adds first version of the expanded as assembler from mikko

lib/elf/object_file.rb

@@ -0,0 +1,89 @@
+module Elf
+  class ObjectFile
+    include ELF
+
+    def initialize(target)
+      @target = target
+
+      @sections = []
+      add_section NullSection.new
+    end
+
+    def add_section(section)
+      @sections << section
+      section.index = @sections.length - 1
+    end
+
+    def write(io)
+      io << "\x7fELF"
+      io.write_uint8 @target[0]
+      io.write_uint8 @target[1]
+      io.write_uint8 EV_CURRENT
+      io.write_uint8 @target[2]
+      io << "\x00" * 8 # pad
+
+      io.write_uint16 ET_REL
+      io.write_uint16 @target[3]
+      io.write_uint32 EV_CURRENT
+      io.write_uint32 0 # entry point
+      io.write_uint32 0 # no program header table
+      sh_offset_pos = io.tell
+      io.write_uint32 0 # section header table offset
+      io.write_uint32 0 # no flags
+      io.write_uint16 52 # header length
+      io.write_uint16 0 # program header length
+      io.write_uint16 0 # program header count
+      io.write_uint16 40 # section header length
+
+      shstrtab = StringTableSection.new(".shstrtab")
+      @sections << shstrtab
+      @sections.each { |section|
+        shstrtab.add_string section.name
+      }
+
+      io.write_uint16 @sections.length # section header count
+
+      io.write_uint16 @sections.length-1 # section name string table index
+
+      # write sections
+
+      section_data = []
+      @sections.each { |section|
+        offset = io.tell
+        section.write(io)
+        size = io.tell - offset
+        section_data << {:section => section, :offset => offset,
+                         :size => size}
+      }
+
+      # write section headers
+
+      sh_offset = io.tell
+
+      section_data.each { |data|
+        section, offset, size = data[:section], data[:offset], data[:size]
+        # write header first
+        io.write_uint32 shstrtab.index_for(section.name)
+        io.write_uint32 section.type
+        io.write_uint32 section.flags
+        io.write_uint32 section.addr
+        if (section.type == SHT_NOBITS)
+          raise 'SHT_NOBITS not handled yet'
+        elsif (section.type == SHT_NULL)
+          io.write_uint32 0
+          io.write_uint32 0
+        else
+          io.write_uint32 offset
+          io.write_uint32 size
+        end
+        io.write_uint32 section.link
+        io.write_uint32 section.info
+        io.write_uint32 section.alignment
+        io.write_uint32 section.ent_size
+      }
+
+      io.seek sh_offset_pos
+      io.write_uint32 sh_offset
+    end
+  end
+end