Jeremy Fitzhardinge wrote:
> H. Peter Anvin wrote:
>> In 32-bit mode? Surely you're joking, Mr. Feynman!
>>
>
> Right, yes.
>
>> What's worse, reloading segments here might be highly unsafe, if the
>> memory previously occupied by the GDT has been overwritten. Keep in
>> mind the GDT is touched on a segment *load*, not on a segment *access*;
>> in areas such as booting that can be a huge difference.
>>
>
> Yep, suits me. I'm happy for the code to assume that at least %cs and
> %ds are sane; I guess %ss too. We could copy %ds into %[efg]s if we
> want to be sure (since I could imagine a bootloader leaving them in a
> less defined state).
No, we shouldn't. %es should be assumed set up (this is 32-bit code,
after all!), and %fs and %gs should not be used.
> But if the gdt could be missing altogether, then, yes, we should not
> touch them at all.
Exactly. Not relying on a set-up GDT is the safest option, IMNSHO.
-hpa
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