Date: Tue, 6 Mar 2012 07:50:45 +0100 From: Milan Obuch <freebsd-ppc@dino.sk> To: Rob Ballantyne <robballantyne3@gmail.com> Cc: freebsd-ppc@freebsd.org Subject: Re: Question about bootup Message-ID: <20120306075045.5be555b9@zeta.dino.sk> In-Reply-To: <CAKLrb5d=fos09L0fHY3Qdf4YRZ5FYBmHTV21iMzEybB65DpoSw@mail.gmail.com> References: <CAKLrb5d=fos09L0fHY3Qdf4YRZ5FYBmHTV21iMzEybB65DpoSw@mail.gmail.com>
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On Mon, 5 Mar 2012 22:24:36 -0800 Rob Ballantyne <robballantyne3@gmail.com> wrote: > Hi All, > > I've been poking around trying to understand the boot up process of > a ppc64 G5 machine. > Hi, I think it is basically the same for G4 too :) > I was slightly surprised to still find an Apple Partition map disk. > I would have thought it was an ordinary fdisk (PC) partition setup. > This is most probably OpenFirmware (or implementation on machine in question) dependency - at least on Apple's boxes ability to load kernel from UFS filesystem in some newer version was removed. > Let me see if I have it right: > > 1 - OpenFirmware (OFW) load Apple_Bootstrap/boot1.elf Actually, there is Apple_Bootstrap/bootinfo.txt, a Forth wrapper script which is loaded first and it loads 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? > I did not investigate here much, but as soon as /boot/kernel/loader is called, it should work 'the usual way' as on any other platform, i. e. /boot/*.4th files are used accordingly. Just a nit-pick, they have no relation to OpenFirmware, all they have in common is they are written in the same language. At least that's the way I understand it. > 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. > It is small partition in Apple's HFS format or whatever the acronym is because it is the only format Apple's OpenFirmware understands now. Basically, there are two files in it - bootinfo.txt and boot1.elf, in a ppc directory. Both are already mentioned above. > 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. > Well, I am not an expert, I am interested in this area too, trying to understand, and be able to modify the boot process too. But as there are some differences with what I already know, sometimes it is not easy :) Regards, Milan
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