[PATCH 2/3] selftests/bpf: Route libarena build artifacts to OUTPUT

[Ricardo B. Marlière (SUSE)]

libarena's BPF objects, linked objects, and skeleton headers are always
written into the source tree regardless of whether an out-of-tree build
directory was specified via O=.

Add OUTPUT support to libarena/Makefile: default OUTPUT to '.' for
standalone builds, prefix all generated file targets with $(OUTPUT)/, and
use addprefix to propagate the directory into the per-object lists. Create
$(OUTPUT) at Makefile-load time with a $(shell mkdir -p) so all rules have
a valid destination.

In the parent bpf/Makefile, pass OUTPUT="$(OUTPUT)/libarena" in
LIBARENA_MAKE_ARGS and update LIBARENA_SKEL/LIBARENA_ASAN_SKEL to reflect
the new location. Pass the absolute target path as the make goal so the
sub-make goal matches the $(OUTPUT)/... rule in libarena/Makefile
regardless of the invocation directory.

Signed-off-by: Ricardo B. Marlière (SUSE) <ricardo@xxxxxxxxxxxx>
---
 tools/testing/selftests/bpf/Makefile          | 11 ++++++-----
 tools/testing/selftests/bpf/libarena/Makefile | 24 ++++++++++++++----------
 2 files changed, 20 insertions(+), 15 deletions(-)

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index b289183475d4..7d42632f9d42 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -826,7 +826,8 @@ LIBARENA_MAKE_ARGS = \
 		CLANG="$(CLANG)" \
 		BPF_CFLAGS="$(BPF_CFLAGS) $(CLANG_CFLAGS)" \
 		BPF_TARGET_ENDIAN="$(BPF_TARGET_ENDIAN)" \
-		Q="$(Q)"
+		Q="$(Q)" \
+		OUTPUT="$(OUTPUT)/libarena"
 
 LIBARENA_BPF_DEPS := $(wildcard libarena/Makefile		\
 				 libarena/include/*		\
@@ -835,17 +836,17 @@ LIBARENA_BPF_DEPS := $(wildcard libarena/Makefile		\
 				 libarena/selftests/*		\
 				 libarena/*.bpf.o)
 
-LIBARENA_SKEL := libarena/libarena.skel.h
+LIBARENA_SKEL := $(OUTPUT)/libarena/libarena.skel.h
 
 $(LIBARENA_SKEL): $(INCLUDE_DIR)/vmlinux.h $(BPFOBJ) $(LIBARENA_BPF_DEPS)
-	+$(MAKE) -C libarena libarena.skel.h $(LIBARENA_MAKE_ARGS)
+	+$(MAKE) -C libarena $(LIBARENA_SKEL) $(LIBARENA_MAKE_ARGS)
 
 ifneq ($(CLANG_HAS_ARENA_ASAN),)
-LIBARENA_ASAN_SKEL := libarena/libarena_asan.skel.h
+LIBARENA_ASAN_SKEL := $(OUTPUT)/libarena/libarena_asan.skel.h
 CFLAGS += -DHAS_BPF_ARENA_ASAN
 
 $(LIBARENA_ASAN_SKEL): $(INCLUDE_DIR)/vmlinux.h $(BPFOBJ) $(LIBARENA_BPF_DEPS)
-	+$(MAKE) -C libarena libarena_asan.skel.h $(LIBARENA_MAKE_ARGS)
+	+$(MAKE) -C libarena $(LIBARENA_ASAN_SKEL) $(LIBARENA_MAKE_ARGS)
 endif
 
 # Define test_progs test runner.
diff --git a/tools/testing/selftests/bpf/libarena/Makefile b/tools/testing/selftests/bpf/libarena/Makefile
index 5e2ab514805e..195d5f833186 100644
--- a/tools/testing/selftests/bpf/libarena/Makefile
+++ b/tools/testing/selftests/bpf/libarena/Makefile
@@ -27,10 +27,14 @@ BPFDIR=$(abspath $(LIBARENA)/..)
 INCLUDE_DIR ?= $(BPFDIR)/tools/include
 LIBBPF_INCLUDE ?= $(INCLUDE_DIR)
 
