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Date:   Tue, 29 Dec 2020 16:01:41 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Song Liu <songliubraving@...com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Mark Rutland <mark.rutland@....com>,
        Jiri Olsa <jolsa@...hat.com>, kernel-team@...com
Subject: Re: [PATCH v6 2/4] perf: support build BPF skeletons with perf

Hello,

On Tue, Dec 29, 2020 at 2:41 AM Song Liu <songliubraving@...com> wrote:
>
> BPF programs are useful in perf to profile BPF programs. BPF skeleton is

I'm having difficulties understanding the first sentence - looks like a
recursion. :)  So do you want to use two (or more) BPF programs?

Thanks,
Namhyung


> by far the easiest way to write BPF tools. Enable building BPF skeletons
> in util/bpf_skel. A dummy bpf skeleton is added. More bpf skeletons will
> be added for different use cases.
>
> Acked-by: Jiri Olsa <jolsa@...hat.com>
> Signed-off-by: Song Liu <songliubraving@...com>
> ---
>  tools/build/Makefile.feature        |  4 ++-
>  tools/perf/Makefile.config          |  9 ++++++
>  tools/perf/Makefile.perf            | 49 +++++++++++++++++++++++++++--
>  tools/perf/util/bpf_skel/.gitignore |  3 ++
>  tools/scripts/Makefile.include      |  1 +
>  5 files changed, 63 insertions(+), 3 deletions(-)
>  create mode 100644 tools/perf/util/bpf_skel/.gitignore
>
> diff --git a/tools/build/Makefile.feature b/tools/build/Makefile.feature
> index 97cbfb31b7625..74e255d58d8d0 100644
> --- a/tools/build/Makefile.feature
> +++ b/tools/build/Makefile.feature
> @@ -99,7 +99,9 @@ FEATURE_TESTS_EXTRA :=                  \
>           clang                          \
>           libbpf                         \
>           libpfm4                        \
> -         libdebuginfod
> +         libdebuginfod                 \
> +         clang-bpf-co-re
> +
>
>  FEATURE_TESTS ?= $(FEATURE_TESTS_BASIC)
>
> diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
> index ce8516e4de34f..d8e59d31399a5 100644
> --- a/tools/perf/Makefile.config
> +++ b/tools/perf/Makefile.config
> @@ -621,6 +621,15 @@ ifndef NO_LIBBPF
>    endif
>  endif
>
> +ifdef BUILD_BPF_SKEL
> +  $(call feature_check,clang-bpf-co-re)
> +  ifeq ($(feature-clang-bpf-co-re), 0)
> +    dummy := $(error Error: clang too old. Please install recent clang)
> +  endif
> +  $(call detected,CONFIG_PERF_BPF_SKEL)
> +  CFLAGS += -DHAVE_BPF_SKEL
> +endif
> +
>  dwarf-post-unwind := 1
>  dwarf-post-unwind-text := BUG
>
> diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
> index 62f3deb1d3a8b..d182a2dbb9bbd 100644
> --- a/tools/perf/Makefile.perf
> +++ b/tools/perf/Makefile.perf
> @@ -126,6 +126,8 @@ include ../scripts/utilities.mak
>  #
>  # Define NO_LIBDEBUGINFOD if you do not want support debuginfod
>  #
> +# Define BUILD_BPF_SKEL to enable BPF skeletons
> +#
>
>  # As per kernel Makefile, avoid funny character set dependencies
>  unexport LC_ALL
> @@ -175,6 +177,12 @@ endef
>
>  LD += $(EXTRA_LDFLAGS)
>
> +HOSTCC  ?= gcc
> +HOSTLD  ?= ld
> +HOSTAR  ?= ar
> +CLANG   ?= clang
> +LLVM_STRIP ?= llvm-strip
> +
>  PKG_CONFIG = $(CROSS_COMPILE)pkg-config
