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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Kris Van Hees <kris.van.hees@oracle.com>
Cc: Network Development <netdev@vger.kernel.org>,
	bpf <bpf@vger.kernel.org>,
	dtrace-devel@oss.oracle.com, LKML <linux-kernel@vger.kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: [RFC PATCH 00/11] bpf, trace, dtrace: DTrace BPF program type implementation and sample use
Date: Mon, 17 Jun 2019 20:01:52 -0700
Message-ID: <CAADnVQ+zAwoH_mjJLhfEgXHHz+3WYkzhEm-mEObP0koLiSvknw@mail.gmail.com> (raw)
In-Reply-To: <20190618015442.GG8794@oracle.com>

On Mon, Jun 17, 2019 at 6:54 PM Kris Van Hees <kris.van.hees@oracle.com> wrote:
>
> It is not hypothetical.  The folowing example works fine:
>
> static int noinline bpf_action(void *ctx, long fd, long buf, long count)
> {
>         int                     cpu = bpf_get_smp_processor_id();
>         struct data {
>                 u64     arg0;
>                 u64     arg1;
>                 u64     arg2;
>         }                       rec;
>
>         memset(&rec, 0, sizeof(rec));
>
>         rec.arg0 = fd;
>         rec.arg1 = buf;
>         rec.arg2 = count;
>
>         bpf_perf_event_output(ctx, &buffers, cpu, &rec, sizeof(rec));
>
>         return 0;
> }
>
> SEC("kprobe/ksys_write")
> int bpf_kprobe(struct pt_regs *ctx)
> {
>         return bpf_action(ctx, ctx->di, ctx->si, ctx->dx);
> }
>
> SEC("tracepoint/syscalls/sys_enter_write")
> int bpf_tp(struct syscalls_enter_write_args *ctx)
> {
>         return bpf_action(ctx, ctx->fd, ctx->buf, ctx->count);
> }
>
> char _license[] SEC("license") = "GPL";
> u32 _version SEC("version") = LINUX_VERSION_CODE;

Great. Then you're all set to proceed with user space dtrace tooling, right?

What you'll discover thought that it works only for simplest things
like above. libbpf assumes that everything in single elf will be used
and passes the whole thing to the kernel.
The verifer removes dead code only from single program.
It disallows unused functions. Hence libbpf needs to start doing
more "linker work" than it does today.
When it loads .o it needs to pass to the kernel only the functions
that are used by the program.
This work should be straightforward to implement.
Unfortunately no one had time to do it.
It's also going to be the first step to multi-elf support.
libbpf would need to do the same "linker work" across .o-s.

  reply index

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-20 23:47 Kris Van Hees
2019-05-21 17:56 ` Alexei Starovoitov
2019-05-21 18:41   ` Kris Van Hees
2019-05-21 20:55     ` Alexei Starovoitov
2019-05-21 21:36       ` Steven Rostedt
2019-05-21 21:43         ` Alexei Starovoitov
2019-05-21 21:48           ` Steven Rostedt
2019-05-22  5:23             ` Kris Van Hees
2019-05-22 20:53               ` Alexei Starovoitov
2019-05-23  5:46                 ` Kris Van Hees
2019-05-23 21:13                   ` Alexei Starovoitov
2019-05-23 23:02                     ` Steven Rostedt
2019-05-24  0:31                       ` Alexei Starovoitov
2019-05-24  1:57                         ` Steven Rostedt
2019-05-24  2:08                           ` Alexei Starovoitov
2019-05-24  2:40                             ` Steven Rostedt
2019-05-24  5:26                             ` Kris Van Hees
2019-05-24  5:10                       ` Kris Van Hees
2019-05-24  4:05                     ` Kris Van Hees
2019-05-24 13:28                       ` Steven Rostedt
2019-05-21 21:36       ` Kris Van Hees
2019-05-21 23:26         ` Alexei Starovoitov
2019-05-22  4:12           ` Kris Van Hees
2019-05-22 20:16             ` Alexei Starovoitov
2019-05-23  5:16               ` Kris Van Hees
2019-05-23 20:28                 ` Alexei Starovoitov
2019-05-30 16:15                   ` Kris Van Hees
2019-05-31 15:25                     ` Chris Mason
2019-06-06 20:58                       ` Kris Van Hees
2019-06-18  1:25                   ` Kris Van Hees
2019-06-18  1:32                     ` Alexei Starovoitov
2019-06-18  1:54                       ` Kris Van Hees
2019-06-18  3:01                         ` Alexei Starovoitov [this message]
2019-06-18  3:19                           ` Kris Van Hees
2019-05-22 14:25   ` Peter Zijlstra
2019-05-22 18:22     ` Kris Van Hees
2019-05-22 19:55       ` Alexei Starovoitov
2019-05-22 20:20         ` David Miller
2019-05-23  5:19         ` Kris Van Hees
2019-05-24  7:27       ` Peter Zijlstra
2019-05-21 20:39 ` [RFC PATCH 01/11] bpf: context casting for tail call Kris Van Hees
2019-05-21 20:39 ` [RFC PATCH 02/11] bpf: add BPF_PROG_TYPE_DTRACE Kris Van Hees
2019-05-21 20:39 ` [RFC PATCH 03/11] bpf: export proto for bpf_perf_event_output helper Kris Van Hees
     [not found] ` <facilities>
2019-05-21 20:39   ` [RFC PATCH 04/11] trace: initial implementation of DTrace based on kernel Kris Van Hees
2019-05-21 20:39 ` [RFC PATCH 05/11] trace: update Kconfig and Makefile to include DTrace Kris Van Hees
     [not found] ` <features>
2019-05-21 20:39   ` [RFC PATCH 06/11] dtrace: tiny userspace tool to exercise DTrace support Kris Van Hees
2019-05-21 20:39 ` [RFC PATCH 07/11] bpf: implement writable buffers in contexts Kris Van Hees
2019-05-21 20:39 ` [RFC PATCH 08/11] perf: add perf_output_begin_forward_in_page Kris Van Hees
     [not found] ` <the>
     [not found]   ` <context>
2019-05-21 20:39     ` [RFC PATCH 09/11] bpf: mark helpers explicitly whether they may change Kris Van Hees
     [not found] ` <helpers>
2019-05-21 20:39   ` [RFC PATCH 10/11] bpf: add bpf_buffer_reserve and bpf_buffer_commit Kris Van Hees
2019-05-21 20:40 ` [RFC PATCH 11/11] dtrace: make use of writable buffers in BPF Kris Van Hees
2019-05-21 20:48 ` [RFC PATCH 00/11] bpf, trace, dtrace: DTrace BPF program type implementation and sample use Kris Van Hees
2019-05-21 20:54   ` Steven Rostedt
2019-05-21 20:56   ` Alexei Starovoitov

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