[fpc-devel] Compiler limitations

[Florian Klaempfl]

Daniël Mantione schrieb:
> 
> 
> Op Fri, 9 May 2008, schreef Florian Klaempfl:
> 
>> Vincent Snijders schrieb:
>>> Florian Klaempfl schreef:
>>>> Miklos Cserzo schrieb:
>>>>>
>>>>> Hi Folks,
>>>>>
>>>>> according the documentation "Arrays are limited to 2 GBytes in size 
>>>>> in the default processor mode." Is there another mode allowing 
>>>>> bigger arrays?
>>>>
>>>> 64 Bit mode/compiler.
>>>>
>>>
>>> Except for darwin.
>>>
>>> Except it doesn't work:
>>> http://www.freepascal.org/testsuite/cgi-bin/testsuite.cgi?action=3&run1id=21737&testfileid=2417 
>>
>>
>> This is operation system dependent also if you can declare static data 
>> structures of this size. Things like
>>
>> type
>>  ta = array[0..$fffffffff] of byte;
>> var
>>  p : ^ta;
>>
>> begin
>>  new(p);
>> end.
>>
>> should work e.g. on linux.
> 
> Yes, this would work, but wrapping it in a record and adding a field to 
> it might not work. The reason is that the x86_64 still uses singed 
> 32-bit displacements in its operands. 

This is only important for static data which requires relocation. For 
heap/stack the compiler simply generates the constants.

> To support this, a different code 
> generation is needed, which we don't have.
> 
> Many compilers have an mcmodel switch. FPC's x86_64 code generation 
> compares to mcmodel=small.