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

[Eero Tamminen]

Hi,

On 07.03.2017 21:37, Frank Binns wrote:
> On 07/03/17 19:22, Frank Binns 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.
>
> Clarification:
> Now configure is going to get the path for the scanner in ${SYSROOT}
> and that path may not exist for the 'build' machine.

Autotools and mass of scripts & half the Posix it's calling during 
configuration phase (and building) isn't really friendly for 
cross-compilation, either between architectures or just different 
setups.  There are just too many gotchas.

However, there are tools for handling that kind of setups.  E.g. in 
Debian there are things like deb-bootstrap, sb2 etc.


	- Eero

>
> Thanks
> Frank
>
>> 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.
>>
>>> 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/
>>
>> Thanks
>> Frank
>>
>>> On the weston case... I simply did want want to annoy people, they
>>> seemed rather attached [1] to having a 'target' wayland-scanner... ;-)
>>>
>>> -Emil
>>>
>>> [1] https://patchwork.freedesktop.org/patch/42511/
>>
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