RFR: JDK-8285675: Temporary fix for arm32 SafeFetch

[Thomas Stuefe]

On Tue, 26 Apr 2022 13:31:00 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

> [JDK-8283326](https://bugs.openjdk.java.net/browse/JDK-8283326) reworked the SafeFetch implementation and, on most platforms, switched to static assembly.
> 
> On arm (32-bit), this change led to strange crashes ([JDK-8284997](https://bugs.openjdk.java.net/browse/JDK-8284997)). These problems are time consuming to analyze (among other things they only occur when building natively on a Rasberry Pi with one particular Docker setup).
> 
> As a temporary workaround I'd like to switch SafeFetch to the sigjmp method for arm, until I find time to analyze these problems in more detail.

> > These problems are time consuming to analyze (among other things they only occur when building natively on a Rasberry Pi with one particular Docker setup).
> 
> Let me know if you would like help in testing this. It takes less than an hour to build OpenJDK natively for _armhf_ on the [Launchpad build farm](https://launchpad.net/~jgneff/openjdk-snap/+snap/openjdk-edge/+build/1739240), so it's very easy for me to recreate the problem or help in its debugging. Note that if you need a faster environment for your own testing, anyone can create a Launchpad account and use their fast ARM servers. I already have it all set up, though, so I'm happy to help out.

Thank you @jgneff for testing and advice. I may use Launchpad once I run out of patience with my local setup.

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PR: https://git.openjdk.java.net/jdk/pull/8399