Re: Netboot on Vax

[Paul Koning <paulkoning%comcast.net@localhost>]

On Jan 3, 2014, at 12:28 PM, Johnny Billquist <bqt%Update.UU.SE@localhost> 
wrote:

> On 2014-01-03 17:32, Matthew Whitehead wrote:
>> Team,
>>   I'm pretty sure the MOP boot program hasn't worked for a long while. The 
>> latests I could get to netboot on a MicroVAX-II is 3.1.1. I think the MOP 
>> boot program needs to have its ELF header stripped.
>> 
>> The problem with using the old 3.1.1 boot is that it doesn't recognize the 
>> newest kernels. It complains "Boot failed: Inappropriate file type or 
>> format".
>> 
>> I will work on this, but I'll need some help.
> 
> No, the problem isn't the ELF header. The problem is that the MOP server do 
> not pass a start address over MOP, and so the boot machine makes the 
> assumption the code starts at address 0, while the code actually starts a bit 
> higher.
> Earlier versions of the mop bootable boot program did actually start at 
> address 0, which is why they worked. Newer versions do not. There is a hack 
> somewhere to actually change to load address to 0, since the code is all PIC 
> anyway. Another option would be to fix the mop server to actually pass the 
> start address. The problem is that I looked briefly at this, and could not 
> find how to pass a start address in the MOP messages, but I believe it should 
> be there *somewhere*.

The message you need is “Memory load with transfer address”.  See the V3 MOP 
spec.  It looks like a standard Memory Load message, except that the opcode is 
0 rather than 2, and a 4 byte (little endian of course) transfer address is 
appended to the end.

        paul