RFR: 8261354: SIGSEGV at MethodIteratorHost

[Jaroslav Bachorik]

On Fri, 21 May 2021 09:56:40 GMT, Jaroslav Bachorik <jbachorik at openjdk.org> wrote:

> The `MethodIteratorHost` will iterate over previous versions of redefined classes but the number of methods in that class is retrieved only for the current version. 
> Since the previous versions may theoretically, and before JDK 15 also practically, contain fewer methods than the current version (hotspot did support adding `private static` methods during retransformation) this can lead to SIGSEGV when the iterator tries accessing out-of-range method element.
> 
> Although for after JDK 15 it is not possible to have differing number of methods between multiple versions of a retransformed class it feels right not to rely on the implementation detail and re-retrieve the number of methods per each class version.
> 
> All jdk_jfr tests are passing on Linux x64 and MacOS x64

I can remove the filter before integrating to make the code less confusing - since the filter has no function right now it would be better if it is not there at all.

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PR: https://git.openjdk.java.net/jdk/pull/4143