RFR: 8265505: findsym does not work on remote debug server [v2]

[Chris Plummer]

On Tue, 20 Apr 2021 23:18:43 GMT, Yasumasa Suenaga <ysuenaga at openjdk.org> wrote:

>> We can see following error when we run `findsym` on CLHSDB which connects to remote debug server.
>> 
>> 
>> hsdb> verbose true
>> hsdb> findsym gHotSpotVMTypes
>> 0x00007f913d4a45b0Error: java.lang.NullPointerException: Cannot invoke "sun.jvm.hotspot.debugger.cdbg.CDebugger.loadObjectContainingPC(sun.jvm.hotspot.debugger.Address)" because "cdbg" is null
>> java.lang.NullPointerException: Cannot invoke "sun.jvm.hotspot.debugger.cdbg.CDebugger.loadObjectContainingPC(sun.jvm.hotspot.debugger.Address)" because "cdbg" is null
>>         at jdk.hotspot.agent/sun.jvm.hotspot.CommandProcessor$7.doit(CommandProcessor.java:618)
>>         at jdk.hotspot.agent/sun.jvm.hotspot.CommandProcessor.executeCommand(CommandProcessor.java:2116)
>>         at jdk.hotspot.agent/sun.jvm.hotspot.CommandProcessor.executeCommand(CommandProcessor.java:2086)
>>         at jdk.hotspot.agent/sun.jvm.hotspot.CommandProcessor.run(CommandProcessor.java:1957)
>>         at jdk.hotspot.agent/sun.jvm.hotspot.CLHSDB.run(CLHSDB.java:112)
>>         at jdk.hotspot.agent/sun.jvm.hotspot.CLHSDB.main(CLHSDB.java:44)
>>         at jdk.hotspot.agent/sun.jvm.hotspot.SALauncher.runCLHSDB(SALauncher.java:282)
>>         at jdk.hotspot.agent/sun.jvm.hotspot.SALauncher.main(SALauncher.java:493)
>> 
>> 
>> The cause of this NPE is that CDebugger is null.  It happens when the debugger is running on debugd server.
>> Command line debugger like CLHSDB can delegate the command to debugd, like `pmap` and `pstack`. `findsym` can also use this scheme.
>> 
>> This PR has passed serviceability/sa tests on Linux x64.
>
> Yasumasa Suenaga has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove unused imports

Marked as reviewed by cjplummer (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/3582