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From:   Andrii Nakryiko <andrii.nakryiko@gmail.com>
Date:   Fri, 5 May 2023 14:21:56 -0700
Message-ID: <CAEf4BzYYnpD6+GSg+wfL1wUY5YasbN2-9NPJ3QkGZ9o963uYdA@mail.gmail.com>
Subject: Re: [PATCH RFC/RFT] perf bpf skels: Stop using vmlinux.h generated
 from BTF, use subset of used structs + CO-RE. was Re: BPF skels in perf .Re:
 [GIT PULL] perf tools changes for v6.4
To:     Jiri Olsa <olsajiri@gmail.com>
Cc:     Ian Rogers <irogers@google.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Namhyung Kim <namhyung@kernel.org>, Song Liu <song@kernel.org>,
        Andrii Nakryiko <andrii@kernel.org>,
        Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Clark Williams <williams@redhat.com>,
        Kate Carcia <kcarcia@redhat.com>, linux-kernel@vger.kernel.org,
        linux-perf-users@vger.kernel.org,
        Adrian Hunter <adrian.hunter@intel.com>,
        Changbin Du <changbin.du@huawei.com>,
        Hao Luo <haoluo@google.com>, James Clark <james.clark@arm.com>,
        Kan Liang <kan.liang@linux.intel.com>,
        Roman Lozko <lozko.roma@gmail.com>,
        Stephane Eranian <eranian@google.com>,
        Thomas Richter <tmricht@linux.ibm.com>,
        Arnaldo Carvalho de Melo <acme@redhat.com>,
        bpf <bpf@vger.kernel.org>, Alexei Starovoitov <ast@kernel.org>,
        Yang Jihong <yangjihong1@huawei.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Paul Clarke <pc@us.ibm.com>
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On Fri, May 5, 2023 at 2:15=E2=80=AFPM Jiri Olsa <olsajiri@gmail.com> wrote=
:
>
> On Fri, May 05, 2023 at 01:46:30PM -0700, Ian Rogers wrote:
> > On Fri, May 5, 2023 at 1:43=E2=80=AFPM Jiri Olsa <olsajiri@gmail.com> w=
rote:
> > >
> > > On Fri, May 05, 2023 at 10:04:47AM -0700, Ian Rogers wrote:
> > > > On Fri, May 5, 2023 at 9:56=E2=80=AFAM Arnaldo Carvalho de Melo <ac=
me@kernel.org> wrote:
> > > > >
> > > > > Em Fri, May 05, 2023 at 10:33:15AM -0300, Arnaldo Carvalho de Mel=
o escreveu:
> > > > > > Em Fri, May 05, 2023 at 01:03:14AM +0200, Jiri Olsa escreveu:
> > > > > > That with the preserve_access_index isn't needed, we need just =
the
> > > > > > fields that we access in the tools, right?
> > > > >
> > > > > I'm now doing build test this in many distro containers, without =
the two
> > > > > reverts, i.e. BPF skels continue as opt-out as in my pull request=
, to
> > > > > test build and also for the functionality tests on the tools usin=
g such
> > > > > bpf skels, see below, no touching of vmlinux nor BTF data during =
the
> > > > > build.
> > > > >
> > > > > - Arnaldo
> > > > >
> > > > > From 882adaee50bc27f85374aeb2fbaa5b76bef60d05 Mon Sep 17 00:00:00=
 2001
> > > > > From: Arnaldo Carvalho de Melo <acme@redhat.com>
> > > > > Date: Thu, 4 May 2023 19:03:51 -0300
> > > > > Subject: [PATCH 1/1] perf bpf skels: Stop using vmlinux.h generat=
ed from BTF,
> > > > >  use subset of used structs + CO-RE
> > > > >
> > > > > Linus reported a build break due to using a vmlinux without a BTF=
 elf
> > > > > section to generate the vmlinux.h header with bpftool for use in =
the BPF
> > > > > tools in tools/perf/util/bpf_skel/*.bpf.c.
> > > > >
> > > > > Instead add a vmlinux.h file with the structs needed with the fie=
lds the
> > > > > tools need, marking the structs with __attribute__((preserve_acce=
ss_index)),
> > > > > so that libbpf's CO-RE code can fixup the struct field offsets.
> > > > >
> > > > > In some cases the vmlinux.h file that was being generated by bpft=
ool
> > > > > from the kernel BTF information was not needed at all, just inclu=
ding
> > > > > linux/bpf.h, sometimes linux/perf_event.h was enough as non-UAPI
> > > > > types were not being used.
> > > > >
> > > > > To keep te patch small, include those UAPI headers from the trimm=
ed down
> > > > > vmlinux.h file, that then provides the tools with just the struct=
s and
> > > > > the subset of its fields needed for them.
> > > > >
> > > > > Testing it:
> > > > >
> > > > >   # perf lock contention -b find / > /dev/null
> > >
> > > I tested perf lock con -abv -L rcu_state sleep 1
> > > and needed fix below
> > >
> > > jirka
> >
> > I thought this was fixed by:
> > https://lore.kernel.org/lkml/20230427234833.1576130-1-namhyung@kernel.o=
rg/
> > but I think that is just in perf-tools-next.
>
> ah ok, missed that one

Please try validating with veristat to check if all of perf's .bpf.o
files are successful. Veristat is part of selftests and can be built
with just `make -C tools/testing/selftests/bpf veristat`. After that;

 sudo ~/bin/veristat tools/perf/util/bpf_skel/.tmp/*.bpf.o

This is a surer way to check that BPF object files are ok at least on
your currently running kernel, than trying to exercise each BPF
program through perf commands.

>
> thanks,
> jirka