RFR: 8286490: JvmtiEventControllerPrivate::set_event_callbacks CLEARING_MASK computation is incorrect

[Serguei Spitsyn]

It was a typo when the original CLEARING_MASK was initially introduced:


 // Mask to clear normal event bits.
  const jlong CLEARING_MASK = (1L >> (TOTAL_MIN_EVENT_TYPE_VAL - TOTAL_MIN_EVENT_TYPE_VAL)) - 1L;
  // Avoid cleaning extension event bits.
  jlong enabled_bits = CLEARING_MASK & env->env_event_enable()->_event_callback_enabled.get_bits();

``` 

The first TOTAL_MIN_EVENT_TYPE_VAL has to be JVMTI_MIN_EVENT_TYPE_VAL as below:
`  const jlong CLEARING_MASK = (1L >> (JVMTI_MIN_EVENT_TYPE_VAL - TOTAL_MIN_EVENT_TYPE_VAL)) - 1L;`

Let me provide some background to understand how this mask is used.

Normal JVMTI event types are numbered from 50 to 88. There are two constants:

  JVMTI_MIN_EVENT_TYPE_VAL = 50
  JVMTI_MAX_EVENT_TYPE_VAL = 88

The extension event types are numbered from 47 to 49. There are also two constants:

  EXT_MIN_EVENT_TYPE_VAL = 47
  EXT_MAX_EVENT_TYPE_VAL = 49


There are also two additional constants:

  TOTAL_MIN_EVENT_TYPE_VAL = 47
  TOTAL_MAX_EVENT_TYPE_VAL = 88


The `enabled_bits` are shifted left by 47, so that the 0-bit in `enabled_bits` is for first extension event type. And the first normal JVMTI event type is numbered 3 in the `enabled_bits` bit mask. The `CLEARING_MASK` is used to clear only normal JVMTI event types but keep the extension event bits (0-2) unchanged.

Testing:
I'll run all JVMTI tests including nsk.jvmti tests and serviceability/jvmti tests including those added in Loom for virtual thread coverage.

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Commit messages:
 - 8286490: JvmtiEventControllerPrivate::set_event_callbacks CLEARING_MASK computation is incorrect

Changes: https://git.openjdk.java.net/jdk/pull/8860/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8860&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8286490
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8860.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8860/head:pull/8860

PR: https://git.openjdk.java.net/jdk/pull/8860