Re: How to modify instructions in BootstrapMethods using ASM?

> De: "David Dunkle" <[email protected]>
> À: "Remi Forax" <[email protected]>
> Cc: "asm" <[email protected]>
> Envoyé: Jeudi 30 Novembre 2017 20:53:51
> Objet: Re: [asm] How to modify instructions in BootstrapMethods using ASM?

> I got an interesting answer on stack overflow:
> [
> https://stackoverflow.com/questions/47561756/how-to-modify-instructions-in-java-bootstrapmethods-using-asm
> |
> https://stackoverflow.com/questions/47561756/how-to-modify-instructions-in-java-bootstrapmethods-using-asm
> ]

> Perhaps that answer is a more verbose statement of the same thing Remi has been
> telling me?

yes, this mysterious Holger is better at explaining things than me :) 

> -David

Rémi 

> On Thu, Nov 30, 2017 at 7:09 AM, David Dunkle < [ mailto:[email protected]
> | [email protected] ] > wrote:

>> I am doing that now, but I don’t see how changing the reference to the bootstrap
>> method allows me to change the instructions of the existing bootstrap methods.

>> Am I missing something?

>> -David

>> On Nov 29, 2017, at 11:09 PM, Remi Forax < [ mailto:[email protected] |
>> [email protected] ] > wrote:

>>> Hi,
>>> those constants are referenced by some invokedynamic instructions in the
>>> bytecode.
>>> When you see an invokedynamic instruction with the MethodVisitor at that point,
>>> you can change the reference to the bootstrap method you want.

>>> cheers,
>>> Rémi

>>> On November 29, 2017 9:54:48 PM GMT+01:00, David Dunkle < [
>>> mailto:[email protected] | [email protected] ] > wrote:
>>>> After compiling with Java 8 and dumping the resulting class files with javap, I
>>>> see this, of which I am only showing the first 2 items:

>>>> BootstrapMethods:

>>>> 0: #174 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;

>>>> Method arguments:

>>>> #175 (Ljava/lang/Object;)Z

>>>> #179 invokestatic llllll/lallll.lambda$printPersons$0:(Lllllll/lallll;)Z

>>>> #180 (Lllllll/lallll;)Z

>>>> 1: #174 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;

>>>> Method arguments:

>>>> #175 (Ljava/lang/Object;)Z

>>>> #191 invokestatic llllll/lallll.lambda$printPersons$1:(Lllllll/lallll;)Z

>>>> #180 (Lllllll/lallll;)Z

>>>> 2: #174 invokestatic
>>>> java/lang/invoke/LambdaMetafactory.metafactory:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/inv

>>>> Can I use ASM to visit the instructions in these bootstrap methods and change,
>>>> say, the names of the methods being called using invokestatic instructions
>>>> above?

>>>> Apparently these methods are not part of the normal methods of a class, and I
>>>> haven't had any luck visiting them using standard ASM class and method
>>>> techniques.

>>>> thanks,

>>>> -David

>>> --
>>> Sent from my Android device with K-9 Mail. Please excuse my brevity.


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