Thread

Re: [BUGS] Some BUG-FIXES to postgreSQL on SCO 3.2v5.0.2

Bruce Momjian <maillist@candle.pha.pa.us> — 1998-01-11T20:45:23Z

Applied with #if defined(sco) for 6.3.  Beta testing Feb 1.

> 
> You wrote:
> 
> > > 2.) For the float8, it's required to edit the file
> > >
> > > ./src/include/utils/memutils.h
> > >
> > > #define DOUBLEALIGN(LEN) INTALIGN(LEN)
> > > #define MAXALIGN(LEN)    INTALIGN(LEN)
> > >
> > > Otherwise the backend will crash at the insertion of any float8.
> > 
> > I am unsure why the existing code did not work.
> 
> Sorry, I am sure. Let me try to convince you.
> 
> I must quote the HTML version of the manual entitled as
> "Programming Tools Guide Appendix A, ANSI implementation-defined
> behavior".
> 
> ****<Beginning of partial partial citation>
> 
> This section describes the implementation-defined characteristics of
> structures, unions, enumerations, and bit-fields. It corresponds to 
> section ``F.3.9 Structures, Unions, Enumerations, and Bit-Fields'' in 
> the ANSI document. 
> ........
> 80x86 does not impose a restriction on the alignment of objects;
> any object can start at any address. However, for certain objects, 
> having a particular starting address can speed up processor access. 
> 
> The C compiler aligns the whole structure on a 4-byte boundary by 
> default (see ``Pragmas''). All [4|8|10]-byte objects are aligned on a 
> 4-byte boundary, 2-byte objects are aligned on a 2-byte boundary, while 
> 1-byte objects are not aligned. 
> 
> ****<End of citation>
> 
> Now, it's clear: the  *double* struct members  will be aligned to a 
> *4-byte* address boundary (on SCO), but *the original code* computes 
> "DOUBLEALIGN" and "MAXALIGN" to a 
> *8-byte boundary*, because it defines the boundary of alignment as 
> *sizeof(double)* which is equal to 8 (on SCO). 
> This may lead to the "segmentation violation error", 
> which is only the  consequence of a correct malloc (palloc) executed 
> after the corruption of administrative areas of malloc caused by 
> erroneous access of double struct members. (I have traced it.)
> 
> Let me make some possibly unneccesary comments:
> This type of assumptions is very "popular" in sytems originally
> developed on other (BSD-derived or RISC-based) sytems. 
> The most popular form is the assumption about the behaviour of *malloc*: 
> it will align an malloc(sizeof(something)) to a *8-byte boundary*.  
> But it isn't the case. 
> Fortunately the postgreSQL not uses this assumption which holds 
> for your reference platform too.
> 
> 
> Regards,
> Tamas
> _________________________________________
> Tamas Laufer
> Voice/Fax: +36-72-447-570  
> Email: lt660@ipisun.jpte.hu 
> H-7632 Pecs, Fulep L. u 26 III/11 Hungary
> 


-- 
Bruce Momjian
maillist@candle.pha.pa.us