Re: [PATCH 4/4] scripts: allow building USB loader tools for target as well

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

On 15.09.21 11:38, Trent Piepho wrote:
> On Wed, Sep 15, 2021 at 1:50 AM Ahmad Fatoum <a.fatoum@pengutronix.de> wrote:
>> On 14.09.21 21:11, Trent Piepho wrote:
>>> On Tue, Sep 14, 2021 at 6:21 AM Ahmad Fatoum <a.fatoum@pengutronix.de> wrote:
>>>>
>>>> Users can override it as necessary, for example, with Yocto, pkg-config
>>>> will be for the cross environment, so target tools can now be built
>>>> with:
>>>
>>> I just added support to Buildroot for building imx-usb-loader from
>>> Barebox, since it's nicer than the standalone version of the program.
>>>
>>> Since pkgconfig was only used for host tools, I didn't need to make
>>> both host and target pkgconfig work.  But of course that will no
>>> longer be true after this patch.
>>
>> It still wouldn't break your workflow, imx-usb-loader wasn't built
>> for target so far.
> 
> But it wouldn't work for anyone who wanted both the host and target versions.

You have two options:

 - provide ${CROSS_COMPILE}pkg-config that calls your wrapper that has
   the necessary options set

 - export CROSS_PKG_CONFIG="YOUR_ENV_VARS pkg-config"

>>> There is a problem with only supplying CROSS_PKG_CONFIG.  To get both
>>> host and target pkgconfig to work, I also need to supply the env
>>> variables used by pkgconfig, PKG_CONFIG_SYSROOT and PKG_CONFIG_LIBDIR.
>>
>> You can set these on the environment before starting barebox build.
>> If you have a $(CROSS_COMPILE)pkg-config that doesn't need any further
>> configuration, you can use that.
> 
> The problem is they need different values for the target and for the
> host version of the package config.  The way you have done this it is
> only possible for there to be one value that is used both when the
> host version is called and the same values when the cross pkg-config
> is called.

The example in the commit message is one way to do it with Yocto.
You could still build both host and target tools in the same go.

>>> The former makes the paths returned by pkgconfig correct and the
>>> latter controls which set, target or host, of .pc files will be used.
>>>
>>> Maybe something like this in the Makefile:
>>>
>>> CROSS_PKG_CONFIG ?= $(CROSS_COMPILE)pkg-config
>>> CROSS_PKG_CONFIG_SYSROOT ?= $(PKG_CONFIG_SYSROOT)
>>> CROSS_PKG_CONFIG_LIBDIR ?= $(PKG_CONFIG_LIBDIR)
>>> CROSS_PKG_CONFIG_ENV := \
>>>        PKG_CONFIG_LIBDIR=$(CROSS_PKG_CONFIG_LIBDIR) \
>>>        PKG_CONFIG_SYSROOT=$(CROSS_PKG_CONFIG_SYSROOT)
>>>
>>> HOST_LIBUSB_CFLAGS := $(shell $(PKG_CONFIG) --cflags)
>>> CROSS_LIBUSB_CFLAGS := $(shell $(CROSS_PKG_CONFIG_ENV)
>>> $(CROSS_PKG_CONFIG) --cflags)
>>>
>>> Then use those everywhere someone wants the libusb cflags.  Repeat for LDFLAGS.
>>
>> I am not really sold on this. Linux doesn't mess with PKG_CONFIG_ variables
>> either. For perf the assume $(CROSS_COMPILE)pkg-config to be available.
>> I think it's a suitbale default for us too. The lines above can go into
>> a shell script wrapper.
> 
> Linux allows you to build the tools individually,  e.g. for tmon we have this:
> 
> make -C $(LINUX_DIR)/tools CC=$(TARGET_CC)
> PKG_CONFIG_PATH=$(STAGING_DIR)/usr/lib/pkgconfig tmon
> 
> Can Barebox build do this?  This way there are multiple make calls,
> with different options, to build a kernel for the target, dtc for the
> host, tmon for the target, and so on.

I don't need this flexibility. I am fine with changing the config
if only specific applications sohuld be built.
 
> So Linux build may not be an ideal pattern to copy.  It can not build
> a tool for both host and target in one build.

And barebox can do this now. So all good?

>>> You'll get fewer repeated invocations of pkg-config this way too.
>>
>> Ye, I thought about that as well, but we do it like this for the host tools,
>> so I left it for now. It's not much overhead and it makes it a bit easier
>> to follow what is used.
> 
> It looks like Linux build assigns pkg-config output to a variable in
> every instance but dtc's build.  I think the existing Barebox
> makefiles are just a bit sloppy in how they call pkg-config.

Send patches?

Cheers,
Ahmad


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