[PATCH 3/8] tools lib traceevent: Detect build environment changes

[Namhyung Kim]

From: Namhyung Kim <namhyung.kim@xxxxxxx>

Cross compiling perf requires setting ARCH and
CROSS_COMPILE variables, but libtraceevent couldn't
detect the changes so it ends up believing no
recompiling is required. Thus the linker failed like:

     LINK perf
 ../lib/traceevent//libtraceevent.a: member ../lib/traceevent//libtraceevent.a(event-parse.o) in archive is not an object
 collect2: ld returned 1 exit status
 make: *** [perf] Error 1

This patch fixes this by adding TRACEEVENT-CFLAGS
file like PERF-CFLAGS to track those changes.

Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
---
 tools/lib/traceevent/Makefile |   12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/tools/lib/traceevent/Makefile b/tools/lib/traceevent/Makefile
index 68a1d088d77e..56daa768b9e3 100644
--- a/tools/lib/traceevent/Makefile
+++ b/tools/lib/traceevent/Makefile
@@ -207,7 +207,7 @@ libtraceevent.so: $(PEVENT_LIB_OBJS)
 libtraceevent.a: $(PEVENT_LIB_OBJS)
 	$(Q)$(do_build_static_lib)
 
-$(PEVENT_LIB_OBJS): %.o: $(src)/%.c
+$(PEVENT_LIB_OBJS): %.o: $(src)/%.c TRACEEVENT-CFLAGS
 	$(Q)$(do_fpic_compile)
 
 define make_version.h
@@ -272,6 +272,16 @@ ifneq ($(dep_includes),)
  include $(dep_includes)
 endif
 
+### Detect environment changes
+TRACK_CFLAGS = $(subst ','\'',$(CFLAGS)):$(ARCH):$(CROSS_COMPILE)
+
+TRACEEVENT-CFLAGS: force
+	@FLAGS='$(TRACK_CFLAGS)'; \
+	    if test x"$$FLAGS" != x"`cat TRACEEVENT-CFLAGS 2>/dev/null`" ; then \
+		echo 1>&2 "    * new build flags or cross compiler"; \
+		echo "$$FLAGS" >TRACEEVENT-CFLAGS; \
+            fi
+
 tags:	force
 	$(RM) tags
 	find . -name '*.[ch]' | xargs ctags --extra=+f --c-kinds=+px
-- 
1.7.10.2

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