On 2022/3/30 10:50 AM, Andrii Nakryiko wrote: > On Tue, Mar 29, 2022 at 7:30 PM Hengqi Chen <hengqi.chen@xxxxxxxxx> wrote: >> >> Hello, Andrii >> >> On 2022/3/30 7:18 AM, Andrii Nakryiko wrote: >>> On Sat, Mar 26, 2022 at 7:43 AM Hengqi Chen <hengqi.chen@xxxxxxxxx> wrote: >>>> >>>> On some old kernels, kprobe auto-attach may fail when attach to symbols >>>> like udp_send_skb.isra.52 . This is because the kernel has kprobe PMU >>>> but don't allow attach to a symbol with '.' ([0]). Add a new option to >>>> bpf_kprobe_opts to allow using the legacy kprobe attach directly. >>>> This way, users can use bpf_program__attach_kprobe_opts in a dedicated >>>> custom sec handler to handle such case. >>>> >>>> [0]: https://github.com/torvalds/linux/blob/v4.18/kernel/trace/trace_kprobe.c#L340-L343 >>>> >>>> Signed-off-by: Hengqi Chen <hengqi.chen@xxxxxxxxx> >>>> --- >>> >>> It's sad, but it makes sense. But, let's have a selftests that >>> validates uses legacy option explicitly (e.g., in >>> prog_tests/attach_probe.c). Also, let's fix this limitation in the >> >> OK, will add a selftest to exercise the new option. >> >>> kernel? It makes no sense to limit attaching to a proper kallsym >>> symbol. >> >> This limitation is lifted in newer kernel. Kernel v5.4 don't have this issue. > > Oh, ok. So how about another plan of attack then: if kprobe target > function has '.' *and* we are on the kernel that doesn't support that, > switch to legacy kprobe automatically? No need for a new option, > libbpf handles this transparently. > That's better, and also eliminate the need for custom SEC() handler. > Still need a test for kprobe with '.' in it, though not sure how > reliable that will be... We can use kallsyms cache to check if > expected xxx.isra.0 (or whatever) is present, and if not - skip > subtest? > Not sure how to do that. Even if such symbol exists, how to reliably trigger it is another problem. >> >>> >>>> tools/lib/bpf/libbpf.c | 9 ++++++++- >>>> tools/lib/bpf/libbpf.h | 4 +++- >>>> 2 files changed, 11 insertions(+), 2 deletions(-) >>>> >>> >>> [...] >> >> -- >> Hengqi
