Messages in this thread | | | Date | Fri, 18 Aug 2023 14:20:33 -0400 | From | Steven Rostedt <> | Subject | Re: [RFC PATCH v1 1/1] tracing/kprobe: Add multi-probe support for 'perf_kprobe' PMU |
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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.
I mentioned having a way to pass in the vmlinux debug info address and subtract the kaslr_offset from it. But that's actually unnecessary. If you have the address of the function you want, and the address of _text, both from the debug info of vmlinux, you can simply pass in "_text+offset", and then use kallsyms to give you _text, and add the offset to give you the address for create_local_trace_kprobe().
-- Steve
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