add linker elf stubs

Author: katsyoshi

lib/caotral/linker.rb

@@ -12,6 +12,8 @@ def link(input: @input, output: @output, debug: @debug, shared: @shared) = IO.po
 
   def link_command(input: @input, output: @output, debug: @debug, shared: @shared)
     ld_path = []
+    return to_elf(input:, output:, debug:) if @linker == "self"
+
     if @shared
       ld_path << "--shared"
       ld_path << "#{libpath}/crti.o"
@@ -36,4 +38,9 @@ def link_command(input: @input, output: @output, debug: @debug, shared: @shared)
 
   def libpath = @libpath ||= File.dirname(Dir.glob("/usr/lib*/**/crti.o").last)
   def gcc_libpath = @gcc_libpath ||= File.dirname(Dir.glob("/usr/lib/gcc/x86_64-*/*/crtbegin.o").last)
+
+  def to_elf(input: @input, output: @output, debug: @debug)
+    elf_obj = Caotral::Linker::ELF::Reader.new(input:, debug:).read
+    Caotral::Linker::ELF::Writer.new(elf_obj:, output:, debug:).write
+  end
 end

lib/caotral/linker/elf.rb

@@ -0,0 +1,7 @@
+class Caotral::Linker::ELF
+  attr_reader :sections, :header
+  def initialize
+    @sections = Caotral::Linker::ELF::Sections.new
+    @header = Caotral::Linker::ELF::Header.new
+  end
+end

lib/caotral/linker/elf/object.rb

@@ -0,0 +1,7 @@
+class Caotral::Linker::ELF::Object
+  attr_reader :bin, :debug
+
+  def initialize(bin:, debug: false)
+    @bin, @debug = bin, debug
+  end
+end

lib/caotral/linker/elf/section.rb

@@ -0,0 +1,13 @@
+class Caotral::Linker::ELF::Section
+  attr_accessor :name
+  attr_reader :section_name, :header, :body
+  def initialize(type:, options: {})
+    type_string = type.to_s.capitalize
+    type_string = type_string.upcase if type_string == "Bss"
+    # section_name is extra information about section type
+    @section_name = type_string.downcase
+    # name is used in section header string table in elf file
+    @name = section_name == "null" ? "" : "\0.#{section_name}"
+    @header, @body = nil, nil
+  end
+end

lib/caotral/linker/elf/section/shstrtab.rb

@@ -0,0 +1,6 @@
+class Caotral::Linker::ELF::Section::Shstrtab
+  include Caotral::Assembler::ELF::Utils
+  def initialize(**opts) = @name = []
+  def build = bytes.flatten.pack("C*")
+  def set!(name:) = (@name << name!(name); self)
+end

lib/caotral/linker/elf/section/strtab.rb

@@ -0,0 +1,5 @@
+class Caotral::Linker::ELF::Section::Strtab
+  include Caotral::Assembler::ELF::Utils
+  def initialize(names = "\0main\0", **opts) = @names = names
+  def build = @names.bytes.pack("C*")
+end

lib/caotral/linker/elf/section/symtab.rb

@@ -0,0 +1,12 @@
+class Caotral::Linker::ELF::Section::Symtab
+  include Caotral::Assembler::ELF::Utils
+  def initialize(**opts)
+    @entsize = []
+    @name = num2bytes(0, 4)
+    @info = num2bytes(0, 1)
+    @other = num2bytes(0, 1)
+    @shndx = num2bytes(0, 2)
+    @value = num2bytes(0, 8)
+    @size = num2bytes(0, 8)
+  end
+end

lib/caotral/linker/elf/section/text.rb

@@ -0,0 +1,4 @@
+class Caotral::Linker::ELF::Section::Text
+  def initialize = @bytes = []
+  def build = @bytes.flatten.pack("C*")
+end

lib/caotral/linker/elf/section_header.rb

@@ -0,0 +1,37 @@
+class Caotral::Linker::ELF::SectionHeader
+  include Caotral::Assembler::ELF::Utils
+  def initialize
+    @name = nil
+    @type = nil
+    @flags = nil
+    @addr = nil
+    @offset = nil
+    @size = nil
+    @link = nil
+    @info = nil
+    @addralign = nil
+    @entsize = nil
+  end
+
+  def build = bytes.flatten.pack("C*")
+
+  def set!(name: nil, type: nil, flags: nil, addr: nil,
+           offset: nil, size: nil, link: nil, info: nil,
+           addralign: nil, entsize: nil)
+    @name = num2bytes(name, 4) if check(name, 4)
+    @type = num2bytes(type, 4) if check(type, 4)
+    @flags = num2bytes(flags, 8)  if check(flags, 8)
+    @addr = num2bytes(addr, 8) if check(addr, 8)
+    @offset = num2bytes(offset, 8) if check(offset, 8)
+    @size = num2bytes(size, 8) if check(size, 8)
+    @link = num2bytes(link, 4) if check(link, 4)
+    @info = num2bytes(info, 4) if check(info, 4)
+    @addralign = num2bytes(addralign, 8) if check(addralign, 8)
+    @entsize = num2bytes(entsize, 8) if check(entsize, 8)
+    self
+  end
+
+  def null! = set!(name: 0, type: 0, flags: 0, addr: 0, offset: 0, size: 0, link: 0, info: 0, addralign: 0, entsize: 0)
+
+  private def bytes = [@name, @type, @flags, @addr, @offset, @size, @link, @info, @addralign, @entsize]
+end

lib/caotral/linker/elf/sections.rb

@@ -0,0 +1,18 @@
+class Caotral::Linker::ELF::Sections
+  include Enumerable
+
+  def initialize = @sections = []
+  def each(&block) = @sections.each(&block)
+  def add(section) = @sections << section
+  alias << add
+  def [](index)
+    case index
+    when Integer
+      @sections[index]
+    when String, Symbol
+      @sections.find { _1.section_name.to_s == index.to_s }
+    else
+      raise ArgumentError, "Invalid index type: #{index.class}"
+    end
+  end
+end