On Thu, 22 Jan 2015 09:32:43 -0800
Alexei Starovoitov <alexei.starovoi...@gmail.com> wrote:
> On Thu, Jan 22, 2015 at 8:01 AM, Michael Holzheu
> <holz...@linux.vnet.ibm.com> wrote:
> > Looks like the "test_maps" test case expects to get the keys in
> > the wrong order when iterating over the elements:
> >
> > test_maps: samples/bpf/test_maps.c:79: test_hashmap_sanity: Assertion
> > `bpf_get_next_key(map_fd, &key, &next_key) == 0 && next_key == 2' failed.
> > Aborted
> >
> > Fix this and test for the correct order.
>
> that will break this test on x86...
> we need to understand first why the order of two elements
> came out different on s390...
> Could it be that jhash() produced different hash for the same
> values on x86 vs s390 ?
Yes I think jhash() produces different results for input > 12 bytes
on big and little endian machines because of the following code
in include/linux/jhash.h:
while (length > 12) {
a += __get_unaligned_cpu32(k);
b += __get_unaligned_cpu32(k + 4);
c += __get_unaligned_cpu32(k + 8);
__jhash_mix(a, b, c);
length -= 12;
k += 12;
}
The contents of "k" is directly used as u32 and the result
of "__get_unaligned_cpu32(k)" is different for big and
little endian.
Michael
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