And also, I have just uploaded version 0.16-3+hurd.of libpciaccess. The issue was that the map_legacy method was completely broken. Ideally it'd be able to use the map_region method, but that'd only work for the proper PCI rom (and even still, since pci-arbiter doesn't get the rom_base from libpciaccess, we don't know it). It happens that Xorg not only maps the VGA rom, but also the whole BIOS roms, the video memory, the interrupt vector table, etc. etc. So I added using the x86 mem_map as a fallback.
Samuel