On 32bit systems VOLK crashes about gr-dvbt HOT 5 CLOSED

The function is_unaligned() doesn't really work as expected (at least on 32-bit systems). It returns False even when the address of one or more parameters is unaligned.

If all the volk functions in ofdm_sym_acquisition_impl.cc and dvbt_demap_impl.cc are forced to be unaligned, there are no GPF's and the flow works perfectly.

from gr-dvbt.

It seem that the alignement need to be taken form volk and set in each block like this:

const int alignment_multiple =
volk_get_alignment() / sizeof(gr_complex);
set_alignment(std::max(1, alignment_multiple));

Also for locally allocated buffers I modified the allocation method from new (c++) to posix_memalign()

The changes are in the latest github commits.

from gr-dvbt.

I can see why you abandoned 32-bit Linux and went to 64-bit. The alignment issues seem quite painful. After testing the new commits, it appears that posix_memalign() is buggy on 32-bit systems. It's causing segfaults and errors in unrelated modules. Here's what I've seen:

[Fri Jan 24 16:29:22 2014] python2[31620]: segfault at 43289bd0 ip b1af6a90 sp bfea11b0 error 4 in libglib-2.0.so.0.3600.0[b1a80000+ff000]

[Fri Jan 24 16:37:19 2014] python2[32631]: segfault at 426dd030 ip b1a62984 sp bf819290 error 4 in libpango-1.0.so.0.3200.5[b1a46000+49000]

and "bad_weak_ptr error" in GRC. Reverting back to the "new" allocation eliminates these issues.

At this point, I'd have to say that you should not waste any more effort on these issues. I'll just make a local patch to force unaligned volk calls.

from gr-dvbt.

Ok, I have now a 32bit machine to see what's going on. VOLK is working fine but the alignment is guaranteed only for out/in buffers. If a buffer is aligned and then one plays with the start of the buffer then it become unaligned. Probably a redesign to make sure ANY buffer passed to VOLK is aligned is necessary.
For now the unaligned functions are used so the flow should not crash.

from gr-dvbt.

Closing this issue as it is fixed for my machines.

from gr-dvbt.