On Fri, 9 Jun 2023 09:44:36 -0700 Jiri Olsa <olsajiri@xxxxxxxxx> 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
