Name: vrC94537 Date: 10/26/2000



The section "4.7.3 The Code Attribute" of 2nd JVM spec says:
"The value of code_length must be greater than zero; the code
array must not be empty."

If a value of code_length item of Code attribute is equal to 0,
then the class file is malformed and therefore must be rejected
by VM class format checker with exception ClassFormatError.
However, JVM (all jdk version till jdk1.4.0beta-b37) throws
VerifyError instead of ClassFormatError.

To reproduce the issue execute following test.
Test tries to load class file with code_length item set to 0.
JVM must reject class test_n with exception ClassFormatError.

------------ test.java ------------------------
public class test {

    public static void main(String args[]) {

        try {
            Class badClass = Class.forName("test_n");
            System.out.println("test failed to reject bad classfile test_n");
        } catch (Throwable e) {
            System.out.println("Loading exception: " + e);
        }
    }

}

------------ test_n.jcod ------------------------
class test_n {
  0xCAFEBABE;
  3; // minor version
  45; // version

  [] { // Constant Pool
    ; // first element is empty
    class #3; // #1
    class #4; // #2
    Utf8 "test_n"; //3
    Utf8 "java/lang/Object"; // #4
    Utf8 "Code"; // #5
    Utf8 "<init>"; // #6
    Utf8 "()V"; // #7
  } // Constant Pool

  0x0001; // access
  #1;// this_cpx
  #2;// super_cpx

  [] { // Interfaces
  } // Interfaces

  [] { // fields
  } // fields

  [] { // methods
    {
      0x0001; // access
      #6; // name_cpx
      #7; // sig_cpx
      [] { // Attributes
        Attr(#5) { // Code
          1; // max_stack
          1; // max_locals
          Bytes[0] { // code_length equals to 0
          };
          [] { // Traps
          } // end Traps
          [] { // Attributes
          } // Attributes
        } // end Code
      } // Attributes
    } // Member
  } // methods

  [] { // Attributes
  } // Attributes
}

------------ Logs ------------------------
%javac test.java
%
%jcod test_n.jcod
%
%java -version
java version "1.4.0beta"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.0beta-b37)
Java HotSpot(TM) Client VM (build 1.4beta-B37, mixed mode)
%
%java -Xfuture test
Loading exception: java.lang.VerifyError: (class: test_n, method: <init> signature: ()V) Empty code

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