> On Aug 8, 2024, at 2:59 AM, Petr Mladek <pmladek@xxxxxxxx> wrote: > > On Wed 2024-08-07 20:48:48, Song Liu wrote: >> >> >>> On Aug 7, 2024, at 8:33 AM, Sami Tolvanen <samitolvanen@xxxxxxxxxx> wrote: >>> >>> Hi, >>> >>> On Wed, 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: >>>> >>>>> 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/20231204214635.2916691-1-alessandro.carminati@xxxxxxxxx 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. Thanks, Song
