diff --git a/ChangeLog b/ChangeLog
index 88702d7..67f302b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,24 @@
+Sun May 10 20:24:13 2009  Minero Aoki  <aamine@loveruby.net>
+
+	* net/loveruby/cflat/asm/Assembler.java -> AssemblyFile.java
+
+	* net/loveruby/cflat/utils/AsmUtils.java: split #align from
+	  AssemblyFile.
+
+	* net/loveruby/cflat/type/StructType.java: use it.
+
+	* net/loveruby/cflat/type/UnionType.java: use it.
+
+	* net/loveruby/cflat/platform: new package to extract platform
+	  dependent operations.
+
+	* net/loveruby/cflat/compiler/Compiler.java: use it.
+
+	* net/loveruby/cflat/compiler/CodeGenerator.java: use it.
+
+	* net/loveruby/cflat/compiler/Options.java: provide Platform
+	  object.
+
 Thu May  7 13:00:09 2009  Minero Aoki  <aamine@loveruby.net>
 
 	* net/loveruby/cflat/compiler/IRGenerator.java: should not return
diff --git a/net/loveruby/cflat/asm/Assembler.java b/net/loveruby/cflat/asm/AssemblyFile.java
similarity index 98%
rename from net/loveruby/cflat/asm/Assembler.java
rename to net/loveruby/cflat/asm/AssemblyFile.java
index 6bd5062..0f55b85 100644
--- a/net/loveruby/cflat/asm/Assembler.java
+++ b/net/loveruby/cflat/asm/AssemblyFile.java
@@ -2,16 +2,12 @@ package net.loveruby.cflat.asm;
 import net.loveruby.cflat.utils.*;
 import java.util.*;
 
-public class Assembler {
+public class AssemblyFile {
     protected List<Assembly> assemblies;
     protected Type naturalType;
     protected int commentIndentLevel;
 
-    static public long align(long n, long alignment) {
-        return (n + alignment - 1) / alignment * alignment;
-    }
-
-    public Assembler(Type naturalType) {
+    public AssemblyFile(Type naturalType) {
         this.assemblies = new ArrayList<Assembly>();
         this.naturalType = naturalType;
         this.commentIndentLevel = 0;
diff --git a/net/loveruby/cflat/compiler/CodeGenerator.java b/net/loveruby/cflat/compiler/CodeGenerator.java
index 82ee44b..13d79cc 100644
--- a/net/loveruby/cflat/compiler/CodeGenerator.java
+++ b/net/loveruby/cflat/compiler/CodeGenerator.java
@@ -1,4 +1,5 @@
 package net.loveruby.cflat.compiler;
+import net.loveruby.cflat.platform.Platform;
 import net.loveruby.cflat.ast.Location;
 import net.loveruby.cflat.entity.*;
 import net.loveruby.cflat.ir.*;
@@ -8,17 +9,20 @@ import java.util.*;
 public class CodeGenerator implements IRVisitor<Void,Void>, ELFConstants {
     // #@@range/ctor{
     protected CodeGeneratorOptions options;
+    protected Platform platform;
     protected ErrorHandler errorHandler;
-    protected LinkedList<Assembler> asStack;
-    protected Assembler as;
+    protected LinkedList<AssemblyFile> asStack;
+    protected AssemblyFile as;
     protected Type naturalType;
     protected Label epilogue;
 
     public CodeGenerator(CodeGeneratorOptions options,
+                         Platform platform,
                          ErrorHandler errorHandler) {
         this.options = options;
+        this.platform = platform;
         this.errorHandler = errorHandler;
-        this.asStack = new LinkedList<Assembler>();
+        this.asStack = new LinkedList<AssemblyFile>();
     }
     // #@@}
 
