linux-kernel - Re: [PATCH v3 1/2] perf build: Properly guard libbpf includes

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Message-ID: <Y716Nt3c/Lc0Z4P5@kernel.org>
Date:   Tue, 10 Jan 2023 11:46:14 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Jiri Olsa <olsajiri@...il.com>, Mike Leach <mike.leach@...aro.org>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, peterz@...radead.org, mingo@...hat.com,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        namhyung@...nel.org
Subject: Re: [PATCH v3 1/2] perf build: Properly guard libbpf includes

Em Tue, Jan 10, 2023 at 11:31:12AM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Mon, Jan 09, 2023 at 11:29:51AM -0800, Ian Rogers escreveu:
> > On Mon, Jan 9, 2023 at 10:37 AM Ian Rogers <irogers@...gle.com> wrote:
> > > -int libbpf_register_prog_handler(const char *sec __maybe_unused,
> > > -                                 enum bpf_prog_type prog_type __maybe_unused,
> > > -                                 enum bpf_attach_type exp_attach_type
> > > __maybe_unused,
> > > -                                 const struct
> > > libbpf_prog_handler_opts *opts __maybe_unused)
> > > +static int libbpf_register_prog_handler(const char *sec __maybe_unused,
> > > +                                       enum bpf_prog_type prog_type
> > > __maybe_unused,
> > > +                                       enum bpf_attach_type
> > > exp_attach_type __maybe_unused,
> > > +                                       const void *opts __maybe_unused)
> > > {
> > >        pr_err("%s: not support, update libbpf\n", __func__);
> > >        return -ENOTSUP;
> > > ```
> > >
> > > There are some other fixes necessary too. I'll try to write the fuller
> > > patch but I have no means for testing except for undefining
> > > HAVE_LIBBPF_BPF_PROGRAM__SET_INSNS.
> > 
> > So libbpf_prog_handler_opts is missing in the failing build, this
> > points to a libbpf before 0.8. I'm somewhat concerned that to work
> > around these linkage problems we're adding runtime errors - we may
> > build but the functionality is totally crippled. Is it worth
> > maintaining these broken builds or to just upfront fail the feature
> > test?
 
> Probably better to make the feature test disable bpf support while
> emitting a warning that features such as a, b, and c won't we available.

This would be the one-liner I think is appropriate for v6.2, ok?

diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
index 9962ae23ab8c5868..5b87846759036f6f 100644
--- a/tools/perf/Makefile.config
+++ b/tools/perf/Makefile.config
@@ -589,6 +589,8 @@ ifndef NO_LIBELF
           $(call feature_check,libbpf-bpf_program__set_insns)
           ifeq ($(feature-libbpf-bpf_program__set_insns), 1)
             CFLAGS += -DHAVE_LIBBPF_BPF_PROGRAM__SET_INSNS
+          else
+            dummy := $(error Error: libbpf devel library needs to be >= 0.8.0 to build with LIBBPF_DYNAMIC, update or build statically with the version that comes with the kernel sources);
           endif
           $(call feature_check,libbpf-btf__raw_data)
           ifeq ($(feature-libbpf-btf__raw_data), 1)