Hi, This is a release announcement of the LTTng kernel tracer for both maintained LTTng stable branches. The main change integrated within the new versions 2.12.1 and 2.11.4 is support for the newly released 5.7 Linux kernel. If you followed the news lately [1], you will notice that LTTng had to work-around a change which un-exports kallsyms symbols, making those inaccessible to GPL modules, which was integrated within Linux 5.7. As a matter of fact, LTTng happens to use kallsyms in some cases to access symbols otherwise not visible to GPL kernel modules. Just to underline the amount of effort that was put into trying to do the right thing, here is an explanation of the alternative approaches that were attempted before going for a work-around using kprobes (taken from commit message of lttng-modules commit a65765406b0 "Unbreak LTTng for kernel 5.7"): Linux commit 0bd476e6c67190b5eb7b6e105c8db8ff61103281 ("kallsyms: unexport kallsyms_lookup_name() and kallsyms_on_each_symbol()") breaks LTTng-modules by removing symbols used by the LTTng-modules out-of-tree tracer. I pointed this out when the change was originally considered before the 5.7 merge window. This generated some discussion but it did not lead to any concrete proposal to fix the issue. [2] The commit has been merged in the 5.7 merge window. At that point, as maintainer of LTTng, I immediately raised a flag about this issue, proposing an alternative approach to solve this: expose the few symbols needed by LTTng to GPL modules. This was NACKed on the ground that the Linux kernel cannot export GPL symbols when there are no in-tree users. [3] Steven Rostedt has shown interest in merging LTTng-modules upstream. LTTng-modules being LGPL, this is very much doable. I have prepared a tree of LTTng-modules "for upstreaming" and sent it to him privately so he can review it. Even if in an ideal scenario LTTng-modules is merged for the following merge window, it leaves LTTng-modules broken on the 5.7 kernel. In order to ensure that the LTTng-modules kernel tracer continues working for my end users on kernels 5.7 onwards, as a very last resort, this is with great reluctance that I created this fix for LTTng modules. It basically uses kprobes to lookup the kallsyms_lookup_name symbol, and continues using kallsyms_lookup_name as before. Steven Rostedt has started looking into lttng-modules, but currently lacks time to look into it further. Understandably, this 15 years old project is larger than he initially expected. Let's hope we receive concrete feedback on how we can improve LTTng to make it acceptable for integration into Linux. Thanks, Mathieu [1] https://lwn.net/Articles/817988/ [2] https://lore.kernel.org/r/20200302192811.n6o5645rsib44vco@localhost [3] https://lore.kernel.org/r/20200409193543.18115-1-mathieu.desnoyers@xxxxxxxxxxxx -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com