@@ -27,7 +31,7 @@ public class CodeGenerator implements IRVisitor<Void,Void>, ELFConstants {
     public String generate(IR ir) {
         this.naturalType = ir.naturalType();
         pushAssembler();
-        SymbolTable constSymbols = new SymbolTable(Assembler.CONST_SYMBOL_BASE);
+        SymbolTable constSymbols = new SymbolTable(AssemblyFile.CONST_SYMBOL_BASE);
         for (ConstantEntry ent : ir.constantTable().entries()) {
             locateConstant(ent, constSymbols);
         }
@@ -44,14 +48,14 @@ public class CodeGenerator implements IRVisitor<Void,Void>, ELFConstants {
 
     // #@@range/pushAssembler{
     protected void pushAssembler() {
-        this.as = new Assembler(naturalType);
+        this.as = new AssemblyFile(naturalType);
         asStack.add(this.as);
     }
     // #@@}
 
     // #@@range/popAssembler{
-    protected Assembler popAssembler() {
-        Assembler popped = asStack.removeLast();
+    protected AssemblyFile popAssembler() {
+        AssemblyFile popped = asStack.removeLast();
         this.as = asStack.isEmpty() ? null : asStack.getLast();
         return popped;
     }
@@ -347,17 +351,6 @@ public class CodeGenerator implements IRVisitor<Void,Void>, ELFConstants {
      * ======================= stack bottom
      */
 
-    /*
-     * Platform Dependent Stack Parameters
-     */
-    // #@@range/stackParams{
-    static final protected boolean stackGrowsLower = true;
-    static final protected long stackWordSize = 4;
-    static final protected long stackAlignment = stackWordSize;
-    static final protected long paramStartWord = 2;
-                                    // return addr and saved bp
-    // #@@}
-
     /** Compiles a function. */
     // #@@range/compileFunction{
     public void compileFunction(DefinedFunction func) {
@@ -383,7 +376,7 @@ public class CodeGenerator implements IRVisitor<Void,Void>, ELFConstants {
         AsmStatistics stats = AsmStatistics.collect(bodyAsms);
         bodyAsms = reduceLabels(bodyAsms, stats);
         List<Register> saveRegs = usedCalleeSavedRegistersWithoutBP(stats);
-        long saveRegsBytes = saveRegs.size() * stackWordSize;
+        long saveRegsBytes = platform.stackSizeFromWordNum(saveRegs.size());
         long lvarBytes = allocateLocalVariables(
                 func.body().scope(), saveRegsBytes);
         fixTmpOffsets(bodyAsms, saveRegsBytes + lvarBytes);
@@ -537,16 +530,14 @@ public class CodeGenerator implements IRVisitor<Void,Void>, ELFConstants {
     // #@@}
 
     // #@@range/allocateParameters{
+    static final private long paramStartWordNum = 2;
+                                    // return addr and saved bp
+
     protected void allocateParameters(DefinedFunction func) {
-        long word = paramStartWord;
+        long numWords = paramStartWordNum;
         for (Parameter var : func.parameters()) {
-            if (stackGrowsLower) {
-                var.setMemref(mem(word * stackWordSize, bp()));
-            }
-            else {
-                throw new Error("unsupported stack layout");
-            }
-            word++;
+            var.setMemref(mem(platform.stackSizeFromWordNum(numWords), bp()));
+            numWords++;
         }
     }
     // #@@}
@@ -579,14 +570,8 @@ public class CodeGenerator implements IRVisitor<Void,Void>, ELFConstants {
     protected long allocateScope(LocalScope scope, long parentStackLen) {
         long len = parentStackLen;
         for (DefinedVariable var : scope.localVariables()) {
-            if (stackGrowsLower) {
-                len = Assembler.align(len + var.allocSize(), stackAlignment);
-                fixMemref((IndirectMemoryReference)var.memref(), -len);
-            }
-            else {
-                fixMemref((IndirectMemoryReference)var.memref(), len);
-                len = Assembler.align(len + var.allocSize(), stackAlignment);
-            }
+            len = platform.alignStack(len + var.allocSize());
+            fixMemref((IndirectMemoryReference)var.memref(), -len);
         }
         // Allocate local variables in child scopes.
         // We allocate child scopes in the same area (overrapped).
@@ -608,12 +593,7 @@ public class CodeGenerator implements IRVisitor<Void,Void>, ELFConstants {
     // #@@range/extendStack{
     protected void extendStack(long len) {
         if (len > 0) {
-            if (stackGrowsLower) {
-                as.sub(imm(len), sp());
-            }
-            else {
-                as.add(imm(len), sp());
-            }
+            as.sub(imm(len), sp());
         }
     }
     // #@@}
@@ -621,12 +601,7 @@ public class CodeGenerator implements IRVisitor<Void,Void>, ELFConstants {
     // #@@range/rewindStack{
     protected void rewindStack(long len) {
         if (len > 0) {
-            if (stackGrowsLower) {
-                as.add(imm(len), sp());
-            }
-            else {
-                as.sub(imm(len), sp());
-            }
+            as.add(imm(len), sp());
         }
     }
     // #@@}
@@ -649,18 +624,13 @@ public class CodeGenerator implements IRVisitor<Void,Void>, ELFConstants {
 