+# Build output directory; defaults to in-tree for standalone builds.
+OUTPUT ?= .
+$(shell mkdir -p $(OUTPUT))
+
 # Scan src/ and selftests/ to generate the final binaries
 LIBARENA_SOURCES = $(wildcard $(LIBARENA)/src/*.bpf.c) $(wildcard $(LIBARENA)/selftests/*.bpf.c)
-LIBARENA_OBJECTS = $(notdir $(LIBARENA_SOURCES:.bpf.c=.bpf.o))
-LIBARENA_OBJECTS_ASAN = $(notdir $(LIBARENA_SOURCES:.bpf.c=_asan.bpf.o))
+LIBARENA_OBJECTS = $(addprefix $(OUTPUT)/,$(notdir $(LIBARENA_SOURCES:.bpf.c=.bpf.o)))
+LIBARENA_OBJECTS_ASAN = $(addprefix $(OUTPUT)/,$(notdir $(LIBARENA_SOURCES:.bpf.c=_asan.bpf.o)))
 
 INCLUDES = -I$(LIBARENA)/include -I$(BPFDIR)
 ifneq ($(INCLUDE_DIR),)
@@ -61,32 +65,32 @@ CFLAGS += $(INCLUDES)
 vpath %.bpf.c $(LIBARENA)/src $(LIBARENA)/selftests
 vpath %.c $(LIBARENA)/src $(LIBARENA)/selftests
 
-skeletons: libarena.skel.h libarena_asan.skel.h
+skeletons: $(OUTPUT)/libarena.skel.h $(OUTPUT)/libarena_asan.skel.h
 .PHONY: skeletons
 
-libarena_asan.skel.h: libarena_asan.bpf.o
+$(OUTPUT)/libarena_asan.skel.h: $(OUTPUT)/libarena_asan.bpf.o
 	$(call msg,GEN-SKEL,libarena,$@)
 	$(Q)$(BPFTOOL) gen skeleton $< name "libarena_asan" > $@
 
-libarena.skel.h: libarena.bpf.o
+$(OUTPUT)/libarena.skel.h: $(OUTPUT)/libarena.bpf.o
 	$(call msg,GEN-SKEL,libarena,$@)
 	$(Q)$(BPFTOOL) gen skeleton $< name "libarena" > $@
 
-libarena_asan.bpf.o: $(LIBARENA_OBJECTS_ASAN)
+$(OUTPUT)/libarena_asan.bpf.o: $(LIBARENA_OBJECTS_ASAN)
 	$(call msg,GEN-OBJ,libarena,$@)
 	$(Q)$(BPFTOOL) gen object $@ $^
 
-libarena.bpf.o: $(LIBARENA_OBJECTS)
+$(OUTPUT)/libarena.bpf.o: $(LIBARENA_OBJECTS)
 	$(call msg,GEN-OBJ,libarena,$@)
 	$(Q)$(BPFTOOL) gen object $@ $^
 
-%_asan.bpf.o: %.bpf.c
+$(OUTPUT)/%_asan.bpf.o: %.bpf.c
 	$(call msg,CLNG-BPF,libarena,$@)
 	$(Q)$(CLANG) $(BPF_CFLAGS) $(ASAN_FLAGS) -DBPF_ARENA_ASAN $(BPF_TARGET_ENDIAN) -c $< -o $@
 
-%.bpf.o: %.bpf.c
+$(OUTPUT)/%.bpf.o: %.bpf.c
 	$(call msg,CLNG-BPF,libarena,$@)
 	$(Q)$(CLANG) $(BPF_CFLAGS) $(BPF_TARGET_ENDIAN) -c $< -o $@
 
 clean:
-	$(Q)rm -f *.skel.h *.bpf.o *.linked*.o
+	$(Q)rm -f $(OUTPUT)/*.skel.h $(OUTPUT)/*.bpf.o $(OUTPUT)/*.linked*.o

-- 
2.55.0