[U-Boot] [PATCH] kbuild,tegra124: add dummy obj- for Kbuild

[U-Boot] [PATCH] kbuild,tegra124: add dummy obj- for Kbuild

[Masahiro Yamada]

In Kbuild, every makefile must have non-empty obj- or obj-y.
Otherwise, built-in.o will not be created and the link stage
will fail.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
---

Tom,
Please apply this along with the Kbuild series.



 arch/arm/cpu/armv7/tegra124/Makefile | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/arm/cpu/armv7/tegra124/Makefile b/arch/arm/cpu/armv7/tegra124/Makefile
index 7f127b1..9478d44 100644
--- a/arch/arm/cpu/armv7/tegra124/Makefile
+++ b/arch/arm/cpu/armv7/tegra124/Makefile
@@ -4,3 +4,6 @@
 #
 # SPDX-License-Identifier:     GPL-2.0+
 #
+
+# necessary to create built-in.o
+obj- := __dummy__.o
-- 
1.8.3.2

[U-Boot] [PATCH] kbuild,tegra124: add dummy obj- for Kbuild

[Albert ARIBAUD]

Hi Masahiro,

On Wed, 19 Feb 2014 22:26:43 +0900, Masahiro Yamada
<yamada.m@jp.panasonic.com> wrote:

> In Kbuild, every makefile must have non-empty obj- or obj-y.
> Otherwise, built-in.o will not be created and the link stage
> will fail.
> 
> Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
> ---
> 
> Tom,
> Please apply this along with the Kbuild series.
> 
> 
> 
>  arch/arm/cpu/armv7/tegra124/Makefile | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/arm/cpu/armv7/tegra124/Makefile b/arch/arm/cpu/armv7/tegra124/Makefile
> index 7f127b1..9478d44 100644
> --- a/arch/arm/cpu/armv7/tegra124/Makefile
> +++ b/arch/arm/cpu/armv7/tegra124/Makefile
> @@ -4,3 +4,6 @@
>  #
>  # SPDX-License-Identifier:     GPL-2.0+
>  #
> +
> +# necessary to create built-in.o
> +obj- := __dummy__.o

Is there really no other way than to specify an unexisting __dummy__.o
in order to build a useless built-in.o?

Amicalement,
-- 
Albert.

[U-Boot] [PATCH] kbuild,tegra124: add dummy obj- for Kbuild

[Stephen Warren]

On 02/19/2014 07:46 AM, Albert ARIBAUD wrote:
> Hi Masahiro,
> 
> On Wed, 19 Feb 2014 22:26:43 +0900, Masahiro Yamada
> <yamada.m@jp.panasonic.com> wrote:
> 
>> In Kbuild, every makefile must have non-empty obj- or obj-y.
>> Otherwise, built-in.o will not be created and the link stage
>> will fail.
...
>> diff --git a/arch/arm/cpu/armv7/tegra124/Makefile b/arch/arm/cpu/armv7/tegra124/Makefile
...
>> +# necessary to create built-in.o
>> +obj- := __dummy__.o

obj- or obj-y?

Adding something to obj-, which presumably isn't used at all, seems very
odd.

> Is there really no other way than to specify an unexisting __dummy__.o
> in order to build a useless built-in.o?

I haven't looked at Kbuild at all, but in the build systems I've
written, for each sub-directory makefile that was included, the
makefiles would include a "pre-makefile" first and a "post-makefile"
after. The "post-makefile" could easily do something like:

ifeq ($(obj-y),)
    obg-y := __dummy__.o
endif

[U-Boot] [PATCH] kbuild,tegra124: add dummy obj- for Kbuild

[Tom Rini]

