[wpe-webkit] Bug within QML based webbrowsers

[Marco Felsch]

Hi all,

this is my first time posting to this list and I'm very new to the
webkit project too. Currently I debug a memory issue and need some help.

The current sw-stack:
 - QT 5.12.6
 - Webkit 2.28.2
 - libwpe 1.6.0
 - wpebackend-fdo 1.6.0

The error pattern:
I get a white (empty) picture when I try to start the QML demo from the
Tools/MiniBrowser/wpe/qt/. This pattern will appear with the wayland and
the eglfs qt backend.

I've debugged this a few days and my findings are:
The code is loooping around trying to find the correct memory to
free within Source/bmalloc/bmalloc/Map.h:94. Freeing the memory
happens due to the string-table re-allocation which happens during
the ResourceResponseBase::ResourceResponseBase() call. I debugged it
using the gdb and saw that the 'oldTable' which should be freed
(Source/WTF/wtf/HashTable.h:1358) using a key which doesn't exist yet.

The bug occured with the update from:
 - Webkit 2.26.3 -> 2.28.2
 - libwpe 1.4.0.1 -> 1.6.0
 - wpebackend-fdo 1.4.1 -> 1.6.0.
The bug isn't triggered if I run the cog browser or the Minibrowser from
Tools/MiniBrowser/wpe. We switched to the system-allocator as workaround
since our target is a 32-Bit ARMv7 Cortex-A9 which can't use the
gigacage security mechanism anyway.

Thanks for your answers =)

Regards,
  Marco