Merge pull request #32 from katsyoshi/support-multi-files-for-linker

Support multi files for linker

Author: katsyoshi

lib/caotral.rb

@@ -14,7 +14,7 @@ def compile!(input:, assembler: "as", linker: "ld", output: "tmp", debug: false,
     execf = "#{basename}#{File.extname(d)}"
     compile(input:, output: basename+".s", debug:, shared:)
     assemble(input: basename+".s", output: basename+".o", assembler:, debug:, shared:)
-    link(input: basename+".o", output: execf, linker:, debug:, shared:)
+    link(input: [basename+".o"], output: execf, linker:, debug:, shared:)
   end
   def compile(input:, output: "tmp.s", debug: false, shared: false)
     Caotral::Compiler.compile!(input:, output:, debug:)
@@ -23,6 +23,7 @@ def assemble(input:, output: "tmp.o", debug: false, shared: false, assembler: "a
     Caotral::Assembler.assemble!(input:, output:, debug:, assembler:, shared:)
   end
   def link(input:, output: "tmp", linker: "ld", debug: false, shared: false)
-    Caotral::Linker.link!(input:, output:, linker:, debug:, shared:)
+    inputs = Array === input ? input : [input]
+    Caotral::Linker.link!(inputs:, output:, linker:, debug:, shared:)
   end
 end

lib/caotral/binary/elf.rb

@@ -25,6 +25,7 @@ def find_by_name(section_name) = @sections.find { |s| section_name == s.section_
       def select_by_name(section_name) = @sections.select { |s| section_name == s.section_name }
       def index(section_name) = @sections.index { |s| section_name == s.section_name }
       def select_by_names(section_names) = @sections.select { |section| section_names.any? { |name| name === section.section_name.to_s } }
+      def without_sections(names) = @sections.reject { |s| names.any? { |name| name === s.section_name.to_s } }
     end
   end
 end

lib/caotral/binary/elf/section/rel.rb

@@ -14,7 +14,7 @@ def initialize(addend: true)
           def set!(offset: nil, info: nil, addend: nil)
             @offset = num2bytes(offset, 8) if check(offset, 8)
             @info = num2bytes(info, 8) if check(info, 8)
-            @addend = num2bytes(addend, 8) if check(addend, 8)
+            @addend = [addend].pack("q<").unpack("C*") if check(addend, 8)
             self
           end
 
@@ -23,7 +23,7 @@ def offset = @offset.pack("C*").unpack1("Q<")
           def info = @info.pack("C*").unpack1("Q<")
           def addend
             raise "No addend field in this REL entry" unless addend?
-            @addend.pack("C*").unpack1("Q<")
+            @addend.pack("C*").unpack1("q<")
           end
           def sym = @info.pack("C*").unpack1("Q<") >> 32
           def type = @info.pack("C*").unpack1("Q<") & 0xffffffff

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

@@ -32,6 +32,9 @@ def set!(name: nil, info: nil, other: nil, shndx: nil, value: nil, size: nil)
           def name_offset = @name.pack("C*").unpack1("L<")
           def value = @value.pack("C*").unpack1("Q<")
           def info = @info.pack("C*").unpack1("C")
+          def shndx = @shndx.pack("C*").unpack1("S<")
+          def bind = info >> 4
+          def type = info & 0x0f
 
           private def bytes = [@name, @info, @other, @shndx, @value, @size]
         end

lib/caotral/linker.rb

@@ -5,21 +5,21 @@
 
 module Caotral
   class Linker
-    def self.link!(input:, output: "a.out", linker: "mold", debug: false, shared: false) = new(input:, output:, linker:, debug:, shared:).link
+    def self.link!(inputs:, output: "a.out", linker: "mold", debug: false, shared: false) = new(inputs:, output:, linker:, debug:, shared:).link
 
-    def initialize(input:, output: "a.out", linker: "mold", linker_options: [], shared: false, debug: false)
-      @input, @output, @linker = input, output, linker
+    def initialize(inputs:, output: "a.out", linker: "mold", linker_options: [], shared: false, debug: false)
+      @inputs, @output, @linker = inputs, output, linker
       @options = linker_options
       @debug, @shared = debug, shared
     end
 