     // #@@range/stackTop{
     protected IndirectMemoryReference stackTop() {
-        if (stackGrowsLower) {
-            return mem(-stackPointer, bp());
-        }
-        else {
-            return mem(stackPointer - stackWordSize, bp());
-        }
+        return mem(-stackPointer, bp());
     }
     // #@@}
 
     // #@@range/virtualPush{
     protected void virtualPush(Register reg) {
-        extendVirtualStack(stackWordSize);
+        extendVirtualStack(platform.stackWordSize());
         as.relocatableMov(reg, stackTop());
         if (options.isVerboseAsm()) {
             as.comment("push " + reg.name() + " -> " + stackTop());
@@ -674,7 +644,7 @@ public class CodeGenerator implements IRVisitor<Void,Void>, ELFConstants {
             as.comment("pop  " + reg.name() + " <- " + stackTop());
         }
         as.relocatableMov(stackTop(), reg);
-        rewindVirtualStack(stackWordSize);
+        rewindVirtualStack(platform.stackWordSize());
     }
     // #@@}
 
@@ -694,7 +664,7 @@ public class CodeGenerator implements IRVisitor<Void,Void>, ELFConstants {
     // #@@range/fixTmpOffsets{
     protected void fixTmpOffsets(List<Assembly> asms, long offset) {
         for (Assembly asm : asms) {
-            asm.fixStackOffset(offset * (stackGrowsLower ? -1 : 1));
+            asm.fixStackOffset(-offset);
         }
     }
     // #@@}
@@ -724,7 +694,7 @@ public class CodeGenerator implements IRVisitor<Void,Void>, ELFConstants {
         }
         // rewind stack
         // >4 bytes arguments are not supported.
-        rewindStack(node.numArgs() * stackWordSize);
+        rewindStack(platform.stackSizeFromWordNum(node.numArgs()));
         return null;
     }
     // #@@}
diff --git a/net/loveruby/cflat/compiler/Compiler.java b/net/loveruby/cflat/compiler/Compiler.java
index 324fd6f..0d54a41 100644
--- a/net/loveruby/cflat/compiler/Compiler.java
+++ b/net/loveruby/cflat/compiler/Compiler.java
@@ -25,12 +25,8 @@ public class Compiler {
     }
     // #@@}
 
-    private TypeTable defaultTypeTable() {
-        return TypeTable.ilp32();
-    }
-
     public void commandMain(String[] origArgs) {
-        Options opts = new Options(defaultTypeTable(), new LibraryLoader());
+        Options opts = new Options();
         List<SourceFile> srcs = null;
         try {
             srcs = opts.parse(Arrays.asList(origArgs));
@@ -118,7 +114,7 @@ public class Compiler {
                 findExpr(ast).dump();
                 return;
             }
-            ast.setTypeTable(opts.typeTable);
+            ast.setTypeTable(opts.typeTable());
             semanticAnalysis(ast, opts);
             switch (opts.mode()) {
             case DumpReference:
@@ -216,7 +212,8 @@ public class Compiler {
     }
 
