adds first version of the expanded as assembler from mikko

lib/elf/constants.rb

@@ -0,0 +1,59 @@
+module ELF
+  module Constants
+    ET_NONE = 0
+    ET_REL = 1
+    ET_EXEC = 2
+    ET_DYN = 3
+    ET_CORE = 4
+
+    EM_NONE = 0
+    EM_M32 = 1
+    EM_SPARC = 2
+    EM_386 = 3
+    EM_68K = 4
+    EM_88K = 5
+    EM_860 = 7
+    EM_MIPS = 8
+    EM_ARM = 40
+  
+    EV_NONE = 0
+    EV_CURRENT = 1
+
+    ELFCLASSNONE = 0
+    ELFCLASS32 = 1
+    ELFCLASS64 = 2
+
+    ELFDATANONE = 0
+    ELFDATA2LSB = 1
+    ELFDATA2MSB = 2
+
+    SHT_NULL = 0
+    SHT_PROGBITS = 1
+    SHT_SYMTAB = 2
+    SHT_STRTAB = 3
+    SHT_RELA = 4
+    SHT_HASH = 5
+    SHT_DYNAMIC = 6
+    SHT_NOTE = 7
+    SHT_NOBITS = 8
+    SHT_REL = 9
+    SHT_SHLIB = 10
+    SHT_DYNSYM = 11
+
+    SHF_WRITE = 0x1
+    SHF_ALLOC = 0x2
+    SHF_EXECINSTR = 0x4
+
+    STB_LOCAL = 0
+    STB_GLOBAL = 1
+    STB_WEAK = 2
+
+    ABI_SYSTEMV = 0
+    ABI_ARM = 0x61
+
+    ARM_INFLOOP = "\x08\xf0\x4f\xe2"
+
+    TARGET_ARM = [ELFCLASS32, ELFDATA2LSB, ABI_ARM, EM_ARM]
+    TARGET_X86 = [ELFCLASS32, ELFDATA2LSB, ABI_SYSTEMV, EM_386]
+  end
+end

lib/elf/null_section.rb

@@ -0,0 +1,18 @@
+module Elf
+  class NullSection < Section
+    def initialize
+      super('')
+    end
+
+    def write(io)
+    end
+
+    def type
+      Elf::Constants::SHT_NULL
+    end
+
+    def alignment
+      0
+    end
+  end
+end

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

lib/elf/relocation_table_section.rb

@@ -0,0 +1,41 @@
+module Elf
+  class RelocationTableSection < Section
+    def initialize(name, symtab, text_section)
+      super(name)
+
+      @symtab = symtab
+      @text_section = text_section
+
+      @relocs = []
+    end
+
+    def add_reloc(offset, name, type)
+      @relocs << [offset, name, type]
+    end
+
+    def type
+      Elf::Constants::SHT_REL
+    end
+
+    def ent_size
+      8
+    end
+
+    def link
+      @symtab.index
+    end
+
+    def info
+      @text_section.index
+    end
+
+    def write(io)
+      @relocs.each { |reloc|
+        name_idx = @symtab.index_for_name(reloc[1])
+        io.write_uint32 reloc[0]
+        # +1 because entry number 0 is und
+        io.write_uint32 reloc[2] | ((name_idx+1) << 8)
+      }
+    end
+  end
+end

lib/elf/section.rb

@@ -0,0 +1,31 @@
+module Elf
+  class Section
+    def initialize(name)
+      @name = name
+    end
+    attr_accessor :name, :index
+
+    def type
+      raise 'Reimplement #type'
+    end
+    def flags
+      0
+    end
+    def addr
+      0
+    end
+    def link
+      0
+    end
+    def info
+      0
+    end
+    def alignment
+      1
+    end
+    def ent_size
+      0
+    end
+  end
+  
+end

lib/elf/string_table_section.rb

@@ -0,0 +1,29 @@
+module Elf
+  class StringTableSection < Section
+    def initialize(*args)
+      super
+
+      @string_data = "\x00"
+      @indices = {"" => 0}
+    end
+
+    def add_string(str)
+      return if @indices[str]
+
+      @indices[str] = @string_data.length
+      @string_data << str << "\x00"
+    end
+
+    def index_for(str)
+      @indices[str]
+    end
+
+    def write(io)
+      io << @string_data
+    end
+
+    def type
+      Elf::Constants::SHT_STRTAB
+    end
+  end
+end

lib/elf/symbol_table_section.rb

@@ -0,0 +1,77 @@
+module Elf
+  class SymbolTableSection < Section
+    def initialize(name, strtab)
+      super(name)
+
+      @strtab = strtab
+
+      @symbols = []
+    end
+
+    def add_func_symbol(name, value, text_section, linkage)
+      @strtab.add_string name
+      arr = [name, value, text_section, linkage]
+      if (linkage == Elf::Constants::STB_LOCAL)
+        @symbols.unshift arr
+      else
+        @symbols.push arr
+      end
+    end
+
+    def index_for_name(name)
+      @symbols.each_with_index { |sym, idx|
+        if (sym[0] == name)
+          return idx
+        end
+      }
+      nil
+    end
+
+    def type
+      Elf::Constants::SHT_SYMTAB
+    end
+
+    def ent_size
+      16
+    end
+
+    def link
+      @strtab.index
+    end
+
+    def info
+      i = -1
+      @symbols.each_with_index { |sym, idx|
+        if (sym[4] == Elf::Constants::STB_LOCAL)
+          i = idx
+        end
+      }
+      i + 1
+    end
+
+    def write(io)
+      # write undefined symbol
+      io.write_uint32 0
+      io.write_uint32 0
+      io.write_uint32 0
+      io.write_uint8 Elf::Constants::STB_LOCAL << 4
+      io.write_uint8 0
+      io.write_uint16 0
+
+      # write other symbols
+      @symbols.each { |sym|
+        io.write_uint32 @strtab.index_for(sym[0])
+        io.write_uint32 sym[1]
+        io.write_uint32 0
+        io.write_uint8((sym[3] << 4) + 0)
+        io.write_uint8 0
+        if (sym[2])
+          io.write_uint16 sym[2].index
+        else
+          # undefined symbol
+          io.write_uint16 0
+        end
+      }
+    end
+  end
+end

lib/elf/text_section.rb

@@ -0,0 +1,21 @@
+module Elf
+  class TextSection < Section
+    attr_accessor :text
+
+    def write(io)
+      io << text
+    end
+
+    def type
+      Elf::Constants::SHT_PROGBITS
+    end
+
+    def flags
+      Elf::Constants::SHF_ALLOC | Elf::Constants::SHF_EXECINSTR
+    end
+  
+    def alignment
+      4
+    end
+  end
+end