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SubjectRe: Profanity in the Linux Kernel?!?!?


On Thu, 10 Jun 1999, Michael B. Trausch wrote:

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>
> On Thu, 10 Jun 1999, David wrote:
> >
> > "oops 00" hmm, very well understood. oops 00.
> >
>
> And that means? Did someting fuck up? Was it minor?
>
> > on the other hand;
> >
> > "fatal exception 0e" a fatal processor exception was trapped. the exception
> > code is 0x0e
> >
>
> I don't buy 0E for a minute. According to my books, 0E is the floppy
> interrupt for the CPU - and what the hell does that have to do with
> anything when it's not even accessed? It tells you nothing.

Then *read* your books. Floppy controller sits on IRQ line 6 and
braindead BIOSes map it on the interrupt gate 0x0e, right. It is *not*
the case for any sane OS - definitely not the case for Linux (where IRQ 6
is mapped to gate 0x26). The reason for that being that interrupt gates up
to 0x11 are reserved for exceptions and can be raised by processor itself.
Gate 0x0e is hardwired to page fault. Normally used for page-ins. If the
requested address is not mapped - SIGSEGV for user mode and Oops in kernel
mode. RTFSource - arch/i386/kernel/traps.c and arch/i386/mm/fault.c
Since this is the time-critical path (paging and copy-on-write go
here) nobody sane would share it with floppy IRQ handling. On 8086-based
boxen reserved range is much smaller - 0--5 instead of 0--0x11, so IBM
guys originally mapped the IRQs to range 8--0x0f. The rest is history -
many DOS programs depend on that setup and even on post-80286 boxen BIOS
uses the same mapping for compatibility reasons. That's it. Nobody sane
would use it in protected mode and IRQs are remapped by the kernel on
very early stages of bootup.
Not that it had any relevance to the censorship idiocy...


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