symbol table now uses offsets instead of absolute addresses

asm/machosymtab.rb

@@ -8,22 +8,12 @@ module Assembler
     
     include MachO
 
-    def const_offset
-      return 0x2000
-    end
-
-    def bss_offset
-      # TODO figure out how to calculate these, or how to let the linker do it!
-      #      ... relocation tables perhaps?
-      return 0x2800
-    end
-
-    def make_symbols(vars, type, segnum)
+    def make_symbols(vars, base_addr, type, segnum)
       # Note: Sorting a Ruby hash gives an alist, e.g. [[<key>, <value>], ...]
       #       We can use map on it as if it were a hash so it works nicely.
       vars.sort { |a,b| a[1] <=> b[1] }.
-           map do |name, addr|
-             MachOSym.new(name, type, segnum, 0, addr)
+           map do |name, offset|
+             MachOSym.new(name, type, segnum, 0, base_addr + offset)
            end
     end
 
@@ -31,12 +21,32 @@ module Assembler
       # TODO FIXME:
       # - the last var exported ends up after main somewhere... WTF?!
       # - All labels are exported.  This should be changed and only functions exported!
-      symbols = make_symbols(@labels, N_SECT | N_EXT, 1) + # Functions (section #1, __text)
-                make_symbols(@consts, N_SECT, 2)         + # Constants (section #2, __const)
-                make_symbols(@vars, N_SECT, 3)             # Variables (section #3, __bss)
+
+      section = 1
+      
+      # Functions (section #1, __text)
+      symbols = make_symbols(@labels, text_offset, N_SECT | N_EXT, section)
+      section += 1
+
+      # Constants (section #2, __const)
+      if @consts.size > 0
+        symbols += make_symbols(@consts, const_offset, N_SECT, section)
+        section += 1
+      end
+
+      # Variables (section #3, __bss)
+      if @vars.size > 0
+        symbols += make_symbols(@vars, bss_offset, N_SECT, section)
+      end
+
       return symbols
     end
 
+    # this is fairly stupid but works
+    def bss_section
+      @consts.size > 0 ? 3 : 2
+    end
+    
     def nlist_ary
       symbols = {}
       strx = 1
@@ -53,10 +63,26 @@ module Assembler
     end
     
     def stab
-      # The empty strings result in a string that begins and ends with
+      # The empty strings result in a string that begins and ends with a null byte
       ['', all_symbols, ''].flatten.map { |sym| sym.to_s }.join("\0")
     end
 
+    def reloc(r_address, r_symbolnum=0, r_length=2, r_extern=0, r_pcrel=0, r_type=0)
+      r_info = (r_type << 28) | (r_extern << 27) | (r_length << 25) |
+        (r_pcrel << 24) | r_symbolnum
+      @reloc_info << RelocationInfo.new(r_address, r_info)
+    end
+
+    def reloc_info
+      n = bss_section
+      @reloc_info.each {|r| r[:r_info] |= n}
+    end
+
+    def calculate_offsets(text_size)
+      @const_offset = @text_offset + text_size
+      @bss_offset = @const_offset + @const_size
+    end
+
   end
   
 end

asm/symtab.rb

@@ -1,13 +1,22 @@
 module Assembler
 
+
+  # Abstract symbol table.
+  #
+  # Basically a big map of variable, constant, and label names to
+  # offsets within their respective sections.  Final addresses are
+  # calculated from these offsets on the 2nd pass when we know where
+  # things will actually live in memory.
+
   class Symtab
     
-    attr_reader :const_data, :bss_size
+    attr_accessor :text_offset, :bss_offset, :const_offset
+    attr_reader :const_data, :const_size, :bss_size, :reloc_info
     
     def initialize
-      @vars = {}                   # Map of variable names to addresses. (bss vars)
-      @consts = {}                 # Map of constant names to addresses.
-      @funcs = {}                  # map of function names to addresses.
+      @vars = {}                   # Map of variable names to offsets. (bss vars)
+      @consts = {}                 # Map of constant names to offsets.
+      @funcs = {}                  # map of function names to offsets.
       
       # Initial data to load into memory (data for __DATA segment).
       @const_data = ''
@@ -19,15 +28,15 @@ module Assembler
       @labels = Hash.new {|h, key| raise "undefined label: #{key}"}
       @num_labels = 0              # Used to generate unique labels.
       @num_labels_with_suffix = Hash.new(0)
+
+      # Relocation info. Subclasses should define a reloc method.
+      @reloc_info = []
+
+      @text_offset = 0
+      @bss_offset = 0
+      @const_offset = 0
     end
     
-    
-    ####
-    ## NB: Concrete subclasses must define methods named:
-    ##       bss_offset, and const_offset
-    ####
-
-    
     # Generate a unique label.
     def unique_label(suffix=nil)
       @num_labels += 1
@@ -39,8 +48,8 @@ module Assembler
       return name
     end
 
-    def deflabel(name, addr)
-      @labels[name] = addr
+    def deflabel(name, offset)
+      @labels[name] = offset
       return name
     end
     
@@ -63,27 +72,27 @@ module Assembler
     end
 
 
-    def defun(name, addr)
-      @funcs[name] = addr
+    def defun(name, offset)
+      @funcs[name] = offset
     end
 
     
     def var(name)
-      bss_offset + @vars[name]
-    end
-    
-    def var?(name)
       @vars[name]
     end
     
-    def const(name)
-      const_offset + @consts[name]
+    def var?(name)
+      @vars.has_key?(name)
     end
     
-    def const?(name)
+    def const(name)
       @consts[name]
     end
 
+    def const?(name)
+      @consts.has_key?(name)
+    end
+
   end
   
 end