Re: Netboot on Vax

[Johnny Billquist <bqt%update.uu.se@localhost>]

On 2014-01-03 20:08, Johnny Billquist wrote:
> To make it clear.
> objdump on a somewhat recent /boot for VAX:
>
> GW:obj/destdir.vax> objdump -x boot
>
> boot:     file format elf32-little
> boot
> architecture: UNKNOWN!, flags 0x00000102:
> EXEC_P, D_PAGED
> start address 0x003f0000
>
> Program Header:
>      LOAD off    0x00000054 vaddr 0x003f0000 paddr 0x003f0000 align 2**2
>           filesz 0x0000e8dc memsz 0x000110dc flags rwx

[...]

Ah. My memory is coming back to me now that I look at it.
There is currently a fix checked in for this, so I think the current 
boot code might work over mop.

The above objdump is unhelpful, since it's a boot which I have modified.

I hope people excuse my confusing messages. The problem was the reverse 
from what I wrote.
The image sent over mop is loaded at address 0, even though the ELF 
header says otherwise. However, mopd *do* pass the transfer address, 
which means it would jump to the wrong address.

There is a "special" symbol defined in the boot image, to solve it. 
"nisse" (which is a silly Swedish name used for a scrap variable name), 
which is set to absolute 0, and the makefile, when building boot, 
actually tells ld to use nisse as the transfer address, instead of 
what's in the image.

Thus, the "fixed" boot file will work, since it will have a start 
address of 0, even though it would appear that the load address is not 
anywhere close to 0.

(Check common/srt0.S and boot/Makefile for VAX)

I don't recall off hand right now, but I think the primary bootstrap do 
another trick of instead assuming that the first loaded address of the 
image is the start address, and do not even check the transfer address 
in the header, and so that also works with this apparently broken ELF 
image that is /boot.

Someone else is of course welcome to check and correct what I wrote. But 
I think I got it right this time. (I should check the primary boot block 
jump to make sure about that one. It jumps to hdr.elf.e_entry, which I 
should check to refresh myself.)

        Johnny