RFR: 8254723: add diagnostic command to write Linux perf map file [v2]

[Nick Gasson]

On Thu, 22 Oct 2020 05:00:10 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

> 
>     1. Like Alexey, I would really wish for an print-at-exit switch. The common naming seems to be xxxAtExit (so not, OnExit). "PrintXxx" seems to be printing stuff out to tty, "DumpXxxx" for writing separate files (e.g. CDS map). So I would name it DumpPerfMapAtExit.
> 

OK, makes sense.

>     2. Dumping to /tmp is unexpected for me, I would prefer if the default were dumping to the current directory. That seems to be the default for other files too (cds map, hs-err file etc).
> 
>     3. Not necessary but nice would be a an option to specify location of the dump file.
> 

The `/tmp/perf-<pid>.map` is hardcoded into perf though ([see here](https://github.com/torvalds/linux/blob/master/tools/perf/util/map.c#L155)), so I don't think it's useful for the user to be able to change the location.

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PR: https://git.openjdk.java.net/jdk/pull/760