-    def link(input: @input, output: @output, debug: @debug, shared: @shared)
-      return to_elf(input:, output:, debug:) if @linker == "self"
+    def link(inputs: @inputs, output: @output, debug: @debug, shared: @shared)
+      return to_elf(inputs:, output:, debug:) if @linker == "self"
 
       IO.popen(link_command).close
     end
 
-    def link_command(input: @input, output: @output, debug: @debug, shared: @shared)
+    def link_command(inputs: @inputs, output: @output)
       ld_path = []
 
       if @shared
@@ -39,18 +39,19 @@ def link_command(input: @input, output: @output, debug: @debug, shared: @shared)
 
       ld_path << "#{libpath}/libc.so"
       ld_path << "#{libpath}/crtn.o"
-      cmd = [@linker, "-o", @output, "-m", "elf_x86_64", *@options, *ld_path, @input].join(' ')
+      cmd = [@linker, "-o", @output, "-m", "elf_x86_64", *@options, *ld_path, *inputs].join(' ')
       puts cmd if @debug
       cmd
     end
 
     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::Binary::ELF::Reader.new(input:, debug:).read
-      builder = Caotral::Linker::Builder.new(elf_obj:)
+    def to_elf(inputs: @inputs, output: @output, debug: @debug)
+      elf_objs = inputs.map { |input| Caotral::Binary::ELF::Reader.new(input:, debug:).read }
+      builder = Caotral::Linker::Builder.new(elf_objs:)
       builder.resolve_symbols
+      elf_obj = builder.build
       Caotral::Linker::Writer.new(elf_obj:, output:, debug:).write
     end
   end

lib/caotral/linker/builder.rb

@@ -4,27 +4,260 @@
 module Caotral
   class Linker
     class Builder
+      include Caotral::Binary::ELF::Utils
+      R_X86_64_PC32 = 2
+      R_X86_64_PLT32 = 4
       SYMTAB_BIND = { locals: 0, globals: 1, weaks: 2, }.freeze
       BIND_BY_VALUE = SYMTAB_BIND.invert.freeze
-      attr_reader :symbols
+      RELOCATION_SECTION_NAMES = [".rela.text", ".rel.text"].freeze
+      ALLOW_RELOCATION_TYPES = [R_X86_64_PC32, R_X86_64_PLT32].freeze
 
