[RFC v2 1/2] perf: support build BPF skeletons with perf

[Song Liu <songliubraving@fb.com>]

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
 
 # 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
 
 $(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
+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
+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, $@)
+	$(Q)$(BPFTOOL) gen skeleton $< > $@
+
+bpf-skel: $(SKELETONS)
+
+$(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(SKEL_TMP_OUT)
+	$(Q)$(MAKE) $(submake_extras) -C $(LIBBPF_SRC)			       \
+		OUTPUT=$(abspath $(dir $@))/ $(abspath $@)
+
+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) $(OUTPUT).config-detected
diff --git a/tools/perf/util/bpf_skel/.gitignore b/tools/perf/util/bpf_skel/.gitignore
new file mode 100644
index 0000000000000..5263e9e6c5d83
--- /dev/null
+++ b/tools/perf/util/bpf_skel/.gitignore
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
+.tmp
+*.skel.h
\ No newline at end of file
diff --git a/tools/perf/util/bpf_skel/dummy.bpf.c b/tools/perf/util/bpf_skel/dummy.bpf.c
new file mode 100644
index 0000000000000..492a43a851deb
--- /dev/null
+++ b/tools/perf/util/bpf_skel/dummy.bpf.c
@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+// Copyright (c) 2020 Facebook
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+struct {
+	__uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
+	__uint(key_size, sizeof(__u32));
+	__uint(value_size, sizeof(__u64));
+} counts SEC(".maps");
+
+SEC("fentry/dummy")
+int BPF_PROG(fentry_dummy)
+{
+	return 0;
+}
+
+char LICENSE[] SEC("license") = "Dual BSD/GPL";
diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include
index a7974638561ca..ed1720dc12194 100644
--- a/tools/scripts/Makefile.include
+++ b/tools/scripts/Makefile.include
@@ -126,6 +126,7 @@ ifneq ($(silent),1)
 	QUIET_CLEAN    = @printf '  CLEAN    %s\n' $1;
 	QUIET_INSTALL  = @printf '  INSTALL  %s\n' $1;
 	QUIET_UNINST   = @printf '  UNINST   %s\n' $1;
+	QUIET_GENSKEL  = @printf '  GEN-SKEL   %s\n' $1;
   endif
 endif
 
-- 
2.24.1