     protected String generateAssembly(IR ir, Options opts) {
-        CodeGenerator gen = new CodeGenerator(opts.genOptions(), errorHandler);
+        CodeGenerator gen = new CodeGenerator(
+                opts.genOptions(), opts.platform(), errorHandler);
         return gen.generate(ir);
     }
 
diff --git a/net/loveruby/cflat/compiler/Options.java b/net/loveruby/cflat/compiler/Options.java
index 02619f3..6eddea9 100644
--- a/net/loveruby/cflat/compiler/Options.java
+++ b/net/loveruby/cflat/compiler/Options.java
@@ -1,4 +1,5 @@
 package net.loveruby.cflat.compiler;
+import net.loveruby.cflat.platform.*;
 import net.loveruby.cflat.type.TypeTable;
 import net.loveruby.cflat.asm.*;
 import net.loveruby.cflat.exception.*;
@@ -7,55 +8,45 @@ import java.io.*;
 
 // package scope
 class Options {
-    protected CompilerMode mode;
-    protected TypeTable typeTable;
-    protected LibraryLoader loader;
-    protected String outputFileName;
-    protected boolean verbose;
-    protected boolean debugParser;
-    protected CodeGeneratorOptions genOptions;
-    protected List<String> asOptions;
-    protected boolean generatingSharedLibrary;
-    protected boolean generatingPIE;
-    protected List<LdArg> ldArgs;
-    protected boolean noStartFiles = false;
-    protected boolean noDefaultLibs = false;
+    CompilerMode mode;
+    LibraryLoader loader = new LibraryLoader();
+    Platform platform = new X86Linux();
+    String outputFileName;
+    boolean verbose = false;
+    boolean debugParser = false;
+    CodeGeneratorOptions genOptions = new CodeGeneratorOptions();
+    List<String> asOptions = new ArrayList<String>();
+    boolean generatingSharedLibrary = false;
+    boolean generatingPIE = false;
+    List<LdArg> ldArgs = new ArrayList<LdArg>();
+    boolean noStartFiles = false;
+    boolean noDefaultLibs = false;
 
-    public Options(TypeTable typeTable, LibraryLoader loader) {
-        this.typeTable = typeTable;
-        this.loader = loader;
-        this.genOptions = new CodeGeneratorOptions();
-        this.asOptions = new ArrayList<String>();
-        this.generatingSharedLibrary = false;
-        this.generatingPIE = false;
-        this.ldArgs = new ArrayList<LdArg>();
-    }
-
-    public CompilerMode mode() {
+    CompilerMode mode() {
         return mode;
     }
 
-    public boolean isAssembleRequired() {
+    boolean isAssembleRequired() {
         return mode.requires(CompilerMode.Assemble);
     }
 
-    public boolean isLinkRequired() {
+    boolean isLinkRequired() {
         return mode.requires(CompilerMode.Link);
     }
 
-    public String outputFileNameFor(CompilerMode mode) {
+    String outputFileNameFor(CompilerMode mode) {
         return this.mode == mode ? outputFileName : null;
     }
 
-    public String exeFileName() {
+    String exeFileName() {
         return getOutputFileName("");
     }
 
-    public String soFileName() {
+    String soFileName() {
         return getOutputFileName(".so");
     }
 
-    protected String getOutputFileName(String newExt) {
+    private String getOutputFileName(String newExt) {
         if (outputFileName != null) {
             return outputFileName;
         }
@@ -68,7 +59,7 @@ class Options {
         }
     }
 
-    protected List<SourceFile> sourceFiles() {
+    private List<SourceFile> sourceFiles() {
         List<SourceFile> result = new ArrayList<SourceFile>();
         for (LdArg arg : ldArgs) {
             if (arg.isSourceFile()) {
@@ -78,56 +69,60 @@ class Options {
         return result;
     }
 
-    public TypeTable typeTable() {
-        return this.typeTable;
+    Platform platform() {
+        return platform;
     }
 
-    public LibraryLoader loader() {
+    TypeTable typeTable() {
+        return platform.typeTable();
+    }
+
+    LibraryLoader loader() {
         return this.loader;
     }
 
-    public String outputFileName() {
+    String outputFileName() {
         return this.outputFileName;
     }
 
