[lttng-dev] UST tracepoint() NULL pointer argument handling

[Ettore Del Negro]

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Thanks David for your reply, next time (i.e. now) i will check the bug tracker first!

I noticed that passing a NULL (string) pointer to a tracepoint()'s argument is not handled
properly (i.e not supposed to happen). It causes the program to SIGSEV because of strlen( NULL )
in ust-tracepoint-event.h:271 .

I tried some trivial patching like

- -       __event_len += __dynamic_len[__dynamic_len_idx++] = strlen(_src) + 1;
+       __event_len += __dynamic_len[__dynamic_len_idx++] = (_src == NULL ? 1 : strlen(_src) + 1);

but then lib_ring_buffer_do_copy causes a SIGSEV because of memcpy( .., NULL, .. ), so i assume a
NULL pointer is not expected at all.

Is there any particular reason to not handle a NULL pointer? That could save the developer a
ternary statement on theorically every string argument given to tracepoint() and, most
importantly, the application from crash because of LTTng.

Thanks,
Ettore


On 10/5/2012 4:46 PM, David Goulet wrote:
> Hey,
> 
> We have right now an opened bug about this exact issue. We will soon fix this and, as you said,
> help considerably the user experience with subbuffer size :)
> 
> Thanks for the report!
> 
> Cheers David
> 
> On 09/05/12 08:51 PM, Ettore Del Negro wrote:
>> Hello, i have a simple question which may lead to a small user experience improvement:
> 
>>> lttng create tsession
>> Session tsession created. Traces will be written in 
>> .../lttng-traces/tsession-20120510-015819
>>> lttng enable-channel tchan -u -s tsession --subbuf-size=1024
>> UST channel tchan enabled for session tsession
> 
>> a message stating that buffer size is set to a value different than default would be nice
> 
>>> lttng enable-channel tchan -u -s tsession --subbuf-size=1022
>> UST channel tchan enabled for session tsession
> 
>> What happens? Is it set to a value not power of 2? Is it set to the default value? (i guess
>> the latter). The help says: --subbuf-size SIZE   Subbuffer size in bytes (default: 4096,
>> kernel default: 262144) Needs to be a power of 2 for kernel and ust tracers
> 
>> Thanks, Ettore
> 
>> _______________________________________________ lttng-dev mailing list 
>> lttng-dev at lists.lttng.org http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
> 
> 
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