On 15/09/20 1:00 am, Arnaldo Carvalho de Melo wrote: > Em Mon, Sep 14, 2020 at 09:39:07PM +0200, Jiri Olsa escreveu: >> On Mon, Sep 14, 2020 at 12:28:41PM -0300, Arnaldo Carvalho de Melo wrote: >>> Em Mon, Sep 14, 2020 at 02:38:27PM +0900, Namhyung Kim escreveu: >>>> On Mon, Sep 14, 2020 at 6:03 AM Jiri Olsa <jo...@kernel.org> wrote: >>>>> Add new version of mmap event. The MMAP3 record is an >>>>> augmented version of MMAP2, it adds build id value to >>>>> identify the exact binary object behind memory map: > >>>>> struct { >>>>> struct perf_event_header header; > >>>>> u32 pid, tid; >>>>> u64 addr; >>>>> u64 len; >>>>> u64 pgoff; >>>>> u32 maj; >>>>> u32 min; >>>>> u64 ino; >>>>> u64 ino_generation; >>>>> u32 prot, flags; >>>>> u32 reserved; > >>> What for this reserved? its all nicely aligned already, u64 followed by >>> two u32 (prot, flags). > >>>>> u8 buildid[20]; > >>>> Do we need maj, min, ino, ino_generation for mmap3 event? >>>> I think they are to compare binaries, then we can do it with >>>> build-id (and I think it'd be better).. > >>> Humm, I thought MMAP2 would be a superset of MMAP and MMAP3 would be a >>> superset of MMAP2. > >>> If we want to ditch useless stuff, then trow away pid, tid too, as we >>> can select those via sample_type. > >>> Having said that, at this point I don't even know if adding new >>> PERF_RECORD_ that are an update for a preexisting one is the right way >>> to proceed. > >>> Perhaps we should attach a BPF program to point where a mmap/munmap is >>> being done (perf_event_mmap()) and allow userspace to ask for whatever >>> it wants? With a kprobes there right now we can implement this MMAP3 >>> easily, no? > >> hmm, I'm always woried about solutions based on kprobes, >> because once the function is moved/removed you're screwed >> and need to keep up with function name changes and be >> backward compatible.. > > Well, I'm not advocating to have it as kprobes permanently, but we can > implement it now using a kprobes, i.e. systems wouldn't have to have its > kernel updated to have this feature, but once then need, for some other > reason, to have their kernel upgraded, then perf would notice that there > is a tracepoint for that and would happily use it. > > So we would be able to use that tracepoint with things like ftrace, > bpftrace, everything that knows about tracepoints, and perf would get > build-ids and whatever else is needed to have a mmap record, in the > future we could even ask for some more (or less) according to the what > is needed for some new feature. > > I.e. the point wasn't about kprobes was about using BPF to state what > we want to collect when a mmap is being put in place.
Isn't the problem with krpobes / tracepoints etc that non-privileged users can't use them.