I don't know if this is related, but I also got, just a few hours ago, a similar error running mirage-mdns on xen 4.4.1, ubuntu trusty, amd64:
sudo xl create -c mdns-resp-test.xl
[sudo] password for nick:
Parsing config from mdns-resp-test.xl
Xen Minimal OS!
start_info: 000000000030d000(VA)
nr_pages: 0x10000
shared_inf: 0x9e733000(MA)
pt_base: 0000000000310000(VA)
nr_pt_frames: 0x5
mfn_list: 000000000028d000(VA)
mod_start: 0x0(VA)
mod_len: 0
flags: 0x0
cmd_line:
stack: 000000000026c2e0-000000000028c2e0
MM: Init
_text: 0000000000000000(VA)
_etext: 000000000013e07f(VA)
_erodata: 000000000017b000(VA)
_edata: 0000000000232b60(VA)
stack start: 000000000026c2e0(VA)
_end: 000000000028c2e0(VA)
start_pfn: 318
max_pfn: 10000
Mapping memory range 0x400000 - 0x10000000
setting 0000000000000000-000000000017b000 readonly
skipped 1000
MM: Initialise page allocator for 396000(396000)-10000000(10000000)
MM: done
Demand map pfns at 10001000-0000002010001000.
Initialising timer interface
Initialising console ... done.
gnttab_table mapped at 0000000010001000.
getenv(OCAMLRUNPARAM) -> null
getenv(CAMLRUNPARAM) -> null
getenv(PATH) -> null
Unsupported function lseek called in Mini-OS kernel
Unsupported function lseek called in Mini-OS kernel
Unsupported function lseek called in Mini-OS kernel
getenv(OCAMLRUNPARAM) -> null
getenv(CAMLRUNPARAM) -> null
getenv(TMPDIR) -> null
getenv(TEMP) -> null
Netif: add resume hook
Netif.connect tap0: could not find device
Fatal error: exception Failure("\n\nnet_tap0: device tap0 not found (available = [ ])\nIf using a tap device, is tun/tap enabled and have you permissions?\n\n")
Raised at file "src/core/lwt.ml", line 788, characters 22-23
Called from file "lib/main.ml", line 58, characters 10-20
Called from file "main.ml", line 85, characters 2-28
Mirage exiting with status 2
Do_exit called!
base is 0x27ff20 caller is 0x1237b1
base is 0x232530 caller is 0x0
base is 0x141783 caller is 0x5241570000000000
base is 0x65676172696d Page fault at linear address 656761726975, rip 13d607, regs 000000000027fe38, sp 27fee0, our_sp 000000000027fdf8, code 0
RIP: e030:[<000000000013d607>]
RSP: e02b:000000000027fee0 EFLAGS: 00010006
RAX: 0000000000000017 RBX: 000065676172696d RCX: 0000000000000743
RDX: 0000000000000743 RSI: 000000000027fd30 RDI: 0000000000000004
RBP: 000000000027ff20 R08: 0000000000000742 R09: 0000000000000020
R10: 0000000000000017 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
base is 0x27ff20 caller is 0x1237b1
base is 0x232530 caller is 0x0
base is 0x141783 caller is 0x5241570000000000
base is 0x65676172696d Page fault in pagetable walk (access to invalid memory?).
