[fedora-arm] WebKit ARMv7 JIT crashes a lot

[Daniel Drake]

Hi,

OLPC has moved from xulrunner to WebKit (yay) and ARMv5 to ARMv7 (yay)
on Fedora 17.

However, we're now facing very crashy behaviour in webkit,
particularly on javascript-heavy pages. Test case: open epiphany and
load a gmail inbox and try to scroll to the bottom. It will almost
always crash (segmentation fault) while loading the page, if not it
will crash while you scroll.
The crash also happens in Sugar's Browse activity, also based on webkitgtk3.

gdb is not that helpful:

(gdb) bt
#0  0x00000024 in ?? ()
#1  0x49f0eaf4 in ?? ()
#2  0x49f0eaf4 in ?? ()

Works fine on our x86 laptops - only ARM is affected.

Recompiling webkitgtk3 with --disable-jit
(http://arm.koji.fedoraproject.org/koji/taskinfo?taskID=767403) works
around the issue.
So it seems to be a bug in the javascript JIT compilation. This would
also explain why gdb doesn't know where the code is coming from.

I've reported this upstream at https://bugs.webkit.org/show_bug.cgi?id=85076

Is anyone interested in helping out figure out this bug? I know there
are several low-level ARM experts on this list.

My plan B, which I'd rather avoid, is disabling the ARM JIT in the
Fedora packages for webkitgtk/webkitgtk3.

Thanks,
Daniel