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SubjectRe: [RFC v2 1/2] perf: support build BPF skeletons with perf
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> On Dec 1, 2020, at 12:54 PM, Jiri Olsa <jolsa@redhat.com> wrote:
>
> On Mon, Nov 30, 2020 at 11:36:46PM -0800, Song Liu wrote:
>> BPF programs are useful in perf to profile BPF programs. BPF skeleton is
>> 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.
>>
>> Signed-off-by: Song Liu <songliubraving@fb.com>
>> ---
>> tools/bpf/bpftool/Makefile | 2 ++
>> tools/build/Makefile.feature | 3 +-
>> tools/perf/Makefile.config | 9 +++++
>> tools/perf/Makefile.perf | 52 ++++++++++++++++++++++++++--
>> tools/perf/util/bpf_skel/.gitignore | 3 ++
>> tools/perf/util/bpf_skel/dummy.bpf.c | 19 ++++++++++
>> tools/scripts/Makefile.include | 1 +
>> 7 files changed, 86 insertions(+), 3 deletions(-)
>> create mode 100644 tools/perf/util/bpf_skel/.gitignore
>> create mode 100644 tools/perf/util/bpf_skel/dummy.bpf.c
>>
>> diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
>> index f60e6ad3a1dff..a01407ec78dc5 100644
>> --- a/tools/bpf/bpftool/Makefile
>> +++ b/tools/bpf/bpftool/Makefile
>> @@ -120,6 +120,8 @@ endif
>>
>> BPFTOOL_BOOTSTRAP := $(if $(OUTPUT),$(OUTPUT)bpftool-bootstrap,./bpftool-bootstrap)
>>
>> +bootstrap: $(BPFTOOL_BOOTSTRAP)
>> +
>> BOOTSTRAP_OBJS = $(addprefix $(OUTPUT),main.o common.o json_writer.o gen.o btf.o)
>> OBJS = $(patsubst %.c,$(OUTPUT)%.o,$(SRCS)) $(OUTPUT)disasm.o
>>
>> diff --git a/tools/build/Makefile.feature b/tools/build/Makefile.feature
>> index 97cbfb31b7625..95a58b5564218 100644
>> --- a/tools/build/Makefile.feature
>> +++ b/tools/build/Makefile.feature
>> @@ -70,7 +70,8 @@ FEATURE_TESTS_BASIC := \
>> libaio \
>> libzstd \
>> disassembler-four-args \
>> - file-handle
>> + file-handle \
>> + clang-bpf-co-re
>
> this needs to go under FEATURE_TESTS_EXTRA and you need to call
> $(call feature_check,clang-bpf-co-re) before checking on $(feature-clang-bpf-co-re)
>
> otherwise the test-all will mark it as detected even if it's not
>
>>
>> # FEATURE_TESTS_BASIC + FEATURE_TESTS_EXTRA is the complete list
>> # of all feature tests
>> diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
>> index ce8516e4de34f..cb0cf06e0bb43 100644
>> --- a/tools/perf/Makefile.config
>> +++ b/tools/perf/Makefile.config
>> @@ -621,6 +621,15 @@ ifndef NO_LIBBPF
>> endif
>> endif
>>
>> +ifeq ($(feature-clang-bpf-co-re), 0)
>> + BUILD_BPF_SKEL := 0
>> +endif
>> +
>> +ifeq ($(BUILD_BPF_SKEL), 1)
>> + $(call detected,CONFIG_PERF_BPF_SKEL)
>> + CFLAGS += -DBUILD_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 7ce3f2e8b9c74..37b7ffe1db27c 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
>> @@ -735,7 +737,8 @@ 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
>
> I think the 'prepare' target is misused already with other stuff,
> there's generated bpf_counter.c dependency on util/bpf_skel/bpf_prog_profiler.skel.h
> in util/.bpf_counter.o.cmd, that should triger the build no?

This doesn't work for me. Once bpf-skel is removed from "prepare", we hit
compilation error before util/.bpf_counter.o.cmd is generated.

>
> we have few other dependencies like that for flex/bison generation
> perhaps we could follow also that
>
>>
>> $(OUTPUT)%.o: %.c prepare FORCE
>> $(Q)$(MAKE) -f $(srctree)/tools/build/Makefile.build dir=$(build-dir) $@
>> @@ -1008,7 +1011,52 @@ 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 util/bpf_skel)
>> +SKEL_TMP_OUT := $(abspath util/bpf_skel/.tmp)
>> +SKELETONS := $(SKEL_OUT)/dummy.skel.h
>> +
>> +ifdef BUILD_BPF_SKEL
>> +CLANG ?= clang
>> +LLVM_STRIP ?= llvm-strip
>
> please move this up where we have similar setup like HOSTCC and others
>
>> +BPFTOOL_CFLAGS := $(filter-out -D_GNU_SOURCE,$(CFLAGS))
>> +BPFTOOL := $(SKEL_TMP_OUT)/bpftool-bootstrap
>> +LIBBPF_SRC := $(abspath ../lib/bpf)
>> +BPFOBJ := $(SKEL_TMP_OUT)/libbpf.a
>
> we already build libbpf.a, chekc 'LIBBPF = $(BPF_PATH)libbpf.a' above

Yeah, this works! Thanks!

>
>> +BPF_INCLUDE := $(SKEL_TMP_OUT)
>> +submake_extras := feature_display=0
>> +
>> +$(SKEL_TMP_OUT):
>> + $(Q)$(MKDIR) -p $@
>> +
>> +$(BPFTOOL): | $(SKEL_TMP_OUT)
>> + CFLAGS= $(MAKE) $(submake_extras) -C ../bpf/bpftool \
>> + OUTPUT=$(SKEL_TMP_OUT)/ bootstrap
>> +
>> +$(SKEL_TMP_OUT)/%.bpf.o: util/bpf_skel/%.bpf.c $(BPFOBJ) | $(SKEL_TMP_OUT)
>> + $(call QUIET_CLANG, $@)
>> + $(Q)$(CLANG) -g -O2 -target bpf -c $(filter util/bpf_skel/%.bpf.c,$^) -o $@ && \
>> + $(LLVM_STRIP) -g $@
>> +
>> +$(SKEL_OUT)/%.skel.h: $(SKEL_TMP_OUT)/%.bpf.o | $(BPFTOOL)
>> + $(call QUIET_GENSKEL, $@)
>
> is there a reason to use call in here? you could define QUIET_GENSKEL
> to use $@ and use it the same way as we use the rest of QUIET_* stuf
> in Makefile.perf

I am not following here. $(CALL QUIET_xx) was used for QUIET_CLEAN and
QUIET_INSTALL in Makefile.perf. What is the preferred pattern here?

>
>> 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/perf/util/bpf_skel/dummy.bpf.c b/tools/perf/util/bpf_skel/dummy.bpf.c
>> new file mode 100644
>> index 0000000000000..492a43a851deb
>> --- /dev/null
>> +++ b/tools/perf/util/bpf_skel/dummy.bpf.c
>
> hum, what's the reason for dummy skeleton? it just adds
> time to compilation no?

It is mostly to test 1/2 of the set works fine. I guess we can remove
it in 2/2?

Thanks,
Song
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