Correct INT Flag 8 to set page table entries to the correct value rather than 1 #24
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So 7 and 8 do the same thing now? |
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@thegrb93 Int 7 changes the pointer to the page table, Int 8 instead changes the number of entries that it will check If you were to have a page table of say, 32 entries, and you put 16 as byte 3 to the interrupt descriptor of an interrupt with flag 8, it will stop checking the indexes past 16, so you can have your less important page mappings lower in the list, and have this interrupt basically "disable" them temporarily, without having to have a secondary copy of your page table that's half empty and setting your page table pointer to that. Right now, it setting PTBE to 1 effectively makes it disable all but the first entry, which iirc holds the global/default run level settings, if the user wanted this behavior they could set byte 3 to 1 themselves. |
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Ok, I'll trust your insight. the code change looks fine |
In the code for the interrupt handler, there is a small table of what the interrupt flags should do
This brings interrupt flag 8, (Replace page table entries with page table byte from interrupt descriptor) closer to what the comment implies it should do, due to a possible mistake in the original implementation in this commit and this second commit claiming to fix it, both from 11 years ago.
Since setting the page table and page table entries are intended to not be possible at the same time, setting page table entries to 1 seems to be a mistake even if it was claimed to be fixed, unless the intended usecase was for the programmer to then go and find the interrupt descriptor and set the number of page table entries themselves now that they're not being remapped?
The original author appears to have no github, somehow, so I can't contact them to ask if this was intended.