> On Aug 7, 2024, at 3:08 AM, Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote: > > 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. It appears there are multiple APIs that may need change. For example, on gcc built kernel, /sys/kernel/tracing/available_filter_functions does not show the suffix: [root@(none)]# grep cmos_irq_enable /proc/kallsyms ffffffff81db5470 t __pfx_cmos_irq_enable.constprop.0 ffffffff81db5480 t cmos_irq_enable.constprop.0 ffffffff822dec6e t cmos_irq_enable.constprop.0.cold [root@(none)]# grep cmos_irq_enable /sys/kernel/tracing/available_filter_functions cmos_irq_enable perf-probe uses _text+<offset> for such cases: [root@(none)]# cat /sys/kernel/tracing/kprobe_events p:probe/cmos_irq_enable _text+14374016 I am not sure which APIs do we need to change here. Thanks, Song
