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List:       openjdk-serviceability-dev
Subject:    Integrated: 8286490: JvmtiEventControllerPrivate::set_event_callbacks CLEARING_MASK computation is i
From:       Serguei Spitsyn <sspitsyn () openjdk ! java ! net>
Date:       2022-05-25 6:27:10
Message-ID: qSTrLYi2IuyMohmqDYtPjkjIwICHLOJr2AvoDG9H8oo=.b9e2f924-93a7-4818-871a-bbf141292445 () github ! com
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On Tue, 24 May 2022 05:45:17 GMT, Serguei Spitsyn <sspitsyn@openjdk.org> wrote:

> 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.

This pull request has now been integrated.

Changeset: a0cccb54
Author:    Serguei Spitsyn <sspitsyn@openjdk.org>
URL:       https://git.openjdk.java.net/jdk/commit/a0cccb54791d954bf08da5aac9b9794e370617c8
                
Stats:     40 lines in 3 files changed: 35 ins; 4 del; 1 mod

8286490: JvmtiEventControllerPrivate::set_event_callbacks CLEARING_MASK computation \
is incorrect

Reviewed-by: jbachorik, lmesnik, amenkov

-------------

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


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