selftests/bpf: Drop the need for LLVM's llc

LLC is meant for compiler development and debugging. Consequently, it
exposes many low level options about its backend. To avoid future bugs
introduced by using the raw LLC tool, use clang directly so that all
appropriate options are passed to the back end.

Additionally, simplify the Makefile by removing the
CLANG_NATIVE_BPF_BUILD_RULE as it is not being use, stop passing
dwarfris attr since elfutils/libdw now supports the bpf backend (which
should work with any recent pahole), and stop passing alu32 since
-mcpu=v3 implies alu32.

Signed-off-by: Andrew Delgadillo <adelg@google.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20201211004344.3355074-1-adelg@google.com

tools/testing/selftests/bpf/Makefile

@@ -19,7 +19,6 @@ ifneq ($(wildcard $(GENHDR)),)
 endif
 
 CLANG		?= clang
-LLC		?= llc
 LLVM_OBJCOPY	?= llvm-objcopy
 BPF_GCC		?= $(shell command -v bpf-gcc;)
 SAN_CFLAGS	?=
@@ -253,31 +252,19 @@ $(OUTPUT)/flow_dissector_load.o: flow_dissector_load.h
 # $1 - input .c file
 # $2 - output .o file
 # $3 - CFLAGS
-# $4 - LDFLAGS
 define CLANG_BPF_BUILD_RULE
-	$(call msg,CLNG-LLC,$(TRUNNER_BINARY),$2)
-	$(Q)($(CLANG) $3 -O2 -target bpf -emit-llvm			\
-		-c $1 -o - || echo "BPF obj compilation failed") | 	\
-	$(LLC) -mattr=dwarfris -march=bpf -mcpu=v3 $4 -filetype=obj -o $2
+	$(call msg,CLNG-BPF,$(TRUNNER_BINARY),$2)
+	$(Q)$(CLANG) $3 -O2 -target bpf -c $1 -o $2 -mcpu=v3
 endef
 # Similar to CLANG_BPF_BUILD_RULE, but with disabled alu32
 define CLANG_NOALU32_BPF_BUILD_RULE
-	$(call msg,CLNG-LLC,$(TRUNNER_BINARY),$2)
-	$(Q)($(CLANG) $3 -O2 -target bpf -emit-llvm			\
-		-c $1 -o - || echo "BPF obj compilation failed") | 	\
-	$(LLC) -march=bpf -mcpu=v2 $4 -filetype=obj -o $2
-endef
-# Similar to CLANG_BPF_BUILD_RULE, but using native Clang and bpf LLC
-define CLANG_NATIVE_BPF_BUILD_RULE
 	$(call msg,CLNG-BPF,$(TRUNNER_BINARY),$2)
-	$(Q)($(CLANG) $3 -O2 -emit-llvm					\
-		-c $1 -o - || echo "BPF obj compilation failed") | 	\
-	$(LLC) -march=bpf -mcpu=v3 $4 -filetype=obj -o $2
+	$(Q)$(CLANG) $3 -O2 -target bpf -c $1 -o $2 -mcpu=v2
 endef
 # Build BPF object using GCC
 define GCC_BPF_BUILD_RULE
 	$(call msg,GCC-BPF,$(TRUNNER_BINARY),$2)
-	$(Q)$(BPF_GCC) $3 $4 -O2 -c $1 -o $2
+	$(Q)$(BPF_GCC) $3 -O2 -c $1 -o $2
 endef
 
 SKEL_BLACKLIST := btf__% test_pinning_invalid.c test_sk_assign.c
@@ -332,8 +319,7 @@ $(TRUNNER_BPF_OBJS): $(TRUNNER_OUTPUT)/%.o:				\
 		     $$(INCLUDE_DIR)/vmlinux.h				\
 		     $(wildcard $(BPFDIR)/bpf_*.h) | $(TRUNNER_OUTPUT)
 	$$(call $(TRUNNER_BPF_BUILD_RULE),$$<,$$@,			\
-					  $(TRUNNER_BPF_CFLAGS),	\
-					  $(TRUNNER_BPF_LDFLAGS))
+					  $(TRUNNER_BPF_CFLAGS))
 
 $(TRUNNER_BPF_SKELS): $(TRUNNER_OUTPUT)/%.skel.h:			\
 		      $(TRUNNER_OUTPUT)/%.o				\
@@ -401,19 +387,16 @@ TRUNNER_EXTRA_FILES := $(OUTPUT)/urandom_read $(OUTPUT)/bpf_testmod.ko	\
 		       $(wildcard progs/btf_dump_test_case_*.c)
 TRUNNER_BPF_BUILD_RULE := CLANG_BPF_BUILD_RULE
 TRUNNER_BPF_CFLAGS := $(BPF_CFLAGS) $(CLANG_CFLAGS)
-TRUNNER_BPF_LDFLAGS := -mattr=+alu32
 $(eval $(call DEFINE_TEST_RUNNER,test_progs))
 
 # Define test_progs-no_alu32 test runner.
 TRUNNER_BPF_BUILD_RULE := CLANG_NOALU32_BPF_BUILD_RULE
-TRUNNER_BPF_LDFLAGS :=
 $(eval $(call DEFINE_TEST_RUNNER,test_progs,no_alu32))
 
 # Define test_progs BPF-GCC-flavored test runner.
 ifneq ($(BPF_GCC),)
 TRUNNER_BPF_BUILD_RULE := GCC_BPF_BUILD_RULE
 TRUNNER_BPF_CFLAGS := $(BPF_CFLAGS) $(call get_sys_includes,gcc)
-TRUNNER_BPF_LDFLAGS :=
 $(eval $(call DEFINE_TEST_RUNNER,test_progs,bpf_gcc))
 endif
 
@@ -424,7 +407,6 @@ TRUNNER_EXTRA_SOURCES := test_maps.c
 TRUNNER_EXTRA_FILES :=
 TRUNNER_BPF_BUILD_RULE := $$(error no BPF objects should be built)
 TRUNNER_BPF_CFLAGS :=
-TRUNNER_BPF_LDFLAGS :=
 $(eval $(call DEFINE_TEST_RUNNER,test_maps))
 
 # Define test_verifier test runner.