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From:   Ian Rogers <irogers@google.com>
Date:   Wed, 7 Jun 2023 00:11:17 -0700
Message-ID: <CAP-5=fVeehz=qyL-eFgc8aa+Q8inmN_mA7N+sGY0z4Sj6Bd9dQ@mail.gmail.com>
Subject: Re: [PATCH v2 4/4] perf build: Filter out BTF sources without a .BTF section
To:     Namhyung Kim <namhyung@kernel.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@kernel.org>,
        Adrian Hunter <adrian.hunter@intel.com>,
        James Clark <james.clark@arm.com>,
        Tiezhu Yang <yangtiezhu@loongson.cn>,
        Yang Jihong <yangjihong1@huawei.com>,
        linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
        bpf@vger.kernel.org
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On Mon, Jun 5, 2023 at 4:35=E2=80=AFPM Namhyung Kim <namhyung@kernel.org> w=
rote:
>
> Hi Ian,
>
> On Mon, Jun 5, 2023 at 1:28=E2=80=AFPM Ian Rogers <irogers@google.com> wr=
ote:
> >
> > If generating vmlinux.h, make the code to generate it more tolerant by
> > filtering out paths to kernels that lack a .BTF section.
> >
> > Signed-off-by: Ian Rogers <irogers@google.com>
> > ---
> >  tools/perf/Makefile.perf | 23 ++++++++++++++++++++---
> >  1 file changed, 20 insertions(+), 3 deletions(-)
> >
> > diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
> > index f1840af195c0..c3bb27a912b0 100644
> > --- a/tools/perf/Makefile.perf
> > +++ b/tools/perf/Makefile.perf
> > @@ -193,6 +193,7 @@ FLEX    ?=3D flex
> >  BISON   ?=3D bison
> >  STRIP   =3D strip
> >  AWK     =3D awk
> > +READELF ?=3D readelf
> >
> >  # include Makefile.config by default and rule out
> >  # non-config cases
> > @@ -1080,12 +1081,28 @@ $(BPFTOOL): | $(SKEL_TMP_OUT)
> >         $(Q)CFLAGS=3D $(MAKE) -C ../bpf/bpftool \
> >                 OUTPUT=3D$(SKEL_TMP_OUT)/ bootstrap
> >
> > -VMLINUX_BTF_PATHS ?=3D $(if $(O),$(O)/vmlinux)                        =
   \
> > +# Paths to search for a kernel to generate vmlinux.h from.
> > +VMLINUX_BTF_ELF_PATHS ?=3D $(if $(O),$(O)/vmlinux)                    =
   \
> >                      $(if $(KBUILD_OUTPUT),$(KBUILD_OUTPUT)/vmlinux)   =
 \
> >                      ../../vmlinux                                     =
 \
> > -                    /sys/kernel/btf/vmlinux                           =
 \
> >                      /boot/vmlinux-$(shell uname -r)
> > -VMLINUX_BTF ?=3D $(abspath $(firstword $(wildcard $(VMLINUX_BTF_PATHS)=
)))
> > +
> > +# Paths to BTF information.
> > +VMLINUX_BTF_BTF_PATHS ?=3D /sys/kernel/btf/vmlinux
> > +
> > +# Filter out kernels that don't exist or without a BTF section.
> > +VMLINUX_BTF_ELF_ABSPATHS ?=3D $(abspath $(wildcard $(VMLINUX_BTF_ELF_P=
ATHS)))
> > +VMLINUX_BTF_PATHS ?=3D $(shell for file in $(VMLINUX_BTF_ELF_ABSPATHS)=
; \
> > +                       do \
> > +                               if [ -f $$file ] && ($(READELF) -t "$$f=
ile" | grep .BTF); \
>
> Wouldn't it be `readelf -S` instead?  Also I think grep needs -q to
> suppress output.

Makes sense, I can change it in v3.

> > +                               then \
> > +                                       echo "$$file"; \
> > +                               fi; \
> > +                       done) \
> > +                       $(wildcard $(VMLINUX_BTF_BTF_PATHS))
>
> This changes the order of processing the sysfs file.
> But I'm not sure it matters much as both /boot/vmlinux and sysfs
> should refer to the running kernel.

Agreed. readelf fails for /sys/kernel/btf/vmlinux as it isn't an elf
file and I'm not sure it is worth worrying too much about the order
here.

Thanks,
Ian

> Thanks,
> Namhyung
>
>
> > +
> > +# Select the first as the source of vmlinux.h.
> > +VMLINUX_BTF ?=3D $(firstword $(VMLINUX_BTF_PATHS))
> >
> >  $(SKEL_OUT)/vmlinux.h: $(VMLINUX_BTF) $(BPFTOOL)
> >  ifeq ($(VMLINUX_H),)
> > --
> > 2.41.0.rc0.172.g3f132b7071-goog
> >