise that a large proportion of the study material is related to recovery of databases & fined grain tuning of Oracle, which is knowledge I don't feel I'm missing out on currently.

I've been playing a fair bit of late with various Solaris 10 Express builds trying (as any techie does) to pick up as much about the new features as possible. Hopefully I'll start having useful information to write about my experiences in future posts, but for the time being you can check out Solaris 10 FCS for free on Sun's web site (http://www.sun.com/software/solaris/).

Its great to see that Solaris 10 is going open source later this year, I've been keeping a keen eye on developments in this area since I first heard about it last year. This for me has been the most compelling reason to learn more about Solaris over the last year (even over the new features of Solaris 10).

Now I'm no kernal hacker, but I want to be in a position to contribute one way or another to this. So I started reading Rich Teer's (he's recently started a blog too http://richteer.blogspot.com/) excellent book "Solaris Systems Programming", this has certainly been helpful in enlightening me about writing useful code for Solaris, but I want to learn more about interacting with the kernel directly & so I thought why not look at writing device drivers. As luck would have it Sun recently published the "Device Driver Tutorial" (http://docs.sun.com/app/docs/doc/817-5789). This looked like the sort of introduction to the subject I needed & I'll (hopefully) be reporting further on my progress with this shortly.

Finally, on the subject of Solaris Internals it appears that an update to the book by the same name is in the pipeline according to Paul Rogers' Blog (http://blogs.sun.com/roller/page/pcr/20050105#solaris_internal). Hopefully there'll be more info on this soon.

Oracle & Linux - Unworkable?

2004-09-06T00:26:00.000+01:00

Oracle & Linux - Unbreakable, are the words of Oracle trying to get everyone to run their software on the Linux platform. In my experience of Oracle & Linux, I'd use the word Unworkable to describe the combination. I recently purchased some new hardware to upgrade my main PC & provide me with a dedicated SuSE 9.1 Pro box to add to my collection of computer's. As I am currently studying for my OCP, I thought it made sense to get Oracle DB running on this box, as who'd ever want to run Oracle in an enterprise environment on a Windows box? How foolish I was.

I started off by trying to run the Oracle Installer from the command line, & received a not so friendly, java runtime library error, even though the jre being run was being copied from the Oracle installation disk. No problem I thought simply find the relevant config file & point to the jre located in my /usr filesystem. Problem solved installer started.

Nextup, installation "starts" & gets stuck at 0% complete. It wasn't going anywhere. Googled for the problem, what a surprise, lots of people have had this problem. There appeared to be one website that everyone referred to to get Oracle running on Linux (although aimed at RHES)(http://www.puschitz.com/InstallingOracle9i.html), I followed these instructions & still didn't manage to get anywhere. I'd spent many hours on this & finally gave up for now. Although this is never the attitude to have when working with computers, I knew I didn't have to run Oracle on Linux, I could just put it on my Solaris box & job done.

It astounds me that Oracle support for Linux is so poor, looking at SuSE's Oracle compatibility matrix (http://www.suse.com/en/business/certifications/
certified_software/oracle/matrix.html) its clear that the only release of SuSE that seems to support Oracle satisfactorily is SuSE Enterprise Server v8 (which starts at minimum of $349 per year to run). This is all well in large enterprise environments, but what about everyone else. I'm very tempted now to replace my trusty SuSE box with a nice Solaris 10 build, on which Oracle will just work.

This experience has convinced me that open source platforms are best suited to open source software & proprietary platforms are there for proprietary software. I'd be interested to hear anyone's comments on this, as I recently got SpamAssassin & Postfix running on Solaris 9, but it was not easy. And if you're not careful you can find SpamAssassin will bring down a Solaris build within 10 minutes of the spamc process being started, if it can't find a certain Perl library. You have been warned.

DTrace

2004-08-28T23:50:00.000+01:00

I recently heard a talk on one of Solaris 10's new features called DTrace (Dynamic Tracing) by Jon Haslam (http://blogs.sun.com/jonh), this I found facinating. In a nutshell it enables you to observe the behaviour of Solaris by setting up probes that record spefic information about the state of a system at a kernel level. Check out Jon Haslam's Blog for lots of examples. Its a very powerful tool, one that I am hoping to experiment when I finally get Solaris 10 recognising my network card. This and Oracle on Linux have been my two greatest annoyances of late.

Welcome to my blog

2004-08-16T00:15:00.000+01:00

I've decided to finally bite the bullet & do what every techie in this day & age seems to be doing & give myself a web presence. I'm not sure what shape its going to take over the next few months, but I'm sure there'll be plenty of rants about my everyday experiences as a Unix/Linux/Oracle techie. If you want to get in touch feel free, I'd be very interested to hear what anyone has to say about this Blog.