[PATCH v2] tools lib traceevent: Robustify do_generate_dynamic_list_file

[David Carrillo-Cisneros <davidcc@google.com>]

v2: Accept "W" and "w" symbol options.

The dynamic-list-file used to export dynamic symbols introduced in

commit e3d09ec8126f ("tools lib traceevent: Export dynamic symbols
used by traceevent plugins")

is generated without any sort of error checking.

I experienced problems due to an old version of nm (v 0.158) that outputs
in a format distinct from the assumed by the script.

Robustify the built of dynamic symbol list  by enforcing that the second
column of $(NM) -u <files> is either "U" (Undefined), "W" or "w" (undefined
weak), which are the possible outputs from non-ancient $(NM) versions.
Print an error if format is unexpected.

Signed-off-by: David Carrillo-Cisneros <davidcc@google.com>
---
 tools/lib/traceevent/Makefile | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/tools/lib/traceevent/Makefile b/tools/lib/traceevent/Makefile
index 2616c66e10c1..a7046ec01a5b 100644
--- a/tools/lib/traceevent/Makefile
+++ b/tools/lib/traceevent/Makefile
@@ -257,10 +257,16 @@ define do_install_plugins
 endef
 
 define do_generate_dynamic_list_file
-	(echo '{';							\
-	$(NM) -u -D $1 | awk 'NF>1 {print "\t"$$2";"}' | sort -u;	\
-	echo '};';							\
-	) > $2
+	symbol_type=`$(NM) -u -D $1 | awk 'NF>1 {print $$1}' | \
+	xargs echo "U W w" | tr ' ' '\n' | sort -u | xargs echo`;\
+	if [ "$$symbol_type" == "U W w" ];then				\
+		(echo '{';						\
+		$(NM) -u -D $1 | awk 'NF>1 {print "\t"$$2";"}' | sort -u;\
+		echo '};';						\
+		) > $2;							\
+	else								\
+		(echo Either missing one of [$1] or bad version of $(NM)) 1>&2;\
+	fi
 endef
 
 install_lib: all_cmd install_plugins
-- 
2.11.0.483.g087da7b7c-goog