Moving from 32-bit to 64-bit Fedora

[Matthew Saltzman]

On Mon, 2012-06-11 at 14:36 -0400, Reindl Harald wrote: 
> 
> Am 11.06.2012 20:10, schrieb Geoffrey Leach:
> > I'm currently running a 32-bit Fedora 16 on a 64-bit capable system. I 
> > intend to upgrade to a 64-bin install for Fedora 17.
> > 
> > My way of moving between releases is to install (from DVD), 
> > reformatting / and /boot, leaving /home and /usr/local (which have 
> > their own partitions) untouched.
> > 
> > My question is what steps do I need to take to ensure that the 
> > necessary 32-bit libraries that I'll need to the stuff I have built 
> > locally get installed, or would it be better to just recompile 
> > everything?
> 
> recompile everything!
> these days there is no need for 32bit
> 
> [harry at srv-rhsoft:~]$ rpm -qa | grep i686 | wc -l
> 0
> [harry at srv-rhsoft:~]$ rpm -qa | grep x86_64 | wc -l
> 1128

Well, there is the issue of whether your code is 64-bit clean.  If
anything in your code relies (possibly unintentionally) on the fact that
integers and pointers are 32 bits, your code is not guaranteed to work
properly if you recompile it for 64 bits.  Failure may manifest itself
in strange ways, such as subtly incorrect results that you may not
recognize as errors at first.

So by all means, recompile, but think first.

It's probably not an issue for you, but 64-bit code can be slower than
32-bit code, depending on the mix of computation and memory transfers.
On Intel architectures, 64-bit code gets access to additional registers,
which may well make up for slower memory transfers.  Non-Intel
architectures may be just plain slower, as memory transfers may be
slower and there may be no additional registers to compensate.
-- 
Matthew Saltzman
Clemson University Math Sciences
mjs AT clemson DOT edu