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Code at 0x9F00 segment after boot (Miscellaneous)

posted by bretjohn Homepage E-mail, Rio Rancho, NM, 09.11.2020, 00:26

> > Hm, is that code active (called)? Does it belongs to some interrupt
> vector?
> > What if you zeto this block?
>
> No interrupt vector in the array points to this code.
I think this might be related to the CSM entry point. I'm not familiar enough with UEFI and CSM to know what's going on, but am guessing that CSM is set up something akin to the old DOS DPMS or Cloaking mechanisms for TSR's. That is, there is a small amount (a "stub") of real-mode code needed to do a small amount of initialization before switching to protected mode and most of the "real" code is located in memory only accessible from protected mode. Particularly if they use high-level languages to virtualize the BIOS, it would be so wasteful of real-mode memory that it would never fly. Old BIOSs were almost always written in assembly for this reason. If this is the case, entries in the IVT would not necessarily point directly at the segment, but would get there indirectly after a few steps into the real-mode interrupt handler code.

That's my best guess, anyway.

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