linux-kernel - Re: [PATCH] Kbuild: Avoid DTB rebuilds if source files are untouched

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Date:	Wed, 03 Apr 2013 10:18:26 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
CC:	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	linux-kernel@...r.kernel.org, Michal Marek <mmarek@...e.cz>,
	Stephen Warren <swarren@...dia.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	linux-kbuild@...r.kernel.org
Subject: Re: [PATCH] Kbuild: Avoid DTB rebuilds if source files are untouched

On 04/03/2013 01:14 AM, Vineet Gupta wrote:
> forgot to CC linux-arch
> 
> On 04/03/2013 12:42 PM, Vineet Gupta wrote:
>> Currently, for every ARC kernel build I see the following:
>>
>> --------------->8-----------------
>>   DTB    arch/arc/boot/dts/angel4.dtb.S
>>   AS      arch/arc/boot/dts/angel4.dtb.o
>>   LD      arch/arc/boot/dts/built-in.o
>> rm arch/arc/boot/dts/angel4.dtb.S        <-- forces rebuild next iter
>>   CHK     kernel/config_data.h
>> --------------->8-----------------

I assume that's because the file is an intermediate file, and only built
due to a chain of build rules, and hence make clean it up itself after
the build?

>> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib

>> +.PRECIOUS: $(obj)/%.dtb.S
>> +
>>  $(obj)/%.dtb.S: $(obj)/%.dtb
>>  	$(call cmd,dt_S_dtb)

I'm not sure if .PRECIOUS is correct here. That prevents make from
deleting the file if make is CTRL-C'd in the middle of generating it.
Couldn't that leave a stale/corrupt file around that'd break the build.
Judging by:

http://www.gnu.org/software/make/manual/html_node/Special-Targets.html

I think .SECONDARY might be a better choice? Does that solve the problem
you're seeing?
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