Bug 103757

eglGetDisplay() is by definition broken on multi-platform implementations, yes.

Any reason you cannot use EGL_KHR_platform_wayland?

(In reply to Pekka Paalanen from comment #1)
> eglGetDisplay() is by definition broken on multi-platform implementations,
> yes.

Ugh. It is broken by definition, but Mesa does go to great lengths to try to make it work by auto-detecting: see _eglNativePlatformDetectNativeDisplay() inside src/egl/main/egldisplay.c.

Michael, I'll attach a compiled but untested patch; can you please let me know if it helps?

Created attachment 135490 [details] [review]
egldisplay-try-interface-name-for-wl-display.patch

<cheeky>
I do recall mentioning that exposing the same symbol(s) will lead to bad experiences. Followed by some ideas...
</cheeky>

WRT eglGetDisplay - I'd recommend moving towards the EGL_*_platform_* extensions ASAP - EGL_EXT_platform_wayland or EGL_KHR_platform_wayland in this case.

A better heuristic would be to use dladdr() for eglGetDisplay. See the analogous GBM patch [1].


https://patchwork.freedesktop.org/patch/187918/

(In reply to Emil Velikov from comment #4)
> <cheeky>
> I do recall mentioning that exposing the same symbol(s) will lead to bad
> experiences. Followed by some ideas...
> </cheeky>

Yep, as per the discussion on inlining wayland_drm_buffer_get. :)

It certainly hurts, but then again breaking ABI and forcing every single Wayland user to rebuild - probably having to change every symbol name in the API to make sure there was no clash between the two when loaded - would be uncharted depths of pain.

On the other hand, the solution is the same: look at the interface name, rather than ever compare pointers equally. Unfortunately, we can't use the same solution since the wayland-drm one only works for wl_resource in libwayland-server rather than a plain wl_interface or a wl_proxy ... oh well.

> A better heuristic would be to use dladdr() for eglGetDisplay. See the
> analogous GBM patch [1].

I don't think that would necessarily fix it, particularly if the wayland-client.so.1 being loaded differed, e.g. due to people linking their own copies?

(In reply to Daniel Stone from comment #2)

> Michael, I'll attach a compiled but untested patch; can you please let me
> know if it helps?

Looks good. It does the right thing for wayland and drm at least.
is _eglPointerIsDereferencable() sufficient to ensure that the whole string is accessible?

(In reply to Michael Olbrich from comment #6)
> (In reply to Daniel Stone from comment #2)
> 
> > Michael, I'll attach a compiled but untested patch; can you please let me
> > know if it helps?
> 
> Looks good. It does the right thing for wayland and drm at least.
> is _eglPointerIsDereferencable() sufficient to ensure that the whole string
> is accessible?

Good point - I guess it'd have to be if (_eglPointerIsDereferencable(child_pointer) && _eglPointerIsDereferencable(((char *) child_pointer) + strlen("wl_display") + 1) && strcmp(interface->name, "wl_display") == 0) ... ugh. Does that work for you?

(In reply to Daniel Stone from comment #7)
> Good point - I guess it'd have to be if
> (_eglPointerIsDereferencable(child_pointer) &&
> _eglPointerIsDereferencable(((char *) child_pointer) + strlen("wl_display")
> + 1) && strcmp(interface->name, "wl_display") == 0) ... ugh. Does that work
> for you?

Yes that works.

(In reply to Pekka Paalanen from comment #1)
> Any reason you cannot use EGL_KHR_platform_wayland?

It's not my code. It's somewhere in gstreamer-vaapi. I was just debugging why my application was crashing.

(In reply to Michael Olbrich from comment #9)
> (In reply to Pekka Paalanen from comment #1)
> > Any reason you cannot use EGL_KHR_platform_wayland?
> 
> It's not my code. It's somewhere in gstreamer-vaapi. I was just debugging
> why my application was crashing.

Ok, while this issue is being worked on in Mesa, I would very much recommend filing a bug against gstreamer-vaapi to start using the EGL platform extensions whenever available. It's the only reliable way forward.

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