[ros-dev] multiboot.S patch in need of review, please

[Hartmut Birr]

Royce Mitchell III schrieb:

> I was in a strange mood and decided to try to implement something Alex 
> wanted.
>
> I've done the leg-work on this, but need someone familiar with boot-up 
> and particularly smp to review this patch. I do not have access to 
> smp, and do not wish to break it.
>
> This patch implements the /3G switch from within multiboot.S, which is 
> necessary in order to configure the page tables correctly.
>
> I noticed some code in _main() that was processing a 3G switch on the 
> command-line, and I can't understand how it could possibly work 
> because it's not readjusting the page tables, nor does it transition 
> to the 0xC0000000 address space that I can see, so I don't think that 
> code actually works. If it does, I'm glad to be proved wrong.
>
> The patch I've written makes an assumption that lowmem is available 
> when application processors execute the code. I can't seem to figure 
> out how or where the application processor(s) actually get told to 
> start executing, so I don't know if this assumption is true. However, 
> if it's not true, if someone could point me to the code that inits the 
> application processors, I can configure them to pass the needed info 
> via %ebp or something.
>
> Finally, I haven't actually tried booting this code. I wanted someone 
> to review it first for obvious blunders, or to tell me, if necessary, 
> that I've wasted my time ;)    If I'm on the right track then, when 
> I'm feeling motivated enough again, I will actually try booting it.
>
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Hi,

I think your patch will never work. There are used some offsets which 
based on the '/3GB' switch and other ones are hard coded by KERNEL_BASE. 
IMHO, the boot code should not search for the '/3GB' option. The kernel 
base address must be send by freeldr. The boot code must not contain any 
KERNEL_BASE value. I've add your patch to my source tree. On the smp 
machine, ros reboots in the very early boot phase. It is before the call 
to _main.

- Hartmut