From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnaldo Carvalho de Melo Subject: Re: [PATCH v3 perf, bpf-next 1/4] perf, bpf: Introduce PERF_RECORD_BPF_EVENT Date: Fri, 14 Dec 2018 10:48:57 -0300 Message-ID: <20181214134857.GR21027@kernel.org> References: <20181211233351.4036381-1-songliubraving@fb.com> <20181211233351.4036381-2-songliubraving@fb.com> <20181212131549.GZ5289@hirez.programming.kicks-ass.net> <20181212180553.GC5289@hirez.programming.kicks-ass.net> <20181212133320.75d5cad8@gandalf.local.home> <20181213184546.GM5289@hirez.programming.kicks-ass.net> <3FC2A5A4-9502-4B33-A944-BEB14B520E23@fb.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Peter Zijlstra , Steven Rostedt , lkml , "netdev@vger.kernel.org" , "ast@kernel.org" , "daniel@iogearbox.net" , Kernel Team To: Song Liu Return-path: Content-Disposition: inline In-Reply-To: <3FC2A5A4-9502-4B33-A944-BEB14B520E23@fb.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org Em Thu, Dec 13, 2018 at 09:48:57PM +0000, Song Liu escreveu: > > > > On Dec 13, 2018, at 10:45 AM, Peter Zijlstra wrote: > > > > On Wed, Dec 12, 2018 at 01:33:20PM -0500, Steven Rostedt wrote: > >> On Wed, 12 Dec 2018 19:05:53 +0100 > >> Peter Zijlstra wrote: > >> > >>> On Wed, Dec 12, 2018 at 05:09:17PM +0000, Song Liu wrote: > >>>>> And while this tracks the bpf kallsyms, it does not do all kallsyms. > >>>>> > >>>>> .... Oooh, I see the problem, everybody is doing their own custom > >>>>> kallsym_{add,del}() thing, instead of having that in generic code :-( > >>>>> > >>>>> This, for example, doesn't track module load/unload nor ftrace > >>>>> trampolines, even though both affect kallsyms. > >>>> > >>>> I think we can use PERF_RECORD_MMAP(or MMAP2) for module load/unload. > >>>> That could be separate sets of patches. > >>> > >>> So I would actually like to move bpf_lock/bpf_kallsyms/bpf_tree + > >>> bpf_prog_kallsyms_*() + __bpf_address_lookup() into kernel/kallsyms.c > >>> and also have ftrace use that. > >>> > >>> Because currently the ftrace stuff is otherwise invisible. > >>> > >>> A generic kallsym register/unregister for any JIT. > >> > >> That's if it needs to look up the symbols that were recorded when init > >> was unloaded. > >> > >> The ftrace kallsyms is used to save the function names of init code > >> that was freed, but may have been recorded. With out the ftrace > >> kallsyms the functions traced at init time would just show up as hex > >> addresses (not very useful). > >> > >> I'm not sure how BPF would need those symbols unless they were executed > >> during init (module or core) and needed to see what the symbols use to > >> be). > > > > Aah, that sounds entirely dodgy and possibly quite broken. We freed that > > init code, so BPF or your trampolines (or a tiny module) could actually > > fit in there and insert their own kallsyms, and then we have overlapping > > symbols, which would be pretty bad. > > > > I thought the ftrace kallsym stuff was for the trampolines, which would > > be fairly similar to what BPF is doing. And why I'm trying to get a > > generic dynamic kallsym thing sorted. There's bound the be other > > code-gen things at some point. > > Hi Peter, > > I guess you are looking for something for all ksym add/delete events, like; > > /* > * PERF_RECORD_KSYMBOL > * > * struct { > * struct perf_event_header header; > * u64 addr; > * u32 len; > * u16 ksym_type; > * u16 flags; > * char name[]; > * struct sample_id sample_id; > * }; > */ Can't this reuse PERF_RECORD_MMAP2 with some bit in the header to mean that the name is the symbol name, not a path to some ELF/whatever? The ksym type could be encoded in the prot field, PROT_EXEC for functions, PROT_READ for read only data, PROT_WRITE for rw data. If we do it that way older tools will show the DSO name and an unresolved symbol, and even an indication if its a function or data, which is better than not showing anything when processing a new PERF_RECORD_KSYMBOL. New tools, seeing the perf_event_attr.header bit will know that this is a "map" with just one symbol and will show that for both DSO name and symbol. > We can use ksym_type to encode BPF_EVENT, trampolines, or other type of ksym. > We can use flags or header.misc to encode ksym add/delete. Is this right? > > If we go this direction, shall we reserve a few more bytes in it for different > types to use, like: > > /* > * PERF_RECORD_KSYMBOL > * > * struct { > * struct perf_event_header header; > * u64 addr; > * u32 len; > * u16 ksym_type; > * u16 flags; > * u64 data[2]; > * char name[]; > * struct sample_id sample_id; > * }; > */ > > Thanks, > Song > -- - Arnaldo