64bit loader

[Mathew Schofield]

On 6/3/05, Peter Wemm <peter at wemm.org> wrote:
> On Thursday 02 June 2005 03:44 pm, Scott Long wrote:
> > Peter Wemm wrote:
> > > On Tuesday 31 May 2005 01:56 pm, John Baldwin wrote:
> > >>On Tuesday 31 May 2005 11:06 am, Michael Reifenberger wrote:
> > >>>On Tue, 31 May 2005, David O'Brien wrote:
> > >>>>Ha!!  We can only have 1 sector worth of code in boot0.  At this
> > >>>>point we only have a few bytes of free code space.  No where near
> > >>>>enough to do the long mode switch.
> > >>>
> > >>>Sorry. I didnt meant boot0 but btx. I do know that boot0 is too
> > >>>small. But btx is already switching to protected mode so it should
> > >>>be possible to switch to 64bit mode too.
> > >>
> > >>Note that the loader uses the BIOS (via virtual 8086 mode) to do
> > >> all the disk I/O, etc.  Since long mode doesn't support vm86 mode,
> > >> you'd end up with a loader that couldn't do any I/O to load the
> > >> kernel, etc. unless you started including device drivers for all
> > >> the different storage and networking hardware, etc.  A 64-bit
> > >> loader really isn't feasible unless your 64-bit machine includes
> > >> firmware that you can use from 64-bit mode like EFI on ia64 or OFW
> > >> on sparc. You probably want to stick with a 32-bit loader on amd64
> > >> for now.
> > >
> > > Yes, there are a lot of good reasons to do it the way it is done,
> > > but this is the killer reason.  We simply cannot do vm86 or bios
> > > calls from a 64 bit loader, period.
> > >
> > > Other "good" reasons, besides the above:
> > > * We don't need to maintain a seperate loader code base
> > > * We can load test kernels with an existing loader on a
> > > FreeBSD/i386 system (and run from a ramdisk or miniroot)
> > > * We would need to maintain 32 bit code to do bios calls anyway,
> > > even if we did switch between 32 bit and 64 bit mode on the fly.
> > > If we have a complete 32 bit BTX environment, we get massive
> > > complexity for little benefit.
> >
> > I'm trying to come up with a good joke about writing OFW-style
> > drivers in 4th, but I'm having a hard time not cracking up too hard
> > while I type =-D
> 
> Actually, we could embed a 64 bit linux kernel in there and use their
> drivers in order to chain load the freebsd kernel..  That would solve
> the bios problem. :-)


That is the joke...Right? o_O

-- 
This is a private letter and only the intended people may read this
message. You may not store, quote or publish this document for any
purposes. The data/information held within this message are for
private use, and no one may disclose it. There are no guarentees that
the information disclosed is accurate, or that the links/attached
files will not be contaminated with Viruses. You use all links, and
all attachments, at your own free will and thus risk. You have been
warned.