Proposal: Post debug Java code to target JVM and exec it

[Laurence Cable]

this is effectively what dynamic agent loading enables, which 
https://openjdk.org/jeps/451 proposes to disable.

Rgds

- Larry Cable

On 7/16/23 10:09 PM, David Holmes wrote:
> On 17/07/2023 12:21 pm, Yi Yang wrote:
>> Actually, this is not a very new and strange idea. I often encounter 
>> similar needs in actual debugging and troubleshooting. In addition, 
>> this feature has also been implemented in some external tools 
>> (https://arthas.aliyun.com/en/doc/ognl.html 
>> <https://arthas.aliyun.com/en/doc/ognl.html>). It would be very 
>> convenient for problem diagnosis if JDK natively had this capability
>
> Okay please take this discussion to serviceability-dev - cc'd.
>
> Thanks,
> David
>
>> ------------------------------------------------------------------
>>     From:David Holmes <david.holmes at oracle.com>
>>     Send Time:2023 Jul. 13 (Thu.) 20:34
>>     To:"YANG, Yi" <qingfeng.yy at alibaba-inc.com>; jdk-dev
>>     <jdk-dev at openjdk.org>
>>     Subject:Re: Proposal: Post debug Java code to target JVM and exec it
>>
>>     On 13/07/2023 8:57 pm, Yi Yang wrote:
>>      > Proposal: Post debug Java code to target JVM and exec it
>>      >
>>      > Hello, I have an early idea to post a piece of Java code to a
>>     local JVM
>>      > process via jcmd or jexec, like this:
>>      >
>>      > jcmd VM.exec Debug.java
>>      > jexec Debug.java
>>      >
>>      > class Debug {
>>      > public static void main(){
>>      > ApplicationProperties c = loadClass("ApplicationProperties");
>>      > // print static field of running Java program
>>      > System.out.println(ApplicationProperties.field1);
>>      > // call static method of running Java program
>>      > ApplicationProperties.printAll();
>>      > // ....
>>      > }
>>      > }
>>      >
>>      > With this approach, we can do some useful things, such as:
>>      > - Get some runtime data of the program
>>      > - Troubleshoot Java problems
>>      > - In rare cases, it can also assist in JVM problem diagnosis
>>      >
>>      > To protect the attach listener, we may need to create a new
>>     ExecThread
>>      > at JVM startup and execute Debug::main in this thread. Do you
>>     have any
>>      > comments on this idea?
>>
>>     So basically you want the ability to ask a running JVM to execute an
>>     arbitrary piece of java code. That may have some uses but in general
>>     seems incredibly dangerous - how would you safeguard such a 
>> facility?
>>
>>     Cheers,
>>     David
>>
>>      > Thank you.