[Mesa-dev] [PATCH] configure.ac: Add --with-wayland-scanner-path

[Jussi Kukkonen]

On 24 May 2017 at 16:39, Emil Velikov <emil.l.velikov at gmail.com> wrote:
>
> Hi Jussi,
>
> On 23 May 2017 at 09:13, Jussi Kukkonen <jussi.kukkonen at intel.com> wrote:
> > Modify wayland-scanner lookup: Use the path given by pkg-config
> > but offer an option to override the path with
> > "--with-wayland-scanner-path=PATH". The latter is useful for
> > cross-compile situations.
> >
> > AC_PATH_PROG is no longer used (if the scanner is installed it should
> > get found by pkg-config). AC_SUBST is added so the output variable is
> > created when only the configure option is used.
> > ---
> >
> > My goal is to standardize wayland-scanner usage in a way that does not
> > require patching when cross-compiling in Yocto (the detailed issue is
> > that in Yocto pkg-config will return a "wayland_scanner" variable but
> > that will contain a _target path_ when we would like to use a native
> > sysroot path instead).
> >
> > I've sent a similar patch to weston and intend to fix other projects
> > if these two patches are well received.
> >
> I might have misread something, but on a quick look the patch does not
> look quite right. Stepping aside for a moment,
>
> Can you explain clearly what's happening/wrong in the whole scenario?
>  - Yocto does has A stage where it does X.
>  - Then it proceeds to B... at which point $file
> foo/wayland-scanner.pc gets picked
>  - That results in an error due to variable containing $bar, due to
> the $step above

Hi Emil,

I'm hoping this is a coherent enough explanation of the issue...

When yocto cross-compiles mesa for target, we already have
  a) All dependency headers and libraries in a target sysroot
  b) Native wayland-scanner in a native sysroot

The problem as I see it is that there is no way to express the _native_
sysroot in pkg-config: PKG_CONFIG_SYSROOT_DIR and pc_sysroot_dir logically
refer to the target sysroot. So when mesa configure does "pkg-config
--variable=wayland_scanner wayland-scanner" it gets a reasonable
"/usr/bin/wayland-scanner" response: this would be the correct path to
wayland-scanner on _target_. In the best case this fails during compile
when the scanner isn't found but unfortunately /usr/bin/wayland-scanner is
often also a valid path to _host_ wayland-scanner which might be from a
completely different and unrelated wayland version...

I could see two options to solve our problem:
* Use AC_PATH_PROG to find wayland-scanner. Weston currently does this and
it works fine for the Yocto case... but I can see how that's not perfect
either as it could find an older installed wayland-scanner in other
situations
* Use something like
"--with-wayland-scanner-path=${NATIVE_SYSROOT_BINDIR}/wayland-scanner" when
calling mesa configure: this adds a configuration item but is much, much
nicer than the current situation where we need to patch configure.ac

Thanks,
  Jussi
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