-    public boolean isVerboseMode() {
+    boolean isVerboseMode() {
         return this.verbose;
     }
 
-    public boolean doesDebugParser() {
+    boolean doesDebugParser() {
         return this.debugParser;
     }
 
-    public CodeGeneratorOptions genOptions() {
+    CodeGeneratorOptions genOptions() {
         return genOptions;
     }
 
-    public List<String> asOptions() {
+    List<String> asOptions() {
         return this.asOptions;
     }
 
-    public boolean isGeneratingSharedLibrary() {
+    boolean isGeneratingSharedLibrary() {
         return this.generatingSharedLibrary;
     }
 
-    public boolean isGeneratingPIE() {
+    boolean isGeneratingPIE() {
         return this.generatingPIE;
     }
 
-    public List<LdArg> ldArgs() {
+    List<LdArg> ldArgs() {
         return this.ldArgs;
     }
 
-    public boolean noStartFiles() {
+    boolean noStartFiles() {
         return this.noStartFiles;
     }
 
-    public boolean noDefaultLibs() {
+    boolean noDefaultLibs() {
         return this.noDefaultLibs;
     }
 
     /** Returns List<SourceFile>. */
-    public List<SourceFile> parse(List<String> argsList) {
+    List<SourceFile> parse(List<String> argsList) {
         List<SourceFile> srcs = new ArrayList<SourceFile>();
         ListIterator<String> args = argsList.listIterator();
         while (args.hasNext()) {
@@ -253,18 +248,18 @@ class Options {
         return srcs;
     }
 
-    protected void parseError(String msg) {
+    private void parseError(String msg) {
         throw new OptionParseError(msg);
     }
 
-    protected void addSourceFile(List<SourceFile> srcs, List<LdArg> ldArgs, String sourceName) {
+    private void addSourceFile(List<SourceFile> srcs, List<LdArg> ldArgs, String sourceName) {
         SourceFile src = new SourceFile(sourceName);
         srcs.add(src);
         // Original argument order does matter when linking.
         ldArgs.add(src);
     }
 
-    protected String getOptArg(String opt, ListIterator<String> args) {
+    private String getOptArg(String opt, ListIterator<String> args) {
         String path = opt.substring(2);
         if (path.length() != 0) {       // -Ipath
             return path;
@@ -274,7 +269,7 @@ class Options {
         }
     }
 
-    protected String nextArg(String opt, ListIterator<String> args) {
+    private String nextArg(String opt, ListIterator<String> args) {
         if (! args.hasNext()) {
             parseError("missing argument for " + opt);
         }
@@ -282,7 +277,7 @@ class Options {
     }
 
     /** "-Wl,-rpath,/usr/local/lib" -> ["-rpath", "/usr/local/lib"] */
-    protected List<String> parseCommaSeparatedOptions(String opt) {
+    private List<String> parseCommaSeparatedOptions(String opt) {
         List<String> opts = Arrays.asList(opt.split(","));
         opts.remove(0);  // remove "-Wl" etc.
         if (opts.isEmpty()) {
@@ -291,7 +286,7 @@ class Options {
         return opts;
     }
 
