netdev - [PATCH v2 bpf] runqslower: fix Makefile

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Date:   Thu, 30 Jan 2020 00:38:32 -0800
From:   Yulia Kartseva <hex@...com>
To:     <bpf@...r.kernel.org>, <hex@...com>, <ast@...nel.org>,
        <daniel@...earbox.net>, <netdev@...r.kernel.org>
CC:     <andriin@...com>
Subject: [PATCH v2 bpf] runqslower: fix Makefile

From: Julia Kartseva <hex@...com>

Fixes: 9c01546d26d2 ("tools/bpf: Add runqslower tool to tools/bpf")
Signed-off-by: Julia Kartseva <hex@...com>
Acked-by: Andrii Nakryiko <andriin@...com>

Fix undefined reference linker errors when building runqslower with
gcc 7.4.0 on Ubuntu 18.04.
The issue is with misplaced -lelf, -lz options in Makefile:
$(Q)$(CC) $(CFLAGS) -lelf -lz $^ -o $@

-lelf, -lz options should follow the list of target dependencies:
$(Q)$(CC) $(CFLAGS) $^ -lelf -lz -o $@
or after substitution
cc -g -Wall runqslower.o libbpf.a -lelf -lz -o runqslower

The current order of gcc params causes failure in libelf symbols resolution,
e.g. undefined reference to `elf_memory'
---
 tools/bpf/runqslower/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/bpf/runqslower/Makefile b/tools/bpf/runqslower/Makefile
index 0c021352b..87eae5be9 100644
--- a/tools/bpf/runqslower/Makefile
+++ b/tools/bpf/runqslower/Makefile
@@ -41,7 +41,7 @@ clean:
 
 $(OUTPUT)/runqslower: $(OUTPUT)/runqslower.o $(BPFOBJ)
 	$(call msg,BINARY,$@)
-	$(Q)$(CC) $(CFLAGS) -lelf -lz $^ -o $@
+	$(Q)$(CC) $(CFLAGS) $^ -lelf -lz -o $@
 
 $(OUTPUT)/runqslower.o: runqslower.h $(OUTPUT)/runqslower.skel.h	      \
 			$(OUTPUT)/runqslower.bpf.o
-- 
2.17.1