parse shstrtab

Author: katsyoshi

lib/caotral/linker/elf/header.rb

@@ -35,8 +35,20 @@ def set!(entry: nil, phoffset: nil, shoffset: nil, shnum: nil, shstrndx: nil)
           @shstrndx = num2bytes(shstrndx, 2) if check(shstrndx, 2)
         end
 
-        private
+        def ehsize = get(:ehsize)
+        def phsize = get(:phsize)
+        def phnum = get(:phnum)
+        def shentsize = get(:shentsize)
+        def shnum = get(:shnum)
+        def shstrndx = get(:shstrndx)
+
+        LONG_TYPES = %w[entry phoffset shoffset].freeze
+        INT_TYPES = %w[type version].freeze
+        SHORT_TYPES = %w[ehsize phsize phnum shentsize shnum shstrndx].freeze
+        CHAR_TYPES = %w[arch flags].freeze
+        private_constant :LONG_TYPES, :INT_TYPES, :SHORT_TYPES, :CHAR_TYPES
 
+        private
         def bytes = [
           @ident, @type, @arch, @version, @entry, @phoffset,
           @shoffset, @flags, @ehsize, @phsize, @phnum, @shentsize,
@@ -62,6 +74,18 @@ def elf(type)
             :NONE
           end
         end
+
+        def get(type)
+          val = instance_variable_get(:"@#{type.to_s}").pack("C*")
+          case type.to_s.downcase
+          when *LONG_TYPES; val.unpack("Q<")
+          when *INT_TYPES; val.unpack("L<")
+          when *SHORT_TYPES; val.unpack("S<")
+          when *CHAR_TYPES; val.unpack("C<")
+          else
+            raise "not specified: #{type}"
+          end.first
+        end
       end
     end
   end

lib/caotral/linker/elf/section.rb

@@ -1,13 +1,15 @@
-class Caotral::Linker::ELF::Section
-  attr_accessor :name, :header
-  attr_reader :section_name, :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
+class Caotral::Linker
+  class ELF
+    class Section
+      attr_accessor :name, :header, :body, :section_name
+      def initialize(type:, options: {})
+        type_string = type.to_s.capitalize
+        type_string = type_string.upcase if type_string == "Bss"
+        @section_name = type.to_s.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
   end
 end

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

@@ -1,5 +1,14 @@
-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*")
+module Caotral
+  class Linker
+    class ELF
+      class Section
+        class Strtab
+          include Caotral::Assembler::ELF::Utils
+          attr_reader :names
+          def initialize(names = "\0main\0", **opts) = @names = names
+          def build = @names.bytes.pack("C*")
+        end
+      end
+    end
+  end
 end

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

@@ -50,8 +50,24 @@ def set!(name: nil, type: nil, flags: nil, addr: nil,
         end
 
         def null! = set!(name: 0, type: 0, flags: 0, addr: 0, offset: 0, size: 0, link: 0, info: 0, addralign: 0, entsize: 0)
+        def name = get(:name)
+        def offset = get(:offset)
+        def size = get(:size)
+        LONG_TYPES = %w[flags addr offset size addralign entsize].freeze
+        INT_TYPES = %w[name type link info].freeze
+
+        private_constant :LONG_TYPES, :INT_TYPES
 
         private def bytes = [@name, @type, @flags, @addr, @offset, @size, @link, @info, @addralign, @entsize]
+        private def get(type)
+          val = instance_variable_get("@#{type.to_s}").pack("C*")
+          case type.to_s
+          when *INT_TYPES; val.unpack("L<")
+          when *LONG_TYPES; val.unpack("Q<")
+          else
+            raise "not specified: #{type}"
+          end.first
+        end
       end
     end
   end

lib/caotral/linker/elf/section_header.rb

@@ -2,6 +2,7 @@
 require_relative "elf"
 require_relative "elf/section"
 require_relative "elf/section_header"
+require_relative "elf/section/strtab"
 
 module Caotral
   class Linker
@@ -47,6 +48,13 @@ def read
           section.header = section_header
           @context.sections.add(section)
         end
+        @context.sections[shstrndx].tap do |shstrtab|
+          @bin.pos = shstrtab.header.offset
+          names = @bin.read(shstrtab.header.size)
+          shstrtab.section_name = "shstrtab"
+          shstrtab.name = "\0.shstrtab"
+          shstrtab.body = Caotral::Linker::ELF::Section::Strtab.new(names)
+        end
         @context
       ensure
         @input.close

lib/caotral/linker/reader.rb

@@ -1,4 +1,25 @@
 class Caotral::Linker::ELF::SectionHeader
   SHT: Hash[Symbol, Integer]
   SHT_BY_VALUE: Hash[Integer, Symbol]
+  LONG_TYPES: Array[String]
+  INT_TYPES: Array[String]
+
+  def initialize: () -> void
+  def build: () -> String
+  def set!: (
+    ?name: Integer?,
+    ?type: Integer?,
+    ?flags: Integer?,
+    ?addr: Integer?,
+    ?offset: Integer?,
+    ?size: Integer?,
+    ?link: Integer?,
+    ?info: Integer?,
+    ?addralign: Integer?,
+    ?entsize: Integer?
+  ) -> self
+  def null!: () -> self
+  def name: () -> Integer
+  def offset: () -> Integer
+  def size: () -> Integer
 end

sig/caotral/linker/elf/section_header.rbs

@@ -8,5 +8,8 @@ def test_read
     assert_equal elf_obj.header.shoffset.pack("C*").unpack("Q<").first, 256
     assert_equal elf_obj.sections.size, 8
     assert_equal elf_obj.sections[0].section_name, "null"
+    shstrtab = elf_obj.sections[elf_obj.header.shstrndx]
+    assert_equal shstrtab.section_name, "shstrtab"
+    assert_equal shstrtab.body.names, "\0.text\0.data\0.bss\0.note\0.symtab\0.strtab\0.shstrtab\0"
   end
 end