[Mesa-dev] [PATCH 3/6] configure.ac: Use PKG_CHECK_VAR for wayland-scanner.

[Emil Velikov]

On 7 March 2017 at 19:22, Frank Binns <frank.binns at imgtec.com> wrote:
> On 07/03/17 17:57, Emil Velikov wrote:
>>
>> On 7 March 2017 at 17:29, Frank Binns <frank.binns at imgtec.com> wrote:
>>>
>>> Hi,
>>>
>>> On 06/03/17 19:06, Matt Turner wrote:
>>>>
>>>> Available since pkg-config-0.28 and pkgconf-0.8.10.
>>>>
>>>> The removal of the AC_PATH_PROG is intentional. Use pkg-config.
>>>
>>>
>>> It doesn't seem possible to cross-compile Mesa out of the box due
>>> to it using the 'host' scanner (found via pkgconfig) instead of the
>>> 'build' scanner. It seems to me that it should actually try finding
>>> the scanner via PATH before falling back to pkgconfig. This is what
>>> Weston does, for example.
>>>
>> Mostly some thinking out loud, feel free to not reply.
>>
>> Consider the following example:
>>
>> You want to use GCC/Python/other tool that is a) not the system
>> installed one or b) not found in the default location.
>> The .pc file makes it easier to know where the tool is rather than
>> guessing and/or manually setting CC=/path/to/my/local/gcc/build/gcc
>> and other variables.
>
>
> But then this can break cross-compilation. For example, if I have the
> following set when running configure:
>  PKG_CONFIG_LIBDIR=${SYSROOT}/usr/lib/pkgconfig
>  PKG_CONFIG_SYSROOT_DIR=${SYSROOT}
>
> Now configure is going to find the scanner in ${SYROOT} and that won't
> run on the 'build' machine. So to get it to use the correct scanner I
> have to prefix /usr/lib/pkgconfig to PKG_CONFIG_LIBDIR.
>
> Now configure is going to find .pc files on the 'build' machine that
> aren't necessarily in ${SYSROOT} and, as a result, the build may end
> up failing.
>
For a second I was wondering how that can happen only to realise that
I've not seen the patch/code you mentioned below.
Thank you for that.

With the original (better imho) behaviour one would need

PKG_CONFIG_LIBDIR=${SYSROOT}/usr/lib/pkgconfig:$path_to_system_or_third_party_host_pkgconfig
PKG_CONFIG_SYSROOT_DIR=${SYSROOT}
or
PKG_CONFIG_PATH=${SYSROOT}/usr/lib/pkgconfig // falls back to the
system default for the build/host wayland-scanner
PKG_CONFIG_SYSROOT_DIR=${SYSROOT}

With the current one

PKG_CONFIG_LIBDIR=$path_to_non_system_host_pkgconfig:${SYSROOT}/usr/lib/pkgconfig
PKG_CONFIG_SYSROOT_DIR=${SYSROOT}

>> I think we can all agree that having those build for 'target' is silly
>> and sub-optimal.
>
>
> I'm not sure everyone agrees:
> https://patchwork.freedesktop.org/patch/53476/
>
Some of the points seem a bit odd, but yes - one might need to have
the 'target' version of the tool.
It's quite interesting how the original behaviour allowed that yet was
deemed wrong/other...

In either case, the ship has sailed so there's no point in nitpicking it imho.

Thanks again,
Emil