> 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, remove suffixes in special APIs during lookup). Thanks, Song
