[syslinux] reboot from com32

[Miguel]

> The most likely explanation IMO is that there is a bug in __farcall.
> Unlike __intcall it hasn't been extensively used.  They do, however,
> share almost all the code.
>
> 	-hpa

com32.inc
---------

com32_farcall:
    pushfd              ; Save IF among other things...
    pushad              ; We only need to save some, but...
    mov eax,[esp+10*4]  ; CS:IP
    jmp com32_syscall


com32_intcall:
    pushfd              ; Save IF among other things...
    pushad              ; We only need to save some, but...

    movzx eax,byte [esp+10*4]  ; INT number
    mov eax,[eax*4]            ; Get CS:IP from low memory

com32_syscall:
    cld
    ...

--------

Theory #1:

I am incapable of following the details of com32_syscall, but here is what
jumps out at me ...

both _farcall and _intcall load up the target address into eax.

That means that the _intcall version is going to have to push the flags
onto the stack because the interrupt handler will do an 'iret'.

But the code that is generally called by _farcall is going to do a 'ret',
not an 'iret'.

Therefore, I am concerned that there is going to be an extra set of flags
pushed on to the stack at some point ... which would interfere with
_farcall behavior.

BUT ... this call to F000:FFF0 should not be returning anyway, so I don't
see how that could affect what is going on here.


Theory #2

Confirm that the stack location of the target address is correct:

           mov eax,[esp+10*4]              ; CS:IP

BUT ... if that wasn't correct then _farcall would never have worked.



Hope this helps,
Miguel