RFR: 8165276: Spec states to invoke the premain method in an agent class if it's public but implementation differs

[Alan Bateman]

On Tue, 8 Dec 2020 19:40:32 GMT, Chris Plummer <cjplummer at openjdk.org> wrote:

>> This change have been already reviewed by Mandy, Sundar, Alan and David.
>> Now, the PR approval is needed.
>> The push was postponed because the CSR was not approved at that time (it is now):
>>    https://bugs.openjdk.java.net/browse/JDK-8248189
>> Investigation of existing popular java agents was requested by Joe.
>> ----------
>> 
>> The java.lang.instrument spec:
>>   https://docs.oracle.com/en/java/javase/15/docs/api/java.instrument/java/lang/instrument/package-summary.html
>> 
>> Summary:
>>   The java.lang.instrument spec clearly states:
>>     "The agent class must implement a public static premain method
>>      similar in principle to the main application entry point."
>>   Current implementation of sun/instrument/InstrumentationImpl.java
>>   allows the premain method be non-public which violates the spec.
>>   This fix aligns the implementation with the spec.
>> 
>> Testing:
>>   A mach5 run of jdk_instrument tests is in progress.
>
>> This change have been already reviewed by Mandy, Sundar, Alan and David.
>> Now, the PR approval is needed.
> 
> Can you provide a link to the discussion? I'm mostly curious if there was some discussion as to why Instrument purposefully allowed non-public premain methods:
> 
>          // the premain method should not be required to be public,
> 508         // make it accessible so we can call it
> 509         // Note: The spec says the following:
> 510         //     The agent class must implement a public static premain method...
> 511         setAccessible(m, true);```

All the discussion is in the bug and CSR:
https://bugs.openjdk.java.net/browse/JDK-8165276
https://bugs.openjdk.java.net/browse/JDK-8248189
We messed up in JDK-5070281 (JDK 6) and it came to light in JDK 9 when auditing the use of setAccessible in the JDK.

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PR: https://git.openjdk.java.net/jdk/pull/1694