bpftool: Only build bpftool-prog-profile if supported by clang

bpftool-prog-profile requires clang to generate BTF for global variables.
When compared with older clang, skip this command. This is achieved by
adding a new feature, clang-bpf-global-var, to tools/build/feature.

Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Quentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/bpf/20200312182332.3953408-2-songliubraving@fb.com

tools/bpf/bpftool/Makefile

@@ -62,8 +62,9 @@ RM ?= rm -f
 CLANG ?= clang
 
 FEATURE_USER = .bpftool
-FEATURE_TESTS = libbfd disassembler-four-args reallocarray zlib
-FEATURE_DISPLAY = libbfd disassembler-four-args zlib
+FEATURE_TESTS = libbfd disassembler-four-args reallocarray zlib \
+	clang-bpf-global-var
+FEATURE_DISPLAY = libbfd disassembler-four-args zlib clang-bpf-global-var
 
 check_feat := 1
 NON_CHECK_FEAT_TARGETS := clean uninstall doc doc-clean doc-install doc-uninstall
@@ -113,6 +114,12 @@ endif
 OBJS = $(patsubst %.c,$(OUTPUT)%.o,$(SRCS)) $(OUTPUT)disasm.o
 _OBJS = $(filter-out $(OUTPUT)prog.o,$(OBJS)) $(OUTPUT)_prog.o
 
+ifeq ($(feature-clang-bpf-global-var),1)
+	__OBJS = $(OBJS)
+else
+	__OBJS = $(_OBJS)
+endif
+
 $(OUTPUT)_prog.o: prog.c
 	$(QUIET_CC)$(COMPILE.c) -MMD -DBPFTOOL_WITHOUT_SKELETONS -o $@ $<
 
@@ -136,8 +143,8 @@ $(OUTPUT)disasm.o: $(srctree)/kernel/bpf/disasm.c
 
 $(OUTPUT)feature.o: | zdep
 
-$(OUTPUT)bpftool: $(OBJS) $(LIBBPF)
-	$(QUIET_LINK)$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $(OBJS) $(LIBS)
+$(OUTPUT)bpftool: $(__OBJS) $(LIBBPF)
+	$(QUIET_LINK)$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $(__OBJS) $(LIBS)
 
 $(OUTPUT)%.o: %.c
 	$(QUIET_CC)$(COMPILE.c) -MMD -o $@ $<

tools/bpf/bpftool/prog.c

@@ -1545,6 +1545,7 @@ static int do_loadall(int argc, char **argv)
 
 static int do_profile(int argc, char **argv)
 {
+	p_err("bpftool prog profile command is not supported. Please build bpftool with clang >= 10.0.0");
 	return 0;
 }
 

tools/build/feature/Makefile

@@ -67,7 +67,8 @@ FILES=                                          \
          test-llvm.bin				\
          test-llvm-version.bin			\
          test-libaio.bin			\
-         test-libzstd.bin
+         test-libzstd.bin			\
+         test-clang-bpf-global-var.bin
 
 FILES := $(addprefix $(OUTPUT),$(FILES))
 
@@ -75,6 +76,7 @@ CC ?= $(CROSS_COMPILE)gcc
 CXX ?= $(CROSS_COMPILE)g++
 PKG_CONFIG ?= $(CROSS_COMPILE)pkg-config
 LLVM_CONFIG ?= llvm-config
+CLANG ?= clang
 
 all: $(FILES)
 
@@ -321,6 +323,11 @@ $(OUTPUT)test-libaio.bin:
 $(OUTPUT)test-libzstd.bin:
 	$(BUILD) -lzstd
 
+$(OUTPUT)test-clang-bpf-global-var.bin:
+	$(CLANG) -S -g -target bpf -o - $(patsubst %.bin,%.c,$(@F)) |	\
+		grep BTF_KIND_VAR
+
+
 ###############################
 
 clean:

tools/build/feature/test-clang-bpf-global-var.c

@@ -0,0 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2020 Facebook
+
+volatile int global_value_for_test = 1;