On Thu 2024-08-08 15:20:26, Song Liu wrote: > > > > 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. 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. Best Regards, Petr