On Wed, Feb 19, 2014 at 09:36:14AM -0700, Stephen Warren wrote:
> On 02/19/2014 07:46 AM, Albert ARIBAUD wrote:
> > Hi Masahiro,
> > 
> > On Wed, 19 Feb 2014 22:26:43 +0900, Masahiro Yamada
> > <yamada.m@jp.panasonic.com> wrote:
> > 
> >> In Kbuild, every makefile must have non-empty obj- or obj-y.
> >> Otherwise, built-in.o will not be created and the link stage
> >> will fail.
> ...
> >> diff --git a/arch/arm/cpu/armv7/tegra124/Makefile b/arch/arm/cpu/armv7/tegra124/Makefile
> ...
> >> +# necessary to create built-in.o
> >> +obj- := __dummy__.o
> 
> obj- or obj-y?
> 
> Adding something to obj-, which presumably isn't used at all, seems very
> odd.

Why do we even need arch/arm/cpu/armv7/tegra124/Makefile ?  I assume we
need the config.mk because we can't stick CONFIG_ARCH_DEVICE_TREE into
the config header?

> 
> > Is there really no other way than to specify an unexisting __dummy__.o
> > in order to build a useless built-in.o?
> 
> I haven't looked at Kbuild at all, but in the build systems I've
> written, for each sub-directory makefile that was included, the
> makefiles would include a "pre-makefile" first and a "post-makefile"
> after. The "post-makefile" could easily do something like:
> 
> ifeq ($(obj-y),)
>     obg-y := __dummy__.o
> endif
> 
> _______________________________________________
> U-Boot mailing list
> U-Boot at lists.denx.de
> http://lists.denx.de/mailman/listinfo/u-boot

-- 
Tom
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[U-Boot] [PATCH] kbuild,tegra124: add dummy obj- for Kbuild

[Stephen Warren]

On 02/19/2014 01:40 PM, Tom Rini wrote:
> On Wed, Feb 19, 2014 at 09:36:14AM -0700, Stephen Warren wrote:
>> On 02/19/2014 07:46 AM, Albert ARIBAUD wrote:
>>> Hi Masahiro,
>>>
>>> On Wed, 19 Feb 2014 22:26:43 +0900, Masahiro Yamada
>>> <yamada.m@jp.panasonic.com> wrote:
>>>
>>>> In Kbuild, every makefile must have non-empty obj- or obj-y.
>>>> Otherwise, built-in.o will not be created and the link stage
>>>> will fail.
>> ...
>>>> diff --git a/arch/arm/cpu/armv7/tegra124/Makefile b/arch/arm/cpu/armv7/tegra124/Makefile
>> ...
>>>> +# necessary to create built-in.o
>>>> +obj- := __dummy__.o
>>
>> obj- or obj-y?
>>
>> Adding something to obj-, which presumably isn't used at all, seems very
>> odd.
> 
> Why do we even need arch/arm/cpu/armv7/tegra124/Makefile ?  I assume we
> need the config.mk because we can't stick CONFIG_ARCH_DEVICE_TREE into
> the config header?

At least with the current build system, if I delete it, the build fails:

> + make BUILD_DIR=/home/swarren/shared/git_wa/tegra-uboot-flasher/_build/venice2/u-boot -s -j9
> /home/swarren/shared/git_wa/tegra-uboot-flasher/u-boot/scripts/Makefile.build:11: Makefile: No such file or directory
> make[1]: *** No rule to make target `Makefile'.  Stop.
> make: *** [/home/swarren/shared/git_wa/tegra-uboot-flasher/_build/venice2/u-boot/arch/arm/cpu/armv7/tegra124/built-in.o] Error 2

[U-Boot] [PATCH] kbuild,tegra124: add dummy obj- for Kbuild

[Tom Rini]

On Wed, Feb 19, 2014 at 10:26:43PM +0900, Masahiro Yamada wrote:

> In Kbuild, every makefile must have non-empty obj- or obj-y.
> Otherwise, built-in.o will not be created and the link stage
> will fail.
> 
> Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
> ---
> 
> Tom,
> Please apply this along with the Kbuild series.

