[fpc-devel]PowerPC, TypInfo

[Mattias Gaertner]

On Sun, 15 Aug 2004 00:20:47 +0200  Florian Klaempfl <F.Klaempfl at gmx.de>
wrote:

> Jonas Maebe wrote:
> 
> > 
> > On 14 aug 2004, at 21:07, Mattias Gaertner wrote:
> > 
> >>> The GetOrdProp is used to read boolean values. It reads a longint and
> >>> applies "and $ff" to get only the lowest byte. Under PowerPC the
> >boolean>> value is stored just like under i386 in the first byte. Reading
> >the>> longint under i386 works, but of course it does not under powerpc.
> >>>
> >>> So, either the compiler is wrong or the GetOrdValue function is wrong.
> >>>
> >>> Which one should I report?
> >>
> >>
> >> I just found out, that this is also the case for ShortInt, SmallInt,
> >Word> and Byte, but not for enums.
> > 
> > 
> > To me, the fact that it always reads a longint regardless of the size of
> > 
> > the property seems to be inherently wrong. What if the last field of a 
> > class is a byte? Then you can read past the end of the class, possibly 
> > into unallocated memory causing a crash, no?
> 
> No. Classes are always allocated on the heap so the memory block is 
> always at least a multiple of 4.

The longint is read from the start of the SmallInt, so if the class is
packed, its adress is not a multiple of 4. Or are all class variables 4 byte
aligned?


Mattias