Yes, if the sys_root key value in meson.cross is present
PKG_CONFIG_SYSROOT_DIR gets set.  Honister patch I confirmed with:
https://github.com/jwinarske/manifests/blob/honister/rpi64/0001-Add-sys_root-to-properties-section.patch

The issue is that meson doesn't pass PKG_CONFIG_SYSROOT_DIR to the shell
environment that runs pkg-config, as with the pkg-config sandbox test it
does work.


On Tue, Nov 30, 2021 at 11:40 AM Alexander Kanavin <[email protected]>
wrote:

> I am seeing in mesonbuild/dependencies/pkgconfig.py
>
>         sysroot = environment.properties[for_machine].get_sys_root()
>         if sysroot:
>             env['PKG_CONFIG_SYSROOT_DIR'] = sysroo
>
> So we probably need to ensure this 'sys_root' is correctly set, and then
> things will simply work?
>
> Alex
>
> On Tue, 30 Nov 2021 at 20:15, Joel Winarske <[email protected]>
> wrote:
>
>> https://github.com/vkmark/vkmark/blob/master/src/meson.build#L9
>>
>> On Tue, Nov 30, 2021 at 10:53 AM Alexander Kanavin <
>> [email protected]> wrote:
>>
>>> I do not quite understand the use case. What is being done with the full
>>> path to the header?
>>>
>>> Alex
>>>
>>> On Tue, 30 Nov 2021 at 19:26, Joel Winarske <[email protected]>
>>> wrote:
>>>
>>>> This pattern works to get the absolute path of the header:
>>>>
>>>> Yocto
>>>>
>>>>     EXTRA_OEMESON += "--prefix ${STAGING_DIR_TARGET}/usr"
>>>>
>>>> Meson
>>>>
>>>>     vulkan_dep = dependency('vulkan')
>>>>     vulkan_hpp = join_paths([
>>>>         vulkan_dep.get_pkgconfig_variable('includedir',
>>>> define_variable: ['prefix', get_option('prefix')]),
>>>>         'vulkan',
>>>>         'vulkan.hpp'
>>>>         ])
>>>>
>>>> Implementation in build/meson-log.txt
>>>>
>>>> Called
>>>> `/b/github-ci/_work/meta-flutter/rpi4-drm-honister-latest/rpi4/tmp/work/cortexa72-poky-linux/vkmark/git-r0/recipe-sysroot-native/usr/bin/pkg-config
>>>> --define-variable=prefix=/b/github-ci/_work/meta-flutter/rpi4-drm-honister-latest/rpi4/tmp/work/cortexa72-poky-linux/vkmark/git-r0/recipe-sysroot/usr
>>>> --variable=includedir vulkan` -> 0
>>>>
>>>>
>>>> One would expect the following meson to work if STAGING_DIR_TARGET were
>>>> set, as that's how pkg-config works:
>>>>
>>>>     vulkan_dep = dependency('vulkan')
>>>>     vulkan_hpp = join_paths([
>>>>         vulkan_dep.get_pkgconfig_variable('includedir'),
>>>>         'vulkan',
>>>>         'vulkan.hpp'
>>>>         ])
>>>>
>>>> This will always return /usr/include/vulkan/vulkan.hpp regardless of
>>>> PKG_CONFIG_SYSROOT_DIR value.  With PKG_CONFIG_SYSROOT_DIR set, it should
>>>> be /usr/include/vulkan/vulkan.hpp with prepend of PKG_CONFIG_SYSROOT_DIR
>>>> value.
>>>>
>>>>
>>>> Sandbox testing of pkg-config
>>>>
>>>>     $ export
>>>> STAGING_DIR_TARGET=/b/github-ci/_work/meta-flutter/rpi4-drm-honister-latest/raspberrypi4-64/tmp/work/cortexa72-poky-linux/vkmark/git-r0/recipe-sysroot
>>>>     $ PKG_CONFIG_SYSROOT_DIR=$STAGING_DIR_TARGET pkg-config
>>>> --define-variable=prefix=/opt --variable=includedir vulkan
>>>>
>>>> /b/github-ci/_work/meta-flutter/rpi4-drm-honister-latest/raspberrypi4-64/tmp/work/cortexa72-poky-linux/vkmark/git-r0/recipe-sysroot/opt/include
>>>>
>>>>
>>>> meson.cross
>>>>
>>>> Setting sys_root in the properties section of meson.cross (patching
>>>> meson.bbclass) indirectly sets PKG_CONFIG_SYSROOT_DIR.  The setting of
>>>> sys_root is present in nativesdk_meson*.bb, not meson*.bb.
>>>>
>>>> The issue for meson is that they are not passing the
>>>> PKG_CONFIG_SYSROOT_DIR variable to the shell that launches pkg-config.
>>>>
>>>> My proposed work around (this email thread) would fix the behavior.  I
>>>> believe the proper fix is for meson to address upstream.  Still waiting on
>>>> a response from them: https://github.com/mesonbuild/meson/issues/9674
>>>>
>>>>
>>>> Joel
>>>>
>>>> On Tue, Nov 30, 2021 at 9:49 AM Alexander Kanavin <
>>>> [email protected]> wrote:
>>>>
>>>>> On Tue, 30 Nov 2021 at 18:20, Joel Winarske <[email protected]>
>>>>> wrote:
>>>>>
>>>>>> Meson does not expose PKG_CONFIG_SYSROOT_DIR to the pkg-config
>>>>>> process.
>>>>>>
>>>>>> Currently meson.cross as generated in meson.bbclass points directly
>>>>>> to the pkg-config executable (no wrapper script).
>>>>>>
>>>>>> PKG_CONFIG_SYSROOT_DIR behaves like a simple string prepend to all
>>>>>> package config variable queries.  So if you want to determine the 
>>>>>> absolute
>>>>>> path of a variable in .pc you set PKG_CONFIG_SYSROOT_DIR and make your
>>>>>> query.  Currently this is not possible with Yocto+Meson.
>>>>>>
>>>>>> I think a simple wrapper script would resolve this.  This is from
>>>>>> https://autotools.io/pkgconfig/cross-compiling.html:
>>>>>>
>>>>>> #!/bin/sh
>>>>>>
>>>>>> SYSROOT=/build/root
>>>>>>
>>>>>> export PKG_CONFIG_PATH=
>>>>>> export 
>>>>>> PKG_CONFIG_LIBDIR=${SYSROOT}/usr/lib/pkgconfig:${SYSROOT}/usr/share/pkgconfig
>>>>>> export PKG_CONFIG_SYSROOT_DIR=${SYSROOT}
>>>>>>
>>>>>> exec pkg-config "$@"
>>>>>>
>>>>>>
>>>>>> The wrapper script would be generated per recipe via meson.bbclass,
>>>>>> meson.cross would then reference this wrapper instead of the pkg-config
>>>>>> executable.
>>>>>>
>>>>>> Thoughts?
>>>>>>
>>>>>
>>>>> I don't think this is correct. Meson's way of doing things is that you
>>>>> are not supposed to get the include/library paths directly from 
>>>>> pkg-config,
>>>>> but rather use
>>>>> https://mesonbuild.com/Reference-manual_functions.html#dependency and
>>>>> meson will take care of any needed prefixes to the paths.
>>>>>
>>>>> For the custom variables defined in .pc that happen to contain paths,
>>>>> PKG_CONFIG_SYSROOT_DIR has no effect at all, so you need to manually
>>>>> prepend it anyway everywhere where they're used. pkg-config does not know
>>>>> what variable is a path and what isn't.
>>>>>
>>>>> Alex
>>>>>
>>>>
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