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VESAMTTR (recovered from Google) (DOSX)

posted by DOS386(R), 23.07.2007, 02:42

Japheth wrote:

> VESAMTRR "switches" to ring 0 to run the privileged instructions.

I wrote:

> * VERY * interesting source :-)

Japheth wrote:

> Rayer's switches to "real-mode" and runs the instructions.
> But since "real-mode" very often is "v86-mode"

I wrote:

> Looks like very bad design :-( He uses DGJPP, and then goes "real" for
> the relevant activity ... 500 Bytes of real mode assembly could probably
> replace the 100 KB from DGJPP :lol:

> Had thought that Rayer found out how to execute privileged
> instructions under DPMI ... but he didn't ... but you did :-)

> Seem to be at least 4 ways how to execute privileged instruction from DPMI code:

> - Go "real" (bad hack needed to switch ?) ... bad
> - Emulate them in the DPMI host (CR accesses & HLT in HDPMI32)
> - Run "client" in Ring0 (CWSDPR0, DOS/32A, other "WATCOM" extenders ?)
> - Shoot a hole into the protection :lol: and jump to Ring0 (VESAMTRR)


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