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

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Date:   Fri, 3 Jun 2022 21:28:20 +0200
From:   Jiri Olsa <olsajiri@...il.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
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 03, 2022 at 11:46:52AM -0700, Andrii Nakryiko wrote:
> 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?

mama mia :)) time to have my eyes checked..  sry, I'll send new version

jirka

> 
> 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;
> >  };
> >
> 
> [...]