On Wed, Jul 12, 2017 at 05:32:25PM -0500, Josh Poimboeuf wrote: > If you want perf to be able to use ORC instead of DWARF for user space > binaries, that's not currently possible, though I don't see any > technical blockers for doing so. Perf would need to be taught to read > ORC data. So the problem with userspace stuff is that the unwind data isn't readily available from NMI context. So the kernel unwinder will trigger a fault and abort. The very best we can hope for is using the EH [*] stuff that all binaries actually have _and_ map. The only problem is that most programs don't actually use the EH stuff much so while its mapped, its not actually paged in, so we're still stuck. [*] C++ ABI requires EH bits for stack unwinding for exception handling and the like, and because C++ can unwind through C code, C ABI also mandates EH bits be present. ORC doesn't much change this. What is currently an option is for perf to simply copy out the top n-Kb of the stack for each sample (talk about expensive) and then have userspace unwind it. And for userspace unwinding in userspace, libunwind and the like are fine, I see absolutely no reason to use ORC bits here. -- To unsubscribe from this list: send the line "unsubscribe live-patching" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
