64bit loader

John Baldwin jhb at FreeBSD.org
Tue May 31 13:56:52 PDT 2005

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.

John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org

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