From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH v2 net-next 04/10] perf, bpf: allow bpf programs attach to tracepoints Date: Thu, 7 Apr 2016 22:58:47 +0200 Message-ID: <20160407205847.GI3448@twins.programming.kicks-ass.net> References: <1459993411-2754735-1-git-send-email-ast@fb.com> <1459993411-2754735-5-git-send-email-ast@fb.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Steven Rostedt , "David S . Miller" , Ingo Molnar , Daniel Borkmann , Arnaldo Carvalho de Melo , Wang Nan , Josef Bacik , Brendan Gregg , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com To: Alexei Starovoitov Return-path: Content-Disposition: inline In-Reply-To: <1459993411-2754735-5-git-send-email-ast@fb.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Wed, Apr 06, 2016 at 06:43:25PM -0700, Alexei Starovoitov wrote: > introduce BPF_PROG_TYPE_TRACEPOINT program type and allow it to be attached > to the perf tracepoint handler, which will copy the arguments into > the per-cpu buffer and pass it to the bpf program as its first argument. > The layout of the fields can be discovered by doing > 'cat /sys/kernel/debug/tracing/events/sched/sched_switch/format' > prior to the compilation of the program with exception that first 8 bytes > are reserved and not accessible to the program. This area is used to store > the pointer to 'struct pt_regs' which some of the bpf helpers will use: > +---------+ > | 8 bytes | hidden 'struct pt_regs *' (inaccessible to bpf program) > +---------+ > | N bytes | static tracepoint fields defined in tracepoint/format (bpf readonly) > +---------+ > | dynamic | __dynamic_array bytes of tracepoint (inaccessible to bpf yet) > +---------+ > > Not that all of the fields are already dumped to user space via perf ring buffer > and broken application access it directly without consulting tracepoint/format. > Same rule applies here: static tracepoint fields should only be accessed > in a format defined in tracepoint/format. The order of fields and > field sizes are not an ABI. > > Signed-off-by: Alexei Starovoitov Acked-by: Peter Zijlstra (Intel)