>  LLVM_CONFIG ?= llvm-config
>
> @@ -731,7 +739,8 @@ prepare: $(OUTPUT)PERF-VERSION-FILE $(OUTPUT)common-cmds.h archheaders $(drm_ioc
>         $(x86_arch_prctl_code_array) \
>         $(rename_flags_array) \
>         $(arch_errno_name_array) \
> -       $(sync_file_range_arrays)
> +       $(sync_file_range_arrays) \
> +       bpf-skel
>
>  $(OUTPUT)%.o: %.c prepare FORCE
>         $(Q)$(MAKE) -f $(srctree)/tools/build/Makefile.build dir=$(build-dir) $@
> @@ -1004,7 +1013,43 @@ config-clean:
>  python-clean:
>         $(python-clean)
>
> -clean:: $(LIBTRACEEVENT)-clean $(LIBAPI)-clean $(LIBBPF)-clean $(LIBSUBCMD)-clean $(LIBPERF)-clean config-clean fixdep-clean python-clean
> +SKEL_OUT := $(abspath $(OUTPUT)util/bpf_skel)
> +SKEL_TMP_OUT := $(abspath $(SKEL_OUT)/.tmp)
> +SKELETONS :=
> +
> +ifdef BUILD_BPF_SKEL
> +BPFTOOL := $(SKEL_TMP_OUT)/bootstrap/bpftool
> +LIBBPF_SRC := $(abspath ../lib/bpf)
> +BPF_INCLUDE := -I$(SKEL_TMP_OUT)/.. -I$(BPF_PATH) -I$(LIBBPF_SRC)/..
> +
> +$(SKEL_TMP_OUT):
> +       $(Q)$(MKDIR) -p $@
> +
> +$(BPFTOOL): | $(SKEL_TMP_OUT)
> +       CFLAGS= $(MAKE) -C ../bpf/bpftool \
> +               OUTPUT=$(SKEL_TMP_OUT)/ bootstrap
> +
> +$(SKEL_TMP_OUT)/%.bpf.o: util/bpf_skel/%.bpf.c $(LIBBPF) | $(SKEL_TMP_OUT)
> +       $(QUIET_CLANG)$(CLANG) -g -O2 -target bpf $(BPF_INCLUDE) \
> +         -c $(filter util/bpf_skel/%.bpf.c,$^) -o $@ && $(LLVM_STRIP) -g $@
> +
> +$(SKEL_OUT)/%.skel.h: $(SKEL_TMP_OUT)/%.bpf.o | $(BPFTOOL)
> +       $(QUIET_GENSKEL)$(BPFTOOL) gen skeleton $< > $@
> +
> +bpf-skel: $(SKELETONS)
> +
> +.PRECIOUS: $(SKEL_TMP_OUT)/%.bpf.o
> +
> +else # BUILD_BPF_SKEL
> +
> +bpf-skel:
> +
> +endif # BUILD_BPF_SKEL
> +
> +bpf-skel-clean:
> +       $(call QUIET_CLEAN, bpf-skel) $(RM) -r $(SKEL_TMP_OUT) $(SKELETONS)
> +
> +clean:: $(LIBTRACEEVENT)-clean $(LIBAPI)-clean $(LIBBPF)-clean $(LIBSUBCMD)-clean $(LIBPERF)-clean config-clean fixdep-clean python-clean bpf-skel-clean
>         $(call QUIET_CLEAN, core-objs)  $(RM) $(LIBPERF_A) $(OUTPUT)perf-archive $(OUTPUT)perf-with-kcore $(LANG_BINDINGS)
>         $(Q)find $(if $(OUTPUT),$(OUTPUT),.) -name '*.o' -delete -o -name '\.*.cmd' -delete -o -name '\.*.d' -delete
>         $(Q)$(RM) $(OUTPUT).config-detected
> diff --git a/tools/perf/util/bpf_skel/.gitignore b/tools/perf/util/bpf_skel/.gitignore
> new file mode 100644
> index 0000000000000..5263e9e6c5d83
> --- /dev/null
> +++ b/tools/perf/util/bpf_skel/.gitignore
> @@ -0,0 +1,3 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +.tmp
> +*.skel.h
> \ No newline at end of file
> diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include
> index 1358e89cdf7d6..62119ce69ad9a 100644
> --- a/tools/scripts/Makefile.include
> +++ b/tools/scripts/Makefile.include
> @@ -127,6 +127,7 @@ ifneq ($(silent),1)
>                          $(MAKE) $(PRINT_DIR) -C $$subdir
>         QUIET_FLEX     = @echo '  FLEX     '$@;
>         QUIET_BISON    = @echo '  BISON    '$@;
> +       QUIET_GENSKEL  = @echo '  GEN-SKEL '$@;
>
>         descend = \
>                 +@...o         '  DESCEND  '$(1); \
> --
> 2.24.1
>

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