Makefile: clean timestamp generation rule

create timestamp by rule without sideeffects.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --git a/trace/Makefile.objs b/trace/Makefile.objs
index 27fe26b5c2743dc06d84573e366ff35add0d07e1..dde9d5784e6003df216210b6182d110506af3800 100644 (file)
--- a/trace/Makefile.objs
+++ b/trace/Makefile.objs
@@ -4,24 +4,24 @@
 # Auto-generated header for tracing routines
 
 $(obj)/generated-tracers.h: $(obj)/generated-tracers.h-timestamp
+       @cmp -s $< $@ || cp $< $@
 $(obj)/generated-tracers.h-timestamp: $(SRC_PATH)/trace-events $(BUILD_DIR)/config-host.mak
        $(call quiet-command,$(TRACETOOL) \
                --format=h \
                --backend=$(TRACE_BACKEND) \
                < $< > $@,"  GEN   $(patsubst %-timestamp,%,$@)")
-       @cmp -s $@ $(patsubst %-timestamp,%,$@) || cp $@ $(patsubst %-timestamp,%,$@)
 
 ######################################################################
 # Auto-generated tracing routines (non-DTrace)
 
 ifneq ($(TRACE_BACKEND),dtrace)
 $(obj)/generated-tracers.c: $(obj)/generated-tracers.c-timestamp
+       @cmp -s $< $@ || cp $< $@
 $(obj)/generated-tracers.c-timestamp: $(SRC_PATH)/trace-events $(BUILD_DIR)/config-host.mak
        $(call quiet-command,$(TRACETOOL) \
                --format=c \
                --backend=$(TRACE_BACKEND) \
                < $< > $@,"  GEN   $(patsubst %-timestamp,%,$@)")
-       @cmp -s $@ $(patsubst %-timestamp,%,$@) || cp $@ $(patsubst %-timestamp,%,$@)
 
 $(obj)/generated-tracers.o: $(obj)/generated-tracers.c $(obj)/generated-tracers.h
 endif