[OpenBIOS] PIC Passthough( VGA )

[Segher Boessenkool]

On Fri, Dec 22, 2017 at 11:11:45AM +0000, Mark Cave-Ayland wrote:
> On 19/12/17 16:20, Jd Lyons wrote:
> 
> >>On Dec 19, 2017, at 10:56 AM, Segher Boessenkool 
> >><segher at kernel.crashing.org> wrote:
> >>>25619: b?branch ( 0x014 ) 0x0026 ( =dec 38)
> >>>25620:     (unnamed-fcode) [0x9bd]
> >>>25621:     b(lit) ( 0x010 ) 0xff
> >>>25622:     and ( 0x023 )
> >>>25623:     my-space ( 0x103 )
> >>>25624:     + ( 0x01e )
> >>>25625:     (unnamed-fcode) [0xa08]
> >>>25626:     b(lit) ( 0x010 ) 0x6
> >>>25627:     and ( 0x023 )
> >>>25628:     b(lit) ( 0x010 ) 0x4
> >>>25629:     = ( 0x03c )
> >>>25630:     b?branch ( 0x014 ) 0x0009 ()
> >>>25631:         b(') ( 0x011 ) (unnamed-fcode) [0x9c1]
> >>>25632:         b(to) ( 0x0c3 ) (unnamed-fcode) [0x9c0]
> >>>25633:     b(>resolve) ( 0x0b2 )
> >>>25634: b(>resolve) ( 0x0b2 )
> >>>
> >>>It seems to break right here……………………………….
> >>
> >>Those b?branch are in interpret mode, I don't know if that is handled
> >>correctly (it is tricky to get right).
> >
> >So, is it hanging at b(>resolve) ( 0x0b2 ) or (unnamed-fcode) [0xddf] ?
> >
> >Do we need to work on how Openbios handles  b?branch?
> 
> Are you sure that b?branch is the culprit here?

No, but it is very suspicious.

> A b?branch...b(>resolve) 
> is a representation of a if() { ... } block which means as soon as you 
> hit the b(>resolve) then you execute the contents of the buffer 
> generated between b?branch and b(>resolve) if you match the condition.

But that is the incorrect thing to do!  A b?branch in interpret mode
(with flag 0) should skip the following code, _not_ try to compile it.

It can be compiled from [IF] instead of IF for example (somewhat comparable
to #if in C).

> Now the Solaris/SPARC boot blocks do some really crazy stuff in Forth 
> which to the best of my knowledge flushed out all the FCode branch bugs 
> - not that there couldn't be a bug remaining, but it's much more likely 
> that something in the b?branch...b(>resolve) is throwing an exception.

Yup, more debugging would help.


Segher