From: mmarek@suse•cz (Michal Marek)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] ARM: kbuild: Fix forced rebuild after 'make dtbs'
Date: Wed, 26 Nov 2014 10:39:48 +0100 [thread overview]
Message-ID: <54759FE4.5030700@suse.cz> (raw)
In-Reply-To: <20141125235150.GH3836@n2100.arm.linux.org.uk>
On 2014-11-26 00:51, Russell King - ARM Linux wrote:
> On Tue, Nov 25, 2014 at 10:41:35PM +0100, Michal Marek wrote:
>> Dne 2.11.2014 v 21:52 Jason Cooper napsal(a):
>>> After this patch:
>>>
>>> f4d4ffc03efc kbuild: dtbs_install: new make target
>>>
>>> was added the kernel tree, Linus Walleij noticed that 'make dtbs' forced
>>> a following 'make zImage' to rebuild the entire tree, even though
>>> nothing had changed. His report:
>>>
>>> After this patch a while back I have observed the following behaviour
>>> of the kernel build:
>>>
>>> make zImage
>>> make zImage
>>> -> incremental build, just relink
>>>
>>> make zImage
>>> make dtbs
>>> make zImage
>>> -> The whole kernel gets rebuilt
>>>
>>> So now if I happen to recompile my device trees, I suddenly want
>>> the entire zImage to be rebuilt to? It's by definition not changes
>>> that affect the kernel build :-(
>>>
>>> I noticed this because my build scripts calls make dtbs && make
>>> zImage, and started to rebuild absolutely everything all the time.
>>>
>>> To fix this, we make only the dtbs_install target depend on the prepare
>>> target. It's needed to make sure KERNELVERSION is calculated prior to
>>> installing.
>>
>> If a mere 'make prepare' causes a rebuild of the whole kernel, then
>> there is something fishy in the ARM Makefiles. However, if you only need
>> the KERNELRELEASE variable, then you do not need to depend on prepare.
>> The main Makefile makes sure that silentoldconfig is ran and therefore
>> KERNELRELEASE set for all targets except make *config.
>
> Running make prepare and then re-running a build doesn't rebuild anything
> for me. However, I always build with O= Also works if I do a make
> dtbs too. So, everything seems to work as expected here.
Good :).
> I think this needs a bit more debugging to see why the whole kernel is
> being rebuilt - the kernel build system has methods to tell you why stuff
> is being built, which would be a good place to start.
Right, this is make V=2.
Michal
prev parent reply other threads:[~2014-11-26 9:39 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CACRpkdYmJWy1_vs0tWRA7SvkQnvbXXKqf7pHpH5b5tZ6vR+KJg@mail.gmail.com>
2014-11-02 20:52 ` [PATCH] ARM: kbuild: Fix forced rebuild after 'make dtbs' Jason Cooper
2014-11-25 21:41 ` Michal Marek
2014-11-25 23:51 ` Russell King - ARM Linux
2014-11-26 0:57 ` Jason Cooper
2014-11-26 13:57 ` Linus Walleij
2014-11-26 14:41 ` Russell King - ARM Linux
2014-11-28 14:10 ` Linus Walleij
2014-12-01 13:55 ` Michal Marek
2014-12-04 11:22 ` Grant Likely
2014-12-04 11:24 ` Russell King - ARM Linux
2014-11-26 9:39 ` Michal Marek [this message]
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