Commit 5f10c1aa authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Daniel Borkmann
Browse files

libbpf: Stop using feature-detection Makefiles 



Libbpf's Makefile relies on Linux tools infrastructure's feature detection
framework, but libbpf's needs are very modest: it detects the presence of
libelf and libz, both of which are mandatory. So it doesn't benefit much from
the framework, but pays significant costs in terms of maintainability and
debugging experience, when something goes wrong. The other feature detector,
testing for the presernce of minimal BPF API in system headers is long
obsolete as well, providing no value.

So stop using feature detection and just assume the presence of libelf and
libz during build time. Worst case, user will get a clear and actionable
linker error, e.g.:

  /usr/bin/ld: cannot find -lelf

On the other hand, we completely bypass recurring issues various users
reported over time with false negatives of feature detection (libelf or libz
not being detected, while they are actually present in the system).

Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarJohn Fastabend <john.fastabend@gmail.com>
Acked-by: default avatarRandy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/bpf/20210203203445.3356114-1-andrii@kernel.org
parent 65e6dcf7

tools/lib/bpf/.gitignore

+0 −1
Original line number Diff line number Diff line 
# SPDX-License-Identifier: GPL-2.0-only

libbpf_version.h

libbpf.pc

FEATURE-DUMP.libbpf

libbpf.so.*

TAGS

tags

tools/lib/bpf/Makefile

+4 −43
Original line number Diff line number Diff line
@@ -58,28 +58,7 @@ ifndef VERBOSE 
  VERBOSE = 0

endif



FEATURE_USER = .libbpf

FEATURE_TESTS = libelf zlib bpf

FEATURE_DISPLAY = libelf zlib bpf



INCLUDES = -I. -I$(srctree)/tools/include -I$(srctree)/tools/include/uapi

FEATURE_CHECK_CFLAGS-bpf = $(INCLUDES)



check_feat := 1

NON_CHECK_FEAT_TARGETS := clean TAGS tags cscope help

ifdef MAKECMDGOALS

ifeq ($(filter-out $(NON_CHECK_FEAT_TARGETS),$(MAKECMDGOALS)),)

  check_feat := 0

endif

endif



ifeq ($(check_feat),1)

ifeq ($(FEATURES_DUMP),)

include $(srctree)/tools/build/Makefile.feature

else

include $(FEATURES_DUMP)

endif

endif



export prefix libdir src obj
@@ -157,7 +136,7 @@ all: fixdep 


all_cmd: $(CMD_TARGETS) check



$(BPF_IN_SHARED): force elfdep zdep bpfdep $(BPF_HELPER_DEFS)

$(BPF_IN_SHARED): force $(BPF_HELPER_DEFS)

	@(test -f ../../include/uapi/linux/bpf.h -a -f ../../../include/uapi/linux/bpf.h && ( \

	(diff -B ../../include/uapi/linux/bpf.h ../../../include/uapi/linux/bpf.h >/dev/null) || \

	echo "Warning: Kernel ABI header at 'tools/include/uapi/linux/bpf.h' differs from latest version at 'include/uapi/linux/bpf.h'" >&2 )) || true
@@ -175,7 +154,7 @@ $(BPF_IN_SHARED): force elfdep zdep bpfdep $(BPF_HELPER_DEFS) 
	echo "Warning: Kernel ABI header at 'tools/include/uapi/linux/if_xdp.h' differs from latest version at 'include/uapi/linux/if_xdp.h'" >&2 )) || true

	$(Q)$(MAKE) $(build)=libbpf OUTPUT=$(SHARED_OBJDIR) CFLAGS="$(CFLAGS) $(SHLIB_FLAGS)"



$(BPF_IN_STATIC): force elfdep zdep bpfdep $(BPF_HELPER_DEFS)

$(BPF_IN_STATIC): force $(BPF_HELPER_DEFS)

	$(Q)$(MAKE) $(build)=libbpf OUTPUT=$(STATIC_OBJDIR)



$(BPF_HELPER_DEFS): $(srctree)/tools/include/uapi/linux/bpf.h
@@ -264,34 +243,16 @@ install_pkgconfig: $(PC_FILE) 


install: install_lib install_pkgconfig install_headers



### Cleaning rules



config-clean:

	$(call QUIET_CLEAN, feature-detect)

	$(Q)$(MAKE) -C $(srctree)/tools/build/feature/ clean >/dev/null



clean: config-clean

clean:

	$(call QUIET_CLEAN, libbpf) $(RM) -rf $(CMD_TARGETS)		     \

		*~ .*.d .*.cmd LIBBPF-CFLAGS $(BPF_HELPER_DEFS)		     \

		$(SHARED_OBJDIR) $(STATIC_OBJDIR)			     \

		$(addprefix $(OUTPUT),					     \

			    *.o *.a *.so *.so.$(LIBBPF_MAJOR_VERSION) *.pc)

	$(call QUIET_CLEAN, core-gen) $(RM) $(OUTPUT)FEATURE-DUMP.libbpf







PHONY += force elfdep zdep bpfdep cscope tags

PHONY += force cscope tags

force:



elfdep:

	@if [ "$(feature-libelf)" != "1" ]; then echo "No libelf found"; exit 1 ; fi



zdep:

	@if [ "$(feature-zlib)" != "1" ]; then echo "No zlib found"; exit 1 ; fi



bpfdep:

	@if [ "$(feature-bpf)" != "1" ]; then echo "BPF API too old"; exit 1 ; fi



cscope:

	ls *.c *.h > cscope.files

	cscope -b -q -I $(srctree)/include -f cscope.out