netdev - Re: [PATCHv3 bpf-next 2/2] perf tools: Rework prologue generation code

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Date:   Fri, 3 Jun 2022 11:46:52 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        "linux-perf-use." <linux-perf-users@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        Ian Rogers <irogers@...gle.com>
Subject: Re: [PATCHv3 bpf-next 2/2] perf tools: Rework prologue generation code

On Fri, Jun 3, 2022 at 2:21 AM Jiri Olsa <jolsa@...nel.org> wrote:
>
> Some functions we use for bpf prologue generation are going to be
> deprecated. This change reworks current code not to use them.
>
> We need to replace following functions/struct:
>    bpf_program__set_prep
>    bpf_program__nth_fd
>    struct bpf_prog_prep_result
>
> Currently we use bpf_program__set_prep to hook perf callback before
> program is loaded and provide new instructions with the prologue.
>
> We replace this function/ality by taking instructions for specific
> program, attaching prologue to them and load such new ebpf programs
> with prologue using separate bpf_prog_load calls (outside libbpf
> load machinery).
>
> Before we can take and use program instructions, we need libbpf to
> actually load it. This way we get the final shape of its instructions
> with all relocations and verifier adjustments).
>
> There's one glitch though.. perf kprobe program already assumes
> generated prologue code with proper values in argument registers,
> so loading such program directly will fail in the verifier.
>
> That's where the fallback pre-load handler fits in and prepends
> the initialization code to the program. Once such program is loaded
> we take its instructions, cut off the initialization code and prepend
> the prologue.
>
> I know.. sorry ;-)
>
> Suggested-by: Andrii Nakryiko <andrii@...nel.org>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  tools/perf/util/bpf-loader.c | 128 ++++++++++++++++++++++++++++++-----
>  1 file changed, 110 insertions(+), 18 deletions(-)
>
> diff --git a/tools/perf/util/bpf-loader.c b/tools/perf/util/bpf-loader.c
> index e7992a0eb477..2ce5f9684863 100644
> --- a/tools/perf/util/bpf-loader.c
> +++ b/tools/perf/util/bpf-loader.c
> @@ -9,6 +9,7 @@
>  #include <linux/bpf.h>
>  #include <bpf/libbpf.h>
>  #include <bpf/bpf.h>
> +#include <linux/filter.h>
>  #include <linux/err.h>
>  #include <linux/kernel.h>
>  #include <linux/string.h>
> @@ -49,6 +50,7 @@ struct bpf_prog_priv {
>         struct bpf_insn *insns_buf;
>         int nr_types;
>         int *type_mapping;
> +       int *proglogue_fds;

massively copy/pasted typo? prologue_fds?

Other than that looks good to me, but we'll need Arnaldo's ack before
merging into bpf-next.

>  };
>
>  struct bpf_perf_object {
> @@ -56,6 +58,11 @@ struct bpf_perf_object {
>         struct bpf_object *obj;
>  };
>

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