Ricardo Neri ricardo.neri-calderon@linux.intel.com writes:
On Thu, 2017-03-30 at 13:10 +0300, Stas Sergeev wrote:
30.03.2017 08:14, Ricardo Neri пишет:
But at least dosemu implements it, so probably it is needed.
Right.
Of course if it is used by one of 100 DOS progs, then there is an option to just add its support to dosemu2 and pretend the compatibility problems did not exist. :)
Do you mean relaying the GP fault to dosemu instead of trapping it and emulating it in the kernel?
Yes, that would be optimal if this does not severely break the current setups. If we can find out that smsw is not in the real use, we can probably do exactly that. But other instructions are not in real use in v86 for sure, so I wouldn't be adding the explicit test-cases to the kernel that will make you depend on some particular behaviour that no one may need. My objection was that we shouldn't write tests before we know exactly how we want this to work.
OK, if only SMSW is used then I'll keep the emulation for SMSW only.
In fact, smsw has an interesting property, which is that no one will ever want to disable its in-kernel emulation to provide its own. So while I'll try to estimate its usage, emulating it in kernel will not be that problematic in either case.
Ah good to know!
As for protected mode, if wine only needs sgdt/sidt, then again, no one will want to disable its emulation. Not the case with sldt, but AFAICS wine doesn't need sldt, and so we can leave sldt without a fixups. Is my understanding correct?
This is my understanding as well. I could not find any use of sldt in wine. Alexandre, would you mind confirming?
Some versions of the Themida software protection are known to use sldt as part of the virtual machine detection code [1]. The check currently fails because it expects the LDT to be zero, so the app is already broken, but sldt segfaulting would still cause a crash where there wasn't one before.
However, I'm only aware of one application using this, and being able to catch and emulate sldt ourselves would actually give us a chance to fix this app in newer Wine versions, so I'm not opposed to having it segfault.
In fact it would be nice to be able to make sidt/sgdt/etc. segfault too. I know a new syscall is a pain, but as far as Wine is concerned, being able to opt out from any emulation would be potentially useful.
[1] https://www.winehq.org/pipermail/wine-bugs/2008-February/094470.html