[dpdk-stable] [PATCH] mk: fix lib filtering

[Olivier Matz <olivier.matz@6wind.com>]

I get the following error when linking the test application:
  build/lib/librte_pmd_thunderx_nicvf.a(nicvf_hw.o):
  In function `nicvf_qsize_regbit':
  drivers/net/thunderx/base/nicvf_hw.c:451: undefined reference to `log2'
  build/lib/librte_pmd_thunderx_nicvf.a(nicvf_hw.o):
  In function `nicvf_rss_reta_update':
  drivers/net/thunderx/base/nicvf_hw.c:804: undefined reference to `log2'
  build/lib/librte_pmd_thunderx_nicvf.a(nicvf_hw.o):
  In function `nicvf_rss_reta_query':
  drivers/net/thunderx/base/nicvf_hw.c:825: undefined reference to `log2'

While I don't know why it does not happen for a default build, the error
can be explained. The link command line is:

   gcc -o test ... *.o ... -Wl,-lm ... -Wl,-lrte_pmd_thunderx_nicvf ...

rte_pmd_thunderx_nicvf needs the math library, and it should be
added after. This is not the case because the test application also
adds the math library.

The makefile already filters the libraries, but it keeps the first
occurrence of the lib. Instead, the last one should be kept.

Fixes: edf4d331dcdb ("mk: eliminate duplicates from libraries list")

Cc: stable@dpdk.org
Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
---
 mk/rte.app.mk | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/mk/rte.app.mk b/mk/rte.app.mk
index fcc3a5795..4c659e971 100644
--- a/mk/rte.app.mk
+++ b/mk/rte.app.mk
@@ -186,10 +186,21 @@ _LDLIBS-y += $(EXECENV_LDLIBS)
 
 LDLIBS += $(_LDLIBS-y) $(CPU_LDLIBS) $(EXTRA_LDLIBS)
 
-# Eliminate duplicates without sorting
-LDLIBS := $(shell echo $(LDLIBS) | \
-	awk '{for (i = 1; i <= NF; i++) { \
-		if ($$i !~ /^-l.*/ || !seen[$$i]++) print $$i }}')
+# all the words except the first one
+allbutfirst = $(wordlist 2,$(words $(1)),$(1))
+
+# Eliminate duplicates without sorting, only keep the last occurrence
+filter-libs = \
+	$(if $(1),$(strip\
+		$(if \
+			$(and \
+				$(filter $(firstword $(1)),$(call allbutfirst,$(1))),\
+				$(filter -l%,$(firstword $(1)))),\
+			,\
+			$(firstword $(1))) \
+		$(call filter-libs,$(call allbutfirst,$(1)))))
+
+LDLIBS := $(call filter-libs,$(LDLIBS))
 
 ifeq ($(RTE_DEVEL_BUILD)$(CONFIG_RTE_BUILD_SHARED_LIB),yy)
 LDFLAGS += -rpath=$(RTE_SDK_BIN)/lib
-- 
2.11.0