On Fri, 9 Jun 2023 09:44:36 -0700
Jiri Olsa [off-list ref] wrote:

On Fri, Jun 09, 2023 at 09:24:10AM +0100, Mark Rutland wrote:

quoted

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