Add Old World loading capabilities

[MCJack123]

This PR adds an extra build step to the arcloader/stage1 makefile which produces an XCOFF file that can be loaded from Old World Open Firmware versions. It uses a small program from the Linux sources to patch the XCOFF that GCC links, which makes the executable bootable.

This is mostly untested, as I don't have a G3 beige system (and DingusPPC is being weird), but the same process works on my OF 1.0.5 PM7600. I also don't know the blessing procedures quite yet, and if OF 1/2 is even able to detect alternate boot devices without changing boot-device in NVRAM.

[Wack0]

About the blessing procedure, I believe from looking at OSX install images, it uses an APM partition with no data storing raw powerpc code, with base address + entrypoint in the partition table entry. OSX uses a mapped binary with mach-o headers present (IDA loads it fine as a mach-o even) but executable headers aren't required.

I was planning on modifying arcfw for clearing bss, and having a load image for oldworld that was basically loaded arcfw+custom loader in bss, placing it in the cd image then patching it after build (as far as I can tell no tool can set up such an APM partition in a hybrid ISO containing only code yet).

For dualboot, could probably add some boot menu in loader (and enable it only if mac partitions were created). Given the 16KB loader limit will be not present at all for oldworld...

[MCJack123]

I just tried booting my 10.0 CD in my 7600 (holding C), and it appears that whatever it boots is a small script that sets the following NVRAM parameters:

• boot-device => scsi-int/@3,0:0 (@3,0:8 under System Disk)
• boot-command => 1 bootr (0 bootr under System Disk)
• use-nvramrc? => true
• nvramrc => some code which defines bootr (which appears to set bootargs before booting), redefines init-program to load other stuff (most of it is in machine code), plus other stuff?
• load-base => 600000

and then resets the system, letting OF then hand it off to the OS X loader on the CD. System Disk appears to do the same thing when booting to an OS X CD. I also happen to have a Server 1.2 CD which is supported on the 7600, but it boots and installs from a Mac OS 8.5 System Folder instead - but the boot device setting from 10.0 still tries to boot Mac OS X Server from CD (which doesn't appear to work, it runs the loader but fails to find a kernel I think).

From a bit of digging, I believe the HFS Standard wrapper over the HFS+ partition holds the C-key boot data. There are three hidden files located on this hidden sub-partition:

• System, which is a standard Mac OS system suitcase file, with a few notable resources:
  • boot, which has the code that does the above reconfiguration (specifically entry 2), and I believe this is what the ROM looks for
  • OFpt, which contains NVRAM patches for each platform (also present in System Disk)
  • OFtb and OFtc, which have tables mapping each hardware ID to the necessary patch in OFpt
• OSXBoot!, which is empty in both forks. Not sure what it's for - maybe it just indicates that this is an OS X disk (or it shadows the boot image)?
• Finder, which is also empty and appears to be a placeholder to ensure the system definitely thinks this disk is bootable.

Also possibly relevant is the HFS boot block, which I'm leaving a link to docs for in case it's necessary.

As for Open Firmware loading, you're correct about it loading from the APM - I'm not sure exactly where it comes from, but I'm guessing that /packages/mac-files looks for the first partition with boot code set up, and loads the entire image into memory. This could be used with either the existing ELF or this PR's XCOFF file, provided the start + base addresses are correct in APM.

So after a lot of investigation, I believe this is the way to make a "truly bootable" CD for an Open Firmware payload:

• Make a hybrid APM+ISO disc image.
• Add in all of the required drivers under APM.
• Add an HFS Standard partition under APM, with a proper boot block and startup file set up.
• Add a system suitcase with similar contents to the OS X suitcase onto the HFS partition. The boot program will set up the boot-device parameter to point to the loader on the ISO filesystem.
• Configure the ISO filesystem to start after the end of the APM area, or otherwise shadow the APM data.
• Place the XCOFF image to boot in the ISO filesystem.

Alternatively, using an APM boot image:

• Do the first four steps above.
• Copy the XCOFF/ELF/whatever image to some place in the image.
• Hack the APM to point to the correct sectors and load addresses for that image.

Now, I don't really think I want to put in the effort to make this work without copying Apple's files - it's a lot of hacking to be able to hold "C" instead of typing a command once. But this is some food for thought, and I might play around with the Apple files a bit on my own to see what's possible.

[Wack0]

"without copying Apple's files" - I already bundle the OS9 IDE drivers, the only way for installing them at all is reformat or having them present for OS9 drive setup to be able to update them... if I could have avoided bundling them (for dualboots) I would have...

Regarding the open firmware nvram changes, that would make sense given OSX BootX comes up in 1024x768 under dingusppc, the same as when dropping to OF prompt, yet OF boot switches back to 640x480.