Re: [RFC bpf-next 0/2] libbpf Userspace Runtime-Defined Tracing (URDT)

[Alan Maguire <alan.maguire@oracle.com>]

On 31/01/2024 16:20, Alan Maguire wrote:
> Adding userspace tracepoints in other languages like python and
> go is a very useful for observability.  libstapsdt [1]
> and language bindings like python-stapsdt [2] that rely on it
> use a clever scheme of emulating static (USDT) userspace tracepoints
> at runtime.  This involves (as I understand it):
> 
> - fabricating a shared library
> - annotating it with ELF notes that describe its tracepoints
> - dlopen()ing it and calling the appropriate probe fire function
>   to trigger probe firing.
> 
> bcc already supports this mechanism (the examples in [2] use
> bcc to list/trigger the tracepoints), so it seems like it
> would be a good candidate for adding support to libbpf.
> 
> However, before doing that, it's worth considering if there
> are simpler ways to support runtime probe firing.  This
> small series demonstrates a simple method based on USDT
> probes added to libbpf itself.
>

[snip]

> The useful thing about this is that by attaching to
> libbpf.so (and firing probes using that library) we
> can get system-wide dynamic probe firing.  It is also
> easy to fire a dynamic probe - no setup is required.
> 
> More examples of auto and manual attach can be found in
> the selftests (patch 2).
> 
> If this approach appears to be worth pursing, we could
> also look at adding support to libstapsdt for it.
>

Proof-of-concept libstapsdt support has been built and tested;
consumers of libstapsdt continue to work the same way but
with URDT support, we can trace dynamic events system-wide.
See

https://github.com/linux-usdt/libstapsdt/compare/main...alan-maguire:libstapsdt:urdt


> Alan Maguire (2):
>   libbpf: add support for Userspace Runtime Dynamic Tracing (URDT)
>   selftests/bpf: add tests for Userspace Runtime Defined Tracepoints
>     (URDT)
> 
>  tools/lib/bpf/Build                           |   2 +-
>  tools/lib/bpf/Makefile                        |   2 +-
>  tools/lib/bpf/libbpf.c                        |  94 ++++++++++
>  tools/lib/bpf/libbpf.h                        |  94 ++++++++++
>  tools/lib/bpf/libbpf.map                      |  13 ++
>  tools/lib/bpf/libbpf_internal.h               |   2 +
>  tools/lib/bpf/urdt.bpf.h                      | 103 +++++++++++
>  tools/lib/bpf/urdt.c                          | 145 +++++++++++++++
>  tools/testing/selftests/bpf/Makefile          |   2 +-
>  tools/testing/selftests/bpf/prog_tests/urdt.c | 173 ++++++++++++++++++
>  tools/testing/selftests/bpf/progs/test_urdt.c | 100 ++++++++++
>  .../selftests/bpf/progs/test_urdt_shared.c    |  59 ++++++
>  12 files changed, 786 insertions(+), 3 deletions(-)
>  create mode 100644 tools/lib/bpf/urdt.bpf.h
>  create mode 100644 tools/lib/bpf/urdt.c
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/urdt.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_urdt.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_urdt_shared.c
>