Re: [patch] vm86: Clear AC on INT

Maciej W. Rozycki (
Thu, 1 Aug 2002 18:40:31 +0200 (MET DST)

On Thu, 1 Aug 2002, Kasper Dupont wrote:

> Ehrm, that wasn't my point. My point was that if the feature exist
> in virtual 86 mode but not in real mode, the kernel should prevent
> it from being used in virtual 86 mode because it is supposed to
> emulate real mode.

The mode is supposed to emulate an 8086 which doesn't have the flag.
Everything else that is available in the mode is a pure implementation
property -- disabling the logic involved is simply not justified by any
means. Any "real mode" code that operates on the AC flag must have been
created after i386 was released as it requires 32-bit instructions. Hence
it has to be prepared to deal with the vm86 mode.

The AC flag doesn't work unless the AM flag is set in cr0 anyway, so
full real mode compatibility may be implemented in software here if

+  Maciej W. Rozycki, Technical University of Gdansk, Poland   +
+        e-mail:, PGP key available        +

- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to More majordomo info at Please read the FAQ at