configure: Make sure libxdp is before libbpf in linker arguments

When libxdp is linked against the submodule libbpf, the order of linker
arguments is important because libxdp.a needs symbols from libbpf.a. Fix up
configure so it ensures this.

Signed-off-by: Toke Høiland-Jørgensen <[email protected]>

Author: tohojo

configure

@@ -196,12 +196,18 @@ check_libxdp()
                 LIBBPF_INCLUDE_DIR="$(readlink -m lib/install/include)" \
                 LIBBPF_UNBUILT=1;
          cd lib/xdp-tools; ./configure)
+
+        # libxdp.a has to come before libbpf.a so the former can pick up symbols
+        # from the latter
+        sed -i 's/-l:libbpf.a/-l:libxdp.a -l:libbpf.a/' $CONFIG
     else
         echo "Configuring libxdp without our libbpf"
         (cd lib/xdp-tools; ./configure)
+
+        echo 'LDLIBS += -l:libxdp.a' >>$CONFIG
     fi
+
     echo 'LDFLAGS += -L$(LIB_DIR)/install/lib' >>$CONFIG
-    echo 'LDLIBS += -l:libxdp.a' >>$CONFIG
     echo 'OBJECT_LIBXDP = $(LIB_DIR)/install/lib/libxdp.a' >>$CONFIG
     if ! [ -d "lib/xdp-tools/lib" ] && [ -f ".gitmodules" ] && [ -e ".git" ]; then
         git submodule init && git submodule update