From: Blue Swirl <blauwirbel@gmail.com>
Date: Sat, 2 Oct 2010 14:28:12 +0000 (+0000)
Subject: trace: avoid unnecessary recompilation if nothing changed
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=a82cdd58fd9ffa8c651f51de8d855f6baf708681;p=qemu.git

trace: avoid unnecessary recompilation if nothing changed

Add logic to detect changes in generated files. If the old
and new files are identical, don't touch the generated file.
This avoids a lot of churn since many files depend on trace.h.

Based on suggestion by Paolo Bonzini.

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
---

diff --git a/Makefile b/Makefile
index 7c71c83a18..04ce07d7c4 100644
--- a/Makefile
+++ b/Makefile
@@ -106,11 +106,15 @@ ui/vnc.o: QEMU_CFLAGS += $(VNC_TLS_CFLAGS)
 
 bt-host.o: QEMU_CFLAGS += $(BLUEZ_CFLAGS)
 
-trace.h: $(SRC_PATH)/trace-events config-host.mak
-	$(call quiet-command,sh $(SRC_PATH)/tracetool --$(TRACE_BACKEND) -h < $< > $@,"  GEN   $@")
-
-trace.c: $(SRC_PATH)/trace-events config-host.mak
-	$(call quiet-command,sh $(SRC_PATH)/tracetool --$(TRACE_BACKEND) -c < $< > $@,"  GEN   $@")
+trace.h: trace.h-timestamp
+trace.h-timestamp: $(SRC_PATH)/trace-events config-host.mak
+	$(call quiet-command,sh $(SRC_PATH)/tracetool --$(TRACE_BACKEND) -h < $< > $@,"  GEN   trace.h")
+	@cmp -s $@ trace.h || cp $@ trace.h
+
+trace.c: trace.c-timestamp
+trace.c-timestamp: $(SRC_PATH)/trace-events config-host.mak
+	$(call quiet-command,sh $(SRC_PATH)/tracetool --$(TRACE_BACKEND) -c < $< > $@,"  GEN   trace.c")
+	@cmp -s $@ trace.c || cp $@ trace.c
 
 trace.o: trace.c $(GENERATED_HEADERS)