Conversation

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@mycoliza
the highest virtual address is now 0x10000000000, which is exactly 1 TB. and the bootloader is now trying to identity map every 4 KB page from 1 GB to 1 TB, which is...something like 2.684Γ—10^8 4K pages. that's...a lot!
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@mycoliza
for each of those 4k pages, the bootloader had to create a page table entry (possibly allocating a new page table for that entry to go on), and execute the `invlpg` instruction to flush the changes to the page table. that's kind of a lot of work to do, especially in an emulator!
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@mycoliza
and the bootloader does all of this identity mapping before it maps the framebuffer region and starts actually logging what it's doing. the earlier bootloader stages, written in assembly, will write to the VGA buffer if they *fail*, but don't write to the screen otherwise...
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@mycoliza
so this loop, which takes about ~3 minutes on my machine, was happening before the bootloader displays any kind of visual indication that it's even alive at all. and i was seeing the black screen for longer than i was used to, and assuming it was totally dead (i'm impatient)
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@mycoliza
when running with gdb attached, i was a bit more patient, because i was at least interacting with the kernel and seeing that it was "doing stuff", and not in some obviously bad state, so i didn't immediately assume it was dead and kill the emulator...
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@mycoliza
so it turns out, there wasn't really a "bug" at all, exactly. i don't know why QEMU started reporting that new reserved region, but i'm assuming it's for *something* i might want someday, and the bootloader was doing what it's supposed to (and mycelium is totally innocentπŸ˜‡)
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@mycoliza
so, the moral of this story is (a) OS dev is a really miserable thing to do, (2) sometimes every component of a system can "work correctly" individually and still result in bad behavior, and (iii) code that runs before a system can print to ANYTHING is a special level of Hell
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