@@ -40,6 +40,14 @@ include $(XEN_ROOT)/tools/libs/libs.mk
$(OBJS-y) $(PIC_OBJS): $(AUTOINCS)
+# Adding the .c conterparts of the headers generated by flex/bison as
+# prerequisite of all objects.
+# This is to tell make that if only the .c file is out-of-date but not the
+# header, it should still wait for the .c file to be rebuilt.
+# Otherwise, make doesn't considered "%.c %.h" as grouped targets, and will run
+# the flex/bison rules in parallel of CC rules which only need the header.
+$(OBJS-y) $(PIC_OBJS): libxlu_cfg_l.c libxlu_cfg_y.c libxlu_disk_l.c
+
%.c %.h:: %.y
@rm -f $*.[ch]
$(BISON) --output=$*.c $<
flex/bison generate two targets, and when those targets are prerequisite of other rules they are considered independently by make. We can have a situation where the .c file is out-of-date but not the .h, git checkout for example. In this case, if a rule only have the .h file as prerequiste, make will procced and start to build the object. In parallel, another target can have the .c file as prerequisite and make will find out it need re-generating and do so, changing the .h at the same time. This parallel task breaks the first one. To avoid this scenario, we put both the header and the source as prerequisite for all object even if they only need the header. Reported-by: Andrew Cooper <Andrew.Cooper3@citrix.com> Signed-off-by: Anthony PERARD <anthony.perard@citrix.com> --- v2: - fix patch context We could add those new prerequisite as order-only, but since the header is going to be re-generated anyway, the object will be too. I tried to simply have something like "libxlu_cfg_l.h: libxlu_cfg_l.c", but make find it to be a circular dependency. I tried to use grouped target ( &: ) with a recent version of make (4.3), but that didn't work. And we couldn't use it as it's a new feature. As reference, this is the minimum dependencies, as not all object needs all generated headers, but keeping that in sync with source change could be problematique: libxlu_cfg_l.o libxlu_cfg_l.opic: libxlu_cfg_y.h libxlu_cfg_y.o libxlu_cfg_y.opic: libxlu_cfg_l.h libxlu_cfg.o libxlu_cfg.opic: libxlu_cfg_y.h libxlu_cfg_l.h libxlu_disk.o libxlu_disk.opic: libxlu_cfg_y.h libxlu_disk_l.h libxlu_vif.o: libxlu_pci.o: And the .c files prerequisite libxlu_cfg_l.o libxlu_cfg_l.opic: libxlu_cfg_y.c libxlu_cfg_y.o libxlu_cfg_y.opic: libxlu_cfg_l.c libxlu_cfg.o libxlu_cfg.opic: libxlu_cfg_y.c libxlu_cfg_l.c libxlu_disk.o libxlu_disk.opic: libxlu_cfg_y.c libxlu_disk_l.c --- tools/libs/util/Makefile | 8 ++++++++ 1 file changed, 8 insertions(+)