asmtools `ldc Dynamic` syntax

[Leonid Kuskov]

Hello,

Your first question is about the JVMS 4.4.8. The CONSTANT_MethodHandle_info Structure 
CONSTANT_MethodHandle_info {
    u1 tag;
    u1 reference_kind;
    u2 reference_index;
}
The format of the ldc instruction is: ldc Dynamic reference_kind:reference_index {ClassName|InterfaceName}.MethodName ....
According to the assertion:

If the value of the reference_kind item is 6 (REF_invokeStatic) or 7 (REF_invokeSpecial), then if the class file version number is less than 52.0, the constant_pool entry at that index must be a CONSTANT_Methodref_info structure representing a class's method for which a method handle is to be created; if the class file version number is 52.0 or above, the constant_pool entry at that index must be either a CONSTANT_Methodref_info structure or a CONSTANT_InterfaceMethodref_info structure (§4.4.2) representing a class's or interface's method for which a method handle is to be created.

i.e. we might have the following pairs: 

ldc Dynamic  REF_invokeSpecial:Method ...... if reference_index is an index of a CONSTANT_Methodref_info structure in CP or 
ldc Dynamic  REF_invokeSpecial: InterfaceMethod... if reference_index points to CONSTANT_InterfaceMethodref_info

2nd issue is the defect, although it doesn't affect a code the bytecode footprint grows.
I will take care of the problem: https://bugs.openjdk.java.net/browse/JDK-8129547

> (it's even didn't assemble back). 
I could not reproduce this. Please send your example. 



On 4/21/21, 3:54 PM, "code-tools-dev on behalf of Maxim Degtyarev" <code-tools-dev-retn at openjdk.java.net on behalf of mdegtyarev at gmail.com> wrote:

    Hello,

    I have 2 questions regarding `ldc Dynamic` syntax:

    1) Consider the following example:

              ldc Dynamic
                  REF_newInvokeSpecial
                  :LdcConDyTwice."<init>"
                  :"(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/Class;)V"
                :LdcConDyTwice
                :"LLdcConDyTwice;";

    Being assembled with `asmtools jasm` and then disassembled with
    `asmtools jdis` above instruction turns to:

            ldc    Dynamic
                REF_newInvokeSpecial
                :Method LdcConDyTwice."<init>"
                :"(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/Class;)V"
                :LdcConDyTwice
                :"LLdcConDyTwice;";

    I assume "Method" in front of the constructor reference is a
    disassembler bug (it's even didn't assemble back).
    Could anyone confirm my assumption?

    2) Is there a way to reference the same Dynamic constant more than
    once with the current jasm syntax?
    Right now two syntactically equal ldc Dynamic instructions create two
    different entries in BootstrapMethods attribute.