[U-Boot] [PATCH] Makefile: remove BUILD_TAG from KBUILD_CFLAGS

[Tom Rini]

On Tue, Feb 09, 2016 at 10:53:48AM -0700, Stephen Warren wrote:
> On 02/09/2016 10:43 AM, Tom Rini wrote:
> >On Tue, Feb 09, 2016 at 10:26:14AM -0700, Stephen Warren wrote:
> >>On 02/09/2016 10:01 AM, Tom Rini wrote:
> >>>On Tue, Feb 09, 2016 at 08:11:15AM -0800, James Chargin wrote:
> >>>>
> >>>>
> >>>>On 02/08/2016 05:32 PM, Stephen Warren wrote:
> >>>>>From: Stephen Warren <swarren at nvidia.com>
> >>>>>
> >>>>>If BUILD_TAG is part of KBUILD_CFLAGS, then any time the value changes,
> >>>>>all files get rebuilt. In a continuous integration environment, the value
> >>>>>will change every build. This wastes time assuming that incremental
> >>>>>builds would otherwise occur.
> >>>>>
> >>>>>To solve this, remove BUILD_TAG from KBUILD_FLAGS and add it to the end of
> >>>>>"local version".
> >>>>>
> >>>>>This has other advantages too:
> >>>>>- The special case for BUILD_TAG in display_options.c can be removed.
> >>>>>- The version printed by the "version" command exactly matches what is
> >>>>>   printed at boot.
> >>>>>
> >>>>>Old sign-on message:
> >>>>>U-Boot 2016.03-rc1-00044-g4085db5e767b (Feb ...), Build: bar-bas
> >>>>>
> >>>>>New sign-on message:
> >>>>>U-Boot 2016.03-rc1-00044-g4085db5e767b-bar-baz (Feb ...)
> >>>>
> >>>>I would urge this not be done. The display of the BUILD_TAG on
> >>>>startup is pretty useful in my environment. It's been there for a
> >>>>long time and some of my users have grown used to it.
> >>>>
> >>>>Of all the parts of the sign-on message, I'd rather the git hash go
> >>>>away than the BUILD_TAG. None of my users really care about the
> >>>>level of detail of the git hash and won't spend the time required to
> >>>>use this hash to determine if they have the version they want. (Some
> >>>>don't have a repo clone, and don't care to, and so can't easily make
> >>>>the correspondence even if they wanted to).
> >>>
> >>>Yeah, I think this is too widely used of a thing to change.  FWIW, I
> >>>really like githashes since it means you can see if $random-binary is
> >>>something you have in $vendor-tree or not.  So I think in this case, NAK
> >>>on the patch and maybe need to poke Travis-CI on how to or not to tag
> >>>things?
> >>
> >>Do you mean you think people currently rely upon the ", Build: xxx"
> >>format in the sign-on message, and the "version" command /not/
> >>printing that information?
> >
> >I mean that the places we construct strings like this are likely relied
> >upon by people, yes.
> >
> >>If so, I'll go back to trying to work out how to get Kbuild to
> >>transfer the environment variable into a CONFIG_XXX option so that
> >>modifying it only causes a rebuild of the one file that uses the
> >>value.
> >
> >A quick peak and I think that:
> >(a) LOCALVERSION needs a little love somewhere to ensure that it in fact
> >does not exceed 64 characters (and pushing upstream to the kernel
> >anything relevant here)
> >(b) Yes, adjusting BUILD_TAG into CONFIG_BUILD_TAG is probably the best
> >answer and probably not even that bad.  I don't think we need an
> >automagic conversion, just noting it in the release emails and the
> >sudden lack of Build: should get people that are using it to update
> >their scripts.
> 
> Unfortunately, simply renaming the variable won't work;
> Kconfig/Kbuild need to know something about it in order to do their
> rebuild-only-on-change magic (and the value must be removed from
> CFLAGS too). I was having a hard time getting that to work, but I'll
> take another look.

Right.  Can't we just make it another string Kconfig like LOCALVERSION,
not need to pass -D.... and then it's set via poking the config file by
CI, etc?

-- 
Tom
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