link: implement uprobe/uretprobe

[mmat11]

Closes #277

TODO

• tests (I've already tested manually (both pmu and tracefs))
• adapt uretprobe example - examples: adapt uretprobe example to use link/uretprobe #280

[mmat11]

I've added unit tests; tests on v4.9 are failing because I think uprobes weren't available at all before v4.17:

https://github.com/torvalds/linux/blob/v4.16/Documentation/trace/uprobetracer.rst
https://github.com/torvalds/linux/blob/v4.17/Documentation/trace/uprobetracer.rst

Edit: nvm https://github.com/torvalds/linux/blob/v4.9/kernel/events/uprobes.c 🤔

[ti-mo]

uprobetracer.txt was renamed to uprobetracer.rst in 4.17, so this is expected. The commit f3f096cfedf8 that introduced /uprobe_events landed in kernel 3.5, so kernel support should not be an issue. This test does pass on our 4.14 CI kernel. I think something must've changed in the config defaults between 4.9 and 4.14, since we don't enable uprobes explicitly in our CI kernels.

It's probably okay to skip the test if tracefsProbe() returns ENOENT there.

[mmat11]

https://elixir.bootlin.com/linux/v4.9/source/kernel/trace/Kconfig#L448
https://elixir.bootlin.com/linux/v4.19/source/kernel/trace/Kconfig#L496

I think we need to set this explicitly here -> https://github.com/cilium/ci-kernels/blob/master/config (or skip the test)

[ti-mo]

@mmat11 Tracking this in cilium/ci-kernels#11, feel free to add a conditional skip.

[lmb]

Some last minute drive by comments, looks great!

[lmb]

@mmat11 Tracking this in cilium/ci-kernels#11, feel free to add a conditional skip.

BRANCH=uprobes ./run-tests.sh 5.10 should work now.

[ti-mo]

Great job on the refactor! Left a few readability comments, but solid overall. 👌