On Aug 28, 2014, at 4:30 AM, Sergey Isakov <isakov...@bk.ru> wrote:
> But what can you do with absolute addressing to _NullSeg?
> -------
> _EntryPoint:
> DD _ToUserCode - ASM_PFX(m16Start)
> DW CODE16
> _16Gdtr:
> DW GDT_SIZE - 1
> _16GdtrBase:
> DQ _NullSeg
>
It looks like Thunk16.S patches the value.
_EntryPoint: .long ASM_PFX(ToUserCode) - ASM_PFX(m16Start)
.word CODE16
_16Gdtr: .word GDT_SIZE - 1
_16GdtrBase: .quad 0
_16Idtr: .word 0x3ff
.long 0
Thanks,
Andrew Fish
> -------
>
> On 28.08.2014, at 15:16, Andrew Fish wrote:
>
>>
>> On Aug 28, 2014, at 12:15 AM, Sergey Isakov <isakov...@bk.ru> wrote:
>>
>>>>
>>>>
>>>> Actually I just noticed you are getting an illegal text-relocation error.
>>>> This is usually caused by an absolute relocation, and clang wants it to be
>>>> IP relative. Basically Xcode/clang only supports a subset of the
>>>> relocations that gcc uses for X64.
>>> If I correctly understand you, compilation for Thunk16 is not possible in
>>> XCLANG toolset because of idea of this codes?
>>>
>>
>> No, but this toolchain puts extra restrictions on how things can be coded.
>>
>> For example Thunk16.asm contains absolute addressing
>> lea r8, @RetFromRealMode
>> But in Thunk16.S this is converted to IP relative addressing to support
>> clang.
>> lea L_RetFromRealMode(%rip), %r8
>> Some of the .set address math in Thunk16.S is also working around addressing
>> mode limitations, as it removes relocations from the code.
>>
>> Thanks,
>>
>> Andrew Fish
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