RFR: JDK-8257828: SafeFetch may crash if invoked in non-JavaThreads

[Kim Barrett]

On Tue, 8 Dec 2020 13:35:24 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>  if (info != NULL && uc != NULL && thread != NULL) {

So the cause of the problem is the `thread != NULL` in that test. And just
removing all of those would fix the problem.

But I agree that eliminating all the (near) copied variants and merging this
functionality into signals_posix is good.

> This is unfortunate since SafeFetch is used [...]

Another place this hits is OopStorage, which uses SafeFetchN in two places.
Correct code shouldn't have a problem with one of them because the access
won't be invalid (if code is correct). But the other could be a problem,
though I think not seen in practice.

Might there be any similar problem on Windows?

This might be kind of related?
https://bugs.openjdk.java.net/browse/JDK-8185734

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Marked as reviewed by kbarrett (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/1695