[OpenBIOS] QEMU OpenBIOS booting?

[Steven Noonan]

On Sun, Apr 19, 2009 at 1:24 PM, Laurent Vivier <Laurent at vivier.eu> wrote:
> Le dimanche 19 avril 2009 à 13:14 -0700, Steven Noonan a écrit :
>> On Sun, Apr 19, 2009 at 1:08 PM, Laurent Vivier <Laurent at lvivier.info> wrote:
>> > Le dimanche 19 avril 2009 à 13:00 -0700, Steven Noonan a écrit :
>> >> On Sun, Apr 19, 2009 at 12:23 PM, Blue Swirl <blauwirbel at gmail.com> wrote:
>> >> > On 4/19/09, Steven Noonan <steven at uplinklabs.net> wrote:
>> >> >> On Sun, Apr 19, 2009 at 1:24 AM, Laurent Vivier <Laurent at lvivier.info> wrote:
>> >> >>  > Le dimanche 19 avril 2009 à 00:50 -0700, Steven Noonan a écrit :
>> >> >>  >> On Tue, Apr 14, 2009 at 10:46 PM, Steven Noonan <steven at uplinklabs.net> wrote:
>> >> >>  >> > On Sun, Apr 12, 2009 at 1:39 AM, Laurent Vivier <Laurent at lvivier.info> wrote:
>> >> >>  >> >> OpenBIOS is not able to boot MacOS X.
>> >> >>  >> >
>> >> [...]
>> >> $=:>> XCOFF - load_xcoff: Loading 'System\Library\CoreServices\BootX'
>> >> >> XCOFF - load_xcoff: XCOFF file with 3 sections entry:fff0a22c
>> >> >> XCOFF - load_xcoff: Read next header (5c)
>> >> >> XCOFF - load_xcoff: Load '.text' section from 5c d4 to 5600000 (28000)
>> >> >> XCOFF - load_xcoff: Read next header (84)
>> >> >> XCOFF - load_xcoff: Load '.data' section from 84 280d4 to 5628000 (2000)
>> >> >> XCOFF - load_xcoff: Read next header (ac)
>> >> >> XCOFF - load_xcoff: Erase '.bss' section at 562a000 size: 3a000
>> >> >> ELF - transfer_control_to_elf: Starting ELF boot loader
>> >> invalid/unsupported opcode: 02 - 0e - 0c (0b717b1c) 05616ed8 1
>> >> invalid/unsupported opcode: 00 - 14 - 13 (000064e8) 000094d0 0
>> >> Alcarin:qemu steven$
>> >>
>> >>
>> >> So at least with my patches, we're getting what people with QEMU 0.8.0
>> >> were getting: http://tinyurl.com/qemu080
>> >>
>> >> So now what's left is resolving -why- that 'invalid/unsupported
>> >> opcode' issue crops up.
>> >
>> > I think the booloader is loaded at addresses overwriting some parts of
>> > openbios.
>> >
>>
>> That would make sense, but that tells me QEMU is loading OpenBIOS to
>
> The problem is in OpenBios: I put some structures in memory without
> knowing this... but this is not part of openfirmware specification.

Agreed, this seems to be an undocumented Apple-ism. But since OSes
other than Mac OS X run on PowerPC macs (i.e. BSD, Linux), I must
assume that they are aware of these quirks and don't hammer those
memory locations. Since that's the case, it may be wise to conform to
what Apple's Open Firmware does, even if it _is_ undocumented.

How easy would it be to get OpenBIOS to load to the position Mac OS X
and BootX expect it to be? Based on what the book says, there are 8MB
of memory available to the Open Firmware, would that be enough for the
OpenBIOS executable image and any allocations it would need to
perform?

>
>> the wrong location. From the book "Mac OS X Internals: A Systems
>> Approach":
>>
>> Table 45. BootX Logical Memory Map
>>
>> Starting Address   Ending Address    Purpose
>> 0x00000000    0x00003FFF    Exception vectors.
>> 0x00004000    0x03FFFFFF    Kernel image, boot structures, and drivers.
>
> I put there some memory allocation information.
>
>> 0x04000000    0x04FFFFFF    File load area.
>> 0x05000000    0x053FFFFF    Simple read-time cache for file system
>> metadata. Cache hits are serviced from memory, whereas cache misses
>> result in disk access.
>> 0x05400000    0x055FFFFF    Malloc zone: a simple memory allocator is
>> implemented in BootX's libclite subproject. The starting and ending
>> addresses of this range define the block of memory used by the
>> allocator.
>
> BootX should use openBIOS functions to allocate memory (as Yaboot
> does...)

Apparently BootX is tricky that way. I don't have the BootX source
code, so I can't verify the author's statement, but I would guess he
knows what he's talking about.

>> 0x05600000    0x057FFFFF    BootX image.
>
> This should be "load-base"
>
>> 0x05800000    0x05FFFFFF    Unused (occupied by the Open Firmware image).
>>
>>
>> So it should be loading OpenBIOS to address 0x05800000, and the BootX
>> image should load to 0x05600000 (the latter does as it should,
>> according to the debug output).
>
> For the moment OpenBIOS is loaded at end physical memory and mapped at
> end of space address (the reset vector is here).
>

Alright, is that location part of the official specification? If so,
good, then we could use that memory for any allocations OpenBIOS would
need to do. If not, then who's to say that location won't get hammered
by the OS or boot loader?