So with this, I then get:
Configuring for venice2 board...
make[2]: *** [arch/arm/dts/tegra124-venice2.dtb] Error 1
make[1]: *** [dts/dt.dtb] Error 2
make: *** [sub-make] Error 2
   text    data     bss     dec     hex filename
 260562   15030  309960  585552   8ef50 venice2/u-boot
  18527     421      72   19020    4a4c venice2/spl/u-boot-spl

Device Tree Source is not correctly specified.
Please define 'CONFIG_DEFAULT_DEVICE_TREE'
or build with 'DEVICE_TREE=<device_tree>' argument

make[2]: *** [arch/arm/dts/tegra124-venice2.dtb] Error 1
make[1]: *** [dts/dt.dtb] Error 2
make: *** [sub-make] Error 2

--------------------- SUMMARY ----------------------------
Boards compiled: 1
Boards with errors: 1 ( venice2 )
----------------------------------------------------------

What's going on as the config file sets CONFIG_DEFAULT_DEVICE_TREE

-- 
Tom
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[U-Boot] [PATCH] kbuild,tegra124: add dummy obj- for Kbuild

[Tom Rini]

On Wed, Feb 19, 2014 at 10:26:43PM +0900, Masahiro Yamada wrote:

> In Kbuild, every makefile must have non-empty obj- or obj-y.
> Otherwise, built-in.o will not be created and the link stage
> will fail.
> 
> Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>

Applied to u-boot/master, thanks!

-- 
Tom
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[U-Boot] [PATCH] kbuild,tegra124: add dummy obj- for Kbuild

[Masahiro Yamada]

Hello Tom,
(ccing Simon and Stephan)



> > Tom,
> > Please apply this along with the Kbuild series.
> 
> So with this, I then get:
> Configuring for venice2 board...
> make[2]: *** [arch/arm/dts/tegra124-venice2.dtb] Error 1
> make[1]: *** [dts/dt.dtb] Error 2
> make: *** [sub-make] Error 2
>    text    data     bss     dec     hex filename
>  260562   15030  309960  585552   8ef50 venice2/u-boot
>   18527     421      72   19020    4a4c venice2/spl/u-boot-spl
> 
> Device Tree Source is not correctly specified.
> Please define 'CONFIG_DEFAULT_DEVICE_TREE'
> or build with 'DEVICE_TREE=<device_tree>' argument
> 
> make[2]: *** [arch/arm/dts/tegra124-venice2.dtb] Error 1
> make[1]: *** [dts/dt.dtb] Error 2
> make: *** [sub-make] Error 2
> 
> --------------------- SUMMARY ----------------------------
> Boards compiled: 1
> Boards with errors: 1 ( venice2 )
> ----------------------------------------------------------
> 
> What's going on as the config file sets CONFIG_DEFAULT_DEVICE_TREE
> 



Commit 5ab502cb89 has been applied and the build system
now expects device tree sources should reside under arch/$(ARCH)/dts/.

But the device tree of venice2 board is still remaining
in board/nvidia/dts/.
This is the cause of the build error.
(Commit 5ab502cb89 had been posted before venice2 board
support was merged. So there happened an unvisible conflict.)

Actually I did not expect dts  series was applied so soon
because Simon and I was still discussing that series.
And I guess Simon is not happy about Commit 5ab502cb89.

Anyway, we need to do something with venice2's build error
immediately.

I think we have two options.

[1] Move also venice2 device tree to arch/arm/dts directory.
I have posted a patch:
http://patchwork.ozlabs.org/patch/322082/

[2] revert the following commits in this order
3284c8b8ca (dts: generate multiple device tree blobs)
5ab502cb89 (dts: move device tree sources to arch/$(ARCH)/dts/)


If we like to gather all device trees to arch/$(ARCH)/dts,
the choice will be [1].

On the other hand, if we like to put *.dtsi to arch/$(ARCH)/dts
whilst *.dts to board/$(VENDOR)/dts, the choice will be [2].



