asmtools `ldc Dynamic` syntax

[Leonid Kuskov]

Correction: The issue for tracking purposes is https://bugs.openjdk.java.net/browse/CODETOOLS-7902888

On 4/21/21, 10:01 PM, "code-tools-dev on behalf of Leonid Kuskov" <code-tools-dev-retn at openjdk.java.net on behalf of leonid.kuskov at oracle.com> wrote:

    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.