Re: kernel goes dark on boot

[Emmanuel Dreyfus <manu%netbsd.org@localhost>]

On Wed, Jan 11, 2023 at 08:30:20AM +0000, Emmanuel Dreyfus wrote:
> An interesting problem on an all-in-one HP PC. Booting
> NetBSD-10.0_BETA/amd64 (or prior versions) works fine until the
> kernel starts displaying its messages. At that point the screen
> turns dark.

So far, the thing seems to crash very early in bootstrap, probably
before main().

By adding printf in bootx64.efi (and commenting out ExitBootServices
call so that I can see it), I know I reach the point where 
startprog64 is called.

Debugging what happens after that is more tricky. This is assembly
code, I am not sure I can printf from there. I try to make the
machine reboot at startprog64() start to see if I just reach that 
place.

Searching the web suggests inserting this at the begining of 
startprog64 could do it:
        /* jmp 0xffff:0 to reset */
        .byte   0xea
        .byte   0x00
        .byte   0x00
        .byte   0xff
        .byte   0xff

With that change, the all-in-one PC still hangs, while another machine
does reboot. That may be a question for port-i386@, but is that
debugging technique relibale? Is there something else to try?

If the technique is reliable, then I can only imagine the stack
got corrupted enough that the call to startprog64() does not even
reach it.



-- 
Emmanuel Dreyfus
manu%netbsd.org@localhost