[fpc-devel] Difficulty in specifying record alignment

[J. Gareth Moreton]

Okay, I got the values to 16 at last!  I needed to include {$PACKRECORDS 
C} as well.  It's ultimately very fiddly though.

Gareth aka. Kit


On 21/10/2019 22:53, J. Gareth Moreton wrote:
> I'm going to have to keep trying.  So far that gets me the following 
> (some debug lines I inserted into the compiler):
>
> record UCOMPLEX.complex
> - alignment = 8
> - aggregatealignment = 8
> - structalignment = 8
> - size = 16
>
> I was wrong about what I said about RECORDMIN=16... the alignment 
> fields are still equal to 8, but it puts the byte offset of the 2nd 
> field to 16.
>
> There might be a bug in my vectorcall code that prevents the correct 
> alignment (plus I need to double-check which alignment field is 
> which).  If there is a bug, I'll post a test and a patch to fix it.
>
> Gareth aka. Kit
>
>
> On 21/10/2019 20:53, Florian Klämpfl wrote:
>> Am 21.10.19 um 21:42 schrieb J. Gareth Moreton:
>>> On 21/10/2019 20:00, Florian Klämpfl wrote:
>>>> What's the problem with
>>>>
>>>> {$push}
>>>> {$codealign RECORDMIN=16}
>>>> type complex = record
>>>>                       re : real;
>>>>                       im : real;
>>>> end;
>>>> {$pop}
>>>>
>>>> ?
>>>
>>> Hi Florian,
>>>
>>> I tried that, but that puts each individual field on a 16-byte boundary 
>>
>> Then do:
>>
>> {$push}
>> {$codealign RECORDMIN=16}
>> type dummyrec = record
>>         b : byte;
>> end;
>>
>> {$pop}
>> type complex = record
>>        case byte of
>>           1 : (
>>                       re : real;
>>                       im : real
>>               );
>>           2 : (alignmentdummy : dummyrec);
>> end;
>>
>> I thought I mentioned this trick even somewhere :)
>>
>>> parameters passed into the function may not be aligned (e.g. when 
>>> deferencing a pointer on the heap after calling, say, 
>>> "New(complex);"), hence why the compiler can only go by the 8-byte 
>>> aggregate alignment.
>>
>> No. Data is guaranteed to be aligned at it's natural boundary when it 
>> is passed without further information.
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>>
>

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