Best Regards
Masahiro Yamada

[U-Boot] [PATCH] kbuild,tegra124: add dummy obj- for Kbuild

[Masahiro Yamada]

Hello Albert, 


> > --- a/arch/arm/cpu/armv7/tegra124/Makefile
> > +++ b/arch/arm/cpu/armv7/tegra124/Makefile
> > @@ -4,3 +4,6 @@
> >  #
> >  # SPDX-License-Identifier:     GPL-2.0+
> >  #
> > +
> > +# necessary to create built-in.o
> > +obj- := __dummy__.o
> 
> Is there really no other way than to specify an unexisting __dummy__.o
> in order to build a useless built-in.o?

I believe this is the simplest workaround we can do now.

But I promise I'll refactor makefiles and delete
arch/arm/cpu/armv7/{tegra114,tegra30}/Makefile  lator.

For now, let me go with this solution..
We still have a mountain of refactoring to do.

Best Regards
Masahiro Yamada

[U-Boot] [PATCH] kbuild,tegra124: add dummy obj- for Kbuild

[Masahiro Yamada]

Hello Stephen,


On Wed, 19 Feb 2014 09:36:14 -0700
Stephen Warren <swarren@wwwdotorg.org> wrote:

> On 02/19/2014 07:46 AM, Albert ARIBAUD wrote:
> > Hi Masahiro,
> > 
> > On Wed, 19 Feb 2014 22:26:43 +0900, Masahiro Yamada
> > <yamada.m@jp.panasonic.com> wrote:
> > 
> >> In Kbuild, every makefile must have non-empty obj- or obj-y.
> >> Otherwise, built-in.o will not be created and the link stage
> >> will fail.
> ...
> >> diff --git a/arch/arm/cpu/armv7/tegra124/Makefile b/arch/arm/cpu/armv7/tegra124/Makefile
> ...
> >> +# necessary to create built-in.o
> >> +obj- := __dummy__.o
> 
> obj- or obj-y?

Definitely obj-.
If you add a non-existing object to obj-y, build will fail.

> Adding something to obj-, which presumably isn't used at all, seems very
> odd.
> 
> > Is there really no other way than to specify an unexisting __dummy__.o
> > in order to build a useless built-in.o?
> 
> I haven't looked at Kbuild at all, but in the build systems I've
> written, for each sub-directory makefile that was included, the
> makefiles would include a "pre-makefile" first and a "post-makefile"
> after. The "post-makefile" could easily do something like:
> 
> ifeq ($(obj-y),)
>     obg-y := __dummy__.o
> endif


You mean
ifeq ($(obj-y),)
     obj- := __dummy__.o
endif

should be put in a common part(scripts/Makefile.build) ?

No, no. We can't do this.

It has a side effect.

If we put it in the common part, build-in.o will be generated
in all sub-directories, including tools/, tools/env,
examples/standalone/, etc.

We do not want built-in.o  in host progs / standalone progs
directories.


Best Regards
Masahiro Yamada

[U-Boot] [PATCH] kbuild,tegra124: add dummy obj- for Kbuild

[Masahiro Yamada]

Hello Stephen,

> >>
> >> Adding something to obj-, which presumably isn't used at all, seems very
> >> odd.
> > 
> > Why do we even need arch/arm/cpu/armv7/tegra124/Makefile ?  I assume we
> > need the config.mk because we can't stick CONFIG_ARCH_DEVICE_TREE into
> > the config header?
> 
> At least with the current build system, if I delete it, the build fails:
> 
> > + make BUILD_DIR=/home/swarren/shared/git_wa/tegra-uboot-flasher/_build/venice2/u-boot -s -j9
> > /home/swarren/shared/git_wa/tegra-uboot-flasher/u-boot/scripts/Makefile.build:11: Makefile: No such file or directory
> > make[1]: *** No rule to make target `Makefile'.  Stop.
> > make: *** [/home/swarren/shared/git_wa/tegra-uboot-flasher/_build/venice2/u-boot/arch/arm/cpu/armv7/tegra124/built-in.o] Error 2

Yes, we can't delete the Makefile. (This is the same as before Kbuild.)

