On Tue, 6 Aug 2024 20:12:55 +0000 Song Liu <songliubraving@xxxxxxxx> wrote: > > > > On Aug 6, 2024, at 1:01 PM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > > > On Tue, 6 Aug 2024 16:00:49 -0400 > > Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > > >>>>> + if (IS_ENABLED(CONFIG_LTO_CLANG) && !addr) > >>>>> + addr = kallsyms_lookup_name_without_suffix(trace_kprobe_symbol(tk)); > >>>>> + > >>>> > >>>> So you do the lookup twice if this is enabled? > >>>> > >>>> Why not just use "kallsyms_lookup_name_without_suffix()" the entire time, > >>>> and it should work just the same as "kallsyms_lookup_name()" if it's not > >>>> needed? > >>> > >>> We still want to give priority to full match. For example, we have: > >>> > >>> [root@~]# grep c_next /proc/kallsyms > >>> ffffffff81419dc0 t c_next.llvm.7567888411731313343 > >>> ffffffff81680600 t c_next > >>> ffffffff81854380 t c_next.llvm.14337844803752139461 > >>> > >>> If the goal is to explicitly trace c_next.llvm.7567888411731313343, the > >>> user can provide the full name. If we always match _without_suffix, all > >>> of the 3 will match to the first one. > >>> > >>> Does this make sense? > >> > >> Yes. Sorry, I missed the "&& !addr)" after the "IS_ENABLED()", which looked > >> like you did the command twice. > > > > But that said, does this only have to be for llvm? Or should we do this for > > even gcc? As I believe gcc can give strange symbols too. > > I think most of the issue comes with LTO, as LTO promotes local static > functions to global functions. IIUC, we don't have GCC built, LTO enabled > kernel yet. > > In my GCC built, we have suffixes like ".constprop.0", ".part.0", ".isra.0", > and ".isra.0.cold". We didn't do anything about these before this set. So I > think we are OK not handling them now. We sure can enable it for GCC built > kernel in the future. Hmm, I think it should be handled as it is. This means it should do as livepatch does. Since I expected user will check kallsyms if gets error, we should keep this as it is. (if a symbol has suffix, it should accept symbol with suffix, or user will get confused because they can not find which symbol is kprobed.) Sorry about the conclusion (so I NAK this), but this is a good discussion. Thanks, > > Thanks, > Song > > > -- Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
