[PATCH][asmtools] Fix incorrect handling of some CPX2 constant pool entries by JDIS

[Leonid Kuskov]

Hi Maxim,

Thank you for the patch. Indeed it does fix a bug - the fix is correct 
but it seems to be overloaded with extra code.
CX2 class contains enough information to split structures into 2 groups: 
referencing to CLASS_info
(Fieldref, Methodref and InterfaceMethodref) and all others, hence the 
marker class CPX2_ClassMember is not necessary.
There you can just add one method to CX2 as follows:
boolean refersClassMember() {
     return tag == CONSTANT_FIELD || tag == CONSTANT_METHOD || tag == 
CONSTANT_INTERFACEMETHOD;
}
and change only 1 line:
-if (cns2.value1 == cd.this_cpx) {

+if ( cns2.value1 == cd.this_cpx && cns2.refersClassMember() ) {

What do you think if I use this shorter fix as your contribution?

Thanks,
Leonid


On 3/12/18 16:52, Maxim Degtyarev wrote:
> The proposed patch (see attached file jdis-cpx2-bug.diff.txt) address
> incorrect handling of some constant pool entries represented with CPX2
> class by ASMTOOLS JDIS.
>
> JDIS incorrectly assume that field CPX2::value1 is always used to hold
> index of constant pool entry of type CONSTANT_CLASS.
> This assumption is valid only for entries of type CONSTANT_FIELD,
> CONSTANT_METHOD and CONSTANT_INTERFACEMETHOD.
> For CONSTANT_NAMEANDTYPE, CONSTANT_METHODHANDLE, CONSTANT_DYNAMIC and
> CONSTANT_INVOKEDYNAMIC this assumption is wrong.
> As a result asmtools jdis may produce malformed output for valid input.
>
> Example:
>
> public class Test {
>
>      // Force `class Test` entry appear in the constant pool before
> InvokeDynamic entries.
>      public Class<?> CLASS = Test.class;
>
>      private static Runnable[] workers = {
>          () -> System.out.println("Test"),
>          () -> System.out.println("Test"),
>          () -> System.out.println("Test"),
>          () -> System.out.println("Test"),
>          () -> System.out.println("Test"),
>          () -> System.out.println("Test"),
>          () -> System.out.println("Test"),
>          () -> System.out.println("Test"),
>          () -> System.out.println("Test"),
>          () -> System.out.println("Test")
>      };
>
>      public static void main(String... args) {
>
>          for(Runnable worker : workers) {
>              worker.run();
>          }
>
>      }
>
> }
>
> One of invokedynamic instructions may be rendered by jdis as
>
>          invokedynamic    InvokeDynamic run:"()Ljava/lang/Runnable;";
>
> instead of
>
>          invokedynamic    InvokeDynamic
> REF_invokeStatic:java/lang/invoke/LambdaMetafactory.metafactory:"(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;":run:"()Ljava/lang/Runnable;"
> MethodType "()V", MethodHandle
> REF_invokeStatic:Test.lambda$static$1:"()V", MethodType "()V";