[Discuss-gnuradio] sync_decimator_ff block with decimation above 262144 gives segfault

[Martin]

Hi all,

When I set the decimation of a fir_filter or integrate block with float 
input and output to 262144 or above, gnuradio crashes with a segfault.
With complex inputs and outputs I get a segfault above 524288.
with short inputs and outputs it is at decimation 131072.

This seems to be the case with most (all) sync_decimator blocks like 
fir_filters or the integration block.

The blocks seem to be are accessing the input buffer outside the valid 
range. Which indicates that the input buffers are too small.

What is strange is that if the datatype is 2 times as large  (float = 4 
bytes, complex = 8 bytes) the decimation factor may also be 2 times 
larger, which indicates that the problem occurs at a bufferposition that 
is 2x2 = 4 times larger.
So the buffersize does not seem to be fixed.


The required buffersizes should be automatically calculated before 
creating the buffers.
Are all buffers still calculated and instantiated in flat_flowgraph.cc ?

I could not yet find any obvious errors in calculating the required 
buffer sizes. But something is going wrong.

The buffersize calculation in flat_flowgraph.cc :
flat_flowgraph::allocate_buffer(basic_block_sptr block, int port) {
...
...
double decimation = (1.0/dgrblock->relative_rate());
int multiple      = dgrblock->output_multiple();
int history       = dgrblock->history();
nitems = std::max(nitems, 
static_cast<int>(2*(decimation*multiple+history)));


When using the integration_ff block gdb debug shows that the segfault is 
at line 61 of integrate_ff_impl.cc

51    integrate_ff_impl::work(int noutput_items,
52                    gr_vector_const_void_star &input_items,
53                    gr_vector_void_star &output_items)
54    {
55      const float *in = (const float *)input_items[0];
56      float *out = (float *)output_items[0];
57
58      for (int i = 0; i < noutput_items; i++) {
59      out[i] = (float)0;
60      for (int j = 0; j < d_decim; j++)
61        out[i] += in[i*d_decim+j];//<== segfault here !!!
62      }


gnuradio-config-info -v
3.7.7git-0-gf0cd5041

With best regards,

Martin Dudok van Heel

test_large_decimation_crash_firfilter_cc.grc
Description: Text Data

test_large_decimation_crash_firfilter_cc.py
Description: Text Data

test_large_decimation_crash_firfilter_ff.py
Description: Text Data

test_large_decimation_crash_integrate_ff.py
Description: Text Data

test_large_decimation_crash_integrate_ss.py
Description: Text Data