-    public void printUsage(PrintStream out) {
+    void printUsage(PrintStream out) {
         out.println("Usage: cbc [options] file...");
         out.println("Global Options:");
         out.println("  --check-syntax   Checks syntax and quit.");
diff --git a/net/loveruby/cflat/platform/Platform.java b/net/loveruby/cflat/platform/Platform.java
new file mode 100644
index 0000000..dbb4654
--- /dev/null
+++ b/net/loveruby/cflat/platform/Platform.java
@@ -0,0 +1,10 @@
+package net.loveruby.cflat.platform;
+
+public interface Platform {
+    net.loveruby.cflat.type.TypeTable typeTable();
+    net.loveruby.cflat.asm.Type naturalType();
+    long align(long size);
+    long stackWordSize();
+    long alignStack(long size);
+    long stackSizeFromWordNum(long numWords);
+}
diff --git a/net/loveruby/cflat/platform/X86Linux.java b/net/loveruby/cflat/platform/X86Linux.java
new file mode 100644
index 0000000..ed6f92d
--- /dev/null
+++ b/net/loveruby/cflat/platform/X86Linux.java
@@ -0,0 +1,36 @@
+package net.loveruby.cflat.platform;
+import net.loveruby.cflat.type.TypeTable;
+import net.loveruby.cflat.asm.Type;
+import net.loveruby.cflat.utils.AsmUtils;
+
+public class X86Linux implements Platform {
+    static final Type naturalType = Type.INT32;
+    static final long alignment = 4;
+    // #@@range/stackParams{
+    static final long stackWordSize = 4;
+    // #@@}
+
+    public TypeTable typeTable() {
+        return TypeTable.ilp32();
+    }
+
+    public Type naturalType() {
+        return naturalType;
+    }
+
+    public long align(long size) {
+        return AsmUtils.align(size, alignment);
+    }
+
+    public long stackWordSize() {
+        return stackWordSize;
+    }
+
+    public long alignStack(long size) {
+        return AsmUtils.align(size, stackWordSize);
+    }
+
+    public long stackSizeFromWordNum(long num) {
+        return num * stackWordSize;
+    }
+}
diff --git a/net/loveruby/cflat/type/StructType.java b/net/loveruby/cflat/type/StructType.java
index 070fd2c..bc8c367 100644
--- a/net/loveruby/cflat/type/StructType.java
+++ b/net/loveruby/cflat/type/StructType.java
@@ -1,7 +1,7 @@
 package net.loveruby.cflat.type;
 import net.loveruby.cflat.ast.Slot;
 import net.loveruby.cflat.ast.Location;
-import net.loveruby.cflat.asm.Assembler;
+import net.loveruby.cflat.utils.AsmUtils;
 import java.util.*;
 
 public class StructType extends CompositeType {
@@ -20,12 +20,12 @@ public class StructType extends CompositeType {
         long offset = 0;
         long maxAlign = 1;
         for (Slot s : members()) {
-            offset = Assembler.align(offset, s.allocSize());
+            offset = AsmUtils.align(offset, s.allocSize());
             s.setOffset(offset);
             offset += s.allocSize();
             maxAlign = Math.max(maxAlign, s.alignment());
         }
-        cachedSize = Assembler.align(offset, maxAlign);
+        cachedSize = AsmUtils.align(offset, maxAlign);
         cachedAlign = maxAlign;
     }
 
diff --git a/net/loveruby/cflat/type/UnionType.java b/net/loveruby/cflat/type/UnionType.java
index 98b7b12..b8707f6 100644
--- a/net/loveruby/cflat/type/UnionType.java
+++ b/net/loveruby/cflat/type/UnionType.java
@@ -1,7 +1,7 @@
 package net.loveruby.cflat.type;
 import net.loveruby.cflat.ast.Slot;
 import net.loveruby.cflat.ast.Location;
-import net.loveruby.cflat.asm.Assembler;
+import net.loveruby.cflat.utils.AsmUtils;
 import java.util.*;
 
 public class UnionType extends CompositeType {
@@ -24,7 +24,7 @@ public class UnionType extends CompositeType {
             maxSize = Math.max(maxSize, s.allocSize());
             maxAlign = Math.max(maxAlign, s.alignment());
         }
-        cachedSize = Assembler.align(maxSize, maxAlign);
+        cachedSize = AsmUtils.align(maxSize, maxAlign);
         cachedAlign = maxAlign;
     }
 
diff --git a/net/loveruby/cflat/utils/AsmUtils.java b/net/loveruby/cflat/utils/AsmUtils.java
new file mode 100644
index 0000000..ab7d493
--- /dev/null
+++ b/net/loveruby/cflat/utils/AsmUtils.java
@@ -0,0 +1,7 @@
+package net.loveruby.cflat.utils;
+
+public abstract class AsmUtils {
+    static public long align(long n, long alignment) {
+        return (n + alignment - 1) / alignment * alignment;
+    }
+}