On Thu, May 02, 2024 at 09:43:02AM -0700, Andrii Nakryiko wrote:

On Thu, May 2, 2024 at 5:23 AM Jiri Olsa [off-list ref] wrote:

quoted

hi,
as part of the effort on speeding up the uprobes [0] coming with
return uprobe optimization by using syscall instead of the trap
on the uretprobe trampoline.

The speed up depends on instruction type that uprobe is installed
and depends on specific HW type, please check patch 1 for details.

Patches 1-6 are based on bpf-next/master, but path 1 and 2 are
apply-able on linux-trace.git tree probes/for-next branch.
Patch 7 is based on man-pages master.

v4 changes:
  - added acks [Oleg,Andrii,Masami]
  - reworded the man page and adding more info to NOTE section [Masami]
  - rewrote bpf tests not to use trace_pipe [Andrii]
  - cc-ed linux-man list

Also available at:
  https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git
  uretprobe_syscall

It looks great to me, thanks! Unfortunately BPF CI build is broken,
probably due to some of the Makefile additions, please investigate and
fix (or we'll need to fix something on BPF CI side), but it looks like
you'll need another revision, unfortunately.

pw-bot: cr

  [0] https://github.com/kernel-patches/bpf/actions/runs/8923849088/job/24509002194

yes, I think it's missing the 32-bit libc for uprobe_compat binary,
probably it needs to be added to github.com:libbpf/ci.git setup-build-env/action.yml ?
hm but I'm not sure how to test it, need to check

But while we are at it.

Masami, Oleg,

What should be the logistics of landing this? Can/should we route this
through the bpf-next tree, given there are lots of BPF-based
selftests? Or you want to take this through
linux-trace/probes/for-next? In the latter case, it's probably better
to apply only the first two patches to probes/for-next and the rest
should still go through the bpf-next tree (otherwise we are running

I think this was the plan, previously mentioned in here:
https://lore.kernel.org/bpf/20240423000943.478ccf1e735a63c6c1b4c66b@kernel.org/ (local)

into conflicts in BPF selftests). Previously we were handling such
cross-tree dependencies by creating a named branch or tag, and merging
it into bpf-next (so that all SHAs are preserved). It's a bunch of
extra work for everyone involved, so the simplest way would be to just
land through bpf-next, of course. But let me know your preferences.

Thanks!

quoted

thanks,
jirka


Notes to check list items in Documentation/process/adding-syscalls.rst:

- System Call Alternatives
  New syscall seems like the best way in here, becase we need

typo (thanks, Gmail): because

ok

quoted

  just to quickly enter kernel with no extra arguments processing,
  which we'd need to do if we decided to use another syscall.

- Designing the API: Planning for Extension
  The uretprobe syscall is very specific and most likely won't be
  extended in the future.

  At the moment it does not take any arguments and even if it does
  in future, it's allowed to be called only from trampoline prepared
  by kernel, so there'll be no broken user.

- Designing the API: Other Considerations
  N/A because uretprobe syscall does not return reference to kernel
  object.

- Proposing the API
  Wiring up of the uretprobe system call si in separate change,

typo: is

ok, thanks

jirka