linux-kernel - [PATCH net-next v1] samples/bpf: Partially fixes the bpf.o build

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Date:   Fri, 26 Jan 2018 01:39:30 +0100
From:   Mickaël Salaün <mic@...ikod.net>
To:     linux-kernel@...r.kernel.org
Cc:     Mickaël Salaün <mic@...ikod.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: [PATCH net-next v1] samples/bpf: Partially fixes the bpf.o build

Do not build lib/bpf/bpf.o with this Makefile but use the one from the
library directory.  This avoid making a buggy bpf.o file (e.g. missing
symbols).

This patch is useful if some code (e.g. Landlock tests) needs both the
bpf.o (from tools/lib/bpf) and the bpf_load.o (from samples/bpf).

Signed-off-by: Mickaël Salaün <mic@...ikod.net>
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Daniel Borkmann <daniel@...earbox.net>
---

This is not a complet fix because the call to multi_depend with
$(host-cmulti) from scripts/Makefile.host force the build of bpf.o
anyway. I'm not sure how to completely avoid this automatic build
though.
---
 samples/bpf/Makefile | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index 7f61a3d57fa7..64335bb94f9f 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -201,13 +201,16 @@ CLANG_ARCH_ARGS = -target $(ARCH)
 endif
 
 # Trick to allow make to be run from this directory
-all:
+all: $(LIBBPF)
 	$(MAKE) -C ../../ $(CURDIR)/
 
 clean:
 	$(MAKE) -C ../../ M=$(CURDIR) clean
 	@rm -f *~
 
+$(LIBBPF): FORCE
+	$(MAKE) -C $(dir $@) $(notdir $@)
+
 $(obj)/syscall_nrs.s:	$(src)/syscall_nrs.c
 	$(call if_changed_dep,cc_s_c)
 
-- 
2.15.1