[gPXE] Machines hangs when exiting from CLI

[Joshua Oreman]

On Wed, Mar 31, 2010 at 2:49 PM, Itay Gazit <itaygazit at gmail.com> wrote:
> Hi Joshua, all,
>
> Continue to our discussion we had a while ago, I continued my testing on
> entering CLI during POST.
>
> At this experiment I changed the main() to a blank function.
>
> I tested 19 different models machines. The results were that 5 of the 19
> hanged when exiting from CLI!   Including machines from HP, IBM and
> SuperMicro.
>
> My conclusion is that regardless the memory consumption, there is a major
> problem in gPXE when exiting from gPXE during POST.
>
> As I mentioned before, having a reliable CLI during POST is important.
>
> I am willing to continue debug this issue, if you have any idea on how to
> solve it then please let me know.

I appreciate the testing you've done.

This is a problem with the BIOS on these machines. On many BIOSes, it
is simply not possible to enter protected mode during POST; attempting
to do so will cause booting to ultimately fail. There are two
solutions:
- have gPXE provide only limited POST-time functionality with real-mode code;
- don't try to use the CLI during POST

The first is extremely difficult. The second is extremely easy.

I don't understand - why is it so necessary that you enter the CLI
during POST, as opposed to doing it when gPXE is invoked as a boot
device?

-- Josh