Venice2 board specify SoC name, tegra124 in boards.cfg.
If $(SOC) is not empty, the build system will descend into the SoC
directory, and Makefile always must be there.

I understand the special situation for Tegra, which has a different CPU
for SPL.

I guess you want to build under arch/arm/cpu/arm720t/tegra124/ for SPL,
whereas there is nothing to build under arch/arm/cpu/armv7/tegra124/.



Best Regards
Masahiro Yamada

[U-Boot] [PATCH] kbuild,tegra124: add dummy obj- for Kbuild

[Albert ARIBAUD]

Hi Masahiro,

On Thu, 20 Feb 2014 17:23:31 +0900, Masahiro Yamada
<yamada.m@jp.panasonic.com> wrote:

> Hello Albert, 
> 
> 
> > > --- a/arch/arm/cpu/armv7/tegra124/Makefile
> > > +++ b/arch/arm/cpu/armv7/tegra124/Makefile
> > > @@ -4,3 +4,6 @@
> > >  #
> > >  # SPDX-License-Identifier:     GPL-2.0+
> > >  #
> > > +
> > > +# necessary to create built-in.o
> > > +obj- := __dummy__.o
> > 
> > Is there really no other way than to specify an unexisting __dummy__.o
> > in order to build a useless built-in.o?
> 
> I believe this is the simplest workaround we can do now.
> 
> But I promise I'll refactor makefiles and delete
> arch/arm/cpu/armv7/{tegra114,tegra30}/Makefile  lator.
> 
> For now, let me go with this solution..
> We still have a mountain of refactoring to do.

Thanks -- as long as this is a known topic, I'm fine with it.

> Best Regards
> Masahiro Yamada

Amicalement,
-- 
Albert.

[U-Boot] [PATCH] kbuild,tegra124: add dummy obj- for Kbuild

[Tom Rini]

On Thu, Feb 20, 2014 at 05:22:27PM +0900, Masahiro Yamada wrote:
> Hello Tom,
> (ccing Simon and Stephan)
> 
> 
> 
> > > Tom,
> > > Please apply this along with the Kbuild series.
> > 
> > So with this, I then get:
> > Configuring for venice2 board...
> > make[2]: *** [arch/arm/dts/tegra124-venice2.dtb] Error 1
> > make[1]: *** [dts/dt.dtb] Error 2
> > make: *** [sub-make] Error 2
> >    text    data     bss     dec     hex filename
> >  260562   15030  309960  585552   8ef50 venice2/u-boot
> >   18527     421      72   19020    4a4c venice2/spl/u-boot-spl
> > 
> > Device Tree Source is not correctly specified.
> > Please define 'CONFIG_DEFAULT_DEVICE_TREE'
> > or build with 'DEVICE_TREE=<device_tree>' argument
> > 
> > make[2]: *** [arch/arm/dts/tegra124-venice2.dtb] Error 1
> > make[1]: *** [dts/dt.dtb] Error 2
> > make: *** [sub-make] Error 2
> > 
> > --------------------- SUMMARY ----------------------------
> > Boards compiled: 1
> > Boards with errors: 1 ( venice2 )
> > ----------------------------------------------------------
> > 
> > What's going on as the config file sets CONFIG_DEFAULT_DEVICE_TREE
> > 
> 
> 
> 
> Commit 5ab502cb89 has been applied and the build system
> now expects device tree sources should reside under arch/$(ARCH)/dts/.
> 
> But the device tree of venice2 board is still remaining
> in board/nvidia/dts/.
> This is the cause of the build error.
> (Commit 5ab502cb89 had been posted before venice2 board
> support was merged. So there happened an unvisible conflict.)
> 
> Actually I did not expect dts  series was applied so soon
> because Simon and I was still discussing that series.
> And I guess Simon is not happy about Commit 5ab502cb89.
> 
> Anyway, we need to do something with venice2's build error
> immediately.
> 
> I think we have two options.
> 
> [1] Move also venice2 device tree to arch/arm/dts directory.
> I have posted a patch:
> http://patchwork.ozlabs.org/patch/322082/
> 
> [2] revert the following commits in this order
> 3284c8b8ca (dts: generate multiple device tree blobs)
> 5ab502cb89 (dts: move device tree sources to arch/$(ARCH)/dts/)
> 
> 
> If we like to gather all device trees to arch/$(ARCH)/dts,
> the choice will be [1].
> 
> On the other hand, if we like to put *.dtsi to arch/$(ARCH)/dts
> whilst *.dts to board/$(VENDOR)/dts, the choice will be [2].

