Re: 64-bit and N32 kernel interfaces

[Daniel Jacobowitz <dan@debian.org>]

On Thu, Sep 05, 2002 at 04:09:11PM +0200, Maciej W. Rozycki wrote:
> On Thu, 5 Sep 2002, Kevin D. Kissell wrote:
> 
> > n32 has the same data types as o32, an "ILP32" C integer 
> > model.  n64 is a pretty normal "LP64" C integer model.
> > 
> > What do you consider to be broken, and how would you
> > have preferred it to have been done?
> 
>  For n32 it would be natural to have:
> 
> - sizeof(int) = 32
> 
> - sizeof(long) = 64
> 
> - sizeof(void *) = 32
> 
> as the underlying hardware directly supports 64-bit operations (n32
> requires at least MIPS III).  Thus there is no penalty for 64-bit
> arithmetics and if one uses longs one normally wants the largest native
> integer type -- using long long typically (i.e. on most platforms) implies
> double-precision arithmetics with all the drawbacks, especially for the
> division and multiplication operations. 
> 
>  With 32-bit long on 64-bit hardware software has no easy way to figure
> using 64-bit operations is still optimal performance-wise.  I can't see
> any technical benefit from such a setup -- is there any?  I doubt it. 

Well, here's one - while we all know that C code which assumes a
pointer and int are the same size is buggy, it makes everything
substantially simpler if long and void* are the same size.  That's true
for both normal LP64 and ILP32 models.  Since n32 was mostly a
transitional tool (SGI was primarily interested in n64 as I understand
it), I imagine they wanted path of least damage...

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer