[fpc-devel] Difficulty in specifying record alignment

[Florian Klämpfl]

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.