Hello, I finally got some time digging into Lttng (using it on Xenomai, see [1] for historic reference).
Since we have a hard realtime system, I chosen to use dynamic probes. That means only liblttng-ust-tracepoint.so wil get pulled into the process (it its available), no threads are spawned, etc. This is to minimize potential issues, without dealing with compiletime selection/macros. (Pre-)loading the tracepoint library will then pull in liblttng-ust.so. So far so good, but I found out that tracepoint/tracef are unusable currently. First you need to link with liblttng-ust.so, then you have vasprintf doing memory allocations. I did a custom solution with dynamic loading. # Outlined custom solution The own binary gets a sourcefile similar to ```c #define TRACEPOINT_DEFINE #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE #include <lttng/lttng-ust-tracelog.h> ``` There is no need to add the definition to the own tracepoint library, the binaries tracepoint library will depend on `liblttng-ust.so` and the definitions are pulled in if the tracepoint library is loaded. There are a own namespaces variant of macros and wrapper functions ## Issues Thats a short recap, easier to quote and address whether some upstream solution is possible ### Use tracelog / tracef with dynamic probes is there an easy solution for doing this? is the solution of creating the stubs yourself valid? ### Allocations in the tracelog / tracef functions Would you accept a change, where first some buffer on the stack and vsnprintf is used, only in case the buffer is to small a dynamic one will be allocated? ### No Include guards in lttng/lttng-ust-tracelog.h and lttng/lttng-ust-tracef.h Some other issue is that `<lttng/lttng-ust-tracelog.h>` does not have include guards and including both the custom implementation and `<lttng/tracelog.h>` will lead to duplicate definitions and compile errors. Regards, Norbert [1] - https://lists.lttng.org/pipermail/lttng-dev/2019-November/029410.html _______________________________________________ lttng-dev mailing list lttng-dev@lists.lttng.org https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
