Re: [OE-core] [RFC] meson needs a pkg-config wrapper script

[Alexander Kanavin <alex.kanavin@gmail.com>]

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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 <joel.winarske@gmail.com> 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=$STAGING_DIR_TARGET pkg-config
> --define-variable=prefix=/opt --variable=includedir vulkan
>
> /b/github-ci/_work/meta-flutter/rpi4-drm-honister-latest/raspberrypi4-64/tmp/work/cortexa72-poky-linux/vkmark/git-r0/recipe-sysroot/opt/include
>
>
> meson.cross
>
> Setting sys_root in the properties section of meson.cross (patching
> meson.bbclass) indirectly sets PKG_CONFIG_SYSROOT_DIR.  The setting of
> sys_root is present in nativesdk_meson*.bb, not meson*.bb.
>
> The issue for meson is that they are not passing the
> PKG_CONFIG_SYSROOT_DIR variable to the shell that launches pkg-config.
>
> My proposed work around (this email thread) would fix the behavior.  I
> believe the proper fix is for meson to address upstream.  Still waiting on
> a response from them: https://github.com/mesonbuild/meson/issues/9674
>
>
> Joel
>
> On Tue, Nov 30, 2021 at 9:49 AM Alexander Kanavin <alex.kanavin@gmail.com>
> wrote:
>
>> On Tue, 30 Nov 2021 at 18:20, Joel Winarske <joel.winarske@gmail.com>
>> wrote:
>>
>>> Meson does not expose PKG_CONFIG_SYSROOT_DIR to the pkg-config process.
>>>
>>> Currently meson.cross as generated in meson.bbclass points directly to
>>> the pkg-config executable (no wrapper script).
>>>
>>> PKG_CONFIG_SYSROOT_DIR behaves like a simple string prepend to all
>>> package config variable queries.  So if you want to determine the absolute
>>> path of a variable in .pc you set PKG_CONFIG_SYSROOT_DIR and make your
>>> query.  Currently this is not possible with Yocto+Meson.
>>>
>>> I think a simple wrapper script would resolve this.  This is from
>>> https://autotools.io/pkgconfig/cross-compiling.html:
>>>
>>> #!/bin/sh
>>>
>>> SYSROOT=/build/root
>>>
>>> export PKG_CONFIG_PATH=
>>> export PKG_CONFIG_LIBDIR=${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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