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

[Chris Plummer]

On Wed, 21 Oct 2020 09:08:06 GMT, Nick Gasson <ngasson at openjdk.org> wrote:

>> src/hotspot/share/code/codeCache.cpp line 1562:
>> 
>>> 1560: }
>>> 1561: 
>>> 1562: void CodeCache::write_perf_map(outputStream* st) {
>> 
>> Should this code (and changes in header files) be included for Linux only? (`#ifdef LINUX` like the change in diagnosticCommand.cpp)
>
> 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?

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