Re: kvm86 kernel option

[Jean-Yves Migeon <jeanyves.migeon%free.fr@localhost>]

Le 08/05/12 11:36, David Laight a écrit :
> Does anyone use (or have used in the last n years) the i386
> kernel VM86, KVM86 or KVM86DEBUG options that (I think) allows
> 16bit user programs to run within a 32bit kernel?

Yes. It allows a program to make 16 bits calls, for example to BIOS.

> My suspicions are that, if it ever worked, it will have bitrotted
> out of existance!

What makes you think that?

> Deleting it seems to be a good idea.

I am all for dumping 16 bits compat code, but please remember that 
bioscalls may be needed by programs like X (setting video mode comes to 
mind).

It injects also a few problematic features, like allowing code to be 
mapped at NULL (0x0) (required for v8086 to work properly).

I would suggest commenting out the option from GENERIC, and see if X 
still works ok with different cards, or old drivers (vesa(4)).
NetBSD does not implement all the latest and greatest DRI2/GEM/KMS, so 
better keep code that can still be used by old systems like VESA.

> Possibly wine uses it for 16bit windows code?

Dunno if wine uses it. For DOS and 16 bits mode, dosbox emulates it just 
fine.

> In any case anything written in 16bit code can probably be emulated
> fast enough to be useful.

True, I would expect it to run faster than decades ago.

However, note that what you get here is an /emulation/. If the purpose 
is to run a legacy application, this is fine. If the purpose is to run 
legacy commands to setup the machine (example: video mode setting), you 
are out of luck.

--
Jean-Yves Migeon
jeanyves.migeon%free.fr@localhost