RFR: 8259070: Add jcmd option to dump CDS

[Ioi Lam]

On Sat, 27 Feb 2021 05:19:01 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> src/hotspot/share/memory/metaspaceShared.cpp line 799:
>> 
>>> 797:       if (strstr(file_name, ".jsa") == nullptr) {
>>> 798:         os::snprintf(filename, sizeof(filename), "%s.jsa", file_name);
>>> 799:         file = filename;
>> 
>> This could potentially overflow the buffer. I think it's best to just leave `file_name` alone. If the user doesn't want the `.jsa` extension, that's fine. Similarly, we don't add `.jsa` to `-XX:ArchiveClassesAtExit` or `-XX:SharedArchiveFile`.
>
> How would it overflow? But I agree, I would not add jsa extension if the user did not specify one. I dislike when programs do that.

`file_name` is user input that comes from the jcmd, so it can be arbitrarily long and exceed JVM_MAXPATHLEN characters.

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PR: https://git.openjdk.java.net/jdk/pull/2737