#!/usr/bin/env ruby
#    This file is part of Metasm, the Ruby assembly manipulation suite
#    Copyright (C) 2006-2009 Yoann GUILLOT
#
#    Licence is LGPL, see LICENCE in the top-level directory

# modifies the standard ruby class String to add #decode and #encode methods
# they will respectively disassemble binary data / assemble asm source
# the default CPU is x86 32bits, change it using eg String.cpu = Metasm::MIPS.new(:big) (mips bigendian)
#
# it also defines the toplevel 'asm' method, that will start an interactive
# assembler shell (type in assembly statements, they are shown assembled in binary escaped form)
#
# eg:
# ruby metasm-shell
# > nop ; nop
# "\x90\x90"
# > exit

require 'metasm'

class String
  @@cpu = Metasm::Ia32.new
  class << self
    def cpu()   @@cpu   end
    def cpu=(c)
      c = Metasm.const_get(c).new if c.kind_of? String
      @@cpu=c
    end
  end

  # encodes the current string as a Shellcode, returns the resulting EncodedData
  def encode_edata
    Metasm::Shellcode.assemble(@@cpu, self).encode.encoded
  end

  # encodes the current string as a Shellcode, returns the resulting binary String
  # outputs warnings on unresolved relocations
  def encode
    ed = encode_edata
    if not ed.reloc.empty?
      puts 'W: encoded string has unresolved relocations: ' + ed.reloc.map { |o, r| r.target.inspect }.join(', ')
    end
    ed.fill
    ed.data
  end

  # decodes the current string as a Shellcode, with specified base address
  # returns the resulting Disassembler
  def decode_blocks(base_addr=0, eip=base_addr)
    sc = Metasm::Shellcode.decode(self, @@cpu)
    sc.base_addr = base_addr
    sc.disassemble(eip)
  end

  # decodes the current string as a Shellcode, with specified base address
  # returns the asm source equivallent
  def decode(base_addr=0, eip=base_addr)
    decode_blocks(base_addr, eip).to_s
  end
end

# get in interactive assembler mode
def asm
  puts 'type "exit" or "quit" to quit', 'use ";" for newline', ''
  while (print "asm> " ; $stdout.flush ; l = gets)
    break if %w[quit exit].include? l.chomp
    if l.chomp == 'help'
      puts "Metasm assembly shell: type in opcodes to see their binary form",
        "You can use ';' to type multi-line stuff",
        "e.g. 'nop nop' will display \"\\x90\\x90\""
      next
    end
  
    begin
      data = l.gsub(';', "\n")
      next if data.strip.empty?
      data = data.encode
      puts '"' + data.unpack('C*').map { |c| '\\x%02x' % c }.join + '"'
    rescue Metasm::Exception => e
      puts "Error: #{e.class} #{e.message}"
    end
  end

  puts
end

if __FILE__ == $0
  asm
end
