fiddle examples

fiddle_examples.rb

#!/usr/bin/env ruby

require 'fiddle'
require 'fiddle/import'
include Fiddle

@libc  = "/usr/lib64/libc.so.6" # location of shared object file on Arch Linux
TC = TrueClass.dup
FC = FalseClass.dup
PR_SET_NAME = 15 # set process name (from /usr/include/linux/prctl.h)
PR_GET_NAME = 16 # get process name ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
CDROMEJECT  = 0x00005309  # (from /usr/include/linux/cdrom.h)
LIBC = @libc

# Some examples using Fiddle (A libffi wrapper for Ruby)

def getpid # returns the process id of the calling process
  p Function.new(Handle.new(@libc)['getpid'], [], TYPE_INT).call
end

def getppid # returns the process id of the parent of the calling process
  p Function.new(Handle.new(@libc)['getppid'], [], TYPE_INT).call
end

def getuid # returns the real user id of the calling process
  p Function.new(Handle.new(@libc)['getuid'], [], TYPE_INT).call
end

def geteuid # returns the effective user id of the calling process
  p Function.new(Handle.new(@libc)['geteuid'], [], TYPE_INT).call
end

def getenv(env_var) # get an environment variable
  p Function.new(Handle.new(@libc)['getenv'], [TYPE_VOIDP], TYPE_VOIDP).call(env_var).to_s
end

def time # returns the time as the number of seconds since the epoch
  p Function.new(Handle.new(@libc)['time'], [TYPE_VOIDP], TYPE_INT).call(NULL)
end

def true2false(kptr1, kptr2, bytes)
  Pointer.new(kptr1.__id__ << 1)[0,bytes] = Pointer.new(kptr2.__id__ << 1)[0,bytes]
  p "1 == 1 #=> #{1 == 1}"
end

def false2true(kptr1, kptr2, bytes)
  Pointer.new(kptr1.__id__ << 1)[0,bytes] = Pointer.new(kptr2.__id__ << 1)[0,bytes]
  p "1 == 2 #=> #{1 == 2}"
end

def set_process_title(name) # set process/thread name 
  Function.new(
    Handle.new(@libc)['prctl'], 
    [ TYPE_INT, TYPE_VOIDP, TYPE_LONG, TYPE_LONG, TYPE_LONG ], 
    TYPE_INT
  ).call(PR_SET_NAME, name, NULL,NULL,NULL)
end

def get_process_title # get process/thread name
  buffer = Pointer.malloc(24)
  Function.new(
    Handle.new(@libc)['prctl'],
    [TYPE_INT, TYPE_VOIDP, *[TYPE_LONG]*3],
    TYPE_INT
  ).call(PR_GET_NAME, ptr, *[NULL]*3)
  p buffer.to_s
end
# call methods
getpid                                #=> 13785
getppid                               #=> 13646
getuid                                #=> 1000
geteuid                               #=> 1000
getenv("SHELL")                       #=> "/bin/bash"
time                                  #=> 1458512941
true2false(TrueClass, FC, 36) #=> false
false2true(FalseClass, TC, 36) #=> true
set_process_title("voodoo") #=> 0 (zero means success)
get_process_title
# example using structs

module Foo
  extend Fiddle::Importer
  dlload LIBC
  extern 'int gettimeofday(void *, void *)'
  T = struct [
    'long tv_sec',
    'long tv_usec',
  ]
end

tv = Foo::T.malloc
x  = Foo.gettimeofday(tv, NULL)
p tv.tv_sec  #=> 1458592642
p tv.tv_usec #=> 829213

# silly trick 
def eject dp
  fd = open(dp, 2048)
  fileno = fd.fileno
  Function.new(Handle.new(@libc)['ioctl'], [TYPE_INT, TYPE_VOIDP, TYPE_INT], TYPE_INT).call(fileno, CDROMEJECT, 0)
  fd.close
end

eject "/dev/sr0"