thursday, 8 february 2007

posted at 08:11
tags:

I spent a couple of days beating my head against the AROS dark magic that holds everything together. I got FATFileSystem building, but on trying to call into it with my loader, I'd get a segfault every time I tried to make any kind of function call.

In desperation I stripped back the library to just a single one-line function that printed some (rather unsavoury) text and exited. That worked. The whole thing only fell over when the rest of the files were linked. The confusing part was the they weren't being used - in theory, they should just be random data along for the ride.

A brief rant in #aros yesterday got an answer from Michal (who else?). Apparently AROS has some lovely magic that automatically makes sure your program has a valid declaration and value for SysBase, which is sort of like the global context for the operating system - most system calls (like AllocMem()) actually take SysBase as an extra argument, though this is #define'd away from the user. Its a nice scheme that works well, unless, as was the case here, you have explicitly declared SysBase in your program. In that case, AROS assumes you know what you're doing, and you're expected to set it to the correct value yourself.

I've now surrounded the declaration in a #ifdef __AROS__ conditional, and its loading fine. I don't mind that this feature is there - it makes sense and is useful - but once again, lack of documentation hurts me.

On the topic of documentation, in the last few days I've managed to procure soft copies of both the ROM Kernel Manuals (thanks Hogga!) and the Guru Book (thanks Michal), though the latter is in poor shape being a scan/OCR of the book. Its serviceable though, and makes for interesting reading. I'm hoping to find time to convert all of these to HTML soon, which should make them much more useful.

Back to the code, I've started implementing the loader code into packet.handler. Once thats done, its onto the first of many tricky bits - re-adding things to the DOS headers that were removed (or at least commented) when AROS switched away from packets. Things like struct FileLock, dp_Port, and other excitement. Those will be the first core changes. Yikes!

Oh, and I haven't heard back about deviceio.library yet. I'll have to start trying a little harder. UtilityBase might be a good place to look.