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

[Ihor Solodrai <ihor.solodrai@linux.dev>]

On 7/28/26 5:06 PM, Ricardo B. Marlière (SUSE) wrote:
> 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 $(OUTPUT)/... rule in libarena/Makefile
> regardless of the invocation directory.
> 
> Signed-off-by: Ricardo B. Marlière (SUSE) <ricardo@marliere.net>
> ---
>  tools/testing/selftests/bpf/Makefile          | 11 ++++++-----
>  tools/testing/selftests/bpf/libarena/Makefile | 24 ++++++++++++++----------
>  2 files changed, 20 insertions(+), 15 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index b289183475d4..7d42632f9d42 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -826,7 +826,8 @@ LIBARENA_MAKE_ARGS = \
>  		CLANG="$(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))

This runs while make parses the file, including under make -n, and
discards mkdir's status. Let's create $(OUTPUT) via order-only
directory prereq instead.

> +
>  # 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
>