diff --git a/asm/asm.rb b/asm/asm.rb
index 4f4383d..b7037d0 100644
--- a/asm/asm.rb
+++ b/asm/asm.rb
@@ -12,7 +12,10 @@ module Assembler
   # implemented to be useful.
   class AssemblerBase
 
-    def initialize(*args)
+    attr_reader :platform
+
+    def initialize(platform='linux', *args)
+      @platform = platform
       @vars = {}                   # Symbol table, maps names to locations in BSS.
       @num_labels = 0              # Used to generate unique labels.
       @num_labels_with_suffix = Hash.new(0)
diff --git a/build.rb b/build.rb
index c928917..16fedc5 100755
--- a/build.rb
+++ b/build.rb
@@ -21,10 +21,10 @@ end
 # filename: input filename
 # asm:      assembler to use
 # returns:  output filename
-def compile(filename, asm, binformat='elf')
+def compile(filename, asm)
 
   File.open(filename, 'r') do |input|
-    compiler = Compiler.new(input, asm, binformat)
+    compiler = Compiler.new(input, asm)
     compiler.compile
   end
 
@@ -81,7 +81,7 @@ def build(filename, platform='linux', format='asm', binformat='elf')
           obj = asm( code, binformat )
           link( obj, platform )
         else # binary
-          obj = compile(filename, Assembler::Binary.new(platform), binformat)
+          obj = compile(filename, Assembler::Binary.new(platform))
           link( obj, platform )
         end
   return bin
diff --git a/compiler.rb b/compiler.rb
index 272acd8..5bf9fcf 100644
--- a/compiler.rb
+++ b/compiler.rb
@@ -29,15 +29,10 @@ class Compiler
   
   attr_reader :asm
 
-  def initialize(input, asm, binformat='elf')
+  def initialize(input, asm)
     # XXX for development only!
     @indent = 0                  # for pretty printing
 
-    # The only binary format our assembler knows right now is ELF.
-    unless binformat == 'elf'
-      raise "Only ELF is supported.  Unsupported binary format: #{binformat}."
-    end
-
     @look = ''                   # Next lookahead char.
     @token = nil                 # Type of last read token.
     @value = nil                 # Value of last read token.
@@ -604,11 +599,36 @@ class Compiler
       dec(:edi)
       shr(:eax, 8)
       loop_(loop_label)
-      mov(:eax, 4)            # SYS_write
-      mov(:ebx, 1)            # STDOUT
-      lea(:ecx, '[HEX]')
-      mov(:edx, 11)           # excluding term, max # of chars to print
-      int(0x80)
+      # write(int fd, char *s, int n)
+      mov(:eax, 4)              # SYS_write
+      lea(:ecx, '[HEX]')        # ecx = &s
+      args = [1,                # fd = 1 (STDOUT)
+              :ecx,             # s = &s
+              11]               # n = 11 (excluding term, max # of chars to print)
+      case platform
+      when 'darwin'             # on the stack, right to left (right @ highest addr)
+        ####
+        # setup bogus stack frame
+        push(:ebp)
+        mov(:ebp, :esp)
+        sub(:esp, 36)
+        ####
+        args.reverse.each { |a| push(a) }
+        push(:eax)
+        int(0x80)
+        ####
+        # teardown bogus stack frame
+        xor(:eax, :eax)
+        add(:esp, 36)
+        pop(:ebx)
+        emit("leave")
+        ####
+      when 'linux'
+        mov(:ebx, args[0])
+        mov(:ecx, args[1])
+        mov(:edx, args[2])
+        int(0x80)
+      end
     end
   end