Messages in this thread | | | From | Song Liu <> | Date | Sat, 19 Aug 2023 08:22:50 -0700 | Subject | Re: [RFC PATCH v1 1/1] tracing/kprobe: Add multi-probe support for 'perf_kprobe' PMU |
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On Fri, Aug 18, 2023 at 6:16 PM Masami Hiramatsu <mhiramat@kernel.org> wrote: > > On Fri, 18 Aug 2023 14:20:33 -0400 > Steven Rostedt <rostedt@goodmis.org> wrote: > > > On Fri, 18 Aug 2023 20:13:43 +0200 > > Francis Laniel <flaniel@linux.microsoft.com> wrote: > > > > > Hi. > > > > > > Le vendredi 18 août 2023, 17:41:41 CEST Steven Rostedt a écrit : > > > > On Fri, 18 Aug 2023 21:37:05 +0900 > > > > > > > > Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote: > > > > > That's why perf probe uses the offset from '_text'. Normal KASLR will just > > > > > moves all symbols. (Finer one will move all symbols randomely) > > > > > This should not need to access /proc/kallsyms but vmlinux or SystemMap. > > > > > > > > We could just pass in: "_text+offset" too. > > > > > > So, the idea would be to change the existing create_local_trace_kprobe() and > > > above functions to indicate the user's offset is to be used against _text and > > > not address? > > > > No, not to modify that function, but if you know the offset from _text (via > > the vmlinux), you can easily calculate it for that function. > > Note that the kprobe-event PMU interface itself allows you to specify > FUNC+OFFSET style; > > https://lore.kernel.org/lkml/20171206224518.3598254-5-songliubraving@fb.com/ > > perf_event_attr::kprobe_func = "_text"; > perf_event_attr::probe_offset = OFFSET; > > Then, it should be able to specify the correct one. Of course you can use > other unique symbols around the target symbol.
Trying to catch up with the thread.
Besides the CAP_* issue, we can do this with
perf_event_attr::kprobe_func = NULL; perf_event_attr::kprobe_addr = address;
Then for the CAP_*, I think we should give CAP_PERFMON access to /proc/kallsyms. Would this work?
Thanks, Song
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