[PATCH bpf] tools/bpf: fix bpftool build with OUTPUT set

[Ilya Leoshkevich <iii@linux.ibm.com>]

Hi Lorenz,

I've been using the following patch for quite some time now.
Please let me know if it works for you.

Best regards,
Ilya

---

When OUTPUT is set, bpftool and libbpf put their objects into the same
directory, and since some of them have the same names, the collision
happens.

Fix by invoking libbpf build in a manner similar to $(call descend) -
descend itself cannot be used, since libbpf is a sibling, and not a
child, of bpftool.

Also, don't link bpftool with libbpf.a twice.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 tools/bpf/bpftool/Makefile | 17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
index a7afea4dec47..2cbc3c166f44 100644
--- a/tools/bpf/bpftool/Makefile
+++ b/tools/bpf/bpftool/Makefile
@@ -15,23 +15,18 @@ else
 endif
 
 BPF_DIR = $(srctree)/tools/lib/bpf/
-
-ifneq ($(OUTPUT),)
-  BPF_PATH = $(OUTPUT)
-else
-  BPF_PATH = $(BPF_DIR)
-endif
-
-LIBBPF = $(BPF_PATH)libbpf.a
+BPF_PATH = $(objtree)/tools/lib/bpf
+LIBBPF = $(BPF_PATH)/libbpf.a
 
 BPFTOOL_VERSION := $(shell make --no-print-directory -sC ../../.. kernelversion)
 
 $(LIBBPF): FORCE
-	$(Q)$(MAKE) -C $(BPF_DIR) OUTPUT=$(OUTPUT) $(OUTPUT)libbpf.a
+	$(Q)mkdir -p $(BPF_PATH)
+	$(Q)$(MAKE) $(COMMAND_O) subdir=tools/lib/bpf -C $(BPF_DIR) $(LIBBPF)
 
 $(LIBBPF)-clean:
 	$(call QUIET_CLEAN, libbpf)
-	$(Q)$(MAKE) -C $(BPF_DIR) OUTPUT=$(OUTPUT) clean >/dev/null
+	$(Q)$(MAKE) $(COMMAND_O) subdir=tools/lib/bpf -C $(BPF_DIR) clean >/dev/null
 
 prefix ?= /usr/local
 bash_compdir ?= /usr/share/bash-completion/completions
@@ -112,7 +107,7 @@ $(OUTPUT)disasm.o: $(srctree)/kernel/bpf/disasm.c
 	$(QUIET_CC)$(COMPILE.c) -MMD -o $@ $<
 
 $(OUTPUT)bpftool: $(OBJS) $(LIBBPF)
-	$(QUIET_LINK)$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $^ $(LIBS)
+	$(QUIET_LINK)$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $(OBJS) $(LIBS)
 
 $(OUTPUT)%.o: %.c
 	$(QUIET_CC)$(COMPILE.c) -MMD -o $@ $<
-- 
2.21.0