[ovs-dev] [PATCH 4/5] test-hash: Fix unaligned pointers.

[Ben Pfaff]

On Thu, May 25, 2017 at 01:18:21PM -0700, Joe Stringer wrote:
> On 25 May 2017 at 10:42, Ben Pfaff <blp at ovn.org> wrote:
> > On Tue, May 23, 2017 at 04:02:15PM -0700, Joe Stringer wrote:
> >> Clang 4.0 complains:
> >>
> >> ../tests/test-hash.c:160:16: error: taking address of packed member 'b' of
> >> class or structure 'offset_ovs_u128' may result in an unaligned pointer value
> >>       [-Werror,-Waddress-of-packed-member]
> >>         in0 = &in0_data.b;
> >>
> >> Rework the 128-bit hash test to have a separate function for setting
> >> bits in the 32-bit offset u128 structure.
> >>
> >> Signed-off-by: Joe Stringer <joe at ovn.org>
> >
> > How about something like this, to reduce code duplication?  I have not
> > tested it with Clang 4.0.
> >
> > diff --git a/tests/test-hash.c b/tests/test-hash.c
> > index d1beead36ed5..f02f0218c71f 100644
> > --- a/tests/test-hash.c
> > +++ b/tests/test-hash.c
> > @@ -153,14 +153,13 @@ check_hash_bytes128(void (*hash)(const void *, size_t, uint32_t, ovs_u128 *),
> >          OVS_PACKED(struct offset_ovs_u128 {
> >              uint32_t a;
> >              ovs_u128 b;
> > -        }) in0_data;
> > -        ovs_u128 *in0, in1;
> > +        }) in0;
> > +        ovs_u128 in1;
> >          ovs_u128 out0, out1;
> >
> > -        in0 = &in0_data.b;
> > -        set_bit128(in0, i, n_bits);
> >          set_bit128(&in1, i, n_bits);
> > -        hash(in0, sizeof(ovs_u128), 0, &out0);
> > +        in0.b = in1;
> > +        hash(&in0.b, sizeof(ovs_u128), 0, &out0);
> >          hash(&in1, sizeof(ovs_u128), 0, &out1);
> >          if (!ovs_u128_equals(out0, out1)) {
> >              printf("%s hash not the same for non-64 aligned data "
> 
> Thanks, this looks like a much better approach and it satisfies clang
> 4.0. Will you propose this formally or shall I? The 256B version needs
> a slight variation on this as well.

I was hoping that you would propose it formally.