#!/usr/bin/env ruby
$LOAD_PATH.unshift File.join(File.dirname(__FILE__), '..', 'lib')
require 'mithril'
module Elf
  def self.newfile
    ElfFile.new.tap {|x|
      x.filetype = ElfFlags::Type::ET_EXEC
      x.machine = ElfFlags::Machine::EM_X86_64 
      x.version = ElfFlags::Version::EV_CURRENT
      x.flags = 0
      x.bits = 64
      x.endian  = :little 
      x.interp =  "/lib64/ld-linux-x86-64.so.2"
    }
  end
  def self.linkfiles(outfile, infiles)
    progbits = {}
    symbols = {}
    sect_map = {}
    sect_offsets = {}
    symbols = {}
    infiles.each {|infile|
      #link actual data
      (infile.progbits + infile.nobits).each {|inbit|
        outbit = (progbits[inbit.name] ||= Elf::ProgBits.new(inbit.name))
        outbit.flags |= inbit.flags
        outbit.align = [inbit.align, outbit.align].max
        outbit.sect_type = inbit.sect_type
        sect_offsets[inbit] = outbit.data.tell
        sect_map[inbit] = outbit
        outbit.data.write inbit.data.read #TODO: Handle align
      }
      # Link together symbol table. Note we do not support versioning in the poc
      infile.symbols.each {|symbol|
        next if symbol.name.empty?
        next unless [Elf::STT::STT_OBJECT, Elf::STT::STT_FUNC, Elf::STT::STT_COMMON, Elf::STT::STT_NOTYPE].include? symbol.type

        if (symbols.include? symbol.name)
          next if symbol.weak? or symbol.undefined?
          raise ArgumentError.new "Duplicate definition of symbol #{symbol.name}"  unless symbols[symbol.name].weak?  or symbols[symbol.name].undefined?  
        end
        symbols[symbol.name] = symbol.clone.tap{|outsym|
          unless outsym.undefined?
            outsym.sectoffset += sect_offsets[outsym.section]
            outsym.section = sect_map[outsym.section]
          end
        }        
      }
    }
    #TODO: mark per-object section symbols
    progbits.values.each {|progbit| outfile.progbits << progbit   }
    symbols.values.each {|sym| outfile.symbols << sym}
    
    infiles.map(&:relocations).flatten.each {|rela|
      outfile.relocations << rela.clone.tap{|x|
        x.offset += sect_offsets[x.section]
        x.section = sect_map[x.section]
        name = x.symbol.name
        x.symbol = symbols[name]
        x.is_dynamic = true
        raise ArgumentError.new "Undefined symbol #{name}" if(x.symbol.nil?)
      }
    } #TODO: Produce dynsym
    raise "Undefined entry point _start " unless symbols.include? "_start"
    entry = symbols["_start"]
    entry.section.addr = 0x40000
    outfile.entry = entry.sectoffset + entry.section.addr
    
    outfile

  end
end
file = Elf::linkfiles(Elf::newfile, ARGV[1..-1].map{|x| Elf::Parser::from_file(x)})

Elf::Writer.to_file(ARGV[0], file)
`chmod +x '#{ARGV[0]}'`