Re: grub_machine_fini

[Hollis Blanchard]

On Feb 15, 2005, at 2:41 PM, Marco Gerards wrote:

> "Yoshinori K. Okuji" <address@hidden> writes:
>
> > I added a new function grub_machine_fini which is an arch-specific
> > function. This function is not called automatically, and used only for
> > grub-emu at the moment. I implemented this function for grub-emu and
> > PC.
> >
> > This function should be implemented for all architectures, and should 
> > be
> > called before GRUB exits. I think it is unnecessary to call this
> > function from reboot or halt, because the machine should be reset
> > completely in this case. So this should be called maybe only from 
> > boot.
>
> This sounds useful.  On the PPC this should be used to free memory, I
> think.  I don't think this is required for linux, so it is not
> implemented yet.

I discovered that this was the source of my boot failures. This is 
PPC's grub_machine_fini:
void
grub_machine_fini (void)
{
  grub_ofdisk_fini ();
  grub_console_fini ();

  grub_ieee1275_release (grub_heap_start, grub_heap_len);
  /* XXX Release memory claimed for Old World firmware.  */
}

The thing is, modules were loaded into heap memory. When we "release" 
that memory, Apple OF (remember, running in translated mode) unmaps it 
or makes it otherwise inaccessible. The very next function called after 
grub_machine_fini is the boot function pointer, which points into a 
module. Some sort of exception occurs (probably a "missing instruction 
mapping"), causing OF to fall over (and it's impossible to get any 
debug info).

In other words, either:
- the boot function must be part of the core, not in a module
- or we cannot release heap memory

If we remove the release call, then all that's left are those two _fini 
calls, which do almost nothing themselves. Also, we may want to print 
debug messages after this point, so grub_console_fini doesn't make 
sense here (luckily it doesn't actually stop grub_printf from 
working)...

So I'm not sure how to use grub_machine_fini properly...?

The good news is that when I comment out the release call, I can boot 
Linux again.

-Hollis