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

[Ahmad Fatoum]

Hello Trent,

On 14.09.21 21:11, Trent Piepho wrote:
> On Tue, Sep 14, 2021 at 6:21 AM Ahmad Fatoum <a.fatoum at pengutronix.de> wrote:
>>
>> We currently build the USB loader tools only for the host (build) system,
>> but it can be useful to cross compile them as well for the target.
>>
>> We already have some target tools, but support for those is easier,
>> because they don't link against libraries. We use pkg-config to get
>> cc and ld flags, but we always assume that pkg-config is for the host
>> system and there is no well-defined way to request pkg-config for the
>> target system.
>>
>> Support this by introducing a new CROSS_PKG_CONFIG. This will be
>> consulted only for target tools and default to
>> $(CROSS_COMPILE)pkgconfig.
>>
>> 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.

> 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 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.

> 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.

Cheers,
Ahmad
 


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