From: Steven Rostedt <rostedt@goodmis.org>
To: Jiri Olsa <olsajiri@gmail.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
Andrii Nakryiko <andrii.nakryiko@gmail.com>,
Masami Hiramatsu <mhiramat@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>,
lkml <linux-kernel@vger.kernel.org>,
linux-trace-kernel@vger.kernel.org, bpf@vger.kernel.org,
Jackie Liu <liu.yun@linux.dev>
Subject: Re: [PATCH RFC] ftrace: Show all functions with addresses in available_filter_functions_addrs
Date: Fri, 9 Jun 2023 13:12:53 -0400 [thread overview]
Message-ID: <20230609131253.0d67e746@gandalf.local.home> (raw)
In-Reply-To: <ZINW9FqIoja76DRa@krava>
On Fri, 9 Jun 2023 09:44:36 -0700
Jiri Olsa <olsajiri@gmail.com> wrote:
> On Fri, Jun 09, 2023 at 09:24:10AM +0100, Mark Rutland wrote:
> >
> > Do you need the address of the function entry-point or the address of the
> > patch-site within the function? Those can differ, and the rec->ip address won't
> > necessarily equal the address in /proc/kallsyms, so the pointer in
> > /proc/kallsyms won't (always) match the address we could print for the ftrace site.
> >
> > On arm64, today we can have offsets of +0, +4, and +8, and within a single
> > kernel image different functions can have different offsets. I suspect in
> > future that we may have more potential offsets (e.g. due to changes for HW/SW
> > CFI).
>
> so we need that for kprobe_multi bpf link, which is based on fprobe,
> and that uses ftrace_set_filter_ips to setup the ftrace_ops filter
>
> and ftrace_set_filter_ips works fine with ip address being the address
> of the patched instruction (it's matched in ftrace_location)
Yes, exactly. And it's off with the old "mcount" way of doing things too.
>
> but right, I did not realize this.. it might cause confusion if people
> don't know it's patch-side addresses.. not sure if there's easy way to
> get real function address out of rec->ip, but it will also get more
> complicated on x86 when IBT is enabled, will check
>
> or we could just use patch-side addresses and reflect that in the file's
> name like 'available_filter_functions_patch_addrs' .. it's already long
> name ;-)
No! "available_filter_function_addrs" is enough to know that it's not
kallsyms. It's the filtered function address, which is enough description.
If people don't RTFM, then too bad ;-)
You can use ftrace_location() that takes an instruction pointer, and will
return the rec->ip of that function as long as it lands in between the
function's kallsyms start and end values.
-- Steve
next prev parent reply other threads:[~2023-06-09 17:13 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-08 21:26 [PATCH RFC] ftrace: Show all functions with addresses in available_filter_functions_addrs Jiri Olsa
2023-06-08 22:43 ` Andrii Nakryiko
2023-06-08 23:27 ` Steven Rostedt
2023-06-08 23:55 ` Andrii Nakryiko
2023-06-09 0:13 ` Jiri Olsa
2023-06-09 8:24 ` Mark Rutland
2023-06-09 16:44 ` Jiri Olsa
2023-06-09 17:12 ` Steven Rostedt [this message]
2023-06-09 18:29 ` Andrii Nakryiko
2023-06-09 20:37 ` Jiri Olsa
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