On 13/09/2023 05:32, Thomas Dreibholz wrote:
Hi,
the issue occurs in this code (radio/USRP/usrp_lib.cpp of OAI), in the
red-marked line (line 757):
samples_received=0;
while(samples_received != nsamps) {
if(cc>1) {
// receive multiple channels (e.g. RF A and RF B)
std::vector<void*> buff_ptrs;
for(inti=0; i<cc; i++) buff_ptrs.push_back(buff_tmp[i]+samples_received);
*samples_received += s->rx_stream->recv(buff_ptrs, nsamps, s->rx_md); *
}else{
// receive a single channel (e.g. from connector RF A)
samples_received +=
s->rx_stream->recv((void*)((int32_t*)buff_tmp[0]+samples_received),
nsamps-samples_received,
s->rx_md);
}
if ((s->wait_for_first_pps == 0) &&
(s->rx_md.error_code!=uhd::rx_metadata_t::ERROR_CODE_NONE))
break;
if((s->wait_for_first_pps == 1) && (samples_received != nsamps)) {
printf("sleep...\n"); //usleep(100);
}
}
Reading the code, it seems to be for reading N channels and reading 1
channel. For reading 1 channel, the length given to s->rx_stream->recv
is nsamps-samples_received. However, for reading N channels, the
length is always nsamps. Since the buffer may have already been
incremented by samples_received > 0, this leads to overwriting the
stack. So, this is very likely a bug in libuhd.
Changing the code by:
for (int i=0; i<cc; i++)
buff_ptrs.push_back(buff_tmp[i]+samples_received);
- samples_received += s->rx_stream->recv(buff_ptrs, nsamps,
s->rx_md);
+ samples_received += s->rx_stream->recv(buff_ptrs,
nsamps-samples_received, s->rx_md);
} else {
lets nr-softmodem proceed without segfault. But then, it prints a lot
of these lines:
[PHY] rx_rf: Asked for 30720 samples, got 20941 from USRP
[PHY] problem receiving samples
LLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLO[HW]
[recv] received 20941 samples out of 30720
[HW] Time: 4.35875 s
ERROR_CODE_OVERFLOW (Overflow)
[PHY] rx_rf: Asked for 30720 samples, got 20941 from USRP
[PHY] problem receiving samples
LLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLO[HW]
[recv] received 20941 samples out of 30720
[HW] Time: 4.41057 s
ERROR_CODE_OVERFLOW (Overflow)
...
On 9/13/23 10:55, Thomas Dreibholz wrote:
I am trying to get OAI's nr-softmodem to run with an Ettus URSP N310,
using
targets/PROJECTS/GENERIC-NR-5GC/CONF/gnb.band78.sa.fr1.106PRB.2x2.usrpn310.conf
with just having adapted the IP addresses of the core and device.
Regardless of trying with UHD 4.1 to 4.4, and regardless of the tags
for OAI used (latest tried: 2023.w36), running nr-softmodem
reproducibly segfaults after a few seconds in libuhd:
--
Best regards / Mit freundlichen Grüßen / Med vennlig hilsen
=======================================================================
Thomas Dreibholz
SimulaMet — Simula Metropolitan Centre for Digital Engineering
Centre for Resilient Networks and Applications
Pilestredet 52
0167 Oslo, Norway
-----------------------------------------------------------------------
E-Mail:dre...@simula.no
Homepage:http://simula.no/people/dreibh
=======================================================================
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Unless I'm badly mistaken, this IS NOT a bug in UHD, but rather a bug in
nr-softmodem--it's mis-managing its buffer pointers.
Nothing that UHD can do about that. C++ doesn't have run-time bounds
checking.
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