Thread

1. Re: [HACKERS] patch for memory overrun on Linux(i386)

   Maurice Gittens <mgittens@gits.nl> — 1998-03-22T09:42:30Z

   >
   >Of course on x86 there is no special requirement any type to be aligned at
   all.
   >Double do not need to be 8 byte aligned. Ints do not need to be on an even
   >address etc. So malloc can return a pointer to any address it wants on an
   x86
   >and still conform to the restriction.
   Yes and I think it returns 4 byte aligned objects for performance reasons.
   (This is more efficient than storing double/int on 1/2 byte boundaries.)
   
   >
   >On a Sparc or an Alpha, objects must to be aligned to the sizeof the type.
   >So shorts are 2 byte aligned, ints 4 byte, and doubles 8 byte. Since malloc
   >has no idea what you are allocating it has to return an 8 byte aligned
   pointer.
   >
   >But all this is a bit of a red herring. The original bug if I recall was
   >caused by the caller assuming that the return from palloc was 8 byte
   aligned.
   >Since the caller "knew" that the pointer was 8 byte aligned it then went on
   >to do some "fancy" pointer arithmetic to arrive at an offset. This is what
   >is broken, not the Linux malloc().
   Yes, I think so too.
   >
   >That said, I have a plan in mind to get a nice performance boost for
   palloc().
   >As a side effect, I will guarantee 8 byte alignment of pointers returned
   >from palloc().
   >
   Does this imply that more memory will be used that strictly necesary under
   linux?
   
   With regards from Maurice.
   
   
   
   
   

2. Re: [HACKERS] patch for memory overrun on Linux(i386)

   Bruce Momjian <maillist@candle.pha.pa.us> — 1998-03-22T20:00:56Z

   > >That said, I have a plan in mind to get a nice performance boost for
   > palloc().
   > >As a side effect, I will guarantee 8 byte alignment of pointers returned
   > >from palloc().
   > >
   > Does this imply that more memory will be used that strictly necesary under
   > linux?
   > 
   > With regards from Maurice.
   
   Actually, perhaps less memory, because malloc memory is not aligned on
   double boundaries, but this is all still just conjecture.
   
   
   -- 
   Bruce Momjian                          |  830 Blythe Avenue
   maillist@candle.pha.pa.us              |  Drexel Hill, Pennsylvania 19026
     +  If your life is a hard drive,     |  (610) 353-9879(w)
     +  Christ can be your backup.        |  (610) 853-3000(h)
   
   

3. Re: [HACKERS] patch for memory overrun on Linux(i386)

   David Gould <dg@illustra.com> — 1998-03-22T22:28:07Z

   > 
   > > >That said, I have a plan in mind to get a nice performance boost for
   > > palloc().
   > > >As a side effect, I will guarantee 8 byte alignment of pointers returned
   > > >from palloc().
   > > >
   > > Does this imply that more memory will be used that strictly necesary under
   > > linux?
   > > 
   > > With regards from Maurice.
   > 
   > Actually, perhaps less memory, because malloc memory is not aligned on
   > double boundaries, but this is all still just conjecture.
   
   
   Ok, you've convinced me. Sheesh...
   
   Change the description to "nice performance boost and use less memory".
   
   ;-)
   
   -dg
    
   David Gould            dg@illustra.com           510.628.3783 or 510.305.9468 
   Informix Software  (No, really)         300 Lakeside Drive  Oakland, CA 94612
    - I realize now that irony has no place in business communications.