In the PC world this would be known as "BIOS modding".
The first two instructions looked legitimate, but the third looked unlikely to be a real instruction.
Given that the first appears to be a branch, that's not surprising. When disassembling, not following the flow will likely not give you anything meaningful. If the author is reading this: have you tried Ghidra?
That said, this seems a lot simpler than PC BIOSes in structure, as the latter are usually written in a combination of C and Asm (I can see why no one wanted to write MIPS Asm) and are self-extracting compressed archives.
At least in comparison to x86 assembly, MIPS assembly seemed very elegant and rich to me at the time. I wanna say that MIP R4K had 32 integer registers and 16/32 double- or single-precision float registers, but don't quote me on that. Either way, it was an embarrassment of riches :)
I often see superbly restored SGI equipment at VCF and also own a few SGI equipment that I hope to get to some point in my life but I have never seen any interesting new software or usage of these machines other than the stock "cool" demo programs(The file manager, the gears demo and others running at the same time). Is there any actual cool homebrew occuring on these platforms?
I think the lack of a real usable emulator for SGIs is holding back any kind of homebrew. I say this as one of the developer's that got SGI Indy emulation working in MAME. Yes, it works, but it's too slow and too old to be usable. I spent some time after the MAME effort working on a custom high performance emulator for Crimson/Onyx/Reality Engine, but I've kind of burned out again. Maybe some day if I'm really driven again, and had help. I've done most of the reverse engineering already, it's just a lot of code.
I think that if a high performance, usable emulator for some of the big systems existed I think some of the old software might be rediscovered and show up on the internet.
I'm not aware of any cool homebrew, but there is a certain level of cool being able to compile the code for some N64 games using the original IDO compiler on original hardware. You can even compile one of the many decompiled games like Super Mario 64, Banjo Kazooie and more that all will produce the exact binary shipped on the cartridge byte for byte, all from reverse engineered work to create byte matching equivalent C code.
Yes! I don't use my O2 a lot (I think the PSU is flaky, and I'm not super interested in IRIX), but I'm aware of at least https://forums.sgi.sh/index.php, among other similar sites, full of people porting/developing software for IRIX. It's a pretty active community for a 90s workstation platform, the most active one I'm aware of!
The main watering hole for the hobbyist community around these machines vanished from the internet a while back, taking the forums and info around porting software with it.. I guess some of it is available via wayback etc.
I've loaded the PROM in Ghidra. The ability to decompile to C is great.
I looked at some particular parts of the PROM that took a while to understand to see if I could have understood them quicker with Ghidra. In particular, the part of `sloader` that searches for the `post1` and `firmware` sections and then calls `post1(&firmware)`. Given that I already understand how this works, I can see that this is happening from the decompiled C, but the lack of labels, comments, etc really hampers my ability to understand from the decompiled C alone.
This might all be down to inexperience with the tool.
The ability to iteratively add a label, rerun the decompiler, reread the decompiled assembly, make more inferences was really the key to building an understanding for me.
Another aspect I'm unsure how to handle in Ghidra is that the base address differs between sections of the firmware. E.g. the `firmware` section is copied to RAM and executed from `0x81000000`. It's not clear to me how to configure this in a granular way, rather than a single base address for the whole PROM image.
Author of Sourcer Frank van Gilluwe also wrote a somewhat companion book "The Undocumented PC, A Programmer's Guide to I/O, CPUs, and Fixed Memory Areas".
The successor to SGI, after several acquisitions and bankruptcies, is Hewlett Packard Enterprise.
There's a forum for abandoned HP products.[1] The SGI O2 has been mentioned, but not in recent years.
userbinator|21 days ago
The first two instructions looked legitimate, but the third looked unlikely to be a real instruction.
Given that the first appears to be a branch, that's not surprising. When disassembling, not following the flow will likely not give you anything meaningful. If the author is reading this: have you tried Ghidra?
That said, this seems a lot simpler than PC BIOSes in structure, as the latter are usually written in a combination of C and Asm (I can see why no one wanted to write MIPS Asm) and are self-extracting compressed archives.
nathan_douglas|20 days ago
At least in comparison to x86 assembly, MIPS assembly seemed very elegant and rich to me at the time. I wanna say that MIP R4K had 32 integer registers and 16/32 double- or single-precision float registers, but don't quote me on that. Either way, it was an embarrassment of riches :)
nebula8804|21 days ago
tyfighter|21 days ago
I think that if a high performance, usable emulator for some of the big systems existed I think some of the old software might be rediscovered and show up on the internet.
foldor|21 days ago
spijdar|21 days ago
jrmcauliffe|21 days ago
ThatGuyRaion|21 days ago
If you want OpenGL demos, well, they exist. An example I made: https://forums.irixnet.org/thread-4796.html
You want newer FOSS?
https://nekoware.me
Every quarter I update it.
the_biot|21 days ago
As somebody else suggested, try Ghidra's decompiler. It produces very sloppy C code, but still reads faster than assembly most of the time.
Now enriching Ghidra's decompiler output to clean up the C code, that would be a neat trick, and one that Ghidra isn't doing.
mattst88|21 days ago
I looked at some particular parts of the PROM that took a while to understand to see if I could have understood them quicker with Ghidra. In particular, the part of `sloader` that searches for the `post1` and `firmware` sections and then calls `post1(&firmware)`. Given that I already understand how this works, I can see that this is happening from the decompiled C, but the lack of labels, comments, etc really hampers my ability to understand from the decompiled C alone.
This might all be down to inexperience with the tool.
The ability to iteratively add a label, rerun the decompiler, reread the decompiled assembly, make more inferences was really the key to building an understanding for me.
Another aspect I'm unsure how to handle in Ghidra is that the base address differs between sections of the firmware. E.g. the `firmware` section is copied to RAM and executed from `0x81000000`. It's not clear to me how to configure this in a granular way, rather than a single base address for the whole PROM image.
rasz|21 days ago
speaking of PC BIOSes there is/was a great disassembler called Sourcer https://corexor.wordpress.com/2015/12/09/sourcer-and-windows... with its Bios Preprocessor producing very readable sources full of comments and enumerated hardware IO.
Author of Sourcer Frank van Gilluwe also wrote a somewhat companion book "The Undocumented PC, A Programmer's Guide to I/O, CPUs, and Fixed Memory Areas".
mattst88|21 days ago
I'll give Ghidra a try!
Animats|21 days ago
[1] https://community.hpe.com
hinkley|21 days ago
mattst88|21 days ago
ThatGuyRaion|21 days ago
unixhero|21 days ago
Number 1 because Mainframes without the microcode is sent to the junkyard.
ThatGuyRaion|21 days ago
Applies here. SGI hardware holds interest because "ooh pretty animations/GL". IBM is great stuff, but it's all workhorses.