> That is the problem right here: .eh_frame-based unwinding is too slow, so it > has to be > done offline in userspace. What about instead adding ORC information to > userspace? That > would be much faster to use.
I'm not familiar with ORC, but there are a few things that initially come to mind in looking towards such a solution. First, are there any examples of perf being able to reference ORC data coming from user-space or is it currently limited to PERF_CONTEXT_KERNEL? For system-wide profiling, we still require that the kernel can do high-velocity unwinding across address contexts. My (limited) understanding of ORC is that the result produced by objtool gets you a series of unwind tables, but those tables require further processing by the kernel at boot. Again, I have limited understanding, but wouldn't something need to be processed as part of spawning and loading executable pages? There are both .orc_unwind and .orc_unwind_ip sections, both of which need to be sorted. I don't know what layer would be responsible for that, or how it adapts to dlopen(), double-mapping pages like libffi, etc... but I'm sure people will have opinions about it. I don't know if this is limited to generating ORC data from DWARF, but the orc-unwinder documentation also refers to difficulty when dealing with inline assembly. That would perhaps mean that this could end up being a lot of work and still not fix the minor-annoyance of strlen/etc not showing up correctly. There is also a risk that ORC data cannot represent the ever-increasing optimizations from GCC. _______________________________________________ devel mailing list -- devel@lists.fedoraproject.org To unsubscribe send an email to devel-le...@lists.fedoraproject.org Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org Do not reply to spam on the list, report it: https://pagure.io/fedora-infrastructure
