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discussion - splitting MCBs again (Developers)

posted by Ninho E-mail, 14.06.2011, 13:38

>> Care to tell why ? At least I hope it's /not/ because something I wrot has
>> you offended

> Well, since you've asked... No, I'm not offended.

Godd, I'm actually relieved...

> I actually find the hypocrisy amusing. You're trying to do the EXACT same thing you told me I couldn't do -- call INT 15.4F from outside an INT 09 handler.
Not so much hypocritical than amusing indeed, it was very counscious and I think it was the reason i mentionned your name in a couple of msgs where I announced "subverting" 15.4F. As to whether it's "the EXACT same" use as your doing I can't pronounce.

You'll be pleased to learn I have renounced this somewhat foolish use of 15.4F (also contradicting by my own conceptions) - not so much because it can't be more than reasonably safe, than because securing the concept and implementation inevitably leads to "baroque" as I called them methods, and ends up costing more in code surface. I couldn't
>
> Just as an aside, I hope you realize that doing this (and the fact that MS
> does it and some of my programs do it) means that your INT 15.4F handler
> must be fully re-entrant. It may already be without you realizing it (I
> haven't looked). But, if the user types a key on the keyboard at the same
> time INT 15.4F is being called from outside INT 09, and it's not fully
> re-entrant, you could have a big problem.
Ah! this is interesting, but more fuel for my and pretty everyone's assumption that int 15/4F should (must?) be /issued/ from the int 9 handler (whether in ROM or otherwise). The case of MS or other software issuing 15/4F53 for the sole purpose of preparing to reboot being set apart, and not sure if even it is assured against reentry in theory (although good enough in practice).

TBH I didn't design the int 15 entry with reentrancy in mind, so there is a high chance that it is not. I would feel concerned (to a point) were my use of 15/4F not already passé :=)


> I don't think any of my programs will directly issue an unprovoked INT
> 15.4FF4, but I have several of them could simulate a scancode of F4h, which
> could cause INT 15.4FF4 to be issued by the INT 09 handler or by one of my
> programs. It's impossible to say exactly what would/could happen in such a
> situation. I will admit that the simulation of an F4h scancode is
> unlikely, but certainly not impossible.
 ....
Thank you, your explanation is great stuff and amply more than I expected to receive. I'm shortening this not out of disinterest but because by coincidence I'm retiring from the scene for a hopefully short period. I'm saving your explanations about your use of the keyboard ecosystem for later deep reading. I'm sure others readers will find them instructive too...

---
Ninho

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