On Wed, 7 Aug 2024 00:19:20 +0000 Song Liu <songliubraving@xxxxxxxx> wrote: > > > > On Aug 6, 2024, at 5:01 PM, Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote: > > > > 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. > > Do you mean we do not want patch 3/3, but would like to keep 1/3 and part > of 2/3 (remove the _without_suffix APIs)? If this is the case, we are > undoing the change by Sami in [1], and thus may break some tracing tools. What tracing tools may be broke and why? For this suffix problem, I would like to add another patch to allow probing on suffixed symbols. (It seems suffixed symbols are not available at this point) The problem is that the suffixed symbols maybe a "part" of the original function, thus user has to carefully use it. > > Sami, could you please share your thoughts on this? Sami, I would like to know what problem you have on kprobes. Thank you, > > If this works, I will send next version with 1/3 and part of 2/3. > > Thanks, > Song > > [1] https://lore.kernel.org/all/20210408182843.1754385-8-samitolvanen@xxxxxxxxxx/ > -- Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
