Re: Default value of x87 registers' reserved bits

[Joerg Sonnenberger <joerg%britannica.bec.de@localhost>]

On Fri, May 28, 2010 at 04:54:50AM +0300, Stathis Kamperis wrote:
> Control, status, etc x87 registers (which are part of the fp
> environment) are 16 bit wide. In protected mode though, they are
> accessed as 32 bit. The upper bits, 31-16, are marked as `reserved'
> and are ought to be ignored. Their default value is _not_ mentioned in
> the CPU specs. At the same time though, when we write to these
> registers we must not tamper with the reserved bits.

The code to extract the state should mask out the high level bits and
code to set it should copy / keep them. The constant should not include
them at all and it should not use a singleton.

Joerg