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

[Nick Gasson]

On Wed, 21 Oct 2020 17:57:46 GMT, Chris Plummer <cjplummer at openjdk.org> wrote:

>> I'm not sure, I didn't want to add too much `#ifdef` mess. The code will compile on other platforms, it just won't be called. Better to add `#ifdef`s around all of it?
>
> Any reason not to have this dcmd supported on all platforms even though the output is really targeted for use with the perf tool on linux? Would a user ever have any other use for the output other than with the perf tool on linux?

@plummercj I'm not sure: it's just a text file so could be easily consumed by tools other than perf. But I'm not aware of any tools on other platforms that could use it.

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