[RFC 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/build/Makefile.feature         |  3 +-
 tools/perf/Makefile.config           |  7 +++
 tools/perf/Makefile.perf             | 15 +++++-
 tools/perf/util/bpf_skel/.gitignore  |  3 ++
 tools/perf/util/bpf_skel/Makefile    | 71 ++++++++++++++++++++++++++++
 tools/perf/util/bpf_skel/dummy.bpf.c | 19 ++++++++
 6 files changed, 115 insertions(+), 3 deletions(-)
 create mode 100644 tools/perf/util/bpf_skel/.gitignore
 create mode 100644 tools/perf/util/bpf_skel/Makefile
 create mode 100644 tools/perf/util/bpf_skel/dummy.bpf.c

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..1c2c0f4badd85 100644
--- a/tools/perf/Makefile.config
+++ b/tools/perf/Makefile.config
@@ -619,6 +619,13 @@ ifndef NO_LIBBPF
     msg := $(warning BPF API too old. Please install recent kernel headers. BPF support in 'perf record' is disabled.)
     NO_LIBBPF := 1
   endif
+
+  ifndef NO_BPF_SKEL
+    ifeq ($(feature-clang-bpf-co-re), 1)
+      BUILD_BPF_SKEL := 1
+      $(call detected,CONFIG_PERF_BPF_SKEL)
+    endif
+  endif
 endif
 
 dwarf-post-unwind := 1
diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
index 7ce3f2e8b9c74..9a9fc71e2ffa4 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 NO_BPF_SKEL if you do not want build 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 +1011,15 @@ config-clean:
 python-clean:
 	$(python-clean)
 
+ifdef BUILD_BPF_SKEL
+bpf-skel:
+	$(Q)$(MAKE) -C util/bpf_skel
+else
+bpf-skel:
+endif
+
 clean:: $(LIBTRACEEVENT)-clean $(LIBAPI)-clean $(LIBBPF)-clean $(LIBSUBCMD)-clean $(LIBPERF)-clean config-clean fixdep-clean python-clean
+	$(call descend,util/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
@@ -1071,7 +1082,7 @@ endif
 
 FORCE:
 
-.PHONY: all install clean config-clean strip install-gtk
+.PHONY: all install clean config-clean strip install-gtk bpf-skel
 .PHONY: shell_compatibility_test please_set_SHELL_PATH_to_a_more_modern_shell
 .PHONY: $(GIT-HEAD-PHONY) TAGS tags cscope FORCE prepare
 .PHONY: libtraceevent_plugins archheaders
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/Makefile b/tools/perf/util/bpf_skel/Makefile
new file mode 100644
index 0000000000000..853bece088f4b
--- /dev/null
+++ b/tools/perf/util/bpf_skel/Makefile
@@ -0,0 +1,71 @@
+# SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
+SKEL_OUTPUT := $(abspath .)
+TMP_OUTPUT := $(abspath .tmp)
+CLANG ?= clang
+LLC ?= llc
+LLVM_STRIP ?= llvm-strip
+DEFAULT_BPFTOOL := $(TMP_OUTPUT)/sbin/bpftool
+BPFTOOL ?= $(DEFAULT_BPFTOOL)
+LIBBPF_SRC := $(abspath ../../../lib/bpf)
+BPFOBJ := $(TMP_OUTPUT)/libbpf.a
+BPF_INCLUDE := $(TMP_OUTPUT)
+INCLUDES := -I$(TMP_OUTPUT) -I$(BPF_INCLUDE) -I$(abspath ../../../lib)        \
+       -I$(abspath ../../../include/uapi)
+CFLAGS := -g -Wall
+
+# Try to detect best kernel BTF source
+KERNEL_REL := $(shell uname -r)
+VMLINUX_BTF_PATHS := /sys/kernel/btf/vmlinux /boot/vmlinux-$(KERNEL_REL)
+VMLINUX_BTF_PATH := $(or $(VMLINUX_BTF),$(firstword			       \
+					  $(wildcard $(VMLINUX_BTF_PATHS))))
+ifeq ($(V),1)
+Q =
+msg =
+else
+Q = @
+msg = @printf '  %-8s %s%s\n' "$(1)" "$(notdir $(2))" "$(if $(3), $(3))";
+MAKEFLAGS += --no-print-directory
+submake_extras := feature_display=0
+endif
+
+SKELETONS := $(SKEL_OUTPUT)/dummy.skel.h
+
+.DELETE_ON_ERROR:
+
+.PHONY: all clean
+all: $(SKELETONS)
+
+clean:
+	$(call msg,CLEAN,bpf_skel)
+	$(Q)rm -rf $(TMP_OUTPUT) $(SKELETONS)
+
+$(SKEL_OUTPUT)/%.skel.h: $(TMP_OUTPUT)/%.bpf.o | $(BPFTOOL)
+	$(call msg,GEN-SKEL,$@)
+	$(Q)$(BPFTOOL) gen skeleton $< > $@
+
+$(TMP_OUTPUT)/%.bpf.o: %.bpf.c $(TMP_OUTPUT)/vmlinux.h $(BPFOBJ) | $(TMP_OUTPUT)
+	$(call msg,BPF,$@)
+	$(Q)$(CLANG) -g -O2 -target bpf $(INCLUDES)			      \
+		 -c $(filter %.c,$^) -o $@ &&				      \
+	$(LLVM_STRIP) -g $@
+
+$(TMP_OUTPUT):
+	$(call msg,MKDIR,$@)
+	$(Q)mkdir -p $(TMP_OUTPUT)
+
+$(TMP_OUTPUT)/vmlinux.h: $(VMLINUX_BTF_PATH) | $(TMP_OUTPUT) $(BPFTOOL)
+	$(call msg,GEN,$@)
+	$(Q)if [ ! -e "$(VMLINUX_BTF_PATH)" ] ; then \
+		echo "Couldn't find kernel BTF; set VMLINUX_BTF to"	       \
+			"specify its location." >&2;			       \
+		exit 1;\
+	fi
+	$(Q)$(BPFTOOL) btf dump file $(VMLINUX_BTF_PATH) format c > $@
+
+$(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(TMP_OUTPUT)
+	$(Q)$(MAKE) $(submake_extras) -C $(LIBBPF_SRC)			       \
+		    OUTPUT=$(abspath $(dir $@))/ $(abspath $@)
+
+$(DEFAULT_BPFTOOL): | $(TMP_OUTPUT)
+	$(Q)$(MAKE) $(submake_extras) -C ../../../bpf/bpftool		      \
+		    prefix= OUTPUT=$(TMP_OUTPUT)/ DESTDIR=$(TMP_OUTPUT) install
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..085fcee1f52cf
--- /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 "vmlinux.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";
-- 
2.24.1