On Fri, 18 Aug 2023 14:20:33 -0400
Steven Rostedt [off-list ref] wrote:
On Fri, 18 Aug 2023 20:13:43 +0200
Francis Laniel [off-list ref] wrote:
quoted
Hi.
Le vendredi 18 août 2023, 17:41:41 CEST Steven Rostedt a écrit :
quoted
On Fri, 18 Aug 2023 21:37:05 +0900
Masami Hiramatsu (Google) [off-list ref] wrote:
quoted
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/ (local)
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.
Thank you,
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
--
Masami Hiramatsu (Google) [off-list ref]