> On Fri, 3 Jun 2005, Leopold Toetsch wrote:
>
> > Nick Glencross wrote:
> >
> > > I fear that there may be some pointer alignment problems in hash because
> > > I'm
> > > getting hangs which seem to be linked to finding strings in hash tables.
> > > (That's pure conjecture)
> >
> > I'm not aware of any problems with alignment in hash.c. *But* we will have
> > troubles on that platform with doubles. Parrot PMCs are allocate off a big
> > piece of mem. A PMC currently happens to be 24 bytes (on 32-bit) but only
> > with
> > the debug-ish version field compiled in. With an --optimze compiled parrot
> > every second PMC would have unaligned doubles.
>
> That's likely to cause a problem. We've been recently hunting down odd
> alignment-related oddities on p5p. As a first approximation, doubles need
> to be aligned at least on the boundaries given by Perl5's
> Config{'alignbytes'}. However, when those doubles are part of a structure,
> it apparently can get more confusing. I don't think we sorted out all the
> possibilities, but Nick C. was the last one fiddling with it.
Yup, you were right. A parrot compiled perl Configure.pl --optimize
core dumps with bus alignment errors almost instantly. As just one
example
$ cat t/op/number_2.pasm
set N0, 42.0
set N1, N0
print N1
print "\n"
end
$ /parrot -b -t -d ff -v t/op/number_2.pasm
debug = 0xff
Reading t/op/number_2.pasm
using optimization '0' (0)
Starting parse...
set %s, %s set
set %s, %s set
print %s print
print %s print
end end
emit set N0, 42.0
emit set N1, N0
emit print N1
emit print "\n"
emit end
6 lines compiled.
Running...
0 set N0, 42 - N0=0.000000,
Bus Error(coredump)
However, recompiling with -misalign (a special directive for Sun's compiler):
-misalign
(SPARC, PowerPC) Informs the compiler that data is not
properly aligned and thus very conservative loads and
stores must be used for data, that is, one byte at a
time. Using this option can cause significant perfor-
mance degradation when running the program. If you
compile and link in separate steps, this option must
appear on both the compile and link command lines.
allows that test to pass.
--
Andy Dougherty [EMAIL PROTECTED]
