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Date: Fri, 18 Oct 2013 16:10:06 +0200
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20131018141006.GC22532@stefanha-thinkpad.redhat.com>
References: <1382078393-11195-1-git-send-email-mohamad.gebai@polymtl.ca>
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In-Reply-To: <1382078393-11195-4-git-send-email-mohamad.gebai@polymtl.ca>
Subject: Re: [Qemu-devel] [PATCH v4 3/5] Adapt Makefiles to the new LTTng
 ust interface.
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To: Mohamad Gebai <mohamad.gebai@gmail.com>
Cc: Mohamad Gebai <mohamad.gebai@polymtl.ca>, alex.bennee@linaro.org, qemu-devel@nongnu.org

On Fri, Oct 18, 2013 at 02:39:51AM -0400, Mohamad Gebai wrote:
>  ######################################################################
> +# Auto-generated event descriptions for LTTng ust code
> +
> +ifeq ($(TRACE_BACKEND),ust)
> +$(obj)/generated-ust-provider.h: $(obj)/generated-ust-provider.h-timestamp
> +$(obj)/generated-ust-provider.h-timestamp: $(SRC_PATH)/trace-events
> +	$(call quiet-command,$(TRACETOOL) \
> +		--format=ust-events-h \
> +		--backend=events \
> +		< $< > $@,"  GEN   $(patsubst %-timestamp,%,$@)")
> +	@cmp -s $@ $(patsubst %-timestamp,%,$@) || cp $@ $(patsubst %-timestamp,%,$@)
> +
> +$(obj)/generated-ust.c: $(obj)/generated-ust.c-timestamp $(BUILD_DIR)/config-host.mak
> +$(obj)/generated-ust.c-timestamp: $(SRC_PATH)/trace-events
> +	$(call quiet-command,$(TRACETOOL) \
> +		--format=ust-events-c \
> +		--backend=events \
> +		< $< > $@,"  GEN   $(patsubst %-timestamp,%,$@)")
> +	@cmp -s $@ $(patsubst %-timestamp,%,$@) || cp $@ $(patsubst %-timestamp,%,$@)
> +
> +ust_provider=$(obj)/generated-ust-provider.h
> +ust=$(obj)/generated-ust.c

I think you can avoid the variables by defining single dependencies
upfront:

$(obj)/generated-events.h: $(obj)/generated-ust-provider.h
$(obj)/generated-events.c: $(obj)/generated-ust.c