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Date: Tue, 12 Jun 2012 10:50:33 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] one question on the makefile
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To: Wei Yang <weiyang.kernel@gmail.com>
Cc: Richard Yang <weiyang@linux.vnet.ibm.com>, qemu-devel@nongnu.org

Il 12/06/2012 10:33, Wei Yang ha scritto:
> .PHONY: $(patsubst %, check-qtest-%, $(QTEST_TARGETS))
> $(patsubst %, check-qtest-%, $(QTEST_TARGETS)): check-qtest-%: $(check-qtest-y)
> 	$(call quiet-command,QTEST_QEMU_BINARY=$*-softmmu/qemu-system-$* \
> 		gtester $(GTESTER_OPTIONS) -m=$(SPEED) $(check-qtest-$*-y),"GTESTER $@")
> 
> I know the general idea is to create a rule for target such as
> check-qtest-x86_64.
> 
> There are two colons, usually there is one colon in dependency.

Search for "Static pattern rules".  Static pattern rules are probably
the single most useful GNU make extension.  They greatly limit the
amount of "magic" the make does, so the resulting Makefiles are more
easily debuggable.  Here is an extract from the GNU make manual:

=====
     TARGETS ...: TARGET-PATTERN: PREREQ-PATTERNS ...
             RECIPE
             ...

The TARGETS list specifies the targets that the rule applies to.  The
targets can contain wildcard characters, just like the targets of
ordinary rules (*note Using Wildcard Characters in File Names:
Wildcards.).

   The TARGET-PATTERN and PREREQ-PATTERNS say how to compute the
prerequisites of each target.  Each target is matched against the
TARGET-PATTERN to extract a part of the target name, called the "stem".
This stem is substituted into each of the PREREQ-PATTERNS to make the
prerequisite names (one from each PREREQ-PATTERN).
=====


$* is also replaced by the stem.  In fact in this case, the stem is not
used in the PREREQ-PATTERNS, it is only used in the commands.

Paolo