-      def initialize(elf_obj:)
-        @elf_obj = elf_obj
+      attr_reader :symbols, :executable, :debug
+
+      def initialize(elf_objs:, executable: true, debug: false)
+        @elf_objs = elf_objs
         @symbols = { locals: Set.new, globals: Set.new, weaks: Set.new }
+        @executable, @debug = executable, debug
       end
+
+      def build
+        raise Caotral::Binary::ELF::Error, "no ELF objects to link" if @elf_objs.empty?
+        elf = Caotral::Binary::ELF.new
+        elf_obj = @elf_objs.first
+        null_section = Caotral::Binary::ELF::Section.new(
+          body: nil,
+          section_name: "",
+          header: Caotral::Binary::ELF::SectionHeader.new
+        )
+        text_section = Caotral::Binary::ELF::Section.new(
+          body: String.new,
+          section_name: ".text",
+          header: Caotral::Binary::ELF::SectionHeader.new
+        )
+        strtab_section = Caotral::Binary::ELF::Section.new(
+          body: Caotral::Binary::ELF::Section::Strtab.new("\0".b),
+          section_name: ".strtab",
+          header: Caotral::Binary::ELF::SectionHeader.new
+        )
+        symtab_section = Caotral::Binary::ELF::Section.new(
+          body: [],
+          section_name: ".symtab",
+          header: Caotral::Binary::ELF::SectionHeader.new
+        )
+        shstrtab_section = Caotral::Binary::ELF::Section.new(
+          body: Caotral::Binary::ELF::Section::Strtab.new("\0".b),
+          section_name: ".shstrtab",
+          header: Caotral::Binary::ELF::SectionHeader.new
+        )
+        start_bytes = [0xe8, *[0] * 4, 0x48, 0x89, 0xc7, 0x48, 0xc7, 0xc0, 0x3c, 0x00, 0x00, 0x00, 0x0f, 0x05]
+        exec_text_offset = 0x1000
+        base_addr = 0x400000
+        vaddr = base_addr + exec_text_offset
+        start_len = start_bytes.length
+        sections = []
+        rel_sections = []
+        elf.header = elf_obj.header.dup
+        strtab_names = []
+        text_offsets = {}
+        text_offset = 0
+        sym_by_elf = Hash.new { |h, k| h[k] = [] }
+        @elf_objs.each do |elf_obj|
+          text = elf_obj.find_by_name(".text")
+          unless text.nil?
+            text_section.body << text.body
+            text_offsets[elf_obj.object_id] = text_offset
+            size = text.body.bytesize
+            text_offset += size
+          end
+          strtab = elf_obj.find_by_name(".strtab")
+          strtab.body.names.split("\0").each { |name| strtab_names << name } unless strtab.nil?
+          symtab = elf_obj.find_by_name(".symtab")
+          base_index = nil
+          unless symtab.nil?
+            base_index = symtab_section.body.size
+            symtab.body.each_with_index do |st, index|
+              sym = Caotral::Binary::ELF::Section::Symtab.new
+              name, info, other, shndx, value, size = st.build.unpack("L<CCS<Q<Q<")
+              sym_by_elf[elf_obj] << sym
+              value += text_offsets.fetch(elf_obj.object_id, 0) if shndx != 0
+              sym.set!(name:, info:, other:, shndx:, value:, size:)
+              sym.name_string = strtab.body.lookup(name) unless strtab.nil?
+              symtab_section.body << sym
+            end
+          end
+          rels = elf_obj.select_by_names(RELOCATION_SECTION_NAMES).map do |section|
+            rel_section = Caotral::Binary::ELF::Section.new(
+              body: [],
+              section_name: section.section_name,
+              header: Caotral::Binary::ELF::SectionHeader.new
+            )
+            section.body.each do |rel|
+              offset = rel.offset + text_offsets.fetch(elf_obj.object_id, 0)
+              addend = rel.addend? ? rel.addend : nil
+              new_rel = Caotral::Binary::ELF::Section::Rel.new(addend: rel.addend?)
+              sym = base_index.nil? ? rel.sym : base_index + rel.sym
+              info = (sym << 32) | rel.type
+              new_rel.set!(offset:, info:, addend:)
+              rel_section.body << new_rel
+            end
+            rel_section
+          end
+          rel_sections += rels
+        end
+        strtab_section.body.names = strtab_names.to_a.sort.join("\0") + "\0"
+        sections << null_section
+
+        main_sym = symtab_section.body.find { |sym| sym.name_string == "main" }
+        raise Caotral::Binary::ELF::Error, "main function not found" if executable && main_sym.nil?
+        main_offset = main_sym.nil? ? 0 : main_sym.value + start_len
+        start_bytes[1, 4] = num2bytes((main_offset - 5), 4)
+        text_section.body.prepend(start_bytes.pack("C*"))
+
+        text_section.header.set!(
+          type: 1,
+          flags: 6,
+          addr: vaddr,
+          offset: exec_text_offset,
+          size: text_section.body.bytesize,
+          addralign: 16
+        )
+
+        sections << text_section
+        strtab_section.header.set!(type: 3, flags: 0, addralign: 1, entsize: 0)
+        sections << strtab_section
+        symtab_section.body.each do |sym|
+          next if sym.shndx == 0
+          name = strtab_section.body.offset_of(sym.name_string)
+          value = sym.value + start_len
+          sym.set!(name:, value:)
+        end
+