Well, I think our long term plan here is (a) mirror the kernel today and
since their long term plan is "move device trees out of tree, then deal
with it there" once they've got a plan there, we can follow (and indeed
should be contributing to the conversation).

-- 
Tom
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[U-Boot] [PATCH] kbuild,tegra124: add dummy obj- for Kbuild

[Stephen Warren]

On 02/20/2014 01:24 AM, Masahiro Yamada wrote:
> Hello Stephen,
> 
> 
> On Wed, 19 Feb 2014 09:36:14 -0700
> Stephen Warren <swarren@wwwdotorg.org> wrote:
> 
>> On 02/19/2014 07:46 AM, Albert ARIBAUD wrote:
>>> Hi Masahiro,
>>>
>>> On Wed, 19 Feb 2014 22:26:43 +0900, Masahiro Yamada
>>> <yamada.m@jp.panasonic.com> wrote:
>>>
>>>> In Kbuild, every makefile must have non-empty obj- or obj-y.
>>>> Otherwise, built-in.o will not be created and the link stage
>>>> will fail.
>> ...
>>>> diff --git a/arch/arm/cpu/armv7/tegra124/Makefile b/arch/arm/cpu/armv7/tegra124/Makefile
>> ...
>>>> +# necessary to create built-in.o
>>>> +obj- := __dummy__.o
>>
>> obj- or obj-y?
> 
> Definitely obj-.

Really? Why would such a variable even exist or be used. Only obj-n or
obj-y should exist; "" isn't a valid y/n value.

[U-Boot] [PATCH] kbuild,tegra124: add dummy obj- for Kbuild

[Masahiro Yamada]

Hello Stefen,


On Thu, 20 Feb 2014 09:15:21 -0700
Stephen Warren <swarren@wwwdotorg.org> wrote:

> On 02/20/2014 01:24 AM, Masahiro Yamada wrote:
> > Hello Stephen,
> > 
> > 
> > On Wed, 19 Feb 2014 09:36:14 -0700
> > Stephen Warren <swarren@wwwdotorg.org> wrote:
> > 
> >> On 02/19/2014 07:46 AM, Albert ARIBAUD wrote:
> >>> Hi Masahiro,
> >>>
> >>> On Wed, 19 Feb 2014 22:26:43 +0900, Masahiro Yamada
> >>> <yamada.m@jp.panasonic.com> wrote:
> >>>
> >>>> In Kbuild, every makefile must have non-empty obj- or obj-y.
> >>>> Otherwise, built-in.o will not be created and the link stage
> >>>> will fail.
> >> ...
> >>>> diff --git a/arch/arm/cpu/armv7/tegra124/Makefile b/arch/arm/cpu/armv7/tegra124/Makefile
> >> ...
> >>>> +# necessary to create built-in.o
> >>>> +obj- := __dummy__.o
> >>
> >> obj- or obj-y?
> > 
> > Definitely obj-.
> 
> Really? Why would such a variable even exist or be used. Only obj-n or
> obj-y should exist; "" isn't a valid y/n value.

