[dpdk-dev] [PATCH v2] mk: fix objects/library order when linking

[David Marchand <david.marchand@6wind.com>]

The initial problem has been seen while building mlx4 pmd as a shared library
on Ubuntu 14.04 (gcc 4.8.4-2ubuntu1~14.04).

Resulting .so will lack the DT_NEEDED entry for libibverbs:

marchand@ubuntu1404:~/dpdk$ ldd ./build/lib/librte_pmd_mlx4.so
	linux-vdso.so.1 =>  (0x00007fff87ebb000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f2ced21a000)
	/lib64/ld-linux-x86-64.so.2 (0x00007f2ced821000)

And trying to load it in testpmd triggers this error:

[...]
EAL: librte_pmd_mlx4.so: undefined symbol: ibv_query_port
[...]

After some strace, the problem comes from the --as-needed option passed to the
linker.

It is safer to specify libraries we depend on after the objects we are linking
into a shared library, especially when the linker is invoked with options like
--as-needed.

Fixes: bef06a8a0655 ("mk: set library dependencies in shared object file")

Signed-off-by: David Marchand <david.marchand@6wind.com>
---

Changes since v1:
- added some details in commitlog since Thomas does not like "safer"
  argument :-)

---

 mk/rte.lib.mk |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mk/rte.lib.mk b/mk/rte.lib.mk
index 06a1519..1f1b6e1 100644
--- a/mk/rte.lib.mk
+++ b/mk/rte.lib.mk
@@ -82,7 +82,7 @@ O_TO_A_DO = @set -e; \
 	$(O_TO_A) && \
 	echo $(O_TO_A_CMD) > $(call exe2cmd,$(@))
 
-O_TO_S = $(LD) $(_CPU_LDFLAGS) $(EXTRA_LDFLAGS) $(LDLIBS) -shared $(OBJS-y) \
+O_TO_S = $(LD) $(_CPU_LDFLAGS) $(EXTRA_LDFLAGS) -shared $(OBJS-y) $(LDLIBS) \
 	 -Wl,-soname,$(LIB) -o $(LIB)
 O_TO_S_STR = $(subst ','\'',$(O_TO_S)) #'# fix syntax highlight
 O_TO_S_DISP = $(if $(V),"$(O_TO_S_STR)","  LD $(@)")
-- 
1.7.10.4