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SubjectRe: CONUNDRUM.


On Thu, 13 Feb 1997, Clive Messer wrote:

> On Thu, 13 Feb 1997, Systemkennung Linux wrote:
>
> > > > First guess Alexey. Linux crt0.s doesnt align the stack on an eight byte
> > > > boundary.
> > >
> > > Any reason why it shouldn't? Could this simple thing case a >10%
> > > performance drop for some applications? If so why wasn't this noticed and
> > > fixed long ago?
> >
> > Alan's first guess makes sense in that the Fortran people have been
> > complaining about exactly that problem for quite some time.
>
> I just noticed in HJ's libc Changelog, 5.4.21-5.4.22 .......
>
> * sysdeps/linux/i386/crt/crt0.S: align stack to 8 bytes.

... which won't help you because the code that GCC generates will happily
break the alignment on all possible occasions (function calls, function entry)

The latest pgcc snapshot has an option "-mstack-align-double" which tries to
keep the stack alignment at 64 bits throughout the whole program. There are
some problems with that option yet, I think they'll be sorted out in the next
version.

Bernd

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