> On Jun 3, 2020, at 6:43 PM, Kinney, Michael D <[email protected]>
> wrote:
>
> Hi Andrew,
>
> I see the following assembly that reads GDTR and IDTR from
> CPU and saves them into the context structure:
>
> ;; UINT32 Gdtr[2], Idtr[2];
> sub esp, 8
> sidt [esp]
> mov eax, [esp + 2]
> xchg eax, [esp]
> and eax, 0xFFFF
> mov [esp+4], eax
>
> sub esp, 8
> sgdt [esp]
> mov eax, [esp + 2]
> xchg eax, [esp]
> and eax, 0xFFFF
> mov [esp+4], eax
>
> This data structure is defined in UEFI Spec, but I do not
> see a detailed description of these 2 arrays and the meaning
> of each entry. Seems like a gap in the spec description.
>
Mike,
Yea that is what I saw too, but I had code code doing the opposite and passing
the context over did not go well. I can think of at least 3 ways ti could be
mapped? Match the instruction, Base 1st, Limit 1st.
Thanks,
Andrew Fish
> Mike
>
>> -----Original Message-----
>> From: Andrew Fish <[email protected]>
>> Sent: Wednesday, June 3, 2020 5:57 PM
>> To: edk2-devel-groups-io <[email protected]>; Kinney,
>> Michael D <[email protected]>
>> Subject: Re: [edk2-devel] Does anyone know the
>> definition of EFI_SYSTEM_CONTEXT_X64.Gdtr[2] and
>> EFI_SYSTEM_CONTEXT_X64.Idtr[2]
>>
>>
>>
>>> On Jun 3, 2020, at 5:37 PM, Michael D Kinney
>> <[email protected]> wrote:
>>>
>>> Hi Andrew,
>>>
>>> Are you referring to the order the fields are filled
>> in by the C code
>>> before the x86 instruction is executed? I do not
>> think that matters.
>>>
>>
>> Mike,
>>
>> The instructions point to a blob of data that is not
>> UINTN aligned. These register point to a limit then base
>> address. If you execute the instruction you get 2 bytes
>> of limit and 4 or 8 bytes of data. But Idtr[0] is base
>> and Intro[1] is limit, so reversed from the instruction
>> order. What defines index 0 vs. index 1 data contents?
>>
>> Thanks,
>>
>> Andrew Fish
>>
>>> Thanks,
>>>
>>> Mike
>>>
>>>> -----Original Message-----
>>>> From: [email protected] <[email protected]> On
>>>> Behalf Of Andrew Fish via groups.io
>>>> Sent: Wednesday, June 3, 2020 4:39 PM
>>>> To: edk2-devel-groups-io <[email protected]>
>>>> Subject: [edk2-devel] Does anyone know the definition
>> of
>>>> EFI_SYSTEM_CONTEXT_X64.Gdtr[2] and
>>>> EFI_SYSTEM_CONTEXT_X64.Idtr[2]
>>>>
>>>> The x86 instructions do limit then base, but the code
>> is
>>>> storing base, then limit. Does anyone remember if
>> this
>>>> is properly defined some place?
>>>>
>>>> Thanks,
>>>>
>>>> Andrew Fish
>>>>
>>>
>>>
>>>
>>>
>
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