docs: add example

chains-project · Aug 5, 2024 · 6ad15f2 · 6ad15f2
1 parent 4b0bf4e
commit 6ad15f2
Showing 1 changed file with 122 additions and 1 deletion.
diff --git a/README.md b/README.md
@@ -1197,4 +1197,125 @@ lot of noise, see example 2.
    java.lang.classfile.CodeModel: CodeModel [334,343]
    at 5]
    ```
-   The diff shows three instructions are added in the new bytecode - `GETSTATIC`, `LDC`, and `INVOKEVIRTUAL`.
+   The diff shows three instructions are added in the new bytecode - `GETSTATIC`, `LDC`, and `INVOKEVIRTUAL`.
+
+4. Diff between bytecode and decompiled-compiled-bytecode
+
+   <details>
+   <summary>
+            <h4>With diffoscope 272</h4>
+            <blockquote>Java 22</blockquote>
+   </summary>
+   <pre>
+   --- /home/aman/Desktop/personal/bytecode-diff/src/test/resources/infiniteRecursion/decompiled/A.class
+   +++ /home/aman/Desktop/personal/bytecode-diff/src/test/resources/infiniteRecursion/original/A.class
+   ├── javap -verbose -constants -s -l -private {}
+   │ @@ -1,8 +1,8 @@
+   │ -  SHA-256 checksum 039eb028d004305c9ee56b5429d116f773b75265617153c072ac6eb1d34d83b4
+   │ +  SHA-256 checksum 44a81df8eb39d7819ae5e8f07f5eb483f7a8fd363776f0307ec0ebfb3057ce6c
+   │    Compiled from "A.java"
+   │  public class A
+   │    minor version: 0
+   │    major version: 65
+   │    flags: (0x0021) ACC_PUBLIC, ACC_SUPER
+   │    this_class: #13                         // A
+   │    super_class: #2                         // java/lang/Object
+   │ @@ -21,34 +21,36 @@
+   │    #11 = Methodref          #9.#3          // java/lang/StringBuffer."<init>":()V
+   │    #12 = Methodref          #13.#14        // A.applyRules:(Ljava/lang/String;Ljava/lang/StringBuffer;)Ljava/lang/StringBuffer;
+   │    #13 = Class              #15            // A
+   │    #14 = NameAndType        #16:#17        // applyRules:(Ljava/lang/String;Ljava/lang/StringBuffer;)Ljava/lang/StringBuffer;
+   │    #15 = Utf8               A
+   │    #16 = Utf8               applyRules
+   │    #17 = Utf8               (Ljava/lang/String;Ljava/lang/StringBuffer;)Ljava/lang/StringBuffer;
+   │ -  #18 = Utf8               Code
+   │ -  #19 = Utf8               LineNumberTable
+   │ -  #20 = Utf8               main
+   │ -  #21 = Utf8               ([Ljava/lang/String;)V
+   │ -  #22 = Utf8               (Ljava/lang/String;Ljava/lang/Appendable;)Ljava/lang/Appendable;
+   │ -  #23 = Utf8               Signature
+   │ -  #24 = Utf8               <B::Ljava/lang/Appendable;>(Ljava/lang/String;TB;)TB;
+   │ -  #25 = Utf8               SourceFile
+   │ -  #26 = Utf8               A.java
+   │ +  #18 = Methodref          #13.#19        // A.applyRules:(Ljava/lang/String;Ljava/lang/Appendable;)Ljava/lang/Appendable;
+   │ +  #19 = NameAndType        #16:#20        // applyRules:(Ljava/lang/String;Ljava/lang/Appendable;)Ljava/lang/Appendable;
+   │ +  #20 = Utf8               (Ljava/lang/String;Ljava/lang/Appendable;)Ljava/lang/Appendable;
+   │ +  #21 = Utf8               Code
+   │ +  #22 = Utf8               LineNumberTable
+   │ +  #23 = Utf8               main
+   │ +  #24 = Utf8               ([Ljava/lang/String;)V
+   │ +  #25 = Utf8               Signature
+   │ +  #26 = Utf8               <B::Ljava/lang/Appendable;>(Ljava/lang/String;TB;)TB;
+   │ +  #27 = Utf8               SourceFile
+   │ +  #28 = Utf8               A.java
+   │  {
+   │    public A();
+   │      descriptor: ()V
+   │      flags: (0x0001) ACC_PUBLIC
+   │      Code:
+   │        stack=1, locals=1, args_size=1
+   │           0: aload_0
+   │           1: invokespecial #1                  // Method java/lang/Object."<init>":()V
+   │           4: return
+   │        LineNumberTable:
+   │ -        line 3: 0
+   │ +        line 4: 0
+   │  
+   │    public static void main(java.lang.String[]);
+   │      descriptor: ([Ljava/lang/String;)V
+   │      flags: (0x0009) ACC_PUBLIC, ACC_STATIC
+   │      Code:
+   │        stack=3, locals=1, args_size=1
+   │           0: ldc           #7                  // String Hello, World!
+   │ @@ -67,22 +69,23 @@
+   │      flags: (0x000a) ACC_PRIVATE, ACC_STATIC
+   │      Code:
+   │        stack=1, locals=2, args_size=2
+   │           0: aload_1
+   │           1: areturn
+   │        LineNumberTable:
+   │          line 10: 0
+   │ -    Signature: #24                          // <B::Ljava/lang/Appendable;>(Ljava/lang/String;TB;)TB;
+   │ +    Signature: #26                          // <B::Ljava/lang/Appendable;>(Ljava/lang/String;TB;)TB;
+   │  
+   │    protected static java.lang.StringBuffer applyRules(java.lang.String, java.lang.StringBuffer);
+   │      descriptor: (Ljava/lang/String;Ljava/lang/StringBuffer;)Ljava/lang/StringBuffer;
+   │      flags: (0x000c) ACC_PROTECTED, ACC_STATIC
+   │      Code:
+   │        stack=2, locals=2, args_size=2
+   │           0: aload_0
+   │           1: aload_1
+   │ -         2: invokestatic  #12                 // Method applyRules:(Ljava/lang/String;Ljava/lang/StringBuffer;)Ljava/lang/StringBuffer;
+   │ -         5: areturn
+   │ +         2: invokestatic  #18                 // Method applyRules:(Ljava/lang/String;Ljava/lang/Appendable;)Ljava/lang/Appendable;
+   │ +         5: checkcast     #9                  // class java/lang/StringBuffer
+   │ +         8: areturn
+   │        LineNumberTable:
+   │          line 14: 0
+   │  }
+   │  SourceFile: "A.java"
+   </pre>
+   </details>
+
+   #### With our tool
+
+   ```text
+   [===
+   update-node
+   ---
+   METHOD_INVOKED_RETURN_TYPE: (Ljava/lang/String;Ljava/lang/Appendable;)Ljava/lang/Appendable; [0,0]
+    replace (Ljava/lang/String;Ljava/lang/Appendable;)Ljava/lang/Appendable; by (Ljava/lang/String;Ljava/lang StringBuffer;)Ljava/lang/StringBuffer;,
+   ===
+   delete-node
+   ---
+   CHECKCAST [0,0]
+   ===]
+   ```
+
+   Our tool precisely detects there has been change in two OPCODEs.
+   Also, `diffiscope` fallbacks to `javap` as they don't detect a change in sources.
+   This bug has been discovered by paper
+   [Java Decompiler Diversity and its Application to Meta-decompilation](https://arxiv.org/abs/2005.11315).
+   Its case study 4.3.2 outlines this case.
+   This bug makes diffoscope diff noisy.
+