> On Aug 9, 2024, at 8:40 AM, Petr Mladek <[email protected]> wrote: > > On Thu 2024-08-08 15:20:26, Song Liu wrote: >> >> >>> On Aug 8, 2024, at 2:59 AM, Petr Mladek <[email protected]> wrote: >>> >>> On Wed 2024-08-07 20:48:48, Song Liu wrote: >>>> >>>> >>>>> On Aug 7, 2024, at 8:33 AM, Sami Tolvanen <[email protected]> wrote: >>>>> >>>>> Hi, >>>>> >>>>> On Wed, Aug 7, 2024 at 3:08 AM Masami Hiramatsu <[email protected]> >>>>> wrote: >>>>>> >>>>>> On Wed, 7 Aug 2024 00:19:20 +0000 >>>>>> Song Liu <[email protected]> wrote: >>>>>> >>>>>>> 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? >>>>> >>>>> This was a few years ago when we were first adding LTO support, but >>>>> the unexpected suffixes in tracing output broke systrace in Android, >>>>> presumably because the tools expected to find specific function names >>>>> without suffixes. I'm not sure if systrace would still be a problem >>>>> today, but other tools might still make assumptions about the function >>>>> name format. At the time, we decided to filter out the suffixes in all >>>>> user space visible output to avoid these issues. >>>>> >>>>>> 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. >>>>> >>>>> The reports we received back then were about registering kprobes for >>>>> static functions, which obviously failed if the compiler added a >>>>> suffix to the function name. This was more of a problem with ThinLTO >>>>> and Clang CFI at the time because the compiler used to rename _all_ >>>>> static functions, but one can obviously run into the same issue with >>>>> just LTO. >>>> >>>> I think newer LLVM/clang no longer add suffixes to all static functions >>>> with LTO and CFI. So this may not be a real issue any more? >>>> >>>> If we still need to allow tracing without suffix, I think the approach >>>> in this patch set is correct (sort syms based on full name, >>> >>> Yes, we should allow to find the symbols via the full name, definitely. >>> >>>> remove suffixes in special APIs during lookup). >>> >>> Just an idea. Alternative solution would be to make make an alias >>> without the suffix when there is only one symbol with the same >>> name. >>> >>> It would be complementary with the patch adding aliases for symbols >>> with the same name, see >>> https://lore.kernel.org/r/[email protected] >> >> I guess v3 plus this work may work well together. >> >>> I would allow to find the symbols with and without the suffix using >>> a single API. >> >> Could you please describe how this API would work? I tried some >> idea in v1, but it turned out to be quite confusing. So I decided >> to leave this logic to the users of kallsyms APIs in v2. > > If we create an alias without the suffix but only when there is only > one symbol with such a name then we have, for example: > > klp_complete_transition.lwn.123456 > klp_complete_transition [alias] > > init_once.lwn.2131221 > init_once.lwn.3443243 > init_once.lwn.4324322 > init_once.lwn.5214121 > init_once.lwn.2153121 > init_once.lwn.4342343 > > This way, it will be possible to find the static symbol > "klp_complete_transition" without the suffix via the alias. > It will have the alias because it has an unique name. > > While "init_once" symbol must always be searched with the suffix > because it is not unique. > > It looks like >99% of static symbols have unique name.
Got it. The idea is to generate the alias at boot time. I think this will indeed work. IIUC, v3 of this set with Alessandro's work (maybe with some variations) should do this. Thanks, Song