All defined CONFIG macros are included in
include/autoconf.mk  (and include/spl-autoconf.mk,
include/tpl-autoconf.mk  for SPL, TPL, respectively)

If CONFIG_FOO is defined in your  config header, 
CONFIG_FOO=y  will apear in include/autoconf.mk
Otherwise, it does not appear in include/autoconf.mk.

As a result,
obj-$(CONFIG_FOO) += foo.o
   becomes
obj-y += foo.o     (if CONFIG_FOO is defined)
    or 
obj- += foo.o       (if CONFIG_FOO is not defined)


Kbuild  checks  $(obj-) as well as  $(obj-y).

Let me explain shortly how Kbuild works.


For example,  assume we have a Makefile like this

obj-$(CONFIG_FOO) += foo.o
obj-$(CONFIG_BAR) += bar.o



[1] 
Let's say  CONFIG_FOO is set, but CONFIG_BAR isn't.

In this case, 
 $(obj-y)  is  "foo.o"
 $(obj-)  is   "bar.o"

Then Kbuild builds only "foo.o" and links it  into built-in.o

[2]
Next, let's say neither CONFIG_FOO nor CONFIG_BAR is set.

In this case, 
 $(obj-y)  is  empty.
  $(obj-)  is "foo.o  bar.o"

Kbuild creates empty built-in.o
if   $(obj-y) is empty but $(obj-) is not empty.

[3]
Last,  let's say Makefile does not have  obj-$(...) lines.

In this case,
  $(obj-y) is empty
  $(obj-) is empty too.

Kbuild does not create built-in.o  when both $(obj-y) and $(obj-)
are empty.
This is the case of tools/Makefile or example/standalone/Makefile.


Is this clearer now?


Best Regards
Masahiro Yamada

[U-Boot] [PATCH] kbuild,tegra124: add dummy obj- for Kbuild

[Stephen Warren]

On 02/21/2014 04:45 AM, Masahiro Yamada wrote:
> On Thu, 20 Feb 2014 09:15:21 -0700 Stephen Warren  wrote:
>> On 02/20/2014 01:24 AM, Masahiro Yamada wrote:
>>> On Wed, 19 Feb 2014 09:36:14 -0700 Stephen Warren wrote:
>>>> On 02/19/2014 07:46 AM, Albert ARIBAUD wrote:
>>>>> On Wed, 19 Feb 2014 22:26:43 +0900, Masahiro wrote:
>>>>>
>>>>>> In Kbuild, every makefile must have non-empty obj- or obj-y.
>>>>>> Otherwise, built-in.o will not be created and the link stage
>>>>>> will fail.
>>>> ...
>>>>>> diff --git a/arch/arm/cpu/armv7/tegra124/Makefile b/arch/arm/cpu/armv7/tegra124/Makefile
>>>> ...
>>>>>> +# necessary to create built-in.o
>>>>>> +obj- := __dummy__.o
>>>>
>>>> obj- or obj-y?
>>>
>>> Definitely obj-.
>>
>> Really? Why would such a variable even exist or be used. Only obj-n or
>> obj-y should exist; "" isn't a valid y/n value.
> 
> All defined CONFIG macros are included in
> include/autoconf.mk  (and include/spl-autoconf.mk,
> include/tpl-autoconf.mk  for SPL, TPL, respectively)
> 
> If CONFIG_FOO is defined in your  config header, 
> CONFIG_FOO=y  will apear in include/autoconf.mk
> Otherwise, it does not appear in include/autoconf.mk.
...
> Is this clearer now?

OK, that makes sense.

I would have expected that Kbuild could detect obj-y is empty, and skip
building builtin.o, and skip attempting to link it in to the parent
directory too. However, if it doesn't do that, then this all makes
sense. Thanks.