RFR: 8294160: misc crash dump improvements [v2]

[David Holmes]

On Tue, 27 Sep 2022 18:22:27 GMT, Dean Long <dlong at openjdk.org> wrote:

>> Try to recover and output meaningful information in more situations, such as:
>> - when a pointer is in Method metadata memory range, but the memory is not committed
>> - when we call a bad address
>> 
>> When calling a bad address, we usually don't get a meaningful stack backtrace, but in many situations we can if we know where to find the caller information.
>
> Dean Long has updated the pull request incrementally with one additional commit since the last revision:
> 
>   revert unneeded changes

src/hotspot/os_cpu/linux_aarch64/os_linux_aarch64.cpp line 357:

> 355:   // point to garbage if entry point in an nmethod is corrupted. Leave
> 356:   // this at the end, and hope for the best.
> 357:   address pc = os::fetch_frame_from_context(uc).pc();

What is the difference between `ucontext_get_pc(uc)` and getting the pc from the frame from the uc? How many pc's can a ucontext have?

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PR: https://git.openjdk.org/jdk/pull/10387