DragonFlyBSD

To reproduce, on an x86_64 machine (tested on a Shuttle SG45H7 and an Intel Core
2 Duo Macbook 2.1), from a current DragonFly v2.5.1 1061.ge9fe2 X86_64_GENERIC
build, install modular xorg and gtk+-2.18.9 from current pkgsrc, and run
git-demo which SIGSEVs. No such SIGSEGV occurs on an i386 machine.

Attached is a gdb backtrace. Of interest are gtk2 GdkImage, in this case,
parameter image, a struct that has a field mem that is if shm is enabled on
x86_64 produces an

invalid address 0x8400000:      Cannot access memory at address 0x8400000

Actually image_info also has a field that points to a list static_image of
GdkImage's.