More return value informations.

[p8nut]

b3/grammar.pegjs

Line 277 in 9ac7092

         return numeric; 

maybe in case of result equal -1 it might be possible to give the errno value

arch_prctl(0x3001 , 0x7ffe4887f480) = -1 EINVAL (Invalid argument)

in this case the result will be

{
   "syscall": "arch_prctl",
   "args": [
      12289,
      [],
      140730115290240
   ],
   "result": "-1 EINVAL (Invalid argument)1",
   "timing": null,
   "pid": null,
   "type": "SYSCALL"
}

maybe, result could be an object with the returned value.
something like

{
   "syscall": "arch_prctl",
   "args": [
      12289,
      [],
      140730115290240
   ],
   "result": {
      "value": -1,
      "errno": "EINVAL"
      "comment": "Invalid argument"
   },
   "timing": null,
   "pid": null,
   "type": "SYSCALL"
}