On Mon, Dec 17, 2018 at 04:06:18PM -0800, Andi Kleen wrote: > On Mon, Dec 17, 2018 at 05:36:44PM -0500, Steven Rostedt wrote: > > On Mon, 17 Dec 2018 15:31:26 -0600 > > Josh Poimboeuf <jpoim...@redhat.com> wrote: > > > > > On Mon, Dec 17, 2018 at 08:29:38PM +0100, Peter Zijlstra wrote: > > > > On Mon, Dec 17, 2018 at 12:16:38PM -0600, Josh Poimboeuf wrote: > > > > > > > > > > Yes LTO causes the to be treated like static functions. > > > > > > > > > > > > I guess noclone is unlikely to be really needed here because these > > > > > > functions are unlikely to be cloned. > > > > > > > > > > > > So as a workaround it could be removed. > > > > > > > > > > > > But note we have other noclone functions in the tree (like in KVM) > > > > > > which actually need it. > > > > > > > > > > How about we just use the __used attribute then? It seems to have the > > > > > same result of preventing IPA optimizations (without the weird side > > > > > effect of missing frame pointers). > > > > > > > > AFAIK we don't have any in-tree LTO, so it can all go in the bin. > > > > > > > > When/if we get the LTO trainwreck sorted -- which very much includes > > > > getting that memory-order-consume fixed -- we can revisit all that. > > > > > > Ok, then if there are no objections I'll just send a revert of: > > > > > > dd3dad0d716d ("ftrace: Mark function tracer test functions > > > noinline/noclone")
Sorry for suggesting this prematurely, my email client stopped syncing and I missed your later replies to Peter about this. > > Should it be reverted, or just remove the noclone, and keep the > > noinline? > > It should not be touched for now, until it is properly debugged. > > IMHO Josh's explanation doesn't make much sense and there > was a lot of handwaving > > And just fixing one case isn't good enough because there are other > noclone functions in the tree. > > It the problem is the plugin the plugin needs to be fixed. > > If the problem is gcc we need a gcc test case and bug, with > some analysis, and then based on that select the proper workaround. The plugin is only used for older versions of GCC. Newer versions have the same functionality builtin with -fsanitize-coverage=trace-pc. So the problem is GCC. We're using a function attribute which at least oneGCC developer doesn't recommend. If you want to keep the LTO support then '__used' seems like a much better choice. -- Josh