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From:   Ian Rogers <irogers@google.com>
Date:   Fri, 5 May 2023 13:46:30 -0700
Message-ID: <CAP-5=fVgJdBvjV8S2xKswAFiSZvyCcUvZTO1bsLyUf-wQ0pBuw@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:     Arnaldo Carvalho de Melo <acme@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrii Nakryiko <andrii.nakryiko@gmail.com>,
        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 1:43=E2=80=AFPM Jiri Olsa <olsajiri@gmail.com> wrote=
:
>
> 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 <acme@k=
ernel.org> wrote:
> > >
> > > Em Fri, May 05, 2023 at 10:33:15AM -0300, Arnaldo Carvalho de Melo es=
creveu:
> > > > 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 using su=
ch
> > > bpf skels, see below, no touching of vmlinux nor BTF data during the
> > > build.
> > >
> > > - Arnaldo
> > >
> > > From 882adaee50bc27f85374aeb2fbaa5b76bef60d05 Mon Sep 17 00:00:00 200=
1
> > > 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 generated f=
rom 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 fields =
the
> > > tools need, marking the structs with __attribute__((preserve_access_i=
ndex)),
> > > 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 bpftool
> > > from the kernel BTF information was not needed at all, just including
> > > 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 trimmed d=
own
> > > vmlinux.h file, that then provides the tools with just the structs an=
d
> > > 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.org/
but I think that is just in perf-tools-next.

Thanks,
Ian

> ---
> From b12aea55f1171dc09cde2957f9019c84bda7adbb Mon Sep 17 00:00:00 2001
> From: Jiri Olsa <jolsa@kernel.org>
> Date: Fri, 5 May 2023 13:28:46 +0200
> Subject: [PATCH] perf tools: Fix lock_contention bpf program
>
> We need to define empty 'struct rq' so the runqueues gets
> resolved properly:
>
>   # ./perf lock con -b
>   libbpf: extern (var ksym) 'runqueues': incompatible types, expected [99=
] fwd rq, but kernel has [19783] struct rq
>   libbpf: failed to load object 'lock_contention_bpf'
>   libbpf: failed to load BPF skeleton 'lock_contention_bpf': -22
>   Failed to load lock-contention BPF skeleton
>
> Also rq__old/rq__new need additional '_' so the suffix is ignored
> properly.
>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
>  tools/perf/util/bpf_skel/lock_contention.bpf.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/tools/perf/util/bpf_skel/lock_contention.bpf.c b/tools/perf/=
util/bpf_skel/lock_contention.bpf.c
> index 8911e2a077d8..c2bf24c68c14 100644
> --- a/tools/perf/util/bpf_skel/lock_contention.bpf.c
> +++ b/tools/perf/util/bpf_skel/lock_contention.bpf.c
> @@ -416,13 +416,15 @@ int contention_end(u64 *ctx)
>         return 0;
>  }
>
> +struct rq {};
> +
>  extern struct rq runqueues __ksym;
>
> -struct rq__old {
> +struct rq___old {
>         raw_spinlock_t lock;
>  } __attribute__((preserve_access_index));
>
> -struct rq__new {
> +struct rq___new {
>         raw_spinlock_t __lock;
>  } __attribute__((preserve_access_index));
>
> @@ -434,8 +436,8 @@ int BPF_PROG(collect_lock_syms)
>
>         for (int i =3D 0; i < MAX_CPUS; i++) {
>                 struct rq *rq =3D bpf_per_cpu_ptr(&runqueues, i);
> -               struct rq__new *rq_new =3D (void *)rq;
> -               struct rq__old *rq_old =3D (void *)rq;
> +               struct rq___new *rq_new =3D (void *)rq;
> +               struct rq___old *rq_old =3D (void *)rq;
>
>                 if (rq =3D=3D NULL)
>                         break;
> --
> 2.40.1
>