Question about bootup

[Jeremy Huddleston]

#1 should be expanded a bit, and hopefully this will satisfy your curiosity about the Apple_bootloader partition.  

OpenFirmware itself is quite complicated.  The "normal" situation is that you have boot-device=hd:2,\\:tbxi and the second partition on your boot drive is an HFS partition (the first partition is actually the partition map).  One of the files on this HFS partition is "blessed" in order to tell OFW to load it.

In actuality, it's not a file that is blessed, but a directory in the HFS partition, and that directory is inspected for a file of the type "tbxi" which is loaded.  In practice, there are usually no subdirectories, so : is blessed, and there are only a handful of files, one of which is either a bootloader or stage-1 kernel, and it is marked "tbxi" using hfsutils or some other tools (eg: 'hattrib -b : && hattrib -t tbxi -c UNIX :grub' will bless : and mark grub as the bootloader).

I'm not an expert on all of this, so there is probably room for expansion on some of my points, but hopefully that gets you in the right direction.

--Jeremy

On Mar 5, 2012, at 10:24 PM, Rob Ballantyne <robballantyne3 at gmail.com> wrote:

> Hi All,
> 
>  I've been poking around trying to understand the boot up process of
> a ppc64 G5 machine.
> 
>  I was slightly surprised to still find an Apple Partition map disk.
> I would have thought it was an ordinary fdisk (PC) partition setup.
> 
>  Let me see if I have it right:
> 
> 1 - OpenFirmware (OFW) load Apple_Bootstrap/boot1.elf
> 2 - boot1.elf runs to gain enough to understand UFS filesystems and
> loads FreeBSD UFS partition /boot/loader
> 3 - loader loads /boot/kernel/kernel
> 
> ... and we're off to the races.
> 
>  This strikes me as fairly simplistic so I'm sure there are more
> details.  I'm curious about /boot/*.4th OpenFirmware forth code, for
> example.  Is it involved in a substantial way?
> 
>  The other thing I'm curious about is the Apple_Bootstrap partition.
> How is it written?  I've discovered parteditor within the bsdinstall
> installer.  I suspect that does it but it doesn't appear to let one
> write their own bootloader code  image.
> 
>  As I said mostly curiosity and trying to understand.  If anyone has
> a few words of confirmation/advice I would be glad to hear them.
> 
> Thanks,
> 
> Rob
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