Killing Mind

Bochs is an open source emulator of the x86 architecture. I had brushed it away earlier, because I figured it would only run on x86 hardware itself, and hadn't heard of anyone using it on the Mac. Well, in a roundabout manner, I eventually came to attempting a compile of Bochs on OS X, and discovered it not only compiled very easily, but ran well. I then discovered an OS X port which came with Applescripts to launch the software, and a GUI for the actual display of the environment. Excellent stuff, but still no huge advantage over Virtual PC, and the configuration was starting to look overwhelming.

But, being the pedantic geek that I am, I continued investigating the software. Using the example OS image provided with the OS X Bochs package as a starting point, I found that simple modifications to the configuration file were all that was necessary to boot the disk images I had been playing with with Virtual PC. I persevered with the process, and managed to install FreeDOS on a hard disk image, so I could run my kernel within the Bochs environment. Already this was looking better than Virtual PC, because I could set the configuration file to way I liked it, and then didn't have to worry about capturing and releasing disk images everytime I re-ran the emulation. So I had a bit of time-saving functionality there, but it had cost me several days setting it up.

The real reward came when I investigated the debugging options of Bochs. I must say I wasn't expecting much. Enabling debugging required a recompilation of the source, with custom options, so I grabbed a hold of the source and followed the install instructions. Configuration and compilation was impressively smooth and the debug version of Bochs ran well. But it wasn't all that useful - all general debugging investigation (disassembly, memory dumps, register dumps) had to be invoked by hand repeatably, which was going to be a real hassle. But there was a mention of a GUI for the Bochs debugger, called bfe, so I had myself a look at that.

Amazingly enough, the debugger compiled almost straight out of the box, and ran very cleanly in the X11 environment. There was a small difficultly in getting the GUI to execute the command line application because of the funny interaction between the command line bochs app, the Mac OS X GUI and the X11 debugger. I was very happy to find that I could copy the shell execution line from the Bochs Applescript and use it in configuring bfe. That is, I passed "cd /usr/local/bochs/myOS; exec /usr/local/bochs/bochs.app/Contents/MacOS/bochs" to bfe as the path to the bochs executable. Works beautifully! Running bfe from the X11 prompt opens a clean GUI. Hitting the "start Bochs" button lauches the OS X GUI for Bochs, using the configuration script in myOS, and I can then debug my application while it executes in another window.

When one considers what combination of technologies being used here - emulation of x86 on PowerPC using an app designed for x86 compiled on PowerPC, executed in a OS X GUI, debugged from a X11 app - it really is amazing it works at all, let alone works so smoothly. I'm left with an awesome development environment for low-level x86 development, in particular for kernel development, which still gives me the advantages of developing on OS X - the rest of the applications, excellent X11 environment, great interaction between the command line and GUI layers, stable disk image platform. Of course, if I had realised the environment was possible a couple of months earlier, the university assignment to develop a kernel would have been a significantly simpler experience.

Well, just in case anyone else wants to do similar development - it is possible, and highly recommended!