Re: [RFC] Platform information services

[Javier Martín]

2008/8/14 Vesa Jääskeläinen <address@hidden>:
> Javier Martín wrote:
>> Hi there everybody,
>>
>> I'm opening the RFC because I want to add some kind of infrastructure to
>> retrieve the address of system/platform structures. I will explain
>> myself: my use case is in i386-pc and for the drivemap module, in which
>> a function installs a TSR int13h handler. This requires the function to
>> have access to two real mode structures, namely the BIOS Data Area,
>> which is based at 0040:0000h; and the Interrupt Vector Table, which
>> conventionally starts at 0 but that could have been placed elsewhere by
>> the use of the LIDT instruction.
>
> But it is designed to use linear address space for memory so no need to
> worry about it. I do not see any reason why there would be paging or
> non-linear memory mapping in GRUB 2 (i386-pcbios).
Yes, but this is a "kernel" design decision that is specified nowhere
to the modules writers. Thus, this could change tomorrow and the
scheme would break down.
>
> Or did I miss something?
>
> So basically I do not see need for such services. As this does not even
> need to be platform independent.
>
> If you need to alter IVT you can modify it on the fly. Though you have
> to remember where to use only LOW mem addresses in there.
Not just low mem addresses, I need to compute the real mode far
pointer (seg:off). Besides, while the BDA always starts at 0040:0000,
the IVT could have been relocated by either the BIOS or GRUB itself,
so I need to use SIDT, which is not a privileged instruction itself
but requires a privileged drop to r-mode to get the IVT address
instead of the pmode IDT.

-Habbit
>
>
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