+        old_syms = symtab_section.body.dup
+        symtab_section.body.sort_by! { |sym| sym.info >> 4 }
+        local_count = symtab_section.body.count { |sym| (sym.info >> 4) == SYMTAB_BIND[:locals] }
+
+        symtab_section.header.set!(
+          type: 2,
+          flags: 0,
+          link: elf.sections.index(strtab_section),
+          info: local_count,
+          addralign: 8,
+          entsize: 24
+        )
+
+        sections << symtab_section
+
+        rel_sections.each { |s| sections << s.dup }
+
+        shstrtab_section.header.set!(
+          type: 3,
+          flags: 0,
+          addralign: 1,
+          entsize: 0
+        )
+
+        @elf_objs.first.without_sections([".text", ".strtab", ".symtab", ".shstrtab", /\.rela?\./]).each do |section|
+          sections << section.dup
+        end
+
+        sections << shstrtab_section
+
+        shstrtab_section_names = [*sections.map(&:section_name), "\0"].join("\0")
+        shstrtab_section.body.names = shstrtab_section_names
+
+        section_map = Hash.new { |h, k| h[k] = {} }
+        @elf_objs.each do |elf_obj|
+          elf_obj.sections.each_with_index do |section, index|
+            newndx = sections.index { |s| s.section_name == section.section_name }
+            section_map[elf_obj][index] = newndx unless newndx.nil?
+          end
+        end
+
+        resolved_index = {}
+        symtab_section.body.each_with_index do |sym, index|
+          name = sym.name_string
+          next if name.empty? || sym.shndx == 0 || sym.bind != 1
+          resolved_index[name] ||= index
+        end
+
+        sym_by_elf.each do |elf_obj, syms|
+          syms.each do |sym|
+            next if sym.shndx == 0
+            shndx = section_map[elf_obj][sym.shndx]
+            sym.set!(shndx:)
+          end
+        end
+
+        rel_sections.each do |rel_section|
+          rel_section.body.each do |rel|
+            orig_sym = old_syms[rel.sym]
+            next if orig_sym.nil?
+            name = orig_sym.name_string
+            new_index = resolved_index[name]
+            next if new_index.nil?
+            rel.set!(info: (new_index << 32) | rel.type)
+          end
+
+          rel_section.header.set!(
+            type: rel_type(rel_section),
+            flags: 0,
+            link: sections.index(symtab_section),
+            info: ref_index(sections, rel_section.section_name),
+            addralign: 8,
+            entsize: rel_entsize(rel_section)
+          )
+        end
+
+        rel_sections.each do |rel|
+          target = sections[rel.header.info]
+          bytes = target.body.dup
+          symtab_body = symtab_section.body
+          rel.body.each do |entry|
+            next unless ALLOW_RELOCATION_TYPES.include?(entry.type)
+            sym = symtab_body[entry.sym]
+            next if sym.nil? || sym.shndx == 0
+            target_addr = target == text_section ? vaddr : target.header.addr
+            sym_addr = sym.shndx >= 0xff00 ? sym.value : sections[sym.shndx].then { |st| st.header.addr + sym.value }
+            sym_offset = entry.offset + start_len
+            sym_addend = entry.addend? ? entry.addend : bytes[sym_offset, 4].unpack1("l<")
+            value = sym_addr + sym_addend - (target_addr + sym_offset)
+            bytes[sym_offset, 4] = [value].pack("l<")
+          end
+          target.body = bytes
+        end
+
+        sections = sections.reject { |section| RELOCATION_SECTION_NAMES.any? { |name| name === section.section_name.to_s } } if executable
+        sections.each { |section| elf.sections << section }
+
+        elf
+      end
+
       def resolve_symbols
-        @elf_obj.find_by_name(".symtab").body.each do |symtab|
-          name = symtab.name_string
-          next if name.empty?
-          info = symtab.info
-          bind = BIND_BY_VALUE.fetch(info >> 4)
-          if bind == :globals && @symbols[bind].include?(name)
-            raise Caotral::Binary::ELF::Error,"cannot add into globals: #{name}"
+        @elf_objs.each do |elf_obj|
+          elf_obj.find_by_name(".symtab").body.each do |symtab|
+            name = symtab.name_string
+            next if name.empty?
+            info = symtab.info
+            bind = BIND_BY_VALUE.fetch(info >> 4)
+            if bind == :globals && @symbols[bind].include?(name) && symtab.shndx != 0
+              raise Caotral::Binary::ELF::Error,"cannot add into globals: #{name}"
+            end
+            @symbols[bind] << name
           end
-          @symbols[bind] << name
         end
         @symbols
       end
+
+      private
+      def ref_index(sections, section_name)
+        raise Caotral::Binary::ELF::Error, "invalid section name: #{section_name}" if section_name.nil?
+        ref_names = "." + section_name.split(".").filter { |sn| !sn.empty? && sn != "rel" && sn != "rela" }.join(".")
+        ref = sections.find { |s| ref_names === s.section_name.to_s }
+        sections.index(ref)
+      end
+
+      def rel_type(section) = section.section_name&.start_with?(".rela.") ? 4 : 9
+      def rel_entsize(section) = section.section_name&.start_with?(".rela.") ? 24 : 16
     end
   end
 end